Graphene-inspired porous polymer network for ethane/ethylene separation and methane purification

Domain: biology
Published: 2026-03-27
Editorial outcome: minor_revision

Abstract
C H and CH are essential for industrial applications. However, contamination with other natural gases is a
2 4 4
challenge to their utilization. Although several sorbents have been investigated, their performance remains limited.
This study introduces graphene-inspired, PPN-20, a porous polymer network (PPN) capable of separating
C H /C H and purifying CH from a C H /C H /CH mixture in a single step. The ultra-microporosity of PPN-20
2 6 2 4 4 3 8 2 6 4
enables preferential C-H···π interactions with C H and C H . As a result, PPN-20 exhibits a C H and C H uptake
2 6 3 8 2 6 3 8
of 3.93 mmol/g and 5.98 mmol/g, respectively, at 298 K and 1 bar, representing the highest reported for any PPN.
It achieves ideal adsorption solution theory (IAST) selectivities of 2.2 for C H /C H ,368.2 for C H /CH ,40.14 for
2 6 2 4 2 6 4
C H /C H , and 294,336 for C H /CH . This selectivity, to the best of our knowledge, is the highest reported for any
3 8 2 6 3 8 4
PPN in the case of C H /C H separation and for any sorbent in the cases of C H /CH , C H /C H , and C H /CH
2 6 2 4 2 6 4 3 8 2 6 3 8 4
separation. Robustness tests, including breakthrough experiments, IAST calculations, etc., demonstrate the
reliability of PPN-20. Its exceptional performance is attributed to precisely engineered pore sizes that enhance the
trapping of guest molecules. These results will pave the way for the design of PPNs for short-chain hydrocarbon
purification.

Introduction
The demand to curb the rising effects of greenhouse gas emissions has led to a very aggressive pursuit recently
from government agencies and industries in response to global warming.1-3 Methane, the second most abundant
after carbon dioxide (CO ) and a more potent greenhouse gas, has a global warming potential that is 21 times that
2
of CO , but can also be used as a source of energy, making its capture and storage a dual-purpose achievement
2
by mitigating global warming while providing an alternative energy source.4 Ethylene, on the other hand, is a vital
feedstock for the production of polymer-based end products or materials used across household items,
automobiles, and aviation facilities.5-7 Industrially, many downstream product development processes are energy-
intensive, motivating the search for more efficient alternatives. Purifying ethylene and methane from other analog
gases is essential, as ethylene is widely used in polymer manufacturing, while methane serves as an essential
energy resource to drive industrialization and curb global warming.8-10 Currently, ethylene and methane purification
are predominantly achieved through cryogenic distillation processes that are energy-intensive, highlighting the need
for an alternative route.11-14 Rising energy prices render this strategy unfeasible for long-term commercial
application in industry, thereby driving the exploration of different kinds of sorbent materials for ethylene and
methane purification.

Furthermore, the quest for alternative energy sources and solutions to global warming has made methane crucial.
However, the primary challenge in utilizing methane lies in its harvesting, capture, and purification. Natural gases
contain varying percentages of hydrocarbons, which limits direct utilization and hence the need for further
purification steps.15 Ethane and propane are among the major contaminants in natural gas and must be effectively
removed to boost the purity of methane, since it cannot be used without their removal, because they lead to
explosion risk due to reduced ignition delay.

Ethane/ethylene separation through cryogenic distillation remains critical in meeting the industrial demand for
ethylene in the production of several high-end polymer-based materials. This process amounts to the consumption
of about 800 PJ annually, which corresponds to about 0.3% of global energy utilization.13,16 Ethylene, a major
industrial feedstock, is notoriously produced through the energy-intensive thermal cracking of hydrocarbons.17,18 To
reduce energy footprint, the development of sorbents for the purification of ethylene from ethane has drawn the
attention of researchers. However, one of the major drawbacks in this direction is achieving the selective capture
of ethane over ethylene, which will enable a single-step purification.19,20 Several adsorbents have been reported in
this regard, but many suffer from weak selectivity for ethane/ethylene9,21,22 or poor ethane uptake capability23,24 that
limits their commercialization and industrial application. The rational design of sorbents for this application requires
the consideration of the quadrupole moment of ethylene (1.50 ×10−26 esu cm2) relative to ethane (0.65 × 10−26 esu
cm2), polarizability difference (ethylene: 42.52 × 10−25 cm3; ethane: 44.7 ×10−25 cm3), and the presence of π
electrons.25 The design of an ethane-selective adsorbent requires the pores to be nonpolar to boost the trapping of
ethane guests in the pores.

Sorbents such as Metal-Organic Frameworks (MOFs),19,26 Hydrogen Organic Framework (HOF),27 and Porous
Organic Cage (POC)28 have been explored in the process to seek a solution to this problem. However, PPNs remain
relatively underexplored. PPNs are a group of sorbent materials that have shown significant application in the
capture and separation of gas molecules.29-32 PPNs have undergone several modifications to achieve target goals
such as carbon capture33 and heavy metal recovery34 but their applications in methane purification from alkanes,
and ethane/ethylene separation have not been explored as extensively as MOFs35,36. Fundamentally, PPNs are a
class of porous materials that are made from the polymerization of organic monomers, resulting in voids suitable
for the capture of gaseous molecules. The tunability, stability, and robustness of these pores to fit the kinetic
diameters of target gases and their re-engineering through post-synthetic modification make PPNs very
exceptional. MOFs differ from PPNs as a type of sorbent material made from metal nodes and organic linkers to
grow porous crystalline moieties, whose downsides are the high cost of starting materials, high reaction
temperature, and low chemical and thermal stability, which makes PPNs stand out.37 Additionally, MOFs and COFs
differ from PPNs because they are crystalline materials formed due to the reversibility of their bonds, while PPNs
possess irreversible bonds and are therefore amorphous.

Herein, we design a robust PPN, PPN-20, featuring a graphene-inspired structure with an effective pore size
distribution, excellent thermal and chemical stability, and facile reaction conditions requirements for C H /C H
2 6 2 4
separation and CH purification from a mixture of C H /C H /CH . This is the first time, to the best of our knowledge,
4 3 8 2 6 4
that PPN has been developed for this kind of ultra-sensitive two-fold application. PPN-20 exhibits the highest
performance among the PPNs reported for these applications. As a result, it will increase the availability of ethylene
and methane as key industrial feedstocks and significantly reduce the energy footprint of industries. Importantly,
this study will open the door for research into PPNs for efficient natural gas separation.

Results
Pore Structure and Morphology of PPN-20
To understand the morphology of the pores, present in PPN-20 (Fig 1a), small-angle X-ray scattering (SAXS)
analysis was conducted. Based on single-component gas adsorption, the pores of this sorbent are ultra-
microporous and microporous and, consequently, aid in the high gas uptake and selectivity capability of PPN-20.
This is corroborated by the radius of gyration (R ) value (14 Å = 1.4 nm) derived from the Guinier approximation of
g
the SAXS result (Fig. 1b), which closely matches the pore size distribution derived from the gas uptake
measurement.

Interestingly, the Porod approximation with a power law exponent of 2.13 indicates that the pores are not smooth
but have fractal surfaces, possibly caused by the irregularity of the pore pattern encountered during the
polymerization process (Fig. 1c). This conclusion is supported by the power law coefficient being below 4 in the
high Q region because of the amorphous nature of the PPN-20, and the inherent interpenetration that makes it
difficult to know the exact shape of the pores.

Framework Structure and Characterization
PPN-20 has porosity that is periodically surrounded by the six-membered benzene rings and derived from the triple
condensation reaction of the acetyl groups of 1,3,5-triacetyl benzene (Supplementary Fig. 1-2). After the reaction,
the resulting material adopts a graphene-inspired hypercross-linked structure, which has quasi-periodic pores that
facilitate gas adsorption. The van der Waals density functional (vdW-DF) level theoretical simulation results show
a pore of 3.782 Å (0.3782 nm) (which is ~5.7 Å (0.57 nm) without the hydrogen atoms, as shown in Fig. 1a) and a
C–C bond length of 1.509 Å in a completely formed aromatic benzene ring and 1.409 Å in an open ring (Fig. 2a).
The calculated C–H bond length is 1.08 Å (Fig. 2a). Additionally, the side view indicates that the hydrogen atoms
are pointing 0.8 Å away from the framework—so, the sheet has a tendency to buckle (Fig. 2b). Specifically, the
monomer was polymerized into a hyper-crosslinked PPN made up mainly of carbon and hydrogen as confirmed by
Fourier Transform Infrared Spectroscopy (FTEIR) and Solid-state Nuclear Magnetic Resonance (ss-NMR)
(Supplementary Fig. 3a-4b).

PPN-20 demonstrated high chemical stability when exposed to water, acid, base, and various organic solvents for
24 hours, which highlights its robustness for gas separation applications even in a harsh chemical environment
(Supplementary Figs. 3b-3c). The CT-H and O-H vibrational stretching, which appeared centered at 2981 cm-1 and
3391 cm-1, respectively, are from the ethanol used to wash the sample. The comparison of the 13C {1H} CP MAS
NMR spectra of 1,3,5-triacetylbenzene (top) and PPN-20 (bottom) recorded at a spinning rate of 12 kHz was
analyzed (Supplementary Figure 4b). As seen, 1,3,5-triacetylbenzene shows the sharp resonances with (iso) of
200.0 and 197.5 ppm (C=O), 148.7, 134.7, 133.1, and 130.6 ppm (aromatic carbons) and 29.2 and 27.9 ppm (CH ).
3
Furthermore, for PPN-20, which has a polymer nature, all the resonances are reasonably broadened, experiencing
slight displacements: (iso) of 200.6 ppm (C=O), 142.5, 139.5, 131.4, and 126.4 ppm (aromatic carbons) and 26.7
ppm (CH ).
3
Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) reveal both the hypercross-
linked morphology of PPN-20 and the stacking of the various layers, which obscure the direct visualization of the
individual pores present in the framework (Supplementary Fig. 5-6). The hypercross-linking substantially enhances
the thermal and chemical stability of the framework compared to the starting monomer, ensuring that it can
withstand both harsh thermal and chemical conditions. To elucidate the chemical stability of PPN-20 for potential
industrial application, it was soaked in acid, base water, and organic solvents, but showed no sign of solubility as
aforementioned. The thermal stability of PPN-20 is up to 360°C, as seen from thermogravimetric analysis (TGA) in
Supplementary Fig. 7. Due to the stacking and interpenetration of several layers of the framework, the Powder X-
ray Diffraction (PXRD) pattern shows no diffraction peaks, confirming that PPN-20 is an amorphous solid
(Supplementary Fig. 8).

Gas Adsorption, Selectivity, Separation, and Enthalpy of Adsorption
The pore-based properties of PPN-20 were studied extensively through a single-component gas uptake
measurement. The nitrogen (N ) uptake and pore distribution measurement were conducted at 77 K and 1 bar to
2
determine the surface area and pore-size distribution (Fig. 3a). It was observed to have a permanent porosity with
a pore volume of 0.94 cm3/g, and a surface area of 1679 m2/g (Supplementary Table 1). The N Isotherm of PPN-
2
20 has a type I adsorption isotherm due to the presence of predominantly ultra-small pores. The pore size
distribution shows a sharp peak at 0.5 nm and other pores between 0.6 nm to 0.9 nm (Fig. 3b). The sharp peak at
0.5 nm indicates that PPN-20 is not only microporous but also exhibits ultra-microporosity. The sizes of these pores
contributed immensely to the enhanced gas uptake, selectivity, and the observed isosteric heat of adsorption (Q )
st
(Fig. 3c and 3d).

Due to the absence of unsaturated bonds in C H , it is more polarizableand has a larger kinetic diameter than
2 6
C H , which gives it a preference for specific pores and inherently increases its selectivity in PPN-20. PPN-20, to
2 4
the best of our knowledge, has the highest selectivity of C H /C H ever reported for any PPN to date due to the
2 6 2 4
presence of ultra-micropores. This factor also contributed to the higher surface area that it has, even higher than
any PPN made using the facile aldol triple condensation (ATC) reaction route reported by Fang et al.38 The presence
of both ultra-microporous and microporous pores in PPN-20 motivated the further investigation of its ability to
adsorb other gases such as methane, propane, ethane, and ethylene. To this effect, the uptake of these gases was
studied at 273 K and 298 K at 1 bar. Impressively, PPN-20 showed 3.93 mmol/g, 3.56 mmol/g, 5.98 mmol/g, and
0.80 mmol/g uptake for C H , C H , C H , and CH , respectively, at 298 K and 1 bar (Supplementary Figs. 9, 10,
2 6 2 4 3 8 4
14, 18, 22).

The IAST selectivity calculation was performed for various mixtures of gases. The selectivity of C H /CH ,
3 8 4
C H /CH , C H /C H , and C H /C H in a 50:50 (1:1) v/v mixture is 294,336.12, 368.16, 40.14, and 2.2, while the
2 6 4 3 8 2 6 2 6 2 4
separation potential from the experimental single-component gas adsorption is 5.18, 3.13, 2.05, and 0.37,
respectively, at 298 K and 1 bar (Supplementary Fig. 10-25 and Supplementary Table 2). The C H /C H IAST
2 6 2 4
selectivity of PPN-20 is significantly higher than the state-of-the-art PAN-AN39 and surpasses all previously reported
sorbents for C H /CH , C H /CH , and C H /C H (Supplementary Table 3-6). Comparison of these performances
3 8 4 2 6 4 3 8 2 6
with other sorbents indicates that PPN-20 is superior in performance and is a good candidate for industrial
application or commercialization (Supplementary Figs. 13, 17, 21, and 25). The Q was also computed to validate
st
the selectivity. At zero coverage, C H , C H , C H , and CH had a Q of 81.7 kJ/mol, 43.04 kJ/mol, 35.9 kJ/mol,
3 8 2 6 2 4 4 st
and 16.25 kJ/mol respectively, which decreased to 27.9 kJ/mol, 22.6 kJ/mol, 17.3 kJ/mol, and 13.3 kJ/mol at 1 bar
(Supplementary Figs. 26-30).

To validate the practical application of the IAST selectivity result of PPN-20, breakthrough measurements were
conducted at 298 K and 1 bar for C H /C H and C H /C H /CH mixtures since these conditions replicate the
2 6 2 4 3 8 2 6 4
industrial scenario. This experiment was conducted for C H /C H and C H /C H /CH in a mixture ratio of 50:50
2 6 2 4 3 8 2 6 4
(v/v) and 30:30:40 (v/v/v), respectively (Fig. 4a and 4b). PPN-20 was packed in a column, and as observed from
the breakthrough curve, the C H breaks before C H after a significant time-lapse(Fig. 4a), which shows that PPN-
2 4 2 6
20 can purify a gas mixture of C H /C H and produce a pure outflow of C H due to the molecular sieving effect of
2 6 2 4 2 4
the sorbent. The mass spectrometer connected to the breakthrough instrument showed that C H has more than
2 4
99% purity. It also demonstrated efficiency in the separation of a ternary mixture of C H /C H /CH , wherethe
3 8 2 6 4
methane gas breaks first, followed sequentially by C H and C H attesting to the molecular sieving effect driving
2 6 3 8,
the performance. The breakthrough pattern observed in the C H /C H /CH mixture is consistent with the kinetic
3 8 2 6 4
diameter of each of the gases, which enabled the molecule with the smallest size to break first before the others.
In the breakthrough experiment of C H /C H /CH (30/30/40, v/v/v), the productivity for CH (purity > 99.5%) is 17.6
3 8 2 6 4 4
L kg-1, and the dynamic adsorption capacities for C H and C H are 5.4 and 50.2 L kg-1, respectively while in the
2 6 3 8
breakthrough experiment of C H /C H , (50:50, v/v) the productivity for C H (99.5%) is 0.63 L kg-1, and the dynamic
2 4 2 6 2 4
adsorption capacity for C H is 21.4 L kg-1. The robustness of PPN-20 was further investigated to ascertain its
2 6
capacity through five (5) breakthrough cycles of the binary (C H /C H ) and ternary (C H /C H /CH ) gas mixtures.
2 6 2 4 3 8 2 6 4
The breakthrough curve after five (5) cycles stayed consistent without any noticeable reduction or depreciation in
the efficiency of PPN-20 in both C H /C H and C H /C H /CH . This observation elucidates the robustness of PPN-
2 6 2 4 3 8 2 6 4
20 and its potential for industrial application (Fig. 4c and 4d).

Binding Mechanism, Gas Separation, and Molecular Sieving Effect
The binding mechanism was investigated using the help of the electron localization function (ELF), which reveals
a strong covalent C–C bond within the framework (Supplementary Fig. 31). To ascertain this, various theoretical
bilayer stacking configurations were investigated to elucidate how the pores are influenced by them (Supplementary
Figs. 32-34). As mentioned above, the pores in the framework facilitate the adsorption of small guest molecules.
Since the exact structure is not known, it was studied by exposing a simplified model, i.e., a local geometry of a
single sheet of the framework, to the C1–C3 hydrocarbons CH , C H , C H , and C H and calculating their binding
4 2 4 2 6 3 8
energy. Two distinct binding sites were found for the guest molecules: one is on top of the pore region and the other
at framework atoms (see Supplementary Figs. 33 and 34). Our calculations suggest that the pore sites are more
favorable, and we refer to them as the primary binding sites. The binding energies at this location at full loading are
0.382 eV, 0.336 eV, 0.290 eV, and 0.183 eV for C H , C H , C H , and CH (Supplementary Table 7). The interaction
3 8 2 6 2 4 4
with guest molecules is energetically still preferable at the secondary binding site on top of framework atoms
(Supplementary Fig. 34); at that location, the binding energies were found to be 0.289 eV, 0.221 eV, 0.177 eV, and
0.131 eV (Supplementary Table 7). The reduction in binding energy at the secondary binding site is consistent with
the increased separation of the guest molecules from the framework (Supplementary Fig. 12, 16, 20, and 24).
Consistently, these calculations successfully reproduced the binding trend observed in the experimental isotherm
measurements.

The binding mechanism was further analyzed for the various gas molecules through induced charge densities, i.e.,
the charge rearrangement upon interaction with the framework, shown in Supplementary Figs. 35-36. These
induced charge densities show a stronger interaction with the guest molecules at the primary sites compared to
secondary sites and follow the exact trend in binding strength. For completeness and accuracy, the intercalation
behavior of the largest guest molecule studied—propane—within the graphene-inspired PPN-20 was also
analyzed. Both the primary and secondary adsorption sites exhibit favorable binding energies for propane. Notably,
the results obtained are consistent not only qualitatively but also quantitatively, with bulk binding energies only
~10% lower than those of the monolayer. Propane adsorption induces a pronounced expansion of the interlayer
spacing relative to the original interlayer distance of 3.752 Å. This is because occupation of the primary binding site
increases the separation to 6.471 Å, reflecting a substantial structural response to the inclusion of the guest
molecule. An even greater expansion is observed when propane resides at the secondary binding site, where the
interlayer spacing reaches 7.115 Å. This larger displacement suggests that the secondary site exerts a stronger
perturbation on the host framework, likely arising from distinct steric constraints and adsorption geometries.
Collectively, these findings demonstrate the high sensitivity of the layered structure to molecular intercalation and
highlight the structural flexibility of PPN-20 that makes it suitable for the adsorption and separation of these gases
whose kinetic diameters are within a close range (Supplementary Table 8).

Methods
Synthesis of PPN-20: Methane sulfonic acid was supplied by ThermoFisher Scientific, while 1,3,5-
triacetylbenzene was purchased from TCI. All reagents were analytical grade and used without further purification.
1,3,5-triacetylbenzene (2.0 g, 0.979 mmol) and methane sulfonic acid (13 ml, 200.3 mmol) were added to a 50 ml
hydrothermal autoclave. Without preheating to homogenize the mixture, as reported by Fang et al38, the vial was
then transferred to an oven and heated at 120°C for 24 hours. After cooling to room temperature, water was added
to quench the reaction. The monolith was thoroughly washed with water and ethanol. Finally, the dark solid product
was crushed and heated in a sand bath to evaporate the solvents. The dried mass of the solid is 1.78 g (~89%
yield).

Sample Characterization: The electron imaging of PPN-20 was done to study the morphology and stacking of the
various layers after the reaction. A combination of Titan Themis3 300 S/TEM and FE-SEM: “(JSM7500, RRID:
SCR_022202) was utilized for TEM and SEM studies, respectively. FTIR of the PPN was performed using a
Shimadzu IRAffinity-1 spectrometer. TGA was conducted at a ramp rate of 5°C/min under dynamic nitrogen flow
over a temperature range of 25-900°C by a Mettler-Toledo TGA/DSC 1. SPXRD was measured at room temperature
with a Powder-ECO Bragg-Brentano Theta/Theta diffractometer equipped with a Lynxeye detector XT.

Small-Angle X-ray Scattering: The nature of the pore surface was studied using a SAXS (Xenocs Xeuss 3.0
system, France). Before the analysis, the powder sample was packed into a 1 mm thick washer with two faces
covered with Capton windows. The scattering pattern was obtained at room temperature. It has a Dectris Eiger 2R
1M-pixel 2D detector and is equipped with a GeniX 3D X-ray beam delivery system. The SAXS beam was from a
monochromatic Cu Kα (λ = 1.54) high-intensity X-ray beam. A sample-to-detector distance of 900 mm was
maintained. The exposure time was 20 minutes and the 2D scattering patterns were acquired with a line-eraser
mode and then reduced into 1D plots after calibration with LaB and silver behenate standards. Guinier and Porod
6
laws equations were used in fitting the SAXS data to determine the radius of gyration, scattering vector, and
scattering intensity.40-42 The equations are given as follows:
Guinier law:
I(q)=I(0)exp(− q^2R^2 / 3) (1)
Porod law:
I(q)∼q^-4 (2)
Where I(q) (unit: cm-1) is the scattering intensity, I(0) (unit: cm-1) is the intensity when q = 0 and is usually referred
to as the forwarding intensity, q (unit: Å-1) is the scattering vector, and R (unit: Å) is the radius of gyration. The
g
equation for the scattering vector is:
q = 4π sin(θ) / λ (3)
Where λ (unit: Å) is the incident radiation wavelength and θ (unit: degree) is the scattering angle. Note: The
SASview 5.0.4 software was used to process the data.

Solid-State NMR: The 13C {1H} MAS ss-NMR experiments were carried out with a Bruker Avance-NEO ss-NMR
spectrometer (400 MHz for 1H nuclei) equipped with a standard two-channel 4 mm MAS probe head. The external
reference was C D (128.6 ppm). The 13C {1H} CP MAS NMR spectra were obtained at a spinning rate from 8 to 12
6 6
kHz with a standard cross-polarization pulse sequence at 1H pulse of 2.5 s 90°), CP contact time of 4.0 ms (power
of 77.2 W), and relaxation delays of 8 s. The standard tppm15 pulse sequence has been used for high-power 1H
decoupling.

Gas Uptake Measurement: The pore size and surface area were determined using Micromeritics ASAP 2020
surface area and porosity analyzer. Ultra-high purity (UHP) nitrogen was used to determine the surface area and
pore size distribution at 77 K and 1 bar. The uptake of propane, ethane, ethylene, and methane at 1 bar was also
measured at 298 K and 273 K, respectively. Before this, the sample was degassed at 120°C for 600 minutes. The
pore size distribution was determined using MicroActive software (Micromeritics), assuming slit-pore geometry for
the analysis. The sample tubes were properly cleaned before use to avoid contamination and interference with the
measurement.

IAST Selectivity: The selectivity of C H /CH , C H /CH , C H /C H , and C H /C H (supplementary table 2) was
3 8 4 2 6 4 3 8 2 6 2 6 2 4
calculated from the single-component adsorption data measured at 298 K. The adsorption data were fitted with the
Extended Langmuir equation below.
y = a·b·p^1-c / (1+b·p^1-c) (4)
Where y (mmol/g) is the amount of gas adsorbed on the surface per gram of the sorbent, a (mmol/g) is the maximum
adsorption capacity of the sorbent. b (1/kPa) is the Langmuir constant. p refers to the normalized pressure of the
adsorbate gas. c represents a deviation from an ideal homogeneous surface and is dimensionless. The plots of the
fitted parameters were used to calculate the selectivity of the gas mixtures (Supplementary Fig. 11, 15, 19, 23).
The IAST selectivity (Supplementary Table 2) was calculated from the Myers and Prausnitz43 equation below and the
Extended Langmuir fitting parameters.
S = (q /q ) / (p /p ) (5)
1 2 1 2
q and q are the mole fractions of the adsorbed bulk phase at any specific pressures (p and p ).
1 2 1 2

Binary Gas Separation Potential
Separation potential can be calculated for PPN-20 since the single-component adsorption has been experimentally
collected, fitted, and used to determine the IAST selectivity at 298 K and 1 bar necessary for the computation.44,45
Using the experimental uptake:
Δ q = q - q (6)
exp 1 2
Using the equimolar mixture:
Δ q = q (1- y / y ) (7)
1 1 2 S
or
Δ q = q (1- 1 / S) (8)
1 1
S = IAST Selectivity. q = Amount of preferred gas molecules adsorbed at a specific temperature and pressure. q
1 2
= Amount of less preferred gas molecules adsorbed at a specific temperature and pressure. y , y = Mole fraction
1 2
of the gas molecules adsorbed.

Isosteric Enthalpy of Adsorption: The interaction between the surface of the sorbent and adsorbate gases is
represented by the Q . The single-component adsorption was measured at 273 K and 298 K and fitted with the
st
Langmuir-Freundlich equation below.
y = a·b·p^c / (1+b·p^c) (9)
Where y (mmol/g) is the adsorbed quantity. P (kPa) is the pressure. a (mmol/g) is the adsorption capacity and b
(1/kPac) are the strength of the affinity between the adsorbate and the adsorbent. c represents a deviation from an
ideal homogeneous surface and is dimensionless. Based on the fitting parameters, the Q was determined from
st
the Clausius-Clapeyron equation given below:
∂(lnP) / ∂(1/T) = - Q / R (10)
st
Where p is gas pressure, R is the universal gas constant, T is the temperature of adsorption, and Q is the enthalpy
st
of adsorption (Supplementary Fig. 30).

Structure Simulation and Binding Energy: All ab initio calculations were performed with the help of the VASP
code.46,47 The standard projector augmented wave (PAW) pseudopotentials were used with a plane-wave basis set
formalism. The kinetic energy cutoff was set to 600 eV, and the Brillouin zone was sampled with a Gamma-centered
5 x 5 x 1 k-point grid. To capture dispersion forces accurately in layered systems, we used a fully non-local vdW-
DF1 functional in all calculations.48 The geometries were considered converged when the forces on each atom
were less than 0.005 eV/Å. The energy convergence criterion for the SCF cycle was 10-6 eV. The geometries were
first relaxed with a conjugate gradient (CG) algorithm and later re-relaxed with a more robust Quasi-Newton (QN)
optimizer.

Breakthrough Experiment: Breakthrough tests were carried out in an auto mixed-gas breakthrough apparatus
(3P MIXSORB). The weight of all test samples packed into the column (I.D. 6 mm, volume 2 mL) was approximately
0.5 g. The packed adsorbent was activated by heating to 120°C for 5 h under helium flow (10 mL/min). The mixed
gases (C H /C H (50/50, v/v); C H /C H /CH (30/30/40, v/v/v)) at a flow rate of 2 mL/min and a helium gas at a
2 6 2 4 3 8 2 6 4
flow rate of 6 mL/min were switched to pass through the adsorption bed. The outlet gas was analyzed by using a
mass spectrometer (MKS).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript presents the design and characterization of a porous polymer network (PPN), namely PPN-20, which is\ndemonstrated to function as a porous graphene-like sheet capable of separating C₂H₆/C₂H₄ and purifying CH₄ from a\nC₃H₈/C₂H₆/CH₄ mixture. The separation performance is attributed to preferential C–H···π interactions with C₂H₆ and C₃H₈.\nThe authors further claim that the observed selectivity represents the highest reported to date for any PPN in the case of\nC₂H₆/C₂H₄ separation, and the highest for any sorbent in the cases of C₂H₆/CH₄, C₃H₈/C₂H₆, and C₃H₈/CH₄ separations.\nPPN-20 is described as a hyper-cross-linked polymer with high thermal stability and reusability, showing no significant loss\nof performance upon multiple separation cycles. Importantly, the computational results support the experimentally observed\nselectivity trends. Overall, the manuscript addresses an important challenge in hydrocarbon separation and presents a\npotentially high-impact material. Some suggestions are listed below: they would very much strengthen the current\nmanuscript and remove serious doubts about the purity and identity of the proposed material.\n1. The solid-state ¹³C NMR spectrum of PPN-20 (Figure S4) shows the presence of a ketone peak. Does this indicate that\nthe material is not fully pure or that unreacted functionalities remain in the framework? If that is the case, additional aromatic\npeaks would be expected for the carbon atoms directly attached to the acetyl group. It would also be helpful to compare the\nspectrum of PPN-20 with that of the 1,3,5-triacetylbenzene monomer to clarify the structural assignments.\n2. Please include the Y-axis (% Transmittance) in the FTIR spectrum. Additionally, the ethanol spectrum appears unusually\nbroad — could this indicate incomplete drying? Please clarify.\n3. The authors mention that PPN-20 is robust in various solvents and at high temperatures. It would be helpful to also\ninclude data or discussion on the pH-dependent stability of PPN-20.\n4. Please add a brief paragraph summarizing why PPN-20 is particularly effective for the separation of gas mixtures,\nhighlighting its unique features or advantages.\n5. The first and second paragraphs of the introduction contain some repetitive discussion. Consider rewriting these sections\nin a more concise and focused manner. Furthermore, on page 1, \"high heat capacity\" should be replaced with \"global\nwarming potential\", and on page two, the description of methane as an alternative source of clean energy is quite inaccurate.\n6. The manuscript currently states: “Sorbents such as Metal-Organic Frameworks (MOF), Hydrogen Organic Framework\n(HOF), and Porous Organic Cage (POC) have been explored…(line 74, page 2)” — Please also include Covalent Organic\nFrameworks (COFs) and briefly discuss how PPNs differ from COFs, as well as from MOFs, to provide a clearer context for\nthe study.\n7. Please increase the font size of the X- and Y-axis labels in Figures 1b and 1c for better readability.\n8. On page 6, 50:50:50 should be replaced with 1:1:1.", "reviewer_2": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature\nCommunications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career\nResearchers who co-review manuscripts.", "reviewer_3": "The manuscript reports a porous polymer network (PPN‑20) that integrates a graphene‑sheet‑like architecture with\nultra‑microporosity, achieving exceptionally high single‑component uptakes for C2H6 and C3H8 as well as large IAST\nselectivities. These results are noteworthy because they surpass most reported values for porous organic polymers and\napproach—or even exceed—the performance of leading MOFs and COFs in natural‑gas separations. The work is promising\nand potentially impactful; therefore, I recommend a minor revision to address the points following before the paper can be\nconsidered for publication.\nAdditional comments:\n1. The manuscript repeatedly refers to PPN‑20 as a “porous graphene sheet.” This description is misleading because the\npolymer network has a high hydrogen‑to‑carbon ratio and lacks the extended sp2 lattice that defines true graphene. I\nrecommend replacing this term with a more accurate descriptor such as “graphene‑inspired porous polymer network” or\nsimply “hyper‑cross‑linked porous polymer,” and clarifying the structural differences in the text.\n2. Since PPN‑20 is amorphous, the exact pore geometry cannot be inferred solely from SAXS, TEM, or PXRD. To provide a\nmore rigorous structural model, the authors should construct an atomistic representation of the polymer using a tool such as\nMaterial Studio and perform molecular‑dynamics (MD) simulations to generate realistic pore‑size distributions. Simulated\nradial distribution functions and pore‑size histograms can then be directly compared with the experimental nitrogen sorption\nand SAXS data, thereby strengthening the claim that the observed ultra‑microporosity is intrinsic to the material rather than\nan artefact of sample preparation.\n3. Beyond reporting IAST selectivities, it is valuable for practitioners to know the theoretical separation potential derived from\nthe single‑component isotherms. The authors should calculate the ideal IAST selectivities and separation potential for each\nbinary/ or ternary mixture. Moreover, by coupling the fitted isotherms with the measured mass‑transfer coefficients, a\nsimulated breakthrough curve can be generated. Presenting these theoretical breakthrough profiles alongside the\nexperimental data will provide a more complete picture of the material’s performance under realistic process conditions and\nwill be highly informative for scale‑up considerations.", "reviewer_4": "This work reported a porous graphene sheet, PPN-20, a porous polymer network (PPN) that can separate C2H6/C2H4 and\npurify methane from a C3H8/C2H6/CH4 mixture in a single step. This PPN exhibits a moderate C2H6 and C3H8 uptake of\n3.93 mmol/g and 5.98 mmol/g, respectively, at 298 K and 1 bar, and achieves IAST selectivity of 2.2 for C2H6/C2H4 mixture.\nThe separation performance was demonstrated by breakthrough experiments. However, the data presentation are relatively\nrough, and there exist many key concerns on structural characterization, separation mechanism and separation assessment,\nwhich lacks enough quality and impact to be published in this journal.\n(1) If PPN-20 is a new porous material, the complete structure should be fully determined by structural characterization\ntechniques. However, there lacked the direct and solid structure characterization on PPN-20. Current structure description\nwas too simple to solidly support their claims on gas separation and mechanism.\n(2) In page 3, the authors claimed that “the vdW-DF level theoretical simulation result shows a pore of 3.782 Å”. However,\npore size distribution in Fig. 3b peaks at 0.5-1.5 nm, which is mismatched with the claim.\n(3) The gas adsorption isotherms should be included in the main text, and also compare the adsorption and separation\nperformance clearly with some promising materials reported, especially for C2H6/C2H4 separation. Otherwise, we cannot\nevaluate whether PPN-20 has a performance advantage or not.\n(4) The same problems also occurred on the breakthrough experiments.\n(5) The separation mechanism presented by this work was also very confused. First, Figure 5 seems to have no any support\nto elucidate the adsorption mechanism. The binding sites in Supplementary Fig. 36 and 37 are also not clear, and do not\nshow the interaction difference between these gases. Furthermore, the second binding sites in Fig. S37 seem to be not\nreasonable, since PPN-20 shows the close stacking between the layers that may have no enough space to adsorb gas\nmolecules. It is suggested the authors to obtain the full crystal structure and thus identify the gas adsorption sites clearly.\n(6) Their descriptions and claims on photocatalytic performance in page 7 have no any relevance with the gas separation\napplications, which seems to be excrescent.", "reviewer_5": "he authors presented a work on ethane/ethylene separation and methane Purification by a porous graphene sheet, PPN-20.\nThe adsorption isotherms, breakthrough experiments, and adsorption mechanisms were systematically investigated. I would\nlike to recommend this article to be published after minor revisions were made:\n1.Under actual operating conditions, moisture is present. Please provide moisture and water stability test results for the\nmaterials.\n2.In the three-component permeation experiment, the volume ratio of C3H8/C2H6/CH4 is 50/50/50, which should be\nincorrect.\n3.Please add the calculation of the dynamic adsorption capacity of C2H6 and C3H8 and high-purity C2H4 and CH4\nproduction in the dynamic breakthrough experiment."}, "author_response": "RESPONSE TO REVIEWERS' COMMENTS\nReviewer #1\nGeneral Comment: The manuscript presents the design and characterization of a porous polymer\nnetwork (PPN), namely PPN-20, which is demonstrated to function as a porous graphene-like sheet\ncapable of separating C₂H₆/C₂H₄ and purifying CH₄ from a C₃H₈/C₂H₆/CH₄ mixture. The separation\nperformance is attributed to preferential C–H···π interactions with C₂H₆ and C₃H₈. The authors\nfurther claim that the observed selectivity represents the highest reported to date for any PPN in\nthe case of C₂H₆/C₂H₄ separation, and the highest for any sorbent in the cases of C₂H₆/CH₄,\nC₃H₈/C₂H₆, and C₃H₈/CH₄ separations. PPN-20 is described as a hyper-cross-linked polymer with\nhigh thermal stability and reusability, showing no significant loss of performance upon multiple\nseparation cycles. Importantly, the computational results support the experimentally observed\nselectivity trends. Overall, the manuscript addresses an important challenge in hydrocarbon\nseparation and presents a potentially high-impact material. Some suggestions are listed below: they\nwould very much strengthen the current manuscript and remove serious doubts about the purity\nand identity of the proposed material.\nResponse: We thank the reviewer for the assessment of our work. We have carefully gone through\nall the comments raised by this reviewer and, in response, have conducted additional experiments\nand revised the manuscript accordingly.\nComment 1: The solid-state ¹³C NMR spectrum of PPN-20 (Figure S4) shows the presence of a\nketone peak. Does this indicate that the material is not fully pure or that unreacted functionalities\nremain in the framework? If that is the case, additional aromatic peaks would be expected for the\ncarbon atoms directly attached to the acetyl group. It would also be helpful to compare the\nspectrum of PPN-20 with that of the 1,3,5-triacetylbenzene monomer to clarify the structural\nassignments.\nResponse: Thank you for this insightful comment. To address this point, we have performed a\ncomparative solid-state 13C NMR (ss-NMR) analysis of PPN-20 and its monomer precursor, 1,3,5-\ntriacetylbenzene, as shown in the newly added Supplementary Figure 4b in the Supplementary\nInformation page 7. The stacked spectra clearly distinguish the resonance corresponding to the\ncarbonyl (C=O) functionality. The carbonyl signal (δ =200.6 ppm) observed in PPN-20 appears\niso\nat a similar chemical shift (δ =200.0 ppm) to that of the monomer but with considerably reduced\niso\nintensity, indicating the presence of a small fraction of residual acetyl groups within the\nframework. This observation is consistent with incomplete condensation at sterically hindered sites\nduring the polymerization process, which is common in hyper-cross-linked porous polymers.\nThe overall spectral features, therefore, substantiate the expected cross-linked structure while\nclarifying that minor unreacted sites are inherent to the synthesis mechanism rather than indicative\nof material impurity. This is also supported by the Fourier Transform Infrared (FTIR) spectra of\n1\nthe PPN-20 and monomer compared in Supplementary Figure 3a, page 3 of Supplementary\nInformation.\nComment 2: Please include the Y-axis (% Transmittance) in the FTIR spectrum. Additionally, the\nethanol spectrum appears unusually broad — could this indicate incomplete drying? Please clarify.\nResponse: Thank you very much for these very insightful comments. In response, we have\nupdated the FTIR figure to include the Y-axis (% Transmittance) on pages 3, 4, and 5 of the\nSupplementary Information. Regarding the ethanol spectrum broadening, it resulted from residual\nethanol trapped within the sorbent pores during data collection. To verify this, we repeated the\nFTIR measurements after washing the sorbent with different solvents. The updated results show\nthat the broadening was only observed when ethanol was used, indicating that the effect arose from\npotential ethanol trapping. As shown in supplementary Figure 3c on page 5 of the supporting\ninformation, no such broadening appeared when the sorbent was washed with other solvents.\nComment 3: The authors mention that PPN-20 is robust in various solvents and at high\ntemperatures. It would be helpful to also include data or discussion on the pH-dependent stability\nof PPN-20.\nResponse: Thank you for this insightful comment. We agree that providing additional data on the\npH-dependent stability of PPN-20 is important. In response, we soaked PPN-20 in 10 M NaOH,\n99% w/w methanesulfonic acid, 12 M HCl, and water separately for 24 hours and analyzed the\nchemical stability of the samples using FTIR. As shown in Supplementary Figure 3b, no noticeable\nstructural changes were observed in the spectra compared to the pristine sample, indicating that\nPPN-20 retains its structural integrity under both strongly acidic, neutral, and basic conditions.\nTogether with the solvent stability data (Supplementary Figure 3c), these results confirm the\nexceptional chemical robustness of PPN-20, capable of withstanding harsh environments across a\nwide pH range.\nComment 4: Please add a brief paragraph summarizing why PPN-20 is particularly effective for\nthe separation of gas mixtures, highlighting its unique features or advantages.\nResponse: We appreciate the reviewer's valuable suggestion. We agree that highlighting the unique\nfeatures of PPN-20 is important for clarifying its effectiveness in gas separation. Accordingly, we\nhave added a brief description on page 2, lines 40-41, summarizing the structural characteristics\nand advantages of PPN-20. This addition emphasizes its high surface area, tunable pore\nenvironment, and chemical robustness, which together contribute to its strong gas selectivity and\nseparation performance.\nComment 5: The first and second paragraphs of the introduction contain some repetitive\n2\ndiscussion. Consider rewriting these sections in a more concise and focused manner. Furthermore,\non page 1, \"high heat capacity\" should be replaced with \"global warming potential\", and on page\ntwo, the description of methane as an alternative source of clean energy is quite inaccurate.\nResponse: We sincerely thank the reviewer for these valuable suggestions. We agree with the\nobservations and have revised the first and second paragraphs of the introduction to make them\nmore concise and focused by removing repetitive content. Additionally, we have replaced “high\nheat capacity” with “global warming potential” (Page 1, line 41-42), as suggested, and corrected\nthe inaccurate description of methane as an alternative clean energy source (page 2, line 6). These\nrevisions improve both the clarity and scientific accuracy of the introduction.\nComment 6: The manuscript currently states: “Sorbents such as Metal-Organic Frameworks\n(MOF), Hydrogen Organic Framework (HOF), and Porous Organic Cage (POC) have been\nexplored…(line 74, page 2)” — Please also include Covalent Organic Frameworks (COFs) and\nbriefly discuss how PPNs differ from COFs, as well as from MOFs, to provide a clearer context\nfor the study.\nResponse: We appreciate the reviewer's valuable suggestion. We agree with the suggestion and\nhave added more details on the difference between COF, MOF, and PPN to provide better\nclarification on the subject (page 2, lines 40-41, 44-46). This addition improves the conceptual\nclarity of the manuscript and helps readers better understand how PPN-20 differs structurally and\nfunctionally from related porous materials.\nComment 7: Please increase the font size of the X- and Y-axis labels in Figures 1b and 1c for\nbetter readability.\nResponse: We thank the reviewer for this helpful suggestion. The font size of the X- and Y-axis\nlabels in Figures 1b and 1c has been increased to enhance readability. The updated figures now\npresent all parameters clearly, thereby making the results easier to comprehend.\nComment 8: On page 6, 50:50:50 should be replaced with 1:1:1.\nResponse: We appreciate the reviewer’s careful observation. This was a typographical error. The\ncorrect ratio used is C H /C H /CH = 3/3/4 or 30/30/40 (v/v/v), as stated elsewhere in the\n3 8 2 6 4\nmanuscript and consistent with the experimental procedure. The error has now been corrected to\nensure accuracy and consistency throughout the text. Thank you once again for the observation.\nReviewer #2\nGeneral Comment: I co-reviewed this manuscript with one of the reviewers who provided the\n3\nlisted reports. This is part of the Nature Communications initiative to facilitate training in peer\nreview and to provide appropriate recognition for Early Career Researchers who co-review\nmanuscripts.\nResponse: We sincerely thank you for your contribution and participation in reviewing our\nmanuscript. We appreciate your time and effort, which have helped improve the clarity and overall\nquality of our work.\nReviewer #3\nGeneral Comment: The manuscript reports a porous polymer network (PPN-20) that integrates a\ngraphene-sheet-like architecture with ultra-microporosity, achieving exceptionally high single-\ncomponent uptakes for C H and C H as well as large IAST selectivities. These results are\n2 6 3 8\nnoteworthy because they surpass most reported values for porous organic polymers and\napproach—or even exceed—the performance of leading MOFs and COFs in natural-gas\nseparations. The work is promising and potentially impactful; therefore, I recommend a minor\nrevision to address the points following before the paper can be considered for publication.\nResponse: We sincerely thank the reviewer for the positive and encouraging comments on our\nwork. We are delighted that the reviewer recognizes the significance of PPN-20’s ultra-\nmicroporosity, exceptional gas uptake, and selectivity performance. We have carefully addressed\nall the specific points raised in the following comments and made the necessary revisions to further\nstrengthen the clarity, accuracy, and overall impact of the manuscript. We truly appreciate the\nreviewer’s constructive feedback and thoughtful assessment, which have helped in improving the\nquality of the manuscript.\nComment 1: The manuscript repeatedly refers to PPN-20 as a “porous graphene sheet.” This\ndescription is misleading because the polymer network has a high hydrogen-to-carbon ratio and\nlacks the extended sp2 lattice that defines true graphene. I recommend replacing this term with a\nmore accurate descriptor, such as “graphene-inspired porous polymer network” or simply\n“hyper-cross-linked porous polymer,” and clarifying the structural differences in the text.\nResponse: We thank the reviewer for this valuable comment and helpful suggestion regarding the\nmanuscript title and terminology. Additionally, we agree that the term “porous graphene sheet”\nmay be misleading. Accordingly, we have revised the title from Porous Graphene Sheets for\nEthane/Ethylene Separation and Methane Purification to Graphene-Inspired Porous Polymer\nNetwork for Ethane/Ethylene Separation and Methane Purification and updated other parts of the\nmanuscript. This updated title more accurately reflects the structure of PPN-20 and better conveys\nthe rationale behind its design and performance in gas separation.\nSAXS, TEM, or PXRD. To provide a more rigorous structural model, the authors should construct\nan atomistic representation of the polymer using a tool such as Material Studio and perform\nmolecular-dynamics (MD) simulations to generate realistic pore-size distributions. Simulated\nradial distribution functions and pore-size histograms can then be directly compared with the\nexperimental nitrogen sorption and SAXS data, thereby strengthening the claim that the observed\nultra-microporosity is intrinsic to the material rather than an artefact of sample preparation.\nResponse: Thank you very much for the insightful comment. Because PPN-20 is amorphous, the\nstructure characterization experimentally as well as theoretically is challenging, particularly for\nthe latter. While we could perform molecular dynamics simulations, the obtained pore-size\ndistributions would highly depend on the local minima chosen for the starting structure, and phase\ntransitions with even moderate barriers are essentially impossible to observe on the time scale\naccessible to ab initio molecular dynamics. As a result, we used ab initio methods to study the\nbinding of guest molecules on single sheets of the monomer (Supplementary Figures 33 and 34)\nas well as intercalation into bulk phases with different stackings (Supplementary Figure 32). In\naddition, we ran some longer MD trajectories at ab initio level with 50000 steps at elevated\ntemperature; however, no meaningful results were obtained despite considering the extended\nstructures and longer MD time.\nIn conclusion, the nitrogen gas adsorption at 77 K and 1 bar, which is the most reliable method to\ndetermine the surface area and pore size distributions of reported sorbents in the literature,\nexperimentally shows that this PPN-20 has ultra-micropores from the pore size distribution plot in\nFigures 3a and 3b in the manuscript on page 7, assuming a DFT type and slit geometry.\nComment 3: Beyond reporting IAST selectivities, it is valuable for practitioners to know the\ntheoretical separation potential derived from the single-component isotherms. The authors should\ncalculate the ideal IAST selectivities and separation potential for each binary/ or ternary mixture.\nMoreover, by coupling the fitted isotherms with the measured mass-transfer coefficients, a\nsimulated breakthrough curve can be generated. Presenting these theoretical breakthrough profiles\nalongside the experimental data will provide a more complete picture of the material’s performance\nunder realistic process conditions and will be highly informative for scale-up considerations.\nResponse: We sincerely thank the reviewer for these insightful comments. We agree that assessing\nthe separation potential, in addition to the IAST selectivities, provides a more comprehensive\nunderstanding of the material’s performance. To address this, we have calculated the separation\npotential for the various gas mixtures used in the study. The corresponding results have been\nsummarized in a table and included in the Supporting Information (Supplementary Table 2, Page\n36). Given the strong consistency of PPN-20 during breakthrough measurements, these findings\nwill serve as a foundation for future upscaling and process optimization efforts. While theoretical\nmodelling is indeed valuable, we have focused here on experimental validation under realistic\n5\nconditions to ensure practical relevance for potential large-scale applications. We greatly\nappreciate this comment, as it has helped strengthen the clarity of the manuscript.\nReviewer #4\nGeneral Comment: This work reported a porous graphene sheet, PPN-20, a porous polymer\nnetwork (PPN) that can separate C H /C H and purify methane from a C H /C H /CH mixture\n2 6 2 4 3 8 2 6 4\nin a single step. This PPN exhibits a moderate C H and C H uptake of 3.93 mmol/g and 5.98\n2 6 3 8\nmmol/g, respectively, at 298 K and 1 bar, and achieves IAST selectivity of 2.2 for C H /C H\n2 6 2 4\nmixture. The separation performance was demonstrated by breakthrough experiments. However,\nthe data presentation are relatively rough, and there exist many key concerns on structural\ncharacterization, separation mechanism, and separation assessment, which lacks enough quality\nand impact to be published in this journal.\nResponse: We thank the reviewer for the assessment and constructive feedback. We appreciate the\nrecognition of the gas separation performance of PPN-20 and have carefully addressed the\nconcerns raised regarding data presentation and structural characterization. In the revised\nmanuscript, we have improved the clarity, organization of the data presentation, and expanded the\ndiscussion on the separation mechanism and performance evaluation. These additions strengthen\nthe reliability of the structural interpretation and provide a more comprehensive understanding of\nPPN-20’s gas separation capability.\nComment 1: If PPN-20 is a new porous material, the complete structure should be fully\ndetermined by structural characterization techniques. However, there lacked the direct and solid\nstructure characterization on PPN-20. Current structure description was too simple to solidly\nsupport their claims on gas separation and mechanism.\nResponse: We sincerely thank the reviewer for this insightful comment. PPN-20 is an amorphous\nporous polymer sorbent, and due to the irreversible nature of its bonds in the polymerization\nprocess, the resulting framework lacks long-range crystallinity. As shown in the PXRD data\n(Supplementary Figure 8, page 9), the absence of sharp diffraction peaks confirms the amorphous\nnature of PPN-20, making it impossible to obtain single crystals as is typically possible for\ncrystalline porous sorbents such as MOFs or COFs. The SEM and TEM images also show that this\nsorbent is amorphous (Supplementary Figures 5 and 6, page 8).\nTo provide a comprehensive structural understanding, we employed a combination of\ncomplementary characterization techniques. Solid-state ¹³C{¹H} CP MAS NMR and FTIR\nanalyses confirm the successful formation of the polymeric framework and show no change in\nstructural features after organic solvents and acid/base stability tests (Supplementary Figures 3a-\n6\n4b, pages 3-7). Additionally, SEM and TEM images (Supplementary Figures 5 and 6, pages 8)\nreveal a uniform, sheet-like morphology with interconnected porous textures, consistent with the\nnetwork architecture. Additionally, Small-Angle X-ray Scattering (SAXS) analysis further\nsupports the amorphous yet well-connected pore framework, confirming the presence of an\nextended microporous structure (Manuscript Figure 1b and 1c, page 4).\nFurthermore, the nitrogen adsorption isotherm at 77 K and 1 bar indicates that PPN-20 possesses\nultra-microporosity, and the calculated pore size distribution aligns well with the molecular sieving\ntrend observed during gas separation experiments (Manuscript Figures 3a and 3b, page 7).\nThe measured sorption behavior corresponds closely with the kinetic diameters of the gases, validating\nthe proposed separation mechanism. Once again, we appreciate the reviewer’s comment, which\nhas helped to strengthen the manuscript.\nComment 2: In page 3, the authors claimed that “the vdW-DF level theoretical simulation result\nshows a pore of 3.782 Å”. However, pore size distribution in Fig. 3b peaks at 0.5-1.5 nm, which\nis mismatched with the claim.\nResponse: Thank you very much for this insightful comment. We apologize for the confusion\ncaused by the wording in the manuscript. The 3.782 Å (0.3782 nm) refers to the distance between\nopposite hydrogen atoms in the pores. Note that the 5.7 Å (0.57 nm) pore size in Supplementary\nFigure 1, page 2, is measured from carbon-to-carbon in the pores because the hydrogen atoms\npoint slightly away from it, while those bigger than that are from defects within the sorbents, as\nwill be expected of a polymer material without a regular periodicity. Overall, both the experimental\nand simulated results are consistent and support the observed gas uptake and separation trend by\nthe sorbent. We have updated the manuscript accordingly to reflect this clarification.\nComment 3: The gas adsorption isotherms should be included in the main text and also compare\nthe adsorption and separation performance clearly with some promising materials reported,\nespecially for C H /C H separation. Otherwise, we cannot evaluate whether PPN-20 has a\n2 6 2 4\nperformance advantage or not.\nResponse: We thank the reviewer for this valuable comment. In response, we have included the\ngas adsorption isotherms of PPN-20 in the manuscript to improve clarity. Furthermore, we have\nexpanded the comparison of the adsorption and separation performance of PPN-20 with other\nstate-of-the-art materials. The comparative data are now summarized in figures (Supporting\nFigures 13, 17, 21, and 25) and tables (supplementary Tables 3, 4, 5, and 6) in the supplementary\ninformation (SI). Because several comparisons were made, this information is presented in the SI\nand properly referenced in the manuscript. Once again, we appreciate your comment, which has\nmade the manuscript clearer and more consistent.\nResponse: We appreciate the reviewer’s careful observation. The breakthrough results are in the\nmanuscript for both the binary and ternary gas mixture and are consistent with the selectivity\ncalculation that has been thoroughly compared with other best-performing sorbents, summarized\nin figures (Supporting Figures 13, 17, 21, and 25) and tables (Supplementary Tables 3, 4, 5, and\n6) included in the supporting information. We really appreciate your comments because they have\nguided us to provide more information to strengthen the manuscript.\nComment 5: The separation mechanism presented by this work was also very confused. First,\nFigure 5 seems to have no any support to elucidate the adsorption mechanism. The binding sites\nin Supplementary Fig. 36 and 37 are also not clear, and do not show the interaction difference\nbetween these gases. Furthermore, the second binding sites in Fig. S37 seem to be not reasonable,\nsince PPN-20 shows the close stacking between the layers that may have no enough space to adsorb\ngas molecules. It is suggested the authors to obtain the full crystal structure and thus identify the\ngas adsorption sites clearly.\nResponse: Thank you very much for this very insightful comment. We agree that the band\nstructure in Fig. 5 does not provide additional insight into the binding mechanism. In fact, it is an\nadditional preliminary study into the electronic structure of this material. In response, we have\nupdated the manuscript and removed this figure and any references to it.\nConcerning the binding sites in Supplementary Figures 33-34, formerly Supplementary Figures\n36-37, we have inserted the labels “top view” and “side view” for better clarification. Furthermore,\nwe have included the guest-host separation and two new figures (Supplementary Figures 35-36)\nin the Supporting Information, showing induced charge densities, i.e., the rearrangement of charge\ndensity, clearly showing the interactions to address the concern about missing interactions. These\ninteractions also explain the differences in the binding energies of the various guest molecules at\nprimary and secondary sites. Finally, concerning the closed stacking, we have performed additional\ncalculations, properly intercalating guest molecules in between the PPN-20 sheets. We find that\nthe material accommodates those guest molecules by expanding its inter-layer separation, as\ndescribed in the updated manuscript. Once again, we appreciate your valuable input and the\nclarification it has added to our manuscript.\nComment 6: Their descriptions and claims on photocatalytic performance in page 7 have no any\nrelevance with the gas separation applications, which seems to be excrescent.\nResponse: Thank you very much for this insightful comment. We fully agree, as this study focuses\non gas separation, and maintaining a clear and consistent scope is essential. Accordingly, we have\nremoved the section on photocatalytic performance and the corresponding figure. The discussion\nof photocatalysis will instead be incorporated into a future study exploring the catalytic\n8\napplications of PPN-20 and related sorbents currently under development in our group. We believe\nthis revision has made the manuscript more concise, focused, and coherent. We sincerely\nappreciate your helpful suggestion.\nReviewer #5\nGeneral Comment: The authors presented a work on ethane/ethylene separation and methane\nPurification by a porous graphene sheet, PPN-20. The adsorption isotherms, breakthrough\nexperiments, and adsorption mechanisms were systematically investigated. I would like to\nrecommend this article to be published after minor revisions were made:\nResponse: We sincerely thank the reviewer for the positive and encouraging feedback. We\nappreciate your recommendation for publication after revisions. In response to the comments, we\nhave carefully revised the manuscript to further enhance its clarity, consistency, and technical\ncompleteness.\nComment 1: Under actual operating conditions, moisture is present. Please provide moisture and\nwater stability test results for the materials.\nResponse: Thank you very much for your insightful comment. To address this, we have evaluated\nthe stability of PPN-20 in water and various solvents using FT-IR spectroscopy. The corresponding\nspectra have been included in the Supporting Information (Supplementary Figure 3b-3c, pages 4-\n5). The FT-IR results show no significant changes in the characteristic bands of PPN-20 after\nexposure, confirming that the material retains its structural integrity and exhibits excellent\nmoisture and solvent stability.\nComment 2: In the three-component permeation experiment, the volume ratio of C H /C H /CH\n3 8 2 6 4\nis 50/50/50, which should be incorrect.\nResponse: Thank you very much for this valuable observation. We agree with your comment. The\noriginally stated gas mixture ratio was a typographical error. The correct composition used in the\nthree-component permeation experiment is C H /C H /CH = 3/3/4 (v/v/v), which corresponds to\n3 8 2 6 4\n30/30/40. This correction has been made in the revised manuscript to ensure full consistency with\nthe experimental procedure.\nComment 3: Please add the calculation of the dynamic adsorption capacity of C H and C H and\n2 6 3 8\nhigh-purity C H and CH production in the dynamic breakthrough experiment.\n2 4 4\nadsorption capacity and productivity following the reviewer’s suggestion. This result has been\nincluded in the updated manuscript on page 7, line 17, and page 8, lines 1-4. Once again, we\nappreciate your comments and the clarity that addressing them has added to our manuscript.\nFinally, we thank you again for your admirable efforts!\nBest regards,\nProfessor Hong-Cai Zhou\nDepartment of Chemistry\nTexas A&M University\nCollege Station, Texas 77843, United States\nE-mail: zhou@chem.tamu.edu\n10"}, {"round": 2, "reviewer_comments": {"reviewer_1": "My impression is that the authors have addressed our concerns in the revised manuscript. I now support its publication as-is.", "reviewer_2": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_3": "I have no further comments, and recommend that this article be accepted for publication in Nature Communications.", "reviewer_4": "The authors have mostly addressed the comments by the reviewers. This manuscript is suitable to be accepted in this journal. It is also suggested the authors to put the figures of gas adsorption sites and interactions with the framework into the main text, which can make the separation mechanism more clear and readable. Moreover, the title of Binding Mechanism part on page 8 should be revised accordingly, since Electronic Properties have been removed.", "reviewer_5": "In the revised version of the manuscript and in their responses to the reviewer, the Authors have thoroughly addressed and clarified all of the reviewer’s questions and comments. In its current form, the Reviewer recommends the manuscript for publication."}, "author_response": "RESPONSE TO REVIEWERS’ COMMENTS\nReviewer #1 (Remarks to the Author):\nMy impression is that the authors have addressed our concerns in the revised\nmanuscript. I now support its publication as-is.\nResponse: We thank the reviewer for their effort in reviewing our manuscript and the\nfeedback, which has significantly improved the manuscript.\nReviewer #2 (Remarks to the Author):\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports.\nThis is part of the Nature Communications initiative to facilitate training in peer review\nand to provide appropriate recognition for Early Career Researchers who co-review\nmanuscripts.\nResponse: Thank you very much for your effort in reviewing our manuscript.\nReviewer #3 (Remarks to the Author):\nI have no further comments, and recommend that this article be accepted for publication\nin Nature Communications.\nResponse: Thank you very much for your effort in reviewing our manuscript.\nReviewer #4 (Remarks to the Author):\nThe authors have mostly addressed the comments by the reviewers. This manuscript is\nsuitable to be accepted in this journal. It is also suggested the authors to put the figures\nof gas adsorption sites and interactions with the framework into the main text, which can\nmake the separation mechanism more clear and readable. Moreover, the title of Binding\nMechanism part on page 8 should be revised accordingly, since Electronic Properties\nhave been removed.\nResponse: Thank you very much for your effort in reviewing our manuscript and your\nsuggestions. The manuscript has been updated accordingly.\nReviewer #5 (Remarks to the Author):\nIn the revised version of the manuscript and in their responses to the reviewer, the Authors\nhave thoroughly addressed and clarified all of the reviewer’s questions and comments. In\nits current form, the Reviewer recommends the manuscript for publication.\nResponse: Thank you very much for your effort in reviewing our manuscript."}]

Decision letter