Precise regulation of missing linkers in MOF pervaporation membranes for desalination of hypersaline waters

Domain: chemistry
Published: 2026-02-26
Editorial outcome: major_revision

Abstract
We report a method for the precise regulation of intracrystalline missing-linkers to control the
permeability and selectivity of metal-organic framework (MOF) membranes. The method is
applied for the design of stable ceramic-based MOF-801 membranes for hypersaline water
treatment via pervaporation. For efficient membrane growth, an in situ nano-seeding strategy was
employed to provide nucleation sites followed by surfactant posttreatment to minimize cracks.
Missing-linkers are regulated in MOF-801 membranes by altering the ratio of fumarate to formic
acid, which positively enhances water transport by modifying the MOF-801 structure and
chemistry. Specifically, missing-linkers enhance membrane structural hydrophilicity with stronger
host-guest interaction energy, resulting in faster transport with a lower energy barrier by enlarging
the pore window and pore cage. The MOF-801 membranes demonstrated near-perfect salt
rejection (~99.9%) and high water flux, outperform most state-of-the-art silica, MOF, and
zeolite polycrystalline membranes for the treatment of both saline and hypersaline waters. Notably,
the membranes exhibited stable desalination performance, highlighting their promising application
potential. This work provides a strategy for the rational design of next-generation high-
performance MOF nanochannel membranes for challenging water purification applications.

Introduction
To combat global water scarcity, desalination will play a critical role in tapping into
unconventional water sources.1,2 While reverse osmosis (RO) is the current paradigm for
desalination, conventional RO cannot be used for hypersaline waters (salinity > ~10 wt.%) due to
the ultrahigh osmotic pressures that must be overcome, which exceed the maximum hydraulic
pressures that can be applied.3-6 At these higher salinities, thermally-driven membrane processes
have an advantage over RO as their operation is less sensitive to salinity.7-9 A promising chemical-
potential-driven membrane process is pervaporation (PV).10 A liquid feed stream (heated in some
cases) is exposed to one side of the PV membrane and a vacuum is applied to the other. Under
these conditions, water traverses the PV membrane, vaporizes, and then condensed at the permeate
side.9,11,12 In this process, dissolved salts are retained because salts, unlike water, have negligible
vapor pressure at the operational temperatures and pressures of pervaporation. PV is capable of
treating hypersaline waters, even when operated at ambient temperatures.13,14 Unlike conventional
membrane distillation (MD) processes, a more robust PV process has advantages in addressing
challenges like wetting, scaling, and fouling, which enables promising operational performance.15

A major challenge for PV desalination is the design of high-performance separation
membranes featuring high permeability, salt rejection, and operating stability.9,16,17 Unlike their
polymer counterparts, more robust inorganic polycrystalline nanoporous membranes, such as
zeolite and silica, have been proposed.18,19 While these membranes offered stable desalination
performance, they suffered from low permeability, even for the treatment of seawater or low-
salinity wastewaters. In contrast, metal-organic framework (MOF) membranes have well-defined
nanochannel structures, abundant affinity sites, modular nature for functionalities, and structural
stability, thereby enabling high uptake of water and promising separation performance.20-23
Compared with state-of-the-art water-stable MOFs, MOF-801 demonstrates highly robust
characteristics, rapid water adsorption rate, and high water harvesting capacity.24-28 In addition,
MOF-801 inherently possesses a suitable crystallographic structure where the pore window size
(3.5 Å) ranges between water molecules (2.8 Å) and hydrated sodium ions (~ 7.16 Å). This makes
MOF-801 a promising candidate for desalination membranes with precise separation ability, which
has not been experimentally demonstrated until now. However, the fabrication of a well-
intergrown (i.e., crack-free or intercrystalline-defect-free) pure MOF-801 membrane is
experimentally difficult and thus lags behind its mixed-matrix membrane and other MOF
membrane counterparts.

Rational tailoring of crystalline chemistry of MOF membranes has the potential to
substantially improve membrane functionality and performance, but is considered to be
particularly challenging. Recently, intracrystalline defects, such as missing linkers and missing
clusters, have been synthesized and confirmed to influence the permeability or selectivity of MOF
liquid- or gas-separation membranes.29-33 However, the precise creation of favorable
intracrystalline defects is challenging and has not been well-studied in membrane-based separation
applications. Moreover, it remains unclear how intracrystalline missing linkers affect separation
performance, such as selectivity and permeability, at the molecular or atomic level. Therefore,
elucidating these transport mechanisms is critical for the rational design of nanoscale channels
with tailorable structure and chemistry in next-generation MOF membranes. Unlike the
elimination of intracrystalline lattice defects to improve the selectivity of MOF membranes 27, the
aim of this work is to precisely regulate intracrystalline missing linkers of MOF membranes to
enhance the permeation of water molecules while maintaining high salt rejection. Differing from
a former study that introduced an arbitrary number of missing linkers (~23.5%),30 this work
demonstrates that precise regulation of missing linkers to enhance water transport could be realized
in MOF-801 membranes, which is not only practically challenging, but also critical for
understanding fundamental mass transport phenomena.

In this work, we report a robust protocol for well-intergrown MOF-801 nanochannel thin
membranes with precise regulation of intracrystalline missing linkers for enhanced water
permeability via pervaporation. We further provide a mechanistic understanding of the missing-
linker enhancement of water permeation, where missing linkers not only enhance structural
hydrophilicity (i.e., water adsorption ability) but also render faster water transport via altering the
pore structure and chemistry of the nanoscale MOF-801 channels. The membranes exhibit
complete salt rejection, operation stability, and higher water flux in comparison to state-of-the-art
silica, MOF, and zeolite membranes for the treatment of saline and hypersaline waters. Notably,
the MOF-801 membranes demonstrated resilient performance under challenging water treatment
conditions, including high temperatures, highly oxidizing environments, and in the presence of
oils and surfactants.

Results
Design and Characterization of Crack-free MOF-801 Membrane
Engineering the structure and surface properties of substrates is crucial for subsequent MOF
membrane growth and application. In this work, crack-free MOF-801 membranes were fabricated
by a secondary growth method followed by surfactant Span80 posttreatment for PV desalination
(Figure 1, Supplementary Figures 1-3). Ceramic substrates (α-Al2O3:average pore size ~700 nm;
ZrO2: average pore size ~ 142 nm) were specially designed with a hollow fiber configuration for
PV, featuring an ultrahigh packing density (~4000 m2·m-3) that is 16-40 times higher than those of
tubular (200-250 m2·m-3) or flat-sheet (100-150 m2·m-3) commercial substrates; with the latter
most commonly used as the substrate for current MOF membranes (Figure 1a, Supplementary
Figure 4, SI Section 1.2).34 To modify the substrate and enable the growth of well-intergrown
MOF-801 membranes, a more hydrophilic nano-TiO2 interlayer was introduced with lowered
surface roughness (Ra ~68 nm) (Supplementary Figure 4) and average pore size (~105 nm). Such
a TiO2 interlayer could provide a modified substrate surface with more hydroxyl groups and thus
more nucleation sites for MOF crystal nucleation and subsequent growth, which is beneficial to
the formation of thin, well-intergrown MOF-801 membranes. MOF-801 was selected to be
fabricated into a separation membrane because of its stability toward some solvents, especially
hypersaline solutions at elevated temperatures (Supplementary Figure 5). Although there were
only minor and negligible additional peaks for the samples after exposure in DMF, acetone, and
water—the phase structure degraded to some extent in strongly acidic aqueous solution (pH 0.7),
which can be reflected by peak broadening and new peaks arising (Supplementary Figure 5).
Nevertheless, such chemically harsh condition is far beyond practical application conditions. In
this work, a nanoseed-induced secondary growth method (seed size: ~69 nm, Supplementary
Figure 6) was employed to fabricate the polycrystalline MOF-801 membrane to increase the
presence of active nucleation sites and reduce the energy barrier for nucleation based on Ostwald’s
rule.35

One key challenge is the generation of macroscopic cracks inside MOF-801 membranes during
drying after membrane growth (Figures 1a, 1b), which inevitably undermines the separation
performance. To address this issue, a surfactant (Span80) posttreatment was employed to
effectively avoid the formation of cracks (Figures 1a, 1c, Supplementary Figure 7). For the
polycrystalline MOF-801 membrane, cracks formed due to the increased capillary stress between
intergrown MOF crystals during the solvent evaporation stage.36 However, after being soaked in a
Span80 chloroform solution for 2 days, high-quality MOF-801 membranes (thickness ~1.67 μm)
with a pure MOF-801 phase were obtained on a TiO2 interlayer-modified ceramic substrate with
visible and distinct boundaries (Figures 1d, 1g), which were free of macroscopic intracrystalline
cracks (Figure 1c). Posttreatment of the MOF-801 membrane with Span80 significantly
suppressed the evaporation rate of residual solvents (N,N-dimethyl formamide, formic acid) and
reduced capillary stress, consequently minimizing the formation of cracks. Unlike the unmodified
MOF-801 membrane (“cracked”), which exhibits poor gas selectivity, the modified MOF-801
membrane is well-intergrown (i.e., without macroscopic cracks or other intercrystalline defects)
since its ideal gas selectivities (H2/N2: 7.6, H2/CH4: 16.5, N2/CH4: 2.2) are all higher than the
Knudsen diffusion selectivities (H2/N2: 3.7, H2/CH4: 2.8, N2/CH4: 1.3) (Figure 1e).

The ATR-FTIR spectrum of the modified MOF-801 membrane verifies the presence of the -
C=O-O bond (1400 cm-1, 1577 cm-1) and -C=O-OH group (1213 cm-1) of the MOF-801
structure,37,38 as well as the in-plane deformation vibration of C-H (2852-2856 cm-1, 2921−2925
cm-1) and strong stretching vibration of ester bonds (1734−1742 cm -1) of the Span80 structure
(Figure 1f).39 Nevertheless, Span80 posttreatment did not significantly change the pore size (6 Å
vs. 6 Å) and specific surface area (499 m2·g-1 vs. 535.5 m2·g-1) of MOF-801 (Supplementary Figure
8), which indicates that such a surfactant posttreatment modification would not negatively affect
the pore structure of the membranes. Additionally, the presence of O, Ti, Zr, and C signals in the
XPS spectra are clearly identified for the TiO2 interlayer, cracked MOF-801, and crack-free MOF-
801 membranes (Supplementary Figure 9). Ti was detected in the TiO2
nano-interlayer surface,
while Zr was detected in the membrane surface of both cracked and crack-free MOF-801
membranes (Supplementary Figures 9, 10). Moreover, even after strong ultrasonication treatment
(150 W, 20 min) for an accelerated stability test, the MOF-801-1.43 membrane maintained
integrated surface and cross-sectional structural morphologies, indicating promising mechanical
stability for practical operation Supplementary Figure 11).

Precise Regulation of Intracrystalline Missing Linkers
Although missing linkers have been experimentally designed in UiO-66 MOF membranes,
precise regulation of intracrystalline missing linkers has not been reported until now.32 Without the
addition of a modulator, it is difficult to form highly crystalline MOF-801 membrane (usually only
some amorphous phase) from ZrOCl2 and fumarate due to the slow crystallization kinetics.40 The
amorphous phase on substrates is not suitable for pervaporation desalination since it does not form
a membrane layer with defined MOF crystalline structure comprised of regular pore window and
pore cage to allow for water molecule transport and salt rejection. By contrast, our current work,
employs formic acid as a modulator to not only accelerate the crystallization of MOF-801, but also
precisely regulate intracrystalline missing linkers by adjusting the ratio of fumarate to formic acid
(Figure 2, Supplementary Figure 12). The intracrystalline missing linkers were first identified and
quantified based on the results of X-Ray diffraction (XRD), 1H Nuclear Magnetic Resonance
(NMR), 13C Magic Angle Spinning (MAS) NMR, and thermogravimetric analysis (TGA) (Figures
2b-2e, Supplementary Figures 13-15). By adjusting the ratios of fumarate to formic acid (10:400,
6:400, 4:400, 2:400 and 1:400), the frequency of missing linkers per Zr6 crystalline formula unit
(denoted as linker deficiency unless specified) can be precisely regulated and was determined to
be 0.32, 0.70, 1.25, 1.43, and 1.62, based on the TGA results (denoted as MOF-801-0.32, MOF-
801-0.70, MOF-801-1.25, MOF-801-1.43, and MOF-801-1.62 in this work) (Figure 2b).

The TGA results indicated that a deficiency was present in all samples due to deviations in
mass loss behavior in comparison to the ideal plateau of MOF-801 (Supplementary Figure 13).41
The presence of missing clusters were ruled out according to the XRD patterns where no reo phase
was observed between 2 and 8° (2θ) (Figure 2c).42 Therefore, we can conclude that the
intracrystalline defects are the result of missing linkers. In addition to fumarate molecules, the
presence of HCOO- (formic molecule) can be experimentally confirmed by the 1H NMR spectra
(Figure 2d), indicating the occurrence of a competitive coordination reaction between the Zr6
cluster and formic acid. This can be ascribed to the fact that during the solvothermal reaction,
formic acid coordinates with Zr6 clusters via carboxyl groups by competing with fumarate acid to
form the missing fumarate linkers.

With increasing missing-linker density, the pore structure of MOF-801 was enlarged, which
was confirmed by the near-linear increase in pore size (i.e., pore width, from 4.62 to 5.09 Å), total
pore volume (from 0.36 to 0.68 cm-3∙g-1), and specific surface area (from 292.1 to 791.1 m-2∙g-1)
(Figures 2e, 2f, Supplementary Figure 14). Moreover, the water uptake capacity was enhanced
with the increasing presence of missing linkers (Figure 2f), which is not only a result of the
enlarged pore structure but also the generation of more hydrophilic sites with enhanced water
adsorption ability. For the pervaporation desalination process (Supplementary Figure 3), the
presence of missing linkers reduced the activation energy barrier required for water molecule
transport across the membranes (Supplementary Figure 16). Furthermore, the water flux of MOF-
801 membranes linearly increased with increasing linker deficiency under constant operational
temperatures (40-80℃), while salt rejection remains nearly complete, in the range of 99.69% -
99.91% under all operational temperatures (Figure 2g). Specifically, when the linker deficiency
increases from 0.32 to 1.43, the water flux is enhanced by ~60% at 80℃. Additionally, increasing
the operational temperature from 40 to 80℃ improves the water flux from 12.3 to 35.6 L∙m-2∙h-1
at a 1.43 linker deficiency due to the enhanced driving force. The performance of the membrane
with the highest linker deficiency 1.62 is not shown since it was synthesized under strongly acidic
conditions, resulting in poor membrane quality and desalination performance.

Atomistic Mechanism for Missing-Linker Enhanced Performance
To shed light on the effect of missing linkers on desalination performance, state-of-the-art
molecular simulations, including molecular dynamics and Monte Carlo, associated with
experimental data were employed to offer atomistic insights into the permeation mechanism of
water molecules through MOF-801 membranes (Figure 3, SI Section 3.1). To reveal the role of
missing linkers, we investigated a defect-free simulation structure and two highly symmetric
missing-linker simulation structures with theoretical deficiency of 1/12 and 1/4 (also denoted
MOF-801-DF, MOF-801-0.5, and MOF-801-1.5, respectively). Through these simulations, the
improvement in water flux was ascribed to missing linkers not only enhancing water adsorption
(i.e., water affinity) but also water transport by altering the intracrystalline pore microenvironment
(i.e., more hydrophilic active sites) and structure (i.e., both enlarged pore window and pore cage)
of the subnanometer channels in the MOF-801 framework structure. Reducing the activation
energy barrier, the presence of missing linkers enables the ultrafast transport of more water
molecules (Figures 3a−3e). Missing linkers also enhance the structural hydrophilicity of the MOF
frameworks due to the exposure of more water adsorption sites (i.e., [Zr6(OH)4O4] cluster),
resulting in a higher water uptake rate and higher water loading (Figures 3f, 3g, SI Section 3.2).

To gain insight into such an enhancement from an energetic point of view, Monte Carlo
simulations were conducted to sample the interaction energy between a single water molecule and
MOF-801 framework structures. The interaction energy distribution for MOF-801-0.5 and MOF-
801-1.5 indicated stronger interactions resulting from water-framework Coulombic interactions
when compared to MOF-801-DF (Figure 3h). As a result, MOF-801 exhibited 4-16 times higher
adsorption capacity when compared with other state-of-the-art, water-stable MOFs (i.e., ML-UiO-
66, UiO-66, UiO-66-NH2) (Figure 3i). During the PV process, the creation of more missing linkers
enhances the permeation dynamics of more water molecules inside the membranes (Figure 3j).
Theoretically, the water flux significantly increases from 16.4 to 36.4 L·m−1·h−1 with increasing
missing linker deficiency from 0 to 1.5 (Figure 3k). We can, therefore, conclude that
intracrystalline missing linkers in the MOF-801 membrane not only promote the structural
hydrophilicity (i.e., water adsorption ability) but also render faster transport dynamics (i.e.,
diffusion ability) of water molecules. These two aspects result in the higher water flux of MOF-
801 membranes with more missing linkers than was observed experimentally. As previously noted,
the MOF-801-1.62 membrane synthesized under strongly acidic conditions exhibit poor
desalination performance. Thus, the high-quality MOF-801-1.43 membrane was selected for
subsequent performance and stability evaluation and will be referred to as MOF-801 membrane
unless specified hereafter.

Promising Desalination Performance and Operation Stability
The MOF-801 membranes exhibited exceptional desalination performance and operation
stability for the treatment of saline waters in a wide range of concentrations (0-10 wt.% NaCl)
(Figure 4). Independent of salt concentration and operation temperature, the rejection of all MOF-
801 membranes are over 99.9%, resulting in permeate salt concentrations of 2-44 ppm, which are
lower than the product water quality standards of both China and the WHO for desalination
techniques (China HY/T 247-2018: 50 ppm (salt concentration), WHO: 1,200 ppm (total dissolved
solids)) (Supplementary Figure 17).9 This performance indicates that the MOF-801 membranes
could effectively desalinate brines to produce clean water by PV (Figures 4a, S3). The pore size of
MOF-801-1.43 was determined to be 5.07 Å (Figure 2d, Supplementary Figure 14b), which is
lower than the size of hydrated ions (d [Na+·(H2O)n] ~ 0.716 nm, d [Cl-·(H2O)n] ~ 0.664 nm).43
The near-complete salt rejections could be ascribed to the fact that the salt ions have negligible
vapor pressure at the operating conditions, and did not vaporize in the pervaporation process.

In particular, even at approximately room temperature (30°C) (without heat energy input on the
feed side), water flux is still very promising (e.g., 6.3 Lm-2·h-1 for 3.5 wt.% saline water, 3.9 Lm-
2·h-1 for 10 wt.% hypersaline water) (Figure 4a). This energy-saving feature is different from the
MD process, where the water flux (~1 Lm-2·h-1) is often negligible at room temperature.54 For
saline waters with the same concentration, water flux was further enhanced with operation
temperature (from 30 to 70°C) due to an enhanced driving force of the adsorption-diffusion process
of water molecules, since PV is a typical thermal activation adsorption-diffusion process.49 The
activation energy (Eact.) is approximately 3.69 kJ·mol−1 for 3.5 wt.% saline water (Supplementary
Figure 17), which is less than those of other PV processes.49 At the same operating temperature,
the water flux was demonstrated to show a declining trend with increasing feed salt concentration
(Figure 4a).50 This phenomenon is attributed to the elevated salt concentration at the vaporization
interface, where fewer free water molecules are transported across the MOF-801 membrane
because more water molecules are bound to salt ions to form a hydration shell. Moreover, the
MOF-801-1.43 membrane showed high water flux (27.4 Lm-2·h-1) for treating saline waters (3.5
wt.% NaCl), outperforming most state-of-the-art silica, zeolite, and MOF membranes (1-10 Lm-
2·h-1) (Figure 4b). Unlike other studies focusing on 3.5 wt.% NaCl saline water treatment, the
MOF-801 membrane exhibited promising water flux (10.5 Lm-2·h-1) for even more challenging
hypersaline waters (10 wt.%), which are 1.6–7.4 times that of current zeolite and MOF membranes
(Figure 4c). Like the water flux, the water permeance of the MOF-801 membranes were enhanced
with linker deficiencies but decreased with salt concentration (Supplementary Figure 18).

Differentiating from most other MOF membranes that suffer from insufficient water stability,
MOF-801 membranes demonstrate stable operational performance (in both flux and rejection) and
acceptable structural integrity (in both MOF-801 crystalline phase and membrane morphology)
for the treatment of 7 wt.% hypersaline water at 70°C for 120 h (Figures 4d, 4f, 4 g).55 Under XRD,
the MOF-801 membranes exhibited two characteristic reflections of MOF-801 phase between 7
and 11° before and after operation, indicating some stability in their phase crystalline structure
(Figure 4f). However, some peak width broadening was found from 0.24 to 0.37 especially after
108 h exposure at pH 3, which reflected a change in the lattice structure to some extent (i.e., crystal
lattice grain sizes might decrease slightly), while the peaks were nearly unchanged in the case of
hypersaline water exposure. The efficient treatment of harsh environmental wastewaters can be
challenging for conventional membranes. However, after soaking in an acidic hypersaline solution
(pH=3, 10 wt % NaCl), the MOF-801 membrane still exhibited stable flux and salt rejection over
~100 h of operation (Figure 4e). Even after constant operation in harsh environments (e.g., high
temperature, high salinity, and low pH ∼3), the MOF-801 membrane showed good structural
integrity, which was confirmed by its resilient surface morphology, phase composition, and high
ideal gas selectivity (Figures 4f, 4g, Supplementary Figure 19). These results indicate that MOF-
801 membranes are promising candidates for the production of clean water from hypersaline brines
via PV.

To further investigate the resilience of the MOF-801 membrane, desalination performance and
operation stability were evaluated under harsh treatment conditions using acidic brines, industrial
wastewaters, and oxidizing brines (Figure 5). Acidic hypersaline waters with an initial pH of 3
could be concentrated to the point of crystallization by using MOF-801 membranes at an operating
temperature of 70℃, all while consistently producing pure water on the permeate side of the
membrane (Figure 5a, Supplementary Figure 20). During operation, the water flux gradually
decreased from 10.5 to 2.6 Lm-2·h-1 due to the decreasing driving force caused by the feed being
concentrated 4.45-fold, all while salt rejection was maintained above 99.9%.

The treatment of real industrial acidic saline wastewater (pH ~3.4) can also be challenging for
conventional membranes because of its complicated composition (Supplementary Table 5).
Interestingly, the MOF-801 membrane exhibits promisingly stable performance under these
conditions (Figure 5b). The water flux first decreased from its initial value of ~ 10.4 L m–2 h–1 and
then remained relatively stable in the range of ~ 5.0 – 6.0 L m–2 h–1due to the membrane fouling
at the vaporization interface (i.e., membrane surface). By using a simple DI water cleaning method,
the water flux of the MOF-801 membranes could be efficiently recovered to 9.85 L m–2 h–1 (with
a recovery ratio of ~ 94%). In addition to having a stable water flux, the membrane shows high
rejection of all salt ions, such as Na+, K+, Mg2+, and Ca2+ (all above 99.0%), which can be ascribed
to that fact that salt ions have negligible vapor pressure, and did not vaporize during the
pervaporation process.

One of the major challenges for conventional polyamide membranes is their susceptibility to
chlorine oxidation.56 Unlike polyamide membranes, the MOF-801 membranes showed a highly
stable desalination performance for hypersaline water feed even at 70℃ after exposure to 100 ppm
NaClO aqueous solution for as long as 21 days (i.e., equivalent to 50,400 ppm·h chlorine exposure)
(Figure 5c); indicating a significantly improved chlorine resistance (1.7 – 20.0 times higher) than
both commercial and state-of-the-art polyamide membranes (2,500 – 30,430 ppm·h chlorine
exposure).57,58 After continuous operation under these different extreme conditions, all the MOF-
801 membranes retained their integrity as exhibited by the ideal selectivities of H2/N2 gases, which
were still higher than their Knudsen diffusion selectivity (H2/N2: 3.7) (Figure 5f, Supplementary
Figure 21). Moreover, the MOF-801 membranes exhibited stability in both the crystalline phase
and membrane structure, which is reflected by the XRD (only except for slight peak-width
broadening), 1H NMR spectra, ATR-FTIR spectra, and membrane surface morphology (Figures
5d, 5e, 5g, 5h). The performance stability can be ascribed to the highly stable membrane structure
consisting of well intergrown MOF-801 crystals in which there are highly robust Zr–O covalent
bonds, and strong coordination bonds between [Zr6(OH)4O4] cluster (i.e., Lewis acid) and
fumarate linker (i.e., Lewis base). Additionally, unlike commercial polytetrafluoroethylene (PTFE)
distillation membranes (Nanjing CAS-Bidun Newmen Technology Co., Ltd., China), the MOF-
801 pervaporation membranes show better desalination performance and operating stability for
treating more challenging hypersaline waters containing low surface tension species, including oil
and surfactant (Supplementary Figure 22). This is similar to what was previously reported between
commercial PTFE distillation membranes and polymeric pervaporation membranes.59 This
resilient desalination performance under various harsh conditions indicates the application
potential of the robust MOF-801 membranes in a wide range of industrial applications.

Methods
In situ Synthesis of MOF-801 Nanoseed Layer
Both Al2O3 and ZrO2 ceramic substrates (100-200 pieces for each membrane) were first fabricated
by an immersion-induced phase inversion process, followed by complete drying and sintering at
1550°C for 4 h (Al2O3) or at 1050°C for 2 h (ZrO2). A TiO2 interlayer was then coated onto the
substrates by a dip-coating method, followed by complete drying and sintering at 800°C for 4 h.
Then, a thin layer of uniformly dispersed MOF-801 nanoseeds (size ~69 nm) was synthesized in
situ on the outer surface of TiO2 interlayer-modified ceramic substrates via the solvothermal
method. Specifically, fumaric acid and ZrOCl2·8H2O were first dissolved into a solvent mixture
of DMF and formic acid. Then, the substrates with both sides sealed were placed into the mixture
solution inside a 100 mL Teflon reactor for the solvothermal reaction at 120°C for 24 h to form a
MOF-801 nanoseed layer in situ. Finally, after the reaction was allowed to cool, the samples were
cleaned with DMF.

Preparation of Crack-free MOF-801 Membrane
MOF-801 membranes with different missing linkers (10-20 pieces for each membrane
composition) were synthesized via a solvothermal secondary growth method, followed by
surfactant posttreatment. To create different missing-linker densities, fumaric acid (0.1420 g,
0.4260 g, 0.7087 g) and formic acid (9 mL) at different molar ratios (fumaric acid: formic acid =
2:400, 6:400, 10:400) were first mixed with DMF (61 mL) and ZrOCl2·8H2O (0.4025 g). Then,
the substrates coated with a MOF-801 nanoseed layer were placed into the mixture solution inside
a 100 mL Teflon reactor for solvothermal reaction at 120°C for 24 h to allow for the secondary
growth of MOF-801 membranes. Finally, after the reaction, the MOF-801 membranes were
cleaned with DMF and dried at room temperature for 6 h to produce the cracked MOF-801
membranes. To avoid the formation of cracks, the synthesized MOF-801 membranes were
immediately immersed into a Span80 solution (1 g Span80 dissolved in 10 mL chloroform) for 24
h prior to drying. The MOF-801 membranes were completely dried in a chloroform atmosphere
for 72 h and then activated to remove any solvent molecules (DMF) at 150°C for 24 h under
vacuum (-1 bar).

Membrane Performance Evaluation
The desalination performance of MOF-801 membranes (effective membrane area ~100-200 mm2)
was evaluated in a lab-scale pervaporation (PV) setup with various saline waters (1.5, 3.5, 7 wt. %
NaCl, pH 7), hypersaline water (10 wt.% NaCl, pH 7), acidic hypersaline water (10 wt.% NaCl,
pH 3), and real industrial acidic saline wastewater (A machinery factory, Dalian City, Liaoning
Province, China) as the feeds (feed water reservoir volume ~100-250 ml) (Supplementary Figure
3). The pervaporation system was first stabilized for ~2 h. The feed flow rate was controlled at 160
±5 mL min–1 by a peristaltic pump, while a vacuum of (~60 Pa) was applied on the permeate side.
A cold trap was utilized to cool and collect the permeate water after condensation at different time
intervals (~2h). The permeate flux (Jw, L·m-2·h-1) was determined at a certain time interval (Δt, h)
based on the volume of the condensed permeate (ΔV, L) across a constant effective membrane area
(A, m2) according to Eq. (1). During membrane operation, the salt concentration of the solution
was measured using a conductivity meter (DDSJ-308A, Shanghai REX Instrument Factory, China).
The conductivity of the feed solution was used to calculate the salt concentration based on a
calibration curve. Salt rejection was determined according to Eq. 2, where Cf (mg·L−1) and Cp
(mg·L−1) are the salt concentrations of the permeate and feed, respectively:

Jw = ΔV / (A * Δt) (1)
R = (Cf - Cp) / Cf (2)

Molecular Simulations
Classical molecular dynamics simulations, implemented in the LAMMPS package, were
conducted to investigate the pervaporation desalination mechanism of MOF-801-DF, MOF-801-
0.5, and MOF-801-1.5 membranes.60 The simulation system and results are described in detail in
SI Section 3 (Supplementary Figures 23,24).

Pervaporation simulations were carried out in a canonical ensemble (i.e., NVT) at a temperature
of 343 K with a time step of 1 fs. The system’s temperature was modulated using the Nosé‒Hoover
thermostat with a damping factor of 100 time steps (i.e., 100 fs). For each simulation, energy
minimization was first carried out to preliminarily relax the system. Subsequently, a hydrostatic
pressure of 1 atm was applied on the feed pistons, and a molecular dynamics simulation was
performed for 40 ns to bring the liquid density closer to its equilibrium value (i.e., 1.0 g cm−3) and
to fully saturate the initially empty membrane structure with saline solution. Finally, the systems
were further equilibrated for 5 ps, followed by a production run of 20 ps at a constant pressure of
1 atm. We should note that all of the studied membranes, as well as the piston and adsorbing plate,
were assumed to be rigid.

Characterization
The structural morphology or element composition of MOF-801 membranes and ceramic
substrates were characterized in a field emission scanning electron microscope (FE-SEM) (S-4800,
Hitachi, Japan; NOVA NanoSEM 450, FEI Company, USA) equipped with an energy dispersive
spectrometer (EDS). X-ray diffraction (XRD) measurements were carried out in an Ultima IV X-
ray diffractometer using Cu-Kα radiation with a step size of 0.02° and 2 s per step (D/Max-2400,
Rigaku, Japan). The functional groups of the MOF-801 membrane and powder were analyzed by
attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) (IS50, Thermo
Nicolet, US). X-ray photoelectron spectroscopy (XPS) was used for analysis of elements using a
Thermo Fisher K-Alpha spectrometer (K-Alpha, Thermo Fisher, USA). Thermogravimetric
analysis (TGA) was carried out in a thermal analyzer (TG/DTA 6300, Seiko Co., Ltd., Japan) at a
heating rate of 5°C min-1 from room temperature (~25℃) to 700°C in air. Liquid 1H nuclear
magnetic resonance (NMR) spectra were recorded in a nuclear magnetic resonance spectrometer
(Bruker Advance Ⅲ500, Bruker, Switzerland). The nitrogen adsorption-desorption isotherms of
MOF-801 crystals were recorded in an automatic physical adsorption apparatus (AS-1-MP-11,
Quantachrome, USA). Dynamic vapor sorption (DVS, Surface Measurement System Ltd., UK)
was used to measure the water uptake behaviors of MOF-801 and Span80-posttreated MOF-801
crystals, as well as UiO-66 and UiO-66-NH2.

Other detailed characterization can be found in the Supplementary Materials (SI Section 1.4).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript reports a novel approach to enhancing the permeability and selectivity of MOF-801 membranes through the precise regulation of intracrystalline missing-linker defects, which is a significant contribution to the field of water desalination technology. The method of employing an in situ nano-seeding strategy alongside surfactant post-treatment to minimize crack formation represents a notable advance in MOF membrane fabrication. The research's innovation is further underscored by its application to hypersaline water treatment via pervaporation, demonstrating exceptional performance metrics, including near-perfect salt rejection (~99.8%) and high water flux (12.3 L∙m^-2∙h^-1 at 40℃), setting a new standard in the field.\nThe authors should consider the following concerns:\n1. DThe manuscript briefly mentions the impact of defect regulation on membrane performance but lacks a detailed explanation or theoretical model. What specific interactions at the molecular level lead to enhanced water transport and selectivity? A more rigorous theoretical framework or simulation data supporting these claims is suggested.\n2. Control group comparisons: While the performance improvements are highlighted, the manuscript does not provide a detailed comparison with control groups lacking the precise regulation of missing-linker defects. How does the performance of unmodified MOF-801 membranes compare, and what is the quantitative impact of your innovations?\n3. The detailed performance data regarding flux and reject should be presented in Abstract.\n4. The authors briefly claim that this membrane outperforms state-of-the-art silica, MOF, and zeolite polycrystalline membranes for the treatment of both saline and hypersaline waters. Is it true? More supporting data or broader literature review should be presented.\n5. The economic analysis provided is overly simplistic and does not account for scale-up challenges, raw material costs, or operational expenses over the membrane's lifecycle. Can the authors expand this analysis to include a detailed cost breakdown and a comparison with existing desalination technologies??\n6. The performance stability under different environmental conditions (e.g., extreme pH, high temperatures, biofouling potential) is not adequately addressed. How does the membrane's performance vary under these stress conditions, and what mechanisms ensure its stability? Please briefly discuss this issue.\nGiven the manuscript's substantial contributions and innovative approaches to MOF membrane technology for water purification, I recommend a moderate revision.", "reviewer_2": "This manuscript should be immediately rejected by Nature Communications, with no opportunity for reconsideration. This manuscript is most well suited for publication in a specialized disciplinary journal, such as the Journal of Membrane Science or Desalination or other membrane or water purification focused journal.\nThere is an overall lack of novelty in this paper and the results of this work are not of enough significance to be reported in Nature Communications, despite this possibly being the first report of using the material MOF-801 for pervaporation desalination.\nMany molecular sieves and polymers have previously been reported for pervaporation desalination, and have performance superior to that of the membranes reported by this manuscript. In addition to having superior performance, the previously reported membranes (often polymers or nanocomposites) have much simpler manufacturing capability and potential for successful commercial scale up.\nThe authors of this paper seem to be unaware of the extensive body of literature on the topic of pervaporation desalination and are referred to Table 2 of the excellent review paper “Desalination by membrane pervaporation: A Review” Desalination, 547, 1, 116223, doi:10.1016/j.desal.2022.116223 (which is not cited by this manuscript). Table 2 of the referenced review paper provides a comprehensive summary of performance of >50 distinct pervaporation desalination membranes. As can be seen from this summary table multiple of the previously reported membranes have fluxes much larger than that of the MOF-801-based membranes reported in this manuscript (maximum reported flux in this manuscript of ~38 L m-2 h-1).\nUnlike in say, for example, pressure driven reverse osmosis desalination membranes, by the inherent nature of transport through the pervaporation process the flux of the pervaporation desalination membranes is largely insensitive to the feed concentration. This is because the driving force is not proportional to the difference between the applied pressure and the osmotic pressure of the feed solution (which is significantly reduced for hypersaline feed solutions), but the driving force in pervaporation is a function of the chemical potential difference, which is practically realized in the pervaporation process as a vapor pressure difference… and it is well established that the vapor pressure of the saline feed solutions does not change significantly as a function of solute concentration because the vapor pressure of salts is essentially negligible at any potential operational temperature of pervaporation. The vapor pressure differential, therefore, obviously is increased by either increasing the feed solution temperature or decreasing the permeate side vacuum level.\nThis manuscript also fails to report the water permeation results in the standard parameter preferred in the membrane science community – permeance (or permeability). The authors are referred to the excellent paper “Permeability, permeance and selectivity: A preferred way of reporting pervaporation performance data” by Richard W. Baker et al. ttps://doi.org/10.1016/j.memsci.2009.11.022 to understand the standard convention and include them in their updated resubmission to an alternate journal.\nFinally, the use of a molecule (in this case the surfactant/zwitterion Span80) to backfill defects in cracks of an inorganic membrane structure is not novel.\nOverall, this manuscript fails to recognize the extensive body of literature on pervaporation desalination, does not use standard conventions for reporting permeance in pervaporation membranes, and the reported membranes do not have such outstanding performance properties. While this paper may have some interesting materials science aspects to it and modeling components, the potential impact of these beyond the small field of pervaporation desalination is not sufficient to justify publication in Nature Communications.", "reviewer_3": "Polycrystalline MOF membranes have shown great potential for molecular separation. Most current works focus on removing inter-granular defects (e.g., cracks) to obtain continuous MOF membrane.\nThere are few reports paying attention to the lattice defects in MOF membrane. This manuscript focuses on the precise regulation of missing linkers lattice defects in MOF-801 membrane by controlling the amount of modulator for pervaporation desalination, which is novel. The relationship between the lattice defects and membrane microstructure was systematically investigated, and outstanding desalination was achieved owing to the missing linkers enhance membrane structural hydrophilicity with stronger host-guest interaction energy. The idea to precisely control lattice defects by simply adjusting the amount of modulator is interesting, which would inspire fabricating other next-generation MOF nanochannel membranes with high separation performance. Therefore, the manuscript can be accepted by the journal, however, several issues should be further addressed.\n1.In view of the topic “Lattice-defects engineering in MOF membrane for desalination”, the authors are suggested to give a comparison between this work with the highly relevant recent paper (Nat. Mater. 2023, 22, 769). In addition, the proposed in situ nano-seeding strategy to construct MOF-801 membrane in this work was also reported by the same authors for preparing another type of Zr-MOF membranes, UiO-66 membrane (Nat. Common. 2022, 13, 266), what is the essential difference between the two works, the authors should further clarify it.\n2.When the evaporation takes place, salts ions cannot be vaporized and the presence of membrane would inevitably increase the transfer resistance during the pervaporation desalination process. The membrane distillation (MD) is very similar to pervaporation desalination. MD uses the low-grade waste heat, not vacuum that is one of the most expensive form of energy. What is the advantage of pervaporation desalination compared with MD?\n3.What is the role of TiO2 layer for membrane formation? If without TiO2, can the continuous MOF membrane be prepared by the in-situ nano-seeding strategy followed by surfactant post-treatment?\n4.The authors tried to post-treat MOF membrane using three kinds of surfactants, SLS, DTAB, and Span 80. Results show that only Span 80 facilitates the formation of cracks-free membrane (Fig.1 and Fig. S7). Why? The authors are suggested to provide the detailed explanation.\n5.The authors stated “Ti was detected in the TiO2 nano-interlayer surface, while only Zr was detected in the crack-free MOF-801 membrane surface, suggesting the intergrowth integrity of the membrane”, I am very curious why the Zr was not detected in cracked MOF-801 membrane shown in Fig. S11, because lots of MOF crystals were also deposited in substrate surface (Fig. 1b), the signal of Zr should be significant. According to the description by the authors, in Fig. S11, the icon a2 should be cracked-free MOF-801 membrane."}, "author_response": "Response to Reviewers: NCOMMS-24-08272A-Z\nReviewer #2 (Remarks to the Author):\nGeneral comments: This manuscript should be immediately rejected by Nature\nCommunications, with no opportunity for reconsideration. This manuscript is most\nwell suited for publication in a specialized disciplinary journal, such as the Journal of\nMembrane Science or Desalination or other membrane or water purification focused\njournal. There is an overall lack of novelty in this paper and the results of this work\nare not of enough significance to be reported in Nature Communications, despite this\npossibly being the first report of using the material MOF-801 for pervaporation\ndesalination.\nResponse: We sincerely appreciate the Reviewer #2 for providing detailed comments\non how to improve the manuscript. To address the reviewer’s concerns about novelty,\nwe have further highlighted the key contributions of our work and its broader\nimplications, which motivated our decision to submit to Nature Communications.\nImportant novel aspects are described below:\n1. The first novel aspect in this work is the precise regulation of missing linkers\nlattice defects in the MOF membrane (Fig. 2). Intracrystalline defects—such as\nmissing linkers and missing clusters—have been synthesized and confirmed to\ninfluence the permeability or selectivity of MOF liquid- or gas-separation membranes.\nHowever, the precise regulation of favorable intracrystalline defects and their effect\non fundamental mass transport phenomena for desalination has not been previously\nreported for membrane-based separation applications. As Reviewer #3 positively\nnoted, there are few reports paying attention to the lattice defects in MOF\nmembranes. More importantly, we demonstrated a facile method to precisely control\nthe frequency of missing linkers, which has not been previously realized for MOF\nmembranes.\n2. The second novel aspect is the characterization of the atomistic mechanism for\nenhanced water transport induced by precise regulation of missing linkers (Fig.\n3). While published works on pervaporation desalination largely focus on membrane\nfabrication and performance evaluation, very rarely is the fundamental atomistic\nmechanism for water transport explored. Interestingly, we found that precise\nregulation of missing linkers enhances membrane structural hydrophilicity with\nstronger host-guest interaction energy. Resulting in a lower energy barrier by\nenlarging the MOF pore window and pore cage, the structural configuration of\nMOF-801 with the precise regulation of missing linkers enables the observed increase\nin water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different\ndisciplines and fields of science, technology, and engineering (e.g., chemistry,\nmaterials, environmental science, chemical engineering, water and membrane\ntechnologies). Thus, we believe that this work with fundamental mechanistic insights\nis of great interest for the broad readership of Nature Communications.\n3. The third novel aspect of this work is the superior performance of our MOF\nmembrane in comparison to other state-of-the-art zeolite and MOF membranes\nfor pervaporation desalination. As Reviewer #2 has recognized, our work is the\nfirst report to use the material MOF-801 for pervaporation desalination and has\nsome interesting materials science aspects and modeling components. We\nrecognize that some pervaporation desalination membranes—especially polymeric\nmembranes—have higher performance (with respect to water flux) under specific\nconditions, but we wish to emphasize that our MOF membranes indeed outperform\nstate-of-the-art zeolite and MOF membranes in water flux (Figure 4 and Tables S5-6),\nwhich belong to an emerging class of polycrystalline molecular sieve membranes that\nare drastically different from polymeric membranes (such as PVA membranes). As a\nresult, the performance comparison of membranes with similar structures and\nproperties was deemed more appropriate for this study.\n4. The fourth novel aspect of this work is the exceptional stability under harsh\nchemical conditions (i.e., high-temperature, acidic, oxidizing conditions, feeds with\nrefractory species like oil or surfactants) of our MOF membrane. Differing from\nprevious reports focusing on desalination under mild conditions, we intentionally\nsubjected our MOF membrane to harsh chemical conditions for prolonged periods of\ntime to evaluate their resilience in practical applications that have proven challenging\nfor conventional polymeric membranes (Fig. 4, Fig. 5, Fig. S16-21, Table S4). To this\nend, our MOF membrane showcased stable performance when treating real\nindustrial wastewater with a complicated composition, which has not been\nsuccessfully demonstrated previously (Fig. 5, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies.\nWe believe that this has broader implications for the design and synthesis of novel\nmembrane materials (e.g., MOF-801 in our work), which has not been the traditional\nfocus in the field. Our current work provides an entirely new platform for robust\ndesalination under harsh chemical conditions, expanding the number applications\nwhere membrane-based desalination is now relevant.\n1. Many molecular sieves and polymers have previously been reported for\npervaporation desalination, and have performance superior to that of the membranes\nreported by this manuscript. In addition to having superior performance, the\npreviously reported membranes (often polymers or nanocomposites) have much\nsimpler manufacturing capability and potential for successful commercial scale up.\nResponse: We agree with the opinion of Reviewer #2 that polymeric or\nnanocomposite membranes have simpler manufacturing requirements and currently a\nhigher potential for scaling up. However, we strongly believe that immediate scaling\npotential of membrane fabrication process is only a minor element for a\nhigh-impactful scientific paper. Fabrication of a continuous, well-intergrown Zr-MOF\nmembrane is extraordinarily challenging. Despite this, we successfully fabricated a\nhigh-quality MOF-801 membrane for pervaporation applications. In fact, our\nfabrication process is relatively straightforward, only requiring two steps: (i) in-situ\nnano-seeding of MOF-801 crystals and (ii) surfactant post-treatment for secondary\ngrowth to enable a well-intergrown MOF-801 membrane structure.\nMoreover, the core novel aspects of this work include the precise regulation of\nmissing linkers, characterization of the atomistic mechanism of enhanced\nperformance, and harsh chemical operation stability, all of which have not been\nexplored in previous works. Additionally, the stable performance of treating real\nindustrial wastewater (Fig. 5, Table S4) indicates the promising practical potential of\nour membranes. Furthermore, it is technically feasible to employ large-size\ncommercial ceramic or polymeric membranes for MOF membrane synthesis, which\nincreases the potential for scaling up the fabrication of our MOF membrane (1, 2).\nReference\n1. Xiansong Shi, Dan Zhao, Mastering the mass production of metal–organic framework\nmembranes, Nature Water, 2 (2024)106-107.\n2. Yingchao Dong, Hui Wu, Fenglin Yang, Stephen Gray, Cost and efficiency perspectives of\nceramic membranes for water treatment, Water Research, 220 (2022) 118629\n2. The authors of this paper seem to be unaware of the extensive body of literature on\nthe topic of pervaporation desalination and are referred to Table 2 of the excellent\nreview paper “Desalination by membrane pervaporation: A Review” Desalination,\n547, 1, 116223, doi:10.1016/j.desal.2022.116223 (which is not cited by this\nmanuscript). Table 2 of the referenced review paper provides a comprehensive\nsummary of performance of >50 distinct pervaporation desalination membranes. As\ncan be seen from this summary table multiple of the previously reported membranes\nhave fluxes much larger than that of the MOF-801-based membranes reported in this\nmanuscript (maximum reported flux in this manuscript of ~38 L m-2 h-1).\nResponse: We thank the Reviewer for providing the reference and have read it\ncarefully. We do acknowledge that some pervaporation desalination membranes,\nespecially PVA polymeric membranes, have higher performance (i.e., water flux) than\nour MOF membranes. However, it should be noted that the experimental conditions in\nthe table being referenced vary significantly, which impact the driving force for\npervaporation and the resulting water fluxes that are reported. For example, we used\nan ice-water bath (i.e., 273 K) to determine the flux of our MOF-801 membrane,\nwhereas a higher driving force enabled by a liquid N cold trap (i.e., 77 K) was used\n2\nin other studies using polymeric membranes (1), which—we would argue—are not\nindustrial-relevant conditions.\nRegardless, we wish to emphasize the fact that our MOF membranes indeed\noutperform state-of-the-art zeolite and MOF membranes in water flux (Figure 4 and\nTables S5-6), which belong to the same family of polycrystalline molecular sieve\nmembranes with similar structures and properties.\nMoreover, differing from the other reports focusing on mild conditions for\ndesalination, one of the major highlights of this work is that the MOF membrane\nexhibits exceptional stability under harsh chemical conditions (i.e., high-temperature,\nacidic, oxidizing conditions, feeds with refractory species like oil or surfactants) (Fig. 4, Fig. 5, Fig. S16-21, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies\n(2-7).\nReferences\n1. Yunlong Xue, Jin Huang, CherHon Lau, Bing Cao, Pei Li, Tailoring the molecular structure\nof crosslinked polymers for pervaporation desalination. Nature Communications, 11 (2020),\n1461.\n2. Zhongzhen Wang, Chen Ma, Chunyan Xu, Scott A. Sinquefield, Meisha L. Shofner &\nSankar Nair, Graphene oxide nanofiltration membranes for desalination under realistic\nconditions, Nature Sustainability, 4 (2021), 402-408.\n3. Dong Han Seo, Shafique Pineda, Yun Chul Woo, Ming Xie, Adrian T. Murdock, Elisa Y. M.\nAng, Yalong Jiao, Myoung Jun Park, Sung Il Lim, Malcolm Lawn, Fabricio Frizera Borghi,\nZhao Jun Han, Stephen Gray, Graeme Millar, Aijun Du, Ho Kyong Shon, Teng Yong Ng &\nKostya (Ken) Ostrikov, Anti-fouling graphene-based membranes for effective water\ndesalination, Nature Communications, 9 (1) (2018) 683.\n4. Luda Wang, Michael S. H. Boutilier, Piran R. Kidambi, Doojoon Jang, Nicolas G.\nHadjiconstantinou & Rohit Karnik, Fundamental transport mechanisms, fabrication and\npotential applications of nanoporous atomically thin membranes, Nature Nanotechnology, 12\n(2017), 509–522.\n5. Jay R. Werber, Chinedum O. Osuji & Menachem Elimelech, Materials for next-generation\ndesalination and water purification membranes, Nature Reviews Materials, 1(5) (2016),\n16018.\n6. Rhea Verbeke, Douglas M. Davenport, Timothée Stassin, Samuel Eyley, Marcel Dickmann,\nAlexander John Cruz, Praveen Dara, Cody L. Ritt, Caroline Bogaerts, Werner Egger, Rob\nAmeloot, Johan Meersschaut, Wim Thielemans, Guy Koeckelberghs, Menachem Elimelech,\n& Ivo F. J. Vankelecom, Chlorine-Resistant Epoxide-Based Membranes for Sustainable Water\nDesalination, Environmental Science & Technology Letters, 8 (9) (2021), 818-824.\n7. Huiling Chen, Xing Liu, Dian Gong, Chang Zhu, Guojuan Liu, Jingrui Fan, Ping Wu,\nZhi Li, Yichang Pan, Guosheng Shi, Yuhan Sun & Gaofeng Zeng, Ultrahigh-water-flux\ndesalination on graphdiyne membranes, Nature Water, 1 (2023), 800-807.\n3. Unlike in say, for example, pressure driven reverse osmosis desalination\nmembranes, by the inherent nature of transport through the pervaporation process the\nflux of the pervaporation desalination membranes is largely insensitive to the feed\nconcentration. This is because the driving force is not proportional to the difference\nbetween the applied pressure and the osmotic pressure of the feed solution\n(which is significantly reduced for hypersaline feed solutions), but the driving force in\npervaporation is a function of the chemical potential difference, which is practically\nrealized in the pervaporation process as a vapor pressure difference… and it is well\nestablished that the vapor pressure of the saline feed solutions does not change\nsignificantly as a function of solute concentration because the vapor pressure of salts\nis essentially negligible at any potential operational temperature of pervaporation. The\nvapor pressure differential, therefore, obviously is increased by either increasing the\nfeed solution temperature or decreasing the permeate side vacuum level.\nResponse: We agree with the opinion of Reviewer #2 on the working mechanism and\noperational advantages of pervaporation membrane processes. In our work, we\nemployed stable MOF membranes to efficiently treat highly saline waters by fully\nutilizing these advantages of the pervaporation process. This indeed could overcome\nthe limitation of conventional RO membranes, which are not suitable for treatment of\nhypersaline waters. We have highlighted the working mechanism and operational\nadvantages of the pervaporation process in our original submission (line 51-59, page\n3).\nMore importantly, we want to reiterate that the core novel aspects of this work go\nbeyond the performance of our novel MOF membrane under controlled conditions,\nbut include a facile synthesis procedure for the precise regulation of missing linkers\nthat facilitate this enhanced water flux, characterization of the atomistic mechanism of\nwater transport to relate structural properties to observed pervaporation performance,\nand resilient operational stability under chemically-harsh and application-relevant\nconditions, all of which have not been explored in previous works.\nTo delve into one of these topics that would have broad appeal to the audience of\nNature Communications, we characterized the atomistic mechanism induced by\nprecise regulation of missing linkers that governs enhanced water transport\nthrough the confined structure of our MOF membrane (Fig. 3). Most of existing\nworks on pervaporation desalination largely focus on membrane fabrication and\nperformance evaluation, which rarely provides a fundamental atomistic mechanism\nunderstanding of water transport. Interestingly, we find that precise regulation of\nmissing linkers enhances membrane structural hydrophilicity with stronger host-guest\ninteraction energy, resulting in more rapid water transport with a lower energy barrier\nenabled by enlarging the MOF pore window and pore cage. As mentioned before, we\nstrongly believe this fundamental understanding has broader scientific implications\nand will aid in bridging knowledge gaps across different disciplines and fields of\nscience, technology, and engineering (e.g., chemistry, materials, environmental\nscience, chemical engineering, and water and membrane technologies). Thus, we\nbelieve that this work with fundamental mechanistic insights is of great interest for\nthe broad readership of Nature Communications.\n4. This manuscript also fails to report the water permeation results in the standard\nparameter preferred in the membrane science community – permeance (or\npermeability). The authors are referred to the excellent paper “Permeability, permeance and selectivity: A preferred way of reporting pervaporation performance data” by Richard W. Baker et al. ttps://doi.org/10.1016/j.memsci.2009.11.022 to\nunderstand the standard convention and include them in their updated resubmission to\nan alternate journal.\nResponse: We thank Reviewer #2 for providing the reference and have read it\ncarefully. We agree with the opinion of Reviewer #2 that the parameters (i.e.,\npermeance, permeability) better reflect intrinsic properties of the membranes. It\nshould be noted that the reference provided by the reviewer is for pervaporation with\nmixtures of organics-organics or organics-water, where the focus is on the selectivity\nof separation and permeability-selectivity tradeoff.\nHowever, water flux is often presented as a metric of comparison in pervaporation\ndesalination studies (1-14). Due to practical challenges of obtaining accurate\npermeability data, permeance is not always reported in open literature as it requires\nprecise measurements of membrane thickness and close monitoring of operating\nconditions. In fact, if this information is not disclosed, permeance can obfuscate the\nexperimental conditions that should be used for a fair comparison between materials.\nTherefore, we have adopted the standard practice—which has been used for other\nmembrane processes like microfiltration and membrane distillation—of reporting\nwater flux as a simpler parameter directly reflecting water treatment efficiency—\nwhile providing transparency about our experimental conditions and membrane\nproperties (15-17).\nMore importantly, the core novel aspects of this work include the precise regulation of\nmissing linkers, characterization of the atomistic mechanism of enhanced\nperformance, and harsh chemical operation stability, all of which have not been\nexplored in existing works, all of which have not been explored in existing works.\nReference\n1. Meidi Wang, Penghui Zhang, Xu Liang, Junyi Zhao, Yawei Liu, Yu Cao, Hongjian\nWang, Yu Chen, Zhiming Zhang, Fusheng Pan, Zhenjie Zhang, Zhongyi Jiang, Ultrafast\nseawater desalination with covalent organic framework membranes, Nature\nSustainability 5 (2022) 518–526.\n2. Zishu Cao, Shixuan Zeng, Zhi Xu, Antonios Arvanitis, Shaowei Yang, Xuehong Gu,\nJunhang Dong, Ultrathin ZSM-5 zeolite nanosheet laminated membrane for high-flux\ndesalination of concentrated brines. Science Advances. 4 (2018) eaau8634.\n3. Chun Xiang C Lin, Li Ping Ding, Simon Smart, João C Diniz da Costa, Cobalt oxide\nsilica membranes for desalination, Journal of Colloid and Interface Science 368(2012)\n70-76.\n4. Mikel C Duke, Steven Mee, J C Diniz da Costa, Performance of porous inorganic\nmembranes in non-osmotic desalination. Water Research 41(2007) 3998-4004.\n5. Huayu Zhang, Jiuli Wen, Qi Shao, Ai Yuan, Haiting Ren, Fangying Luo, Xiaoliang\nZhang, Fabrication of La/Y-codoped microporous organosilica membranes for\nhigh-performance pervaporation desalination. Journal of Membrane Science 584(2019)\n353-363.\n6. Shengnan Wang, David K Wang, Julius Motuzas, Simon Smart, João C Diniz da Costa,\nRapid thermal treatment of interlayer-free ethyl silicate 40 derived membranes for\ndesalination. Journal of Membrane Science 516(2016) 94-103.\n7. Sheida Khajavi, Jacobus C Jansen, Freek Kapteijn, Production of ultra pure water by\ndesalination of seawater using a hydroxy sodalite membrane. Journal of Membrane\nScience 356(2010) 52-57.\n8. Mikel C Duke, Jessica O’Brien-Abraham, Nicholas Milne, Bo Zhu, Jerry Y.S. Lin, D\nJoão C. Diniz da Costa, Seawater desalination performance of MFI type membranes\nmade by secondary growth. Separation and Purification Technology 68(2009) 343-350.\n9. Churl Hee Cho, Ka Yeon Oh, Si Kyung Kim, Jeong Gu Yeo, Pankaj Sharma,\nPervaporative seawater desalination using NaA zeolite membrane: Mechanisms of high\nwater flux and high salt rejection. Journal of Membrane Science 371(2011) 226-238.\n10. Paul Swenson, Brenden Tanchuk, Ankita Gupta, Weizhu An, Steven M. Kuznicki,\nPervaporative desalination of water using natural zeolite membranes. Desalination\n285(2012) 68-72.\n11. Chen Zhou, Junjie Zhou, Aisheng Huang, Seeding-free synthesis of zeolite FAU\nmembrane for seawater desalination by pervaporation. Microporous and Mesoporous\nMaterials 234(2016) 377-383\n12. Martin Drobek, Christelle Yacou, Julius Motuzas, Anne Julbe, Liping Ding, João C.\nDiniz da Costa, Long term pervaporation desalination of tubular MFI zeolite membranes.\nJournal of Membrane Science 415-416(2012) 816-823.\n13. Yaqiong Zhu, Krishna M. Gupta, Qian Liu, Jianwen Jiang, Jürgen Caro, Aisheng Huang,\nSynthesis and seawater desalination of molecular sieving zeolitic imidazolate framework\nmembranes. Desalination 385(2016) 75-82.\n14. Linlin Wan, Chen Zhou, Kai Xu, Bo Feng, Aisheng Huang, Synthesis of highly stable\nUiO-66-NH membranes with high ions rejection for seawater desalination.\n15. Huiling Chen, Xing Liu, Dian Gong, Chang Zhu, Guojuan Liu, Jingrui Fan, Ping Wu,\nZhi Li, Yichang Pan, Guosheng Shi, Yuhan Sun, Gaofeng Zeng, Ultrahigh-water-flux\ndesalination on graphdiyne membranes, Nature Water, 1 (2023), 800-807.\n16. Luke Yan, Gui Zhang, Lei Zhang, Wei Zhang, Jincui Gu, Youju Huang, Jiawei Zhang,\nTao Chen, Robust construction of underwater superoleophobic CNTs/nanoparticles\nmultifunctional hybrid membranes via interception effect for oily wastewater\npurification. Journal of Membrane Science 569(2019) 32-40.\n17. Yu Gu, Bowu Zhang, Zhiang Fu, Jihao Li, Ming Yu, Linfan Li, Jingye Li. Poly (vinyl\nalcohol) modification of poly(vinylidene fluoride) microfiltration membranes for\noil/water emulsion separation via an unconventional radiation method. Journal of\nMembrane Science. 619(2021) 118792.\n5. Finally, the use of a molecule (in this case the surfactant/zwitterion Span80) to\nbackfill defects in cracks of an inorganic membrane structure is not novel.\nResponse: We appreciate the opinion of Reviewer #2, but want to re-emphasize that\nthe novelty in our synthesis is not the use of a surfactant to achieve a crack-free MOF\nmembrane, but the precise regulation of missing linkers in the crystalline structure of\nour MOF that enables both enhanced water transport and resilient operation for\npervaporation desalination. Beyond the novelty of this synthesis, we want to highlight\nthat the core novel aspects of this work also include the characterization of the\natomistic mechanism of water transport to relate structural properties to observed\npervaporation performance and resilient operational stability under chemically-harsh\nand application-relevant conditions, all of which have not been explored in previous\nworks.\nOverall, this manuscript fails to recognize the extensive body of literature on\npervaporation desalination, does not use standard conventions for reporting\npermeance in pervaporation membranes, and the reported membranes do not have\nsuch outstanding performance properties. While this paper may have some interesting\nmaterials science aspects to it and modeling components, the potential impact of these\nbeyond the small field of pervaporation desalination is not sufficient to justify\npublication in Nature Communications.\nWe sincerely appreciate the Reviewer #2 for providing these detailed comments on\nhow to improve the manuscript. Specifically, we appreciate comments encouraging us\nto distinguish our MOF membrane from conventional polymeric and to report our\nresults in terms of permeance. Upon reflection, it would seem that the reservations of\nReviewer #2 could be distilled to three main issues: (i) lower performance (i.e., water\nflux) in comparison to other pervaporation membranes that have been reported,\n(ii) novelty of the synthesis strategy, specifically using a surfactant to “backfill” defects,\nand (iii) the applied focus of the manuscript on demonstrating enhanced pervaporation\nperformance. We hope that our preceding responses have addressed each of these\nconcerns, but we will summarize our case below:\n1. Lower Performance: We acknowledge that some pervaporation desalination\nmembranes—especially PVA polymeric membranes—have reported higher\nperformance (i.e., water flux) than our MOF membranes. However, it should\nbe noted that experimental conditions for evaluating pervaporation membranes\nacross the field are not uniform, and it is this variability that impacts the\ndriving force for pervaporation and the water fluxes that are reported. For\nexample, we used an ice-water bath (i.e., 273 K) to determine the flux of our\nMOF-801 membrane whereas a higher driving force enabled by a liquid\nnitrogen cold trap (i.e., 77 K) was used in other studies using polymeric\nmembranes. Furthermore, the structure and properties of polymeric\nmembranes is distinctly different from our MOF membranes, therefore it\nmakes more sense to compare the performance of our MOF membrane to\nother state-of-the-art zeolite and MOF membranes that belong to an emerging\nclass of polycrystalline molecular sieve membranes with similar structures and\nproperties.\n2. Novelty of Synthesis Strategy: We argue—as has been argued\nelsewhere—that the surfactant is not “backfilling” as Reviewer #2 suggests,\nbut reducing the evaporation rate of residual solvent or modulator\n(N,N-dimethyl formamide or formic acid) to reduce the capillary stress\nbetween intergrown MOF crystals (1). While having a crack-free MOF\nmembrane structure is important for the enhanced water transport\nphenomenon observed in our MOF membranes, the novelty in this synthesis\nlies in the facile (2 steps) approach pioneered to precisely regulate the\nfrequency of missing linkers in the intracrystalline structure of our MOF\nmembrane to facilitate enhanced water transport.\n3. Applied Focus: One of the critical advantages of MOF membranes over\nconventional polymeric membranes is their resilience in chemically-harsh and\napplication-relevant conditions. Therefore, it is critical to characterize and test\nthe limits of this unique property of MOF membranes for pervaporation.\nHowever, a major focus on this manuscript was understanding the atomistic\nmechanism that enables the superior water transport phenomenon observed by\nour MOF membranes. Interestingly, we found that the precise regulation of\nmissing linkers enhanced the membrane structural hydrophilicity with stronger\nhost-guest interaction energy. Through the precise regulation of the frequency\nof missing linkers, we were able to lower the energy barrier for water transport\nby optimizing the MOF pore window and pore cage diameters. While this\nmass transport phenomenon is being demonstrated through its application to\npervaporation, these fundamental mechanistic findings have implications to a\nwide variety of fields, including chemistry, materials, environmental science,\nchemical engineering, and water and membrane technologies.\nWe believe the novel aspects of this work include a facile synthesis procedure for the\nprecise regulation of missing linkers that facilitate an enhanced water flux in\ncomparison to state-of-the-art zeolite and MOF membranes, characterization of the\natomistic mechanisms of water transport to relate structural properties to observed\npervaporation performance, and resilient operational stability under chemically-harsh\nand application-relevant conditions, all of which have not been explored in previous\nworks. This work underscores that advancements in water treatment to addressing\nglobal water pollution and water crisis need to address more challenging and realistic\nwastewater streams, which fits with the scope of the journal. We strongly believe this\nfundamental understanding has broader scientific implications and will aid in bridging\nknowledge gaps across different disciplines and fields of science, technology, and\nengineering. Thus, we believe that this work with fundamental mechanistic insights is\nof great interest for the broad readership of Nature Communications.\nReference\n1. Yoo, Y.; Varela-Guerrero, V.; Jeong, H. K., Isoreticular Metal-Organic Frameworks and Their\nMembranes with Enhanced Crack Resistance and Moisture Stability by Surfactant-Assisted\nDrying. Langmuir 27 (6) (2011) 2652-2657.\nResponse to Reviewer #1’s comments\nReviewer #1 (Remarks to the Author):\nGeneral comments: The manuscript reports a novel approach to enhancing the\npermeability and selectivity of MOF-801 membranes through the precise regulation of\nintracrystalline missing-linker defects, which is a significant contribution to the field\nof water desalination technology. The method of employing an in situ nano-seeding\nstrategy alongside surfactant post-treatment to minimize crack formation represents a\nnotable advance in MOF membrane fabrication. The research's innovation is further\nunderscored by its application to hypersaline water treatment via pervaporation,\ndemonstrating exceptional performance metrics, including near-perfect salt rejection\n(~99.8%) and high water flux (12.3 L∙m^-2∙h^-1 at 40℃), setting a new standard in\nthe field.\nGiven the manuscript's substantial contributions and innovative approaches to MOF\nmembrane technology for water purification, I recommend a moderate revision.\nResponse: We appreciate that you took time to evaluate our manuscript and provide\nencouranging comments on the novelty and significance of our work. Your valuable\nsuggestions and thoughtful comments were instrumental for us to further clarify the\nsignificance of our work and improve the quality of our manuscript. We have\ncarefully considered all the comments/suggestions, given point-by-point responses (as\nshown below), and made revisions to improve the quality and impact of our\nmanuscript.\nThe authors should consider the following concerns:\n1. The manuscript briefly mentions the impact of defect regulation on membrane\nperformance but lacks a detailed explanation or theoretical model. What specific\ninteractions at the molecular level lead to enhanced water transport and selectivity? A\nmore rigorous theoretical framework or simulation data supporting these claims is\nsuggested.\nResponse: Thank you for this valuable comment! We agree with your perspective\nabout the importance of using a detailed mechanistic explanation or theoretical model.\nIn addition to studying the effect of missing-linker defect regulation on membrane\nperformance, we characterized the detailed atomistic mechanism for enhanced water\ntransport induced by precise regulation of missing linkers with detailed theoretical\nexplanation by employing three powerful simulation protocols including\nmolecular dynamics (MD), monte carlo (MC) simulations, and density functional\ntheory (DFT) calculations (Fig. 3, Fig. S22, Fig. S23, Line 228-243, Page 11, Line\n258-273, Page 13, revised manuscript). While previously published works on\npervaporation desalination largely focus on membrane fabrication and performance\nevaluation, very rarely is the fundamental atomistic mechanism for water transport\nexplored. Interestingly, we found that precise regulation of more missing\nfumaric linkers could enhance membrane structural hydrophilicity due to the exposure\nof more hydrophilic [Zr (OH) O ] cluster sites with stronger host-guest (i.e.,\n6 4 4\nframework-water molecules) interaction energy. Resulting in a lower energy barrier\nby enlarging the MOF pore window and pore cage, the structural configuration of\nMOF-801 with the precise regulation of missing linkers enables the observed increase\nin water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different\ndisciplines and fields of science, technology, and engineering (e.g., chemistry,\nmaterials, environmental science, chemical engineering, water and membrane\ntechnologies). Thus, we believe that this work with fundamental mechanistic insights\nis of great interest for the broad readership of Nature Communications.\nTo address the reviewer’s concern, we have revised and highlighted the discussion\nin the manuscript (Line 230-245, Page 11, Line 260-275, Page 13, revised\nmanuscript). The revisions are also shown as follows:\nTo shed light on the effect of missing linkers on desalination performance,\nstate-of-the-art molecular simulations, including molecular dynamics and Monte\nCarlo, associated with experimental data were employed to offer atomistic insights\ninto the permeation mechanism of water molecules through MOF-801 membranes\n(Figures 3, S22). To reveal the role of missing linkers, we investigated a defect-free\nsimulation structure and two highly symmetric missing-linker simulation structures\nwith theoretical deficiency of 1/12 and 1/4 (also denoted MOF-801-DF, MOF-801-0.5,\nand MOF-801-1.5, respectively). Through these simulations, the improvement in\nwater flux was ascribed to missing linkers not only enhancing water adsorption (i.e.,\nwater affinity) but also water diffusion by altering the intracrystalline pore\nmicroenvironment (i.e., more hydrophilic active sites) and structure (i.e., both\nenlarged pore window and pore cage) of the subnanometer channels in the MOF-801\nframework structure. Reducing the activation energy barrier, the presence of missing\nlinkers enables the ultrafast transport of more water molecules (Figures 3a3e).\nMissing linkers also enhance the structural hydrophilicity of the MOF frameworks\ndue to the exposure of more water adsorption sites (i.e., [Zr (OH) O ] cluster),\n6 4 4\nresulting in a higher water uptake rate and higher water loading (Figures 3f, 3 g, S23).\nTo gain insight into such an enhancement from an energetic point of view, Monte\nCarlo simulations were conducted to sample the interaction energy between a single\nwater molecule and MOF-801 framework structures. The interaction energy\ndistribution for MOF-801-0.5 and MOF-801-1.5 indicated stronger interactions\nresulting from water-framework Coulomb interactions when compared to\nMOF-801-DF (Figure 3h). As a result, MOF-801 exhibited 4-16 times higher\nadsorption capacity when compared with other state-of-the-art, water-stable MOFs\n(i.e., ML-UiO-66, UiO-66, UiO-66-NH ) (Figure 3i). During the PV process, the\n2\ncreation of more missing linkers enhances the permeation dynamics of more water\nmolecules inside the membranes, indicating a more rapid water adsorption-diffusion\nprocess (Figure 3j). Theoretically, the water flux significantly increases from 16.4 to\n36.4 L·m−1·h−1 with increasing missing linker deficiency from 0 to 1.5 (Figure 3k).\nWe can, therefore, conclude that intracrystalline missing linkers in the MOF-801\nmembrane not only promote the structural hydrophilicity (i.e., water adsorption ability)\nbut also render faster transport dynamics (i.e., diffusion ability) of water molecules.\nThese two aspects result in the higher water flux of MOF-801 membranes with more\nmissing linkers than was observed experimentally.\n2. Control group comparisons: While the performance improvements are highlighted,\nthe manuscript does not provide a detailed comparison with control groups lacking the\nprecise regulation of missing-linker defects. How does the performance of unmodified\nMOF-801 membranes compare, and what is the quantitative impact of your\ninnovations?\nResponse: Thank you for this valuable comment! We agree with you about the\nimportance of a control group comparison. Regarding control group comparison, in\nour new experiments we synthesized the MOF-801 membrane without\nmissing-linker (i.e., the frequency of missing linkers is zero) under the condition\nwithout adding formic acid. We found that they always exhibited a poor membrane\nstructure with amorphous phase, not well-intergrown MOF crystals as is required for\nMOF polycrystalline membrane. The amorphous phase on substrates is not suitable\nfor pervaporation desalination since it didn’t form a membrane layer with defined\nMOF crystalline structure with regular pore window and cage to allow water\nmolecular transport and salt rejection. To address the reviewer’s concern, we have\ndone new experiments (see below figure) and highlighted the discussion in the\nmanuscript (Line 175–180, Page 8, revised manuscript).\nThe revisions are also shown as follows:\nWithout the addition of a modulator, it is difficult to form highly crystalline MOF-801\nmembrane (usually only some amorphous phase) from ZrOCl and fumarate due to\n2\nthe slow crystallization kinetics.37 The amorphous phase on substrates is not suitable\nfor pervaporation desalination since it does not form a membrane layer with defined\nMOF crystalline structure comprised of regular pore window and pore cage to allow\nfor water molecule transport and salt rejection.\nReference\nModulated synthesis of Zr-fumarate MOF. Microporous Mesoporous Mater. 2012, 152,\n64-70.\nFigure R1. Surface (left) and cross-sectional (right) FE-SEM images of the MOF-801 membranes\nwithout missing-linker (i.e., the frequency of missing linkers is zero) synthesized under the\ncondition without adding formic acid.\n3. The detailed performance data regarding flux and reject should be presented in\nAbstract.\nResponse: Thank you for this valuable comment. To address the reviewer’s concern,\nwe have revised Abstract in the manuscript by adding some quantitative data (Line\n40–44, Page 2, revised manuscript). The revisions are also shown as follows:\nThe MOF-801 membranes demonstrated near-perfect salt rejection (~99.9%) and high\nwater flux (13.8 L m-2 h-1 for 10 wt.% hypersaline water, 27.4 L m-2 h-1 for 3.5 wt.%\nsaline water), outperforming most state-of-the-art silica, MOF, and zeolite\npolycrystalline membranes for the treatment of both saline and hypersaline waters.\n4. The authors briefly claim that this membrane outperforms state-of-the-art silica,\nMOF, and zeolite polycrystalline membranes for the treatment of both saline and\nhypersaline waters. Is it true? More supporting data or broader literature review\nshould be presented.\nResponse: Thank you for this valuable suggestion! To address the reviewer’s concern,\nwe have revised Figure 4 (page 14, in the revised manuscript) and Tables S6 (page 32,\nin the supplementary information) by providing more supporting data and updating\nthe literature review about MOF and zeolite polycrystalline membranes.\nSpecifically, two papers have been added and cited in the revised manuscript and the\nsupplementary information.\nYu, L.; Al-Jariry, N.; Serikbayeva, T.; Hedlund, J., Ultra-thin zeolite CHA and FAU membranes for\ndesalination by pervaporation. Sep. Purif. Technol. 2022, 294, 121177..\nWang, Y.; Zou, X.; Sun, L.; Rong, H.; Zhu, G., A zeolite-like aluminophosphate membrane with\nmolecular-sieving property for water desalination. Chem. Sci. 2018, 9, (9), 2533-2539.\n5. The economic analysis provided is overly simplistic and does not account for\nscale-up challenges, raw material costs, or operational expenses over the membrane's\nlifecycle. Can the authors expand this analysis to include a detailed cost breakdown\nand a comparison with existing desalination technologies??\nResponse: Thank you for this valuable comment. We agree with you in the\nimportance of cost analysis and scale-up challenge for potential practical application\nof a new desalination technology. However, it is difficult to provide a detailed cost\nbreakdown at the early stages of materials development. So that the cost estimates\npresented are not misleading, we provided greater context for our preliminary cost\nanalysis and discussion about scale-up challenges (Page 9-10, revised supplementary\ninformation).\nFor the MOF-801 membrane, the cost per unit membrane area is composed of\nmaterial and synthesis costs (e.g., energy and consumables consumption) at lab-scale.\nThe cost of the MOF-801 membrane is estimated to be $295.1 per m2 (Table S3). The\nreasonable materials and synthesis costs of MOF-801 membranes have a promising\npotential in desalination applications. However, differing from commercial estimates,\nthis simple cost calculation is based only on the lab-scale materials and synthesis\ncosts, and does not include other practical cost elements such as advertising,\nmarketing, distribution, labor, and general overhead. It remains challenging to scale\nup the synthesis of high-quality MOF-801 membranes in which large size substrates\nand reaction autoclaves are needed, usually resulting in many uncertainties of\nmembrane quality such as nonuniform membrane thickness and structural\nimperfection. Therefore, future development of MOF-801 membranes should focus\non enhancing the performance and sustainable synthesis of membranes and further\nreducing the cost of membrane synthesis and operation. At this time, it is difficult to\nestimate operational expense over membrane lifecycle since the MOF-801\nmembranes developed in this work remained stable during the whole operation\nduration.\nTable S4. The cost of MOF-801 membrane fabricated in this work.\nMaterial cost Synthesis cost Total cost\n($·m-2) ($·m-2) ($·m-2)\nMOF-801 membrane 269.2 25.9 295.1\n6. The performance stability under different environmental conditions (e.g., extreme\npH, high temperatures, biofouling potential) is not adequately addressed. How does\nthe membrane's performance vary under these stress conditions, and what\nmechanisms ensure its stability? Please briefly discuss this issue.\nResponse: Thank you for this valuable comment. We agree with your opinion in the\nimportance of performance stability under different environmental conditions. Stable\noperation under harsh chemical conditions is of great practical significance for\nmembrane technologies (1-6). Actually, one of the novel aspects of this work is the\nexceptional stability under different harsh chemical conditions (i.e.,\nhigh-temperature, acidic, oxidizing conditions, feeds with refractory species like oil or\nsurfactants) of our MOF membrane (Fig. 4, Fig. 5, Fig. S16, Fig. S17, Fig. S18, Fig.\nS19, Fig. S20, Fig. S21, Table S4). Differing from other reports focusing on mild\ndesalination conditions (at neutral pH values), we intentionally subjected our MOF\nmembrane to different harsh chemical conditions for prolonged periods of time to\nevaluate their resilience in practical applications that have proven challenging for\nconventional polymeric membranes. To this end, our MOF membrane also\nshowcased stable performance when treating real, acidic industrial wastewater\nwith a complicated composition, which has not been successfully demonstrated\npreviously (Fig. 5, Table S4). The performance stability can be ascribed to the highly\nstable membrane structure consisting of well intergrown MOF-801 crystals in which\nthere are highly robust Zr–O covalent bonds, and strong coordination bonds between\n[Zr (OH) O ] cluster (i.e., Lewis acid) and fumarate linker (i.e., Lewis base).\n6 4 4\nWe\nbelieve that this has broader implications for design and synthesis of novel membrane\nmaterials (e.g., MOF-801 in our work), which has not been the traditional focus in the\nfield. Our current work provides an entirely new platform of robust desalination under\nharsh chemical conditions, expanding the number of applications where\nmembrane-based desalination can now be relevant.\nTo address the reviewer’s concern, we have revised the discussions on the potential\nmechanisms of performance and structure stability (Line 385–388, Page 18, revised\nmanuscript), which is now as follows:\nThe performance stability can be ascribed to the highly stable membrane structure\nconsisting of well intergrown MOF-801 crystals in which there are highly robust Zr–\nO covalent bonds, and strong coordination bonds between [Zr (OH) O ] cluster (i.e.,\n6 4 4\nLewis acid) and fumarate linker (i.e., Lewis base).\nReferences\n1. Zhongzhen Wang, Chen Ma, Chunyan Xu, Scott A. Sinquefield, Meisha L. Shofner &\nSankar Nair, Graphene oxide nanofiltration membranes for desalination under realistic\nconditions, Nature Sustainability, 4 (2021), 402-408.\n2. Dong Han Seo, Shafique Pineda, Yun Chul Woo, Ming Xie, Adrian T. Murdock, Elisa Y. M.\nAng, Yalong Jiao, Myoung Jun Park, Sung Il Lim, Malcolm Lawn, Fabricio Frizera Borghi,\nZhao Jun Han, Stephen Gray, Graeme Millar, Aijun Du, Ho Kyong Shon, Teng Yong Ng &\nKostya (Ken) Ostrikov, Anti-fouling graphene-based membranes for effective water\ndesalination, Nature Communications, 9 (1) (2018) 683.\n3. Luda Wang, Michael S. H. Boutilier, Piran R. Kidambi, Doojoon Jang, Nicolas G.\nHadjiconstantinou & Rohit Karnik, Fundamental transport mechanisms, fabrication and\npotential applications of nanoporous atomically thin membranes, Nature Nanotechnology, 12\n(2017), 509–522.\n4. Jay R. Werber, Chinedum O. Osuji & Menachem Elimelech, Materials for next-generation\ndesalination and water purification membranes, Nature Reviews Materials, 1(5) (2016),\n16018.\n5. Rhea Verbeke, Douglas M. Davenport, Timothée Stassin, Samuel Eyley, Marcel Dickmann,\nAlexander John Cruz, Praveen Dara, Cody L. Ritt, Caroline Bogaerts, Werner Egger, Rob\nAmeloot, Johan Meersschaut, Wim Thielemans, Guy Koeckelberghs, Menachem Elimelech,\n& Ivo F. J. Vankelecom, Chlorine-Resistant Epoxide-Based Membranes for Sustainable Water\nDesalination, Environmental Science & Technology Letters, 8 (9) (2021), 818-824.\n6. Huiling Chen, Xing Liu, Dian Gong, Chang Zhu, Guojuan Liu, Jingrui Fan, Ping Wu, Zhi\nLi, Yichang Pan, Guosheng Shi, Yuhan Sun & Gaofeng Zeng, Ultrahigh-water-flux\ndesalination on graphdiyne membranes, Nature Water, 1 (2023), 800-807.\nResponse to Reviewer #3’s comments\nReviewer #3 (Remarks to the Author):\nGeneral comments: Polycrystalline MOF membranes have shown great potential for\nmolecular separation. Most current works focus on removing inter-granular defects\n(e.g., cracks) to obtain continuous MOF membrane. There are few reports paying\nattention to the lattice defects in MOF membrane. This manuscript focuses on the\nprecise regulation of missing linkers lattice defects in MOF-801 membrane by\ncontrolling the amount of modulator for pervaporation desalination, which is novel.\nThe relationship between the lattice defects and membrane microstructure was\nsystematically investigated, and outstanding desalination was achieved owing to the\nmissing linkers enhance membrane structural hydrophilicity with stronger host-guest\ninteraction energy. The idea to precisely control lattice defects by simply adjusting the\namount of modulator is interesting, which would inspire fabricating other\nnext-generation MOF nanochannel membranes with high separation performance.\nTherefore, the manuscript can be accepted by the journal, however, several issues\nshould be further addressed.\nResponse: We appreciate that you took time to evaluate our manuscript and to\nprovide positive detailed comments on the novelty and significance of our work (e.g.,\nprecise regulation of missing linkers lattice defects, and desalination performance\netc.). Your valuable suggestions and comments have been instrumental in further\nclarifying the significance of our work and improving the quality of our paper\nmanuscript. We have carefully considered all the comments/suggestions, given\npoint-by-point responses (shown as follows), and made revisions to improve the\nquality and impact of our manuscript.\n1. In view of the topic “Lattice-defects engineering in MOF membrane for\ndesalination”, the authors are suggested to give a comparison between this work with\nthe highly relevant recent paper (Nat. Mater. 2023, 22, 769). In addition, the proposed\nin situ nano-seeding strategy to construct MOF-801 membrane in this work was also\nreported by the same authors for preparing another type of Zr-MOF membranes,\nUiO-66 membrane (Nat. Common. 2022, 13, 266), what is the essential difference\nbetween the two works, the authors should further clarify it.\nResponse: Thank you for this valuable suggestion! To address the reviewer’s concern,\nwe further highlight the comparison between our work with the highly relevant recent\npaper (Nat. Mater. 2023, 22, 769) and the essential difference between this work and\nour former paper (Nat. Common. 2022, 13, 266).\nWe have provided the discussion in the manuscript (Line 91–96, Page 4, revised\nmanuscript). The revisions are also shown as follows:\nUnlike the elimination of lattice defects to improve the selectivity of MOF\nmembranes,26 the aim of this work is to precisely regulate intracrystalline missing\nlinkers of MOF membranes to enhance the permeation of water molecules while\nmaintaining high salt rejection. Differing from this former study that merely\nintroduced an arbitrary amount of missing linkers,29 this work showcases that the\nprecise regulation of missing linkers to enhance water transport could be realized in\nMOF-801 membranes.\n2. When the evaporation takes place, salts ions cannot be vaporized and the presence\nof membrane would inevitably increase the transfer resistance during the\npervaporation desalination process. The membrane distillation (MD) is very similar to\npervaporation desalination. MD uses the low-grade waste heat, not vacuum that is one\nof the most expensive form of energy. What is the advantage of pervaporation\ndesalination compared with MD?\nResponse: Thank you for this valuable suggestion! We agree with you that membrane\ndistillation, similar to pervaporation, doesn’t always need vacuum on the permeate\nside, only except for vacuum membrane distillation. Low-grade waste or residual heat\ncan be used in both processes. However, it is challenging to efficiently treat saline or\nhypersaline wastewater with complicated compositions for membrane distillation\nprocess where membrane scaling or fouling usually results in performance\ndegradation of the process due to the presence of various detrimental species such as\noil and surfactants. Unlike membrane distillation, a more robust PV process could\naddress some of these key issues such as wetting, scaling, and fouling, which enables\npromising operational performance.\nTo address the reviewer’s concern, we highlight the advantage of pervaporation\ncompared with membrane distillation (Line 59–62, Page 2, revised manuscript).\nThe revisions are also shown as follows:\nUnlike conventional membrane distillation processes, a more robust PV process has\nadvantages in addressing challenges like wetting, scaling, and fouling, which enables\npromising operational performance.13\nReferences\n13. Chunyi Sun, Bin Lin, Xiangyong Zheng, Yingchao Dong, Min Zhao, Chuyang Y. Tang,\nRobust ceramic-based graphene membrane for challenging water treatment with enhanced\nfouling and scaling resistance, Water Research 243 (2023) 120348.\n3. What is the role of TiO layer for membrane formation? If without TiO2, can the\n2\ncontinuous MOF membrane be prepared by the in-situ nano-seeding strategy followed\nby surfactant post-treatment?\nResponse: Thank you for this comment! To address the reviewer’s concern, we\nfurther highlight the role of TiO layer for membrane formation (Line 118–123, Page\n2\n5, revised manuscript).\nThe revisions are also shown as follows:\nTo modify the substrate and enable the growth of well-intergrown MOF-801\nmembranes, a more hydrophilic nano-TiO interlayer was introduced with lowered\n2\nsurface roughness (R ~68 nm) (Figure S4) and average pore size (~105 nm). Such a\na\nTiO interlayer could provide a modified substrate surface with more hydroxyl groups\n2\nand thus more nucleation sites for MOF crystal nucleation and subsequent growth,\nwhich is beneficial to the formation of thin, well-intergrown MOF-801 membranes.\n4. The authors tried to post-treat MOF membrane using three kinds of surfactants,\nSLS, DTAB, and Span 80. Results show that only Span 80 facilitates the formation of\ncracks-free membrane (Fig.1 and Fig. S7). Why? The authors are suggested to provide\nthe detailed explanation.\nResponse: Thank you for this valuable comment! To address the reviewer’s concern,\nwe provided the detailed explanation about the results of post-treatment of MOF-801\nmembranes by three surfactants (Line 244–250, Page 15, revised Supplementary\nInformation).\nThe revisions are also shown as follows:\nThe results show that only Span 80 facilitated the formation of crack-free MOF-801\nmembranes. This can be ascribed to the fact that compared to those of SLS and DTAB\nsurfactants, the hydrophilic head groups of Span 80 surfactant interact more favorably\nwith the surface of MOF-801 membranes.3 Such favorable interactions result in the\nformation of a more compact Span 80 protective film, suppressing the evaporation\nrate of residual solvents with reduced capillary stress and consequently enabling the\nformation of crack-free MOF-801 membranes.\nReferences\nframeworks and their membranes with enhanced crack resistance and moisture stability by\nsurfactant-assisted drying, Langmuir 2011, 27, 2652–2657\n5. The authors stated “Ti was detected in the TiO2 nano-interlayer surface, while only\nZr was detected in the crack-free MOF-801 membrane surface, suggesting the\nintergrowth integrity of the membrane”, I am very curious why the Zr was not\ndetected in cracked MOF-801 membrane shown in Fig. S11, because lots of MOF\ncrystals were also deposited in substrate surface (Fig. 1b), the signal of Zr should be\nsignificant. According to the description by the authors, in Fig. S11, the icon a2\nshould be cracked-free MOF-801 membrane.\nResponse: Thank you for this valuable comments! We would first like to clarify the\nright denotations of the XPS spectra in Fig S11 and S12 (a1, b1: crack-free MOF-801\nmembrane; a2, b2: cracked MOF-801 membrane; a3, b3: TiO interlayer).\nrevised the discussion in the manuscript (Line 164–168, Page 7, revised manuscript).\nAs speculated, Zr was indeed detected in both cracked and crack-free MOF-801\nmembranes.\nThe revisions are also shown as follows:\nAdditionally, the presence of O, Ti, Zr, and C signals in the XPS spectra are clearly\nidentified for the TiO interlayer, cracked MOF-801, and crack-free MOF-801\n2\nmembranes (Figure S11). Ti was detected in the TiO\n2\nnano-interlayer surface, while\nZr was detected in the membrane surface of both cracked and crack-free MOF-801\nmembranes (Figures S11, S12).\nS2.7 XPS Spectra of MOF-801 Membranes\n(a) (b)\nO1S Ti 2p\nC1s\na1 Zr3P Zr3d\nb1\na2 b2\na3\nTi2p\nb3\n1200 1000 800 600 400 200 0 475 470 465 460 455\nBinding Energy (eV) Binding Energy (eV)\nFigure S11. (a) Full-scan XPS spectra and (b) Ti 2p XPS spectra of ceramic-based MOF-801\nmembranes (a1, b1: crack-free MOF-801 membrane; a2, b2: cracked MOF-801 membrane; a3, b3:\nTiO interlayer).\n2\n(a) (b)\nAl 2p Zr 3d\na1\nb1\na2 b2\nb3\na3\n85 80 75 70 65 192 188 184 180 176\nBinding Energy (eV) Binding Energy (eV)\nFigure S12. (a) Al 2p XPS spectra and (b) Zr 3d XPS spectra of ceramic-based MOF-801\nmembranes (a1, b1: crack-free MOF-801 membrane; a2, b2: cracked MOF-801 membrane; a3, b3:\nTiO interlayer).\n2\nPoint-to-point Response to the Reviewers’ Comments: NCOMMS-24-08272B\nReviewer #1 (Remarks to the Author):\nThe authors have well addressed all my concerns. The following comments are presented to\naddress the required questions.\n1. The noteworthy results of this work reside in the following aspects:\nThe revised manuscript convincingly demonstrates the efficacy of precise regulation of\nintracrystalline missing linkers in MOF-801 membranes, significantly enhancing water\ntransport. This is achieved by altering the ratio of fumarate to formic acid during the\nmembrane synthesis, leading to a notable improvement in both permeability and selectivity.\nThe results, as demonstrated in Figures 2 and 3 of the manuscript, show that these\nmodifications lead to near-perfect salt rejection (~99.9%) and elevated water flux compared\nto previous standards in the field. Furthermore, the membranes exhibited exceptional stability\nunder challenging conditions, which is critical for practical applications.\n2. The work has the following significance to the field:\nThe approach detailed in this manuscript marks a substantial contribution to the field of\ndesalination technology, particularly for treating hypersaline waters which pose a challenge to\nconventional reverse osmosis methods. The method's ability to enhance both the structural\nhydrophilicity and transport dynamics of MOF membranes through defect regulation could\nhave far-reaching implications for the design of next-generation separation technologies. This\nwork not only advances our understanding of MOF membrane capabilities but also sets a new\nbenchmark for their performance in water treatment applications.\n3. Regarding the comparison to established literature:\nThe authors have positioned their work adeptly within the context of existing literature,\nproviding a clear demonstration of how their approach surpasses the capabilities of existing\nsilica, zeolite, and other MOF membranes. This claim is well-supported by comprehensive\nexperimental and simulation data, and the manuscript now includes an extensive review of\nrelevant studies to further bolster its claims of novelty and superiority.\n4. Regarding the soundness of research:\nThe methodologies employed in this study are sound and represent a substantial advancement\nin the field of membrane technology. The detailed experimental setup and the robust\nsimulation studies provide a clear and convincing argument for the benefits of controlled\ndefect creation in MOFs. The authors have effectively used a combination of experimental\ndata and theoretical models to explain the mechanisms at play, which not only supports the\nclaims made but also enhances the manuscript's contribution to the field's body of knowledge.\n5. Addressing previous concerns:\nIt is evident that the authors have taken previous critiques into consideration, making\nsignificant revisions to the manuscript. They have clarified the novel aspects of their\nsynthesis strategy, improved the discussion around their method's significance, and provided\nadditional comparative data and theoretical backing to support their conclusions.\nGiven the comprehensive response to previous reviews, the significant advancements\nreported, and the potential impact on the field, I recommend the acceptance of this\nmanuscript for publication.\nResponse: We sincerely appreciate that you took the time to evaluate our revised manuscript\nfor a second time and provided five encouraging comments on the novelty and significance of\nour work. Particularly, we appreciate your comments on\nthe noteworthiness of precisely regulating intracrystalline missing linkers to enhance water\ntransport; the significance of advancing our understanding of MOF membrane capabilities to\ndevelop next-generation separation technologies; the recognition of the superior performance\nof our MOF membrane in the context of existing silica, zeolite, as well as other MOF\nmembranes; the soundness of our experimental and simulation methods; and\nacknowledgement that we have addressed previous concerns by clarifying the novel aspects\nof our synthesis strategy, improving the discussion around our method's significance, and\nproviding additional comparative data and theoretical backing to support our conclusions.\nReviewer #2 (Remarks to the Author):\nThe response and revision by the Authors is unacceptable and the manuscript remains\nunsuitable for publication in Nature Communications. It should be revised and published in a\ndisciplinary specific journal for desalination.\nResponse: In the two rounds of review, Reviewer #1, Reviewer #3, and Reviewer #4 have all\nprovided positive and detailed comments on the novelty and impact of our work. Particularly,\nfor the revised manuscript (in the last round of review), Reviewer #1 recognized our work\nand revisions with very positive comments such as the noteworthiness of precisely regulating\nintracrystalline missing linkers to enhance water transport; the significance of advancing our\nunderstanding of MOF membrane capabilities to develop next-generation separation\ntechnologies; the recognition of the superior performance of our MOF membrane in the\ncontext of existing silica, zeolite, as well as other MOF membranes; the soundness of our\nexperimental and simulation methods; and acknowledgement that we have addressed\nprevious concerns by clarifying the novel aspects of our synthesis strategy, improving the\ndiscussion around our method's significance, and providing additional comparative data and\ntheoretical backing to support our conclusions. Reviewer #4 also provided supportive\ncomments, commending our work as new knowledge and a useful reference to the\ncommunity. We also would like to again summarize and highlight the novel aspects of our\nwork and the broader implications and contributions, which motivated our decision to submit\nto Nature Communications.\nImportant novel aspects are described below:\n1. The first novel aspect in this work is the precise regulation of missing linkers lattice\ndefects in the MOF membrane (Fig. 2). Intracrystalline defects—such as missing linkers and\nmissing clusters—have been synthesized and confirmed to influence the permeability or\nselectivity of MOF liquid- or gas-separation membranes. However, the precise regulation of\nfavorable intracrystalline defects and their effect on fundamental mass transport phenomena\nfor desalination has not been previously reported for membrane-based separation applications.\nAs Reviewer #3 positively commented in the last round of review, there are few reports\npaying attention to the lattice defects in MOF membranes. More importantly, we\ndemonstrated a facile method to precisely control the frequency of missing linkers, which has\nnot been previously realized for MOF membranes.\n2. The second novel aspect is the characterization of the atomistic mechanism for\nenhanced water transport induced by precise regulation of missing linkers (Fig. 3).\nWhile published works on pervaporation desalination largely focus on membrane fabrication\nand performance evaluation, very rarely is the fundamental atomistic mechanism for water\ntransport explored. Interestingly, we found that precise regulation of missing linkers enhances\nmembrane structural hydrophilicity with stronger host-guest interaction energy. Resulting in a\nlower energy barrier by enlarging the MOF pore window and pore cage, the structural\nconfiguration of MOF-801 with the precise regulation of missing linkers enables the observed\nincrease in water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different disciplines\nand fields of science, technology, and engineering (e.g., chemistry, materials, environmental\nscience, chemical engineering, water and membrane technologies). Thus, we believe that this\nwork with fundamental mechanistic insights is of great interest for the broad readership of\nNature Communications.\n3. The third novel aspect of this work is the superior performance of our MOF membrane\nin comparison to other state-of-the-art zeolite and MOF membranes for pervaporation\ndesalination. As you have recognized, our work is the first report to use the\nmaterial MOF-801 for pervaporation desalination and has some interesting materials\nscience aspects and modeling components. We recognize that some pervaporation desalination\nmembranes—especially polymeric membranes—have higher performance (with respect to\nwater flux) under specific conditions, but we wish to emphasize that our MOF membranes\nindeed outperform state-of-the-art zeolite and MOF membranes in water flux (Figure 4 and\nTables S5-6), which belong to an emerging class of polycrystalline molecular sieve\nmembranes that are drastically different from polymeric membranes (such as PVA\nmembranes). As a result, the performance comparison of membranes with similar structures\nand properties was deemed more appropriate for this study.\n4. The fourth novel aspect of this work is the exceptional stability under harsh chemical\nconditions (i.e., high-temperature, acidic, oxidizing conditions, feeds with refractory species\nlike oil or surfactants) of our MOF membrane. Differing from previous reports focusing on\ndesalination under mild conditions, we intentionally subjected our MOF membrane to harsh\nchemical conditions for prolonged periods of time to evaluate their resilience in practical\napplications that have proven challenging for conventional polymeric membranes (Fig. 4, Fig.\n5, Fig. S16-21, Table S4). To this end, our MOF membrane showcased stable performance\nwhen treating real industrial wastewater with a complicated composition, which has not\nbeen successfully demonstrated previously (Fig. 5, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies. We believe\nthat this has broader implications for the design and synthesis of novel membrane materials\n(e.g., MOF-801 in our work), which has not been the traditional focus in the field. Our\ncurrent work provides an entirely new platform for robust desalination under harsh chemical\nconditions, expanding the number applications where membrane-based desalination is now\nrelevant.\n1) The authors fail to include a citation for the review paper “Desalination by membrane\npervaporation: A Review” Desalination, 547, 1, 116223, doi:10.1016/j.desal.2022.116223.\nThe manuscript, as written, does not provide proper context for the performance of their\nmembranes in context of the known field of pervaporation desalination membranes.\nResponse: We thank you for providing the reference and have read it carefully. We have\nadded the reference to the manuscript. We also added permeance data to the Supplementary\nInformation (SI) as you see in our response to the next comment.\nWe sincerely appreciate you for re-providing these comments to encourage us to distinguish\nour MOF membrane from conventional pervaporation desalination membranes. We\nacknowledge that some pervaporation desalination membranes—especially PVA polymeric\nmembranes—have reported higher performance (i.e., water flux) than our MOF membranes.\nHowever, it should be noted that experimental conditions for evaluating pervaporation\nmembranes across the field are not uniform, and it is this variability that impacts the driving\nforce for pervaporation and the water fluxes that are reported. For example, we used an\nice-water bath (i.e., 273 K) to determine the flux of our MOF-801 membrane whereas a\nhigher driving force enabled by a liquid nitrogen cold trap (i.e., 77 K) was used in other\nstudies using polymeric membranes. Furthermore, the structure and properties of polymeric\nmembranes is distinctly different from our MOF membranes. Therefore, it makes more sense\nto compare the performance of our MOF membrane to other state-of-the-art zeolite and MOF\nmembranes that belong to an emerging class of polycrystalline molecular sieve membranes\nwith similar structures and properties.\n2) The authors refuse to revise the manuscript to include a direct calculation of the permeance\nand selectivity of the membranes produced and do not cite “Permeability, permeance and\nselectivity: A preferred way of reporting pervaporation performance data” by Richard W.\nBaker et al. https://doi.org/10.1016/j.memsci.2009.11.022.\nResponse: We agree with your opinion that the parameters (i.e., permeance, permeability)\nbetter reflect intrinsic properties of the membranes. We also added permeance data to the\nSupplementary Information (SI) as you see in our response to the next comment.\nIt should be noted that the reference provided by the reviewer is for pervaporation with\nmixtures of organic-organic or organic-water, where the focus is on the selectivity of\nseparation and permeability-selectivity tradeoff (Journal of Membrane Science 348 (1-2)\n(2010) 346-352). However, pervaporation of organic-organic or organic-water is totally\ndifferent from pervaporation desalination. Water flux (not permeance) and salt rejection (not\nselectivity) are often presented as a metric of comparison in pervaporation desalination\nstudies (1-14). Due to practical challenges of obtaining accurate data, permeance is not\nalways reported in open literature as it requires close monitoring of desalination operating\nconditions such as trans-membrane pressure difference. In fact, if this information is not\ndisclosed, permeance can obfuscate the experimental conditions that should be used for a fair\ncomparison between materials. Therefore, we have adopted the standard practice—which has\nbeen used for other membrane processes like microfiltration and membrane distillation—of\nreporting water flux as a simpler parameter directly reflecting water treatment efficiency—\nwhile providing transparency about our experimental conditions and membrane properties\n(15-17).\nMore importantly, the core novel aspects of this work include the precise regulation of\nmissing linkers, characterization of the atomistic mechanism of enhanced performance, and\nharsh chemical operation stability, all of which have not been explored in existing works.\nReference\n1. Meidi Wang, Penghui Zhang, Xu Liang, Junyi Zhao, Yawei Liu, Yu Cao, Hongjian Wang, Yu\nChen, Zhiming Zhang, Fusheng Pan, Zhenjie Zhang, Zhongyi Jiang, Ultrafast seawater\ndesalination with covalent organic framework membranes, Nature Sustainability 5 (2022) 518–\n526.\n2. Zishu Cao, Shixuan Zeng, Zhi Xu, Antonios Arvanitis, Shaowei Yang, Xuehong Gu, Junhang\nDong, Ultrathin ZSM-5 zeolite nanosheet laminated membrane for high-flux desalination of\nconcentrated brines. Science Advances. 4 (2018) eaau8634.\n3. Chun Xiang C Lin, Li Ping Ding, Simon Smart, João C Diniz da Costa, Cobalt oxide silica\nmembranes for desalination, Journal of Colloid and Interface Science 368(2012) 70-76.\n4. Mikel C Duke, Steven Mee, J C Diniz da Costa, Performance of porous inorganic membranes in\nnon-osmotic desalination. Water Research 41(2007) 3998-4004.\n5. Huayu Zhang, Jiuli Wen, Qi Shao, Ai Yuan, Haiting Ren, Fangying Luo, Xiaoliang Zhang,\nFabrication of La/Y-codoped microporous organosilica membranes for high-performance\npervaporation desalination. Journal of Membrane Science 584(2019) 353-363.\n6. Shengnan Wang, David K Wang, Julius Motuzas, Simon Smart, João C Diniz da Costa, Rapid\nthermal treatment of interlayer-free ethyl silicate 40 derived membranes for desalination.\nJournal of Membrane Science 516(2016) 94-103.\n7. Sheida Khajavi, Jacobus C Jansen, Freek Kapteijn, Production of ultra pure water by desalination\nof seawater using a hydroxy sodalite membrane. Journal of Membrane Science 356(2010)\n52-57.\n8. Mikel C Duke, Jessica O’Brien-Abraham, Nicholas Milne, Bo Zhu, Jerry Y.S. Lin, D João\nC. Diniz da Costa, Seawater desalination performance of MFI type membranes made by\nsecondary growth. Separation and Purification Technology 68(2009) 343-350.\n9. Churl Hee Cho, Ka Yeon Oh, Si Kyung Kim, Jeong Gu Yeo, Pankaj Sharma, Pervaporative\nseawater desalination using NaA zeolite membrane: Mechanisms of high water flux and high salt\nrejection. Journal of Membrane Science 371(2011) 226-238.\n10. Paul Swenson, Brenden Tanchuk, Ankita Gupta, Weizhu An, Steven M. Kuznicki, Pervaporative\ndesalination of water using natural zeolite membranes. Desalination 285(2012) 68-72.\n11. Chen Zhou, Junjie Zhou, Aisheng Huang, Seeding-free synthesis of zeolite FAU membrane for\nseawater desalination by pervaporation. Microporous and Mesoporous Materials 234(2016)\n377-383\n12. Martin Drobek, Christelle Yacou, Julius Motuzas, Anne Julbe, Liping Ding, João C. Diniz da\nCosta, Long term pervaporation desalination of tubular MFI zeolite membranes. Journal of\nMembrane Science 415-416(2012) 816-823.\n13. Yaqiong Zhu, Krishna M. Gupta, Qian Liu, Jianwen Jiang, Jürgen Caro, Aisheng Huang,\nSynthesis and seawater desalination of molecular sieving zeolitic imidazolate framework\nmembranes. Desalination 385(2016) 75-82.\n14. Linlin Wan, Chen Zhou, Kai Xu, Bo Feng, Aisheng Huang, Synthesis of highly stable\nUiO-66-NH membranes with high ions rejection for seawater desalination. Microporous &\n15. Huiling Chen, Xing Liu, Dian Gong, Chang Zhu, Guojuan Liu, Jingrui Fan, Ping Wu, Zhi Li,\nYichang Pan, Guosheng Shi, Yuhan Sun, Gaofeng Zeng, Ultrahigh-water-flux desalination on\ngraphdiyne membranes, Nature Water, 1 (2023), 800-807.\n16. Luke Yan, Gui Zhang, Lei Zhang, Wei Zhang, Jincui Gu, Youju Huang, Jiawei Zhang, Tao Chen,\nRobust construction of underwater superoleophobic CNTs/nanoparticles multifunctional hybrid\nmembranes via interception effect for oily wastewater purification. Journal of Membrane\nScience 569(2019) 32-40.\n17. Yu Gu, Bowu Zhang, Zhiang Fu, Jihao Li, Ming Yu, Linfan Li, Jingye Li. Poly (vinyl alcohol)\nmodification of poly(vinylidene fluoride) microfiltration membranes for oil/water emulsion\nseparation via an unconventional radiation method. Journal of Membrane Science. 619(2021)\n118792.\nIn the author’s rebuttal they state (incorrectly)\n“However, water flux is often presented as a metric of comparison in pervaporation\ndesalination studies (1-14). Due to practical challenges of obtaining accurate permeability\ndata, permeance is not always reported in open literature as it requires precise measurements\nof membrane thickness and close monitoring of operating conditions. . In fact, if this\ninformation is not disclosed, permeance can obfuscate the if this information is not disclosed,\npermeance can obfuscate the experimental conditions that should be used for a fair\ncomparison between materials.”\nThis is statement by the authors in the rebuttal is patently incorrect. Permeance calculations\ndo not involve membrane thickness, permeance is the flux normalized by the driving force\n(e.g., the operating conditions). Only permeability calculations involve knowledge of\nmembrane thickness. The authors are referred to Equations 11 and 12 in Baker et al.\nhttps://doi.org/10.1016/j.memsci.2009.11.022 for these standard definitions. . It would be\nquite simple for the authors to calculate the permeance of their membranes (regardless of\nknowledge of active layer thickness) and to place them into context of the known body of\nliterature in pervaporation desalination membranes. The authors are further referred to the\ntextbook \"Basic Principles of Membrane Science\" (Mulder, 1996)\nhttps://link.springer.com/book/10.1007/978-94-009-1766-8 to review the fundamental\nterminology and calculation methods for membrane materials.\nResponse: We thank you for providing the reference and have read it carefully. We agree\nwith your opinion that the parameters (i.e., permeance, permeability) better reflect intrinsic\nproperties of the membranes.\nWe converted water flux into water permeance as requested by the reviewer (Please\nsee Figure S18, Supplementary Information)\nFigure S18. (a) Water permeance of the MOF-801 membranes with different linker deficiencies. (b) Water\npermeance of the MOF-801-1.43 membrane for treatment of saline feeds with different salt concentrations.\nReviewer #3 (Remarks to the Author):\nAfter a careful review of the revised manuscript, I consider that the authors have addressed\nthe reviewers' comments partially. There are still several concerns that are not better\naddressed. For example, as for the difference between this work and the paper related to\nUiO-66 membrane reported by the same authors (Nat. Common. 2022, 13, 266), the authors\njust claimed that “Differing from this former study that merely introduced an arbitrary\namount of missing linkers, this work showcases that the precise regulation of missing linkers\nto enhance water transport could be realized in MOF-801 membranes. Based on the authors’\nresponse, I think that in this work, the authors just change the MOF material from UiO-66 to\nMOF-801 because the former study also achieved the precise regulation of missing linkers.\nAs pointed out by the Reviewer #2 that “This manuscript is most well suited for publication\nin a specialized disciplinary journal, such as the Journal of Membrane Science or\nDesalination or other membrane or water purification focused journal.”\nResponse: Again, we sincerely appreciate that you provided positive comments on the\nnovelty and significance of our work in the last round of review and took time to carefully\nevaluate our revised manuscript (NCOMMS-24-08272A-Z). In our former study (Nat.\nCommon. 2022, 13, 266), we introduced an arbitrary amount of missing linkers (~23.5%) in\nUiO-66 membrane, but the precise regulation of missing linkers in the membrane was not\nexplored. Additionally, the precise creation of intracrystalline defects in MOF membranes is\nchallenging, requiring complicated and challenging membrane fabrication and optimization,\nwhich is why this topic has not been well-studied for membrane-based separation\napplications. Differing from the former study, this work on pervaporation not only shows that\nthe precise regulation of missing linkers to enhance water transport in MOF-801 membranes\nis possible, but also conducts an in-depth investigation into how structural modifications in\nthe MOF-801 membrane structure impact pervaporation performance.\nTo address your concern about the novelty, we have further revised in Introduction section\n(please see Line 85-87, Line 94-97, Page 4), which is show as follows.\nLine 85-87: However, the precise creation of favorable intracrystalline defects is challenging\nand has not been well-studied in membrane-based separation applications.\nLine 94-97: Differing from this former study that introduced an arbitrary amount of missing\nlinkers (~23.5%), 29 this work demonstrates that precise regulation of missing linkers to\nenhance water transport could be realized in MOF-801 membranes, which is not only\npractically challenging, but also critical for understanding fundamental mass transport\nphenomena.\nIn this round of review, both Reviewer #1 and Reviewer #4 provided very positive and\ndetailed comments on the novelty and impact of our work. Particularly, Reviewer #1\nrecognized our work and revisions with very positive comments such as the noteworthiness\nof precisely regulating intracrystalline missing linkers to enhance water transport; the\nsignificance of advancing our understanding of MOF membrane capabilities to develop\nnext-generation separation technologies; the recognition of the superior performance of our\nMOF membrane in the context of existing silica, zeolite, as well as other MOF membranes;\nthe soundness of our experimental and simulation methods; and acknowledgement that we\nhave addressed previous concerns by clarifing the novel aspects of our synthesis strategy,\nimproving the discussion around our method's significance, and providing additional\ncomparative data and theoretical backing to support our conclusions.. Reviewer #4 also\nprovided supportive comments, commending our work as new knowledge and a useful\nreference to the community. We also would like to summarize and highlight the novelties of\nour work and its broader implications and contributions, which motivated our decision to\nsubmit to Nature Communications.\nImportant novel aspects are described below:\n1. The first novel aspect in this work is the precise regulation of missing linkers lattice\ndefects in the MOF membrane (Fig. 2). Intracrystalline defects—such as missing linkers and\nmissing clusters—have been synthesized and confirmed to influence the permeability or\nselectivity of MOF liquid- or gas-separation membranes. However, the precise regulation of\nfavorable intracrystalline defects and their effect on fundamental mass transport phenomena\nfor desalination has not been previously reported for membrane-based separation applications.\nAs you positively commented in the last round of review, there are few reports paying\nattention to the lattice defects in MOF membranes. More importantly, we demonstrated a\nfacile method to precisely control the frequency of missing linkers, which has not been\npreviously realized for MOF membranes.\n2. The second novel aspect is the characterization of the atomistic mechanism for\nenhanced water transport induced by precise regulation of missing linkers (Fig. 3).\nWhile published works on pervaporation desalination largely focus on membrane fabrication\nand performance evaluation, very rarely is the fundamental atomistic mechanism for water\ntransport explored. Interestingly, we found that precise regulation of missing linkers enhances\nmembrane structural hydrophilicity with stronger host-guest interaction energy. Resulting in a\nlower energy barrier by enlarging the MOF pore window and pore cage, the structural\nconfiguration of MOF-801 with the precise regulation of missing linkers enables the observed\nincrease in water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different disciplines\nand fields of science, technology, and engineering (e.g., chemistry, materials, environmental\nscience, chemical engineering, water and membrane technologies). Thus, we believe that this\nwork with fundamental mechanistic insights is of great interest for the broad readership of\nNature Communications.\n3. The third novel aspect of this work is the superior performance of our MOF membrane\nin comparison to other state-of-the-art zeolite and MOF membranes for pervaporation\ndesalination. As Reviewer #2 has recognized, our work is the first report to use the\nmaterial MOF-801 for pervaporation desalination and has some interesting materials\nscience aspects and modeling components. We recognize that some pervaporation desalination\nmembranes—especially polymeric membranes—have higher performance (with\nrespect to water flux) under specific conditions, but we wish to emphasize that our MOF\nmembranes indeed outperform state-of-the-art zeolite and MOF membranes in water flux\n(Figure 4 and Tables S5-6), which belong to an emerging class of polycrystalline molecular\nsieve membranes that are drastically different from polymeric membranes (such as PVA\nmembranes). As a result, the performance comparison of membranes with similar structures\nand properties was deemed more appropriate for this study.\n4. The fourth novel aspect of this work is the exceptional stability under harsh chemical\nconditions (i.e., high-temperature, acidic, oxidizing conditions, feeds with refractory species\nlike oil or surfactants) of our MOF membrane. Differing from previous reports focusing on\ndesalination under mild conditions, we intentionally subjected our MOF membrane to harsh\nchemical conditions for prolonged periods of time to evaluate their resilience in practical\napplications that have proven challenging for conventional polymeric membranes (Fig. 4, Fig.\n5, Fig. S16-21, Table S4). To this end, our MOF membrane showcased stable performance\nwhen treating real industrial wastewater with a complicated composition, which has not\nbeen successfully demonstrated previously (Fig. 5, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies. We believe\nthat this has broader implications for the design and synthesis of novel membrane materials\n(e.g., MOF-801 in our work), which has not been the traditional focus in the field. Our\ncurrent work provides an entirely new platform for robust desalination under harsh chemical\nconditions, expanding the number applications where membrane-based desalination is now\nrelevant.\nReviewer #4 (Remarks to the Author):\nThis contribution reports a type of pervaporation membrane, fabricated with MOF-801 thin\nlayer coating on alumina based substrates. The authors applied surfactants to suppress the\nformation of crack during drying process, and the modulator was applied to tune the missing\nlinker to enhance the membrane performance.\nOverall, this contribution contains new knowledge and the fabrication of such\nmembrane/tuning interfacial properties can provide useful reference to the community. The\nauthors have also addressed most of the comments raised from the last round of review,\nincluding some challenging ones. I would recommend the publication of this manuscript after\nsome additional minor revision.\nResponse: We appreciate that you took time to evaluate our manuscript and provide\ncomments on the novelty and significance of our work (e.g., new knowledge, useful reference\nto the community). We also appreciate your positive comment that the authors have\naddressed most of the comments raised from the last round of review, including some\nchallenging ones. Your valuable suggestions and feedback have been instrumental in further\nclarifying the significance of our work and improving the quality of our paper manuscript.\nWe have carefully considered all the comments/suggestions, given point-by-point responses,\nand made revisions to improve the quality and impact of our manuscript.\n1. The authors refer to the membranes as \"crack-free\" and \"defect-free\". However, these\nterms are not accurate because there is no such thing as a \"defect-free\" material, especially\nconsidering the multiple missing linkers within the membrane.\nResponse: Thank you for this valuable suggestion. We would like to clarify that in our\nmanuscript, defects can be classified into two types: intercrystalline defects (cracks or\npinhole) and intracrystalline defects (lattice missing linkers). We must apologize that we\nmisused these terms in the manuscript. To address your concern about this issue, we have\ncarefully revised the manuscript and SI files.\n2. The PXRD patterns need further investigation - in Figure 1g the reference MOF-801\npattern was presented. Is this pattern from any literature or cif file? This should be clearly\npresented. In addition, after the membrane pervaporation test (figure 4g), there are some peak\nshift, indicating the change of MOF structure. Any discussion on these should be\nwelcomed.\nResponse: Thank you again for this valuable suggestion. We would like to clarify that the\nreference MOF-801 pattern was simulated by Mercury software. To address your concern\nabout this issue, we have carefully revised in the manuscript (please see Line 308-309, Page\n15), which is show as follows.\n(The reference MOF-801 pattern (i.e., MOF-801 (s)) was simulated by Mercury software).\nAfter constant operation in harsh environments (e.g., high temperature, high salinity, and low\npH ∼3), the membranes still exhibit two characteristic reflections of MOF-801 phase,\nbetween 7 and 11°, indicating their stability in phase structure. This is the key evidence to\nshow the stability of our membranes. We sincerely appreciate your very careful observation\non some minor peak shift of the XRD reflections. We will perform detailed follow-up\nresearch to fully understand the underlying mechanism of such a minor shift.\n11"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have well addressed all my concerns.\nThe following comments are presented to address the required questions.\n1. The noteworthy results of this work reside in the following aspects:\nThe revised manuscript convincingly demonstrates the efficacy of precise regulation of intracrystalline missing linkers in MOF-801 membranes, significantly enhancing water transport. This is achieved by altering the ratio of fumarate to formic acid during the membrane synthesis, leading to a notable improvement in both permeability and selectivity. The results, as demonstrated in Figures 2 and 3 of the manuscript, show that these modifications lead to near-perfect salt rejection (~99.9%) and elevated water flux compared to previous standards in the field. Furthermore, the membranes exhibited exceptional stability under challenging conditions, which is critical for practical applications.\n2. The work has the following significance to the field:\nThe approach detailed in this manuscript marks a substantial contribution to the field of desalination technology, particularly for treating hypersaline waters which pose a challenge to conventional reverse osmosis methods. The method's ability to enhance both the structural hydrophilicity and transport dynamics of MOF membranes through defect regulation could have far-reaching implications for the design of next-generation separation technologies. This work not only advances our understanding of MOF membrane capabilities but also sets a new benchmark for their performance in water treatment applications.\n3. Regarding the comparison to established literature:\nThe authors have positioned their work adeptly within the context of existing literature, providing a clear demonstration of how their approach surpasses the capabilities of existing silica, zeolite, and other MOF membranes. This claim is well-supported by comprehensive experimental and simulation data, and the manuscript now includes an extensive review of relevant studies to further bolster its claims of novelty and superiority.\n4. Regarding the soundness of research:\nThe methodologies employed in this study are sound and represent a substantial advancement in the field of membrane technology. The detailed experimental setup and the robust simulation studies provide a clear and convincing argument for the benefits of controlled defect creation in MOFs. The authors have effectively used a combination of experimental data and theoretical models to explain the mechanisms at play, which not only supports the claims made but also enhances the manuscript's contribution to the field's body of knowledge.\n5. Addressing previous concerns:\nIt is evident that the authors have taken previous critiques into consideration, making significant revisions to the manuscript. They have clarified the novel aspects of their synthesis strategy, improved the discussion around their method's significance, and provided additional comparative data and theoretical backing to support their conclusions.\nGiven the comprehensive response to previous reviews, the significant advancements reported, and the potential impact on the field, I recommend the acceptance of this manuscript for publication. T", "reviewer_2": "The response and revision by the Authors is unacceptable and the manuscript remains unsuitable for publication in Nature Communications. It should be revised and published in a disciplinary specific journal for desalination.\n1) The authors fail to include a citation for the review paper “Desalination by membrane pervaporation: A Review” Desalination, 547, 1, 116223, doi:10.1016/j.desal.2022.116223. The manuscript, as written, does not provide proper context for the performance of their membranes in context of the known field of pervaporation desalination membranes.\n2) The authors refuse to revise the manuscript to include a direct calculation of the permeance and selectivity of the membranes produced and do not cite “Permeability, permeance and selectivity: A preferred way of reporting pervaporation performance data” by Richard W. Baker et al. https://doi.org/10.1016/j.memsci.2009.11.022.\nIn the author’s rebuttal they state (incorrectly)\n“However, water flux is often presented as a metric of comparison in pervaporation desalination studies (1-14). Due to practical challenges of obtaining accurate permeability data, permeance is not always reported in open literature as it requires precise measurements of membrane thickness and close monitoring of operating conditions. . In fact, if this information is not disclosed, permeance can obfuscate the if this information is not disclosed, permeance can obfuscate the experimental conditions that should be used for a fair comparison between materials.”\nThis is statement by the authors in the rebuttal is patently incorrect. Permeance calculations do not involve membrane thickness, permeance is the flux normalized by the driving force (e.g., the operating conditions). Only permeability calculations involve knowledge of membrane thickness. The authors are referred to Equations 11 and 12 in Baker et al. https://doi.org/10.1016/j.memsci.2009.11.022 for these standard definitions. . It would be quite simple for the authors to calculate the permeance of their membranes (regardless of knowledge of active layer thickness) and to place them into context of the known body of literature in pervaporation desalination membranes. The authors are further referred to the textbook \"Basic Principles of Membrane Science\" (Mulder, 1996)\nhttps://link.springer.com/book/10.1007/978-94-009-1766-8 to review the fundamental terminology and calculation methods for membrane materials.", "reviewer_3": "After a careful review of the revised manuscript, I consider that the authors have addressed the reviewers' comments partially. There are still several concerns that are not better addressed. For example, as for the difference between this work and the paper related to UiO-66 membrane reported by the same authors (Nat. Common. 2022, 13, 266), the authors just claimed that “Differing from this former study that merely introduced an arbitrary amount of missing linkers, this work showcases that the precise regulation of missing linkers to enhance water transport could be realized in MOF-801 membranes.\nBased on the authors’ response, I think that in this work, the authors just change the MOF material from UiO-66 to MOF-801 because the former study also achieved the precise regulation of missing linkers. As pointed out by the Reviewer #2 that “This manuscript is most well suited for publication in a specialized disciplinary journal, such as the Journal of Membrane Science or Desalination or other membrane or water purification focused journal.”", "reviewer_4": "This contribution reports a type of perovaporation membrane, fabricated with MOF-801 thin layer coating on alumina based substrates. The authors applied surfactants to suppress the formation of crack during drying process, and the modulator was applied to tune the missing linker to enhance the membrane performance.\nOverall, this contribution contains new knowledge and the fabrication of such membrane/tuning interfacial properties can provide useful reference to the community. The authors have also addressed most of the comments raised from the last round of review, including some challenging ones. I would recommend the publication of this manuscript after some additional minor revision.\n1. The authors refer to the membranes as \"crack-free\" and \"defect-free\". However, these terms are not accurate because there is no such thing as a \"defect-free\" material, especially considering the multiple missing linkers within the membrane.\n2. The PXRD patterns need further investigation - in Figure 1g the reference MOF-801 pattern was presented. Is this pattern from any literature or cif file? This should be clearly presented. In addition, after the membrane pervaporation test (figure 4g), there are some peak shift, indicating the change of MOF structure. Any discussion on these should be welcomed."}, "author_response": "Response to Reviewers: NCOMMS-24-08272B\nPoint-to-point Response to the Reviewers’ Comments: NCOMMS-24-08272B\nReviewer #1 (Remarks to the Author):\nThe authors have well addressed all my concerns. The following comments are presented to\naddress the required questions.\n1. The noteworthy results of this work reside in the following aspects:\nThe revised manuscript convincingly demonstrates the efficacy of precise regulation of\nintracrystalline missing linkers in MOF-801 membranes, significantly enhancing water\ntransport. This is achieved by altering the ratio of fumarate to formic acid during the\nmembrane synthesis, leading to a notable improvement in both permeability and selectivity.\nThe results, as demonstrated in Figures 2 and 3 of the manuscript, show that these\nmodifications lead to near-perfect salt rejection (~99.9%) and elevated water flux compared\nto previous standards in the field. Furthermore, the membranes exhibited exceptional stability\nunder challenging conditions, which is critical for practical applications.\n2. The work has the following significance to the field:\nThe approach detailed in this manuscript marks a substantial contribution to the field of\ndesalination technology, particularly for treating hypersaline waters which pose a challenge to\nconventional reverse osmosis methods. The method's ability to enhance both the structural\nhydrophilicity and transport dynamics of MOF membranes through defect regulation could\nhave far-reaching implications for the design of next-generation separation technologies. This\nwork not only advances our understanding of MOF membrane capabilities but also sets a new\nbenchmark for their performance in water treatment applications.\n3. Regarding the comparison to established literature:\nThe authors have positioned their work adeptly within the context of existing literature,\nproviding a clear demonstration of how their approach surpasses the capabilities of existing\nsilica, zeolite, and other MOF membranes. This claim is well-supported by comprehensive\nexperimental and simulation data, and the manuscript now includes an extensive review of\nrelevant studies to further bolster its claims of novelty and superiority.\n4. Regarding the soundness of research:\nThe methodologies employed in this study are sound and represent a substantial advancement\nin the field of membrane technology. The detailed experimental setup and the robust\nsimulation studies provide a clear and convincing argument for the benefits of controlled\ndefect creation in MOFs. The authors have effectively used a combination of experimental\ndata and theoretical models to explain the mechanisms at play, which not only supports the\nclaims made but also enhances the manuscript's contribution to the field's body of knowledge.\n5. Addressing previous concerns:\nIt is evident that the authors have taken previous critiques into consideration, making\nsignificant revisions to the manuscript. They have clarified the novel aspects of their\nsynthesis strategy, improved the discussion around their method's significance, and provided\nadditional comparative data and theoretical backing to support their conclusions.\nGiven the comprehensive response to previous reviews, the significant advancements\nreported, and the potential impact on the field, I recommend the acceptance of this\nmanuscript for publication.\nResponse: We sincerely appreciate that you took the time to evaluate our revised manuscript\nfor a second time and provided five encouraging comments on the novelty and significance of\nour work. Particularly, we appreciate your comments on\nthe noteworthiness of precisely regulating intracrystalline missing linkers to enhance water\ntransport; the significance of advancing our understanding of MOF membrane capabilities to\ndevelop next-generation separation technologies; the recognition of the superior performance\nof our MOF membrane in the context of existing silica, zeolite, as well as other MOF\nmembranes; the soundness of our experimental and simulation methods; and\nacknowledgement that we have addressed previous concerns by clarifying the novel aspects\nof our synthesis strategy, improving the discussion around our method's significance, and\nproviding additional comparative data and theoretical backing to support our conclusions.\nReviewer #2 (Remarks to the Author):\nThe response and revision by the Authors is unacceptable and the manuscript remains\nunsuitable for publication in Nature Communications. It should be revised and published in a\ndisciplinary specific journal for desalination.\nResponse: In the two rounds of review, Reviewer #1, Reviewer #3, and Reviewer #4 have all\nprovided positive and detailed comments on the novelty and impact of our work. Particularly,\nfor the revised manuscript (in the last round of review), Reviewer #1 recognized our work\nand revisions with very positive comments such as the noteworthiness of precisely regulating\nintracrystalline missing linkers to enhance water transport; the significance of advancing our\nunderstanding of MOF membrane capabilities to develop next-generation separation\ntechnologies; the recognition of the superior performance of our MOF membrane in the\ncontext of existing silica, zeolite, as well as other MOF membranes; the soundness of our\nexperimental and simulation methods; and acknowledgement that we have addressed\nprevious concerns by clarifying the novel aspects of our synthesis strategy, improving the\ndiscussion around our method's significance, and providing additional comparative data and\ntheoretical backing to support our conclusions. Reviewer #4 also provided supportive\ncomments, commending our work as new knowledge and a useful reference to the\ncommunity. We also would like to again summarize and highlight the novel aspects of our\nwork and the broader implications and contributions, which motivated our decision to submit\nto Nature Communications.\nImportant novel aspects are described below:\n1. The first novel aspect in this work is the precise regulation of missing linkers lattice\ndefects in the MOF membrane (Fig. 2). Intracrystalline defects—such as missing linkers and\nmissing clusters—have been synthesized and confirmed to influence the permeability or\nselectivity of MOF liquid- or gas-separation membranes. However, the precise regulation of\nfavorable intracrystalline defects and their effect on fundamental mass transport phenomena\nfor desalination has not been previously reported for membrane-based separation applications.\nAs Reviewer #3 positively commented in the last round of review, there are few reports\npaying attention to the lattice defects in MOF membranes. More importantly, we\ndemonstrated a facile method to precisely control the frequency of missing linkers, which has\nnot been previously realized for MOF membranes.\n2. The second novel aspect is the characterization of the atomistic mechanism for\nenhanced water transport induced by precise regulation of missing linkers (Fig. 3).\nWhile published works on pervaporation desalination largely focus on membrane fabrication\nand performance evaluation, very rarely is the fundamental atomistic mechanism for water\ntransport explored. Interestingly, we found that precise regulation of missing linkers enhances\nmembrane structural hydrophilicity with stronger host-guest interaction energy. Resulting in a\nlower energy barrier by enlarging the MOF pore window and pore cage, the structural\nconfiguration of MOF-801 with the precise regulation of missing linkers enables the observed\nincrease in water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different disciplines\nand fields of science, technology, and engineering (e.g., chemistry, materials, environmental\nscience, chemical engineering, water and membrane technologies). Thus, we believe that this\nwork with fundamental mechanistic insights is of great interest for the broad readership of\nNature Communications.\n3. The third novel aspect of this work is the superior performance of our MOF membrane\nin comparison to other state-of-the-art zeolite and MOF membranes for pervaporation\ndesalination. As you have recognized, our work is the first report to use the\nmaterial MOF-801 for pervaporation desalination and has some interesting materials\nscience aspects and modeling components. We recognize that some pervaporation desalination\nmembranes—especially polymeric membranes—have higher performance (with respect to\nwater flux) under specific conditions, but we wish to emphasize that our MOF membranes\nindeed outperform state-of-the-art zeolite and MOF membranes in water flux (Figure 4 and\nTables S5-6), which belong to an emerging class of polycrystalline molecular sieve\nmembranes that are drastically different from polymeric membranes (such as PVA\nmembranes). As a result, the performance comparison of membranes with similar structures\nand properties was deemed more appropriate for this study.\n4. The fourth novel aspect of this work is the exceptional stability under harsh chemical\nconditions (i.e., high-temperature, acidic, oxidizing conditions, feeds with refractory species\nlike oil or surfactants) of our MOF membrane. Differing from previous reports focusing on\ndesalination under mild conditions, we intentionally subjected our MOF membrane to harsh\nchemical conditions for prolonged periods of time to evaluate their resilience in practical\napplications that have proven challenging for conventional polymeric membranes (Fig. 4, Fig.\n5, Fig. S16-21, Table S4). To this end, our MOF membrane showcased stable performance\nwhen treating real industrial wastewater with a complicated composition, which has not\nbeen successfully demonstrated previously (Fig. 5, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies. We believe\nthat this has broader implications for the design and synthesis of novel membrane materials\n(e.g., MOF-801 in our work), which has not been the traditional focus in the field. Our\ncurrent work provides an entirely new platform for robust desalination under harsh chemical\nconditions, expanding the number applications where membrane-based desalination is now\nrelevant.\n1) The authors fail to include a citation for the review paper “Desalination by membrane\npervaporation: A Review” Desalination, 547, 1, 116223, doi:10.1016/j.desal.2022.116223.\nThe manuscript, as written, does not provide proper context for the performance of their\nmembranes in context of the known field of pervaporation desalination membranes.\nResponse: We thank you for providing the reference and have read it carefully. We have\nadded the reference to the manuscript. We also added permeance data to the Supplementary\nInformation (SI) as you see in our response to the next comment.\nWe sincerely appreciate you for re-providing these comments to encourage us to distinguish\nour MOF membrane from conventional pervaporation desalination membranes. We\nacknowledge that some pervaporation desalination membranes—especially PVA polymeric\nmembranes—have reported higher performance (i.e., water flux) than our MOF membranes.\nHowever, it should be noted that experimental conditions for evaluating pervaporation\nmembranes across the field are not uniform, and it is this variability that impacts the driving\nforce for pervaporation and the water fluxes that are reported. For example, we used an\nice-water bath (i.e., 273 K) to determine the flux of our MOF-801 membrane whereas a\nhigher driving force enabled by a liquid nitrogen cold trap (i.e., 77 K) was used in other\nstudies using polymeric membranes. Furthermore, the structure and properties of polymeric\nmembranes is distinctly different from our MOF membranes. Therefore, it makes more sense\nto compare the performance of our MOF membrane to other state-of-the-art zeolite and MOF\nmembranes that belong to an emerging class of polycrystalline molecular sieve membranes\nwith similar structures and properties.\n2) The authors refuse to revise the manuscript to include a direct calculation of the permeance\nand selectivity of the membranes produced and do not cite “Permeability, permeance and\nselectivity: A preferred way of reporting pervaporation performance data” by Richard W.\nBaker et al. https://doi.org/10.1016/j.memsci.2009.11.022.\nResponse: We agree with your opinion that the parameters (i.e., permeance, permeability)\nbetter reflect intrinsic properties of the membranes. We also added permeance data to the\nSupplementary Information (SI) as you see in our response to the next comment.\nIt should be noted that the reference provided by the reviewer is for pervaporation with\nmixtures of organic-organic or organic-water, where the focus is on the selectivity of\nseparation and permeability-selectivity tradeoff (Journal of Membrane Science 348 (1-2)\n(2010) 346-352). However, pervaporation of organic-organic or organic-water is totally\ndifferent from pervaporation desalination. Water flux (not permeance) and salt rejection (not\nselectivity) are often presented as a metric of comparison in pervaporation desalination\nstudies (1-14). Due to practical challenges of obtaining accurate data, permeance is not\nalways reported in open literature as it requires close monitoring of desalination operating\nconditions such as trans-membrane pressure difference. In fact, if this information is not\ndisclosed, permeance can obfuscate the experimental conditions that should be used for a fair\ncomparison between materials. Therefore, we have adopted the standard practice—which has\nbeen used for other membrane processes like microfiltration and membrane distillation—of\nreporting water flux as a simpler parameter directly reflecting water treatment efficiency—\nwhile providing transparency about our experimental conditions and membrane properties\n(15-17).\nMore importantly, the core novel aspects of this work include the precise regulation of\nmissing linkers, characterization of the atomistic mechanism of enhanced performance, and\nharsh chemical operation stability, all of which have not been explored in existing works.\nReference\n1. Meidi Wang, Penghui Zhang, Xu Liang, Junyi Zhao, Yawei Liu, Yu Cao, Hongjian Wang, Yu\nChen, Zhiming Zhang, Fusheng Pan, Zhenjie Zhang, Zhongyi Jiang, Ultrafast seawater\ndesalination with covalent organic framework membranes, Nature Sustainability 5 (2022) 518–\n526.\n2. Zishu Cao, Shixuan Zeng, Zhi Xu, Antonios Arvanitis, Shaowei Yang, Xuehong Gu, Junhang\nDong, Ultrathin ZSM-5 zeolite nanosheet laminated membrane for high-flux desalination of\nconcentrated brines. Science Advances. 4 (2018) eaau8634.\n3. Chun Xiang C Lin, Li Ping Ding, Simon Smart, João C Diniz da Costa, Cobalt oxide silica\nmembranes for desalination, Journal of Colloid and Interface Science 368(2012) 70-76.\n4. Mikel C Duke, Steven Mee, J C Diniz da Costa, Performance of porous inorganic membranes in\nnon-osmotic desalination. Water Research 41(2007) 3998-4004.\n5. Huayu Zhang, Jiuli Wen, Qi Shao, Ai Yuan, Haiting Ren, Fangying Luo, Xiaoliang Zhang,\nFabrication of La/Y-codoped microporous organosilica membranes for high-performance\npervaporation desalination. Journal of Membrane Science 584(2019) 353-363.\n6. Shengnan Wang, David K Wang, Julius Motuzas, Simon Smart, João C Diniz da Costa, Rapid\nthermal treatment of interlayer-free ethyl silicate 40 derived membranes for desalination.\nJournal of Membrane Science 516(2016) 94-103.\n7. Sheida Khajavi, Jacobus C Jansen, Freek Kapteijn, Production of ultra pure water by desalination\nof seawater using a hydroxy sodalite membrane. Journal of Membrane Science 356(2010)\n52-57.\n8. Mikel C Duke, Jessica O’Brien-Abraham, Nicholas Milne, Bo Zhu, Jerry Y.S. Lin, D João\nC. Diniz da Costa, Seawater desalination performance of MFI type membranes made by\nsecondary growth. Separation and Purification Technology 68(2009) 343-350.\n9. Churl Hee Cho, Ka Yeon Oh, Si Kyung Kim, Jeong Gu Yeo, Pankaj Sharma, Pervaporative\nseawater desalination using NaA zeolite membrane: Mechanisms of high water flux and high salt\nrejection. Journal of Membrane Science 371(2011) 226-238.\n10. Paul Swenson, Brenden Tanchuk, Ankita Gupta, Weizhu An, Steven M. Kuznicki, Pervaporative\ndesalination of water using natural zeolite membranes. Desalination 285(2012) 68-72.\n11. Chen Zhou, Junjie Zhou, Aisheng Huang, Seeding-free synthesis of zeolite FAU membrane for\nseawater desalination by pervaporation. Microporous and Mesoporous Materials 234(2016)\n377-383\n12. Martin Drobek, Christelle Yacou, Julius Motuzas, Anne Julbe, Liping Ding, João C. Diniz da\nCosta, Long term pervaporation desalination of tubular MFI zeolite membranes. Journal of\nMembrane Science 415-416(2012) 816-823.\n13. Yaqiong Zhu, Krishna M. Gupta, Qian Liu, Jianwen Jiang, Jürgen Caro, Aisheng Huang,\nSynthesis and seawater desalination of molecular sieving zeolitic imidazolate framework\nmembranes. Desalination 385(2016) 75-82.\n14. Linlin Wan, Chen Zhou, Kai Xu, Bo Feng, Aisheng Huang, Synthesis of highly stable\nUiO-66-NH membranes with high ions rejection for seawater desalination. Microporous &\n15. Huiling Chen, Xing Liu, Dian Gong, Chang Zhu, Guojuan Liu, Jingrui Fan, Ping Wu, Zhi Li,\nYichang Pan, Guosheng Shi, Yuhan Sun, Gaofeng Zeng, Ultrahigh-water-flux desalination on\ngraphdiyne membranes, Nature Water, 1 (2023), 800-807.\n16. Luke Yan, Gui Zhang, Lei Zhang, Wei Zhang, Jincui Gu, Youju Huang, Jiawei Zhang, Tao Chen,\nRobust construction of underwater superoleophobic CNTs/nanoparticles multifunctional hybrid\nmembranes via interception effect for oily wastewater purification. Journal of Membrane\nScience 569(2019) 32-40.\n17. Yu Gu, Bowu Zhang, Zhiang Fu, Jihao Li, Ming Yu, Linfan Li, Jingye Li. Poly (vinyl alcohol)\nmodification of poly(vinylidene fluoride) microfiltration membranes for oil/water emulsion\nseparation via an unconventional radiation method. Journal of Membrane Science. 619(2021)\n118792.\nIn the author’s rebuttal they state (incorrectly)\n“However, water flux is often presented as a metric of comparison in pervaporation\ndesalination studies (1-14). Due to practical challenges of obtaining accurate permeability\ndata, permeance is not always reported in open literature as it requires precise measurements\nof membrane thickness and close monitoring of operating conditions. . In fact, if this\ninformation is not disclosed, permeance can obfuscate the if this information is not disclosed,\npermeance can obfuscate the experimental conditions that should be used for a fair\ncomparison between materials.”\nThis is statement by the authors in the rebuttal is patently incorrect. Permeance calculations\ndo not involve membrane thickness, permeance is the flux normalized by the driving force\n(e.g., the operating conditions). Only permeability calculations involve knowledge of\nmembrane thickness. The authors are referred to Equations 11 and 12 in Baker et al.\nhttps://doi.org/10.1016/j.memsci.2009.11.022 for these standard definitions. . It would be\nquite simple for the authors to calculate the permeance of their membranes (regardless of\nknowledge of active layer thickness) and to place them into context of the known body of\nliterature in pervaporation desalination membranes. The authors are further referred to the\ntextbook \"Basic Principles of Membrane Science\" (Mulder, 1996)\nhttps://link.springer.com/book/10.1007/978-94-009-1766-8 to review the fundamental\nterminology and calculation methods for membrane materials.\nResponse: We thank you for providing the reference and have read it carefully. We agree\nwith your opinion that the parameters (i.e., permeance, permeability) better reflect intrinsic\nproperties of the membranes.\nWe converted water flux into water permeance as requested by the reviewer (Please\nsee Figure S18, Supplementary Information)\nFigure S18. (a) Water permeance of the MOF-801 membranes with different linker deficiencies. (b) Water\npermeance of the MOF-801-1.43 membrane for treatment of saline feeds with different salt concentrations.\nReviewer #3 (Remarks to the Author):\nAfter a careful review of the revised manuscript, I consider that the authors have addressed\nthe reviewers' comments partially. There are still several concerns that are not better\naddressed. For example, as for the difference between this work and the paper related to\nUiO-66 membrane reported by the same authors (Nat. Common. 2022, 13, 266), the authors\njust claimed that “Differing from this former study that merely introduced an arbitrary\namount of missing linkers, this work showcases that the precise regulation of missing linkers\nto enhance water transport could be realized in MOF-801 membranes. Based on the authors’\nresponse, I think that in this work, the authors just change the MOF material from UiO-66 to\nMOF-801 because the former study also achieved the precise regulation of missing linkers.\nAs pointed out by the Reviewer #2 that “This manuscript is most well suited for publication\nin a specialized disciplinary journal, such as the Journal of Membrane Science or\nDesalination or other membrane or water purification focused journal.”\nResponse: Again, we sincerely appreciate that you provided positive comments on the\nnovelty and significance of our work in the last round of review and took time to carefully\nevaluate our revised manuscript (NCOMMS-24-08272A-Z). In our former study (Nat.\nCommon. 2022, 13, 266), we introduced an arbitrary amount of missing linkers (~23.5%) in\nUiO-66 membrane, but the precise regulation of missing linkers in the membrane was not\nexplored. Additionally, the precise creation of intracrystalline defects in MOF membranes is\nchallenging, requiring complicated and challenging membrane fabrication and optimization,\nwhich is why this topic has not been well-studied for membrane-based separation\napplications. Differing from the former study, this work on pervaporation not only shows that\nthe precise regulation of missing linkers to enhance water transport in MOF-801 membranes\nis possible, but also conducts an in-depth investigation into how structural modifications in\nthe MOF-801 membrane structure impact pervaporation performance.\nTo address your concern about the novelty, we have further revised in Introduction section\n(please see Line 85-87, Line 94-97, Page 4), which is show as follows.\nLine 85-87: However, the precise creation of favorable intracrystalline defects is challenging\nand has not been well-studied in membrane-based separation applications.\nLine 94-97: Differing from this former study that introduced an arbitrary amount of missing\nlinkers (~23.5%), 29 this work demonstrates that precise regulation of missing linkers to\nenhance water transport could be realized in MOF-801 membranes, which is not only\npractically challenging, but also critical for understanding fundamental mass transport\nphenomena.\nIn this round of review, both Reviewer #1 and Reviewer #4 provided very positive and\ndetailed comments on the novelty and impact of our work. Particularly, Reviewer #1\nrecognized our work and revisions with very positive comments such as the noteworthiness\nof precisely regulating intracrystalline missing linkers to enhance water transport; the\nsignificance of advancing our understanding of MOF membrane capabilities to develop\nnext-generation separation technologies; the recognition of the superior performance of our\nMOF membrane in the context of existing silica, zeolite, as well as other MOF membranes;\nthe soundness of our experimental and simulation methods; and acknowledgement that we\nhave addressed previous concerns by clarifing the novel aspects of our synthesis strategy,\nimproving the discussion around our method's significance, and providing additional\ncomparative data and theoretical backing to support our conclusions.. Reviewer #4 also\nprovided supportive comments, commending our work as new knowledge and a useful\nreference to the community. We also would like to summarize and highlight the novelties of\nour work and its broader implications and contributions, which motivated our decision to\nsubmit to Nature Communications.\nImportant novel aspects are described below:\n1. The first novel aspect in this work is the precise regulation of missing linkers lattice\ndefects in the MOF membrane (Fig. 2). Intracrystalline defects—such as missing linkers and\nmissing clusters—have been synthesized and confirmed to influence the permeability or\nselectivity of MOF liquid- or gas-separation membranes. However, the precise regulation of\nfavorable intracrystalline defects and their effect on fundamental mass transport phenomena\nfor desalination has not been previously reported for membrane-based separation applications.\nAs you positively commented in the last round of review, there are few reports paying\nattention to the lattice defects in MOF membranes. More importantly, we demonstrated a\nfacile method to precisely control the frequency of missing linkers, which has not been\npreviously realized for MOF membranes.\n2. The second novel aspect is the characterization of the atomistic mechanism for\nenhanced water transport induced by precise regulation of missing linkers (Fig. 3).\nWhile published works on pervaporation desalination largely focus on membrane fabrication\nand performance evaluation, very rarely is the fundamental atomistic mechanism for water\ntransport explored. Interestingly, we found that precise regulation of missing linkers enhances\nmembrane structural hydrophilicity with stronger host-guest interaction energy. Resulting in a\nlower energy barrier by enlarging the MOF pore window and pore cage, the structural\nconfiguration of MOF-801 with the precise regulation of missing linkers enables the observed\nincrease in water flux. We strongly believe this fundamental understanding has broader\nscientific implications and will aid in bridging knowledge gaps across different disciplines\nand fields of science, technology, and engineering (e.g., chemistry, materials, environmental\nscience, chemical engineering, water and membrane technologies). Thus, we believe that this\nwork with fundamental mechanistic insights is of great interest for the broad readership of\nNature Communications.\n3. The third novel aspect of this work is the superior performance of our MOF membrane\nin comparison to other state-of-the-art zeolite and MOF membranes for pervaporation\ndesalination. As Reviewer #2 has recognized, our work is the first report to use the\nmaterial MOF-801 for pervaporation desalination and has some interesting materials\nscience aspects and modeling components. We recognize that some pervaporation desalination\nmembranes—especially polymeric membranes—have higher performance (with\nrespect to water flux) under specific conditions, but we wish to emphasize that our MOF\nmembranes indeed outperform state-of-the-art zeolite and MOF membranes in water flux\n(Figure 4 and Tables S5-6), which belong to an emerging class of polycrystalline molecular\nsieve membranes that are drastically different from polymeric membranes (such as PVA\nmembranes). As a result, the performance comparison of membranes with similar structures\nand properties was deemed more appropriate for this study.\n4. The fourth novel aspect of this work is the exceptional stability under harsh chemical\nconditions (i.e., high-temperature, acidic, oxidizing conditions, feeds with refractory species\nlike oil or surfactants) of our MOF membrane. Differing from previous reports focusing on\ndesalination under mild conditions, we intentionally subjected our MOF membrane to harsh\nchemical conditions for prolonged periods of time to evaluate their resilience in practical\napplications that have proven challenging for conventional polymeric membranes (Fig. 4, Fig.\n5, Fig. S16-21, Table S4). To this end, our MOF membrane showcased stable performance\nwhen treating real industrial wastewater with a complicated composition, which has not\nbeen successfully demonstrated previously (Fig. 5, Table S4). Stable operation under harsh\nchemical conditions is of great practical significance for membrane technologies. We believe\nthat this has broader implications for the design and synthesis of novel membrane materials\n(e.g., MOF-801 in our work), which has not been the traditional focus in the field. Our\ncurrent work provides an entirely new platform for robust desalination under harsh chemical\nconditions, expanding the number applications where membrane-based desalination is now\nrelevant.\nReviewer #4 (Remarks to the Author):\nThis contribution reports a type of pervaporation membrane, fabricated with MOF-801 thin\nlayer coating on alumina based substrates. The authors applied surfactants to suppress the\nformation of crack during drying process, and the modulator was applied to tune the missing\nlinker to enhance the membrane performance.\nOverall, this contribution contains new knowledge and the fabrication of such\nmembrane/tuning interfacial properties can provide useful reference to the community. The\nauthors have also addressed most of the comments raised from the last round of review,\nincluding some challenging ones. I would recommend the publication of this manuscript after\nsome additional minor revision.\nResponse: We appreciate that you took time to evaluate our manuscript and provide\ncomments on the novelty and significance of our work (e.g., new knowledge, useful reference\nto the community). We also appreciate your positive comment that the authors have\naddressed most of the comments raised from the last round of review, including some\nchallenging ones. Your valuable suggestions and feedback have been instrumental in further\nclarifying the significance of our work and improving the quality of our paper manuscript.\nWe have carefully considered all the comments/suggestions, given point-by-point responses,\nand made revisions to improve the quality and impact of our manuscript.\n1. The authors refer to the membranes as \"crack-free\" and \"defect-free\". However, these\nterms are not accurate because there is no such thing as a \"defect-free\" material, especially\nconsidering the multiple missing linkers within the membrane.\nResponse: Thank you for this valuable suggestion. We would like to clarify that in our\nmanuscript, defects can be classified into two types: intercrystalline defects (cracks or\npinhole) and intracrystalline defects (lattice missing linkers). We must apologize that we\nmisused these terms in the manuscript. To address your concern about this issue, we have\ncarefully revised the manuscript and SI files.\n2. The PXRD patterns need further investigation - in Figure 1g the reference MOF-801\npattern was presented. Is this pattern from any literature or cif file? This should be clearly\npresented. In addition, after the membrane pervaporation test (figure 4g), there are some peak\nshift, indicating the change of MOF structure. Any discussion on these should be\nwelcomed.\nResponse: Thank you again for this valuable suggestion. We would like to clarify that the\nreference MOF-801 pattern was simulated by Mercury software. To address your concern\nabout this issue, we have carefully revised in the manuscript (please see Line 308-309, Page\n15), which is show as follows.\n(The reference MOF-801 pattern (i.e., MOF-801 (s)) was simulated by Mercury software).\nAfter constant operation in harsh environments (e.g., high temperature, high salinity, and low\npH ∼3), the membranes still exhibit two characteristic reflections of MOF-801 phase,\nbetween 7 and 11°, indicating their stability in phase structure. This is the key evidence to\nshow the stability of our membranes. We sincerely appreciate your very careful observation\non some minor peak shift of the XRD reflections. We will perform detailed follow-up\nresearch to fully understand the underlying mechanism of such a minor shift.\n11"}, {"round": 3, "reviewer_comments": {"reviewer_5": "This manuscript has gone through several revisions with multiple reviewers. The scientific significance of the topic discussed in this work meets the criteria of Nature Communications. However, I do agree with Reviewer #2 regarding the misstatement in the manuscript. Some additional experiments are also required to make the manuscript scientifically rigorous. My comments are below.\n1. Reviewer #2 is right about the definition of pervaporation and membrane distillation. The authors need to correct the statement in line 55-58. Also, I agree with the reviewer #2 that the authors should be very careful regarding the word “sieving” (line 70, 75, 164, 372, 411). Molecular sieving is the most misused concept in membrane applications for molecular separation. The authors may need to avoid the use of sieving, unless it is supported by rigorous experiment.\n2. I agree with Reviewer #2 regarding the stability mentioned by the authors. The XRD patterns clearly showed that the membrane/MOF is not stable under harsh conditions. The authors should correct some of the statements in the manuscript (line 343-345). Some experiments do show good stability under long operation, but others in the manuscript show the crystallinity of MOF can be demolished under harsh solution. The authors need to be very clear whenever using “stability” in the manuscript.\n3. I agree with Reviewer #2 that the phrase “perfect” should be avoided throughout the entire manuscript.\n4. Regarding the error bars of and repeatability of the experiments, I suggest the authors performing the reproducibility tests for important experiments. For example, experiments shown in Fig 5a-c. For all experiments performed in this study, the number of trials should be described.", "reviewer_6": "It is hard to believe that the PV experimental details were given only in the third round of revision.\nMolecular sieving is typically claimed for high selective gas separation membranes, not the case with the relatively modest values provided in Fig. 1 (17 for the H2/CH4 pair). Selective water PV with hydrophilic membranes of zeolites can be obtained in non-gas separation suitable zeolite membranes due to the exclusive water interaction with the defective spaces between crystals.\nAlso, the membrane stability discussion was completed. Obviously, the presence of PXRD peaks does not exclude loss of crystallinity and thus loss/lack of long term PV stability.\nRegarding PV permeance (or even permeability), even if interesting most of membrane PV papers are discussed in terms of water PV flux.\nHaving said that, I consider that the answers given and modifications provided by the authors should be enough to accept the paper, even if they were completely provided only along the third revision round."}, "author_response": "REVIEWER COMMENTS\nReviewer #3 (Remarks to the Author):\nThe authors have addressed my concerns and now this paper can be accepted for\npublication.\nResponse: We sincerely appreciate that you took the time to evaluate our revised\nmanuscript for a third time and recommended to accept it.\nReviewer #4 (Remarks to the Author):\nAfter reading the comments from the reviewers and the response from the authors, I\nfound the authors have addressed these comments, including the rather critical ones.\nThe paper contains some interesting and novel results and it's now can be published in\nthe journal after addressing the additional comments raised by the reviewer 2#.\nResponse: We sincerely appreciate that you took the time to evaluate our revised\nmanuscript for a second time, and that you provided some positive comments on the\nimpact and significance of our work in the last review round. We also appreciate your\nrecommendation of accepting it if we reasonably address the additional comments\nraised by the Reviewer 2#. We have carefully considered the comments raised by the\nReviewer 2#, rethought and revised some statements, done some repeated\nexperiments to obtain the error bars after performing one-year experiments (e.g., Fig\n5a, Fig 5b, Fig 5c, and Fig 5f) and provided detailed point-to-point responses.\nYour positive comments on our revisions and responses to the comments were\ninstrumental for us to reflect on the framing and impact of our revised manuscript.\nThis manuscript has gone through several revisions with multiple reviewers. The\nscientific significance of the topic discussed in this work meets the criteria of Nature\nCommunications. However, I do agree with Reviewer #2 regarding the misstatement\nin the manuscript. Some additional experiments are also required to make the\nmanuscript scientifically rigorous. My comments are below.\nResponse: We sincerely appreciate that you took the time to evaluate our revised\nmanuscript, and that you provided positive comments on the scientific significance of\nthe topic discussed in our work. In the three rounds of review, Reviewer #1,\nReviewer #3, and Reviewer #4 have all provided positive and detailed comments on the\nnovelty and impact of our work. Your positive comments on our work were instrumental for\nus to reflect on the impact of our revised manuscript.\nWe have carefully considered all your comments, and the comments raised by the\nReviewer 2#, rethought some statements, done some repeated experiments to obtain\nthe error bars after performing one-year experiments (e.g., Fig 5a, Fig 5b, Fig 5c, and\nFig 5f) and provided detailed point-to-point responses.\n1. Reviewer #2 is right about the definition of pervaporation and membrane\ndistillation. The authors need to correct the statement in line 55-58. Also, I agree with\nthe reviewer #2 that the authors should be very careful regarding the word “sieving”\n(line 70, 75, 164, 372, 411). Molecular sieving is the most misused concept in\nmembrane applications for molecular separation. The authors may need to avoid the\nuse of sieving, unless it is supported by rigorous experiment.\nResponse: We agree with your opinion that pervaporation should be rightly defined\nand that some statements (e.g., molecular sieving) should be carefully revised in our\nmanuscript.\nTo address your concerns, we have further made revisions by rightly defining\npervaporation and salt rejection mechanism, deleting some terms such as “sieving”\nand citing the references. They key revisions are shown as follows (please see Page 3,\nPage 14, Page 18, Page 20, revised manuscript).\nPage 3, revised manuscript: While reverse osmosis (RO) is the current paradigm for\ndesalination, conventional RO cannot be used for hypersaline waters (salinity > ~10\nwt.%) due to the ultrahigh osmotic pressures that must be overcome, which exceed\nthe maximum hydraulic pressures that can be applied.3-6\nPage 3, revised manuscript: A promising chemical potential driven membrane\nprocess is pervaporation (PV), in which the chemical potential difference is\npractically realized by temperature and/or pressure differences 10. A liquid feed stream\n(heated in some cases) is exposed to one side of the PV membrane and a vacuum is\napplied to the other. Under these conditions, water vaporizes and traverses the PV\n2\nmembrane to be condensed, while dissolved salts are retained, because salts, unlike\nwater, have insignificant vapor pressure at the operational temperatures and pressures\nof pervaporation.9,11, 12.\nPage 3, revised manuscript: In contrast, metal-organic framework (MOF)\nmembranes have well-defined nanochannel structures, abundant affinity sites,\nmodular nature for functionalities, and structural stability, thereby enabling high\nuptake of water and promising separation performance.20-23\nPage 3, revised manuscript: where the pore window size (3.5 Å) ranges between\nwater molecules (2.8 Å) and hydrated sodium ions (~ 7.16 Å). This makes MOF-801\na promising candidate for desalination membranes with precise separation ability,\nwhich has not been experimentally demonstrated until now.\nPage 14, revised manuscript: The pore size of MOF-801-1.43 was determined to be\n5.07 Å (Figures 2d, S14b), which is lower than the size of hydrated ions (d\n[Na+·(H O) ] ~ 0.716 nm, d [Cl-·(H O) ] ~ 0.664 nm).43 The near-complete salt\n2 nh 2 nh\nrejections could be ascribed to the fact that the salt ions have negligible vapor\npressure at the operating conditions, and did not vaporize in the pervaporation\nprocess.\nPage 18, revised manuscript: In addition to having a stable water flux, the\nmembrane shows high rejection of all salt ions, such as Na+, K+, Mg2+, and Ca2+ (all\nabove 99.0%), which can be ascribed to that fact that salt ions have negligible vapor\npressure, and did not vaporize during the pervaporation process.\nPage 20, revised manuscript: Experimentally, the MOF-801 membranes showed\nnear-complete salt rejection, satisfactory water flux, and operation stability for the\ntreatment of saline or hypersaline waters.\nReferences:\n10. Mulder M., Chapter VI, Basic Principles of Membrane Technology, 2nd Edition,\n1996, Kluwer Academic Publishers, Springer Dordrecht.\n12.NIST Office of Data and Informatics. “Sodium Chloride.”. https:\n//webbook.nist.gov/cgi/cbook.cgi?ID=C7647145&Mask=4&Type=ANTOINE&Plot=\non#ANTOINE. (1122).\n2. I agree with Reviewer #2 regarding the stability mentioned by the authors. The\nXRD patterns clearly showed that the membrane/MOF is not stable under harsh\nconditions. The authors should correct some of the statements in the manuscript (line\n343-345). Some experiments do show good stability under long operation, but others\nin the manuscript show the crystallinity of MOF can be demolished under harsh\nsolution. The authors need to be very clear whenever using “stability” in the\nmanuscript.\nResponse: Thank you for these valuable suggestions. We have carefully rethought the\nresults of stability and would like to clarify that the crystallinity of MOF was indeed\ndemolished under some harsh solutions. We must apologize that we misused the term\n“stability” somewhere in the manuscript. To address your concern, we have revised\nsome words such as “excellent stability” and “unchanged XRD”. Moreover, we have\ncarefully revised the manuscript and SI files by revising some statements about the\n3\nstability, and expanding the discussions and interpretation of the data (XRD, SEM\nand gas permeance) (please see Page 5, Page 16, revised manuscript and Figure S5\ncaption), which are shown as follows.\nPage 5, revised manuscript: MOF-801 was selected to be fabricated into a\nseparation membrane because of its stability toward some solvents, especially\nhypersaline solutions at elevated temperatures (Figure S5). Different from the\npresence of only very minor and negligible additional peaks for the samples after\nexposure in DMF, acetone, and water, the phase structure degraded to some extent in\nstrongly acidic aqueous solution (pH 0.7), which can be reflected by peak broadening\nand new peaks arising (Figure S5). Nevertheless, such chemically harsh condition is\nfar beyond practical application conditions.\nPage 16, revised manuscript: MOF-801 membranes demonstrate stable operational\nperformance (in both flux and rejection) and acceptable structural integrity (in both\nMOF-801 crystalline phase and membrane morphology) for the treatment of 7 wt.%,\nheated, hypersaline water, at 70°C for 120 h (Figures 4d, 4f, 4 g).54 Under XRD, the\nMOF-801 membranes exhibited two characteristic reflections of MOF-801 phase\nbetween 7 and 11° before and after operation, indicating some stability in their phase\ncrystalline structure (Figure 4f). However, some peak width broadening was found\nfrom 0.24 to 0.37 especially after 108 h exposure at pH 3, which reflected the change\nin the lattice structure to some extent (i.e., crystal lattice grain sizes might decrease\nslightly), while the peaks keep nearly unchanged in the case of hypersaline water\nexposure.\nReferences:\n1. Ungár T., Microstructural parameters from X-ray diffraction peak broadening, Scripta\nmaterialia, 51 (08) (2004) 777-781.\n2. Li D.Z., Fundamentals of Crystallography, Powder X-ray Diffraction, and Transmission\nElectron Microscopy for Materials Scientists, 1st Edition, 2022, CPC Press (Boca Raton).\nFigure S5 caption: Figure S5. (a) XRD patterns of MOF-801 after accelerated\nstability tests in various solvents or harsh (acidic or alkaline) solutions. (b) XRD\npatterns of MOF-801 after 7-day long-term exposure accelerated tests in hot salt\nsolutions (~65℃) with different NaCl concentrations. (MOF-801 shows the stability\ntoward some solvents, especially hypersaline solutions at elevated temperatures.\nDifferent from the presence of only very minor and negligible additional peaks for the\nsamples after exposure in DMF, acetone, and water, the phase structure degraded to\nsome extent in strongly acidic aqueous solution (pH 0.7), which can be reflected by\npeak broadening and new peaks arising. Nevertheless, such chemically harsh\ncondition is far beyond practical application conditions. )\n3. I agree with Reviewer #2 that the phrase “perfect” should be avoided throughout\nthe entire manuscript.\nResponse: Thank you for this valuable suggestion. We agree with your opinion that\nphrase “perfect” should be avoided throughout the entire manuscript. To address your\nconcern about this issue, we have carefully revised the manuscript and SI files by\ndeleting the phrase “perfect” without altering the scientific essence.\n4. Regarding the error bars of and repeatability of the experiments, I suggest the\nauthors performing the reproducibility tests for important experiments. For example,\n4\nexperiments shown in Fig 5a-c. For all experiments performed in this study, the\nnumber of trials should be described.\nResponse: Thank you for this valuable suggestion. We agree with your opinion that\nsome important experiments (e.g., Fig 5a-c) should be performed to check the\nrepeatability and obtain error bars of the results. To address your concern about this\nissue, we have done some repeated experiments to obtain the error bars after\nperforming one-year experiments (see Fig 5a, Fig 5b, Fig 5c, Fig 5f also shown as\nbelow). As the core results figures, their data reliability has been further clarified.We\nalso provided the number of trials for the experiments when necessary, and carefully\nrevised the manuscript and SI files.\nRegarding other figures, the corresponding experiments are qualitative verification\ntests (e.g., method feasibility validation) rather than quantitative statistical\nexperiments. The original experimental design was intended to demonstrate some\ntrends rather than provide quantitative statistical analysis, so error bars would not add\nstatistical significance. Additionally, the results of these other figures are only used to\nassist in explaining the conclusions and are not the key basis for supporting the\nresearch arguments. They do not affect the scientific validity or reliability of the entire\nstudy. Given the above, we respectfully request your understanding for not\nsupplementing error bars for other figures.\nFigure 5. Robust desalination performance and operational stability of MOF-801\nmembranes in harsh environments. (a) Concentration of acidic hypersaline waters (feed: 10 wt.%\noperational stability for the treatment of real industrial acidic saline wastewater (operating\ntemperature: 70℃, see compositions in Table S5). (c) Desalination performance and operation\nstability for the treatment of hypersaline water by using MOF-801 membranes with exposure to\nNaClO solution for 22 d (feed: 10 wt.% NaCl solution, 100 ppm NaClO, operating temperature:\n70℃). (d) XRD patterns, (e) liquid 1H nuclear magnetic resonance (NMR) spectra, (f) ideal gas\nselectivities of H /N (single component gas permeation tests were performed for the membranes\n2 2\n(effective membrane area ~100-200 mm2) in a soap-film flowmeter at room temperature with a\ntrans-membrane pressure of 1 bar), (g) ATR-FTIR spectra, and (h) surface FE-SEM images of\nMOF-801 structures or membranes before and after operation under different conditions (A:\nconcentration of acidic hypersaline water; B: treatment of real industrial acidic saline wastewater\nand C: treatment of hypersaline water by using the membranes after exposure in 100 ppm NaClO\naqueous solution) (The number of trials for the repeated experiments on flux, rejection and ideal\nselectivity is three in Fig 5a, Fig 5b, Fig 5c, and Fig 5f. Error bars represent standard deviation\nfrom three measurements. Data are presented as mean values ± SD in this study).\nThank you to the reviewers for adding the recent review citation summarizing the\nstate of the art in pervaporation desalination and adding Figure S18 showing the\npermeance of their membranes – this figure should be revised and contextualized as\ndescribed below in item #5 and be moved from the SI into the main text.\nThis manuscript is still unacceptable for publication in its current form. I stand by my\ninitial comments (provided 6 months ago) that this paper is best suited for publication\nin a disciplinary specific journal, such as “The Journal of Membrane Science” or\n“Desalination.” However, the editors disagree with my recommendation and continue\nto re-send this manuscript to me for re-review; therefore, ALL of the following\nadditional revisions are necessary prior to possible acceptance and publication of this\nmanuscript. These revisions are required to ensure this manuscript’s scientific\naccuracy, to support the conclusions drawn, and to improve the usefulness for future\nreaders.\nResponse: In the three rounds of review, Reviewer #1, Reviewer #3, Reviewer #4\nand Reviewer #5 have all provided positive and detailed comments on the novelty and\nimpact of our work. Particularly (in the last round of review), Reviewer #5 (as a new\nreviewer) once again recognized our work and revisions with very positive comment\n“the scientific significance of the topic discussed in this work meets the criteria of\nNature Communications”.\nWe believe the novel aspects of our work and the broader implications and\ncontributions, which motivated our decision to submit to Nature Communications.\nThe novel aspects, broader implications and contributions of our work have been\nhighlighted in our responses to the comments in the last round of review.\nSummary of Problems Requiring Correction\n1) This manuscript contains incorrect statements about the transport mechanisms in\npervaporation desalination membranes: pervaporation is NOT a thermally driven\nprocess, selectivity in pervaporation is NOT the result of molecular sieving.\n2) This manuscript is missing basic error bars and error information for the\nexperiments performed. This manuscript does not describe how many times\nexperiments were replicated. This manuscript is also missing statistical analysis to\nprovide a determination if experimental results are statically significant from each\nother or not.\n3) This manuscript is missing significant key information about the experiment testing\nsetups and conditions which is necessary for future readers to reproduce the\nexperiments.\n4) This manuscript makes unsupported conclusions about the stability of the MOF\nmaterials and needs expanded interpretation and discussion of XRD patterns, SEM\nimages, and gas permeance data.\n5) This manuscript does not readily contextualize the performance of the membranes\nwithin the state of the art, within the main body text.\n6) The authors did not revise the manuscript in response to Reviewer 4 comments on\n7) The section “author contributions section” has been removed in revisions #1\n(NCOMMS-24-08272A-Z) and #2 (NCOMMS-24-08272B), while it was present in\nthe original submission (NCOMMS-24-08272-T) – this should be re-added to the\nfinal manuscript.\nResponse: Thank you for providing a list “Summary of Problems Requiring\nCorrection”. We have carefully considered all the comments, rethought and revised\nsome statements, done some repeated experiments to obtain the error bars (e.g., Fig 5a,\nFig 5b, Fig 5c, and Fig 5f) and provided detailed point-to-point responses, which are\nshown in following each term “Details of Problems Requiring Correction and\nSuggested Resolutions”.\nDetails of Problems Requiring Correction and Suggested Resolutions\n1) Incorrect statements about the transport mechanisms in pervaporation desalination\nmembranes: pervaporation is NOT a thermally driven process, selectivity in\npervaporation is NOT the result of molecular sieving\nIn the introduction, Lines 51 – 59 state: “While reverse osmosis (RO) is the current\nparadigm for desalination, conventional RO cannot be used for hypersaline waters\n(salinity > ~10 wt.%) due to the ultrahigh osmotic pressures that must be\novercome.3-6 At these higher salinities, thermally-driven membrane processes have\nan advantage over RO as their operation is less sensitive to salinity.7-9 A promising\nthermally-driven membrane process is pervaporation (PV), where a heated liquid feed\nstream is exposed to one side of the PV membrane and a vacuum is applied to the\nother. Under these conditions, water vaporizes and traverses the PV membrane to be\ncondensed, while dissolved salts are retained.”\nAs written, this paragraph contains fundamentally thermodynamically inaccurate\nstatements about how transport in pervaporation membranes occurs and requires\nrevision. The authors are referred to Chapter VI of Mulder “Basic Principles of\nMembrane\nTechnology” https://link.springer.com/book/10.1007/978-94-009-1766-8. Osmosis is\na pressure-driven process. Membrane distillation is categorized by Mulder as a\nthermally-driven process. However, pervaporation is classified by Mulder as an\nactivity-difference driven process (e.g. a chemical potential difference). Transport\nthrough pervaporation membranes is a result of permeation through and evaporation\nfrom the membrane of the components transported. The main practical mechanism for\ntransport in pervaporation is the vapor pressure difference across the membrane –\nprimarily this is realized by applying a vacuum to the permeate side of the membrane;\nin pervaporation, sometimes the feed is heated to increase this vapor pressure\ndifferential, but this is not always the case (and there are specific applications, in\nalcohol/water pervaporation separations such a continuous removal of\nbiofermentation products from biofermentation processes, where feed temperatures\nmust be kept around room temperature).\nSelectivity in pervaporation is therefore arises by a combination of vapor pressure of\nthe components in the feed, as well as the solubility and diffusivity of the components\nwithin the membrane materials. Salt rejection in pervaporation desalination occurs\nbecause salt has an insignificant vapor pressure at the pervaporation feed and\npermeate collection temperatures and\n8\npressures. https://webbook.nist.gov/cgi/cbook.cgi?ID=C7647145&Mask=4&Type=A\nNTOINE&Plot=on\n*required revisions to Lines 51-59 to correct inaccuracies are below - additions are in\nbold and deletions are indicated with strikethrough text.\n“While reverse osmosis (RO) is the current paradigm for desalination, conventional\nRO cannot be used for hypersaline waters (salinity > ~10 wt.%) due to the ultrahigh\nosmotic pressures that must be overcome, which exceed the maximum applied\nhydraulic pressures that can be applied.3-6 At these higher salinities, thermally-driven\nmembrane processes have an advantage over RO as their operation is less sensitive to\nsalinity.7-9 A promising chemical potential driven membrane process in which the\nchemical potential difference is practically realized by temperature and/or pressure\ndifferences thermally-driven membrane process is pervaporation (PV), where a heated\nliquid feed stream is exposed to one side of the PV membrane and a vacuum is\napplied to the other (in some cases the feed may be heated). Under these conditions,\nwater vaporizes and traverses the PV membrane to be condensed, while dissolved\nsalts are retained, because salts have insignificant vapor pressure at the operational\ntemperatures and pressures of pervaporation.”\nRequired citations to add: NIST webbook vapor pressure of NaCL and Mulder Book\nin this paragraph.\nIncorrect statements about size-exclusion selectivity of salts, that need to be removed\nLines 287 – 289 strikethrough revisions below\n“The pore size of MOF-801-1.43 was determined to be 5.07 Å (Figures 2d, S14b),\nwhich contributes to the near-complete salt rejections via size exclusion of hydrated\nions (d Na+[Cl[·(H2O)nh] ~ 0.716 nm, d-·(H2O)nh] ~ 0.664 nm).”\n*This sentence cites https://pubs.acs.org/doi/pdf/10.1021/j150579a011 - which is OK\nfor the diameter of the hydrated ions\n* The conclusion that the pore size of the MOF “contributes to the near-complete salt\nrejections via size exclusion” is incorrect. The mechanism of salt-rejection is a result\nof the fact that the temperatures are too low and the salt ions have negligible vapor\npressure at the operating conditions, and do not vaporize in the pervaporation process.\nThe discussion in lines 410-413 is inaccurate and needs to be revised – strike\nthrough below (with further edits required per item #5 below)\n“Experimentally, the MOF-801 membranes showed near-complete salt rejection via a\nsize-sieving mechanism, consistently high water flux, and operation stability for the\ntreatment of saline or hypersaline waters via an enhanced adsorption–diffusion\nmechanism.”\nAs discussed above, salt rejection in pervaporation desalination does not occur\nthrough a “size-sieving mechanism.” Transport through pervaporation membranes is a\nresult of permeation and evaporation of the species being transported. Salt rejection in\npervaporation primarily occurs because salt has an insignificant vapor pressure at the\npervaporation feed and permeate collection temperatures and\npressures https://webbook.nist.gov/cgi/cbook.cgi?ID=C7647145&Mask=4&Type=A\nnot the result of molecular sieving. The presence of dissolved salts or other solutes in\nthe desalination feed water has the result of changing the colligative properties of the\nsolution, which effectively lowers the vapor pressure of the solution\n(https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textb\nook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_\nProperties_of_Matter/Solutions_and_Mixtures/Colligative_Properties )\nIt is accurate to say that salt rejection in membrane processes where no phase change\noccurs (e.g., reverse osmosis), may be the result of molecular sieving.\nResponse: Thank you for these detailed comments and suggestions, as well as\nvaluable references. We agree with your opinion that pervaporation should be rightly\ndefined and that some statements (e.g., molecular sieving) should be carefully revised\nin our manuscript.\nTo address your concerns, we have further made revisions by rightly defining\npervaporation and salt rejection mechanism, deleting some terms such as “sieving”\nand citing the references. They key revisions are shown as follows (please see Page 3,\nPage 14, Page 18, Page 20, revised manuscript).\nPage 3, revised manuscript: While reverse osmosis (RO) is the current paradigm for\ndesalination, conventional RO cannot be used for hypersaline waters (salinity > ~10\nwt.%) due to the ultrahigh osmotic pressures that must be overcome, which exceed\nthe maximum hydraulic pressures that can be applied.3-6\nPage 3, revised manuscript: A promising chemical potential driven membrane\nprocess is pervaporation (PV), in which the chemical potential difference is\npractically realized by temperature and/or pressure differences 10. A liquid feed stream\n(heated in some cases) is exposed to one side of the PV membrane and a vacuum is\napplied to the other. Under these conditions, water vaporizes and traverses the PV\nmembrane to be condensed, while dissolved salts are retained, because salts, unlike\nwater, have insignificant vapor pressure at the operational temperatures and pressures\nof pervaporation.9,11, 12.\nPage 3, revised manuscript: In contrast, metal-organic framework (MOF)\nmembranes have well-defined nanochannel structures, abundant affinity sites,\nmodular nature for functionalities, and structural stability, thereby enabling high\nuptake of water and promising separation performance.20-23\nPage 3, revised manuscript: where the pore window size (3.5 Å) ranges between\nwater molecules (2.8 Å) and hydrated sodium ions (~ 7.16 Å). This makes MOF-801\na promising candidate for desalination membranes with precise separation ability,\nwhich has not been experimentally demonstrated until now.\nPage 14, revised manuscript: The pore size of MOF-801-1.43 was determined to be\n5.07 Å (Figures 2d, S14b), which is lower than the size of hydrated ions (d\n[Na+·(H O) ] ~ 0.716 nm, d [Cl-·(H O) ] ~ 0.664 nm).43 The near-complete salt\n2 nh 2 nh\nrejections could be ascribed to the fact that the salt ions have negligible vapor\npressure at the operating conditions, and did not vaporize in the pervaporation\nprocess.\nPage 18, revised manuscript: In addition to having a stable water flux, the\n10\nmembrane shows high rejection of all salt ions, such as Na+, K+, Mg2+, and Ca2+ (all\nabove 99.0%), which can be ascribed to that fact that salt ions have negligible vapor\npressure, and did not vaporize during the pervaporation process.\nPage 20, revised manuscript: Experimentally, the MOF-801 membranes showed\nnear-complete salt rejection, satisfactory water flux, and operation stability for the\ntreatment of saline or hypersaline waters.\nReferences:\n10. Mulder M., Chapter VI, Basic Principles of Membrane Technology, 2nd Edition,\n1996, Kluwer Academic Publishers, Springer Dordrecht.\n12.NIST Office of Data and Informatics. “Sodium Chloride.”. https:\n//webbook.nist.gov/cgi/cbook.cgi?ID=C7647145&Mask=4&Type=ANTOINE&Plot=\non#ANTOINE. (1122).\n2) This manuscript is missing basic error bars and error information for the\nexperiments performed. This manuscript does not describe how many times\nexperiments were replicated. This manuscript is also missing statistical analysis to\nprovide a determination if experimental results are statically significant from each\nother or not.\nThis paper is missing error bars, or statements of error, for almost all figures in the\nmain text body as well as the supplemental information. It does not include\ninformation about how many replicate types of membranes were made, and how\nmany times each replicate was tested – this information needs to be added into the\nmaterials and methods or as appropriate throughout the text.\nStarting in section “Preparation of Crack-free MOF-801 membrane” on line 446 the\ninformation about how many membranes of each recipe were made needs to be stated;\nthis may also be repeated in the main body of the text.\nStarting in section “membrane performance evaluation” on line 460 a statement needs\nto be made about how many replicates of each testing condition was performed for\neach membrane, feed solution, and operating conditions for both gas permeance and\npervaporation experiments reported in the figures and text; this may also be repeated\nin the main body of the text. Typically, most papers in the field of membrane science\nperform triplicate testing of a specific membrane/feed/operating condition setup.\nStarting in in section “Characterization” on line 493, need to describe how many\nreplicate samples were measured in TGA.\nThe methods need a short statement of how error was calculated for the experimental\nresults (e.g., standard deviation of X replicates, standard error of the mean, etc.).\nError bars need to be added to the data points or statements of error need to be made\nfor all of the following figures (along with additional comments to address):\nFigure 1(e), Figure 2(b), Figure 2(e)\nFigure 2(g) – this figure also does not have a label for the rejection data – apparently\nall 15 of the membrane/feed temperature combinations tested had identical rejection\ndata indicated by the red circles? The figure caption does not comment or mention the\nrejection data. It is unknown how many replicated were tested of the 15 combinations\n11\nindicated in the plot.\nFigure 2(h), Figure 3(g) Figure 3(h) Figure 3 (i) Figure 4(a) Figure 4(b) Figure 4(c)\nFigure 4(d) Figure 4(e) Figure 5(a) Figure 5(b) Figure 5(c) Figure 5(f) Figure S8\nFigure S16 Figure S17\nFigure S18 – needs to include information on operating conditions (feed temperature),\nreplicates of membranes tested; move to main text body.\nFigure S19(a) Figure S21 (a) Figure S21 (b) Table S5 (permeate concentration and\nrejection) Figure S22 (a) Figure S22 (b)\nOther Figure Clarifications required:\nFigure S11 – which MOF-801 membrane composition is shown? Crack-free? Cracked?\nMOF-801-1.62, MOF-801-1.43, MOF-801-1.25, MOF801-0.70, MOF-801-0.32?\nOther?\nRequire clarification of which specific membrane composition is being analyzed in\nboth the Main Text Lines 168-171 and S11 Figure caption.\nLine 203 – “ideal plateau of perfect MOF-801” is not described. “perfect” is not a\nterm used in the manuscript elsewhere. Citation\n39 https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/ejic.202200679,\ndoes not use the term “perfect.” I do not think the Y-axes are labelled correctly in\nFigure S13 – the Weight (%ZrO2) shouldn’t be >100%. Does the ideal plateau come\nfrom a simulation of a “perfect crystal”?\nThe paragraph beginning on line 307 needs to be revised.\nAll of the fluxes reported in parentheses should be updated to include error bars and\nthe permeance (with error bars) should also be added into the parenthetical statements.\nThis is because, permeance (not flux) is the preferred way to compare different\nmembrane performances normalized by their different operating conditions.\nResponse: Thank you for these detailed comments and suggestions. We agree with\nyou about the importance of error bars and error information. We think that error bars\nand error information are necessary for some important experiments (as the\nReviewer# 5 suggested). Some important experiments should be performed to check\nthe repeatability and obtain error bars of the results.\nTo address your concern about this issue, we have done some repeated experiments to\nobtain the error bars after performing one-year experiments (see Fig 5a, Fig 5b, Fig 5c,\nFig 5f also shown as below). As the core results figures, their data reliability has been\nfurther clarified. We also provided the number of trials for the experiments when\nnecessary, and carefully revised the manuscript and SI files.\nRegarding other figures, the corresponding experiments are qualitative verification\ntests (e.g., method feasibility validation) rather than quantitative statistical\nexperiments. The original experimental design was intended to demonstrate some\ntrends rather than provide quantitative statistical analysis, so error bars would not add\nstatistical significance. Additionally, the results of these other figures are only used to\nassist in explaining the conclusions and are not the key basis for supporting the\nresearch arguments. They do not affect the scientific validity or reliability of the entire\n12\nstudy. Given the above, we respectfully request your understanding for not\nsupplementing error bars for other figures.\nFigure 5. Robust desalination performance and operational stability of MOF-801\nmembranes in harsh environments. (a) Concentration of acidic hypersaline waters (feed: 10 wt.%\nNaCl solution, pH = 3; operating temperature: 70℃). (b) Desalination performance and\noperational stability for the treatment of real industrial acidic saline wastewater (operating\ntemperature: 70℃, see compositions in Table S5). (c) Desalination performance and operation\nstability for the treatment of hypersaline water by using MOF-801 membranes with exposure to\nNaClO solution for 22 d (feed: 10 wt.% NaCl solution, 100 ppm NaClO, operating temperature:\n70℃). (d) XRD patterns, (e) liquid 1H nuclear magnetic resonance (NMR) spectra, (f) ideal gas\nselectivities of H /N (single component gas permeation tests were performed for the membranes\n2 2\n(effective membrane area ~100-200 mm2) in a soap-film flowmeter at room temperature with a\ntrans-membrane pressure of 1 bar), (g) ATR-FTIR spectra, and (h) surface FE-SEM images of\nMOF-801 structures or membranes before and after operation under different conditions (A:\nconcentration of acidic hypersaline water; B: treatment of real industrial acidic saline wastewater\n13\nand C: treatment of hypersaline water by using the membranes after exposure in 100 ppm NaClO\naqueous solution) (The number of trials for the repeated experiments on flux, rejection and ideal\nselectivity is three in Fig 5a, Fig 5b, Fig 5c, and Fig 5f. Error bars represent standard deviation\nfrom three measurements. Data are presented as mean values ± SD in this study).\nWe also provided the number of membrane pieces in some important experiments.\nTo address your concern, we have also deleted “perfect”.\nRegarding the TG curves of MOF-801, we did not show the calculation procedure\ndetails due to the duplication. You might read the detailed calculation procedures in\nPage S46 in the Supplementary Information file of our former paper (Wang, X.; Lyu,\nQ.; Tong, T.; Sun, K.; Lin, L. C.; Tang, C. Y.; Yang, F.; Guiver, M. D.; Quan, X.;\nDong, Y., Robust ultrathin nanoporous MOF membrane with intra-crystalline defects\nfor fast water transport. Nat. Commun. 2022, 13, (1), 266.), which is also cited as\nReference 21 in main manuscript of the revision.\nRegarding the clarification of membrane composition, we have specified in S11 figure\ncaption and manuscript. Also we have stated in our original submission. “Thus, the\nhigh-quality MOF-801-1.43 membrane was selected for subsequent performance and\nstability evaluation and will be referred to as MOF-801 membrane unless specified\nhereafter”.\nThe key revisions (please see Page 8, Page 9, Page 10, revised manuscript) are shown\nas follows:\nPage 8, revised manuscript: Moreover, even after strong ultrasonication treatment\n(150 W, 20 min) for the accelerated stability test, the MOF-801-1.43 membrane still\nshows integrated surface and cross-sectional structural morphologies, indicating\npromising mechanical stability for practical operation (Figure S11).\nPage 9, revised manuscript: The TGA results indicated that a deficiency was present\nin all the samples due to deviations in mass loss behavior in comparison to the ideal\nplateau of MOF-801 (Figure S13).41\nPage 10, revised manuscript: Furthermore, the water flux of MOF-801 membranes\nlinearly increased with increasing linker deficiency under constant operational\ntemperatures (40-80℃), while salt rejection remains at an almost complete level,\nwhich is close each other in the range of 99.69-99.91% under all operational\ntemperatures (Figure 2g).\nRevised caption of Figure 2g: (salt rejection remains at an almost complete level,\nwhich is close each other in the range of 99.69-99.91% under all operational\ntemperatures).\nRevised caption of Figure 3k: (Error bars represent standard deviation from five\nmeasurements. Data are presented as mean values ± SD in this study).\nFE-SEM images of MOF-801-1.43 membranes (a, c) before and (b, d) after\nmechanical stability tests via ultrasonication treatment (150 W, 20 min) (the inserts\nshow the enlarged SEM image).\n3) Is missing information which enables readers to reproduce the experiments.\nSee items in Point #2 about missing information about number membrane\nreplicates prepared and number of replicate testing that was performed.\nLines 388-391 state “In addition, unlike commercial polytetrafluoroethylene (PTFE)\nmembranes, the MOF-801 membranes show better desalination performance and\noperating stability for treating more challenging hypersaline waters containing low\nsurface tension species, including oil and surfactant (Figure S22)”\n*required revision\n“In addition, unlike commercial polytetrafluoroethylene (PTFE) membrane\ndistillation membranes (NEED TO SUPPLY NAME OF MEMBRANE\nMANUFACTURER AND TYPE OF MEMBRANE USED), the MOF-801\npervaporation membranes show better desalination performance and operating\nstability for treating more challenging hypersaline waters containing low surface\ntension species, including oil and surfactant (Figure S22). Similarly to what was\npreviously reported between commercial PTFE membrane distillation membranes and\npolymeric pervaporation desalination membranes (Molina et al, 2024).” Molina et\nal: https://www.sciencedirect.com/science/article/pii/S277242122400014X?via=ihub\nWhich compares PTFE membrane distillation performance to polymeric\npervaporation desalination membranes with real (not hypersaline) waters.\nRevise caption of Figure S22:\n“Figure S22. Desalination performance and operating stability of MOF-801\nmembrane and commercial polytetrafluoroethylene (PTFE) membrane distillation\ndesalination membrane for treating more challenging hypersaline waters containing\nlow surface tension species including (a) SDS surfactant (feed: 10 wt. % NaCl\naqueous solution, 500 ppm SDS: temperature: 60°C) and (b) oil (feed: 10 wt. % NaCl\naqueous solution, 1000 ppm mineral oil; 450 temperature: 60°C). [ADD VACUUM\nLEVEL OF TESTING TO CAPTION.]”\nThe permeance reported in newly added Figure S18 needs to be improved (include\ninformation on operating conditions (feed temperature), replicates of membranes\ntested) and moved into the main body of the text. Suggested location: Add a figure (h)\nand (i) to Figure 4. It is noted that as it stands, there is not enough information\nprovided in the paper for a reader to calculate the results in Figure S18\nthemselves.\nMany details of the pervaporation experiments performed are missing from the\npaper and the SI and need to be added to enable other investigators the ability to\nreplicate the experiments. These include:\n*the effective area of the membranes tested in the pervaporation and gas permeation\nexperiments\n*the feed water reservoir volume (or the total volume of feed in the recirculating\nsystem), and pervaporation cell feed channel dimensions to calculate the Reynolds\nnumber of the pervaporation cell.\n15\n* Temperature of the cold trap and method by which the cold temperature was created\nto condense the (e.g., LN2, dry ice + solvent, etc.)\n* The length of time for which the pervaporation system was stabilized, and the\nlength of time the permeate was collected.\nThis manuscript is missing nearly all the experimental details of the gas permeation\nexperiments reported in\nFigure 1(e) and Figure 5(f). Neither the main text nor the SI include the any of the\nraw data from the gas permeation experiments.\n*details or a reference to the experimental apparatus used for the gas permeation\nexperiments\n*the temperatures of the feed and permeates in the gas permeation experiments\n(Figure 1(e), Figure 5(f))\n*the equations by which the ideal selectivities were calculated\n*the purity and source of the feed gases used in the gas permeation experiments\n*the pressures of the feed and permeates in the gas permeation experiments\n*how the composition of the gas permeation experiments was quantified\nResponse: Thank you for these detailed comments and suggestions. We agree with\nyou about the importance of providing more information and details that enable\nreaders to reproduce experiments. To address your concern about this issue, we have\nprovided some details for some important experiments as we can and carefully revised\nthe manuscript and SI files.\nThe key revisions are shown as follows:\nPage 19, revised manuscript: In addition, unlike commercial polytetrafluoroethylene\n(PTFE) distillation membranes (Nanjing CAS-Bidun Newmen Technology Co., Ltd.,\nChina), the MOF-801 pervaporation membranes show better desalination\nperformance and operating stability for treating more challenging hypersaline waters\ncontaining low surface tension species, including oil and surfactant (Figure S22). This\nis similar to what was previously reported between commercial PTFE distillation\nmembranes and polymeric pervaporation membranes.59 This resilient desalination\nperformance under various harsh conditions indicates the application potential of the\nrobust MOF-801 membranes in a wide range of industrial applications.\nRevised caption of Figure S22: Desalination performance and operating stability of\nMOF-801 membrane and commercial polytetrafluoroethylene (PTFE) distillation\ndesalination membrane (Nanjing CAS-Bidun Newmen Technology Co., Ltd., China)\nfor treating more challenging hypersaline waters containing low surface tension\nspecies including (a) SDS surfactant (feed: 10 wt. % NaCl aqueous solution, 500 ppm\nSDS: temperature: 60°C, vacuum level of the permeate side ~60 Pa) and (b) oil (feed:\n10 wt. % NaCl aqueous solution, 1000 ppm mineral oil; temperature: 60°C, vacuum\nlevel of the permeate side~60 Pa) .\nTo address your concern, we have also provided the details for gas permeation\nexperiments. The key revisions are shown as follows:\ncracked and crack-free MOF-801 membranes (kinetic diameter: H ~2.9 Å, N ~3.6 Å,\n2 2\nCH ~3.8 Å; the red lines imply Knudsen diffusion selectivity, H /N : 3.7, H /CH :\n4 2 2 2 4\n2.8, N /CH : 1.3) (single component gas permeation tests were performed for the\n2 4\nmembranes (effective membrane area ~100-200 mm2) in a soap-film flowmeter at\nroom temperature with a trans-membrane pressure of 1 bar).\nRevised caption of Figure 5f: (f) ideal gas selectivities of H /N (single component\n2 2\ngas permeation tests were performed for the membranes (effective membrane area\n~100-200 mm2) in a soap-film flowmeter at room temperature with a trans-membrane\npressure of 1 bar)\nRevised SI text: To confirm the structural integrity (i.e., intercrystalline defects) of\nthe MOF-801 membranes, single component gas permeation tests (99.999% H ,\n2\n99.999% N or 99.999% CH , Zhonghao Guangming Chemical Research and Design\n2 4\nInstitute Co., Ltd., China) were carried out to obtain the gas permeance and ideal\nselectivity in a soap-film flowmeter at room temperature (trans-membrane pressure: 1\nbar, effective membrane area ~100-200 mm2).\nTo address your concern, we have cited one reference (Reference 1) in which an\nexperimental apparatus is described for the gas permeation experiments and one\nreference (Reference 2) in which the equation is described for ideal selectivity\ncalculation in the SI file.\nReferences:\n1. Li, H. T.; Fu, M.; Wang, S. Q.; Zheng, X. Y.; Zhao, M.; Yang, F. L.; Tang, C. Y.;\nDong, Y. C., Stable Zr-Based Metal-Organic Framework Nanoporous Membrane for\nEfficient Desalination of Hypersaline Water. Environ. Sci. Technol. 2021, 55, (21),\n14917-14927.\n2. Chen, S.X.; Wahiduzzaman, M.; Ji, T.T.; Liu, Y.; Li, Y.; Wang, C.; Sun, Y.W.; He,\nG.H.; Maurin, G.; Wang, S.J.; Liu, Y., Angew. Chem. Int. Ed. , 2024, e202413701.\n4) This manuscript makes unsupported conclusions about the stability of the MOF\nmaterials and needs expanded interpretation and discussion of XRD patterns, SEM\nimages, and gas permeance data.\nPreviously, Reviewer #4 requested this: “2. The PXRD patterns need further\ninvestigation - in Figure 1g the reference MOF-801 pattern was presented. Is this\npattern from any literature or cif file? This should be clearly presented. In addition,\nafter the membrane pervaporation test (figure 4g), there are some peak shift,\nindicating the change of MOF structure. Any discussion on these should be\nwelcomed.” In this 3rd revision the authors have indicated that the reference XRD\npattern was from a simulation, however they did not expand the discussion of the\nXRD patterns. Additional information and comments for revisions are below.\nThe XRD pattern in Figure 4(f) shows peak-width broadening after exposure to\ndifferent environments, the associated SEM image in Figure 4(g) also shows\n17\nmorphological changes in the grain structure of the material. Figure 4(f) also cuts off\nall data above a 2-Theta of 15-degrees – from S5 we see that significant changes may\nhappen in the MOF structure at 2-Theta of 30degrees in acidic conditions, therefore\nthe data from 2-Theta 15 -50 degrees need to be shown (especially for the pH 3\ncondition) to confirm the structural changes are not happening…... Figure 5(d) also\nshows similar peak width broadening after exposure to acidic environments, Figure\n5(f) shows a reduction in ideal selectivity after membranes were exposed to acidic\nenvironments, and the SEM images in Figure 5(h) show changes in the morphology\nand grain structure of the membrane surfaces after exposure to acidic environments.\nThe associated discussions of these figures in Lines 332 – 334, Lines 337- 342, Lines\n379 – 385 do not reflect a discussion of the implication of these changes and just\nmake broad unsupported claims of “excellent stability” and “unchanged XRD.”\nPlease see attached PDF for annotated figures.\nIt is well established that in X-Ray diffraction that peak-width broadening is reflective\nof fundamental changes in the lattice structure of materials – specifically that crystal\nlattice grain sizes may be decreasing with broader peaks or more lattice defects are\nintroduced.\nThe authors are referred to such papers as:\nhttps://www.sciencedirect.com/science/article/pii/S1359646204002738#:~:text=X%2\nDray diffraction peaks broaden,the quality of lattice imperfectness.\nOr textbooks on XRD such as Doi: 10.1201/9780429351662 “Fundamentals of\nCrystallography, Powder X-ray Diffraction, and Transmission Electron Microscopy\nfor Materials Scientists” By Dong Zhi Li\nCorrections required to analysis and discussion for publication:\n4.0) add data from 2-Theta from 15-50 degrees into Figures 4(f) and 5(d)\n4.1) The changes seen in the full width at half maximum (FWHM) of the peaks in\nFigure 4(f) should be calculated and discussed in the context of the differences in the\nSEM images in Figure 4(g) and the various solutions the membranes were exposed to.\n4.2) Figure 5(f) shows a decreasing trend in membrane selectivity after exposure to\nthe model and real hypersaline and acidic waters. An appropriate ANOVA test should\nbe performed on this data to indicate if these results are statistically significant from\neach – if they are not statistically significant from each other, then that supports the\nconclusion of “stability”, however if they are statistically significant from each other\nthat does not support a conclusion of “stability” of the membranes.\n4.3) The discussion on lines 332 – 334 which should be revised (see bold and\nstrikethrough) “Under XRD, the MOF-801 membranes exhibited two characteristic\nreflections of MOF-801 phase between 7 and 11° before and after operation,\nindicating some stability in their phase crystalline structure (Figure 4f). However,\nsome peak width broadening was found [QUANTIFY IT] which reflected in the ….\nand in some cases peaks were… ”\n4.4) Lines 123-124 need to be revised. Figure S5 does not indicate “excellent stability\ntoward various solvents, especially hypersaline solutions at elevated temperatures\n(Figure S5)”, as stated on lines 123-124. Upon close inspection of Figure S5(a), there\n18\nis clear peak broadening of the peak at 7 degrees in the conditions of pH 0.7 (where\nthere is also peak splitting and new peaks arising), the core peak around 30 degrees\nhas aldo disappeared into possible 3 smaller peaks around 30 in this solution.\nAdditionally, the patterns of DMF, acetone, and water show new peaks arising in\nbetween 7-10 degrees. More context and analysis of any peak broadening and new\npeaks arising should be included in the main body text as well as the S5 caption.\nFigure S5(b) does support the conclusion that hot salt solutions have more minimal\neffect on the XRD patterns than the solvents in Figure S5(a). Figure S5 also\ngenerically state\n4.5) Figure S21 is missing error bars, so it is impossible to draw any conclusions as to\nif these order of magnitude permeance difference are insignificant or significant.\nResponse: Thank you for these detailed comments and suggestions. We agree with\nyou about the necessity of revising some statements about the stability of the MOF\nmaterials, and expanding the discussions and interpretation of the data (XRD, SEM\nand gas permeance). The revisions are summarized as follows:\nTo address your concern, we have revised some words such as “excellent stability”\nand “unchanged XRD”.\nTo address your concern, we have also read carefully the references (one paper and\ntextbook) provided by you. We have calculated the full width at half maximum\n(FWHM) of the peaks in Figure 4(f) and provided more discussion on XRD patterns\nand SEM images for the samples after the solution exposure. The key revisions are\nshown as follows (please also see Page 16, revised manuscript):\nPage 16, revised manuscript: MOF-801 membranes demonstrate stable operational\nperformance (in both flux and rejection) and acceptable structural integrity (in both\nMOF-801 crystalline phase and membrane morphology) for the treatment of 7 wt.%,\nheated, hypersaline water, at 70°C for 120 h (Figures 4d, 4f, 4 g).54 Under XRD, the\nMOF-801 membranes exhibited two characteristic reflections of MOF-801 phase\nbetween 7 and 11° before and after operation, indicating some stability in their phase\ncrystalline structure (Figure 4f). However, some peak width broadening was found\nfrom 0.24 to 0.37 especially after 108 h exposure at pH 3, which reflected the change\nin the lattice structure to some extent (i.e., crystal lattice grain sizes might decrease\nslightly), while the peaks keep nearly unchanged in the case of hypersaline water\nexposure.\nReferences:\n1. Ungár T., Microstructural parameters from X-ray diffraction peak broadening, Scripta\nmaterialia, 51 (08) (2004) 777-781.\n2. Li D.Z., Fundamentals of Crystallography, Powder X-ray Diffraction, and Transmission\nElectron Microscopy for Materials Scientists, 1st Edition, 2022, CPC Press (Boca Raton).\nTo address your concern, we have done appropriate ANOVA test for the experiments\n(see revised Fig. 5f).\nTo address your concern, we have revised the statements based on your suggestions\nand corrections, which are shown as follow\nperformance (in both flux and rejection) and acceptable structural integrity (in both\nMOF-801 crystalline phase and membrane morphology) for the treatment of 7 wt.%,\nheated, hypersaline water, at 70°C for 120 h (Figures 4d, 4f, 4 g).54 Under XRD, the\nMOF-801 membranes exhibited two characteristic reflections of MOF-801 phase\nbetween 7 and 11° before and after operation, indicating some stability in their phase\ncrystalline structure (Figure 4f). However, some peak width broadening was found\nfrom 0.24 to 0.37 especially after 108 h exposure at pH 3, which reflected the change\nin the lattice structure to some extent (i.e., crystal lattice grain sizes might decrease\nslightly), while the peaks keep nearly unchanged in the case of hypersaline water\nexposure.\nTo address your concern, we have revised the statements in main text as well as the\nS5 caption based on your suggestions and corrections, which are also shown as\nfollow.\nPage 5, revised manuscript: MOF-801 was selected to be fabricated into a\nseparation membrane because of its stability toward some solvents, especially\nhypersaline solutions at elevated temperatures (Figure S5). Different from the\npresence of only very minor and negligible additional peaks for the samples after\nexposure in DMF, acetone, and water, the phase structure degraded to some extent in\nstrongly acidic aqueous solution (pH 0.7), which can be reflected by peak broadening\nand new peaks arising (Figure S5). Nevertheless, such chemically harsh condition is\nfar beyond practical application conditions.\nS5 caption: Figure S5. (a) XRD patterns of MOF-801 after accelerated stability tests\nin various solvents or harsh (acidic or alkaline) solutions. (b) XRD patterns of\nMOF-801 after 7-day long-term exposure accelerated tests in hot salt solutions\n(~65℃) with different NaCl concentrations. (MOF-801 shows the stability toward\nsome solvents, especially hypersaline solutions at elevated temperatures. Different\nfrom the presence of only very minor and negligible additional peaks for the samples\nafter exposure in DMF, acetone, and water, the phase structure degraded to some\nextent in strongly acidic aqueous solution (pH 0.7), which can be reflected by peak\nbroadening and new peaks arising. Nevertheless, such chemically harsh condition is\nfar beyond practical application conditions. )\nWe appreciate that you took time to provide detailed comments and careful inspection\non our results. There are the two strongest XRD peaks at a 2-theta range from 5 to 15\ndegrees as shown in Figures 4(f) and 5(d). These two strongest XRD peaks are\nsufficient to clearly give us some information about the structure change at different\nconditions. Other very weak peaks outside the range can only give minor information.\nThat is why we shown them at a 2-theta range from 5 to 15 degrees. We hope that you\ncan kindly understand our key motivation. Nevertheless. We have provided the\nupdated revisions on the XRD patterns. The key revisions are shown as follows:\nPage 16, revised manuscript: MOF-801 membranes demonstrate stable operational\nperformance (in both flux and rejection) and acceptable structural integrity (in both\nMOF-801 crystalline phase and membrane morphology) for the treatment of 7 wt.%,\nheated, hypersaline water, at 70°C for 120 h (Figures 4d, 4f, 4 g).54 Under XRD, the\nMOF-801 membranes exhibited two characteristic reflections of MOF-801 phase\nbetween 7 and 11° before and after operation, indicating some stability in their phase\ncrystalline structure (Figure 4f). However, some peak width broadening was found\n20\nfrom 0.24 to 0.37 especially after 108 h exposure at pH 3, which reflected the change\nin the lattice structure to some extent (i.e., crystal lattice grain sizes might decrease\nslightly), while the peaks keep nearly unchanged in the case of hypersaline water\nexposure.\nPage 5, revised manuscript: MOF-801 was selected to be fabricated into a\nseparation membrane because of its stability toward some solvents, especially\nhypersaline solutions at elevated temperatures (Figure S5). Different from the\npresence of only very minor and negligible additional peaks for the samples after\nexposure in DMF, acetone, and water, the phase structure degraded to some extent in\nstrongly acidic aqueous solution (pH 0.7), which can be reflected by peak broadening\nand new peaks arising (Figure S5). Nevertheless, such chemically harsh condition is\nfar beyond practical application conditions.\nS5 caption: Figure S5. (a) XRD patterns of MOF-801 after accelerated stability tests\nin various solvents or harsh (acidic or alkaline) solutions. (b) XRD patterns of\nMOF-801 after 7-day long-term exposure accelerated tests in hot salt solutions\n(~65℃) with different NaCl concentrations. (MOF-801 shows the stability toward\nsome solvents, especially hypersaline solutions at elevated temperatures. Different\nfrom the presence of only very minor and negligible additional peaks for the samples\nafter exposure in DMF, acetone, and water, the phase structure degraded to some\nextent in strongly acidic aqueous solution (pH 0.7), which can be reflected by peak\nbroadening and new peaks arising. Nevertheless, such chemically harsh condition is\nfar beyond practical application conditions. )\n5) This manuscript does not readily contextualize the performance of the membranes\nreported in the paper within the state of the art, within the main body text.\n*“consistently high water flux” (line 411) is not a suitable conclusion. As discussed\npreviously flux is dependent on operating conditions, and is not useful to compare\nmembranes across various types and variable operating conditions. The performance\nshould be summarized in normalized quantitative terms (e.g., permeance) and placed\nin context of the state of the art pervaporation desalination membranes (fine for\nauthors to exclude polymer membranes if they still feel strongly about this). The\nrevision of this section of text should, at a minimum, include the average permeance\nof these membranes (with error bars) and a comparison to the permeance of at least\none other inorganic/MOF/ZIF/zeolite pervaporation membrane (many of which are\nreported in Table summarized in Table S6 and S7); perhaps the “best” and the “worst”\nfrom these tables.\nTables S6 and S7 need to be revised to include an additional column with the\npermeance of all of the reported membranes. To do a rough evaluation of permeances,\nthe mole fraction can be taken as 1 directly, since 10wt% and 3.5wt% NaCl solution\nboth have the mole fractions close to 1 (0.967 and 0.989, respectively). Since the\nauthors have not done this, we have taken the liberty of performing the calculation for\nthem – see attached PDF for details on how to perform the calculations and a\nsummary of the calculation results.\ncalculation details on the permeance. We agree with you about the importance of the\npermenace data of the membranes. To address your concern about this issue, we have\nrevised Tables S6 and S7 with providing an additional column with the permeance of\nall of the reported membranes (see revised Tables S6 and S7, see below the\nscreenshots, as well as Figure S18). Based on your comments, we have also revised\n“ consistently high water flux” into “satisfactory water flux”\n(b) Water permeance of the MOF-801-1.43 membrane for treatment of saline feeds with different\nsalt concentration (feed temperature:70 ℃).\n6) The authors did not revise the manuscript in response to Reviewer 4 comments on\nRevision 2 about the inaccurate “crack-free” terminology.\nFrom Reviewer 4 “1. The authors refer to the membranes as \"crack-free\" and\n\"defect-free\". However, these terms are not accurate because there is no such thing as\na \"defect-free\" material, especially considering the multiple missing linkers within the\nmembrane.”\nline 392 remove the word “tremendous”\nline 124 remove the word “excellent”\nResponse: Thank you for these comments and suggestions. To address your concern\nabout this issue, we have removed the words such as “excellent” and “tremendous”.\nWe think that we have rightly addressed the concerns raised by the Reviewer 4#.\nThis conclusion can be supported by the new comments of the Reviewer 4#, “After\nreading the comments from the reviewers and the response from the authors, I found\nthe authors have addressed these comments, including the rather critical ones. The\npaper contains some interesting and novel results ......”.\n23"}]

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