Fluorous modification of commercial resins for ultrashort and short chain PFAS removal

Abstract

The invention is directed to modified resins containing perfluoroalkyl ethyl moieties that are capable of removing PFAS species from solutions, including water sources. Resin bases are modified with perfluoroalkyl ethyl moieties in a one-step modification, resulting in modified resins incorporating the perfluoroalkyl ethyl moieties via strong covalent bonds. Varying the perfluoroalkyl ethyl chain length and stoichiometric equivalents used in the modification reaction produces modified resins with different PFAS removal efficiencies. The modified resins of the present disclosure demonstrate cost-efficient removal of short chain and ultrashort chain PFAS species in practical conditions, such as removal from aqueous solutions with or without natural organic matter. This removal of challenging, persistent PFAS species is applicable to water treatment in commercial and individual settings.

Description

Fluorous Modification of Commercial Resins for Ultrashort and Short Chain PFASRemovalRELATED APPLICATION DATA

[0001] The present application claims priority pursuant to Article 8 of the Patent Cooperation Treaty to United States Provisional Patent Application Serial Number 63 / 670,308 filed July 12, 2024 and United States Provisional Patent Application Serial Number 63 / 805,733 filed May 14, 2025, each of which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to modified resins and methods of using same for the removal of per-and polyfluoroalkyl substances (PFAS) species from PFAS-containing solutions.SUMMARY

[0003] Generally, the present disclosure is directed to a modified resin and methods of making and using same. The modified resin includes a pristine resin (PR) base modified with at least one perfluoroalkyl ethyl moiety.

[0004] In some embodiments, the PR base is an anion exchange resin. In some embodiments, the PR base is in a form of a macroporous spherical bead. In some embodiments, each perfluoroalkyl ethyl moiety is attached to the PR base via linkage at amine groups of the PR base. In some embodiments, the modified resin is of the formula: PR-NHy[(CH2)2(CF2)n-iCF3]2-y, where PR-NHyis the pristine resin, wherein n is an integer ranging from 2-8, and wherein y is an integer ranging from 1-2. In some embodiments, the modified resin is configured to be regenerated for more than one cycle of PFAS species removal.

[0005] In another aspect of the present disclosure, there is provided a method of forming a modified resin. The method includes providing a pristine resin (PR) base and contacting the PR base with a perfluoroalkyl alkyl halide. The method further includes the step of producing the modified resin having at least one perfluoroalkyl alkyl moiety.

[0006] In some embodiments, the PR base is a resin with counter ions exchanged with hydroxide. In some embodiments, the PR base is a divinylbenzene crosslinked polymer having primary amine groups. In some embodiments, the perfluoroalkyl ethyl halide is contacted with the PR base in the presence of N,N-diisopropylethylamine, propanol, and water. In someembodiments, a perfluoroalkyl ethyl moiety of the perfluoroalkyl alkyl halide attaches to the PR base via linkage at amine groups of the PR base.

[0007] In another aspect of the present disclosure, there is provided a method of PFAS removal using a modified resin. The method includes providing a modified resin comprising a pristine resin (PR) base and at least one perfluoroalkyl alkyl moiety and contacting the modified resin with an initial solution containing at least one PFAS species. The method includes producing a treated solution wherein the at least one PFAS species is removed from the initial solution by the modified resin.

[0008] In some embodiments, the modified resin is provided at 0.05-1 g / L.

[0009] In some embodiments, the modified resin is of the formula: PR-NHy[(CH2)2(CF2)n- iCF3]2-y, where PR-NHyis the pristine resin, where n is an integer ranging from 2-8, and where y is an integer ranging from 1-2. In some instances, n is an integer ranging from 3-5 and y is 1. In some instances, a dosage equivalence ratio between the at least one perfluoroalkyl alkyl moiety and the PR base is 0.5.

[0010] In some embodiments, the PR base is a divinylbenzene crosslinked polymer having primary amine groups. In some embodiments, the at least one perfluoroalkyl alkyl moiety is attached to the PR base via linkage at amine groups of the PR base. In some embodiments, the initial solution contains at least one short chain or ultrashort chain PFAS species. In some embodiments, the initial solution is a multi-solute water solution containing at least one short chain or ultrashort chain PFAS species, and wherein the at least one short chain or ultrashort chain PFAS species is substantially absent in the treated solution. In some instances, the multisolute solution further includes natural organic matter. In some instances, the multi-solute solution has a pH range of 5 to 9. In some instances, the multi-solute solution includes up to 10 mM of NaCl.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. l is a schematic representation of a resin modification scheme by which a pristine resin (PR) base is modified with a perfluoroalkyl ethyl iodide (PRAEI-Cn) to produce a modified resin, PR-Cn-x, having a perfluoroalkyl ethyl moiety.

[0012] FIG. 2 is a graphical representation of Fourier-transform infrared spectroscopy (FT-IR) spectra, XPS spectra, and water contact angle analysis for starting materials and the modifiedresin product of the scheme of FIG. 1. In the left panel, FT-IR spectra compare OC Unmod, the OC-C2 series, and the C2 modifier, showing progressive intensification of the C-F absorption band with increasing modifier content. In the middle panel, high-resolution XPS spectra of OC Unmod, OC-C2-0.5, and OC-C2-5, provide direct evidence of covalent attachment through emerging amine signatures. In the right panel, water contact angle progression across the OC-C2 series is shown, where rising values (to 148°) demonstrate enhanced hydrophobicity at higher loadings; "N / A" denotes cases where swelling or absorption prevented accurate measurement.

[0013] FIG. 3 is a graphical representation of characterization of modified resins. SEM images confirm preservation of spherical particle morphology and surface integrity throughout modification, with representative images shown for OC Unmod and modified OC-C2 counterparts.

[0014] FIG. 4 is a graphical representation of FT-IR spectra of OC Unmod, OC-C2 modified resin series, and C2 modifier. As m increased, peak intensity at 1182 cm'1, characteristic of the C2 modifier, also increased indicative of higher modifier loading leading to an increase in modification yield confirming the success of the procedure.

[0015] FIG. 5 is a graphical representation of FT-IR spectra of OC Unmod, OC-C4 modified resin series, and C4 modifier. As m increased, peak intensity at 1205 and 1130 cm'1, characteristic of the C4 modifier, also increased indicative of higher modifier loading leading to an increase in modification yield confirming the success of the procedure.

[0016] FIG. 6 is a graphical representation of FT-IR spectra of OC Unmod, OC-C6 modified resin series, and C6 modifier. As m increased, peak intensity at 1234, 1180, and 1141 cm'1, characteristic of the C6 modifier, also increased indicative of higher modifier loading leading to an increase in modification yield confirming the success of the procedure.

[0017] FIG. 7 is a graphical representation of FT-IR spectra of OC Unmod, OC-C8 modified resin series, and C8 modifier. As m increased, peak intensity at 1195 and 1145 cm'1, characteristic of the C6 modifier, also increased indicative of higher modifier loading leading to an increase in modification yield confirming the success of the procedure.

[0018] FIG. 8 is a graphical representation of FT-IR spectra of Al 10 Unmod, Al 10-C2 modified resin series, and C2 modifier. As m increased, peak intensity at 1182 cm'1, characteristic of the C2 modifier, also increased indicative of higher modifier loading leading to an increase in modification yield confirming the success of the procedure.

[0019] FIG. 9 is a graphical representation of XPS spectra of OC Unmod, OC-C2-0.5, OC-C4- 0.5, and OC-C6-0.5 highlighting the characteristic peaks of C-N-C bonds (red) and C-NH2 bonds (blue) under the cumulative spectra fitting (purple line) with the raw data points (yellow dots).

[0020] FIG. 10 is a graphical representation of contact angle measurements for OC Unmod and OC-C2 modified resins. N / A indicates that a measurement cannot be determined due to swelling of the material.

[0021] FIG. 11 is a graphical representation of contact angle measurements for OC Unmod and OC-C4 modified resins. N / A indicates that a measurement cannot be determined due to swelling of the material.

[0022] FIG. 12 is a graphical representation of contact angle measurements for OC Unmod and OC-C6 modified resins. N / A indicates that a measurement cannot be determined due to swelling of the material. “Roll” indicates that the water droplet rolled once in contact with the material surface inhibiting accurate measurement, indicating superhydrophobicity.

[0023] FIG. 13 is a graphical representation of contact angle measurements for OC Unmod and OC-C8 modified resins. N / A indicates that a measurement cannot be determined due to swelling of the material. “Roll” indicates that the water droplet rolled once in contact with the material surface inhibiting accurate measurement, indicating superhydrophobicity.

[0024] FIG. 14 is a graphical representation of scanning electron microscopy (SEM) imaging for the (leftmost images) C2, (middle-left images) C4, (middle-right images) C6, and (rightmost images) C8 modified resin series at 35x magnification on the left and 80x magnification on the right for each image panel.

[0025] FIG. 15 is a graphical representation of PFCA removal performance of modified and unmodified resins. Both OC-C2-0.5 and OC-C4-0.5 demonstrated higher removal efficiencies compared to the pristine OC Unmod resin.

[0026] FIG. 16 is a graphical representation of adsorption kinetics of PFCAs on pristine and modified OC materials. Kinetic profiles of all five target PFCAs for (left panel) OC Unmod, (middle panel) OC-C2-0.5, and (right panel) OC-C4-0.5.

[0027] FIG. 17 is a graphical representation of adsorption kinetics of PFCAs on pristine and modified OC materials. Influence of fluorous modification on the kinetic uptake of individual PFCAs, (left panel) TFA, (middle panel) PFPrA, and (right panel) PFBA.

[0028] FIG. 18 is a graphical representation of adsorption kinetics of PFCAs on pristine and modified OC materials. Influence of fluorous modification on the kinetic uptake of individual PFCAs, (left panel) PFPeA and (right panel) PFHxA.

[0029] FIG. 19 is a graphical representation of adsorption thermodynamics of PFCAs on pristine and modified OC materials. Thermodynamics profiles of all five PFCAs for (left panel) OC Unmod, (middle panel) OC-C2-0.5, and (right panel) OC-C4-0.5.

[0030] FIG. 20 is a graphical representation of adsorption thermodynamics of PFCAs on pristine and modified OC materials. Influence of fluorous modification on the uptake thermodynamics of individual PFCAs, (left panel) TFA, (middle panel) PFPrA, and (right panel) PFBA.

[0031] FIG. 21 is a graphical representation of adsorption thermodynamics of PFCAs on pristine and modified OC materials. Influence of fluorous modification on the uptake thermodynamics of individual PFCAs, (left panel) PFPeA and (right panel) PFHxA.

[0032] FIG. 22 is a graphical representation of PFCA removal efficiencies in the presence of common competing species such as (top left panel) NOM, (top right panel) salinity, and (bottom panel) pH in water.

[0033] FIG. 23 is a graphical representation of removal percentages of the target PFCAs through five cycles for (top left panel) OC-C2-0.5 and (top right panel) OC-C4-0.5 with their respective recovery percentages between removal cycles (bottom left panel) and (bottom right panel).DETAILED DESCRIPTION

[0034] Ultrashort (C < 3) and short chain (C < 6) per- and polyfluoroalkyl substances (PF AS) represent an emerging class of micropollutants that extend beyond the well-studied and regulated legacy PF AS. These compounds present unique sorptive removal challenges due to their weaker hydrophobic interactions with conventional sorbents and their pronounced ionic character in natural water matrices, where they are easily outcompeted by more prevalent inorganic ions. Here, a novel modification reaction is introduced, where it is applicable to commercial resins, to enable the incorporation of a tunable fluorous effect. Twenty modified resins are synthesized with varying degrees of fluorous affinity, allowing systematic evaluation of how F F interactions enhance ultrashort and short chain PFAS removal. Successful modification isconfirmed through multiple characterization techniques. Notably, OC-C4-0.5 demonstrated exceptional trifluoroacetate (TFA) retention, with less than 2% capacity loss over 72 h — far outperforming the pristine resin (15% loss). Both OC-C2-0.5 and OC-C4-0.5 also showed substantially higher TFA uptake in thermodynamic studies. This highlights the potential of fluorous-effect tuning to enhance sorbent affinity for ultrashort and short chain PFAS, offering a promising strategy for next-generation concentration technologies.

[0035] Ultrashort (C < 3) and short chain (C < 6) PFAS represent a growing environmental and public health concern as emerging micropollutants. These compounds have recently become increasingly prevalent due to their use as replacements for regulated long-chain PFAS, as well as their formation as degradation intermediates, by- or end-products (e.g., trifluoroacetic acid, TFA) during PFAS breakdown processes. Unlike their long-chain counterparts, ultrashort and shortchain PFAS exhibit higher mobility in the environment due to their stronger electrostatic interactions and reduced hydro- / oleophobicity, leading to distinct transport behaviors. Despite being less studied than legacy long-chain PFAS, emerging toxicity data suggests that these shorter-chain alternatives may still pose significant risks. Given their rising environmental prevalence, enhanced mobility, and potential adverse health effects, there is an urgent need to develop effective treatment strategies for ultrashort and short-chain PFAS.

[0036] The sorptive removal of ultrashort and short-chain PFAS remains less studied and significantly more challenging compared to their long-chain counterparts. Sorption is one of the most promising remediation strategies for PFAS contamination due to its cost efficiency and compatibility with existing water treatment infrastructure. However, conventional sorbents such as activated carbon (AC) and anion exchange resins (AER) rely primarily on hydrophobic and electrostatic interactions, which often prove insufficient for the effective uptake of ultrashort and short-chain PFAS. These smaller PFAS species exhibit lower hydrophobicity — owing to their shorter fluorinated chains — and face strong competition from abundant environmental ions and natural organic matter. As a result, there is a pressing need for more efficient and cost-effective sorbents to safeguard water quality and public health.

[0037] Herein, the first fluorous-functionalized modification of a commercial AER designed to target ultrashort and short chain perfluoroalkyl carboxylic acids (PFCAs) is described, a dominant and challenging PFAS subclass. The fluorous effect herein is achieved through per- / polyfluorinated alkyl chain incorporation. Unlike generic hydrophobic or electrostaticinteractions, this orthogonal mechanism relies on strong, selective intermolecular forces that drive self-aggregation and phase separation. Its unique selectivity allows for short-chain PF AS removal. Using a commercially available resin, a one-step modification strategy was developed to incorporate tunable fluorous functionality, generating a series of fluorinated resins. The addition of the fluorous effect was evaluated regarding enhanced adsorption of ultrashort and short chain PFAS through kinetic uptake, thermodynamic capacity, selectivity, and regenerative studies. The success of the modification was confirmed through systematic solid-state characterization. Furthermore, in-depth adsorption kinetics, thermodynamics, and selectivity studies reveal how the fluorous effect synergizes with inherent electrostatic and hydrophobic interactions to preferentially capture ultrashort chain PFAS.

[0038] These and other embodiments are further illustrated in the following non-limiting examples.EXAMPLES

[0039] The present examples provide aspects of embodiments of the present disclosure. These examples are not meant to limit embodiments solely to such examples herein, but rather to illustrate some possible implementations.EXAMPLEMATERIAL AND METHODSMaterials

[0040] The present disclosure is focused on five ultrashort and short chain perfluoroalkyl carboxylic acids (PFCAs): trifluoroacetic acid (TFA), perfluoropropanoic acid (PFPrA), perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), and perfluorohexanoic acid (PFHxA). Neat PFAS compounds were obtained from Synquest Laboratories. Mass-labeled standards for TFA and PFPrA were purchased from Cambridge Isotope Laboratories, while all other mass-labeled standards were sourced from Wellington Laboratories. Additional chemicals and solvents were acquired from Fisher Scientific and Oakwood Chemical. All commercial reagents were of analytical grade and used without further purification. Lewatit® VP OC 1065 resin was provided by LANXESS, and Al 10 resin was purchased from Purolite™.Material Synthesis

[0041] The parent resin, Lewatit® VP OC 1065, was first converted to its free base form by treatment with NaOH (1 M). Following extensive washing with MQ water and solvent exchange with acetone, the resins were vacuum-dried prior to modification. For the modification reaction, 20 mg of resin was added to 1 mb of a 1:1 (v / v) PrOH:MQ water solution along with N,N- diisopropylethylamine (DIEA, 1292.4 mg, 10 mmol) and perfluoroethyl iodide (containing 2, 4, 6, or 8 fluorinated carbons, 10 mmol for loading rations 1 :5, 6 mmol for 1 :3, 3 mmol for 1 : 1.5, 2 mmol for 1: 1, and 1 mmol for 1 :0.5). The mixture was then microwaved at 160°C for 4 hours at 300 W power. Upon reaction completion, the modified resins underwent sequential washing with NaCl solution (0.086 mol), MQ water, and acetone, followed by vacuum drying. The prepared resins were then used for PFCA removal experiments. As a control, unmodified resin underwent identical solvent exchange (NaCl-MQ water-acetone) drying pretreatment to ensure parallel processing conditions.Material Characterization

[0042] Functionalization success was characterized through Fourier-transform infrared spectroscopy (FT-IR) on a Shimadzu IRAffinitiy- 1 S spectrometer (64 scans at 4 cm1resolution) and X-ray photoelectron spectroscopy (XPS) using a PHI VersaProbe system with monochromatic Al Ka radiation (100 pm diameter, 15kV X-ray beam). Surface properties were evaluated via contact angle measurements (2 pL DI water droplets) and scanning electron microscopy (FEI Nova Nanolab 200 SEM operated at 15 kV with a 5 - 10 mm working distance).Performance StudyPFCA Removal Experiments as Initial Performance Assessment

[0043] MQ water was spiked with five PFCAs to achieve a final concentration of 100 ppb for each analyte. Resins were then added at an adsorbent dosage of 500 mg / L, and the samples were shaken at 150 rpm at room temperature. After shaking, the resins were separated, and the solution was analyzed via LC-MS / MS.PFCA Adsorption Kinetics Experiments

[0044] Batch adsorption kinetics experiments were conducted to evaluate the removal of five PFCAs. MQ water was spiked to achieve an initial concentration of 100 ppb for each PFCA, and a resin dosage of 500 mg / L was applied. The samples were shaken at 150 rpm at roomtemperature, and approximately 1.5 mL aliquots were collected at 30 s, 1 min, 5 min, 10 min, 15 min, 30 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 5 h, 10 h, 15 h, 24 h, 48 h, and 72 h. The adsorption kinetics was best described by the pseudo-second-order model (Eq. 1), with detailed parameters provided in Table 2. t(It = — - - (Eq- 1) k2qe+ePFCA Adsorption Thermodynamic Experiments

[0045] Batch adsorption thermodynamic experiments were conducted to evaluate the removal of five PFCAs. MQ water was spiked to achieve an initial concentration of 0, 10, 50, 100, 500, 1000, 3000, 5000, 10000 ppb for each PFCA, and a resin dosage of 500 mg / L was used. The samples were shaken at 150 rpm at room temperature for 15 hours. After shaking, the resins were separated, and the solution was analyzed via LC-MS / MS. The adsorption thermodynamics were best described by the Freundlich model (Eq. 2), with detailed parameters provided in Table 3.PFCA Uptake with the Co-Existence ofNOM

[0046] Suwannee River Organic Matter was dissolved in MQ water at a concentration of 10 mg / L, sonicated for 30 minutes, and vacuum-filtered through a 0.45 pm PES membrane. The solution was then spiked with five PFCAs to a final concentration of 100 ppb each. Prior to PFCA addition, the total organic carbon (TOC) content was measured at 32.04 mg / L. Resins were added at an adsorbent dosage of 500 mg / L, and the samples were shaken at 150 rpm at room temperature. After shaking, the resins were separated, and the supernatant was analyzed via LC-MS / MS.PFCA Uptake with Co-Existence ofNaCl

[0047] A 10 mM NaCl solution served as the water matrix and was prepared using the same filtration method prior to batch adsorption experiments. The solution was spiked with five PFCAs to a final concentration of 100 ppb each. Resins were added at a dosage of 500 mg / L, and the samples were shaken at 150 rpm at room temperature. After shaking, the resins were separated, and the supernatant was analyzed via LC-MS / MS. SPE was required for TFAanalysis, while PFPrA, PFBA, PFPeA, and PFHxA were quantified directly without additional pretreatment.PFCA Uptake at Various pHs

[0048] The pH of MQ water spiked with 100 ppb of five PFCAs was measured as 8.01. Buffer solutions at pH 5 (using -17.4 M AcOH) and pH 9 (using -15M NH4OH) were prepared. Each solution was then spiked with the five PFCAs to achieve a final concentration of 100 ppb per analyte. Resins were added at a dosage of 500 mg / L, and the samples were shaken at 150 rpm at room temperature. Following equilibration, the resins were separated, and the supernatant was analyzed by LC-MS / MS.Resin Regeneration

[0049] The resins were preloaded with the five target PFCAs using the batch adsorption procedure described previously, and the adsorbed PFAS mass was quantified. For regeneration, the PFCA-laden resins were treated with a 70:30 (v / v) 100 mM NH40H / Me0H solution under agitation (150 rpm, > 3 h). The PFAS concentration in the regeneration solution was then measured, while the regenerated resins were collected for subsequent adsorption cycles.Analytical Methods

[0050] PFAS concentrations were analyzed by a Thermo Scientific Accela liquid chromatography (LC) coupled with a Thermo Scientific TSQ Quantum Ultra triple quadrupole tandem mass spectrometry (MS / MS). The analytes were separated through an ion-exchange column (RSpak JJ-50 2D; 2.0mm x 150mm, 5pm; Shodex). Mobile phase A was 100 mM ammonium acetate in Milli-Q® (MQ) water, and mobile phase B was HPLC-grade methanol. The flow rate was 0.15 mL / min for the whole elution (22 minutes: 8 minutes equilibrium, 10.5 minutes analysis, and 3.5 minutes wash). Gradient elution started from 80% B to 50% B in 11 minutes and held for 10 minutes. The electrospray ionization MS / MS with multiple reaction monitoring (MRM) was operated in negative mode. For LC-MS / MS analysis, samples were first filtered through a 0.2 pm nylon membrane filter. An aliquot of 200 pL filtered sample was then mixed with 20 pL of internal standard solution (100 ppb) and analyzed by LC-MS / MS with a 100 pL injection volume.RESULTSResin Modification

[0051] A nucleophilic substitution reaction in organic syntheses was adapted, for the first time, to be employed in the incorporation of the fluorous effect on AER (FIG. 1). As a proof of concept, the parent resin, Lewatit® VP OC 1065 (designated as OC in the following discussion) bearing a primary amine, was selected due to its compatibility with the modification reaction and its potential as a regenerable PFAS sorbent, given its weak-base nature. The OC resin was first converted to its free base form. The following modification involved a single-step reaction, outlined in detail below, with microwave synthesis significantly accelerating the process.

[0052] Briefly, resin modifications were carried out using a CEM Discover SP Microwave Synthesizer. Functionalization success was characterized through FT-IR on a Shimadzu IRAffmitiy-lS spectrometer (64 scans at 4 cnr1resolution) and X-ray photoelectron spectroscopy (XPS) using a PHI VersaProbe system with monochromatic Al Ka radiation (100 pm diameter, 15kV X-ray beam). Surface properties were evaluated via contact angle measurements (2 pL DI water droplets) and scanning electron microscopy (FEI Nova Nanolab 200 SEM operated at 15 kV with a 5 - 10 mm working distance). Total organic carbon content was quantified by catalytic combustion at 850°C using a Skalar Formacs HT Combustion analyzer. Table 1 displays targeted analytes for ESI-PFAS analysis.Table 1. Targeted analytes for ESI- PFAS analysis.NeutralChemical Name Acronym Molecular Internal StandardFormulaTrifluoroacetic Acid TFA C2NO2F3 13C2-TFAPerfluoropropanoic Acid PFPrA C3HO2F5 13C3-PFPrAPerfluorobutanoic Acid PFBA C4HO2F7 13C4-PFBAPerfluoropentanoic Acid PFPeA C5HO2F9 13C5-PFPeAPerfluorohexanoic Acid PFHxA C6HO2F11 13C5PFHxA

[0053] After reaction completion, the resins retained their original appearance and were collected for solvent exchange and drying before further characterization and PFAS removal evaluation. The modified resins were named following the convention OC-Cn-m, where n denotes the number of fluorinated carbons from the modifier, and m represents the dosageequivalence ratio between the modifier and the resin. Leveraging the high feasibility of our newly developed modification method, 20 modified resins were synthesized and a sorbent library was built to enable systematic investigation of how the fluorous effect influenced the capture of ultrashort and short chain PF AS.Resin Characterization

[0054] The modified resins were characterized to confirm successful modification, evaluate chemical conversions, and assess surface changes resulting from the modification process. FT-IR analysis of the OC-C2 series revealed a strong, characteristic C-F stretching band atconsistent with the spectrum of the C2 modifier (FIG. 2, left panel, and FIG. 4). The intensity of this band increased with higher m values, and a similar trend was observed for the OC-C4, OC- C6, and OC-C8 resin series (FIGS. 5, 6, and 7). This indicates that the greater the modifier loading, the higher the modification yields, which is further supported by XPS analysis (FIG. 2, middle panel). High-resolution XPS spectra of Nls showed a progression from no detectable secondary amine absorbance in OC Unmod to strong absorbance in OC-C2-0.5 and OC-C2-5, confirming covalent bonding between the resin and the modifier thus the successful execution of the targeted modification. A comparison of the XPS spectra for OC-C2-0.5, OC-C4-0.5, and OC- C6-0.5 (FIG. 9) revealed a decrease in C-N-C absorbance as the modifier's chain length increased, suggesting, though not intending to be bound by theory, that lower reaction yields are likely due to greater steric hindrance.

[0055] The incorporation of the fluorous effect significantly altered surface tension, as evidenced by wettability analysis (FIG. 2, right panel). Contact angle measurements revealed substantial swelling in OC Unmod — a typical behavior for resin materials — which prevented reliable measurements. For resins with lower C2 loadings (m = 0.5 and 1), only minor swelling occurred, but immediate water sorption upon droplet contact still hindered accurate readings. In contrast, higher C2 loadings (m = 1.5 and 3) induced pronounced hydrophobicity, with contact angles sharply rising to 77° and 148°, respectively. However, further increasing the fluorous modification (e.g., OC-C2-5) did not enhance hydrophobicity beyond this threshold, suggesting, while not wishing to be bound by theory, a saturation effect. The OC-C4, OC-C6, and OC-C8 resin series exhibited comparable wettability trends (FIGS. 10, 11, 12, and 13). In the higher modifier chain length series, water droplets tended to roll upon contact, indicating high hydrophobicity but complicating precise measurement. SEM imaging confirmed that allmodified resins retained their spherical morphology and smooth surfaces post-modification (FIG. 3 and FIG. 14). Collectively, these characterizations verify the successful targeted modification.Initial Performance Assessment of Modified Resins for Ultrashort and Short Chain PFCA Removal

[0056] All 20 modified resins and OC Unmod were evaluated for their removal efficiency toward five ultrashort and short chain PFCAs, namely TFA, PFPrA, PFPeA, PFBA, and PFHxA, ranging from C2-C6. (FIG. 15). Initial analysis revealed that resins with higher degrees of fluorous modification (increased m and / or n values) exhibited poorer PFAS removal performance. Without wishing to be bound by theory, it is hypothesized that excessive fluorous moiety incorporation may introduce extreme hydrophobicity, thereby limiting resin-water interactions and ultimately impairing PFAS sequestration. This observation also aligns with similar previous findings reported for other hydrophobic materials. Among the tested resins, OC- C2-0.5 and OC-C4-0.5 demonstrated PFAS removal efficiencies comparable to or exceeding that of the unmodified resin. Specifically, OC-C2-0.5 outperformed OC Unmod and OC-C4-0.5 for PFPrA, PFBA, PFPeA, and PFHxA but showed relatively low TFA removal, whereas OC-C4- 0.5 exhibited consistently higher removal efficiency across all five ultrashort and short chain PFCAs. Based on these results, OC-C2-0.5 and OC-C4-0.5 were selected for further investigation.Adsorption Kinetics of Modified Resins

[0057] PFCA adsorption kinetics were then evaluated to assess the fluorous effect’s influence on OC resins (FIGS. 16, 17, and 18). The observed higher uptake equivalents of shorter-chain PFCAs across all resins (FIG. 16) can be attributed to their smaller size that leads to faster mass transfer. TFA adsorption kinetics (FIG. 17, left panel) displays spontaneous TFA desorption from OC Unmod and OC-C2-0.5 — a phenomenon previously reported for other sorbents and consistent with TFA’ s tendency for faster breakthrough. OC Unmod began desorbing TFA at 10 h, losing -15% of its capacity by 72 h, while OC-C2-0.5 exhibited markedly shorter retention (-3 h) and a -60% capacity loss. In contrast, OC-C4-0.5 displayed negligible desorption (-2%), maintaining robust retention. Competitive displacement by longer-chain PFCAs was ruled out as the cause of this phenomenon, since other PFCA species had already reached near- saturation when TFA desorption began. Instead, without wishing to be bound by theory, it was speculated that desorption likely stemmed from weak TFA binding affinity, dictated by the fluorinatedamine environment (FIG. 1). In OC Unmod, protonated primary amines drove TFA capture via electrostatic forces, whereas OC-C2-0.5’s weaker fluorous effect (shorter C2 modifiers), but much higher loading (higher modification yield), introduced steric hindrance that weakened electrostatic interaction. OC-C4-0.5, however, achieved an optimal balance between electrostatic and F F interactions: while electrostatic forces facilitated efficient initial TFA mass transport and capture from solution, the fluorous effect enabled subsequent retention of adsorbed TFA. This finding is consistent with established reports showing enhanced efficiency of F F interactions at shorter intermolecular distances.

[0058] For longer chain PFCAs (PFPrA, PFBA, PFPeA, PFHxA), all resins achieved equilibrium adsorption within 10 hours, with minimal or no desorption observed (FIG. 17 and FIG. 18). The trend in desorption followed: OC-C4-0.5 < OC Unmod < OC-C2-0.5 for PFPrA, consistent with what was observed for TFA. The distinct kinetics difference between TFA and PFPrA further reinforced that even three-carbon PFPrA is much easier to be captured and retained, highlighting the role of PFAS chain lengths in their sorptive removal efficacy. Pseudo- second-order kinetics provided the best fit for all PFAS analytes (Table 2). Notably, OC-C4-0.5 exhibited a higher k2 value for the ultrashort PFCA species, TFA and PFPrA, along with the short chain species, PFBA and PFPeA, once again suggesting, without wishing to be bound by theory, that an optimal degree of fluorous modification — balanced with electrostatic interactions — enhances adsorption kinetics, particularly for ultrashort-chain PFCAs. Based on this kinetics data, all subsequent PFCA removal experiments were conducted for 15 hours to ensure uptake equilibrium for PFPrA, PFBA, PFPeA, and PFHxA, while minimizing substantial desorption of TFA.Table 2. Parameters of pseudo-second-order kinetics model calculated from experimental data. k2(rng g ' hrResin Type qe(jig / mg) ') R2OC Unmod 0.189 13.8 0.994TFA OC-C2-0.5 0.161 33.7 0.997OC-C4-0.5 0.190 34.1 0.999OC Unmod 0.194 9.37 0.995PFPrA OC-C2-0.5 0.187 12.4 0.998OC-C4-0.5 0.194 12.8 0.999OC Unmod 0.229 5.31 0.999PFBA OC-C2-0.5 0.227 8.19 0.999OC-C4-0.5 0.231 9.10 0.999OC Unmod 0.224 4.03 0.999PFPeA OC-C2-0.5 0.223 6.00 0.999OC-C4-0.5 0.225 6.35 0.999OC Unmod 0.248 4.24 0.997PFHxA OC-C2-0.5 0.248 3.79 0.997OC-C4-0.5 0.249 3.77 0.999Adsorption Thermodynamics of Modified Resins

[0059] The PFAS uptake capacities of OC Unmod, OC-C2-0.5, and OC-C4-0.5 were evaluated, and none of the resins reached their maximum uptake capacity, even at equilibrium concentrations of 700 ppb or higher (FIG. 19). Among all unmodified and modified resins, PFHxA exhibited the lowest adsorption capacity. However, this trend was not as evident in our general PFAS removal experiments at a lower initial concentration (Co) of 100 ppb. Without wishing to be bound by theory, this may stem from the weaker electrostatic interactions associated with PFHxA — a longer-chain PFCA — compared to shorter-chain PFCAs. These findings align with previous studies suggest that ion-exchange resins are more effective at capturing shorter-chain PFAS species.

[0060] For all five PFCA species, incorporating the fluorous effect had the most significant positive impact for TFA uptake thermodynamics (FIG. 20, left panel), consistent with the kinetics data, illustrating the potential of the fluorous effect in promoting ultrashort chain PFAS capture selectivity. The Freundlich model provided a satisfactory fit for all sorption isotherms (FIG. 20, FIG. 21, and Table 3). Overall, OC-C4-0.5 exhibited higher KF and 1 / n values, indicating higher capacity and more favorable binding affinity for PFAS. This further demonstrated that an optimal degree of F F interactions is critical for enhancing PFAS capture. When compared to other sorbents (e.g. activated carbons) the disclosed resins demonstrated significantly higher KF values, consistent with prior studies showing the higher efficiency of ionexchange resins for shorter chain PFAS capture. Notably, thermodynamic data for TFA andPFPrA adsorption remain unavailable to date, highlighting a critical research gap in ultrashort chain PFAS removal in prior existing studies.Table 3. Parameters of Freundlich model calculated from experimental data.Resin TypeOC Unmod 0.121 0.748 0.985TFA OC-C2-0.5 0.0878 0.850 0.989OC-C4-0.5 0.156 0.764 0.995OC Unmod 0.318 0.498 0.942PFPrA OC-C2-0.5 0.458 0.431 0.985OC-C4-0.5 0.487 0.570 0.981OC Unmod 0.396 0.720 0.987PFBA OC-C2-0.5 0.0421 0.848 0.973OC-C4-0.5 0.321 0.703 0.981OC Unmod 0.154 0.761 0.970PFPeA OC-C2-0.5 0.293 0.674 0.997OC-C4-0.5 0.148 0.756 0.959OC Unmod 0.415 0.782 0.944PFHxA OC-C2-0.5 0.306 0.635 0.954OC-C4-0.5 0.165 0.911 0.977PFAS Removal in Complex Water Matrices

[0061] PFAS removal performance of the disclosed resins in multi-solute systems was next evaluated, including natural organic matter (NOM), salinity (NaCl), and pH variations. In the presence of NOM (32.04 mg / L TOC), OC Unmod and OC-C2-0.5 exhibited a slight decline in PFAS removal efficiency, whereas OC-C4-0.5 largely maintained its binding capacity, likely due to the additional selective F F interaction (FIG. 22, top left panel). Notably, all resins showed enhanced TFA uptake, particularly OC-C2-0.5, likely due to TFA binding to NOM and coremoved. Overall, the data revealed that NOM did not significantly compete with ultrashort- and short-chain PFCAs, suggesting that their capture occurs through distinct mechanisms.

[0062] The co-existence of NaCl (10 mM) had a greater impact on PF AS removal (FIG. 22, top right panel). In general, PFPeA and PFHxA exhibited smaller reductions in removal efficiency (< 30%) in the presence of NaCl, further confirming that electrostatic interaction is not the dominant capture mechanism for these longer-chain PF AS. Among the three resins tested, OC-C2-0 5 and OC-C4-0.5 showed higher PF AS removal efficiencies and greater resistance to high ionic strength compared to OC Unmod. This was particularly evident in the capture of PFPrA by OC-C2-0.5, suggesting that the incorporation of C2 and C4 fluorinated moi eties enhances binding affinity for ultrashort-chain PFAS species.

[0063] The performance of three resins under varying pH conditions (5, 7, and 9; FIG. 22, bottom panel) was also evaluated. For all three resins, as the solution shifted from acidic (pH 5) to neutral (pH 7), a slight decline in PFAS removal efficiency was observed, suggesting that, without wishing to be bound by theory, most amino groups remained protonated and continued to facilitate synergistic electrostatic, hydrophobic, and F F interactions. Interestingly, PFHxA exhibited an opposite trend across all three resins, which is attributed to the greater influence of London dispersion forces — including hydrophobic and fluorous effects — over electrostatic interactions in longer-chain PFAS capture. When the pH further increased to 9, a sharp drop in removal efficiency occurred for all PFAS, though PFHxA maintained the highest retention. This further supports the dominance of electrostatic interactions in shorter chain PFAS removal, whereas PFHxA — despite having only five fluorinated carbons — retained sufficient hydrophobic and F F interactions to bind to neutral resin surfaces. Among the three resins, OC-C4-0.5 consistently outperformed OC Unmod in PFAS removal, demonstrating the efficacy of the fluorous effect regardless of pH.Resin Regeneration

[0064] Saturated resins can be regenerated for reuse. Among all tested conditions, a 30 / 70 (v / v) 100 mM NH4OH (aq) / MeOH solution proved to be the most effective regenerant for the disclosed modified resins (FIG. 23). This aligns with the previous finding that synergistic electrostatic, hydrophobic, and F F interactions require both salt and organic solvent components for efficient sorbent regeneration. The regenerated resins largely retained their original PFPeA and PFHxA removal efficiencies (FIG. 23, top left and right panels). However, a significant decline in removal efficiency was observed for shorter chain PFCAs (TFA, PFPrA, and PFBA) after the first regeneration cycle, with the loss being more pronounced for theshortest-chain compounds. Beyond the first cycle, removal efficiencies remained relatively stable for subsequent regenerations. Without wishing to be bound by theory, it is hypothesized that upon regeneration, residual adsorbed PFAS may have obstructed the positively charged amino binding sites, which are critical for ultrashort chain PFAS capture.

Claims

CLAIMS1. A modified resin, comprising: a pristine resin (PR) base modified with at least one perfluoroalkyl ethyl moiety.

2. The modified resin of claim 1, wherein the PR base is an anion exchange resin.

3. The modified resin of claim 2, wherein the PR base is in a form of a macroporous spherical bead.

4. The modified resin of claim 2, wherein each perfluoroalkyl ethyl moiety is attached to the PR base via linkage at amine groups of the PR base.

5. The modified resin of claim 1, wherein the modified resin is of the formula:PR-NHy[(CH2)2(CF2)n-lCF3]2-y wherein PR-NHyis the pristine resin, wherein n is an integer ranging from 2-8, and wherein y is an integer ranging from 1-2.

6. The modified resin of claim 1, wherein the modified resin is configured to be regenerated for more than one cycle of PFAS species removal.

7. A method of forming a modified resin comprising: providing a pristine resin (PR) base; contacting the PR base with a perfluoroalkyl alkyl halide; and producing the modified resin having at least one perfluoroalkyl alkyl moiety.

8. The method of claim 7, wherein the PR base is a resin with counter ions exchanged with hydroxide.

9. The method of claim 7, wherein the PR base is a divinylbenzene crosslinked polymer having primary amine groups.

10. The method of claim 7, wherein the perfluoroalkyl ethyl halide is contacted with the PR base in the presence of N,N-diisopropylethylamine, propanol, and water.

11. The method of claim 7, wherein a perfluoroalkyl ethyl moiety of the perfluoroalkyl alkyl halide attaches to the PR base via linkage at amine groups of the PR base.

12. A method of PFAS removal using a modified resin, comprising: providing a modified resin comprising a pristine resin (PR) base and at least one perfluoroalkyl alkyl moiety; contacting the modified resin with an initial solution containing at least one PFAS species; andproducing a treated solution wherein the at least one PF AS species is removed from the initial solution by the modified resin.

13. The method of claim 12, wherein the modified resin is provided at 0.05-1 g / L.

14. The method of claim 12, wherein the modified resin is of the formula:PR-NHy[(CH2)2(CF2)n-lCF3]2-y wherein PR-NHyis the pristine resin, wherein n is an integer ranging from 2-8, and wherein y is an integer ranging from 1-2.

15. The method of claim 14, wherein n is an integer ranging from 3-5 and y is 1.

16. The method of claim 14, wherein a dosage equivalence ratio between the at least one perfluoroalkyl alkyl moiety and the PR base is 0.5.

17. The method of claim 12, wherein the PR base is a divinylbenzene crosslinked polymer having primary amine groups.

18. The method of claim 12, wherein the at least one perfluoroalkyl alkyl moiety is attached to the PR base via linkage at amine groups of the PR base.

19. The method of claim 12, wherein the initial solution contains at least one short chain or ultrashort chain PFAS species.

20. The method of claim 12, wherein the initial solution is a multi-solute water solution containing at least one short chain or ultrashort chain PFAS species, and wherein the at least one short chain or ultrashort chain PFAS species is substantially absent in the treated solution.

21. The method of claim 20, wherein the multi-solute solution further includes natural organic matter.

22. The method of claim 20, wherein the multi-solute solution has a pH range of 5 to 9.

23. The method of claim 20, wherein the multi-solute solution includes up to 10 mM of NaCl.

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