Charge switchable ion exchange resin, methods of manufacture and use thereof

Abstract

There is provided a charge switchable ion exchange (IX) resin comprising solid microparticles made of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group. A method for manufacturing this resin is also provided. Methods for capturing ions from a feed, exchanging ions in a feed, for concentrating a contaminant by capturing and accumulating ions of said contaminant and then releasing and electrostatically repulsing said ions, and for regenerating the resin are also provided.

Description

CHARGE SWITCHABLE ION EXCHANGE RESIN, METHODS OF MANUFACTURE AND USE THEREOFCROSS REFERENCE TO RELATED APPLICATIONSThis application claims benefit, under 35 U.S.C. § 119(e), of U.S. provisional application Serial No. 63 / 710,137, filed on October 22, 2024. All documents above are incorporated herein in their entirety by reference.FIELD OF THE INVENTION

[0001] The present invention relates to charge switchable ion exchange resin. More specifically, the present invention is concerned with charge switchable ion exchange resin that can switch between a positive and a negative charge when exposed to different pHs.BACKGROUND OF THE INVENTION

[0002] Charged polymers, containing either zwitterionic groups or a mixture of anionic and cationic groups, have shown high selective adsorption properties to specific proteins and chemicals in response to their surrounding environments, such as pH change, redox status, reactive oxygen species levels, light, and enzyme.1 5To date, the charged polymers with negative or positive charge have been dominantly utilized for the nanotechnology below 100 nm such as nanoparticle-based drug delivery to enhance interaction with the targeting cancer cell.1’3The large size microspheres having tens or hundreds of micrometers (urn) suggest other uses, such as pollutant filtering in drinking water through the use of enhanced adsorbents of hazardous chemicals, like per- and polyfluoroalkyl substances (PFAS), by the strengthened polymer-poll utant interaction as well as exhibition of water clearance.47However, such large size microspheres still need to have desirable high adsorption capacity, recyclability, non-toxicity, and cost-effectiveness. Large size microsphere incorporated with the charged polymer, which is named as ion-exchange (IX) resin, has been developed for water treatment for environmental and health protection.820For example, Dupont, Resin Tech. Inc., Urbans Aqu., Mitsubishi Chemical, Purolite, and Dow companies have developed styrene-divinylbenzene-based ion exchange resin with surface functionalization of quaternary ammonium, tributylamine, and dimethyl ethanol ammonium and demonstrated high ion exchange capacity of ~1.3 eq / L.8 16Dupont and Purolite companies prepared the polyacrylate moieties with amine functionalization to show high adsorption properties of 4750 and 864 umol / g, respectively.1720Despite successful removal of PFAS from drinking water, their recyclability and reusability with charge-switchable properties has not been reported and it is involved in protection of secondary pollution in eco system.

[0003] The charge switchable microsphere led to the discovery of intelligent adsorbent with their reversible stimuli-responsible properties.4The intelligent adsorbents can alter their structures or properties under certain chemical or physical changes, such as pH. By utilizing these intelligent properties, the adsorbent with charge conversion can be fabricated for manipulating the control of capturing / releasing PFAS and may provide an efficient solution to the high cost issue, from which are suffered the limited current technology of destructive PFAS at highly diluted condition as ngPFAS / L tap water.21The performance of the IX in removing PFAS can be affected by the resin properties, including polymer matrix, porosity, and functional groups.17 22Among them, particle size directly impacts solute retention because the ion species can diffuse through between the polymeric chains of the three-dimensional polyelectrolyte resin and the diffusion is attributed to the different kinetic in specific surface area of the particle.23Additionally, high rate of water flux for filter application is also needed for packed column of the microspheres with large size of 5-1000 urn.6’17

[0004] From the synthetic point of view for large size particles, suspension polymerization technique is one of best methods.2428The suspension polymerization is a heterogeneous radical polymerization process that uses mechanical agitation to disperse droplets of the hydrophobic monomer-containing phase in a continuous liquid phase and polymeric spheres are produced inside the drops. Conversely, inverse suspension polymerization is to form polymer particle from water soluble monomer, such as amine or carboxylic acid-functionalized acrylate or styrene moieties, with high stability, narrow particle size distribution, fast process rate, and high conversion. Hence, the performance of the microsphere filter, such as adsorption capacity, water flux, chemical composition, etc., can be medicated by the suspension polymerization conditions. To synthesize stimuli responsible polymers, our group have developed a gas-responsive composites of cellulose nanocrystals grafted with poly(2-(N, N-diethylaminoethyl) methacrylate) (PDEAEMA) and showed the different solubility of the polymers between water and organic solvent as a result of gas-switchable properties.29Yolk-Shell nanoparticles containing core of gold nanoparticle and shell of the PDEAEMA was prepared via a sol-gel reaction and permeability of the nanoparticles was changed with different gases in solution between CO2 and N2.30Furthermore, water-soluble copolymers of poly(acrylic acid-co-N-vinylcaprolactam) and poly(acrylic acid-co-Nvinylcaprolactam-co-dimethyl acrylamide) were synthesized by free radical polymerization. UCST (upper critical solution temperature) or LOST (lower critical solution temperature) of the polymers was switched at different pH and temperature.31SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, there is provided:1. A charge switchable ion exchange (IX) resin comprising solid microparticles made of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group2. The resin of embodiment 1 , wherein the resin can undergo reversible transitions of its surface charge from positive to neutral to negative and from negative to neutral to positive.3. The resin of embodiment 1 or 2, being a reversible positive-to-neutral-to-negative charge switchable ion exchange resin.4. The resin of any one of embodiments 1 to 3, being a reversible positive-to-neutral-to-negative pH-responsive charge switchable ion exchange resin.5. The resin of any one of embodiments 1 to 4, switching surface charge via pH adjustment.6. The resin of any one of embodiments 1 to 5, wherein at a pH equal to an isoelectric point of the resin, the resin surface is neutral; at pHs lower that said isoelectric point, the resin surface is positively charged; and at pHs higher that said isoelectric point, the resin surface is negatively charged state.7. The resin of any one of embodiments 1 to 6, being a capture-and-release ion exchange resin8. The resin of any one of embodiments 1 to 7, wherein said microparticles retain their shape and structural integrity when subjected to a compressive force of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa, without undergoing plastic deformation or flow.9. The resin of any one of embodiments 1 to 8, wherein said microparticles have a compressive strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa.10. The resin of any one of embodiments 1 to 9, wherein said microparticles have a yield strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa.11. The resin of any one of embodiments 1 to 10, wherein said microparticles consists of the copolyelectrolyte only.12. The resin of any one of embodiments 1 to 11, wherein said microparticles are spheroidal in shape, preferably spherical in shape.13. The resin of any one of embodiments 1 to 12, wherein said microparticles have a sphericity of at least 0.85, preferably at least 0.90, more preferably at least 0.95, and most preferably at least 0.98.14. The resin of any one of embodiments 1 to 13, wherein said microparticles are agglomerated together.15. The resin of embodiment 14, wherein the agglomerated microparticles form a network of interconnected microparticles with voids between the microparticles defining pores in the resin.16. The resin of any one of embodiments 1 to 15, wherein said microparticles are about 10 pm or more in average diameter, preferably up to 2500 pm in average diameter, when measured in deionized water.17. The resin of any one of embodiments 1 to 16, wherein said microparticles are from about 200 pm to about 1100 pm, preferably from about 100 pm to about 1000 pm, more preferably from about 300 pm to about 900 pm, yet more preferably from about 500 pm to about 800 urn, and most preferably about 700 pm in average diameter. 18. The resin of any one of embodiments 1 to 17, wherein said microparticles have a D50 between about 10 pm and about 1000 pm, preferably between about 20 pm and about 600 pm, more preferably between about 20 pm and about 100 pm. In embodiments, the microparticles19. The resin of any one of embodiments 1 to 18, wherein said microparticles have a D90 between about 25 pm and about 2000 pm, preferably between about 50 pm and about 1400 pm, more preferably between about 50 pm and about 250 pm.20. The resin of any one of embodiments 1 to 19, having a swelling ratio between about 1000% and about 4000%, preferably between 1200% and about 3400%.21. The resin of any one of embodiments 1 to 20, having a swelling ratio between about 90% and about 120%, preferably of about 110%.22. The resin of any one of embodiments 1 to 21 , having a packing density of between about 25 % and about 75 %, preferably between about 35 % and about 65 %.23. The resin of any one of embodiments 1 to 22, having an apparent density between about 0.6 and about 1.3, preferably between about 0.9 to about 1.3.24. The resin of any one of embodiments 1 to 23, having a water retention capacity between about 40% and about 60%, preferably of 50%.25. The resin of any one of embodiments 1 to 24, having an average pore size between about 0.5 pm and 4.5 pm, preferably of about 2.5 pm as measured by SEM.26. The resin of any one of embodiments 1 to 25, wherein the copolyelectrolyte is a random copolyelectrolyte.27. The resin of any one of embodiments 1 to 26, wherein the copolyelectrolyte is randomly crosslinked.28. The resin of any one of embodiments 1 to 27, wherein the copolyelectrolyte has a molecular weight (Mw) between about 5 and about 1000 kDa, preferably between about 10 and about 30 kDa.29. The resin of any one of embodiments 1 to 28, wherein the positively ionizable weak base functional group is an amidine, guanidine, amine (primary, secondary and / or ternary), imidazole, and / or pyridine.30. The resin of any one of embodiments 1 to 29, the repeat units (A) are repeat units of31. poly(N-methyltetrahydropyrimidine) (PMTHP),32. poly(p-azidomethylstyrene-co-styrene),33. poly[2-methyl-1 -(4-vinylbenzyl)-1 ,4,5,6-tetrahydropyrimidine],34. poly (dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and35. poly (ethylene oxide)-b-poly((N-amidino)dodecyl acrylamide).36. poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA),37. poly (2-(diethylamino)ethyl methacrylate) (PDEAEMA), and38. poly (3-N1, N'-dimethylaminopropyl acrylamide) (PDMAPMA), or39. poly (L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM),40. preferably PMTHP, PDMAEMA or PDMAPMA; and more preferably PMTHP.41. The resin of any one of embodiments 1 to 30, wherein the negatively ionizable weak acid functional group is a carboxylic acid, sulfonic acid, and / or phosphoric acid.42. The resin of any one of embodiments 1 to 31 , wherein the repeat units (B) are repeat units of:43. a polyacrylic acid such as polyacrylic acid or poly (ethyl acrylic acid), a polymethacrylic acid such as polymethacrylic acid or poly (ethyl methacrylic acid), and another repeat unit bearing a carboxyl (-COOH) group, 44. a polysulfate such as poly (vinyl sulfate) PVS or poly (styrene sulfonate),45. a polyphosphoric acid such as poly (vinylphosphonic acid),46. preferably polymethacrylic acid or polyacrylic acid, more preferably polyacrylic acid.47. The resin of any one of embodiments 1 to 32, wherein the copolyelectrolyte further comprises repeat units (C)bearing a polymerizable group, wherein the polymerizable group has been incorporated by polymerization into another chain of the copolyelectrolyte to form a crosslink or remains unreacted.48. The resin of any one of embodiments 1 to 33, wherein the repeat units (C) comprise as a pendant group, an alkylene, for example ethylene or methylene, preferably methylene, to which the polymerizable group is attached.49. The resin of any one of embodiments 1 to 34, wherein the polymerizable group in repeat units (C) is an acrylate or a methacrylate, preferably a methacrylate, wherein the acrylate or methacrylate has been incorporated by polymerization into another chain of the copolyelectrolyte or remains unreacted.50. The resin of any one of embodiments 1 to 35, wherein repeat units (C) are51. a diacrylate repeat units, such as alkyl diacrylate,52. a dimethacrylate repeat units, such as alkyl dimethacrylate, for example a repeat unit of ethylene glycol dimethacrylate (EGDMA):, wherein R1represents another chain of the copolyelectrolyte, or -C(=CH2)-CH3, or54. a dimethacrylamide repeat units, such as alkyl dimethacrylamide, for example a repeat unit of N,N'- methylenebis(acrylamide) (BisMAA):, wherein R2represents another chain of the copolyelectrolyte, or -CH(=CH2).56. The resin of any one of embodiments 1 to 36, wherein repeat units (C) are repeat units of EGDMA or BisMAA, preferably BisMAA.57. The resin of any one of embodiments 1 to 37, wherein the isoelectric point of the resin is between about 3 and about 10, preferably between 5 and 9, more preferably between 7 and 9, most preferably about 8.58. The resin of any one of embodiments 1 to 38, wherein:59. a repeat unit ratio a varies between about 5 % and about 95 %, preferably between 35 % and 85 %;60. a repeat unit ratio b varies between about 10 % and about 90 %, preferably between 15 % and 40 %; and / or 61. a repeat unit ratio c varies between about 1 % and about 200 %, preferably between about 5 % and about 100%, more preferably between about 10% to about 85%,62. wherein repeat unit ratios a, b, and c, are expressed as percentages and calculated from the number of repeat units A, B, and C, respectively, based on the total number of repeat units A and B.63. The resin of any one of embodiments 1 to 39, wherein the copolyelectrolyte has a degree of crosslinking betweenabout 1 % and about 50%.The resin of any one of embodiments 1 to 40, wherein the copolyelectrolyte is of formula:preferably of formula (III) or (IV) most preferably of formula (III), or alternatively of formula (IV),wherein R1and R2are as defined above, and a, b, and c represent said repeat unit ratios a, b, and c, respectively, pereferably wherein a = about 80-85% and b = about 15-20%.A method from manufacturing a charge switchable ion exchange (IX) resin comprising spheroidal solid microparticles of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group, such as the resin of any one of embodiments 1 to 41.The method of embodiment 42, comprising the steps of:copolymerizing monomer (A) bearing a positively ionizable weak base functional group and monomer (B) bearing a negatively ionizable weak acid functional group in the presence of a crosslinker via inverse suspension copolymerization, thereby producing and crosslinking the copolyelectrolyte into the shape of said spheroidal solid microparticles, andagglomerating said spheroidal solid microparticles to form an interconnected network of spheroids, thus yielding the charge switchable ion exchange (IX) resin.71. wherein monomers A and B are monomers that, upon polymerization, yield repeat units (A) and (B) as defined in any one of embodiments 1 to 41, respectively, and wherein the microparticles are as defined in any one of embodiments 1 to 41.72. The method of embodiment 42 or 43, wherein the crosslinker is bifunctional or multi-functional, preferably bifunctional73. The method of any one of embodiments 42 to 44, wherein the crosslinker is monomer (C), which upon polymerization, yield repeat unit (C), as defined any one of embodiments 42 to 44.74. The method of any one of embodiments 42 to 45, wherein the monomer (C) is a diacrylate monomer, such as a alkyl diacrylate monomer, a dimethacrylate monomer, such as a alkyl dimethacrylate monomer, for example EGDMA, or a dimethacrylamide monomer, such as a alkyl dimethacrylamide monomer, for example BisMAA, preferably the monomer (C) is EGDMA or BisMAA, preferably BisMAA, or alternatively EGDMA.75. The method of any one of embodiments 42 to 46, wherein the copolymerizing and the crosslinking at step (I) are carried out in droplets of an aqueous solution of monomer A, monomer B, and the crosslinker in an aqueous solvent, wherein said droplets are dispersed in a continuous organic phase of an organic solvent immiscible or partially miscible with water to form an emulsion or a dispersion, preferably an emulsion.76. The method of any one of embodiments 42 to 47, wherein step (I) comprises:77. dissolving monomer (A), monomer (B), and the crosslinker in the aqueous solvent to form the aqueous solution, 78. providing the organic solvent,79. dispersing the aqueous solution in the organic solvent to produce a biphasic system comprising said droplets of the aqueous solution dispersed in the continuous organic phase, and80. allowing copolymerization and crosslinking within said droplets, yielding the spheroidal solid microparticles. 81. The method of embodiment 48, further comprising the step (e) isolating the spheroidal solid microparticles from the emulsion or dispersion, for example by filtration or centrifugation.82. The method of embodiment 48 or 49, further comprising the step (f) of purifying the spheroidal solid microparticles, for example by washing one or more time (preferably 2 or more times, more preferably 3 or more times) with an appropriate washing solvent such as an organic solvent or water, preferably n-hexane, ethanol, or distilled water.83. The method of any one of embodiments 48 to 50, wherein step (c) comprises adding the aqueous solution to the organic solvent, preferably at a temperature between about 40°C and about 60 °C.84. The method of any one of embodiments 48 to 51, wherein step (d) is carried out at a temperature between about 25°C and about 90°C, preferably between about 45°C and about 70°C.85. The method of any one of embodiments 48 to 52, wherein, at step (d), the emulsion or dispersion is stirred, preferably at a stirring rate of between about 50 and about 1000 rpm, preferably between about 50 about 500 rpm, more preferably between about 80 rpm to about 200 rpm, and most preferably between about 80 rpm to about 130 rpm.86. The method of any one of embodiments 48 to 53, wherein the aqueous solvent is deionized water, optionally in admixture with a water-miscible polar solvent such as an alcohol, for example methanol, ethanol, propanol, or butanol.87. The method of embodiment 54, wherein the water and the alcohol are used in a water:alcohol weight ratio between about 2:1 and about 1:2, preferably between about 1:1 and about 1:1.4.88. The method of any one of embodiments 48 to 55, wherein the aqueous solvent is deionized water without a polar solvent.89. The method of any one of embodiments 48 to 56, wherein the organic solvent is cyclohexane, heptane, toluene, or an oil, preferably an oil.90. The method of any one of embodiments 48 to 57, wherein the oil is a vegetable oil (such as corn oil, soybean oil, canola oil, sunflower oil, olive oil, palm oil, and coconut oil), a seed oil (such as castor oil, jojoba oil, safflower oil, peanut oil, and grapeseed oil), a synthetic oil (such as mineral oil, paraffin oil, and silicone oil), or an ester-based oil (such as methyl oleate and isopropyl myristate); preferably the oil is canola oil, olive oil, sunflower oil, soybean oil, or mineral oil.91. The method of any one of embodiments 48 to 58, wherein the aqueous solvent and organic solvent are used in an organic solvent: aqueous solvent weight ratio between about 10:1 and about 1:1, preferably between about 7.5:1 and about 2:1, more preferably between about 5.1:1 and about 2: 1 , yet more preferably between about 2.5:1 and about 2.1 , and preferably of about 2.3:1.92. The method of any one of embodiments 48 to 59, wherein the crosslinker is used in the aqueous solution in a concentration CL expressed in w / w%, based on the total weight of monomers A and B, between about 1 w / w% and about 90 w / w%, preferably between about 5 w / w% and about 80 w / w%, more preferably between about 10 w / w% and about 52 w / w.93. The method of embodiment 60, further comprising modifying the swelling ratio (SW) of the microparticles of the resin by adjusting the concentration CL of the crosslinker.94. The method of embodiment 60 or 61 , further comprising modifying the packing density of the microparticles of the resin by adjusting the concentration CL of the crosslinker.95. The method of any one of embodiments 48 to 62, wherein a surfactant is used to disperse said droplets of the aqueous solution in the continuous organic phase.96. The method of embodiment 63, wherein before step (c), the surfactant is dissolved in the organic solvent.97. The method of embodiment 63 or 64, wherein the surfactant is an ionic surfactant, a nonionic surfactant or a mixture thereof.98. The method of any one of embodiments 63 to 65, wherein the surfactant is a cellulose derivative (such as ethyl cellulose, etc.), a water-soluble surfactant (such as sorbitan monooleate e.g., sold under the tradename Span® 80, and polyvinylpyrrolidone), a cationic surfactant (such as dodecyltrimethylammonium bromide), an anionicsurfactant (such as dioctyl sodium sulfosuccinate, sold as Aerosol OT (“AOT”)), a nonionic surfactant (such as polyoxyethylene-polyoxypropylene glycol, sold as Pluronic® L-61 ("PL-61”)), or a mixture thereof (such as a SPAN80 / AOT mixture and a PL-61 / A0T mixture), preferably the surfactant is sorbitan monooleate, AOT, and PL- 61 / AOT mixtures.99. The method of any one of embodiments 63 to 66, wherein the surfactant is used in a concentration S expressed in w / w%, based on the total weight of monomers A, B, and C, between about 0.05 and about 10 w / w%, preferably between about 1 and about 50 w / w%.100. The method of any one of embodiments 48 to 67, wherein an initiator is used to initiate the polymerization.101. The method of embodiment 68, wherein the initiator is dissolved in the aqueous solvent before step (d).102. The method of embodiment 68 or 69, wherein the initiator bears a persulfate moiety (such as ammonium persulfate (APS)), nitrile moiety (such as azobisisobutyronitrile (ABN)) or azo moiety (such as 2,2'-azobis[2-(2- imidazolin-2-yl)propane] dihydrochloride (VA-044)), preferably the initiator is 2,2'-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride.103. The method of any one of embodiments 69 to 70, wherein the initiator is used in a concentration between about 0.1 w / w% to about 5 w / w%, preferably between about 0.1 w / w% to about 4 w / w%, based on the total weight of the monomer A and monomer B.104. The method of any one of embodiments 48 to 71, wherein a porogen is used to create pores in the spheroidal solid microparticles.105. The method of embodiment 72, wherein the porogen is dissolved in the aqueous solvent before step (d).106. The method of embodiment 72 or 73, wherein the porogen is polyethylene glycol (PEG), polyvinyl alcohol (PVA), Pluronic 108 (poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol)), or a mixture thereof; preferably PEG, more preferably a molecular weight from 1000Da to 10OOkDa, preferably from 5000 g / mol to 35000 g / mol, and most preferably of 20000 g / mol.107. The method of any one of embodiments 72 to 74, wherein the porogen is used in a concentration between about 0.5 w / w% to about 20w / w%, preferably between about 1 w / w% to about 10 w / w%, based on the total weight of the monomer A, the monomer B, and the crosslinker.108. The method of any one of embodiments 48 to 75, wherein the monomer A is used is used in a concentration between about 10 and about 90 w / w%, preferably a concentration of about 50 w / w%, based on the total weight of the biphasic system.109. The method of any one of embodiments 48 to 76, wherein the monomer B is used is used in a concentration between about 2 and about 15 w / w%, preferably a concentration of about 7 w / w%, based on the total weight of the biphasic system.110. The method of any one of embodiments 48 to 77, further comprising adjusting molar ratios a' and b', wherein the molar ratios a', b', and c' represent the relative quantities in mol of each monomer, expressed as a percentage,calculated based the number of mols of monomer A, B, and C, respectively, in the aqueous solution based on the total number of moles of monomer A and B in the aqueous solution.111. The method of embodiment 78, further comprising tuning the isoelectric point of the resin by selecting monomer A and monomer B and adjusting a' and b'.112. The resin of any one of embodiments 1 to 41 being for capturing ions from a feed or exchanging ions in a feed.113. A method of capturing ions from a feed or exchanging ions in a feed, the method comprising the step of contacting the feed with the charge switchable ion exchange resin of any one of embodiments 1 to 41.114. Use of the charge switchable ion exchange resin of any one of embodiments 1 to 41 for capturing ions from a feed or exchanging ions in a feed.115. The method / use / resin for use of any one of embodiments 80 to 82, wherein the feed is water or another liquid.116. The method / use / resin for use of any one of embodiments 80 to 83, wherein the ions are pollutants.117. The method / use / resin for use of any one of embodiments 80 to 84, wherein the ions are negatively charged molecules, preferably dyes, per- and polyfluoroalkyl substances (PFAS), or proteins, most preferably PFAS. 118. The method / use / resin for use of embodiment 85, wherein the feed is water.119. The method / use / resin for use of any one of embodiments 80 to 84, wherein the ions are positively charged molecules.120. The method / use / resin for use of any one of embodiments 80 to 87, wherein a pH of the feed is adjusted so that the resin has a surface charge opposite to a charge of said ions.121. The method / use / resin for use of any one of embodiments 80 to 88, wherein the resin is selected such that the resin has an isoelectric point such that, when contacted with the feed, the resin has a surface charge opposite to a charge of said ions.122. The method / use / resin for use of any one of embodiments 80 to 89, for concentrating a contaminant by capturing and accumulating ions of said contaminant and then releasing and electrostatically repulsing said ions.123. The method / use / resin for use of embodiment 90, wherein, after said ions have been captured, the resin is contacted with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions.124. The method / use / resin for use of embodiment 90 or 91, wherein said ions are released into a destruction media 125. The method / use / resin for use of any one of embodiments 80 to 92, wherein, after said ions have been captured, the resin is regenerated by releasing said ions.126. The method / use / resin for use of embodiment 93, wherein the resin is regenerated by contacting the resin with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions and regenerating the resin.127. The method / use / resin for use of embodiment 93 or 94, wherein, after regenerating the resin, the resin is reused to capture ions from a feed.128. The method / use / resin for use of any one of embodiments 93 to 95, wherein the resin is regenerated and reused one or more times, preferably a plurality of times.129. The method / use / resin for use of any one of embodiments 91 to 96, wherein the regenerating liquid is the feed with an adjusted pH or another liquid, for example water.130. The method / use / resin for use of any one of embodiments 90 to 97, wherein the releasing / regenerating is carried out by adjusting the pH of the feed so that the resin has a surface charge that is the same as the charge of said ions.131. The method / use / resin for use of any one of embodiments 90 to 98, wherein the pH is adjusted by adding an acid to the feed.132. The method / use / resin for use of any one of embodiments 90 to 98, wherein the pH is adjusted by adding a base to the feed.133. The method / use / resin for use of any one of embodiments 90 to 98, wherein the pH is adjusted by introducing a gas in the feed.134. The method / use / resin for use of any one of embodiments 90 to 101, wherein the releasing / regenerating step is free from the use of any other chemical except those for adjusting the pH of the feed.135. The method / use / resin for use of any one of embodiments 90 to 102, wherein resin is charged in a column, and the feed is passed through the column at for said capturing and the regenerating liquid is passed through the column for releasing the ions and for regenerating the resin.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In the appended drawings:Figure 1 is a schematic illustration of the reverse suspension polymerization used to prepare charge-switchable IX resin microparticles as well as the chemical structures of the used monomers, crosslinker and the resulting crosslinked random copolymer.Figure 2 shows the FT-IR spectra of IX Resin (PH3) and the two monomers of DMAEMA and MAA.Figure 3 shows SEM images of the IX resins (A) PH1, (B) PH2, (C) PH3, (D) PH4, (E) PL1, (F) PL2, (G) PL3 and (H) PL4.Figure 4 shows the particle size distribution curves measured by laser diffraction method for resins (A) PH1, (B) PH2, (C) PH3, (D) PH4, (E) PL1, (F) PL2, (G) PL3 and (H) PL4.Figure 5 shows plots of diameter and gel fraction of the IX resin - (A) resins PH1 to PH4 and (B) resins PL1-PL4 - in wet condition as a function of cross-linking ratios.Figure 6 shows plots of swelling ratio of the IX resin - (A) resins PH1 to PH4 and (B) resins PL1-PL4 - in wet conditionas a function of cross-linking ratios.Figure 7 shows the potentiometric titration curves of the resins - (A) PH1, (B) PH2, (C) PH3, (D) PH4, (E) PL1 , (F) PL2, (G) PL3 and (H) PL4 - in water with adding NaOH solution.Figure 8 shows plots of ion-exchange capacity (IEC) and isoelectric point of the resins - (A) resins PH1 to PH4 and (B) resins PL1-PL4 - as a function of cross-linking ratio.Figure 9 shows plots of eluted water volume for the resins with different cross-linking ratios - (A) resins PH1 to PH4 and (B) resins PL1-PL4 - as a function of elution time.Figure 10 shows the UV-Vis absorption spectra of MO (A) before and (B) after the adsorption by the resins.Figure 11 shows plots of the adsorption capacity of the resins (A) PH1 to PH4 and (B) PL1 to PL4 as a function of the cross-linking ratio.Figure 12 shows the charge-switchable testing of the resins at two different pH values.Figure 13 shows the adsorption / desorption testing of the resins with (A) perfluorooctanoic acid (PFOA) and (B) perfluorobutanesulfonic acid (PFBS) as the molecular contaminant.Figure 14 are plots showing the effect of pH on removal and release (%) of PFBS and PFOA with contact time. Figure 14 shows the removal of PFBS and PFOA at A) pH 7 and (B) pH 12 and the release of PFBS and PFOA (C) at pH 7 and (D) pH 12.Figure 15 shows the IX resins of breakthrough curves for PFBS and PFOA.Figure 16 shows SEM micrographs of the surface morphology according to an embodiment of the invention at (A) low magnification, (B) higher magnification, and (C) even higher magnification.DETAILED DESCRIPTION OF THE INVENTION

[0007] Turning now to the invention in more details, there is provided a charge switchable ion exchange (IX) resin.

[0008] The resin of the invention is a charge switchable resin. This means that the resin can undergo reversible transitions of its surface charge from positive to neutral to negative and from negative to neutral to positive. In other words, the resin of the invention is a reversible positive-to-neutral-to-negative charge switchable ion exchange resin. The surface charge switch is induced by pH: at low pH levels, the resin surface becomes positively charged, while at high pH levels, it shifts to a negative charge, and at the isoelectric point, it remains neutral. Thus, it can be said that the resin of the invention is a reversible positive-to-neutral-to-negative pH-responsive charge switchable ion exchange resin. Notably, the surface charge includes the charge of all the resin surface. In other words, it includes the internal surface of any pores in the resin in addition to the external surface of the resin.

[0009] Of note, the reversible positive-to-neutral-to-negative charge switchable ion exchange resin is significantly different from any resin that may have the capacity of switching change from neutral to positive or from neutral to negative. To the best of the inventors’ knowledge, published reports have only discussed pH-responsive ion exchangeresins that shift from positive to neutral or negative to neutral, without addressing the switch all the way from positive to negative. Unlike any other reported technology, the resin of the invention offers reversible charge switchability from positive to negative.

[0010] As noted above, in the resin of the invention, the surface charge switch is induced by pH. By incorporating a reversible positive-to-neutral-to-negative pH-responsive copolyelectrolyte, the resin of the invention gains the ability to dynamically switch surface charge in response to pH variations. At low pH levels, the resin surface becomes positively charged, while at high pH levels, it shifts to a negatively charged state and in between, at its isoelectric point, it remains neutral. The charge change can be easily obtained by exposing the resin of the invention to a solution of an appropriate pH. For the resin, this can easily be achieved on-site via a feed contacting the resin. This technology creates a unique capability on resin for specific applications which requires charge switching properties.

[0011] The ability to switch surface charge on demand via pH adjustment confers several significant technical advantages to the ion exchange resin of the invention.

[0012] The resin of the invention can capture either positively or negatively charged ions depending on the pH. It has been shown in the Examples below that it is very efficacious for capturing per- and polyfluoroalkyl substances (PFAS), which are typically negatively charged. In fact, the resin has demonstrated below in the Examples, an exceptional affinity for PFAS compounds, achieving near-complete removal from contaminated water even at very low concentrations. Thus, the invention represents a key required technology for solving issue of water treatment in per- and polyfluoroalkyl substances (PFAS) issue. Unlike traditional methods that rely on harsh and toxic chemicals for PFAS recovery, the resin of the invention operates within a safe pH range, eliminating the need for such chemicals. This not only reduces environmental impact but also ensures safer handling and operation.

[0013] The charge-switching capability allows the resin of the invention release captured ions during acid or basic cleaning cycles, which constitute another advantage of the invention. Thus, it can be said that the resin of the invention is a capture-and-release ion exchange resin The resin can repel contaminants through electrostatic repulsion and facilitate easy release. This dynamic behavior allows regenerating and reusing the resin several times. Thus, it can be said that the resin of the invention is reusable. The resin of the invention thus distinguishes itself by its longevity and sustainability: it can be regenerated simply by adjusting pH and thus releasing any contaminants, allowing for repeated use without losing effectiveness; enabling the resin to be reused for many cycles. On other words, the resin of the invention shows remarkable recyclability and reusability.

[0014] Together, these capture and release abilities form an environmentally friendly approach ensures effective removal of contaminants such as PFAS, while minimizing waste and operational costs, contributing to a cleaner and safer water supply for communities worldwide. Unlike other ion exchange resins on the market, which lack this capture and release capability, which create disposal issues for contaminants and the contaminated resin, the resin of the invention offers a sustainable solution. Indeed, the contaminants are first captured and accumulated and then released preferably in a controlled manner, for example, in a manner that will allow their easy disposal or destruction. In other words, theresin of the invention facilitates the destruction of harmful compounds. For example, highly diluted PFAS (a few ng / L) can be concentrated into high concentrated solutions that can then be treated by e.g., catalytic degradation, which is more effective at higher concentrations. This circumvents the problem of for destruction of highly diluted PFAS, which is costly and wastes a lot of water.

[0015] The nature of the copolyelectrolyte used in the resin allows tailoring the resin and its charge switching ability for various applications. Thus, the pH at which the charge switches (the isoelectric point) can be tailored as well as the charge of the resin at a given pH. This will be explained further in the next sections. Thus, it is possible to target specific pH ranges for different applications.

[0016] The copolyelectrolyte in the resin has the ability to function within a safe pH change range during recovery ensures minimal environmental impact and facilitates a straightforward recovery process. This feature enhances the overall sustainability of contaminant removal process.

[0017] Overall, the resin of the invention, in the Examples below, showed excellent ion-exchange capacity, adsorption capacity, water flux, and charge switching property to reversibly capture and release contaminants and models compounds.

[0018] Other advantages of the invention will be described further below.Ion Exchange Resin

[0019] The charge switchable ion exchange (IX) resin of the invention comprises solid microparticles made of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group.

[0020] As used herein, "solid microparticles” means microparticles that retain their shape and structural integrity when subjected to a compressive force of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa, without undergoing plastic deformation or flow. Notably, "solid” does not encompass semi-solids, such as gels. In embodiments, the solid microparticles have a compressive strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa. In embodiments, the solid microparticles have a yield strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa.

[0021] In embodiments, the microparticles consists of the copolyelectrolyte only.

[0022] In embodiments, the microparticles are spheroidal in shape, preferably spherical in shape. In embodiments, the microparticles have a sphericity of at least 0.85, preferably at least 0.90, more preferably at least 0.95, and most preferably at least 0.98. The sphericity, , of an object is the ratio of the surface area of a sphere with the same volume to the object's surface area:ir^Wp)273Apwhere is volume of the object and is the surface area of the object. The sphericity of a sphere is by definition and, by the isoperimetric inequality, any shape which is not a sphere will have sphericity of less than 1.

[0023] In embodiments, the microparticles are agglomerated together. In embodiments, the agglomerated microparticles form a network of interconnected microparticles with voids between the microparticles defining pores in the ion exchange (IX) resin.

[0024] In embodiments, the microparticles are about 10 pm or more in average diameter, preferably up to 2500 pm in average diameter, when measured in deionized water. In preferred embodiments, the microparticles are from about 200 pm to about 1100 pm, preferably from about 100 pm to about 1000 pm, more preferably from about 300 pm to about 900 pm, yet more preferably from about 500 pm to about 800 urn, and most preferably about 700 pm in average diameter. A method of measurement of this diameter comprises sonicating the resin in deionized water to prevent aggregation of the microparticles, and analyzing the microparticles by laser diffraction analysis. Another method involves quantifying the diameter from optical images using a Leica DMRP trinocular microscope and Imaged Pro software.

[0025] In embodiments, the microparticles have a D50 between about 10 pm and about 1000 pm, preferably between about 20 pm and about 600 pm, more preferably between about 20 pm and about 100 pm. In embodiments, the microparticles have a D90 between about 25 pm and about 2000 pm, preferably between about 50 pm and about 1400 pm, more preferably between about 50 pm and about 250 pm.

[0026] In embodiments, the resin has a swelling ratio between about 1000% and about 4000%, preferably between 1200% and about 3400%. In alternative preferred embodiments, the microparticles have a swelling ratio between about 90% and about 120%, preferably of about 110%. Herein, the swelling ratio is SW =Weight of water-swolen microparticles — Weight of dry microparticlesn n- - ■_ - ■_ - xWeight of dry micropartiles 100.

[0027] In embodiments, the resin has a packing density of between about 25 % and about 75 %, preferably between about 35 % and about 65 %. Herein the packing density is c =volume°ftheparticlesxtotal volume of the packing

[0028] In embodiments, the resin has an apparent density between about 0.6 and about 1.3, preferably between about 0.9 to about 1.3.

[0029] In embodiments, the resin has a water retention capacity between about 40% and about 60%, preferably of 50%.

[0030] In embodiments, the resin has an average pore size between about 0.5 pm and 4.5 pm, preferably of about 2.5 pm as measured by SEM.

[0031] In embodiments, the copolyelectrolyte is a random copolyelectrolyte. Herein, "random” means that the repeat units are arranged in a sequence dictated by the reaction kinetics of the monomers. This term is commonly usedinterchangeably with "statistical” in the literature.

[0032] In embodiments, the copolyelectrolyte is randomly crosslinked. Herein, "randomly crosslinked” means that crosslink junctions are formed at statistically non-programmed positions along polymer chains due to non-selective reaction of a distribution of reactive groups, such that the location of crosslinks is not predetermined by chain termini, pre-formed nodes, or sequence-defined motifs. For the avoidance of doubt, "randomly crosslinked” excludes (i) end-linked networks formed predominantly by reactions of terminal (telechelic) functional groups, and (ii) non-random architectures in which crosslink placement is predetermined or programmed, including star, multi-arm, comb, bottlebrush, ladder, double-network, or block-junction architectures, and networks assembled from pre-fabricated multifunctional hubs.

[0033] In embodiments, the copolyelectrolyte has a molecular weight (Mw) between about 5 and about 1000 kDa, preferably between about 10 and about 30 kDa.

[0034] Herein, a "weak base” is a base with a 3 < pKa< 11. Herein, a positively ionizable weak base functional group is a functional group that can accept a hydrogen atom at low pH to become ionized, i.e. positively charged in that case. Of note, a quaternary ammonium is permanently charged (cationic) regardless of pH and is thus not encompassed in "positively ionizable weak base functional groups”. In embodiments, the positively ionizable weak base functional groups are amidines, guanidines, amines (primary, secondary and / or ternary), imidazoles, and / or pyridines. In embodiments, the repeat units (A) bearing positively ionizable weak base functional groups are repeat units of• poly (N-methyltetrahydropyrimidine) (PMTHP),• poly(p-azidomethylstyrene-co-styrene),• poly[2-methyl-1-(4-vinylbenzyl)-1 ,4,5,6-tetrahydropyrimidine],• poly(dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and• poly (ethylene oxide)-b-poly ((N-amidino)dodecyl acrylamide).• poly [(2-dimethylamino) ethyl methacrylate] (PDMAEMA),• poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and• poly(3-N',N'-dimethylaminopropyl acrylamide) (PDMAPMA), or• poly (L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM).

[0035] In preferred embodiments, the repeat units bearing weak base functional groups are repeat units of PMTHP, PDMAEMA or PDMAPMA. In more preferred embodiments, the repeat units bearing weak base functional groups are repeat units of PMTHP.

[0036] Herein, a "weak acid” is an acid with 3 < pKa< 9. Herein, a positively ionizable weak acid functional group is a functional group that can donate a hydrogen atom at high pH to become ionized, i.e. negatively charged in that case. In embodiments, the negatively ionizable weak acid functional groups are carboxylic acids, sulfonic acids, and / orphosphoric acids. In embodiments, the repeat unit (B) bearing weak base functional group are repeat unit of:• polyacrylic acids, such as polyacrylic acid and poly (ethyl acrylic acid), polymethacrylic acids, such as polymethacrylic acid and poly (ethyl methacrylic acid), and other repeat units bearing a carboxyl (-COOH) group, • polysulfates, such as poly (vinyl sulfate) PVS, and poly (styrene sulfonate),• polyphosphoric acids, such as poly (vinylphosphonic acid).

[0037] In embodiments, the repeat units bearing a weak base functional group are repeat units of polymethacrylic acid or polyacrylic acid, preferably polyacrylic acid.

[0038] In embodiments, the copolyelectrolyte further comprises repeat units (C) bearing a polymerizable group, wherein the polymerizable group has been incorporated by polymerization into another chain of the copolyelectrolyte to form a crosslink or remains unreacted.

[0039] In the copolyelectrolyte, repeat unit ratios a, b, and c can be used to represent the relative quantities of each type of repeat units. More specifically, repeat unit ratios a, b, and c, are expressed as percentages and calculated from the number of repeat units A, B, and C, respectively, based on the total number of repeat units A and B.

[0040] The repeat unit ratios a and b will depend on the desired isoelectric point of the resin. It is an important advantage of the invention that the isoelectric point of the resin can be tailored simply by modifying the ratio of repeat units bearing weak base functional groups and repeat units bearing weak acid functional groups. The isoelectric point is the pH at which the resin has an overall neutral charge; their negative charges being equal to their positive charges. This behavior can be attributed to the differing pKavalues of the weak acid and weak base functional groups. The weak base will remain protonated and positively charged at pH < pKaof the weak base, and gradually deprotonate as the pH increases. In contrast, the weak acid has lower pKaresulting in it being mostly protonated and neutral at low pH, and deprotonating to become negatively charged at pH > pKaof the weak acid.

[0041] It will be apparent from the above that the isoelectric point of the resin depends not only from ratios a and b, but also from the exact pKa of the weak acid functional group and the pKb of the weak base functional groups; that is from the nature of the weak acid and weak base functional groups themselves. This will be explained in further details below.

[0042] In embodiments, the isoelectric point of the resin is between about 3 and about 10, preferably between 5 and 9, more preferably between 7 and 9, most preferably about 8.

[0043] In embodiments, the repeat unit ratio a varies between about 5 % and about 95 %, preferably between 35 % and 85 %.

[0044] In embodiments, the repeat unit ratio b varies between about 10 % and about 90 %, preferably between 15 % and 40 %.

[0045] In embodiments, the repeat unit ratio c, also called herein the cross-linking ratio, varies between about 1 % and about 200 %, preferably between about 5 % and about 100%, more preferably between about 10% to about 85%.

[0046] In embodiments, the copolyelectrolyte has a degree of crosslinking between about 1% and about 50%. Herein, the degree of crosslinking is the percentage of copolyelectrolyte chains that are interconnected with other copolyelectrolyte chains.

[0047] The isoelectric point also depends from ratio c, and thus the degree of crosslinking of the copolyelectrolyte. Indeed, higher crosslinking might inhibit ionization and thus slightly lower the isoelectric point.

[0048] Furthermore, the ion-exchange capacity (I EC) of the resin tends to decrease with increasing ratio c, and thus the degree of crosslinking of the copolyelectrolyte. Herein, the IEC is defined as the total number of weak acid or base functional groups for ion exchange by unit mass of the resin. The mass fraction of monomer A and monomer B in the copolyelectrolyte decreases with mass fraction of monomer and this therefore reduces IEC.

[0049] The liquid flow rate through the resin tends to increase with increasing ratio c, and thus the degree of crosslinking of the copolyelectrolyte.

[0050] Repeat units (A), (B), and (C) are typically hydrophilic as their bear charges.

[0051] Herein, hydrophobic means a material that repels water. For example, it can be characterized by a high contact angle when a water droplet is placed on its surface. Conversely, herein, hydrophilic means a material that attracts water. For example, it can be characterized by a low contact angle when a water droplet is placed on its surface. Notably these contact angles can be measured using the well-known sessile drop technique in which a drop of deionized water is placed on a surface and photographed immediately. The contact angle is measured between the tangent to the droplet's surface and the surface of the material and is determined using the photograph. Using this technique, a hydrophobic material exhibits a contact angle greater than 90 degrees while a hydrophilic material exhibits a contact angle smaller than 90 degrees. It should be understood that in the context of the invention, when discussing e.g. a hydrophobic repeat unit, the contact angle for the repeat unit should be made using a polymer comprising only the repeat unit.

[0052] In embodiments, repeat units (C) comprise as a pendant group, an alkylene, for example ethylene or methylene, preferably methylene, to which the polymerizable group is attached.

[0053] In embodiments, the polymerizable group in repeat units (C) is an acrylate or a methacrylate, preferably a methacrylate, wherein the acrylate or methacrylate has been incorporated by polymerization into another chain of the copolyelectrolyte or remains unreacted.

[0054] In embodiments, repeat unit (C) isa diacrylate repeat unit, such as alkyl diacrylate,a dimethacrylate repeat unit, such as alkyl dimethacrylate, for example a repeat unit of ethylene glycol dimethacrylate (EGDMA):, wherein R1represents another chain of the copolyelectrolyte,• a dimethacrylamide repeat unit, such as alkyl dimethacrylamide, for example a repeat unit of N,N'- methylenebis(acrylamide) (BisMAA):\ 2H-jC— k NH / O O , wherein R2represents another chain of the copolyelectrolyte, or -CH(=CH2).

[0055] In preferred embodiments, the repeat unit (C) is a repeat unit of EGDMA or BisMAA, preferably BisMAA.

[0056] When R1or R2represents another chain of the copolyelectrolyte, repeat unit C is crosslinked to said chain of the copolyelectrolyte (in other words, both polymerizable groups of the monomer (e.g., ethylene glycol dimethacrylate) have reacted during polymerization). When R1or R2represents -C(=CH2)-CH3 or-CH(=CH2), repeat unit C is not crosslinked to another chain of the copolyelectrolyte (in other words, only one of the two polymerizable groups of the monomer has reacted during polymerization).

[0057] In preferred embodiments, the copolyelectrolyte is of formula:(IV),wherein R1and R2are as defined above, and a, b, and c represent said repeat unit ratios a, b, and c, respectively.

[0058] In such a copolyelectrolyte, repeat unit ratios of a= about 80-85% and b= about 15-20% yield a resin with a positive charge at around neutral condition (pH = about 7) and a negative charge in basic condition (pH = 11-12). More specifically, the tertiary amine groups in the weak base repeat units are protonated and become positively charged at pH about 7 (pH< 7.5-8.2), while at this pH, the carboxylic acid groups in methacrylic acid repeat units are deprotonated and bear negative charges; but as the number of positive charges outmatch the number of negative charges, the resin is positively charged. At higher pHs of 11-12, the weak base units are all deprotonated and are thus neutral, while MMA units remain deprotonated, and therefore the resin is negatively charged.Method for manufacturing

[0059] In another aspect of the invention, there is provided a method from manufacturing a charge switchable ion exchange (IX) resin comprising spheroidal solid microparticles of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group, such as the resin of the invention as described above.

[0060] In embodiments, the method of the invention comprises the steps of:(I) copolymerizing monomer (A) bearing a positively ionizable weak base functional group and monomer (B) bearing a negatively ionizable weak acid functional group in the presence of a crosslinker via inverse suspension copolymerization, thereby producing and crosslinking the copolyelectrolyte into the shape of said spheroidal solid microparticles, and(II) agglomerating said spheroidal solid microparticles to form an interconnected network of spheroids, thus yielding the charge switchable ion exchange (IX) resin.

[0061] Monomer A is a monomer that, upon polymerization, yield repeat unit (A), as described above.

[0062] Monomer B is a monomer that, upon polymerization, yield repeat unit (B), as described above.

[0063] At step (II), the crosslinked copolyelectrolyte is directly produced in the shape of the spheroidal solid microparticles. These have the same characteristics as the "solid microparticles” described in the previous section.

[0064] At step (II), the crosslinker crosslinks the chains of the copolyelectrolyte as they form. In embodiments, the crosslinker is bifunctional or multi-functional, preferably bifunctional. Herein, "bifunctional” means that the crosslinker comprises two functional groups that can get attached to the copolyelectrolyte chain. Conversely, "multifunctional” means that the crosslinker comprises 3 or more functional groups that can get attached to the copolyelectrolyte chain.

[0065] In embodiments, the crosslinker is monomer (C), which is copolymerized with monomer (A) and monomer (B) and thus incorporated into the crosslinked copolyelectrolyte. Monomer C is a monomer that, upon polymerization, yield repeat unit (C), as described above. Therefore, in preferred embodiments, the crosslinker I monomer (C) is a diacrylate monomer, such as alkyl diacrylates, a dimethacrylate monomer, such as alkyl dimethacrylates, for example EGDMA, or a dimethacrylamide monomer, such as alkyl dimethacrylamides, for example BisMAA. In preferred embodiments, the crosslinker I monomer (C) is EGDMA or BisMAA, preferably BisMAA, or alternatively EGDMA.

[0066] In preferred embodiments, as is typical in inverse suspension copolymerization, the copolymerizing and the crosslinking at step (I) are carried out in droplets of an aqueous solution of monomer A, monomer B, and the crosslinker in an aqueous solvent, wherein said droplets are dispersed in a continuous organic phase of an organic solvent immiscible or partially miscible with water to form an emulsion or a dispersion, preferably an emulsion. In preferred embodiments, step (I) comprises:a) dissolving monomer (A), monomer (B), and the crosslinker in the aqueous solvent to form the aqueous solution, b) providing the organic solvent,c) dispersing the aqueous solution in the organic solvent to produce a biphasic system comprising said droplets of the aqueous solution dispersed in the continuous organic phase, andd) allowing copolymerization and crosslinking within said droplets, yielding the spheroidal solid microparticles.

[0067] Such inverse suspension copolymerization process typically results spheroidal (or even spherical) particles that can easily be isolated from the continuous organic phase e.g. by filtration or centrifugation. Thus, in embodiments, the method of the invention further comprises the step (e) isolating the spheroidal solid microparticles from the emulsion or dispersion, for example by filtration or centrifugation.

[0068] In embodiments, the method of the invention further comprises the step (f) of purifying the spheroidal solid microparticles, for example by washing one or more time (preferably 2 or more times, more preferably 3 or more times) with an appropriate washing solvent. Non-limiting examples washing solvents include organic solvents and water, preferably n-hexane, ethanol, and distilled water.

[0069] In embodiments, step (c) comprises adding the aqueous solution to the organic solvent, preferably at a temperature between about 40°C and about 60 °C. The mode of addition is not critical, and the aqueous solution can beadded to the organic solvent dropwise or all at once.

[0070] In embodiments, step (d) is carried out at a temperature between about 25°C and about 90°C, preferably between about 45°C and about 70°C.

[0071] In embodiments, at step (d), the emulsion or dispersion is stirred. Preferably, the emulsion or dispersion is stirred at a stirring rate of between about 50 and about 1000 rpm, preferably between about 50 about 500 rpm, more preferably between about 80 rpm to about 200 rpm, and most preferably between about 80 rpm to about 130 rpm. It Relatively lower stirring speed tends to increase the average size of the spheroidal solid microparticles.

[0072] In embodiments, the aqueous solvent is deionized water, optionally in admixture with a water-miscible polar solvent. The water-miscible polar solvent might be used, for example, to improve the solubility of the crosslinking agent. Non-limiting examples of water-miscible polar solvents include alcohols. Preferred alcohols include methanol, ethanol, propanol, and butanol.

[0073] In embodiments where the aqueous solvent is a mixture of deionized water and an alcohol, the water and the alcohol are used in a water:alcohol weight ratio between about 2:1 and about 1 :2, preferably between about 1:1 and about 1:1.4.

[0074] In alternative embodiments, the aqueous solvent is deionized water without a polar solvent.

[0075] In embodiments, the organic solvent is cyclohexane, heptane, toluene, or an oil, preferably an oil. Non-limiting examples of oils include vegetable oils (such as corn oil, soybean oil, canola oil, sunflower oil, olive oil, palm oil, and coconut oil), seed oils (such as castor oil, jojoba oil, safflower oil, peanut oil, and grapeseed oil), synthetic oils (such as mineral oil, paraffin oil, and silicone oil), and ester-based oils (such as methyl oleate and isopropyl myristate). Preferred oils include canola oil, olive oil, sunflower oil, soybean oil, and mineral oil.

[0076] The aqueous solvent and organic solvent are used in an organic solvent:aqueous solvent weight ratio between about 10:1 and about 1:1, preferably between about 7.5:1 and about 2:1, more preferably between about 5.1:1 and about 2:1, yet more preferably between about 2.5:1 and about 2.1, and preferably of about 2.3:1.

[0077] The crosslinker is used in the aqueous solution in a concentration CL expressed in w / w%, based on the total weight of monomers A and B. In embodiments, the concentration CL is between about 1 w / w% and about 90 w / w%, preferably between about 5 w / w% and about 80 w / w%, more preferably between about 10 w / w% and about 52 w / w. A higher concentration of the crosslinker will typically increases the cross-linking ratio.

[0078] In embodiments, a surfactant is used to disperse said droplets of the aqueous solution in the continuous organic phase. Such surfactant stabilizes the dispersion. In such embodiments, before step (c) (for example at step (b) or between steps (b) and (c)), the surfactant is dissolved in the organic solvent. In embodiments, the surfactant and the organic solvent are mixed until dissolution of the surfactant. This can take various amounts of times depending on the exact nature of the surfactant and the organic solvent. For example, ACT can be mixed with an oil for at about room temperature for about 12 h or at about 50°C for about 5 h.

[0079] The surfactant can be an ionic surfactant, a nonionic surfactant or a mixture thereof. In embodiments, the surfactant is a cellulose derivative (such as ethyl cellulose, etc.), a water-soluble surfactant (such as sorbitan monooleate e.g., sold under the tradename Span® 80, and polyvinylpyrrolidone), a cationic surfactant (such as dodecyltrimethylammonium bromide), an anionic surfactant (such as dioctyl sodium sulfosuccinate, sold as Aerosol OT (“AOT”)), a nonionic surfactant (such as polyoxyethylene-polyoxypropylene glycol, sold as Pluronic® L-61 ("PL-61”)), or a mixture thereof (such as a SPAN80 / AOT mixture and a PL-61 / AOT mixture). Preferred surfactants include sorbitan monooleate, AOT, and PL-61 / AOT mixtures.

[0080] The surfactant is used in a concentration S expressed in w / w%, based on the total weight of monomers A, B, and C. In embodiments, the concentration S is between about 0.05 and about 10 w / w%, preferably between about 1 and about 50 w / w%, based on the total weight of monomers A, B, and C. The concentration S of the surfactant has an influence on the isoelectric point. Indeed, the surfactant is involved in the stability of the initial droplets in the suspension before polymerization. Conversely, droplet stability relates with polymerization conversion of each monomer. So, when using more surfactant, each monomer is polymerized without loss and the ratios of the monomers impacts the isoelectric points.

[0081] In embodiments, an initiator is used to initiate the polymerization. In preferred embodiments, an initiator is dissolved in the aqueous solvent before step (d), for example at step (a). Thus, in most preferred embodiments, at step (a), the initiator together with monomer (A), monomer (B), and the crosslinker are dissolved in the aqueous solvent (preferably a mixture of water and methanol) to form the aqueous solution.

[0082] Non-limiting examples of initiator include those bearing a persulfate moiety (such as ammonium persulfate (APS)), nitrile moiety (such as azobisisobutyronitrile (ABN)) or azo moiety (such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044)). In preferred embodiments, the initiator is 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride.

[0083] Typically, the initiator is used in a concentration between about 0.1 w / w% to about 5 w / w%, preferably between about 0.1 w / w% to about 4 w / w%, based on the total weight of the monomer A and monomer B.

[0084] In embodiments, a porogen is used to create pores in the spheroidal solid microparticles. In preferred embodiments, the porogen is dissolved in the aqueous solvent before step (d), for example at step (a).

[0085] Non-limiting examples of porogens include polyethylene glycol (PEG), polyvinyl alcohol (PVA), Pluronic 108 (Poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol)), or a mixture thereof. In preferred embodiments, the initiator is PEG, which can have a molecular weight from 1000Da to 1000kDa. Preferred molecular weights include 5000 g / mol and 35000 g / mol, preferably 20000 g / mol.

[0086] Typically, the porogen is used in a concentration between about 0.5 w / w% to about 20w / w%, preferably between about 1 w / w% to about 10 w / w%, based on the total weight of the monomer A, the monomer B, and the crosslinker.

[0087] In embodiments, monomer A is used is used in a concentration between about 10 and about 90 Vo, preferably a concentration of about 50 w / w%, based on the total weight of the biphasic system.

[0088] In embodiments, monomer B is used is used in a concentration between about 2 and about 15 w / w%, preferably a concentration of about 7 w / w%, based on the total weight of the biphasic system.

[0089] In the method of the invention, molar ratios a', b', and c' represent the relative quantities in mol of each type of monomer. More specifically, molar ratios a', b', and c', are expressed as percentages and calculated from the number of mols of monomer A, B, and C, respectively, in the aqueous solution based on the total number of moles of monomer A and B in the aqueous solution. Typically, the relative quantities of monomer A, B, and C in the aqueous solution will translate into the repeat unit ratios a, b, and c described above. In other words, a=a’; b=b' and c=c’. In embodiments, the method of the invention further comprises modifying the repeat unit ratios a and b by adjusting the molar ratios a' and b'.

[0090] In embodiments, the method of the invention further comprises tuning the isoelectric point of the resin by selecting monomer A and monomer B and adjusting a' and b'. Indeed, using a stronger acid (lower pKa) as the weak acid functional group will lower the isoelectric point while using a stronger base (lower pKb) as the weak base functional group will increase the isoelectric point. Using more monomer B (higher b', higher b) will increase the isoelectric point, while using more monomer A (higher a', higher a) will decrease the isoelectric point.

[0091] In embodiments, the method of the invention further comprises modifying the swelling ratio (SW) of the microparticles of the resin by adjusting the concentration CL of the crosslinker. Indeed, it has also been shown in the Examples below that a higher crosslinking degree, achieved by using a higher concentration CL of the crosslinker, leads to microparticles with lower swelling ratios.

[0092] In embodiments, the method of the invention further comprises modifying the packing density of the microparticles of the resin by adjusting the concentration CL of the crosslinker. Indeed, it has been shown in the Examples below that an increase in the concentration CL of the crosslinker, thus in the degree of crosslinking, leads to the formation of a denser network and simultaneously interrupts growth of polymer droplets with shrunk surface during polymerization. With increasing degrees of crosslinking, there is more agglomeration of the microparticles as the higher concentration CL of the crosslinker seems to produce a more branched network as well as higher chain entanglement during polymerization.Method of using

[0093] In a related aspect of the invention, there is provided a method of capturing ions from a feed or exchanging ions in a feed, the method comprising the step of contacting the feed with the charge switchable ion exchange resin of the invention as described above. There is also provided the use of the charge switchable ion exchange resin of the invention for capturing ions from a feed or exchanging ions in a feed.

[0094] There is also provided the above resin for use in capturing ions from a feed or exchanging ions in a feed.

[0095] In embodiments, the feed is water or another liquid.

[0096] The charged sites, either positive or negative, of the crosslinked copolyelectrolyte acts as active sites to capture the ions from the feed, the captured ions being exchanged with ions from ion exchange resin (for example H+ or OH-). In other words, these charged sites allow ion exchange. In embodiments, the ions captured from the feed are pollutants.

[0097] In embodiments, the ions from the feed are negatively charged molecules. In embodiments, the negatively charged molecules are dyes, per- and polyfluoroalkyl substances (PFAS), or proteins. In such embodiments, the feed is preferably water. In alternative embodiments, the ions are positively charged molecules.

[0098] In embodiments, the pH of the feed is adjusted so that the resin has a surface charge opposite to the charge of the ions to be captured. In alternative embodiments, the method of the invention comprises selecting the resin such that the resin has an isoelectric point such that, when contacted with the feed, the resin has a surface charge opposite to a charge of said ions. Indeed, the pH of the feed must be lower than the isoelectric point of the resin for the resin to be positively charged and thus capture negatively charged molecules. Conversely, the pH of the feed must be higher than the isoelectric point of the resin for the resin to be negatively charged and thus capture the positively charged molecules.

[0099] In embodiments, the method I use I resin of the invention are for use in concentrating a contaminant by capturing and accumulating ions of said contaminant and then releasing and electrostatically repulsing said ions. In embodiments, after said ions have been captured, the resin is contacted with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions. In embodiments, the ions are released into a destruction media. This advantageously allows disposing of these ions in controlled and sustainable manner.

[0100] In embodiments, after said ions have been captured, the resin is regenerated by releasing said ions. In embodiments, the resin is regenerated by contacting the resin with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions and regenerating the resin. Indeed, the pH of the regenerating liquid must be higher than the isoelectric point of the resin for the resin to be negatively charged and thus release the negatively charged molecules. Conversely, the pH of the regenerating liquid must be lower than the isoelectric point of the resin for the resin to be positively charged and thus release the positively charged molecules.

[0101] The regenerating liquid can be the feed with an adjusted pH or another liquid, for example water for washing out the resin. Thus, in preferred embodiments, the regenerating is carried out by adjusting the pH of the feed so that the resin has a surface charge that is the same as the charge of said ions.

[0102] For example, per- and polyfluoroalkyl substances (PFAS) in tap water is captured by the resin of the invention at pH 7 and released from the resin at pH 11.

[0103] In embodiments, after regenerating the resin, the resin is reused to capture ions from a feed. In embodiments, wherein the resin is regenerated and reused one or more times, preferably a plurality of times. This step regenerates theresin, allowing it to be reuse. It has been shown in the Examples below that the capture efficiency of the resin is maintained across several cycles. In embodiments, the resin maintains at least 95% of its capture efficiency after 30 cycles. In embodiments, the resin maintains at least 80% of its capture efficiency after 50 cycles. The resin of the invention has thus consistent performance in capturing and releasing contaminants over extended operational periods.

[0104] In embodiments, the regenerating step is free from the use of any other chemical except those for changing the pH. This constitutes an advantage of the invention.

[0105] In embodiments, the pH is adjusted by adding an acid to the feed or to the aqueous liquid. In embodiments, the pH is adjusted by adding a base to the feed or to the aqueous liquid. In embodiments, the pH is adjusted by introducing a gas in the feed or in the aqueous liquid. In embodiments, the gas is carbon dioxide (CO2), which acidifies water. In alternative embodiments, the gas is nitrogen (N2), which reverse the effect of the carbon dioxide.

[0106] In embodiments, the resin is charged in a column, and the feed is passed through the column for capturing the ions and the regenerating liquid is passed through the column for releasing the ions and for regenerating the resin. Definitions

[0107] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0108] The terms "comprising, "having, "including, and "containing are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted. In contrast, the phrase "consisting of” excludes any unspecified element, step, ingredient, or the like. The phrase "consisting essentially of' limits the scope to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the invention.

[0109] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All subsets of values within the ranges are also incorporated into the specification as if they were individually recited herein.

[0110] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

[0111] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

[0112] No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0113] Herein, the term "about1has its ordinary meaning. In embodiments, it may mean plus or minus 10% or plus or minus 5% of the numerical value qualified.

[0114] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0115] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0116] The present invention is illustrated in further details by the following non-limiting examples.Example 1 - Charge-Switchable Ion Exchange ResinAbstract

[0117] A large size (>10 urn) ion exchange (IX) resin with charge-switchable property was firstly explored through inverse suspension polymerization. The IX resins of PH1-4 were synthesized at 70 °C under 400 rpm of stirring speed, and compared with PL1-4 at 40 °C of mild reaction temperature and 200 rpm of slow stirring speed. Successful synthesis of the resins was confirmed by FT-IR analysis. SEM images revealed interconnected spherical network structures.Different cross-linking ratios from 25% to 100% influenced linear decrease in size of PH1 (44 urn) to PH4 (24 urn). By contrast, PL1-4 exhibited irregular relationship of size with the cross-linking ratios due to aggregating issue. Additionally, swelling indices for the series of PH and PL resins were gradually dropped depending on the cross-linking ratios.Decreasing trends of ion-exchange capacity (4.65-3.72 mmol / g) for PH1-4 and PL1-4 were proportional to the content of 2-(N,N-diethylaminoethyl) methacrylate (DMAEMA) in the resins. Adsorption capacity (-1.06 mmol / g) was measured using UV-Vis absorption spectroscopy. The effect of large size of the resins was investigated by preparation of columns in which tap water was reasonably permeable through resin columns to show good water flux (~ 6.17 mL / min). In the columns, excellent charge switchable properties of the resins were demonstrated by recyclable adsorption / desorption test of methyl orange dye at different pH 7 and pH 11. To further elucidate remarkable charge switchable property, per- and polyfluoroalkyl substances (PFAS) in tap water was successfully captured in the IX resins at pH 7 and released from the resin columns at pH 11. The PFAS capture and removal is reversible using the same resin column.Introduction

[0118] A novel material of large size (> 10um) charge-switchable ion exchange (IX) resins incorporated with cationic functional groups of poly (2-(N, N-diethylaminoethyl) methacrylate) (PDEAEMA) and anionic groups of polymethacrylic acid (PMAA) has been developed. The cross-linked copolymers for the IX resin were synthesized by inverse suspension polymerization from droplet-form of water-in-oil. Parametric studies with different cross-linking ratio, stirring speeds, and reaction temperature were performed to optimize the shape and size of the IX resins. To define charge-switchableproperties, the IX resins were tested for PFAS-filtering in tap water at different pH values.Experimental SectionMaterials

[0119] 2-(Dimethylamino)ethyl methacrylate (DMAEMA, Sigma-Aldrich), Methacrylic Acid (MAA, Sigma-Aldrich), Span 80 (TCI America), Ethylene glycol dimethacrylate (EGDMA, Thermo Scientific), Mineral oil (Fisher Scientific), Ammonium persulfate (APS, Sigma-Aldrich), Tetramethylethylenediamine (TEMED, Sigma-Aldrich), Methyl orange (MO, Sigma-Aldrich), Perfluorooctanoic Acid (PFOA, Sigma-Aldrich), and Perfluorobutanesulfonic acid (PFBS, Sigma-Aldrich) were used as received.Instruments and Analyses

[0120] The FT-IR spectrometer used was a Thermo Nicolet Avatar 360 ESP with a MKII Golden Gate and single reflection ATR system.

[0121] The surface structure of the hydrogel beads was characterized with a scanning electron microscope (SEM, ThermoFisher Scientific Phenom XL G1). The samples were mounted directly onto the SEM sample holder using doublesided sticking tape and were sputter-coated with gold / palladium in vacuum prior to measurements.

[0122] The particle diameter in deionized water as dispersant was analyzed using a laser diffraction particle size distribution analyzer (Microtrac SYNC).

[0123] The swelling ratio of hydrogel beads was measured by immersing samples into the deionized water (DIW) at 25 °C for 48 h, the swollen beads were weighed (Ws) and then compared with weights of dried beads (Wd). The swelling ratio (SR) was obtained from the average of five runs of measurements and calculated according to the Eq. SR = (Ws-Wd) / Wd.

[0124] The ion exchange capacity and the isoelectric point in the hydrogel beads was inspected by the classical potentiometric titration method. The criterion for this evaluation was based on determining the protonation-deprotonation process preferentially in the hydrogel beads with amine functional groups. Briefly, a solution of 50 mg of the beads in 50 mL of acidified water (pH 2) was titrated by the addition of small aliquots of 0.1 mL of NaOH 0.01 N until constant pH value. The titration curve was obtained by recording the pH values after adding each NaOH volume.

[0125] For adsorption capacity studies of dye solutions, methyl orange (MO) solutions were used. A stock solution was prepared at a concentration of 25 mg / 150 mL and the adsorbent was stirred with this dye solution overnight. The amount of dye adsorbed by the adsorbent was determined by measuring the dye concentration in solution before and after the adsorption experiment using UV-Visible spectroscopy. The equilibrium adsorption amount qe(mmol / g) was calculated using equation as qe= (Co- Ce)*V / m*Mn, where Co is the initial dye concentration (mg / L), Ceis the equilibrium dye concentration (mg / L), m is the weight of adsorbent (g) and V is the volume of the dye solution (L), and Mnwas molecular weight of methyl orange.

[0126] The reversible adsorption / desorption efficiencies of the IX resins for Perfluorooctanoic Acid (PFOA) and perfluorobutanesulfonic acid (PFBS) of the PFAS were evaluated in a series of controlled laboratory experiments. These experiments utilized a cylindrical column (diameter = 2.5 cm), filled up to 15 cm height with respective resin. The column setup was used to pass through 25 mL of the aqueous PFOA and PFBS solution at an initial concentration of 1000 ng / L and a pH of 7. The effluent, or permeate, was collected post-filtration for analysis. Following initial adsorption, the resin was flushed with 100 mL of tap water to collect any residual permeate. The desorption process involved the treatment of the resin with 500 mL of alkaline tap water (pH adjusted to 11 using NaOH), with all effluent being collected. A final washing acidic tap water (pH 2) was conducted until the effluent pH neutralized. This cycle was repeated for additional adsorption and desorption assessments. All permeate samples were analyzed using a Xevo TQ-S micro— Triple Quadrupole Mass Spectrometry (LC-MS / MS) system, and calibration curves for PFOA were established to quantify PFAS concentrations accurately. The adsorption efficiency (Qe) was calculated for each permeate using the formula: Qe= (1-Cp / Cf) * 100, where Cpand are the concentrations of PFAS in the permeate and feed solutions, respectively.Pollutant-Filter Application of IX Resin

[0127] For minimum contact time experiment, adsorption experiments were conducted using 0.01 g of ion exchange resin placed in small vials. Five samples were prepared, and 5 mL of a 1000 ng / L perfluorooctanoic acid (PFOA) solution was added to each vial. The vials were subjected to vortexing, and aliquots were taken at different time intervals: 30 seconds, 1 minute, 3 minutes, 5 minutes, and 10 minutes. After vortexing, the resin was filtered from the solution. For the desorption process, the resin was placed in 10 mL of a basic solution to facilitate the desorption of the adsorbed PFAS, regenerating the ion exchange resin. The vials were vortexed, and samples were collected at 30 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes, and 20 minutes. The concentrations of PFAS in the samples were analyzed using mass spectrometry. The same procedure was repeated using perfluorobutanesulfonic acid (PFBS) to study the adsorption and desorption of short-chained PFAS.

[0128] Breakthrough curve experiments were conducted using 0.1 g of ion exchange (IX) resin placed in a column with a diameter of 0.5 cm and a resin bed height of 3 cm. A 2-liter tap water solution containing PFOA and PFBS, each at a concentration of 1000 ng / L, was passed through the IX resin. Breakthrough was monitored by measuring the effluent concentration of PFAS until the breakthrough levels of both PFOA and PFBS exceeded 20%. Once the breakthrough threshold was reached, the resin was regenerated by passing 100 mL of a basic solution at pH 12 through the column to desorb the adsorbed PFAS. The desorption process was followed by another adsorption cycle using fresh PFAS solution. Samples were collected every 200 mL during the adsorption phase to monitor the breakthrough, and the concentration of PFAS in the permeate was determined using mass spectrometry.Preparation of Cross-Linked IX Resins (PH3)

[0129] A mixed solution of oil-soluble surfactant Span 80 (1.3 g) and Mineral oil (50 mL) was charged in a two-necked flask. After this oil phase was heated to 40 °C, 2-(dimethylamino)ethyl methacrylate (DMAEMA, 3.52g, 22.38 mmol),methacrylic acid (MAA, 0.48g, 5.60 mmol), and ethylene glycol dimethacrylate (EGDMA, 2.08g, 20.99 mmol) in deionized water (DI W, 4mL) was added into the mixed oil solution under N2 condition. The resulting mixture was heated to 70 °C with a 400 rpm stirring speed. Polymerization of the mixture was initiated by quick addition of ammonium persulfate (APS, 0.021g, 0.093 mmol) and tetramethylethylenediamine (TEMED, 0.0062g, 0.053 mmol) and then kept in the reaction during 2 h. White solid was obtained by purification through washed with hexane and acetone several times.Results and discussionSynthesis of IX Resins

[0130] The cross-linked random copolymers of the IX resins, poly (2-(dimethylamino)ethyl methacrylate-co-methacrylic acid), were synthesized by inverse suspension polymerization of 2-(dimethylamino)ethyl methacrylate) (DMAEMA) and methacrylic acid (MAA) with ethylene glycol dimethacrylate (EGDMA) at 70 °C under 400 rpm or 40 °C under 200 rpm, as shown in Figure 1. Charged status of polymer could be changed depending on different ratio of cationic and anionic functional groups or different pH condition.32

[0131] Herein, the feed ratio of each monomers was kept as [DMAEMA]o:[MAA]o = 80:20 to design resins with positive charge at neutral condition (pH = 7) and switch to negative charge in alkali condition (pH = 11-12). More specifically, the tertiary amine groups in DMAEMA units can be protonated to become positively charged at pH about 7 (pH< 8.2),33while at this pH, the carboxylic acid groups in MMA units are deprotonated and bear negative charges;34but as the number of positive charges outmatch the number of negative charges, the IX resin is positively charged. At higher pH 11-12, as DMAEMA units are all deprotonated and become neutral, while MMA units remain deprotonated, the IX resin is thus negatively charged. This charge sign switch is reversible and easily controllable by pH change.

[0132] The chemical structures and compositions of the cross-linked reins were confirmed by FT-IR analysis as shown in Figure 2. After polymerization, the peak of the C=C stretching peak at 1600 cm-1 clearly disappeared indicating successful inverse suspension polymerization. Otherwise, the peak of C-H stretching vibration of N(CH3)2 moieties at 2842 cm-1 in the DMAEMA was obtained in the copolymer. The broad peak in the range of 3400-3200 cm-1 as hydroxyl group (O-H) in the MAA was also detected in the copolymer. The extension vibration peak of the C=O group in copolymer newly appeared in range of 1700-1600 cm-1 corresponding to the C=O group of each monomer.Effect of Cross-linking Ratio, Stirring Speed, and Reaction Temperature on Morphology and Size of the IX Resins.

[0133] To precisely control the properties of the adsorbent IX resin microparticles in terms of adsorption capacity, water flux, etc., the size of the particle is important.6’23As summarized in Table 1, the size and shape of the IX resins were controlled by varying the cross-linking ratio between 25, 50, 75, and 100% at 70 °C under 400 rpm of stirring speed (PH1-4) at 40 °C under 200 rpm (PL1-4).

[0134] Scanning electron microscopy (SEM) was used to confirm the structural morphology of the cross-linked IXresins in dry condition as shown in Figure 3. After polymerization, all the IX resins possessed interconnected spherical shapes. PH1 with lower cross-linking ratio of 25% showed about 35 um size of particles. However, the size of PH2, PH3, and PH4 with 50, 75, and 100% was dramatically decreased, preventing precise size measurements. The increase in the amount of cross-linker of EGDMA provided formation of a denser network and simultaneously interrupted growth of polymer droplet with shrunk surface during polymerization.35’36Furthermore, the interconnected spherical network of the particles was attributed to conglomerates effect. With increasing cross-linking ratio, network formation of the resins in PH2, PH3, and PH4 became more conglomerated because higher ratio of cross-linker seems to produce more branched networking structure as well as higher chain entanglement during polymerization. The interconnected networking formation is typically obtained in suspension polymerization.26

[0135] PL2 to PL4 showed larger size of the particles than PH2 to PH3 in Figure 3. Particle size and stirring speed (or reaction temperature) both were inversely proportional to each other. It is well known in the literature that size distribution of initial droplet critically influences the final particle size and size distribution and it is mediated by stirring speed and reaction temperature.24’36Surface morphology of PH1-4 with higher stirring speed and reaction temperature also showed more uniformity than the PL1-4 because of improvement of the contact between the two phases.

[0136] Laser diffraction analysis was used to quantitatively determine size of particles in wet condition in Figure 4. Deionized water was employed as a solvent for the experiments under the wet condition to obtain an environment close to the potential application of PFAS filtering in drinking water. The resins were sonicated in DIW to prevent aggregation before analysis. The results of this analysis are summarized in Table 1. When the cross-linking ratio was increased from 25 to 100%, the size of PH1 to PH4 in wet condition were decreased from 44 um to 23 um because of kinetic trap during polymerization, as shown in Figure 4. Otherwise, the large size of 87 um for PL1 was dropped to 35 um for PL2 as expected. However, PL3 and PL4 showed the increased size of 44 um and 579 um, respectively. Presumably, slow stirring speed at low reaction temperature could induce inhomogeneous contacts between the minidroplets and thus lead to more branched network structures with larger size of resins. Figure 5 shows a linear decreasing trend of size from PH1 to PH4 depending on different cross-linking ratio, indicating homogeneous growth of the resins. In contrast, no clear trend can be seen for PL1-PL4 for the reasons mentioned above.

[0137] Table 1. Characteristics of the IX resinsSample fx- Temp. Stirring DiameterbSwelling IPdGel IEC Adsorption WaterlinkeraSpeed Ratio0Fraction Capacity ElutionRatioEntry (mol%) (°C) (rpm) (D, pm) (%) (pH) (%) Ideal Observedd(qe, (mL / min)mmol / g)PH1 25 70 400 44 1400 8.17 83 4.77 4.13 1.06 1.16PH2 50 70 400 35 1273 8.05 89 4.41 4.04 0.97 1.33PH3 75 70 400 29 1211 8.01 >99 3.68 3.86 0.95 1.59PH4 100 70 400 23 1046 7.93 >99 3.30 3.72 0.74 1.67PL1 25 40 200 87 3401 8.22 94 4.77 4.65 0.88 0.58PL2 50 40 200 35 2900 8.19 >99 4.15 4.28 0.95 0.95PL3 75 40 200 44 2496 8.15 >99 3.68 4.10 0.93 2.57PL4 100 40 200 579 1294 8.04 >99 3.30 4.02 0.64 6.175aFeeding ratio of cross-linker of ethylene glycol dimethacrylate (EGDMA) to monomers of 2-(D I methy lami no)ethy I methacrylate) (DMAEMA) and Methacrylic acid (MAA).'’Determined by Laser diffraction analysis.cSwelling ratio was decided by water-induced swelling technique.“'Determined by base-acid titration.“Determined by UV-Vis spectroscope using methyl orange as indicator.0 'Water elution ratio was decided by flowing tap water into a column with packed resins and comparing volumes of the water at interval time.Swelling Ratio of IX Resins.

[0138] Swelling ratio additionally supported the incorporating ratios of cross-linker as shown in Figure 6 and summarized in Table 1. The equilibrium swelling of PH1 to PH4 was decreased from 1400 to 1046 % with increasing the cross-linking ratio from 25 to 100 %, meaning inverse relationship to each other. In the IX resins of PL1-4 under low stirring speed and reaction temperature, Figure 6 shows decreasing trend of swelling ratios from 3401 to 1294 %, of which is similar to PH series with high speed and temperature, even though the size of PL3 and PL4 as 44 urn and 579 urn was larger than 87 urn of PL1 and 35 urn of PL2, respectively. This means that the decreasing trend of equilibrium swelling is dominantly mediated by the cross-linker ratio as compared with the shape and size of the particles.Furthermore, the 3401% swelling degree of PL1 was significantly higher than 1400% of PH1 at same cross-linker concentration and other resins of PL2-4 showed similar compared to PH2-4. This phenomenon was resulted from that larger particles are the assemblies of nanometer-sized smaller particles based on previous literature in particle formation and growth mechanism.37Hence, larger IX resins have a higher swelling capacity compared to smaller ones.Ion Exchange Capacity of IX Resins.

[0139] Ion exchange capacity (I EC) is defined as the incorporating ratio of ionizable amine group. The I EC within IX resin is a significant factor since the property will have an impact on the polymer-PFAS binding strength.38’39The presence of the tertiary amine groups in DMAEMA comonomer units in the copolymers makes them more protonable over a broad pH range. Hence, the copolymers of poly (2-(dimethylamino)ethyl methacrylate-co-methacrylic acid) with amine content in the cross-linked IX resin were examined by acid-base titrations. The IX resin-included solution in water was pre-adjusted to pH 2.00, and then titrated with 0.01 N NaOH solution in range to pH 10.00. As shown in Figure 7, the profiles of titration curves with NaOH showed two single plateau regions at about pH 6.5 and in the pH range from 7.9 to 8.2 for all sample, respectively. While the 1stpeak at about 6.5 was derived from equilibrium of pure water,38the 2ndpeak in the pH range from 7.9 to 8.2 was from equilibrium of base-acid, indicating that all the amine group in the system are completely neutralized, and therefore further addition of NaOH into the IX resin solution causes an increases of the pH. As a results, amine functionality in the copolymers was quantitatively calculated from 2ndequilibrium region. The results of amine ratios and isoelectric points of the copolymers were summarized in Table 1. Figure 8 shows decreasing trend of the I EC with increasing the different cross-linking ratio. When the cross-linking ratio was increased from 25 to 100%, the lECs of PH1 to PH4 and PL1 to PL4 were decreased from 4.13 to 3.72 mmol / g and 4.77 to 4.02 mmol / g, respectively. The IEC was defined as the total of active sites or functional groups responsible for ion exchange at the unit mass of the resin. The mass fraction of DMAEMA monomers in each copolymer was decreased with higher ratios of cross-linker and it was dominantly involved in reduction relationship between the IEC and cross-linking ratios regardless of the size effect. Furthermore, when comparing the IEC at same mass fraction of amine, PL1-4 have higher IEC = 4.77 ~ 4.02 mmol / g than PH1 — 4 (IEC = 4.13 ~ 3.72 mmol / g), meaning that larger size of PL (~ 579 urn) may affect on more active sites of the amine group than the smaller sized PH (~44 urn).Water Flux of the IX Resins.

[0140] When assessing the usability of an adsorbent for application of PFAS-filter in drinking water, the IX resins can be used as stationary phase of ion exchange chromatography.7It is important to study the changes in the solvent flux profiles as a function of the time. The solvent flux is normally determined along with porosity and dimensions of the column, and the porosity is mediated by size and properties of the particles.40Large size (~1.2 mm) of the resins for this application are generally found in the literatures.6’17For the water flux test of our IX resins, about 100 mg was charged in 1.6 cm diameter of syringe, and then water was fluxed into this system. As shown in Figure 9, with increasing crosslinking ratio from 25% to 100%, solvent flow rates of PH1 to PH4 and PL1 to PL4 were increased from 1.16 to 1.67 mL / min and 0.58 to 6.17 mL / min, respectively. The results were explained by the column back pressure equation as a resistance to the desired flow of fluid through pipes, AP = qFL / K°nr2dp2, where q, F, L, K°, nr2, and dp2are viscosity, column length, flow rate, specific permeability, column radius, and particle sizes, respectively.41The higher cross-linked resins generally become more rigid with smaller pore size (dp) and thus providing higher column back pressure (AP). Hence, it is more difficult for the solvent as eluent or the analyte to penetrate into the resin and the distribution constant decreased with increasing cross-linking. However, the opposite trends in PH1-4 and PL1-4 were observed with increasing cross-linking from 25% to 100%, as shown in Figure 9. The properties of the adsorbent such as increased hydrophilicity and swelling ratio significantly influence the retention volume (Vo). The lower cross-linked resin has a greater amount of water retention and it may interrupt water flux.42Adsorption Capacity of the IX Resins.

[0141] Adsorption experiments were performed with varying cross-linking ratio of the IX resin from 25% to 100%, keeping all other parameters fixed including pH = 7 and the concentration of the methyl orange (MO) dye. The adsorption capacity was quantitatively determined from UV-Vis spectroscopic measurements by comparing the initial and residual concentration of the MO after passing through the column, as shown in Figure 10 and summarized in Table 1. Figure 10 shows that as the cross-linking ratio in PH of the IX resins increased from 25% to 100%, the intensity of MO absorption increased, indicating that the amount of residual MO became larger after adsorption of the resins. These results are interpreted as dominant relationship of swelling capability of the resins with cross-linking ratios. Lower cross-linking of the PH1 may capture higher amount of the MO and thus providing higher adsorption capacity comparing with lower adsorption capability of higher cross-linked PH4. As for the PL resins, the intensity of the MO absorption from PL2 to PL3 was increased with higher cross-linking ratio, meaning less adsorption of the MO, which is similar trend as for the PH resins. However, PL1 showed higher intensity of the MO absorption than PL2 and PL3. It can be explained in previous literatures that adsorption capability is affected by competitiveness between the swelling properties and size of the particles, and larger size of particles generally results in lower adsorption.43 44Figure 11 shows the relationship between adsorption capacity and cross-linking ratio in PH and PL resins. The increasing trend of cross-linking ratio in PH1— 4 and PL2-4 was less favorable to adsorption of the MO due to swelling effect. Large size of PL1 (87 urn) displayed lower capacity than PL2 (35 urn) and PL3 (44 urn).Charge-Switchable Properties of the IX Resins.

[0142] To realize the reusable functionality of the IX resins, the charge should be reversibly switched by different ionic groups at specific condition.1 3Our resins were designed to feature pH-triggered switchable-charge (reversible change between positively and negatively charged state), which enables reversible adsorption (capture) and desorption (release) of charged dyes or molecular contaminants. As shown in Figure 12, the adsorption and desorption were visualized at different two pH values using the negative-charged MO as a probe. The resins were charged in a 2.5 cm diameter column, and then the MO solution in DIW was passed over a column packed with IX resins. At pH 7, essentially colorless water came out from the column while the orange-colored MO stayed in the middle of the column, indicating that the positively charge IX resin acts as the adsorbent of the negative charged dye molecules via attractive electrostatic interaction. Afterward, by passing DIW at pH 12, the captured MO was clearly moved from the resin column because the IX resin turned to be negatively charged, repelling the negatively charged MO molecules and allowing them to be dissolved in the washing DIW. The capture and release cycle was repeated in Figure 12, demonstrating the reusability of the IX resin column.

[0143] The pH-responsive charge-switchable properties of the resins were additionally confirmed by application of per-and polyfluoroalkyl substances (PFAS)-filter in drinking water, as shown in Figure 13. The total number of PFAS moieties may be as high as 5000-10000, and their concentration in tap water was in range of ~15 ng / L.45Among them, per-fluoro octanoic acid (PFOA) and per-fluorobutanesulfonic acid (PFBS) was chosen by comparing different chain lengths (4C and 8C) and functional groups (-COOH and -S(O)2OH). 25 mL of an aqueous PFOA and PFBS solution in concentration of 1000 ng / L was introduced into a cylindrical column charged with the resins. Elemental analysis was used to determine adsorption / desorption ratio of the PFOA and PFBS by comparing the initial solution with the passed solution. After feeding PFOA and PFBS solution of concentration of 1000 ng / L, the PFOA molecules were captured in the IX resin without any residual ratio of elution at pH 7, indicating quantitative adsorption. This resulted from ion exchange interaction of protonated amino groups in the copolymer resin with negative charged carboxylate group in PFOA as well as sulfonate group in PFBS. After adjusting the pH 11, the PFOA and PFBS was released from the resin column with a desorption ratio ranging from 96 % to 99 % and 98 % to 99 %, respectively. The IX resins effectively captured and released the PFOA and PFBS even though different chain lengths and functional group. Furthermore, three consecutive cycles of PFOA capture and release were carried out, and the results indicate a constant ratio of the adsorption / desorption, demonstrating the reliability in reusing the IX resin column.Pollutant-Filter Application in Drinking Tap Water of the IX Resins.

[0144] The objective of the adsorption and desorption experiments was to determine the minimal contact time needed for efficient adsorption of PFOA (a long-chained PFAS) and PFBS (a short-chained PFAS) onto ion exchange (IX) resin, as well as the time required for complete desorption using a basic solution at pH 12 to regenerate the resin (Figure 14).At pH 7, the IX resin is positively charged, enhancing electrostatic interactions with the negatively charged PFAS, leading to rapid adsorption. The results showed that PFBS achieved nearly 100% adsorption efficiency within approximately 3minutes, while PFOA reached similar efficiency in about 5 minutes. This difference is likely due to PFBS having a higher charge density, which increases electrostatic attraction and results in faster adsorption compared to the longer, less densely charged PFOA. For desorption, the resin was exposed to a basic solution (pH 12), switching the resin to a negative charge and repelling the PFAS. Both PFBS and PFOA achieved complete desorption within 10 minutes, demonstrating effective regeneration of the IX resin. These findings underscore the significant role of electrostatic interactions and charge density in the adsorption and desorption kinetics of PFAS on IX resins. The graph illustrates the breakthrough curves for PFBS and PFOA during multiple adsorption-regeneration cycles using the ion exchange (IX) resin, highlighting the resin's excellent performance and regeneration capabilities. The normalized concentration (C / Co) is plotted against the bed volumes (BV) processed, showing distinct adsorption behaviors for each PFAS (Figure 15). Initially, PFBS reaches a 20% breakthrough at approximately 3200 BV, while PFOA shows breakthrough at around 4400 BV. The earlier breakthrough for PFBS can be attributed to its higher charge density and smaller molecular size, which enhance its electrostatic interactions with the positively charged resin at pH 7 but also lead to faster resin saturation. PFOA, with a larger molecular size and lower charge density, adsorbs more gradually, resulting in a delayed breakthrough, demonstrating the resin's capacity to selectively adsorb different PFAS. After the adsorption phase, the resin undergoes regeneration with a basic solution at pH 12, reversing its charge to negative, which efficiently desorbs the adsorbed PFAS. The regeneration efficiency is demonstrated by the second adsorption cycle, where PFBS reaches breakthrough at 2700 BV, representing 84% of the initial cycle's BV, and PFOA reaches breakthrough at 4000 BV, achieving 90% regeneration efficiency. These values underscore the resin's exceptional regeneration efficiency. This high regeneration efficiency showcases the resin's robustness and sustainability for repeated use in PFAS removal applications. The ability to restore and even enhance adsorption capacity across cycles highlights the resin's superior performance, making it an excellent choice for long-term water treatment processes targeting a range of PFAS contaminants.

[0145] Figure 16 shows SEM micrographs of the surface morphology according to an embodiment of the invention at (A) low magnification, (B) higher magnification, and (C) even higher magnification. The results revealed predominantly spherical particles with a highly porous surface, exhibiting pore sizes around 2 pm.REFERENCES

[0146] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. These documents include, but are not limited to, the following:1. Li, Y.; Yang, H. Y. ; Thambi, T.; Park, J. H. ; Lee, D. S., Charge-convertible polymers for improved tumor targeting and enhanced therapy. Biomaterials 2019, 217.2. Singh, J.; Nayak, P., pH-responsive polymers for drug delivery: Trends and opportunities. Journal of Polymer Science 2023, 61, (22), 2828-2850.3. Yang, H. Y.; Li, Y.; Lee, D. S., Recent Advances of pH-lnduced Charge-Convertible Polymer-Mediated InorganicNanoparticles for Biomedical Applications. Macromolecular Rapid Communications 2020, 41, (21).4. Liu, F. Q.; Pignatello, J. J.; Sun, R. Z.; Guan, X. H.; Xiao, F., A Comprehensive Review of Novel Adsorbents for Per- and Polyfluoroalkyl Substances in Water. Acs Es&T Water 2024, 4, (4), 1191-1205.5. 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A.; Huang, J.; Yu, G., Removal of perfluorooctane sulfonate from wastewater by anion exchange resins: Effects of resin properties and solution chemistry. Water Research 2010, 44, (18), 5188-5195.16. Bullen, J. C.; Saleesongsom, S.; Gallagher, K.; Weiss, D. J., A Revised Pseudo-Second-Order Kinetic Model for Adsorption, Sensitive to Changes in Adsorbate and Adsorbent Concentrations. Langmuir 2021, 37, (10), 3189- 3201.17. Gagliano, E.; Sgroi, M.; Falciglia, P. P.; Vagliasindi, F. G. A.; Roccaro, P., Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter andchallenges in adsorbent regeneration. Water Research 2020, 171.18. del Moral, L. L; Choi, Y. J.; Boyer, T. H., Comparative removal of Suwannee River natural organic matter and perfluoroalkyl acids by anion exchange: Impact of polymer composition and mobile counterion. Water Research 2020, 178.19. Dixit, F.; Barbeau, B.; Mostafavi, S. G.; Mohseni, M., Efficient removal of GenX (HFPO-DA) and other perfluorinated ether acids from drinking and recycled waters using anion exchange resins. Journal of Hazardous Materials 2020, 384.20. Schuricht, F.; Borovinskaya, E. S.; Reschetilowski, W., Removal of perfluorinated surfactants from wastewater by adsorption and ion exchange - Influence of material properties, sorption mechanism and modeling. Journal of Environmental Sciences 2017, 54, 160-170.21. Meegoda, J. N.; de Souza, B. B.; Casarini, M. M.; Kewalramani, J. A., A Review of PFAS Destruction Technologies. International Journal of Environmental Research and Public Health 2022, 19, (24).22. Dixit, F.; Dutta, R.; Barbeau, B.; Berube, P.; Mohseni, M., PFAS removal by ion exchange resins: A review.Chemosphere 2021, 272.23. Amen, R.; Ibrahim, A.; Shafqat, W.; Hassan, E., A Critical Review on PFAS Removal from Water: Removal Mechanism and Future Challenges. Sustainability 2023, 15, (23).24. Chaudhary, V.; Sharma, S. , Suspension polymerization technique: parameters affecting polymer properties and application in oxidation reactions. Journal of Polymer Research 2019, 26, (5).25. Gokmen, M. T.; Du Prez, F. E. , Porous polymer particles-A comprehensive guide to synthesis, characterization, functionalization and applications. Progress in Polymer Science 2012, 37, (3), 365-405.26. Gomez, C. G.; Pastrana, G.; Serrano, D.; Zuzek, E.; Villar, M. A.; Strumia, M. C., Macroporous poly(EGDMA-co- HEMA) networks: Morphological characterization from their behaviour in the swelling process. Polymer 2012, 53, (14), 2949-2955.27. Khazdooz, L; Zarei, A.; Meletharayil, G.; Kapoor, R.; Abbaspourrad, A., Synthesis of a Cation-Exchange Resin by Inverse Suspension Polymerization for Lactoferrin Extraction from Whey. Acs Omega 2023.28. Ortiz-Palacios, J.; Cardoso, J.; de la Cruz, M.; Anleu, E., Functionalization in copolymers based on 4VP:DVB for the removal of Cr(VI) ions from aqueous solution. Journal of Applied Polymer Science 2017, 134, (47).29. Farnia, F.; Fan, W. Z.; Dory, Y.; Zhao, Y., Making Nanocomposites of Hydrophilic and Hydrophobic Polymers Using Gas-Responsive Cellulose Nanocrystals. Macromolecular Rapid Communications 2019, 40, (12).30. Al Akoumy, C.; Auge, A.; Ma, D. L; Zhao, Y., Yolk-Shell Nanoparticles with CO2-Responsive Outer Shells for Gas- Controlled Catalysis. Acs Applied Nano Materials 2022, 5, (12), 18237-18246.31. Cheng, R. D.; Jiang, J.; Hou, J. B.; Li, G.; Jiang, J. Q.; Zhao, Y., Water-soluble copolymers and their hydrogelswith pH-tunable diverse thermoresponsive behaviors enabled by hydrogen bonding. Polymer Chemistry 2022, 13, (40), 5700-5706.32. Kocak, G.; Tuncer, C.; Butun, V., pH-Responsive polymers. Polymer Chemistry 2017, 8, (1), 144-176.33. Daniels, C. R.; Tauzin, L. J.; Foster, E.; Advincula, R. C.; Landes, C. F., On the pH-Responsive, Charge- Selective, Polymer-Brush-Mediated Transport Probed by Traditional and Scanning Fluorescence Correlation Spectroscopy. Journal of Physical Chemistry B 2013, 117, (16), 4284-4290.34. Han, X.; Zhang, X. X.; Zhu, H. F.; Yin, Q. Y.; Liu, H. L; Hu, Y., Effect of Composition of PDMAEMA-b- PAA Block Copolymers on Their pH- and Temperature-Responsive Behaviors. Langmuir 2013, 29, (4), 1024- 1034.35. Sekerak, N. M.; Hutchins, K. M.; Luo, B. B.; Kang, J. G.; Braun, P. V.; Chen, C.; Moore, J. S., Size control of cross-linked carboxy-functionalized polystyrene particles: Four orders of magnitude of dimensional versatility. European Polymer Journal 2018, 101, 202-210.36. Chaudhary, V.; Sharma, S. , Effect of various synthesis parameters on styrene-divinylbenzene copolymer properties. Journal of Porous Materials 2019, 26, (6), 1559-1571.37. Shimizu, H.; Wada, R.; Okabe, M., Preparation and Characterization of Micrometer-Sized Poly (N- isopropylacrylamide) Hydrogel Particles. Polymer Journal 2009, 41, (9), 771-777.38. Lee, H.; Son, S. H.; Sharma, R.; Won, Y. Y., A Discussion of the pH-Dependent Protonation Behaviors of Poly (2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and Poly (ethylenimine-ran-2-ethyl-2-oxazoline) (P(EI-r-EOz)). Journal of Physical Chemistry B 2011, 115, (5), 844-860.39. Christodoulakis, K. E.; Vamvakaki, M., Amphoteric Core-Shell Microgels: Contraphilic Two-Compartment Colloidal Particles. Langmuir 2010, 26, (2), 639-647.40. Liu, Y. L; Sun, M., Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water. Water Research 2021, 207.41. Panchumarthy Ravisankar, S. A., Kommanaboina Supriya, U. Ajith Kumar, Fundamental Chromatographic Parameters. International Journal of Pharmaceutical Sciences Review and Research 2019, 55, 46.42. Kai Ling Ng, G. W. D., Paul R. Haddad, Effects of Stationary Phase Cross-Linking and Ion-Exchange Capacity on the Retention of Carboxylic Acids in Ion-Exclusion Chromatography Using Sulfonated Resins. Analytical Sciences 2001, 17, 1117.43. Auda Jabbar Braihi, S. I. S., Fadhel Abbas Hashem, Jaleel Kareem Ahmed, Proposed cross-linking model for carboxymethyl cellulose / starch superabsorbent polymer blend. International Journal of Materials Science and Applications 2014, 3, 363.44. Joey A. Roberts, L. K., Giorgio Carta, Effects of molecule size and resin structure on protein adsorption onmultimodal anion exchange chromatography media. Journal of Chromatography A 2020, 1628, 461444. Council), 1. 1. T. R., PFAS Technical and Regulatory Guidance Document and Fact Sheets PFAS-1. 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Claims

1. CLAIMS:

1. A charge switchable ion exchange (IX) resin comprising solid microparticles made of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral-to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group2. The resin of claim 1 , wherein the resin can undergo reversible transitions of its surface charge from positive to neutral to negative and from negative to neutral to positive.

3. The resin of claim 1 or 2, being a reversible positive-to-neutral-to-negative charge switchable ion exchange resin.

4. The resin of any one of claims 1 to 3, being a reversible positive-to-neutral-to-negative pH-responsive charge switchable ion exchange resin.

5. The resin of any one of claims 1 to 4, switching surface charge via pH adjustment.

6. The resin of any one of claims 1 to 5, wherein at a pH equal to an isoelectric point of the resin, the resin surface is neutral; at pHs lower that said isoelectric point, the resin surface is positively charged; and at pHs higher that said isoelectric point, the resin surface is negatively charged state.

7. The resin of any one of claims 1 to 6, being a capture-and-release ion exchange resin8. The resin of any one of claims 1 to 7, wherein said microparticles retain their shape and structural integrity when subjected to a compressive force of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa, without undergoing plastic deformation or flow.

9. The resin of any one of claims 1 to 8, wherein said microparticles have a compressive strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa.

10. The resin of any one of claims 1 to 9, wherein said microparticles have a yield strength of at least 1 MPa, preferably at least 10 MPa, and more preferably at least 25 MPa.

11. The resin of any one of claims 1 to 10, wherein said microparticles consists of the copolyelectrolyte only.

12. The resin of any one of claims 1 to 11, wherein said microparticles are spheroidal in shape, preferably spherical in shape.

13. The resin of any one of claims 1 to 12, wherein said microparticles have a sphericity of at least 0.85, preferably at least 0.90, more preferably at least 0.95, and most preferably at least 0.98.

14. The resin of any one of claims 1 to 13, wherein said microparticles are agglomerated together.

15. The resin of claim 14, wherein the agglomerated microparticles form a network of interconnected microparticles with voids between the microparticles defining pores in the resin.

16. The resin of any one of claims 1 to 15, wherein said microparticles are about 10 pm or more in average diameter, preferably up to 2500 pm in average diameter, when measured in deionized water.

17. The resin of any one of claims 1 to 16, wherein said microparticles are from about 200 pm to about 1100 pm, preferably from about 100 pm to about 1000 pm, more preferably from about 300 pm to about 900 pm, yet more preferably from about 500 pm to about 800 urn, and most preferably about 700 pm in average diameter.

18. The resin of any one of claims 1 to 17, wherein said microparticles have a D50 between about 10 pm and about 1000 pm, preferably between about 20 pm and about 600 pm, more preferably between about 20 pm and about 100 pm. In embodiments, the microparticles19. The resin of any one of claims 1 to 18, wherein said microparticles have a D90 between about 25 pm and about 2000 pm, preferably between about 50 pm and about 1400 pm, more preferably between about 50 pm and about 250 pm.

20. The resin of any one of claims 1 to 19, having a swelling ratio between about 1000% and about 4000%, preferably between 1200% and about 3400%.

21. The resin of any one of claims 1 to 20, having a swelling ratio between about 90% and about 120%, preferably of about 110%.

22. The resin of any one of claims 1 to 21 , having a packing density of between about 25 % and about 75 %, preferably between about 35 % and about 65 %.

23. The resin of any one of claims 1 to 22, having an apparent density between about 0.6 and about 1.3, preferably between about 0.9 to about 1.3.

24. The resin of any one of claims 1 to 23, having a water retention capacity between about 40% and about 60%, preferably of 50%.

25. The resin of any one of claims 1 to 24, having an average pore size between about 0.5 pm and 4.5 pm, preferably of about 2.5 pm as measured by SEM.

26. The resin of any one of claims 1 to 25, wherein the copolyelectrolyte is a random copolyelectrolyte.

27. The resin of any one of claims 1 to 26, wherein the copolyelectrolyte is randomly crosslinked.

28. The resin of any one of claims 1 to 27, wherein the copolyelectrolyte has a molecular weight (Mw) between about 5 and about 1000 kDa, preferably between about 10 and about 30 kDa.

29. The resin of any one of claims 1 to 28, wherein the positively ionizable weak base functional group is an amidine, guanidine, amine (primary, secondary and / or ternary), imidazole, and / or pyridine.

30. The resin of any one of claims 1 to 29, the repeat units (A) are repeat units of30.poly(N-methyltetrahydropyrimidine) (PMTHP),31.poly(p-azidomethylstyrene-co-styrene),32.poly[2-methyl-1-(4-vinylbenzyl)-1,4,5,6-tetrahydropyrimidine],33.poly (dimethyl acrylamide-co-(N-amidino)ethyl acrylamide) (P(DMA-co-NAEAA)), and34.poly (ethylene oxide)-b-poly((N-amidino)dodecyl acrylamide).35.poly[(2-dimethylamino) ethyl methacrylate] (PDMAEMA),36.poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA), and37.poly(3-N',N'-dimethylaminopropyl acrylamide) (PDMAPMA), or38.poly (L-arginine methyl ester acrylamide-co-N-cyclopropyl acrylamide) (poly(AME-co-CPAM),39.preferably PMTHP, PDMAEMA or PDMAPMA; and more preferably PMTHP.

31. The resin of any one of claims 1 to 30, wherein the negatively ionizable weak acid functional group is a carboxylic acid, sulfonic acid, and / or phosphoric acid.

32. The resin of any one of claims 1 to 31 , wherein the repeat units (B) are repeat units of:a polyacrylic acid such as polyacrylic acid or poly (ethyl acrylic acid), a polymethacrylic acid such as polymethacrylic acid or poly (ethyl methacrylic acid), and another repeat unit bearing a carboxyl (-COOH) group,42.a polysulfate such as poly (vinyl sulfate) PVS or poly (styrene sulfonate),43.a polyphosphoric acid such as poly (viny Iphosphonic acid),44.preferably polymethacrylic acid or polyacrylic acid, more preferably polyacrylic acid.

33. The resin of any one of claims 1 to 32, wherein the copolyelectrolyte further comprises repeat units (C) bearing a polymerizable group, wherein the polymerizable group has been incorporated by polymerization into another chain of the copolyelectrolyte to form a crosslink or remains unreacted.

34. The resin of any one of claims 1 to 33, wherein the repeat units (C) comprise as a pendant group, an alkylene, for example ethylene or methylene, preferably methylene, to which the polymerizable group is attached.

35. The resin of any one of claims 1 to 34, wherein the polymerizable group in repeat units (C) is an acrylate or a methacrylate, preferably a methacrylate, wherein the acrylate or methacrylate has been incorporated by polymerization into another chain of the copolyelectrolyte or remains unreacted.

36. The resin of any one of claims 1 to 35, wherein repeat units (C) are49.a diacrylate repeat units, such as alkyl diacrylate,50.a dimethacrylate repeat units, such as alkyl dimethacrylate, for example a repeat unit of ethylene glycol dimethacrylate (EGDMA):

52.

53. , wherein R1represents another chain of the copolyelectrolyte, or -C(=CH2)-CH3, or54.a dimethacrylamide repeat units, such as alkyl dimethacrylamide, for example a repeat unit of N,N'- methylenebis(acrylamide) (BisMAA): 255.NH .R56.r58.

59. ° , wherein R2represents another chain of the copolyelectrolyte, or -CH(=CH2).

37. The resin of any one of claims 1 to 36, wherein repeat units (C) are repeat units of EGDMA or BisMAA, preferably BisMAA.

38. The resin of any one of claims 1 to 37, wherein the isoelectric point of the resin is between about 3 and about 10, preferably between 5 and 9, more preferably between 7 and 9, most preferably about 8.

39. The resin of any one of claims 1 to 38, wherein:63.a repeat unit ratio a varies between about 5 % and about 95 %, preferably between 35 % and 85 %;64.a repeat unit ratio b varies between about 10 % and about 90 %, preferably between 15 % and 40 %; and / or65.a repeat unit ratio c varies between about 1 % and about 200 %, preferably between about 5 % and about 100%, more preferably between about 10% to about 85%,66.wherein repeat unit ratios a, b, and c, are expressed as percentages and calculated from the number of repeat units A, B, and C, respectively, based on the total number of repeat units A and B.

40. The resin of any one of claims 1 to 39, wherein the copolyelectrolyte has a degree of crosslinking between about 1 % and about 50%.

41. The resin of any one of claims 1 to 40, wherein the copolyelectrolyte is of formula:

69.

70. preferably of formula (III) or (IV) most preferably of formula (III), or alternatively of formula (IV),71.wherein R1and R2are as defined above, and a, b, and c represent said repeat unit ratios a, b, and c, respectively, pereferably wherein a = about 80-85% and b = about 15-20%.

42. A method from manufacturing a charge switchable ion exchange (IX) resin comprising spheroidal solid microparticles of a crosslinked copolyelectrolyte, wherein the copolyelectrolyte is a reversible positive-to-neutral- to-negative charge switchable copolyelectrolyte comprising repeat units (A) bearing a positively ionizable weak base functional group and repeat units (B) bearing a negatively ionizable weak acid functional group, such as the resin of any one of claims 1 to 41.

43. The method of claim 42, comprising the steps of:74.(I) copolymerizing monomer (A) bearing a positively ionizable weak base functional group and monomer (B) bearing a negatively ionizable weak acid functional group in the presence of a crosslinker via inverse suspension copolymerization, thereby producing and crosslinking the copolyelectrolyte into the shape of said spheroidal solid microparticles, and (II) agglomerating said spheroidal solid microparticles to form an interconnected network of spheroids, thus yielding the charge switchable ion exchange (IX) resin.75.wherein monomers A and B are monomers that, upon polymerization, yield repeat units (A) and (B) as defined in any one of claims 1 to 41 , respectively, and wherein the microparticles are as defined in any one of claims 1 to 41.

44. The method of claim 42 or 43, wherein the crosslinker is bifunctional or multi-functional, preferably bifunctional45. The method of any one of claims 42 to 44, wherein the crosslinker is monomer (C), which upon polymerization, yield repeat unit (C), as defined any one of claims 42 to 44.

46. The method of any one of claims 42 to 45, wherein the monomer (C) is a diacrylate monomer, such as a alkyl diacrylate monomer, a dimethacrylate monomer, such as a alkyl dimethacrylate monomer, for example EGDMA, or a dimethacrylamide monomer, such as a alkyl dimethacrylamide monomer, for example BisMAA, preferably the monomer (C) is EGDMA or BisMAA, preferably BisMAA, or alternatively EGDMA.

47. The method of any one of claims 42 to 46, wherein the copolymerizing and the crosslinking at step (I) are carried out in droplets of an aqueous solution of monomer A, monomer B, and the crosslinker in an aqueous solvent, wherein said droplets are dispersed in a continuous organic phase of an organic solvent immiscible or partially miscible with water to form an emulsion or a dispersion, preferably an emulsion.

48. The method of any one of claims 42 to 47, wherein step (I) comprises:81.a) dissolving monomer (A), monomer (B), and the crosslinker in the aqueous solvent to form the aqueous solution,82.b) providing the organic solvent,83.c) dispersing the aqueous solution in the organic solvent to produce a biphasic system comprising said droplets of the aqueous solution dispersed in the continuous organic phase, and84.d) allowing copolymerization and crosslinking within said droplets, yielding the spheroidal solid microparticles.

49. The method of claim 48, further comprising the step (e) isolating the spheroidal solid microparticles from the emulsion or dispersion, for example by filtration or centrifugation.

50. The method of claim 48 or 49, further comprising the step (f) of purifying the spheroidal solid microparticles, for example by washing one or more time (preferably 2 or more times, more preferably 3 or more times) with an appropriate washing solvent such as an organic solvent or water, preferably n-hexane, ethanol, or distilled water.

51. The method of any one of claims 48 to 50, wherein step (c) comprises adding the aqueous solution to the organic solvent, preferably at a temperature between about 40°C and about 60 °C.

52. The method of any one of claims 48 to 51 , wherein step (d) is carried out at a temperature between about 25°C and about 90°C, preferably between about 45°C and about 70°C.

53. The method of any one of claims 48 to 52, wherein, at step (d), the emulsion or dispersion is stirred, preferably at a stirring rate of between about 50 and about 1000 rpm, preferably between about 50 about 500 rpm, more preferably between about 80 rpm to about 200 rpm, and most preferably between about 80 rpm to about 130 rpm.

54. The method of any one of claims 48 to 53, wherein the aqueous solvent is deionized water, optionally in admixture with a water-miscible polar solvent such as an alcohol, for example methanol, ethanol, propanol, or butanol.

55. The method of claim 54, wherein the water and the alcohol are used in a watenalcohol weight ratio between about 2:1 and about 1:2, preferably between about 1:1 and about 1:1.4.

56. The method of any one of claims 48 to 55, wherein the aqueous solvent is deionized water without a polar solvent.

57. The method of any one of claims 48 to 56, wherein the organic solvent is cyclohexane, heptane, toluene, or an oil, preferably an oil.

58. The method of any one of claims 48 to 57, wherein the oil is a vegetable oil (such as corn oil, soybean oil, canola oil, sunflower oil, olive oil, palm oil, and coconut oil), a seed oil (such as castor oil, jojoba oil, safflower oil, peanut oil, and grapeseed oil), a synthetic oil (such as mineral oil, paraffin oil, and silicone oil), or an ester-based oil (such as methyl oleate and isopropyl myristate); preferably the oil is canola oil, olive oil, sunflower oil, soybean oil, or mineral oil.

59. The method of any one of claims 48 to 58, wherein the aqueous solvent and organic solvent are used in an organic solvent: aqueous solvent weight ratio between about 10:1 and about 1:1, preferably between about 7.5:1 and about 2:1, more preferably between about 5.1:1 and about 2: 1 , yet more preferably between about 2.5:1 and about 2.1 , and preferably of about 2.3:1.

60. The method of any one of claims 48 to 59, wherein the crosslinker is used in the aqueous solution in a concentration CL expressed in w / w%, based on the total weight of monomers A and B, between about 1 w / w%and about 90 Vo, preferably between about 5 w / w% and about 80 Vo, more preferably between about 10 w / w% and about 52 w / w.

61. The method of claim 60, further comprising modifying the swelling ratio (SW) of the microparticles of the resin by adjusting the concentration CL of the crosslinker.

62. The method of claim 60 or 61 , further comprising modifying the packing density of the microparticles of the resin by adjusting the concentration CL of the crosslinker.

63. The method of any one of claims 48 to 62, wherein a surfactant is used to disperse said droplets of the aqueous solution in the continuous organic phase.

64. The method of claim 63, wherein before step (c), the surfactant is dissolved in the organic solvent.

65. The method of claim 63 or 64, wherein the surfactant is an ionic surfactant, a nonionic surfactant or a mixture thereof.

66. The method of any one of claims 63 to 65, wherein the surfactant is a cellulose derivative (such as ethyl cellulose, etc.), a water-soluble surfactant (such as sorbitan monooleate e.g., sold under the tradename Span® 80, and polyvinylpyrrolidone), a cationic surfactant (such as dodecyltrimethylammonium bromide), an anionic surfactant (such as dioctyl sodium sulfosuccinate, sold as Aerosol OT (“AOT")), a nonionic surfactant (such as polyoxyethylene-polyoxypropylene glycol, sold as Pluronic® L-61 ("PL-61”)), or a mixture thereof (such as a SPAN80 / AOT mixture and a PL-61 / AOT mixture), preferably the surfactant is sorbitan monooleate, AOT, and PL- 61 / AOT mixtures.

67. The method of any one of claims 63 to 66, wherein the surfactant is used in a concentration S expressed in w / w%, based on the total weight of monomers A, B, and C, between about 0.05 and about 10 w / w%, preferably between about 1 and about 50 w / w%.

68. The method of any one of claims 48 to 67, wherein an initiator is used to initiate the polymerization.

69. The method of claim 68, wherein the initiator is dissolved in the aqueous solvent before step (d).

70. The method of claim 68 or 69, wherein the initiator bears a persulfate moiety (such as ammonium persulfate (APS)), nitrile moiety (such as azobisisobutyronitrile (ABN)) or azo moiety (such as 2,2'-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride (VA-044)), preferably the initiator is 2,2'-azobis[2-(2-imidazolin-2-y l)propane] dihydrochloride.

71. The method of any one of claims 69 to 70, wherein the initiator is used in a concentration between about 0.1 w / w% to about 5 w / w%, preferably between about 0.1 w / w% to about 4 w / w%, based on the total weight of the monomer A and monomer B.

72. The method of any one of claims 48 to 71, wherein a porogen is used to create pores in the spheroidal solid microparticles.

73. The method of claim 72, wherein the porogen is dissolved in the aqueous solvent before step (d).

74. The method of claim 72 or 73, wherein the porogen is polyethylene glycol (PEG), polyvinyl alcohol (PVA), Pluronic 108 (poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol)), or a mixture thereof; preferably PEG, more preferably a molecular weight from 1000Da to 10OOkDa, preferably from 5000 g / mol to 35000 g / mol, and most preferably of 20000 g / mol.

75. The method of any one of claims 72 to 74, wherein the porogen is used in a concentration between about 0.5 w / w% to about 20w / w%, preferably between about 1 w / w% to about 10 w / w%, based on the total weight of the monomer A, the monomer B, and the crosslinker.

76. The method of any one of claims 48 to 75, wherein the monomer A is used is used in a concentration between about 10 and about 90 w / w%, preferably a concentration of about 50 w / w%, based on the total weight of the biphasic system.

77. The method of any one of claims 48 to 76, wherein the monomer B is used is used in a concentration between about 2 and about 15 w / w%, preferably a concentration of about 7 w / w%, based on the total weight of the biphasic system.

78. The method of any one of claims 48 to 77, further comprising adjusting molar ratios a' and b', wherein the molar ratios a', b', and c' represent the relative quantities in mol of each monomer, expressed as a percentage, calculated based the number of mols of monomer A, B, and C, respectively, in the aqueous solution based on the total number of moles of monomer A and B in the aqueous solution.

79. The method of claim 78, further comprising tuning the isoelectric point of the resin by selecting monomer A and monomer B and adjusting a' and b'.

80. The resin of any one of claims 1 to 41 being for capturing ions from a feed or exchanging ions in a feed.

81. A method of capturing ions from a feed or exchanging ions in a feed, the method comprising the step of contacting the feed with the charge switchable ion exchange resin of any one of claims 1 to 41.

82. Use of the charge switchable ion exchange resin of any one of claims 1 to 41 for capturing ions from a feed or exchanging ions in a feed.

83. The method / use / resin for use of any one of claims 80 to 82, wherein the feed is water or another liquid.

84. The method / use / resin for use of any one of claims 80 to 83, wherein the ions are pollutants.

85. The method / use / resin for use of any one of claims 80 to 84, wherein the ions are negatively charged molecules, preferably dyes, per- and polyfluoroalkyl substances (PFAS), or proteins, most preferably PFAS.

86. The method / use / resin for use of claim 85, wherein the feed is water.

87. The method / use / resin for use of any one of claims 80 to 84, wherein the ions are positively charged molecules.

88. The method / use / resin for use of any one of claims 80 to 87, wherein a pH of the feed is adjusted so that the resin has a surface charge opposite to a charge of said ions.

89. The method / use / resin for use of any one of claims 80 to 88, wherein the resin is selected such that the resin has an isoelectric point such that, when contacted with the feed, the resin has a surface charge opposite to a charge of said ions.

90. The method / use / resin for use of any one of claims 80 to 89, for concentrating a contaminant by capturing and accumulating ions of said contaminant and then releasing and electrostatically repulsing said ions.

91. The method / use / resin for use of claim 90, wherein, after said ions have been captured, the resin is contacted with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions.

92. The method / use / resin for use of claim 90 or 91 , wherein said ions are released into a destruction media93. The method / use / resin for use of any one of claims 80 to 92, wherein, after said ions have been captured, the resin is regenerated by releasing said ions.

94. The method / use / resin for use of claim 93, wherein the resin is regenerated by contacting the resin with a regenerating liquid having a pH such that the resin, upon contact with the regenerating liquid, has a surface charge that is the same as the charge of said ions, thereby releasing and electrostatically repulsing said ions and regenerating the resin.

95. The method / use / resin for use of claim 93 or 94, wherein, after regenerating the resin, the resin is reused to capture ions from a feed.

96. The method / use / resin for use of any one of claims 93 to 95, wherein the resin is regenerated and reused one or more times, preferably a plurality of times.

97. The method / use / resin for use of any one of claims 91 to 96, wherein the regenerating liquid is the feed with an adjusted pH or another liquid, for example water.

98. The method / use / resin for use of any one of claims 90 to 97, wherein the releasing / regenerating is carried out by adjusting the pH of the feed so that the resin has a surface charge that is the same as the charge of said ions.

99. The method / use / resin for use of any one of claims 90 to 98, wherein the pH is adjusted by adding an acid to the feed.

100. The method / use / resin for use of any one of claims 90 to 98, wherein the pH is adjusted by adding a base to the feed.

101. The method / use / resin for use of any one of claims 90 to 98, wherein the pH is adjusted by introducing a gas in the feed.

102. The method / use / resin for use of any one of claims 90 to 101, wherein the releasing / regenerating step is free from the use of any other chemical except those for adjusting the pH of the feed.

103. The method / use / resin for use of any one of claims 90 to 102, wherein resin is charged in a column, and the feed is passed through the column at for said capturing and the regenerating liquid is passed through the column for releasing the ions and for regenerating the resin.

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