Dynamic hydroxyl cycle of zeolite for short and ultra-short chain PFAS free potable water

Domain: biology
Published: 2026-03-10
Editorial outcome: major_revision

Abstract
The global shift in per- and polyfluoroalkyl substance (PFAS) crisis towards (ultra-)short-chain congeners highlights the urgent need to design adsorbents with hydrophilic functions. However, current functional group immobilization modifications fail to balance efficiency with regeneration, limiting access to affordable (ultra-)short-chain PFAS-free potable water. Herein, we present a non-immobilized dynamic hydroxyl cycling strategy that uses only water to circularly drive commercial zeolite adsorption-regeneration processes, efficiently and sustainably removing various (ultra-)short-chain PFASs (C-F number: 1-6) from potable water. The enhanced nanopore accessibility and the formation of a “zeolite framework-confined water” dual-binding mode make the modified zeolite one of the highest capacity adsorbents reported (233.82-733.13 mg g-1). Notably, this methodology offers a potential low-cost, in-situ upgrade for existing purifiers, potentially providing healthy water to underdeveloped regions through 179 days of full-scale purification.

Introduction
Per- and polyfluoroalkyl substances (PFASs), often referred to as “forever chemicals”, are extensively utilized across various sectors, making them pervasive in daily life1. The continuous accumulation of PFASs in the environment, coupled with increasing evidence of their harmful effects on humans even at ultra-trace exposure levels, prompted the European Parliament and Council (EPC) to establish a maximum limit of 500 ng L-1 for all PFASs in drinking water in 20212,3. Although legacy long-chain PFASs (chain length > 7), e.g., perfluorooctanoic acid (PFOA), have been phased out in recent years, ultra-short-chain PFASs (chain length < 4) and short-chain PFASs (chain length = 4-7) have replaced them and now dominate in potable water4-6. However, growing evidence suggests that (ultra-)short-chain PFASs may exhibit similar or even greater biological toxicity than long-chain PFASs5,7. The worse reality is that conventional water treatment methods (e.g., coagulation and advanced oxidation) are ineffective in eliminating (ultra-)short-chain PFASs, leaving individuals are unknowingly exposed to PFAS levels that exceed safe limits through their tap water4,5. Hence, it is imperative to employ advanced water purification technologies (e.g., reverse osmosis) at the point-of-use. However, even in developed nations, only about 40% of the population can afford these costly solutions8.

Adsorption process offers a cost-effective method for removing PFASs through solid-liquid mass transfer methods, thereby enabling affordable point-of-use purification of drinking water. Still, adsorption techniques face significant limitations in the purification of (ultra-)short-chain PFASs: 1) Conventional hydrophobic mass transfer mechanisms leads to a significant decrease in the adsorption affinity of adsorbents for hydrophilic (ultra-)short-chain PFASs as chain length decreases, resulting in diminished or even negative removal efficiency4,9. To address this issue, the current approaches focus on grafting of hydrophilic functional groups (e.g., -OH or -NH )10,11. Yet, 2 this introduces a second limitation: 2) The hydrophilic functional groups are prone to degradation, becoming inactivated during post-disposal of the PFAS adsorbent (e.g., thermal treatment). Despite substantial efforts, currently proposed solutions tend to optimize either efficiency (e.g., β-cyclodextrin polymer, hollow covalent organic framework, magnetic fluorinated polymer, and metal-organic framework) or reusability (e.g., electrochemical and microwave)10-17, leading to increased costs over the full adsorption-regeneration life cycle. Thus, the key to providing affordable (ultra-)short-chain PFAS-free potable water lies in resolving the inherent trade-off between adsorption efficiency and reusability.

We present a non-immobilized modification strategy based on dynamic hydroxyl cycling in commercial zeolites for the adsorption and regeneration of (ultra-)short-chain PFASs. Unlike alternative enhancement strategies, the approach described here requires only the introduction of a reagent-free, low-cost water vapor diffusion technique into the conventional adsorption-regeneration process, enabling dynamic cycling of Si-OH and confined water-hydroxyl networks across various commercial zeolites (Fig. 1a and 1b). This non-immobilized strategy effectively improves the mass transfer process of (ultra-)short-chain PFASs within the nanopores and established a “zeolite framework-confined water” dual-binding mode, thus achieving the highest reported adsorption capacity and stable recycling. More importantly, this protocol is directly applicable for the purification of (ultra-)short-chain PFASs in real potable water, as validated by a full-scale household purifier over a period of 182 days.

Results
Design of dynamic hydroxyl cycle process
The grand challenge in designing a dynamic adsorption process lies in identifying a non-immobilized enhanced media that balances the efficiency and reusability. High efficiency is required to provide specific binding sites that enable the adsorbent to capture concentrations of (ultra-)short-chain PFASs at concentrations as low as one part per 100 billion in complex environmental systems. Meanwhile, a suitable reusability allows the enhanced media to bind to the adsorbent through non-chemical bonds, facilitating easy cycles of functionalization and de-functionalization while maintaining the structural stability.

Zeolite, a commonly used adsorbent, exerts a hydrophobic effect on the C-F chains of PFASs through its Si-O framework, but lacks a hydrophilic mode of action18. One of the most promising enhanced media that can meet aforementioned requirements, while remaining compatible with the zeolite framework, is confined water. Due to the surface tension, the liquid water molecules require pressures of >80 MPa to penetrate the hydrophobic nanopores, resulting in cavities within the zeolite19. However, if water molecules are pre-confined within zeolite nanopores through interfacial interactions, they can potentially form non-immobilized hydrophilic sites for special in-site binding of (ultra-)short-chain PFAS20. Additionally, confined water is non-chemically bound to the nanopore walls, allowing for green and low-cost cycles of functionalization and de-functionalization through diffusion and thermal processes, using only water. Base on this concept, we designed an adsorption-regeneration scheme using the dynamic hydroxyl cycle. This process involves the introduction of water vapor diffusion into the traditional adsorption-thermal regeneration process of zeolites, achieving a three-stage “construction-utilization-removal” of the dynamic hydroxyl cycle (Fig. 1a and 1b).

To verify the feasibility of the dynamic hydroxyl cycling scheme and determine the optimal zeolite substrate, we investigated the adsorption efficiency of a series of commercial zeolites with systematically varied pore sizes (0.52-1.12 nm) and surface hydrophilicity (Si/Al ratio: 25-600, Supplementary Fig. 1 and Table 1) for 9 (ultra-)short-chain PFASs (C-F number = 1-6, Supplementary Table 2) within the dynamic hydroxyl cycle. Notably, we observed an enhanced removal efficiency (4%-88%→31%-100%) across all commercial zeolites confirming the broad applicability of the dynamic hydroxyl cycle strategy (Fig. 1c). Among the tested zeolites, those with moderate pore size (0.56-0.74 nm, BEA crystal) and high hydrophobicity (Si/Al ratio ≥ 200) achieved the optimal removal efficiency (> 61%) for all (ultra-)short-chain PFASs. These results validate the basic assumption that the dynamic hydroxyl cycle increases adsorption efficiency.

Demonstration of dynamic hydroxyl cycle process
Based on the optimal β200 zeolite (BEA crystal, Si/Al ratio = 200), we further elucidated the change in structural modifications and adsorption properties during the hydroxyl “construction-utilization-removal” cycle. Initially, we thermally treated the original β200 to simulate the structure of the regenerated zeolite (D-β200). After calcination at 800 ℃, the Si-OH characteristic peak (954 cm-1) in the infrared spectrum of D-β200 zeolite disappeared, indicating high-temperature-induced ortho-hydroxyl condensation (Fig. 2a and Supplementary Fig. 3) and a reduction in surface polarity (ζ potential: -43.3 mV→-16.6 mV, Supplementary Fig. 2). Despite these changes, the D-β200 retained a well-preserved Si-O-Si framework (1082 cm-1 and 800 cm-1) and maintained its X-ray diffraction crystal facets (Fig. 2b) even under thermal treatment. High-resolution transmission electron microscopy images and pore size analysis of the D-β200 confirmed the preservation of particle morphology and microporous structure (1.894 nm vs. 1.971 nm, Fig. 2c and Supplementary Table 3).

To construct the hydroxyl groups, the D-β200 was exposed to a high humidity (90%-100%) environment to prepare S-D-β200, facilitating the self-assembly of confined water structures through the vapor diffusion method. After this construction process, the characteristic peaks of the confined water hydrogen-bond network (3750 cm-1-3000 cm-1) and Si-OH (954 cm-1) appeared in the infrared spectrum of S-D-β200, providing evidence for the successful loading of confined water and the rehydration of the unsteady Si-O-Si bonds (ζ potential: -16.6 mV→-41.6 mV, Supplementary Fig. 2 and 3). These results demonstrated that water vapor encapsulation created a confined water structure in the β200 nanopore and achieved orderly regulation of the hydrophilicity/ hydrophobicity (Si-OH and Si-O-Si) of the zeolite surface through the chemical transfer of water molecules (Supplementary Fig. 3). The water balance control (W-β200, Fig. 2a) showed no characteristic peaks, indicating that the water molecules were confined to the nanopore and not attached to the surface. Advanced 2D 1H-1H single/double quantum magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy was used to investigate the confined water hydrogen-bond network and its binding state21. In S-D-β200, confined water appeared as water molecular chains within channels (δ=1.04 ppm) and water clusters at intersections (δ=5.54 ppm), interacting with Si-OH (δ=2.13 ppm) and Al-OH (δ=1.73 ppm, 7.72 ppm) groups (Fig. 2d)22. In terms of proton-proton proximities, only the water cluster exhibited diagonal peaks (11.08, 5.54), with interactions involving other protons displayed non-diagonal peaks ((6.58, 5.54); (7.27, 5.54); (7.67, 5.54)). These results confirm that the confined water modified the zeolite cavity environment in a non-immobilized manner and formed a hydrophilic center of water clusters at the intersections of channels (Supplementary Fig. 4).

The successful construction of the non-immobilized confined water hydrogen-bond network motivated us to conduct adsorption efficiency tests on S-D-β200. S-D-β200 demonstrated rapid, irreversible adsorption of all (ultra-)short-chain PFASs, reaching equilibrium within 2 hours (Supplementary Fig. 5). Compared to the original β200, we observed both an increase in equilibrium adsorption capacity and a decrease in the adsorption rate (Supplementary Table 4), indicating the occurrence of enhanced adsorption behavior during rate-limiting steps, such as intra-particle diffusion23. The maximum adsorption capacity of S-D-β200 for all (ultra-)short-chain PFASs was 1.41-2.26 times higher than that of β200 (Supplementary Fig. 6 and Table 5), suggesting an increase in accessible adsorption sites. The hydroxyl groups (confined water and Si-OH) in S-D-β200 were crucial for providing binding sites (Supplementary Fig. 7), where confined water clusters offered increased adsorption site to selectively bind with the hydrophilic heads of PFASs, leading to deionization (Iδ=9.00 ppm, (14.98, 5.98)) and re-exposure of partially hydrated Brönsted-acid sites (δ=2.91 ppm, Fig. 2e)22. Meanwhile, the shielding effect of confined water also helps to weaken the electrostatic repulsion between (ultra-)short-chain PFASs and S-D-β200, as well as other PFASs24. It is noteworthy that the adsorption capacity of S-D-β200 surpassed that of currently reported optimal adsorbents (Fig. 2f and Supplementary Table 6), such as NU-100025, and showed a comparative advantage (e.g., preparation costs and energy consumption) when compared to the latest electroassisted adsorption materials (i.e., P(A), P(A98F2), and P(A39T53F8))26. Moreover, S-D-β200 exhibited suitable (ultra-)short-chain PFAS (20 μg L-1) selectivity with only a 0%-10.9% decreased (Supplementary Fig. 8) when exposed to simulate environmental water samples (humic acid=2 mg L-1, NaCl=20 mg L-1), demonstrating its potential for practical applications.

To initiate the next hydroxyl cycle and degrade PFASs, the saturated S-D-β200 was calcined again via thermal treatment at 800 ℃. Four complete dynamic hydroxyl cycles were conducted using simulated environmental water samples (humic acid = 2 mg L-1, NaCl = 20 mg L-1), recovering 94.3%-101.3% of the adsorption capacity of S-D-β200 for (ultra-)short-chain PFASs (Supplementary Fig. 9). These results demonstrated that high-temperature (800 ℃) calcination effectively removes hydroxyl groups of confined water and Si-OH (Fig. 2a and Supplementary Fig. 2), while completely degrading PFASs27, thereby breaking the persistent PFASs cycle in the environment. In addition, the stability of the Si-O-Si framework, XRD crystal facets and pore structure of β200 were further confirmed after cycling (Fig. 2a, 2b and Supplementary Table 3), while the slightly increased specific surface area (12.5%) promoted the adsorption capacity for certain PFASs to a level that exceeds that of the original S-D-β200.

In summary, the proposed cyclic adsorption-regeneration scheme enables dynamic regulation of the hydrogen-bond network of confined water, addressing the inherent trade-off between efficiency and reusability through a non-immobilized combination strategy. Besides the demonstrated optimal structure (i.e., β200), other zeolites with varying pore sizes and surface hydrophilicity also exhibit similar dynamic hydroxyl cycles during the process (Supplementary Fig. 10), offering broader possibilities for implementing the dynamic hydroxyl cycle strategy and addressing more complex pollution issues.

Enhanced adsorption mechanism
The increased adsorption capacity of S-D-β200 is primarily attributed to the introduction of a confined water structure, as detailed in the previous section. To further clarify the confined water adsorption behavior, we constructed a three-phase full-atom model of “bulk water-confined water-zeolite” with a BEA structure (Si/Al ratio: 200). This model allowed us to demonstrate the structural differences before and after cyclic adsorption in the presence or absence of confined water (Supplementary Fig. 11). We quantified the adsorption free energy (i.e., potential of mean force, PMF) for (ultra-)short-chain PFASs from bulk water into β200 and S-D-β200 along the straight-channels21, revealing a characteristic two-stage transition in the mass-transfer energy landscape (Fig. 3a, 3b and Supplementary Fig. 12-15). Stage (1) involved the surface adsorption of PFAS molecules immobilized by zeolite, where the hydrophobic interactions derived the transfer of C-F chains onto the zeolite framework (Window #10 to #3). During this stage, the adsorption free energy of (ultra-)short-chain PFASs decreased significantly (e.g., -10.70 kcal mol-1 → -26.14 kcal mol-1 for perfluoroheptanoic acid (PFHpA) in β200, Fig. 3a), although hydrophilic homologues (e.g., trifluoroacetic acid (TFA)) benefited less from this process (Fig. 3c). Stage (2), involves the (ultra-)short-chain PFASs undergoing the pore diffusion process, during which the C-F chain progressed further along the channel while the hydrophilic head remined exposed to water (Window #3 to #0). Unlike the first stage, the energy gain from the interaction between the zeolite framework and the (ultra-)short-chain PFAS was insufficient to offset the substantial dehydration penalty (e.g., 23.72 to 3.81 for PFHpA, Supplementary Fig. 16), resulting in non-spontaneous diffusion within the nanochannel (e.g., -26.14 kcal mol-1 → 0 kcal mol-1 for PFHpA in β200). Interestingly, the pore adsorption energy barriers induced by the chain length of (ultra-)short-chain PFAS were markedly disparate in different range (Fig. 3c); for instance, as the chain length increased (chain length ≥ 4), the interaction energy raised concomitantly (i.e., perfluorobutane sulfonic acid (PFBS) → PFHpA), whereas as the chain length decreased (chain length ≤ 5), the steric effect became less pronounced (i.e., perfluoropentanoic acid (PFPeA) → TFA).

After enhancement by the cyclic adsorption scheme (Fig. 3b), introducing confined water reduced dehydration penalties (e.g., 7.93 vs. 1.83 for PFHpA, Supplementary Fig. 16) and surface binding energy state (-11.40 kcal mol-1 vs. -26.14 kcal mol-1 for PFHpA), resulting in a smoother overall solid-liquid mass transfer energy. Consequently, the simulation results suggest enhanced nanopore accessibility for all (ultra-)short-chain PFASs in S-D-β200, which aligns with the experimental observations showing an increasing in nanopore occupancy from 0.5% to 22% (Fig. 3d and 3e)25. Additionally, this enhancement generally improved the mass transfer state of PFASs, regardless of chain length and functional groups (Fig. 3c and Supplementary Fig. 12-15). This result differs from previous studies that indicated a hydrophilic binding pattern dominated by confined water20, suggesting the presence of other cooperative binding mechanisms (e.g., zeolite frameworks) in the S-D-β200 pore adsorption process.

To further elucidate the pattern of interaction in S-D-β200 nanopores, the stress mode of (ultra-)short-chain PFASs was investigated. Analysis of average non-covalent interactions and thermal fluctuations indicated that the confined water had a stable hydrogen bonding interaction with the hydrophilic head (i.e., -COO- or -SO -) of (ultra-)short-chain PFASs (blue isosurface, Fig. 3f and Supplementary Fig. 17). Meanwhile, the independent gradient model analysis revealed that the C-F chains reside in the zeolite a- and b- straight channels, and binding to the zeolite framework through van der Waals forces (green isosurface, Fig. 3g and Supplementary Fig. 18). These findings confirm that (ultra-)short-chain PFASs bind to both the zeolite framework and confined water, forming a unique double-binding pattern, which aligns with the results of 2D-NMR analysis results for S-D-β200 (Fig. 2e and Supplementary Fig. 19). Previous studies have demonstrated that the compact arrangement of long-chain PFASs within β zeolite nanochannels, along with hydrogen-bonded pairs in the intersections, serve as the foundation for their suitable selective adsorption21. In this work, through non-immobilized confined water structures, (ultra-)short-chain PFASs can achieve stable adsorption without hydrophilic head pairing, further expanding the application potential of zeolites. Furthermore, we quantified interaction strength of the zeolite framework and the confined water towards PFASs by the sum δg index, radial distribution function (G(r)), and coordination number (N(r)) (Fig. 3h and Supplementary Fig. 20). Interestingly, the confined water interaction strength (G(r)) was negatively correlated with chain length (e.g., C3 > C4) and functional group (e.g., -COO- > -SO -). In contrast, the interaction strength with the zeolite framework (δg) was positively correlated with chain length (e.g., C4 > C3) and functional group (e.g., -COO- < -SO -). The difference between these two binding modes may be the potential reason that the enhanced pore adsorption process of S-D-β200 does not specific respond to the PFAS structure. This was demonstrated by further density functional theory analyses, which revealed that the trend of the binding energy change of (ultra-)short-chain PFASs after double binding, achieved by donating electrons (0.389 e-0.457 e) to both the zeolite framework and the confined water, is consistent with that of PMF (Fig. 3c and Supplementary Fig. 21-23). Meanwhile, we further expanded the molecular dynamics model to the equilibrium state (Supplementary Fig. 24-25). The results demonstrated the dominant role of the dual-binding pattern in the adsorption of (ultra-)short-chain PFASs by S-D-β200, especially for chain lengths less than 6 (pore adsorption ratio: 71.1-83.0%). In nearly saturated S-D-β200 nanopores, the hydrophobic tails of (ultra)short-chain PFASs are bound by zeolite channels, whereas the hydrophilic heads converge at confined water clusters and carry cations to eliminate electrostatic repulsion (charge compensation rate: 92.0-101.6%).

Full-scale application
In our scenario, the dynamic hydroxyl cycle scheme enables direct installation of S-D-β200 in existing domestic purifiers, providing a low-cost and in-site resolution to the crisis associated with (ultra-)short-chain PFASs. In a proof-of-concept experiment, we substituted the compressed activated carbon (CAC) adsorption column in the final stage of a full-scale three-stage domestic water purifier with a custom-designed S-D-β200 adsorption column (Fig. 4a, 4b, and Supplementary Fig. 26). Whole-process simulation experiments were conducted over a continuous period of 182 days, simulating real household water consumption patterns (8 L day-1, Fig. 4c)28 and using the highest reported concentrations (Supplementary Table 7) of (ultra-)short-chain PFASs in potable water as documented in various studies29,30. In this full-scale simulation (Supplementary Fig. 27), the dynamic hydroxyl purifier achieved an average removal efficiency for (ultra-)short-chain PFASs ranging from 73% to 95%, which surpasses the performance of the commercial purifier (44%-90%) and shows promising potential as a viable alternative to the most efficient reverse osmosis purifiers (75%-99%)31. The dynamic hydroxyl purifier effectively reduced concentrations of (ultra-)short-chain PFASs in real potable water to meet the proposed EPC health standard (estimated at 450 ng L-1 based on 90% of reported general abundance levels) within approximately 6 months (179 days)5,6. This reduction significantly mitigated the potential risk of PFAS exposure associated with the utilization of the commercial purifier (0-day, Fig. 4d). Notably, the evaluation result obtained under the highest PFAS load and showed no effect on other decontamination capacities, such as removal of dissolved organic matter and heavy metal (Supplementary Table 8), indicating its potential to effectively address most potable water treatment demands. Furthermore, the proposed dynamic hydroxyl cycle scheme introduces only water as an enhanced medium in the traditional adsorption-desorption process (Fig. 1a and 1b) and offers suitable reusability (Supplementary Fig. 9), significantly reducing the overall cost of the adsorption process.

Methods
Materials
To evaluate the adsorption efficiency of dynamic hydroxyl cycling schemes, 8 typical ultra-short-chain PFASs (C-F number: 1-6), trifluoroacetic acid (TFA, 99%, Aladdin, Shanghai, China), perfluoropropionic acid (PFPrA, 97%, Aladdin, Shanghai, China), perfluorobutanoic acid (PFBA, 98%, Macklin, Shanghai, China), perfluorobutane sulfonic acid (PFBS, 98%, Macklin, Shanghai, China), perfluoropentanoic acid (PFPeA, 97%, Macklin, Shanghai, China), perfluorohexanoic acid (PFHxA, 98%, Macklin, Shanghai, China), perfluorohexane sulfonic acid (PFHxS, 95%, Macklin, Shanghai, China), and perfluoroheptanoic acid (PFHpA, 95%, Macklin, Shanghai, China), were selected in this study. These (ultra-)short-chain PFASs exhibit a range of structural variations, including differences in chain length and functional groups (Supplementary Table 2), which allow for a comprehensive evaluation of the adsorption efficiency for dynamic hydroxyl cycle and the establishment of a fundamental response law governing the structural characteristics of (ultra-)short-chain PFASs. Concurrently, these ultra-short-chain PFAS are markedly prevalent in the environment4-6 and constitute a substantial proportion of the total PFAS pollution6, which is of considerable importance for the assessment of the practical applicability of dynamic hydroxyl cycling.

To evaluate the effect of crystal configuration on dynamic hydroxyl cycling schemes, three commercial zeolites (Zhuoran Environmental Protection Co., Ltd, Dalian, China) with the same Si/Al ratio (200) but different crystal types (Z200 of MFI crystal, β200 of BEA crystal, and Y200 of FAU crystal) was selected to conduct relevant experiments. The pore sizes (supercage) of the three zeolites were 0.51-0.56 nm, 0.56-0.77 nm and 0.74-1.12 nm, respectively (Supplementary Table 1), creating nanospaces of different sizes for confined water32. Meanwhile, the surface hydrophilicity of zeolite is controlled by the ratio of Si and Al atoms in its framework; the higher the Si/Al ratios, the more hydrophobic the zeolite33. Therefore, five BEA zeolites with different Si/Al ratios (β25, β68, β150, β200, and β600) were selected for the relevant experiments (Supplementary Table 1), which provide a platform for studying the response of confined water enhanced effect to zeolites’ hydrophilicity (varying Si/Al ratio in the range of 25-600).

Other reagents were purchased in reagent grade from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used without further purification, unless otherwise described.

Dynamic hydroxyl cycling
To simulate the structure of the regenerated zeolites, the commercial zeolites were thermally treated as follows. First, commercial zeolite was stirred in ultra-pure water at room temperature for 4 h, repeated three times, and then dried in a blast drying oven at 70 ℃ for 12 h, in a vacuum drying oven at -1.0 MPa, dried at 105 ℃ for 6 h, and finally calcined in a muffle furnace (Thermo Scientific, USA) at 800 ℃ for 6 h (10 ℃ min-1). Defunctionalized zeolites add "D-" before their names, for example “D-β200”.

To circumvent the hindrance posed by liquid surface tension, a water vapor diffusion method was employed to construct confined water structures at the zeolite nanopores in situ34. The specific steps were as follows: the defunctionalized zeolite was placed in a vacuum drying oven for vacuum degassing for 12 h and then immediately placed in a closed space with high humidity (relative humidity of 90% to 100%) for water vapor diffusion for 24 h to achieve confined water self-assembly. Subsequently, the sample was transferred to pure water and left to stand overnight to stabilize the confined water structure. Finally, excess surface moisture was evaporated at 40 °C for 20-30 min. Confined water-encapsulated zeolites are preceded by the addition of “S-”, for example “S-D-β200”.

Confined water-encapsulated zeolites were evaluated using different adsorption experiments to determine the adsorption performance and behavior for (ultra-)short-chain PFASs, including removal efficiency, adsorption kinetics, adsorption isotherms, and competitive adsorption experiments. Details of experiments and (ultra-)short-chain PFAS measurements are listed in the Supplementary method 1-4.

Saturated zeolites were heated in a muffle furnace at a rate of 10 ℃ min-1, until the temperature reached 800 ℃. The temperature was maintained at a constant level for 6 h to ensure full degradation of the PFASs. Subsequently, the zeolite samples were allowed to cool foe an adequate period, resulting in a temperature that was consistent with that of the surrounding environment. Finally, related adsorption experiments were performed to determine the removal efficiency of (ultra-)short-chain PFASs.

During the process, the materials were characterized at several stages to identify chemical and other characteristics. The details of the material characterization are available in Supplementary method 5.

Molecular dynamics simulation
To understand the mass energy transfer state and binding mode of (ultra-)short-chain PFASs in zeolite, a “zeolite-bulk water-confined water” three-phase periodic model was constructed, as shown in Supplementary Fig.11. Specifically, a supercell consisting of 3×3×3 BEA zeolite crystal cells was placed in the middle of the simulated box, cut along the 010 and 001 crystal faces, and compensated for unsaturated silicon-oxygen bonds with hydroxyl (-OH) groups35. Based on the ζ potential and the Gouy-Chapman formula (Equations 1 and 2), the surface charge densities of β200 and S-D-β200 were calculated to be -0.11 C m-2 and -0.105 C m-2, respectively36. Therefore, two Si-OH groups were randomly deprotonated, resulting in a negatively charged zeolite surface.

Fξ
sinh( )
σ=-εκξ E 2RT (1)
Fξ
R2RT
P
1⁄
κ-1=( εRT ) 2 (2)
2F2C0
where ε (6.933 × 10-10 F m-1) is the permittivity, κ-1 (m) is the Debye length, ξ (V) is the ζ potential, F (96485 C mol-1) is the Faraday constant, R (8.3145 J (mol × K)-1) is the gas constant, and C (mol m-3) is the concentration of the electrolyte.
0
The zeolite structure was constructed according to the BEA zeolite in the International Zeolite Association database, and a certain number of Si atoms was randomly replaced by Al atoms to obtain a β200 molecular sieve model with a Si/Al ratio of 200. The distribution of Si and Al is assigned according to two rules: Lowenstein's rule requires avoiding Al-O-Al bonds37, and Dempsey's rule requires the maximum separation of Al atoms given the Si/Al ratio38. After replacement, the generated negative charge is compensated by hydrogen protons, and the specific standard is implemented in reference35. Under the periodic boundary condition, water molecules were placed at both ends of the zeolite cutting surface, and their density met the standard of 303 K and 1 atm.

The CVFF model was used to describe the zeolite structure. The (ultra-)short-chain PFAS molecules were constructed utilizing the OPLS-AA model, and Na+ was incorporated to neutralize the system charge. The SPC/E model was used to describe the water molecules. The LAMMPS software package was used for molecular dynamics simulation. 12-6 Lennard-Jones empirical force field and geometric mixing rules were used to calculate the van der Waals interactions between the non-bonded atoms. The specific equations are shown in (3), (4), and (5).

12 6
U(r )=4ε [( σij) -( σij) ] (3)
ij ij
rij rij
ε =√εε (4)
ij i j
σ =√σσ (5)
ij i j
where r is the distance between particles, σ is the radius of the minimum potential energy, ij and ε is the depth of the potential well.

For the van der Waals interaction, a 10 Å cutoff distance was implemented. The particle-particle-particle-mesh method was employed to evaluate the long-range Coulomb interaction, with a 10-4 kcal mol-1 convergence tolerance. All simulations were conducted under NVT conditions, with temperature maintained at 303 K using the Nose-Hoover thermostat. Prior to running the simulation, the system’s energy was minimized. Subsequently, a 1 ns equilibration was performed using a 1 fs time step.

Potential of mean force (PMF) calculation
To further obtain the binding free energy variation of the adsorption pathway of (ultra-)short-chain PFASs into nanopores, the PMF was calculated using the umbrella sampling method39-41. The process of (ultra-)short-chain PFASs adsorbing from bulk water onto zeolite nanopores was segmented into an average of 11 reaction windows, with each window separated by 2 Å along the Z axis. Once equilibrium was achieved in the system, a steered molecular dynamics technique employing a harmonic potential (spring constant of 25 kcal mol∙Å-1, tension velocity of 0.001 Å fs-1) was utilized to drag the (ultra-)short-chain PFASs into a designated reaction window. Subsequently, the (ultra-)short-chain PFASs were stabilized at the reaction window for a 300 ps equilibrium period using a harmonic potential with a low spring constant (2 kcal (mol × Å)-1). The simulation was then extended for an additional 100 ps, during which the PFAS reaction coordinates were documented every 100 fs. The data from the reaction coordinate was transformed into PMF free energy by weighted histogram analysis41:

W = −K ×T×lnP (6)
window b window
where K is the Boltzmann constant, T is the temperature, and P is the probability of b window finding (ultra-)short-chain PFASs at the observation window.

Average non-covalent interaction (aNCI) calculation
The aNCI method proposed by Wu et al.42 was used to analyze the average non-covalent interactions of (ultra-)short-chain PFASs in dynamic systems. The principle of the aNCI method is to show the weak interaction region by the reducing density gradient (RDG) function isosurface and then project the sign(λ )rho function onto the RDG isosurface of different colors to show the 2 S type of weak interaction43. The electron density, electron density gradient, and electron density Hessian matrix used to calculate the RDG and sign(λ )rho functions were obtained by averaging 2 R the multi-frame trajectory structure43. Blue, green, and red represent hydrogen bond, van der Waals interactions, and steric effects, respectively. The average RDG was calculated using the following Equation (7):

̅̅̅
D
̅̅
G
̅̅(̅̅
v
̅̅)= 1 ǀ∇̅̅ρ̅̅(̅r̅)̅ǀ
(7)
2(3π2) 1/3 ρ̅̅(̅̅r̅) 4/3
where 𝜌(𝑟) is the average electron density, ∇𝜌(𝑟) is the average electron density gradient.
Additionally, the average RDG method defines a thermal fluctuation index (TFI) to represent the stability of weak interactions in different regions42. TFI is mapped to the average RDG equivalence surface using different colors, and the stability of the weak interaction in other regions can be judged by the colors43. A bluer isosurface indicates a more stable interaction, whereas a redder isosurface indicates an unstable one. TFI was calculated using Equation (8):

std({ρ })
TFI= i(r) (8)
aνg({ρ })
i(r)
where avg({ρ }) and std({ρ }) are the mean and variance, respectively, of the electron i(r) i(r) density of the entire trajectory. The optimal structure for aNCI analysis was obtained by molecular dynamics simulations. The (ultra-)short-chain PFAS molecules were fixed, and equilibrium simulations were performed for 1 ns. The aNCI analysis used structures from the last 2000 frame trajectories. All the aNCI and TFI calculations were performed using the Multiwfn package (version 3.8).

Independent gradient model (IGM) calculation
In this study, we used the IGM method proposed by Hénon et al.44 to analyze the interactions between (ultra-)short-chain PFASs and zeolite framework. In IGM analysis, the δginter isosurface is often used to visualize the interaction region. Meanwhile, the sign(λ )ρ function is usually 2 mapped in different colors on the isosurface to intuitively characterize the nature of the interaction. The sign(λ )ρ represents the product of the sign(λ ), the second-largest eigenvalue of the Hessian 2 2 matrix of electron density ρ, and ρ. The ρ of the interaction region is generally positively correlated with the interaction strength, and the sign(λ ) has the ability to distinguish whether the interaction 2 is attractive or repulsive45. The color criterion of the IGM analysis was consistent with aNCI. δginter was calculated using Equations (9), (10), and (11):

ginter(r)=|∑ ∑ ∇ρfree(r)| (9)
A i∈A i
gIEGM,inter(r)=∑ |∑ ∇ρfree(r)| (10)
A i∈A i
δginter(r)=gIGM,inter(r)-ginter(r) (11)
where ginter is the size of superposition of all debris density gradients, gIGM, inter is the sum of the size of all debris density gradients, A loops through all fragments, and i loops through all atoms in the corresponding fragment. IGM calculations were performed using the Multiwfn package (version 3.8).

Radial distribution function (RDF) calculation
To investigate the intensity of the interaction between the confined water and (ultra-)short-chain PFASs, the RDF between their atomic pairs were calculated46,47. The RDF estimates the density of a pair of atoms at a given distance using Equation (12):

G(r)=Vρ(r)/4Nπr2∆r (12)
where V is the system volume, ρ(r) is the number of atomic pairs found in the range of r to r+∆r shell, and N is the total number of selected atomic pairs. The G(r) peak indicates the frequency of the occurrence of the atom pair and can be used to infer the interaction strength between the two atoms.

Coordination number calculation
The coordination number represents the number of corresponding molecules within each spherical coordination range of the selected atom46,47. Specifically, integrating G(r) in spherical coordinates with the first minimum value of the RDF yields the coordination number of the corresponding molecule. The specific Equation (13) for calculating the coordination number is as follows.

N(r')=4πρ∫
r'
G(r)r2dr (13)
0
where r' is the cutoff distance of the solvent layer, ρ is the system density, and G(r) is the radial distribution function of the selected atomic pair.

Density functional theory (DFT) calculation
The DFT calculations were carried out using DMol3 modules of Material Studio. The generalized gradient approximation (GGA) method with Perdew-Burke-Ernzerhof (PBE) function was employed to describe the interactions between core and electrons. Spin-polarization with DFT semi-core Pseudopots was included in all calculations. It is essential to take into account the van der Waals forces for adsorption. Hence, the Tkatchenko-Scheffler (TS) method for DFT-D correction was used for this purpose. Double numerical plus polarization (DNP) functions were adopted as the basis set. The force and energy convergence criterion were set to 0.002 Ha Å-1 and 10-5 Ha, respectively. When the optimization was completed, the binding energy (ΔE) was calculated as Equation (14).

ΔE=27.212×(E -E -E ) (14)
total 1 2
where the E is the energy of the optimized system; E is the energy of the S-D-β200; E is total 1 2 the energy of (ultra-)short-chain PFASs.

Full-scale water purification
In this study, a full-scale water purifier was constructed to evaluate the removal efficiency of (ultra-)short-chain PFASs from potable water using S-D-β200. The full-scale water purifier employed a three-stage treatment process (size: 36 cm×33 cm×13 cm), including polypropylene (PP) cotton filtration (filtration accuracy: 1 μm, size: 25.4 cm×6 cm, Anhui Letou Water Purification Technology Co., Ltd., China), granular activated carbon (size: 25 cm×7 cm, Anhui Letou Water Purification Technology Co., Ltd., China), and the confined water enhanced zeolite (i.e., S-D-β200, size: 25 cm×7 cm). A commercial household water purifier was also tested as a control, including PP cotton filtration, granular activated carbon, and compressed activated carbon.

The experimental operation mode of the full-scale water purifier was based on the water intake pattern of an ordinary 4-member family, as shown in Fig. 4c. Potable water treatment was carried out at breakfast, lunch, and dinner times every day for 0.5 h, 2 h, and 1.5 h respectively. The influent flow rate was controlled at 2 L h-1 to obtain the recommended drinking water intake of 8 L per day for 4 people28. In addition, a 10-min backwash was carried out in the early morning hours of each day to prevent adsorption column clogging and biofilm formation. To prevent nanosized zeolite particles from causing excessive pressure drop in the adsorption column, commercial β200 spherical zeolite (particle size: 0.4-0.9 mm, Dalian Zhuoran Environmental Protection Technology Co., Ltd., China) was used in the full-scale water purifier.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Ren and co-workers have presented a notable advancement in PFAS removal through a nonimmobilized dynamic hydroxyl cycling strategy that utilizes only water to circularly drive commercial zeolite adsorption-regeneration processes. This approach efficiently and sustainably removes a range of (ultra-)short-chain PFAS (C-F number: 1-6) from potable water. The study highlights enhanced nanopore accessibility and the formation of a “zeolite framework-confined water” dual-binding mode, resulting in a modified zeolite with one of the highest reported adsorption capacities (233.82–733.13 mg/g). Additionally, the proposed methodology holds promise as a low-cost, in situ upgrade for existing water purifiers, offering the potential to provide safe drinking water in underdeveloped regions through 179 days of full-scale purification. While this work represents a significant contribution, there are several issues that warrant further clarification and discussion. From the perspective of this reviewer, the publication of this manuscript in Nature Communications should be reconsidered following major revisions.\n\n1. The manuscript states that “High-resolution transmission electron microscopy images of the D-β200 confirmed the preservation of particle morphology and microporous structure (Fig. 2C).” However, it is crucial to quantitatively measure the pore size and provide additional evidence to substantiate the claim of a microporous structure.\n\n2. Please demonstrate the chemical transformation process underlying the dynamic hydroxyl cycle process.\n\n3. Is it possible to demonstrate or model the structure of the confined water hydrogen-bond network?\n\n4. The manuscript states that “The hydroxyl groups in S-D-β200 were crucial for providing binding sites (Fig. 2E), where confined water molecular clusters selectively bind to the hydrophilic heads of PFASs.” However, the distinction between the roles of hydroxyl groups and confined water in PFAS adsorption is unclear. From our viewpoint, both may bind to the hydrophilic heads of PFAS through hydrogen bonding.\n\n5. In Table S5, the authors compare the PFAS adsorption capacity of NU-1000. While this comparison is useful, many other MOFs have been studied for PFAS adsorption. Please give a comprehensive summary of these adsorbents.\n\n6. The manuscript reports that the PFAS adsorption capacity of S-D-β200 can exceed 100% after regeneration over different cycles. Please offer a detailed explanation of the underlying reasons for this phenomenon, as it appears to deviate from typical adsorption-regeneration behavior.", "reviewer_2": "This manuscript investigates an adsorption-regeneration strategy for removing ultra-short-chain PFAS from potable water using commercially available zeolites and water-based dynamic hydroxyl cycling. They utilize a multifaceted approach comprising bench-scale experiments, coarse-grained simulations, and pilot-scale investigations to rigorously validate the proposed methodology.\nSuch alternative strategy has a significant potential, and the manuscript has a good quality of research. To conclude, the content of the paper is publishable with following edits:\n1. The computational approach based on LAMMPS software has yielded promising results. It might be beneficial to include ab initio-level approaches (such as Density Functional Theory, DFT) to further validate the dual-binding mode of PFAS removal, particularly for more detailed insight into the system's electronic structure and binding interactions.\n2. It might be useful to look into works by Prof. Wriedt and Prof. Farha, specifically published in Chemistry of Materials in 2021, which explores removal of short-chain PFAS using porous materials."}, "author_response": "Response to reviewers\nReviewer #1’s comments:\nRen and co-workers have presented a notable advancement in PFAS removal through\na nonimmobilized dynamic hydroxyl cycling strategy that utilizes only water to\ncircularly drive commercial zeolite adsorption-regeneration processes. This approach\nefficiently and sustainably removes a range of (ultra-)short-chain PFAS (C-F number:\n1-6) from potable water. The study highlights enhanced nanopore accessibility and the\nformation of a “zeolite framework-confined water” dual-binding mode, resulting in a\nmodified zeolite with one of the highest reported adsorption capacities (233.82–733.13\nmg/g). Additionally, the proposed methodology holds promise as a low-cost, in situ\nupgrade for existing water purifiers, offering the potential to provide safe drinking\nwater in underdeveloped regions through 179 days of full-scale purification. While this\nwork represents a significant contribution, there are several issues that warrant further\nclarification and discussion. From the perspective of this reviewer, the publication of\nthis manuscript in Nature Communications should be reconsidered following major\nrevisions.\nResponse: Thank you for the excellent suggestions and critical examinations that\ngreatly improved the quality of this manuscript after revision. Please also see our point-\nby-point responses to your comments, which we have carefully considered and revised\nthe manuscript accordingly.\n1. The manuscript states that “High-resolution transmission electron microscopy\nimages of the D-β200 confirmed the preservation of particle morphology and\nmicroporous structure (Fig. 2C).” However, it is crucial to quantitatively measure the\npore size and provide additional evidence to substantiate the claim of a microporous\nstructure.\nResponse: We appreciate your valuable suggestion. To address this concern, the BET\nmethod (N adsorption-desorption, ASAP 2460) was used to test the average pore\ndiameter and pore volume of the β200 before and after calcination (Table R1). The\nresults show that the average pore diameter (4.1%) and pore volume change rate of D-\nβ200 after calcination were less than 5%, which proves the stability of the micropore\nstructure of zeolite. We have added relevant data and information to the manuscript.\nThank you again for your valuable comment.\nTable R1. Specific surface area and pore structure of β200 and D-β200.\nSample S (m2/g) b D (nm) c V (cm3/g) d\nBET P P\nβ200 588.30 1.894 0.268\nD-β200 637.81 1.971 0.271\nCR a 8.4% 4.1% 1.1%\na CR: Rate of change relative to β200.\nb S : Brunauer-Emmett-Teller (BET) specific surface area.\nBET\nc D : Average pore diameter.\nP\nd V : Total pore volume.\nP\nRevisions (in the marked manuscript):\n1. “High-resolution transmission electron microscopy images of the D-β200 confirmed\nthe preservation of particle morphology and microporous structure (Fig. 2C)” in Line\n117-119 was changed to “High-resolution transmission electron microscopy images\nand pore size analysis of the D-β200 confirmed the preservation of particle morphology\nand microporous structure (1.894 nm vs. 1.971 nm, Fig. 2C and Supplementary Table\nS3)”.\n2. Table S3 was added to Supplementary information.\nTable S3. Specific surface areas and pore structures of zeolites during the dynamic\nhydroxyl cycle.\nSample S (m2/g) c D (nm) d V (cm3/g) e\nBET P P\nβ200 588.30 1.894 0.268\nD-β200 637.81 1.971 0.271\nCR a 8.4% 4.1% 1.1%\nRecycle 717.64 2.052 0.282\nCR b 12.5% 4.1% 4.1%\na CR: Rate of change relative to β200.\nb CR: Rate of change relative to D-β200.\nc S : Brunauer-Emmett-Teller (BET) specific surface area.\nBET\nd D : Average pore diameter.\nP\ne V : Total pore volume.\nP\nR2\n2. Please demonstrate the chemical transformation process underlying the dynamic\nhydroxyl cycle process.\nResponse: Thank you for pointing this out. The dynamic hydroxyl cycle includes two\naspects: the Si-OH and confined water hydrogen-bond network. In this study, we\nsuccessfully demonstrated the \"construction-utilization-removal\" dynamic cycle\nbehavior of the confined water hydrogen-bond network and Si-OH in the adsorption-\nregeneration process using attenuated total reflection Fourier infrared spectroscopy\n(ATR-FTIR, Figure 2A). The removal and reconstruction of Si-OH groups mediated by\nheat (regeneration) and water are involved in chemical transfer. To further explain the\nunderlying mechanism, we reveal the chemical transfer of “Si-OH→ Si-O-Si→ Si-OH”\nusing 29Si cross-polarized NMR and X-ray photoelectron spectroscopy (XPS, Fig. R1).\nAfter thermal (regeneration) treatment, the resonance band (-99 ppm) and XPS peak\n(532.4 eV) attributed to Si-OH in D-β200 disappeared, while the Si-O-Si resonance\nband (-108 ppm and -117 ppm) and XPS peak (533.4 eV) occupied all elemental forms1-\n3. These results indicate that the adjacent Si-OH of zeolite underwent dehydration\ncondensation after heat treatment, forming Si-O-Si bonds and increasing the surface\nhydrophobicity. However, after S-D-β200 was subjected to water vapor diffusion, the\nSi-OH resonance and XPS peaks reappeared in similar proportions, indicating that Si-\nO-Si produced by previous condensation was hydrolyzed under water vapor exposure.\nTherefore, the above experimental results demonstrate the chemical transfer process of\nSi-OH in the dynamic hydroxyl cycle. Meanwhile, the hydrophilicity/hydrophobicity\nof the zeolite surface can be dynamically regulated by this cycle, becoming\nhydrophobic to promote diffusion during water vapor encapsulation and becoming\nhydrophilic to prevent particle agglomeration and enhance the adsorption of\n(ultra-)short-chain PFASs during utilization. We have added relevant results and\ndiscussion. Thank you again for your valuable comment.\nR3\nFig. R1. Chemical transfer process of Si-OH in the dynamic hydroxyl cycle. (A) 29Si\nMAS NMR spectra of β200, D-β200, and S-D-β200; (B) X-ray photoelectron spectra\n(XPS) of β200, D-β200, and S-D-β200; (C) schematic diagram of the change in zeolite\nSi-OH during the dynamic hydroxyl cycle.\nRevisions (in the marked manuscript):\n1. “These results demonstrated that water vapor encapsulation created a confined water\nstructure in the β200 nanopore and achieved orderly regulation of the hydrophilicity/\nhydrophobicity (Si-OH and Si-O-Si) of the zeolite surface through the chemical transfer\nof water molecules (Supplementary Fig. S3)” was added in Line 127-130.\n2. Fig. R1 was added in Supplementary information as Fig. S3.\n3. “To further explain the chemical transfer of “Si-OH→ Si-O-Si→ Si-OH”, 29Si cross-\npolarized NMR and X-ray photoelectron spectroscopy (XPS, Supplementary Fig. S3)\nwere performed. After thermal (regeneration) treatment, the resonance band (-99 ppm)\nand XPS peak (532.4 eV) attributed to Si-OH in D-β200 disappeared, while the Si-O-\nSi resonance band (-108 ppm and -117 ppm) and XPS peak (533.4 eV) occupied all\nelemental formsS4-S6. These results indicate that the adjacent Si-OH of zeolite\nunderwent dehydration condensation after heat treatment, forming Si-O-Si bonds and\nR4\nincreasing the surface hydrophobicity. However, after S-D-β200 was subjected to water\nvapor diffusion, the Si-OH resonance and XPS peaks reappeared in similar proportions,\nindicating that Si-O-Si produced by previous condensation was hydrolyzed under water\nvapor exposure. Therefore, the above experimental results demonstrate the chemical\ntransfer process of Si-OH in the dynamic hydroxyl cycle. Meanwhile, the\nhydrophilicity/hydrophobicity of the zeolite surface can be dynamically regulated by\nthis cycle, becoming hydrophobic to promote diffusion during water vapor\nencapsulation and hydrophilic to prevent particle agglomeration and enhance the\nadsorption of (ultra-)short-chain PFASs during utilization” was added in\nSupplementary information, Page S10.\n4. “After calcination at 800 ℃, the Si-OH characteristic peak (954 cm-1) in the infrared\nspectrum of D-β200 zeolite disappeared, indicating high-temperature-induced ortho-\nhydroxyl condensation (Fig. 2A) and a reduction in surface polarity (ζ potential: -43.3\nmV→-16.6 mV, Fig. S2)” in Line 110-114 was changed to “After calcination at 800 ℃,\nthe Si-OH characteristic peak (954 cm-1) in the infrared spectrum of D-β200 zeolite\ndisappeared, indicating high-temperature-induced ortho-hydroxyl condensation (Fig.\n2A and Supplementary Fig. S3) and a reduction in surface polarity (ζ potential: -43.3\nmV→-16.6 mV, Supplementary Fig. S2)”.\n5. “After this construction process, the characteristic peaks of the confined water\nhydrogen-bond network (3750 cm-1-3000 cm-1) and Si-OH (954 cm-1) appeared in the\ninfrared spectrum of S-D-β200, providing evidence for the successful loading of\nconfined water and the rehydration of the unsteady Si-O-Si bonds (ζ potential: -16.6\nmV→-41.6 mV, Fig. S2)” in Line 122-127 was changed to “After this construction\nprocess, the characteristic peaks of the confined water hydrogen-bond network (3750\ncm-1-3000 cm-1) and Si-OH (954 cm-1) appeared in the infrared spectrum of S-D-β200,\nproviding evidence for the successful loading of confined water and the rehydration of\nthe unsteady Si-O-Si bonds (ζ potential: -16.6 mV→-41.6 mV, Supplementary Fig. S2\nand S3)”.\n6. “X-ray photoelectron spectroscopy\nThe change in surface states during dynamic hydroxyl cycle was characterized by\nR5\nX-ray photoelectron spectroscopy (XPS, K-Alpha, Thermo Scientific, USA). Samples\nwere analyzed using an Al Kα X-ray source. All binding energies were referenced to\nthe organic contaminant C1s peak at 284.8 eV to compensate for surface charging\neffects. The XPS Peak 4.1 software package was used to fit the XPS peaks, and a\nconstant fullwidth at half-maximum was maintained for all components in a particular\nspectrum” was added in Supplementary information as part of Supplementary\nnote S4.\n7. “Solid-state nuclear magnetic resonance (NMR) spectra\nCross-polarization (CP) 29Si-MAS NMR experiments were performed using a 400\nMHz NMR spectrometer (Bruker, Germany) and a 7 mm probe. The spin rate was 10\nKHz, recovery time was 4 s, and pre-scan delay was 6.5 μs” was added in\nSupplementary information as part of Supplementary note S4.\n8. “Prodinger, S. et al. Improving Stability of Zeolites in Aqueous Phase via Selective\nRemoval of Structural Defects. J. Am. Chem. Soc. 138, 4408-4415 (2016)” was added\nin Supplementary information as Supplementary references.\n9. “Zhu, Z., Xu, H., Jiang, J., Wu, H. & Wu, P. Hydrophobic nanosized all-silica beta\nzeolite: efficient synthesis and adsorption application. ACS Appl. Mater. Interfaces 9,\n27273-27283 (2017)” was added in Supplementary information as Supplementary\nreferences.\n10. “Wang, X., Wang, K., Plackowski, C. A. & Nguyen, A. V. Sulfuric acid dissolution\nof 4A and Na-Y synthetic zeolites and effects on Na-Y surface and particle properties.\nAppl. Surf. Sci. 367, 281-290 (2016)” was added in Supplementary information as\nSupplementary references.\nReferences:\nStructural Defects. J. Am. Chem. Soc. 138, 4408-4415 (2016).\nefficient synthesis and adsorption application. ACS Appl. Mater. Interfaces 9, 27273-27283 (2017).\nNa-Y synthetic zeolites and effects on Na-Y surface and particle properties. Appl. Surf. Sci. 367,\n281-290 (2016).\nR6\n3. Is it possible to demonstrate or model the structure of the confined water hydrogen-\nbond network?\nResponse: Thank you for your suggestion. Owing to the limitations of nanoscale sizes,\ndirect observation of confined water structures remains a challenge. Therefore, in this\nwork, we adopted two methods, attenuated total reflection Fourier infrared\nspectroscopy (ATR-FTIR) and two-dimensional magic angle spinning solid-state\nnuclear magnetic resonance (2D-MAS-NMR), to characterize the structure of confined\nwater. By ATR-FTIR (Figure 2A), we identified the characteristic peaks (3750 cm-1-\n3000 cm-1) attributed to the hydrogen-bonded network of confined water, confirming\nthe successful loading of the confined water structure within the zeolite nanopores.\nFurthermore, 1H-1H single/double quantum 2D-NMR spectroscopy revealed two\ndistinct configurations of confined water within the zeolite nanopores: water molecular\nchains (δ=1.04 ppm) at the channels and water clusters (δ=5.54 ppm) at the\nintersections (Figure 2D). These results form the basis of our understanding of the\nconfined water structure in S-D-β200. Based on your suggestions and for further\nunderstanding, we used molecular dynamics simulations to model the structure of the\nconfined water hydrogen-bond network (Fig. R2A). The simulation results proved that\nthe confined water molecules were connected by hydrogen bonds to form molecular\nchains and clusters in channels and intersections, respectively, and cross-linked to form\na network structure. Therefore, the confined water molecules formed a different number\nof hydrogen bonds in the pores, and more binding sites were exposed, which was also\nconsistent with the FTIR results of further deconvolution analysis (HB0:3146 cm-1,\nHB1: 3268 cm-1, HB2: 3388 cm-1, HB3: 3480 cm-1, and HB4: 3617 cm-1, Fig. R2B)1,2.\nThese results strongly indicated the formation of a hydrogen-bond network of confined\nwater in the zeolite. We have added the relevant results to the manuscript. Thanks again\nfor your valuable comment.\nR7\nFig. R2. (A) Diagram of hydrogen-bond network in confined water; (B) the distribution\nof water species and the corresponding water bands in the S-D-β200 as derived from\ndeconvolution.\nRevisions (in the marked manuscript):\n1. Fig. R2 was added in Supplementary information as Fig. S4.\n2. “To further understand the hydrogen-bond network of confined water, we used\nmolecular dynamics simulations to model the structure of confined water\n(Supplementary Fig. S4A). The simulation results proved that the confined water\nmolecules were connected by hydrogen bonds to form molecular chains and clusters in\nchannels and intersections, respectively, and cross-linked to form a network structure.\nTherefore, the confined water molecules formed a different number of hydrogen bonds\nin the pores and more binding sites were exposed, which was also consistent with the\nFTIR results of further deconvolution analysis (HB0:3146 cm-1, HB1: 3268 cm-1,\nHB2: 3388 cm-1, HB3: 3480 cm-1, and HB4: 3617 cm-1, Supplementary Fig. S4B)S7,S8. These\nresults strongly indicated the formation of a hydrogen-bond network of confined water\nin the zeolite” was added in Supplementary information, Page S11.\n3. “These results confirm that the confined water modified the zeolite cavity\nR8\nenvironment in a non-immobilized manner and formed a hydrophilic center of water\nclusters at the intersections of channels” in Line 140-143 was changed to “These\nresults confirm that the confined water modified the zeolite cavity environment in a\nnon-immobilized manner and formed a hydrophilic center of water clusters at the\nintersections of channels (Supplementary Fig. S4)”.\n4. “Disalvo, E. A. & Frias, M. A. Water state and carbonyl distribution populations in\nconfined regions of lipid bilayers observed by FTIR spectroscopy. Langmuir 29, 6969-\n6974 (2013)” was added in Supplementary information as Supplementary\nreferences.\n5. “Sun, Y., Yu, F., Li, C., Dai, X. & Ma, J. Nano-/Micro-confined water in graphene\nhydrogel as superadsorbents for water purification. Nano-Micro Lett. 12, 2 (2019)” was\nadded in Supplementary information as Supplementary references.\nReferences:\nregions of lipid bilayers observed by FTIR spectroscopy. Langmuir 29, 6969-6974 (2013).\nsuperadsorbents for water purification. Nano-Micro Lett. 12, 2 (2019).\n4. The manuscript states that “The hydroxyl groups in S-D-β200 were crucial for\nproviding binding sites (Fig. 2E), where confined water molecular clusters selectively\nbind to the hydrophilic heads of PFASs.” However, the distinction between the roles of\nhydroxyl groups and confined water in PFAS adsorption is unclear. From our\nviewpoint, both may bind to the hydrophilic heads of PFAS through hydrogen bonding.\nResponse: Thank you for your advice. To identify the confined water adsorption sites,\n2D-MAS-NMR was used to determine the 1H-1H single/double quantum spectrum\nchanges before and after PFAS adsorption (Figure 2D and 2E). The results proved that\nthe confined water cluster binds to the (ultra-) short-chain PFAS carboxyl group at the\nchannel intersection, forming a carboxyl group resonance band (δ=9.00 ppm) and\ninteracting with the confined water resonance band ((14.98, 5.98), Fig. 2E).\nSimultaneously, it was determined that the water molecules bound to Al-OH were\nR9\nremoved following adsorption (δ=2.91 ppm), thereby demonstrating that the\n(ultra-)short-chain PFAS hydrophilic heads bound to the hydrophilic center of the\nzeolite (i.e., channel intersections). However, owing to the minimal Al content (β200 <\n1%), its contribution to the adsorption site is rendered almost negligible (the carboxyl\ngroup has no interaction resonance with Al-OH). We therefore employed ATR-FTIR to\nascertain the functional group changes in S-D-β200 before and after PFAS adsorption,\nwith a particular focus on the interaction between Si-OH and (ultra-)short-chain PFASs\n(Fig. R3). The characteristic peak (950 cm-1) attributed to Si-OH was significantly\nweakened after adsorption, demonstrating its role as an adsorption site for PFASs;\nthat is, the binding of the contributing proton to the carboxyl ions of PFASs weakened the\nSi-OH vibrations. Concurrently, the confined water characteristic peak (3750cm-1-3000\ncm-1) underwent substantial changes, once again confirming its association with\n(ultra-)short-chain PFASs. Therefore, these results indicate that Si-OH and confined\nwater in the zeolite are involved in the adsorption of (ultra-)short-chain PFASs. Notably,\nSi-OH was the original functional group of β200 (Fig. R1); therefore, the increased\nadsorption site was mainly provided by the confined water. We have added the relevant\nresults to the manuscript. Thank you again for your valuable comment.\nR10\nFig. R3. Fourier infrared spectroscopy of S-D-β200 before and after PFAS adsorption;\nthe location of PFAS characteristic peaks were referred to the previous report1.\nRevisions (in the marked manuscript):\n1. “The hydroxyl groups in S-D-β200 were crucial for providing binding sites (Fig. 2E),\nwhere confined water clusters selectively bind to the hydrophilic heads of PFASs,\nleading to deionization (δ=9.00 ppm) and re-exposure of partially hydrated Brönsted-\nacid sites (δ=2.91 ppm)” in Line 153-157 was changed to “The hydroxyl groups\n(confined water and Si-OH) in S-D-β200 were crucial for providing binding sites\n(Supplementary Fig. S7), where confined water clusters offered increased adsorption\nsite to selectively bind with the hydrophilic heads of PFASs, leading to deionization\n(δ=9.00 ppm, (14.98, 5.98)) and re-exposure of partially hydrated Brönsted-acid sites\n(δ=2.91 ppm, Fig. 2E)”.\n2. Fig. R3 was added in Supplementary information as Fig. S7.\n3. “We employed ATR-FTIR to ascertain the functional group changes in S-D-β200\nbefore and after PFAS adsorption (Supplementary Fig. S7). The characteristic peak\n(950 cm-1) attributed to Si-OH was significantly weakened after adsorption,\ndemonstrating its role as an adsorption site for PFASs, that is the binding of the\ncontributing proton to the carboxyl ions of PFASs weakened the Si-OH vibrations.\nConcurrently, the confined water characteristic peak (3750 cm-1-3000 cm-1) underwent\nsubstantial changes, once again confirming its association with (ultra-)short-chain\nPFASs. Therefore, these results indicate that Si-OH and confined water in the zeolite\nare involved in the adsorption process of (ultra-)short-chain PFASs. Notably, Si-OH\nwas the original functional group of β200 (Supplementary Fig. S3); therefore, the\nincreased adsorption site was mainly provided by confined water” was added in\nSupplementary information, Page S14.\nReferences:\ninduced by per- and polyfluoroalkyl substances (PFASs) with FTIR spectroscopy. Environ. Pollut.\n317, 120671 (2023).\n5. In Table S5, the authors compare the PFAS adsorption capacity of NU-1000. While\nthis comparison is useful, many other MOFs have been studied for PFAS adsorption.\nPlease give a comprehensive summary of these adsorbents.\nResponse: Thank you for your advice. We reviewed the research on the PFAS\nadsorption by metal-organic framework (MOFs) materials in recent years1-5. Most of\nthese studies have focused on traditional long-chain PFASs (e.g., PFOS and PFOA);\nR11\nhowever, in recent years, there has been an increasing number of studies on\n(ultra-)short-chain PFASs. In addition to some studies that could not be compared (no\nmaximum adsorption capacity reported)4, we sorted and compared the adsorption\ncapacities of 7 types of MOFs for (ultra-)short-chain PFASs (Table R2)6-9. The results\nshow that the adsorption capacity of S-D-β200 for (ultra-)short-chain PFASs is superior\nto that of newly reported MOFs, which supports the validity of the results of our work\nover a wider range. We have added the relevant discussion. Thank you again for your\nvaluable comments.\nTable R2. The adsorption capacity of metal-organic framework materials on\n(ultra-)short-chain PFASs reported.\nPFASs Adsorbents Adsorption capacity (mg/g) References\nS-D-β200 687.96 This study\nPFHxS\nPCN-224 517 6\nS-D-β200 627.21 This study\naUi-66-4 170.13 7\nPFHxA UiO-66 50.385 7\nTFA-MOF-808 436 8\nMOF-808 262 8\nS-D-β200 559.86 This study\nUiO-66-10-HCl 162 9\nPFBS\nUiO-66-25 192 9\nPCN-224 394.7 6\nS-D-β200 334.31 This study\naUi-66-4 118.17 7\nPFBA UiO-66 75.54 7\nTFA-MOF-808 311 8\nMOF-808 232 8\nRevisions (in the marked manuscript):\n1. Table R2 was added in Supplementary information as part of Table S6.\n2. Fig. 2F was changed as below.\nR12\nFig. 2F. Comparison of adsorption capacity of on S-D-ꞵ200 and other adsorbents\nreported for (ultra-)short-chain PFASs.\n3. “Despite substantial efforts, currently proposed solutions tend to optimize either\nefficiency (e.g., β-cyclodextrin polymer, hollow covalent organic framework, and\nmagnetic fluorinated polymer) or reusability (e.g., electrochemical and microwave)10-\n15” in Line 50-53 was changed to “Despite substantial efforts, currently proposed\nsolutions tend to optimize either efficiency (e.g., β-cyclodextrin polymer, hollow\ncovalent organic framework, magnetic fluorinated polymer, and metal-organic\nframework) or reusability (e.g., electrochemical and microwave)10-17”.\n4. “Li, R., Adarsh, N. N., Lu, H. & Wriedt, M. Metal-organic frameworks as platforms\nfor the removal of per- and polyfluoroalkyl substances from contaminated waters.\nMatter 5, 3161-3193 (2022)” was added to References.\n5. “Li, R. et al. Systematic study on the removal of per- and polyfluoroalkyl substances\nfrom contaminated groundwater using metal-organic frameworks. Environ. Sci.\nTechnol. 55, 15162-15171 (2021)” was added to References.\n6. “Zhang, Y. et al. A porphyrinic metal‐organic framework with cooperative\nadsorption domains for PFAS removal from water. ChemSusChem 17, e202400069\n(2024)” was added to Supplementary information as Supplementary references.\n7. “Yin, Y., Fan, C., Cheng, L. & Shan, Y. Adsorption of perfluoroalkyl substances on\ndeep eutectic solvent-based amorphous metal-organic framework: Structure and\nmechanism. Environ. Res. 248, 118261 (2024)” was added to Supplementary\ninformation as Supplementary references.\nR13\n8. “Loukopoulos, E. et al. Chemically tailored metal‐organic frameworks for enhanced\ncapture of short‐ and long‐chain per‐ and polyfluoroalkyl substances from water. Adv.\nFunct. Mater. 34, 2409932 (2024)” was added to Supplementary information as\nSupplementary references.\n9. “Clark, C. A., Heck, K. N., Powell, C. D. & Wong, M. S. Highly defective UiO-66\nmaterials for the adsorptive removal of perfluorooctanesulfonate. ACS Sustainable\nChem. Eng. 7, 6619-6628 (2019)” was added to Supplementary information as\nSupplementary references.\nReferences:\nremoval of per- and polyfluoroalkyl substances from contaminated waters. Matter 5, 3161-3193\n(2022).\npolyfluoroalkyl substances from water. Langmuir 40, 2815-2829 (2024).\nusing MOFs and COFs: A review. Rev. Environ. Sci. Bio/Technol. (2024).\nhttps://doi.org/10.1007/s11157-024-09715-1\ncontaminated groundwater using metal-organic frameworks. Environ. Sci. Technol. 55, 15162-\n15171 (2021).\nof their PFAS adsorption performance. J. Hazard. Mater. 425, 127810 (2022).\nfor PFAS removal from water. ChemSusChem 17, e202400069 (2024).\neutectic solvent-based amorphous metal-organic framework: Structure and mechanism. Environ.\nRes. 248, 118261 (2024).\nshort- and long-chain per- and polyfluoroalkyl substances from water. Adv. Funct. Mater. 34,\n2409932 (2024).\nadsorptive removal of perfluorooctanesulfonate. ACS Sustainable Chem. Eng. 7, 6619-6628 (2019).\n6. The manuscript reports that the PFAS adsorption capacity of S-D-β200 can exceed\n100% after regeneration over different cycles. Please offer a detailed explanation of\nthe underlying reasons for this phenomenon, as it appears to deviate from typical\nadsorption regeneration behavior.\nR14\nResponse: Thank you for pointing this out. As you mentioned, the conventional\nadsorption-regeneration process does not lead to the emergence of new adsorption sites,\nwhich indicates that the zeolite structure may have changed during the dynamic\nhydroxy cycle. To explain this problem, we reanalyzed the structural changes of the\nzeolite in the cycle and added specific surface area and pore size analysis. After five\ncycles, no significant changes were observed in the zeolite crystals (Figure 2B),\nfunctional groups (Figure 2A), or pore structure (Table R2); however, the specific\nsurface area slightly increased by 12.5%. These results indicate that during the cycling\nprocess, some zeolites might have exposed new external surfaces; for example,\ncalcination disperses the agglomerated particles1, providing new adsorption sites for\n(ultra-)short-chain PFASs. We have added relevant information and data to the text.\nThank you again for your valuable comment.\nTable R3. Specific surface areas and pore structures of D-β200 and recycled zeolite.\nSample S (m2/g) b D (nm) c V (cm3/g) d\nBET P P\nD-β200 637.81 1.971 0.271\nRecycle 717.64 2.052 0.282\nCR a 12.5% 4.1% 4.1%\na CR: Rate of change relative to D-β200.\nb S : Brunauer-Emmett-Teller (BET) specific surface area.\nBET\nc D : Average pore diameter.\nP\nd V : Total pore volume.\nP\nRevisions (in the marked manuscript):\n1. “In addition, the stability of the Si-O-Si framework and XRD crystal facets of β200\nwere further confirmed after cycling (Fig. 2A and B)” in Line 174-178 was changed\nto “In addition, the stability of the Si-O-Si framework, XRD crystal facets and pore\nstructure of β200 were further confirmed after cycling (Fig. 2A, 2B and Supplementary\nTable S3), while the slightly increased specific surface area (12.5%) promoted the\nadsorption capacity for certain PFASs to a level that exceeds that of the original S-D-\nβ200”.\n2. Table R3 was added in Supplementary information as part of Table S3.\nR15\nReferences:\nproduce smaller particles of zeolite? Powder Technol. 301, 911-919 (2016).\nR16\nReviewer #2’s comments:\nThis manuscript investigates an adsorption-regeneration strategy for removing ultra-\nshort-chain PFAS from potable water using commercially available zeolites and water-\nbased dynamic hydroxyl cycling. They utilize a multifaceted approach comprising\nbench-scale experiments, coarse-grained simulations, and pilot-scale investigations to\nrigorously validate the proposed methodology.\nSuch alternative strategy has a significant potential, and the manuscript has a good\nquality of research. To conclude, the content of the paper is publishable with following\nedits:\nResponse: We appreciate your excellent suggestions for improving our manuscript.\nBased on your comments, we have made detailed revisions to the manuscript. We\nsincerely hope that the revised version addresses your comments and meets the\npublication requirements.\n1. The computational approach based on LAMMPS software has yielded promising\nresults. It might be beneficial to include ab initio-level approaches (such as Density\nFunctional Theory, DFT) to further validate the dual-binding mode of PFAS removal,\nparticularly for more detailed insight into the system's electronic structure and binding\ninteractions.\nResponse: Thank you for your advice. To further improve the computational work, we\nextracted structures (i.e., zeolite framework, confined water, and (ultra-)short-chain\nPFASs) from the molecular dynamics simulation results of nanopore adsorption and\ncalculated their binding energies using density functional theory (DFT, Fig. R4). To our\ndelight, the binding energy of the (ultra-)short-chain PFASs maintained a consistent\ntrend with the previous potential of the mean force (PMF) in nanopore adsorption\n(Figure 3C), thereby substantiating the hypothesis that the dual-binding mode is the\nprimary factor contributing to the variation in mass transfer within the nanopores.\nR17\nFig. R4. (A) Structural model and (B) binding energy of (ultra-)short-chain PFASs in\nS-D-B200 nanopores.\nTo further explore the potential mechanism of the dual-binding mode, the charge\ntransfer of (ultra-)short-chain PFASs in zeolite nanopores was qualitatively and\nquantitatively analyzed using differential and Mulliken charges (Fig. R5). Significant\ncharge transfer of (ultra-)short-chain PFASs was observed, and the degree of electron\nloss was highly correlated with the bonding energy. These results demonstrate that\nelectron donation is the primary mechanism of (ultra-)short-chain PFASs binding to the\nzeolite framework and confined water. Simultaneously, both the confined water and\nzeolite frameworks acted as key electron acceptors. Following the removal of the\nconfined water, there was a significant reduction in the charge transfer (0.457 e vs.\n0.371 e) and binding energy (-5.22 eV vs. -3.85 eV) of PFASs binding with only the\nzeolite frameworks (Fig. R6). In summary, the DFT results provide more detailed\ninsight into the \"zeolite framework-confined water\" dual-binding model, incorporating\nthe electronic structure and binding interactions. We have added the relevant results and\ndiscussion to the manuscript. Thank you again for your valuable comment.\nR18\nFig. R5. (A) Differential charge and (B) Mulliken charge transfer of (ultra-)short-chain\nPFASs in S-D-B200 nanopore.\nFig. R6. (A) Structural model and differential charge of TFA in S-D-β200 nanopore and\nzeolite framework; (B) binding energy and Mulliken charge transfer of TFA in S-D-\nβ200 nanopore and zeolite framework.\nRevisions (in the marked manuscript):\n1. “This was demonstrated by further density functional theory analyses, which\nrevealed that the trend of the binding energy change of (ultra-)short-chain PFASs after\nR19\ndouble binding, achieved by donating electrons (0.389 e-0.457 e) to both the zeolite\nframework and the confined water, is consistent with that of PMF (Fig. 3C and\nSupplementary Fig. S21-S23)” was added to Line 255-259.\n2. Fig. R4-R6 was added in Supplementary information as Fig. S21-S23.\n3. “To obtain a more detailed insight into the dual-binding mode, we extracted\nstructures (i.e., zeolite framework, confined water, and (ultra-)short-chain PFASs)\nfrom the molecular dynamics simulation results of pore adsorption and calculated their\nbinding energies using density functional theory (Supplementary Fig. S21). The\nbinding energy of (ultra-)short-chain PFASs maintained a consistent trend with the\nprevious potential of mean force (PMF) in nanopore adsorption (Fig. 3C), thereby\nsubstantiating the hypothesis that the dual-binding mode is the primary factor\ncontributing to the variation in the mass transfer within the nanopores” was added in\nSupplementary information, Page S28.\n4. “To further explore the potential mechanism of the dual-binding mode, the charge\ntransfer of (ultra-)short-chain PFASs in zeolite nanopores was qualitatively and\nquantitatively analyzed using differential and Mulliken charges (Supplementary Fig.\nS22). Significant charge transfer of (ultra-)short-chain PFASs was observed, and the\ndegree of electron loss was highly correlated with the bonding energy. These results\ndemonstrate that electron donation is the primary mechanism of (ultra-)short-chain\nPFASs binding to the zeolite framework and confined water. Simultaneously, both the\nconfined water and zeolite frameworks acted as key electron acceptors. Following the\nremoval of confined water (Fig. S23), there was a significant reduction in the charge\ntransfer (0.457 e vs. 0.371 e) and binding energy (-5.22 eV vs. -3.85 eV) of PFASs\nbinding with only the zeolite frameworks” was added in Supplementary information,\nPage S29.\n5. “Density functional theory (DFT) calculation\nThe DFT calculations were carried out using DMol3 modules of Material Studio.\nThe generalized gradient approximation (GGA) method with Perdew-Burke-Ernzerhof\n(PBE) function was employed to describe the interactions between core and electrons.\nSpin-polarization with DFT semi-core Pseudopots was included in all calculations. It is\nR20\nessential to take into account the van der Waals forces for adsorption. Hence, the\nTkatchenko-Scheffler (TS) method for DFT-D correction was used for this purpose.\nDouble numerical plus polarization (DNP) functions were adopted as the basis set. The\nforce and energy convergence criterion were set to 0.002 Ha Å-1 and 10-5 Ha,\nrespectively. When the optimization was completed, the binding energy (ΔE) was\ncalculated as Equation (12).\nΔE(cid:3404)27.212(cid:3400)(cid:4666)E -E-E(cid:4667) (12)\ntotal 1 2\nwhere the E is the energy of the optimized system; E is the energy of the S-D-\ntotal 1\nβ200; E is the energy of (ultra-)short-chain PFASs” was added in Line 484-497.\n2\n2. It might be useful to look into works by Prof. Wriedt and Prof. Farha, specifically\npublished in Chemistry of Materials in 2021, which explores removal of short-chain\nPFAS using porous materials.\nResponse: Thank you for pointing this out to us. Based on your suggestions, we\nconducted a comprehensive review of papers published by Prof. Wriedt and Prof. Farha\nin 20211, as well as other reports on PFAS adsorption2,3. The excellent work of the two\nprofessors on the application of materials such as metal-organic frameworks in the\nadsorption treatment of PFAS strongly supports our comprehensive evaluation of the\ndynamic hydroxyl cycle performance (Table R4). In addition, their approach to explore\nadsorption mechanisms (e.g., FTIR, Pore size distribution, and DFT analysis) further\nguided our research (Fig. 3D, 3E, S7, and S21-S23)1. We have incorporated the relevant\nreferences into the manuscript. Thank you again for your valuable comment.\nTable R4. The adsorption capacity of (ultra-)short-chain PFAS adsorbents reported\nfrom Prof. Wriedt and Prof. Farha.\nPFASs Adsorbents Adsorption capacity (mg/g) References\nS-D-β200 733.13 This study\nPFHpA\nNU-1000 421 1\nS-D-β200 687.96 This study\nPFHxS\nNU-1000 547 1\nS-D-β200 345.77 This study\nPFPeA\nNU-1000 344 1\nR21\nPFASs Adsorbents Adsorption capacity (mg/g) References\nS-D-β200 559.86 This study\nUiO-66-10-HCl 162 2, 4\nPFBS\nUiO-66-25 192 2, 4\nNU-1000 404 1\nS-D-β200 334.31 This study\nPFBA\nNU-1000 274 1\nS-D-β200 223.82 This study\nTFA\nNU-1000 201 1\nRevisions (in the marked manuscript):\n1. Table R4 was added in Supplementary information as part of Table S6.\n2. Fig. 2F was changed as below.\nFig. 2F. Comparison of adsorption capacity of on S-D-ꞵ200 and other adsorbents\nreported for (ultra-)short-chain PFASs.\n3. “Despite substantial efforts, currently proposed solutions tend to optimize either\nefficiency (e.g., β-cyclodextrin polymer, hollow covalent organic framework, and\nmagnetic fluorinated polymer) or reusability (e.g., electrochemical and microwave)10-\n15” in Line 50-53 was changed to “Despite substantial efforts, currently proposed\nsolutions tend to optimize either efficiency (e.g., β-cyclodextrin polymer, hollow\ncovalent organic framework, magnetic fluorinated polymer, and metal-organic\nframework) or reusability (e.g., electrochemical and microwave)10-17”.\n4. “Consequently, the simulation results suggest enhanced nanopore accessibility for all\n(ultra-)short-chain PFASs in S-D-β200, which aligns with the experimental\nR22\nobservations showing an increasing in nanopore occupancy from 0.5% to 22% (Fig. 3D\nand 3E)” in Line 221-224 was changed to “Consequently, the simulation results\nsuggest enhanced nanopore accessibility for all (ultra-)short-chain PFASs in S-D-β200,\nwhich aligns with the experimental observations showing an increasing in nanopore\noccupancy from 0.5% to 22% (Fig. 3D and 3E)24”.\n5. “Li, R., Adarsh, N. N., Lu, H. & Wriedt, M. Metal-organic frameworks as platforms\nfor the removal of per- and polyfluoroalkyl substances from contaminated waters.\nMatter 5, 3161-3193 (2022)” was added to References.\n6. “Li, R. et al. Systematic study on the removal of per- and polyfluoroalkyl substances\nfrom contaminated groundwater using metal-organic frameworks. Environ. Sci.\nTechnol. 55, 15162-15171 (2021)” was added to References.\nReferences:\n1. Li, R. et al. Efficient removal of per- and polyfluoroalkyl substances from water with\nzirconium-based metal-organic frameworks. Chem. Mater. 33, 3276-3285 (2021).\n2. Li, R., Adarsh, N. N., Lu, H. & Wriedt, M. Metal-organic frameworks as platforms for the\nremoval of per- and polyfluoroalkyl substances from contaminated waters. Matter 5, 3161-3193\n(2022).\n3. Li, R. et al. Systematic study on the removal of per- and polyfluoroalkyl substances from\ncontaminated groundwater using metal-organic frameworks. Environ. Sci. Technol. 55, 15162-\n15171 (2021).\nR23"}, {"round": 2, "reviewer_comments": {"reviewer_2": "The revision addresses all the previous concerns satisfactorily. To conclude, the content of the paper is publishable without any further edits.", "reviewer_3": "It is challenging to determine whether the authors have fully addressed the reviewers’ comments without reviewing the complete manuscript and understanding the broader context. Overall, the authors appear to have reasonably addressed the reviewers’ concerns; however, I cannot speak on behalf of Reviewer #1, and therefore my evaluation reflects only my own assessment.\nWhile the manuscript presents a creative approach for enhancing short-chain PFAS adsorption through confined water structures in zeolite nanopores, several of its central claims appear fundamentally inconsistent with established physicochemical principles. Most notably, the reported adsorption capacities reaching as high as 733.13 mg/g seemed implausible based on the nature of the interactions described. The authors attribute the exceptionally high uptake to a non-covalent dual-binding mechanism involving van der Waals interactions with the zeolite framework and hydrogen bonding mediated by confined water. However, for highly hydrated, negatively charged ultrashort-chain PFAS, this mechanism alone is insufficient to account for such extreme loading.\nIt is well established that electrostatic interactions dominate the adsorption behavior of (ultra-)short-chain PFAS. Given that the zeolite surface itself carries a significant negative charge (zeta potential of –41.6 mV), the proposed mechanism becomes even more questionable. Adsorption of large quantities of anionic PFAS would only intensify the surface negativity, further disfavoring adsorption. Moreover, the authors’ own interpretation suggests that confined water hydrates the PFAS headgroups, confirming that the PFAS remain in their anionic form during adsorption: an effect that would exacerbate, rather than alleviate, the electrostatic barrier.\nCompounding these concerns, the simulations assume a charge-neutral system, with protons balancing framework charges, but do not account for realistic ion dynamics or the evolution of surface charge. This omission significantly undermines the reliability of the modeling results and casts serious doubt on the overall credibility of the proposed mechanistic explanation."}, "author_response": "Response to reviewers\nReviewer #3’s comments:\nIt is challenging to determine whether the authors have fully addressed the reviewers’\ncomments without reviewing the complete manuscript and understanding the broader\ncontext. Overall, the authors appear to have reasonably addressed the reviewers’\nconcerns; however, I cannot speak on behalf of Reviewer #1, and therefore my\nevaluation reflects only my own assessment.\nWhile the manuscript presents a creative approach for enhancing short-chain PFAS\nadsorption through confined water structures in zeolite nanopores, several of its central\nclaims appear fundamentally inconsistent with established physicochemical principles.\nMost notably, the reported adsorption capacities reaching as high as 733.13 mg/g\nseemed implausible based on the nature of the interactions described. The authors\nattribute the exceptionally high uptake to a non-covalent dual-binding mechanism\ninvolving van der Waals interactions with the zeolite framework and hydrogen bonding\nmediated by confined water. However, for highly hydrated, negatively charged\nultrashort-chain PFAS, this mechanism alone is insufficient to account for such extreme\nloading.\nIt is well established that electrostatic interactions dominate the adsorption behavior\nof (ultra-)short-chain PFAS. Given that the zeolite surface itself carries a significant\nnegative charge (zeta potential of –41.6 mV), the proposed mechanism becomes even\nmore questionable. Adsorption of large quantities of anionic PFAS would only intensify\nthe surface negativity, further disfavoring adsorption. Moreover, the authors’ own\ninterpretation suggests that confined water hydrates the PFAS headgroups, confirming\nthat the PFAS remain in their anionic form during adsorption: an effect that would\nexacerbate, rather than alleviate, the electrostatic barrier.\nCompounding these concerns, the simulations assume a charge-neutral system, with\nprotons balancing framework charges, but do not account for realistic ion dynamics or\nthe evolution of surface charge. This omission significantly undermines the reliability\nR1\nof the modeling results and casts serious doubt on the overall credibility of the proposed\nmechanistic explanation.\nResponse: We appreciate your constructive comments that helped clarify and improve\nour manuscript. Thank you very much for bringing this issue to our attention. We agree\nwith your concern regarding the influence of electrostatic repulsion on adsorption\ncapacity. After careful assessment, we believe that electrostatic repulsion has a limited\nimpact on the S-D-β200 adsorption process. The main reasons are as follows: (1) only\na small amount of hydroxyl groups on the zeolite surface undergo deprotonation, and\nthe electrostatic repulsion effect is limited. Based on the ζ potential (β200: -43.3 mV &\nS-D-β200: -41.6 mV) obtained from the experiment, we used the Gouy-Chapman\nequation to calculate the surface charge densities of the β200 and S-D-β200 as -0.11\nC/m2 and -0.105 C/m2, respectively1,2. Therefore, taking the zeolite model we\npreviously established as an example, only ~2 (β200: 2.03 & S-D-β200: 1.93) Si-OH\ngroups underwent deprotonation and acquired negative charges, accounting for 2.78%\n(2/72) of the total number of hydroxyl groups. To correct this error and evaluate the\ninfluence of negative charges on the adsorption of (ultra-)short-chain PFASs, we\nrandomly selected two Si-OH groups in the initial model and deprotonated them (using\nNa+ in the aqueous solution to balance the charge of the system). Subsequently, we\nrecalculated the adsorption free energies of all the (ultra-)short-chain PFASs in β200\nand S-D-β200. The results confirmed that the introduction of trace negative charges\nonly resulted in a minor repulsive effect, leading to an increase in the surface adsorption\n(0.07-1.96 kcal/mol), pore adsorption (0.01-0.95 kcal/mol), and total energy (0.15-2.59\nkcal/mol). The overall adsorption pathways of β200 and S-D-β200 did not change\nsignificantly (Fig. R1A and R1B), and their adsorption patterns for different\n(ultra-)short-chain PFASs still conform to our previous conclusions (Fig. R1C and\nR1D). Therefore, we believe that in this study, the few negative charges carried by the\nzeolite have a limited negative impact on the (ultra-)short-chain PFASs, and there are\nstill a large number of available adsorption sites that perform effective adsorption. This\nphenomenon has been confirmed in previous studies3,4. They confirmed that charge\nR2\nadjustment through pH had no significant impact on PFAS adsorption by β zeolite.\nFig. R1. Potential of mean force (PMF) calculated from umbrella trajectories when\nPFHpA enters (A) ꞵ200 and (B) S-D-ꞵ200 nanochannels using weighted histogram\nanalysis method; pore adsorption energy, surface adsorption energy, and total energy\nchanges of (ultra-)short-chain PFASs entering S-D-ꞵ200’s and ꞵ200’s nanopores using\n(C) deprotonation model and (D) initial model.\n(2) Owing to unique chain structures, PFASs can achieve high adsorption loading while\nsimultaneously alleviating the electrostatic repulsion between each other. Unlike\ntraditional pollutants, the structure of PFASs consists of a hydrophilic head and a\nhydrophobic tail. This design enables the two parts to interact independently to a certain\nextent, thereby avoiding the negative effects of electrostatic repulsion. For example, in\nthe adsorption process dominated by hydrophobic interactions, PFASs form hemi-\nmicelle-like structures with hydrophobic heads aggregating and hydrophilic heads\ndispersed, thereby weakening the effect of electrostatic repulsion and resulting in\nexcessive adsorption (Fig. R2)5, 6. Therefore, previous studies have shown that even a\nsingle functional adsorbent with a negative charge (solution pH < point of zero charge)\ncan exhibit a relatively high adsorption capacity for PFASs (Table R1).\nR3\nFig. R2. Schematic diagram for self-aggregations in PFAS adsorption5, 6.\nTable R1. The adsorption performance of the negatively charged adsorbents for PFAS.\nAdsorption\nAdsorbent PZCa Adsorbate pH References\ncapacity (mg/g)\nSWCNT 3.9 PFOS 712\nMWCNT10 3.2 PFOS 7 656 7\nMWCNT50 3.5 PFOS 514\nPFOA 203\nPAC 3.3 5.0 8\nPFOS 535\nGAC 3.2 GenX 260\n4.0 9\nPAC 3.2 GenX 260\nPFBS 162\nUiO-66-10 6.4 5-9\nPFOS 375\nUiO-66-25 4.7 5-9\nPFOS 350\na PZC: Point of zero charge.\n(3) The confined water structure can shield the electrostatic interactions of the PFAS\nhydrophilic heads, avoiding further enhancement of the electrostatic repulsion.\nAccording to Coulomb’s law, the electrostatic interaction constant (k) is inversely\nproportional to the dielectric constant (ε) of the medium (k = 1/4πε); that is, the greater\nthe dielectric constant, the smaller the electrostatic interaction. As a high dielectric\nconstant (ε ≈ 80) medium, water molecules exhibit a significant electrostatic shielding\nr\neffect11,12. The electrostatic effect of charges in water is only 1/80 of that in a vacuum.\nTherefore, the hydrophilic heads of PFASs in S-D-β200 are bonded by confined water,\nleading to a lower electrostatic repulsion between them and the zeolite, as well as other\nPFASs, than that in β200. This adds to the potential mechanism by which confined\nwater enhances the adsorption capacity of β200 for PFASs. Based on the above\ndiscussion, we have made corrections to the molecular dynamics analysis in the\nmanuscript and added clarifications regarding relevant mechanisms. Thank you once\nR4\nagain for your valuable comments.\nRevisions (in the marked manuscript):\n1. “Meanwhile, the shielding effect of confined water also helps to weaken the\nelectrostatic repulsion between (ultra-)short-chain PFASs and S-D-β200, as well as\nother PFASs24” was added to Line 158-159.\n2. “Specifically, a supercell consisting of 3×3×3 BEA zeolite crystal cells was placed\nin the middle of the simulated box, cut along the 010 and 001 crystal faces, and\ncompensated for unsaturated silicon-oxygen bonds with hydroxyl (-OH) groups to\nmaintain surface charge neutrality35” in Line 377-380 was changed to “Specifically, a\nsupercell consisting of 3×3×3 BEA zeolite crystal cells was placed in the middle of the\nsimulated box, cut along the 010 and 001 crystal faces, and compensated for unsaturated\nsilicon-oxygen bonds with hydroxyl (-OH) groups to maintain surface charge\nneutrality35”\n3. “Based on the ζ potential and the Gouy-Chapman formula (Equations 1 and 2), the\nsurface charge densities of β200 and S-D-β200 were calculated to be -0.11 C/m2 and -\n0.105 C/m2, respectively36. Therefore, two Si-OH groups were randomly deprotonated,\nresulting in a negatively charged zeolite surface.\n(cid:3255)(cid:3341)\n(cid:3046)(cid:3036)(cid:3041)(cid:3035)(cid:4672) (cid:4673)\n𝜎 (cid:3404) (cid:3398)𝜀𝜅𝜉 (cid:3118)(cid:3267)(cid:3269) (1)\n(cid:3255)(cid:3341)\n(cid:3118)(cid:3267)(cid:3269)\n(cid:2869)(cid:3415)\n𝜅(cid:2879)(cid:2869) (cid:3404) (cid:4672) (cid:3084)(cid:3019)(cid:3021) (cid:4673) (cid:2870) (2)\n(cid:2870)(cid:3007)(cid:3118)(cid:3004)(cid:3116)\nwhere ε (6.933 × 10-10 F/m) is the permittivity, κ-1 (m) is the Debye length, 𝜉 (V)\nis the ζ potential, F (96485 C/mol) is the Faraday constant, R (8.3145 J/(mol × K)) is\nthe gas constant, and C (mol/m-3) is the concentration of the electrolyte.” was added\n0\nto Line 381-389.\n4. “During this stage, the adsorption free energy of (ultra-)short-chain PFASs decreased\nsignificantly (e.g., -9.12 kcal/mol → -25.96 kcal/mol for perfluoroheptanoic acid\n(PFHpA) in β200, Fig. 3A), although hydrophilic homologues (e.g., trifluoroacetic acid\n(TFA)) benefited less from this process (Fig. 3C)” in Line 202-205 was changed to\n“ During this stage, the adsorption free energy of (ultra-)short-chain PFASs decreased\nR5\nsignificantly (e.g., -10.70 kcal/mol → -26.14 kcal/mol for perfluoroheptanoic acid\n(PFHpA) in β200, Fig. 3A), although hydrophilic homologues (e.g., trifluoroacetic acid\n(TFA)) benefited less from this process (Fig. 3C)”.\n5. “Unlike the first stage, the energy gain from the interaction between the zeolite\nframework and the (ultra-)short-chain PFAS was insufficient to offset the substantial\ndehydration penalty (e.g., 23.72 to 3.81 for PFHpA, Supplementary Fig. S16),\nresulting in non-spontaneous diffusion within the nanochannel (e.g., -25.96 kcal/mol → 0\nkcal/mol for PFHpA in β200)” in Line 208-212 was changed to “Unlike the first stage,\nthe energy gain from the interaction between the zeolite framework and the\n(ultra-)short-chain PFAS was insufficient to offset the substantial dehydration penalty\n(e.g., 23.72 to 3.81 for PFHpA, Supplementary Fig. S16), resulting in non-spontaneous\ndiffusion within the nanochannel (e.g., -26.14 kcal/mol → 0 kcal/mol for PFHpA in\nβ200)”.\n6. “After enhancement by the cyclic adsorption scheme (Fig. 3B), introducing confined\nwater reduced dehydration penalties (e.g., 7.93 vs. 1.83 for PFHpA, Supplementary Fig.\nS16) and surface binding energy state (-11.12 kcal/mol vs. -25.96 kcal/mol for PFHpA),\nresulting in a smoother overall solid-liquid mass transfer energy” in Line 219-222 was\nchanged to “After enhancement by the cyclic adsorption scheme (Fig. 3B), introducing\nconfined water reduced dehydration penalties (e.g., 7.93 vs. 1.83 for PFHpA, Supplementary Fig.\nS16) and surface binding energy state (-11.40 kcal/mol vs. -26.14 kcal/mol for PFHpA),\nresulting in a smoother overall solid-liquid mass transfer energy”.\n7. “24. Xu, R., Kang, Y., Zhang, W., Pan, B. & Zhang, X. Two-dimensional MXene\nmembranes with biomimetic sub-nanochannels for enhanced cation sieving. Nat.\nCommun. 14, 4907 (2023)” was added to References.\n8. “36. Wang, S., Walker-Gibbons, R., Watkins, B., Flynn, M. & Krishnan, M. A\ncharge-dependent long-ranged force drives tailored assembly of matter in solution. Nat.\nNanotechnol. 19, 485-493 (2024)” was added to References.\n9. The PMF analysis in Fig. 3a, 3b, and 3c were revised according the results of\ndeprotonation model. The specific contents are as follows:\nR6\n10. The PMF analysis of TFA, PFPrA, PFBA, PFBS, PFPeA, PFHxA, and PFHxS\nin Supplementary materials, Fig. S12-S15 were revised according the results of\ndeprotonation model. The specific contents are as follows:\nR7\nReferences:\nmembranes with biomimetic sub-nanochannels for enhanced cation sieving. Nat.\nCommun. 14, 4907 (2023).\nenhanced anion sieving and removal of organic micropollutants. Nat. Water 3, 704-713\n(2025).\ncharacteristics. Chemosphere 378, 144414 (2025).\nZeolite beta: Insights into the Effect of the Water Matrix, Regeneration of the Material,\nand Continuous PFAS Adsorption. ACS Appl. Mater. Interfaces 15, 52612-52621\n(2023).\napproaches, engineering applications, challenges, and opportunities. Environ. Pollut.\n321, 121138 (2023).\nA review of their PFAS adsorption performance. J. Hazard. Mater. 425, 127810 (2022).\nof perfluorooctane sulfonate (PFOS) by chars, ash and carbon nanotubes. Chemosphere\n83, 1313-1319 (2011).\nsulfonate and perfluorooctanoate on polyacrylonitrile fiber-derived activated carbon\nfibers: In comparison with activated carbon. RSC Adv. 7, 927-938 (2017).\npropoxypropanoic acid (GenX) on activated carbons and resins. Chem. Eng. J. 364,\nR8\n132-138 (2019).\nmaterials for the adsorptive removal of perfluorooctanesulfonate. ACS Sustainable\nChem. Eng. 7, 6619-6628 (2019).\ntransport properties of high resistance natural fibers. Sci. Rep. 8, 2726 (2018).\ndependent long-ranged force drives tailored assembly of matter in solution. Nat.\nNanotechnol. 19, 485-493 (2024).\nR9"}, {"round": 3, "reviewer_comments": {"reviewer_3": "The reviewer appreciates the effort the authors have made in preparing their rebuttal. However, the core concern raised in the initial review remains unaddressed. The response focuses on peripheral explanations rather than directly engaging with the primary issue at hand.\nWhile the reviewer acknowledges that adsorption of anionic PFAS on negatively charged surfaces is possible, particularly for long-chain PFAS where hydrophobic interactions play a dominant role, the situation is markedly different for ultrashort-chain PFAS such as trifluoroacetic acid (TFA). These molecules possess minimal hydrophobicity and are strongly hydrated in aqueous environments, making their adsorption an entropically unfavorable process. The examples presented in Table R1 by the authors to support adsorption onto negatively charged surfaces predominantly involve PFAS with chain lengths of C5 or greater, and are therefore not appropriate analogs for validating the reported adsorption of ultrashort-chain compounds like TFA.\nThe high adsorption capacities claimed for TFA (e.g., 233.82 mg/g) are difficult to rationalize based on the proposed adsorption mechanism, which appears insufficient to account for the substantial enthalpic compensation required to overcome the unfavorable entropy change. In addition, such high uptake of anionic species would be expected to significantly increase the net surface negativity of the material, intensifying electrostatic repulsion and limiting further adsorption. However, the authors only present surface charge density calculations for the fresh S-D-β200 material and do not account for the evolving surface charge as adsorption proceeds.\nTo substantiate the claims, the reviewer recommends that the authors expand their modeling framework to explicitly account for the evolving surface charge as adsorption progresses. Demonstrating how adsorption energy changes with increasing surface negativity could provide a more realistic representation of the thermodynamic constraints and clarify whether such high uptake values are theoretically achievable under equilibrium conditions."}, "author_response": "Response to reviewers\nReviewer #3’s comments:\nThe reviewer appreciates the effort the authors have made in preparing their rebuttal.\nHowever, the core concern raised in the initial review remains unaddressed. The\nresponse focuses on peripheral explanations rather than directly engaging with the\nprimary issue at hand.\nWhile the reviewer acknowledges that adsorption of anionic PFAS on negatively\ncharged surfaces is possible, particularly for long-chain PFAS where hydrophobic\ninteractions play a dominant role, the situation is markedly different for ultrashort-\nchain PFAS such as trifluoroacetic acid (TFA). These molecules possess minimal\nhydrophobicity and are strongly hydrated in aqueous environments, making their\nadsorption an entropically unfavorable process. The examples presented in Table R1\nby the authors to support adsorption onto negatively charged surfaces predominantly\ninvolve PFAS with chain lengths of C5 or greater, and are therefore not appropriate\nanalogs for validating the reported adsorption of ultrashort-chain compounds like TFA.\nThe high adsorption capacities claimed for TFA (e.g., 233.82 mg/g) are difficult to\nrationalize based on the proposed adsorption mechanism, which appears insufficient\nto account for the substantial enthalpic compensation required to overcome the\nunfavorable entropy change. In addition, such high uptake of anionic species would be\nexpected to significantly increase the net surface negativity of the material, intensifying\nelectrostatic repulsion and limiting further adsorption. However, the authors only\npresent surface charge density calculations for the fresh S-D-β200 material and do not\naccount for the evolving surface charge as adsorption proceeds.\nTo substantiate the claims, the reviewer recommends that the authors expand their\nmodeling framework to explicitly account for the evolving surface charge as adsorption\nprogresses. Demonstrating how adsorption energy changes with increasing surface\nnegativity could provide a more realistic representation of the thermodynamic\nconstraints and clarify whether such high uptake values are theoretically achievable\nunder equilibrium conditions.\nResponse: We appreciate your additional comments and the opportunity to further\nimprove our work. We apologize for the previous response failing to address your\nconcern regarding the accumulation of negative charges. Based on your suggestion, we\nfurther expanded the molecular dynamics simulation system and studied equilibrium\nadsorption behaviors of S-D-β200 for all (ultra-)short-chain PFASs at near-saturated\nadsorption capacity (the maximum adsorption capacity is only a theoretical value,\nmaking it difficult to construct a balanced model). Using the Langmuir-Freundlich\nisothermal model (Equation S3), the number of (ultra-)short-chain PFASs in S-D-β200\nand water was calculated when 90% of the maximum adsorption capacity was reached.\nAccording to the calculation results, 124-194 PFASs were added to our previous\nworking model, and their behaviors were observed during adsorption. Thus, the\nnegative charges of S-D-β200 surface (ζ potential: -41.6 mV) and accumulation of\n(ultra-)short-chain PFASs (210-660 mg/g) were fully considered in the new model. A\nbalance dynamics simulation lasting for 5 ns was conducted to achieve equilibrium (i.e.,\nthe number of adsorbed PFASs remained relatively constant). The data were collected\n1 ns after equilibrium, and the adsorption patterns of all (ultra-)short-chain PFASs were\nfurther analyzed (Fig. R1A).\nFigure R1. (A) Adsorption patterns of (ultra-)short-chain PFASs under equilibrium\nadsorption model; molecular snapshots of (B) TFA and (C) PFHpA equilibrium\nadsorption model (blue balls represent Na+).\nR2\nTo our delight, the average adsorption capacity of S-D-β200 for all (ultra-)short-\nchain PFASs reached 94-100% of the theoretical adsorption capacity, demonstrating the\ntheoretical possibility of high adsorption by S-D-β200 (Fig. R1A). Meanwhile, by\nfurther investigating the evolving charge, binding energy, and adsorption patterns as\nadsorption progresses, we believe that the following two mechanisms explain why S-\nD-β200 avoids the accumulation of negative charges and achieves high uptake: (a)\ncharge compensation of positive ions. The simulation results indicated that S-D-β200\nforms a “zeolite framework-confined water” dual-binding pattern with (ultra)-short-\nchain PFASs (Fig. R1B), while adsorbing an equal amount of positively charged ions\n(Na+/PFAS-: 92.0-101.6%). PMF analysis indicated that confined water not only\nenhanced the adsorption of (ultra-)short-chain PFASs, but also significantly reduced the\nenergy required for typical positive ions (-24.34 kcal/mol for Na+ and -43.22 kcal/mol\nfor H O+, Fig. R2B and R2C) to enter the S-D-β200 nanopores. In this case, the\n3\nadsorption of oppositely charged ions resulted in the cancellation of the electric field\neffects, thereby not influencing the binding energy of (ultra-)short-chain PFASs (-4.46\nto -12.8 kcal/mol, Fig. R2A). Therefore, when S-D-β200 adsorbs (ultra-)short-chain\nPFASs, positive ions in the system also undergo adsorption (as indicated by the TFA\nadsorption experiment, where the pH increased from 3.34 to 3.56, Fig. R2D), thereby\neliminating the repulsive effect caused by the excessive accumulation of negative\nelectric fields. (b) (Hemi-)micelle-like adsorption structures. In the simulation of\nexcessive adsorption, we observed the formation of (ultra-)short-chain PFAS\n(hemi-)micelle-like adsorption structures during surface adsorption (Fig. R1C). As\nexplained in the previous reply, the (hemi-)micelle-like structures are hydrophobic\nheads aggregating and hydrophilic heads dispersed, thereby weakening the effect of\nelectrostatic repulsion1, 2. However, as you have stated, these structures were mostly\nfound in PFASs with a chain length of 6 or more, whose surface adsorption played a\nmore important role than shorter chain (47.3-57.0%, Fig. R1B).Therefore, for PFASs\nwith shorter chains, positive charge compensation is the main mechanism for\neliminating negative charges (Na+/PFAS-:99.6-101.6%, pore adsorption ratio: 71.1-\n83.0%), while the (hemi-)micelle-like structures play an important role in alleviating\nelectrostatic repulsion for PFASs with a chain length ≥6 (Na+/PFAS-:92.0-96.5%, pore\nadsorption ratio: 43.0-52.7%).\nR3\nTake all, by expanding model to account for the evolving charge, binding energy,\nand adsorption patterns as adsorption progresses, we have improved the mechanism by\nwhich S-D-β200 eliminated the electrostatic repulsion effects via enhancing the\nadsorption of positive ions and forming (hemi-)micelle-like adsorption structures on\nthe surface. For the adsorption of (ultra-)short-chain PFASs (especially those with chain\nlengths <6), S-D-β200 could continuously adsorb the corresponding positive ions,\nmaintaining the charge balance of the system, which has been experimentally verified\n(Fig. R2D). Therefore, under the stable thermodynamic benefits of the “zeolite\nframework-confined water” dual-binding pattern (Fig. R2A), the nanopores of S-D-\nβ200 could be densely filled, leading to high uptake values under equilibrium\nconditions (Fig. R1A). We have included these results in the corresponding text. Once\nagain, we thank you for your valuable comments, which enabled us to gain a deeper\nunderstanding of the mechanism of confined water-enhanced adsorption of\n(ultra-)short-chain PFASs.\nFigure R2. (A) Binding energy of (ultra-)short-chain PFASs under equilibrium\nadsorption model (calculate the traction force required to disrupt the adsorption\nequilibrium of (ultra-)short-chain PFASs by the steered MD method); potential of mean\nforce (PMF) calculated from umbrella trajectories when (B) H O+ and (C) Na+ enter\n3\nꞵ200 and S-D-ꞵ200 nanochannels using weighted histogram analysis method; (D) the\nchange in pH of the TFA solution before and after S-D-β200 adsorption (TFA = 50 mg/L;\nDose = 5 mg/20 mL).\nR4\nRevisions (in the marked manuscript):\n1. “Meanwhile, we further expanded the molecular dynamics model to the equilibrium\nstate (Supplementary Fig. S24-S25). The results demonstrated the dominant role of the\ndual-binding pattern in the adsorption of (ultra-)short-chain PFASs by S-D-β200,\nespecially for chain lengths less than 6 (pore adsorption ratio: 71.1-83.0%). In nearly\nsaturated S-D-β200 nanopores, the hydrophobic tails of (ultra)short-chain PFASs are\nbound by zeolite channels, whereas the hydrophilic heads converge at confined water\nclusters and carry positive ions to eliminate electrostatic repulsion (charge\ncompensation ratio: 92.0-101.6%).” was added to Line 261-268.\n2. “We further expanded the molecular dynamics simulation system and studied the\nequilibrium adsorption behavior of S-D-β200 for all (ultra-)short-chain PFASs at near-\nsaturated adsorption capacity. According to the adsorption results (90% maximum\nadsorption capacity), 124-194 PFASs were added to the model (Fig. S11), and the data\nwere collected 1 ns after equilibrium (5 ns). The average adsorption capacity of S-D-\nβ200 for all (ultra-)short-chain PFASs reached 94-100% of the theoretical adsorption\ncapacity, demonstrating the theoretical possibility of high adsorption by S-D-β200.\nMeanwhile, the simulation results indicated that the (ultra-)short-chain PFASs\nexhibited two adsorption modes: pore adsorption and surface adsorption. For pore\nadsorption, the (ultra-)short-chain PFASs formed a “zeolite framework-confined water”\ndual-binding pattern in the S-D-β200 nanopores (Fig. S24B), while enhancing the\nadsorption of positive ions to alleviate the electrostatic repulsion effect (charge\ncompensation rate: 92.0-101.6%, Fig. S25A-D). Surface adsorption predominantly\noccurred in PFASs with longer chain lengths (≥6, pore adsorption ratio: 43.0-52.7%),\nachieving high uptake through the formation of (hemi-)micelle-like structures (Fig.\nS24C).” was added to Supplementary information, Page S31.\n3. Fig. R1 and R2 were added in Supplementary information as Fig. S24 and S25.\nReferences:\n1. Lei, X. et al. A review of PFAS adsorption from aqueous solutions: Current\napproaches, engineering applications, challenges, and opportunities. Environ. Pollut.\n321, 121138 (2023).\nR5\n2. Pauletto, P. S. & Bandosz, T. J. Activated carbon versus metal-organic frameworks:\nA review of their PFAS adsorption performance. J. Hazard. Mater. 425, 127810 (2022).\nR6"}, {"round": 4, "reviewer_comments": {"reviewer_3": "The reviewer appreciates that the authors have made additional efforts to expand their simulations and to discuss possible mechanisms involving charge compensation. While recognizing the efforts of the authors, I feel these new analyses still do not adequately address the core concerns previously raised. The manuscript, in its current form, would require or benefit from further experimental confirmation and a clearer, quantitatively supported mechanistic framework before it can be considered suitable for publication. My suggestions are given below, which hopefully could help demonstrate the hypothesis of the authors. Additionally, the term “positive ions” should be avoided.\nWhile the inclusion of a near-saturated adsorption model and the consideration of 210–660 mg/g PFAS loading are welcome steps, the explanation for how the negatively charged S D β200 framework can sustain such high uptake of ultrashort chain species like TFA remains speculative. The proposed in situ charge neutralization by co-adsorbed sodium ions is presented as the key mechanism mitigating electrostatic repulsion, yet this remains a hypothesis unsupported by direct experimental or quantitative computational evidence.\nThe only empirical support offered is a minor pH increase from 3.34 to 3.56 following adsorption. However, this change is minimal and could be attributed to a variety of unrelated processes. As such, it is neither a specific nor a sufficient indicator of sodium uptake. Monitoring sodium or other cation concentrations during the adsorption process using a straightforward analytical technique such as inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS), would directly confirm whether cation adsorption accompanies PFAS adsorption. This experiment could be completed with minimal effort and would provide decisive mechanistic validation. Furthermore, monitoring the sequence of cation and PFAS adsorption would clarify whether the process involves ion pair formation or electrostatic association, both of which are critical to understanding the true driving forces behind the reported adsorption capacities.\nAt present, the explanation remains largely qualitative, relying on speculative interpretations rather than rigorous validation. The reviewer also notes that the repeated use of the phrase “positive ions” should be replaced with the standard term “cations” to maintain professional and scientific accuracy, especially given the standards expected for a submission to Nature Communications."}, "author_response": "Response to reviewers\nReviewer #3’s comments:\nThe reviewer appreciates that the authors have made additional efforts to expand their\nsimulations and to discuss possible mechanisms involving charge compensation. While\nrecognizing the efforts of the authors, I feel these new analyses still do not adequately\naddress the core concerns previously raised. The manuscript, in its current form, would\nrequire or benefit from further experimental confirmation and a clearer, quantitatively\nsupported mechanistic framework before it can be considered suitable for publication.\nMy suggestions are given below, which hopefully could help demonstrate the hypothesis\nof the authors. Additionally, the term “positive ions” should be avoided.\nWhile the inclusion of a near-saturated adsorption model and the consideration of 210–\n660 mg/g PFAS loading are welcome steps, the explanation for how the negatively\ncharged S D β200 framework can sustain such high uptake of ultrashort chain species\nlike TFA remains speculative. The proposed in situ charge neutralization by co-\nadsorbed sodium ions is presented as the key mechanism mitigating electrostatic\nrepulsion, yet this remains a hypothesis unsupported by direct experimental or\nquantitative computational evidence.\nThe only empirical support offered is a minor pH increase from 3.34 to 3.56 following\nadsorption. However, this change is minimal and could be attributed to a variety of\nunrelated processes. As such, it is neither a specific nor a sufficient indicator of sodium\nuptake. Monitoring sodium or other cation concentrations during the adsorption\nprocess using a straightforward analytical technique such as inductively coupled\nplasma mass spectrometry (ICP-MS) or atomic absorption spectroscopy (AAS), would\ndirectly confirm whether cation adsorption accompanies PFAS adsorption. This\nexperiment could be completed with minimal effort and would provide decisive\nmechanistic validation. Furthermore, monitoring the sequence of cation and PFAS\nadsorption would clarify whether the process involves ion pair formation or\nelectrostatic association, both of which are critical to understanding the true driving\nforces behind the reported adsorption capacities.\nAt present, the explanation remains largely qualitative, relying on speculative\ninterpretations rather than rigorous validation. The reviewer also notes that the\nrepeated use of the phrase “positive ions” should be replaced with the standard term\n“cations” to maintain professional and scientific accuracy, especially given the\nstandards expected for a submission to Nature Communications.\nResponse: We appreciate your additional comments, which make us realize the\nsignificance of clarifying the mechanism of the charge compensation for cations.\nAccording to your suggestion, we utilized the inductively coupled plasma optical\nemission spectrometry to monitor the co-adsorption behavior of cations (Na+) and\ntypical (ultra-)short-chain PFASs (TFA and PFHpA) during the S-D-β200 adsorption\nprocess. To accurately evaluate the charge compensation mechanism, it was ensured at\nthe initial stage that the amounts of PFASs and Na+ in the solution were equal, and the\nadsorption amounts (mmol/g) of PFASs and Na+ on S-D-β200 at different times were\ncollected. As shown in Figure R1, the experimental results proved the occurrence of\ncharge compensation phenomenon. While S-D-β200 was in an equilibrium state of\nPFAS adsorption (i.e., 24 h), it also adsorbed a large amount of Na+ to alleviate the\nelectrostatic repulsion, which was consistent with our previous equilibrium simulation\nresults. Besides, the adsorption of PFASs occurred significantly earlier than that of Na+,\nwhich indicated that the S-D-β200 primarily drove PFASs into its nanopores through\nhydrophobic interaction, and then attracted the Na+ with electrostatic forces for charge\ncompensation. Therefore, the adsorption of PFASs by S-D-β200 does not involve co-\nadsorption of ionic pairs, and the main driving force is not electrostatic attraction, which\nis in line with our previous conclusion. We have incorporated the above results into the\nmanuscript, deleted pH experiment results, and revised unprofessional expression\nregarding “positive ions”. Thank you again for your valuable comments!\nFigure R1. The adsorption amounts (mmol/g) of (A) TFA, (B) PFHpA, and Na+ on S-\nD-β200 at different times ([TFA] =2.6 mmol/L, [PFHpA] =0.82 mmol/L, dosage: 10\n0 0\nmg/20 mL).\nR2\nRevisions (in the marked manuscript):\n1. “In nearly saturated S-D-β200 nanopores, the hydrophobic tails of (ultra)short-chain\nPFASs are bound by zeolite channels, whereas the hydrophilic heads converge at\nconfined water clusters and carry positive ions to eliminate electrostatic repulsion\n(charge compensation ratio: 92.0-101.6%)” in Line 265-268 was changed to “In nearly\nsaturated S-D-β200 nanopores, the hydrophobic tails of (ultra)short-chain PFASs are\nbound by zeolite channels, whereas the hydrophilic heads converge at confined water\nclusters and carry cations to eliminate electrostatic repulsion (charge compensation\nratio: 92.0-101.6%)”.\n2. “For pore adsorption, the (ultra-)short-chain PFASs formed a “zeolite framework-\nconfined water” dual-binding pattern in the S-D-β200 nanopores (Fig. S24B), while\nenhancing the adsorption of positive ions to alleviate the electrostatic repulsion effect\n(charge compensation rate: 92.0-101.6%, Fig. S25A-D)” in Supplementary\ninformation, Page S31 was changed to “For pore adsorption, the (ultra-)short-chain\nPFASs formed a “zeolite framework-confined water” dual-binding pattern in the S-D-\nβ200 nanopores (Fig. S24B), while enhancing the adsorption of cations (e.g., Na+ and\nH+) through electrostatic attraction and mass transfer optimization to alleviate the\nelectrostatic repulsion effect (charge compensation rate: 92.0-101.6%, Fig. S25A-E)”.\n3. “To further verify the charge compensation effect, we utilized the inductively\ncoupled plasma optical emission spectrometry to monitor the co-adsorption behavior of\ncations (Na+) and typical (ultra-)short-chain PFASs (TFA and PFHpA) during the S-D-\nβ200 adsorption process (Fig. S25D and E). Consistent with the simulation results,\nwhile S-D-β200 was in an equilibrium state of PFAS adsorption (i.e., 24 h), it also\nadsorbed a large amount of Na+ to alleviate the electrostatic repulsion. Besides, the\nadsorption of PFASs occurred significantly earlier than that of Na+, which indicated\nthat the S-D-β200 primarily drove PFASs into its nanopores through hydrophobic\ninteraction, and then attracted the Na+ with electrostatic forces for charge compensation”\nwas added in Supplementary information, Page S32.\nR3\n4. Fig. R1 was added as a part of Fig. S25.\nFig. S25. (A) Binding energy of (ultra-)short-chain PFASs under equilibrium\nadsorption model (calculate the traction force required to disrupt the adsorption\nequilibrium of (ultra-)short-chain PFASs by the steered MD method); potential of mean\nforce (PMF) calculated from umbrella trajectories when (B) H O+ and (C) Na+ enter\n3\nꞵ200 and S-D-ꞵ200 nanochannels using weighted histogram analysis method; the\nadsorption amounts (mmol/g) of (D) TFA, (E) PFHpA, and Na+ on S-D-β200 at\ndifferent times ([TFA] =[Na+] =2.6 mmol/L, [PFHpA] =[Na+] =0.82 mmol/L, dosage:\n0 0 0 0\n10 mg/20 mL).\nR4"}, {"round": 5, "reviewer_comments": {"reviewer_3": "The authors addressed one’s previous comments. The reviewer appreciates the additional experiment included to quantify cation adsorption and acknowledges that this represents a meaningful step toward clarifying the proposed charge compensation mechanism. I want to bring the following to the attention of the editor and the authors:\n1. Discrepancy in adsorption capacity data\nThere is a major inconsistency between the adsorption capacities reported in the original manuscript and the values obtained in the new sodium-form experiment. The manuscript previously reported a TFA adsorption capacity of 233.82 mg/g (≈2.05 mmol/g), yet the new data show <0.6 mmol/g at equilibrium (1440 min): less than 30% of the original claim. This discrepancy raises concerns about data reproducibility and reliability. The authors should clarify whether both measurements were conducted under comparable experimental conditions and provide a scientifically supported explanation for the deviation.\n2. Incomplete description of analytical methods for ultrashort-chain PFAS\nIn reviewing the analytical section in light of comment #1, several critical methodological details remain missing. Although the Supplementary Information notes filtration and internal standard addition, the quantification workflow is not adequately described. Key information - identity of internal standards, calibration approach, use of isotopically labeled analogs, assessment of matrix effects, and QA/QC procedures - is absent. These elements are essential for accurate quantification of small, hydrophilic PFAS such as TFA and PFPrA, especially on a C18 column. Given that mass-labeled TFA and PFPrA standards only recently became commercially available, I guess the authors did not use the corresponding IS for these two chemicals; the lack of a validated analytical method limits confidence in the reported concentrations.\n3. Recovery and desorption issues in SPE-based analysis\nWhen using SPE to concentrate ultrashort-chain PFAS, recovery values must be reported, as recoveries for TFA and PFPrA can vary widely. Without recovery data or correction, low analytical signal may be mistaken for strong adsorption rather than analytical loss.\nComments #2 and #3 could be clarified simply by providing negative-control data - running the entire procedure without adsorbent - to reveal background SPE contributions, filtration losses, container effects etc. I am sure the study already included such control experiments.", "reviewer_4": "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."}, "author_response": "Response to reviewers\nReviewer #3’s comments:\nThe authors addressed one’s previous comments. The reviewer appreciates the\nadditional experiment included to quantify cation adsorption and acknowledges that\nthis represents a meaningful step toward clarifying the proposed charge compensation\nmechanism. I want to bring the following to the attention of the editor and the authors:\nResponse: Thank you very much for your recognition of our work. Based on your\nadditional comments and suggestions, we have further supplemented the missing\ninformation in this manuscript. We believe that these revisions further enhance the\nreliability and reproducibility of our work.\n1. Discrepancy in adsorption capacity data\nThere is a major inconsistency between the adsorption capacities reported in the\noriginal manuscript and the values obtained in the new sodium-form experiment. The\nmanuscript previously reported a TFA adsorption capacity of 233.82 mg/g (≈2.05\nmmol/g), yet the new data show <0.6 mmol/g at equilibrium (1440 min): less than 30%\nof the original claim. This discrepancy raises concerns about data reproducibility and\nreliability. The authors should clarify whether both measurements were conducted\nunder comparable experimental conditions and provide a scientifically supported\nexplanation for the deviation.\nResponse: We sincerely apologize for this misunderstanding caused by insufficient\ndisclosure of the experimental operating conditions. We conducted the cation\nadsorption experiment using an initial concentration of 300 mg/L (i.e., 2.6 mmol/L) of\nTFA. At this concentration, S-D-β200 failed to reach its maximum adsorption capacity.\nTherefore, the truly comparable conditions should be the isothermal adsorption data\nwithin the initial concentrations of 240 mg/L (Fig. R1A, copied from Supplementary\ninformation Fig. S6A). At the approximate initial concentration (240 mg/L vs. 300\nmg/L, Fig. R1B), the adsorption capacity of the cation adsorption experiment was only\n16.8% lower than that of the isothermal adsorption experiment. The decrease in\nadsorption capacity can be attributed to the significant increase in the adsorbent dosage\nR1\n(5 mg/20 mL→10 mg/20 mL). The adjustment of the experimental conditions is\nprimarily aimed at increasing the concentration variations of Na+ and PFASs to evaluate\nthe differences in their adsorption behaviors. However, previous studies have reported\nthat under the same experimental conditions, an increase in the adsorbent dosage leads\nto competition for adsorption sites, resulting in a decrease in the adsorption capacity\nper unit of adsorbent (Fig. R1C and R1D)1,2. When the dosage of the adsorbent was\nreduced (C(TFA) : ~300 mg/L, dosage: 5 mg/20 mL), the adsorption capacity of S-D-\n0\nβ200 significantly increased (Fig. R1B). In addition, we conducted verification\nexperiments under the same experimental conditions (C(TFA) : ~240 mg/L, dosage: 5\n0\nmg/20 mL) to verify the accuracy of the obtained adsorption results (with a difference\nof less than 1%, Fig. R1B). Therefore, under the same experimental conditions, the\nresults obtained in this study exhibited suitable reproducibility. We apologize for the\nonly disclosing some of the experimental procedures in the figure legend and failing to\nprovide crucial information regarding the comparability of the experiments before and\nafter. To address this concern, we have included relevant experimental information in\nthe text to avoid further confusion. Thank you for your valuable comments.\nFigure R1. (A) Isothermal adsorption of β200 and S-D-β200 on TFA; (B) comparison\nof adsorption capacity of S-D-β200 under different experimental conditions; (C)\nadsorption isotherms of Cu (II) on kaolinite at different sorbent concentrations (Cs,\nCopied from Reference 1); (D) effect of adsorbent dose on methylene blue adsorption\nonto the Syringa vulgaris leaf (Copied from Reference 2).\nR2\nRevisions (in the marked manuscript):\n1. “To further verify the charge compensation effect, we utilized the inductively\ncoupled plasma optical emission spectrometry to monitor the co-adsorption behavior of\ncations (Na+) and typical (ultra-)short-chain PFASs (TFA and PFHpA) during the S-D-\nβ200 adsorption process (Fig. S25D and E)” in Supplementary information, Page\nS32 was changed to “To further verify the charge compensation effect, we utilized the\ninductively coupled plasma optical emission spectrometry to monitor the co-adsorption\nbehavior of cations (Na+) and typical (ultra-)short-chain PFASs (TFA and PFHpA)\nduring the S-D-β200 adsorption process (experiment condition: C(PFAS) =300 mg/L,\n0 0\nReferences\n1. Zhao, L. et al. A sorbent concentration-dependent Langmuir isotherm. Acta Phys.-\nChim. Sin. 28(12), 2905-2910 (2012).\n2. Mosoarca, G. et al. Syringa vulgaris leaves powder a novel low-cost adsorbent for\nmethylene blue removal: isotherms, kinetics, thermodynamic and optimization by\nTaguchi method. Sci. Rep. 10, 17676 (2020).\n2. Incomplete description of analytical methods for ultrashort-chain PFAS\nIn reviewing the analytical section in light of comment #1, several critical\nmethodological details remain missing. Although the Supplementary Information notes\nfiltration and internal standard addition, the quantification workflow is not adequately\ndescribed. Key information - identity of internal standards, calibration approach, use\nof isotopically labeled analogs, assessment of matrix effects, and QA/QC procedures -\nis absent. These elements are essential for accurate quantification of small, hydrophilic\nPFAS such as TFA and PFPrA, especially on a C18 column. Given that mass-labeled\nTFA and PFPrA standards only recently became commercially available, I guess the\nauthors did not use the corresponding IS for these two chemicals; the lack of a validated\nanalytical method limits confidence in the reported concentrations.\n3. Recovery and desorption issues in SPE-based analysis\nWhen using SPE to concentrate ultrashort-chain PFAS, recovery values must be\nreported, as recoveries for TFA and PFPrA can vary widely. Without recovery data or\nR3\ncorrection, low analytical signal may be mistaken for strong adsorption rather than\nanalytical loss.\nComments #2 and #3 could be clarified simply by providing negative-control data -\nrunning the entire procedure without adsorbent - to reveal background SPE\ncontributions, filtration losses, container effects etc. I am sure the study already\nincluded such control experiments.\nResponse: Thank you for bringing these issues to our attention. Our laboratory has\nspecifically focused on the detection of PFASs in environmental-related water and has\nestablished a complete workflow to ensure the accuracy of the data1-3. Therefore, this\nwork was conducted under strict quality assurance and control procedures. The specific\nmeasures include the following:\n(1) Evaluation of sample recovery: In previous experiments, we indeed conducted a\nnegative control experiment, namely the matrix-spiked sample test, to obtain the\nrecovery rate of (ultra-)short-chain PFASs (Table R1). The results indicate that after\nsample treatment (including filtration, SPE, etc.), our analytical method has an\nacceptable recovery level (70.2%-94.1%). Therefore, after being processed using the\nstandard procedure, the loss of (ultra-)short-chain PFASs in the samples is controllable,\nand the obtained data will not lead to misjudgment due to strong adsorption during\nprocessing.\nTable R1. Spike recoveries, and relative standard deviations of (ultra-)short-chain\nPFASs.\nRecoveries Relative standard deviation\nPFASs\n(%, mean ± sd, n=5) intra-day (%, n=3) inter-day (%, n=3)\nTFA 71.7 ± 6.9 4.2 9.1\nPFPrA 70.2 ± 4.1 6.5 8.2\nPFBA 74.6 ± 7.8 2.1 2.8\nPFBS 79.2 ± 10.4 0.9 1.3\nPFPeA 90.0 ± 9.1 1.2 2.2\nPFHxA 94.1 ± 10.7 2.6 3.4\nPFHxS 87.5 ± 15.1 3.2 3.5\nPFHpA 81.9 ± 10.9 4.5 5.1\nR4\n(2) Addition of internal standard: To further minimize potential errors in the analysis\nof individual samples, we calibrated the response values of the peaks by adding stable\nisotope labelled (ultra-)short-chain PFASs (all supplied by Wellington) to the samples\nbefore processing (Table R2). For compounds without a corresponding labelled analog\nstandard (i.e., TFA and PFPrA), a mass-labeled standard with a similar functional group\nand contiguous carbon chain length was used (i.e., M4PFBA). Previous studies have\ndemonstrated that this alternative method has acceptable recovery rates and precision4.\nTable R2. Information about the (ultra-)short-chain PFAS standards and their internal\nstandards.\nPrecursor ion Product ion Internal\nPFASs Formula Supplier\n(m/z) (m/z) standards\nTFA C HF O ANPEL 112.9 69.0 M4PFBA\n2 3 2\nPFPrA C HF O ANPEL 162.9 119.0 M4PFBA\n3 5 2\nPFBA C HF O AccuStandard 212.9 169.0 M4PFBA\n4 7 2\nPFBS C HF O S Wellington 298.9 80.1 M3PFBS\n4 9 3\nPFPeA C HF O AccuStandard 262.9 219.0 M5PFPeA\n5 9 2\nPFHxA C HF O Wellington 312.9 269.0 M5PFHxA\n6 11 2\nPFHxS C HF O S Wellington 398.9 80.2 M3PFHxS\n6 13 3\nPFHpA C HF O Wellington 362.9 319.0 M4PFHpA\n7 13 2\n(3) Instrument calibration: Prior to conducting mass spectrometry measurements, the\nmass axis and drift cell were calibrated using the Major Mix solution from the Major\nMix IMS/Tof Calibration kit (Waters). Leucine enkephalin, with an m/z of 554.2621 in\nnegative ionization mode, was injected every two minutes to real-time correct the mass\nand maintain an instrument resolution (maximum half-peak width) of approximately\n40000.\n(4) Evaluation of stability: The stability of the instrument was assessed using the\nrelative standard deviation (RSD) of repeated injections of PFAS standards responses\nboth inter-day and intra-day, with all RSD values below 10% (Table R1).\n(5) Elimination of other influences: The possible matrix effect on ionization was\nevaluated by comparing the peak areas for the injection standards in the sample and\nthose in a pure solvent. Procedure blanks were injected to determine the background\nR5\nvalues of various batch processes and measurements. Before analyzing the data,\nblank responses were subtracted from the sample signal.\nWe believe that, through the above rigorous quality assurance and control procedures,\nthe data in this work are highly reproducible and reliable. We have incorporated the\nabove-mentioned quality assurance and control procedures into this manuscript. Thank\nyou for your valuable comments.\nRevisions (in the marked manuscript):\n1. “Note S4. Quality assurance and quality control\nPrior to conducting mass spectrometry measurements, the mass axis and drift cell\nwere calibrated using the Major Mix solution from the Major Mix IMS/Tof Calibration\nkit (Waters). Leucine enkephalin, with an m/z of 554.2621 in negative ionization mode,\nwas injected every two minutes to real-time correct the mass and maintain an instrument\nresolution (maximum half-peak width) of approximately 40000. The recovery of\nmatrix-spiked samples was performed to evaluate the sample treatment process,\nshowing a high degree of accuracy, with mean recovery rates ranging from 70.2% to\n94.1% (Table S9). The stability of the instrument was assessed using the relative\nstandard deviation (RSD) of repeated injections of PFAS standard responses both inter-\nday and intra-day, with all RSD values below 10%. The possible matrix effect on\nionization was evaluated by comparing of the peak areas for the injection standards in\nthe sample and those in a pure solvent. The response values of the peaks in the samples\nwere calibrated using the corresponding internal standards (all supplied by Wellington).\nFor compounds without a corresponding labelled analog standard (i.e., TFA and PFPrA),\na mass-labeled standard with a similar functional group and contiguous carbon-chain\nlength was used (i.e., M4PFBA, Table S10). Previous studies have demonstrated that\nthis alternative method has acceptable recovery rates and precisionS1. Procedure blanks\nwere injected to determine the background values of various batch processes and\nmeasurements. Before analyzing the data, blank responses were subtracted from the\nsample signal.” was added in Supplementary information, Page S5-S6.\n2. “The instrument automatically injected a leucine enkephalin (m/z=554.2621, Waters,\nR6\nUSA) solution every two minutes for real-time quality correction, maintaining an\ninstrument resolution (maximum half-peak width) of approximately 40000” in\nSupplementary information, Page S3 was deleted.\n3. Table R1 and R2 were added in Supplementary information, Page S45-S46 as\nTable S9 and S10.\nReferences\n1. Mu, H. et al. Identification and characterization of diverse isomers of per- and polyfluoroalkyl\nsubstances in Chinese municipal wastewater. Water Res. 230, 119580 (2023).\n2. Mu, H. et al. Distribution, source and ecological risk of per- and polyfluoroalkyl substances in\nChinese municipal wastewater treatment plants. Environ. Int. 167, 107447 (2022).\n3. Mu, H. et al. Combination of suspect and nontarget screening with exposure assessment for per-\nand polyfluoroalkyl substance prioritization in Chinese municipal wastewater. Environ. Int. 198,\n109384 (2025).\n4. Dong, B. et al. Trace analysis method based on UPLC-MS/MS for the determination of (C2-C18)\nper- and polyfluoroalkyl substances and its application to tap water and bottled water. Anal. Chem.\n95, 695-702 (2023).\nR7\nResponse to reviewers\nReviewer #2 (Remarks to the Author):\nThe revision addresses all the previous concerns satisfactorily. To conclude, the content\nof the paper is publishable without any further edits.\nResponse: We are delighted to have addressed your concerns. We sincerely appreciate\nyour valuable comments, which have significantly enhanced the quality of our work.\nReviewer #3’s comments:\nThe authors have adequately addressed the reviewers’ concerns and comments, and the\nmanuscript is acceptable for publication.\nResponse: We are delighted to have addressed your concerns. We sincerely appreciate\nyour valuable comments, which have significantly enhanced the quality of our work.\nReviewer #4’s comments:\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 time in reviewing. Your valuable comments\nhave greatly improved our manuscript.\nR1"}]

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