SIEVING

BACKGROUND

[0001] Organic solvent nanofiltration (OSN) is a membrane technology that offers an energy-efficient alternative to traditional thermal separations. However, it requires materials that are stable in a wide range of organic solvents. Polybenzimidazole (PBI) is known to have good solvent resistant properties towards many organic solvents, namely ketones, ethers, alcohols, and non-polar solvents. Consequently, PBI has recently been explored for OSN. Nevertheless, PBI membranes are not stable in harsh polar aprotic solvents, such as N,N- Dimethylacetamide (DMAc), /V, /V-Di mcthylf rmam idc (DMF), and dimethyl sulfoxide (DMSO) without crosslinking.

[0002] To obtain solvent-resistant membranes, crosslinking is commonly required, usually by immersing the membrane in a solution of a reactive crosslinking agent such as dibromoxylene, bisepoxides, diamines, and acyl chlorides. Metal derivatives, thermal rearrangement, and interpenetrating polymer networks have recently been proposed to improve membrane stability. Metal-organic coordination has been extensively explored for crosslinking polyphenols in the field of materials science, but membrane fabrication based on metal- polymer coordination (MPC) is scarce.

[0003] Metal chelation on a polymer has been attempted through a self-assembly and chelation assisted non-solvent induced phase separation technique for polysulfone films by applying strong acid hydrolysis and the addition of Q1SO4 or FcCh into the coagulation bath. Complexation-induced phase separation has also been reported as an approach to fabricate metal-polymer composite membranes. Soft metal ions such as silver and palladium resulted in thinner dense layers than that of borderline metal ions such as cobalt and nickel. This method achieves formation of a metal-polymer coordination only on the outer part of the membrane layer. As a result, the inner part of the membrane cannot resist the solvents that can dissolve the polymer. The aforementioned phase inversion techniques provide cross! inked membranes; however, the metal-polymer coordination was not investigated. Moreover, none of the published literatures report metal chelation on nitrogen-heterocyclic containing polymer, such as polybenzimidazole (PBI). To implement OSN membranes/process in practical applications there is a need for methods of improving polymeric membrane stability. SUMMARY

[0004] The present disclosure provides materials and methods for crosslinking of heterocyclic containing polymeric membranes, such as polybenzimidazole membranes, through coordination with metal salts (e.g., copper(I) iodide). For example, heterocyclic containing polymers can be coordinated using the methods described herein to form solvent resistant and stable membranes or materials. The methods can be used for efficient preparation of metal-polymer coordination membranes for molecular sieving, including for versatile OSN applications involving polar and non-polar solvents and/or extreme conditions.

[0005] In a first aspect, the present disclosure features a method of preparing a metal- polymer coordination membrane comprising: immersing a pre-formed membrane in a crosslinking bath containing a non-solvent and a polymer coordinating agent having at least one metal, wherein the pre-formed membrane includes non-crosslinked polymer chains comprising repeat units having a heterocycle, whereby the metal coordinates with the heterocycle to form crosslinks between the polymer chains. The pre-formed membrane can be prepared by casting, evaporation, template leaching, extrusion stretching, plasma polymerization, phase inversion, spin coating, dip coating, spray coating, interfacial polymerization, or electrospinning. The pre-formed membrane can include a support, optionally a non-woven support, or be an unsupported membrane. The method can further include preparing the pre-formed membrane by: (a) casting a polymer solution comprising the polymer chains comprising repeat units having a heterocycle to obtain a cast membrane; and (b) immersing the cast membrane in a non-solvent coagulation bath to obtain a pre-formed membrane. In some cases, the polymer solution contains a solvent selected from the group consisting of dimethyl sulfoxide, N-Methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and acetonitrile. In some cases, the polymer solution includes about 1% to 50%, 5% to 45%, 10% to 40% or about 15% to 35% by weight polymer chains. In one or more embodiments, the non-solvent coagulation bath contains one or more of water, methanol, ethanol and isopropanol. The pre-formed membrane can be an integrally skinned asymmetric membrane. At least one of the polymer solution and the non-solvent coagulation bath can be free of the polymer coordinating agent. The non-solvent of the non-solvent coagulation bath and the crosslinking bath can be the same. In some cases, the non-solvent coagulation bath and the crosslinking bath do not include the same non-solvent. At least a portion of the polymer coordinating agent can be dissolved in the crosslinking bath. The pre-formed membrane can be immersed for sufficient time for the metal to coordinate with the heterocycle homogeneously throughout the membrane. In some cases, the time is about 2 to 24 hours. The crosslinking bath can contain about 10 to about 1000 ppm polymer coordinating agent. The polymer chains can be selected from single strand linear polymers and double strand linear polymers (e.g., ladder polymers). The heterocycle can be selected from the group consisting of nitrogen-containing heterocycles, sulfur-containing heterocycles, and oxygen-containing heterocycles. The heterocycle can be incorporated into the polymer backbone, attached to the polymer backbone as a pendent group, or a combination thereof. The heterocycle can be selected from the group consisting of:

The polymer chain can include a polymer selected from the group consisting of poly- thiosemicarbazide (PTSC), poly-thiourea (PTU), polybenzimidazole (PBI), polymers containing azole groups in their backbone, or azole groups as pendant groups, polyazoles, copolyazoles, polyoxadiazoles, poly(5 -vinyl tetrazole), copolymers of 5 -vinyl tetrazole with acrylonitrile, poly(N-alkyl-5-vinyl tetrazole)s, polysulfone bearing triazole functions, and tetrazole-containing polymers of intrinsic microporosity. The metal can be selected from the group consisting of copper, silver, zinc, iron, nickel, cobalt, manganese, aluminum and combinations thereof. The polymer coordinating agent can be selected from the group consisting of metal oxides, metal salts, metal complexes, and combinations thereof. The polymer coordinating agent can be selected from the group consisting of metal halides, metal sulfates, metal nitrates, metal oxides, and combinations thereof. The polymer coordinating agent can have the formula MX _a , where M is a metal cation selected from the group consisting of Cu ⁺ , Cu ²⁺ , Mn ²⁺ , Co ²⁺ , Ag ⁺ , Zn ²⁺ , Fe ²⁺ , Fe ³⁺ , Ni ²⁺ , and Al ³⁺ ; X is an anion selected from the group consisting of Br, Cl, F, I, SO4, NO3, O, O2, and combinations thereof; and a is from 1 to 4. In some cases, the crosslinks are reversible crosslinks.

[0006] A second aspect of the present disclosure features a metal-polymer coordination membrane prepared by any embodiment of the first aspect or any combination of the embodiments of the first aspect. The metal can be homogeneously distributed throughout the surface and bulk of the membrane. As compared with the preformed membrane, the membrane can have one or more of the following properties: (a) increased hardness; (b) lower contact angle; (c) increased roughness; (d) reduced plasticization; and (e) increased stability in at least one of «-heptane, toluene, ethanol, methanol, tetrahydrofuran, acetone, acetonitrile, N,N- Dimethylacetamide, N,N-DimethyIformamide, dimethyl sulfoxide, and an alkaline solution. In some cases, the alkaline solution has a pFi greater than 7 to about 12. The membrane can be macroscopically a single-phase material.

[0007] A third aspect of the present disclosure features a method of separating one or more chemical species, the method comprising contacting a metal-polymer coordination membrane of any one of the embodiments of the second aspect with a liquid feed stream comprising a first solute and a first solvent to separate the first solute or the first solvent from liquid feed stream. The liquid of the feed stream can be an aqueous liquid, an organic liquid, or a combination thereof. In some cases, the liquid is wastewater. The first solute can be selected from the group consisting of sugars, salts, amino acids, flavors, genotoxins, colorants, dyes, pigments, catalysts, peptides, antibiotics, proteins, enzymes, and active pharmaceutical ingredients. The at least one chemical species can be separated by ultrafiltration, nanofiltration, or microfiltration. In both microfiltration and ultrafiltration, the separation mechanism is mainly based on molecular sieving using porous membranes with increasingly fine pores (size exclusion). In general, microfiltration is used to separate suspended particles with diameters between 0.1 and 10 pm from the liquid of the feed stream; this size range includes a wide variety of natural and industrial particles. The separation can include dead end filtration or cross-flow filtration. In some cases, separating includes concentrating the first solute, recovering the first solvent or a combination thereof. The liquid feed stream can include at least two solvents. In some cases, the method can further include solvent exchange. The liquid feed stream can include at least two solutes. In some cases, the method further includes purifying the first solute of the at least two solutes. Contacting can be performed under an operating pressure higher than 10 bar, optionally up to about 100 bar. The first solvent can be selected from the group consisting of alcohols, methanol, ethanol, isopropanol, butanol, acetone, alkanes, pentane, «-hexane, «-heptane, cyclohexane, alkyl acetates, butyl acetate, ethyl acetate, ethers, methyl ethyl ketone, diethyl ether dichloroethane, chloroform, trichloroethane, methyl isobutyl ketone, formaldehyde, ethylene glycol, propylene oxide, methylene chloride, nitrobenzene, tetrahydrofuran, toluene, diethyl ether, acetonitrile, carbon tetrachloride, xylene, dioxane, dimethyl sulfoxide, dimethylformamide, N-methyl pyrrolidone, and dimethylacetamide. The method can further include contacting at least one additional membrane with a filtered feed stream comprising the separated first solute or the separated first solute. In some cases, the method further includes recycling the metal-polymer coordination membrane by reversing the crosslinks and recovering the polymer coordinating agent. Recycling can include treating the membrane with an aqueous acid solution.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] The present disclosure includes illustrative embodiments that are non-limiting and non-exhaustive. The drawings illustrate by way of example various embodiments discussed below, in which:

[0009] FIG. 1 is a reaction scheme illustrating crosslinking of polymer chains through coordination with a metal (MX, including metal oxide, metal salt, and metal complexes), according to one or more embodiments of the invention. Repeat units containing aromatic rings (A and B, which can be the same or different) having none, one, or multi substituents Ri - R3 _, , include at least one heterocycle Z. The polymer can include any number of repeat units («). [0010] FIG. 2 is a flowchart describing a method of making a metal-polymer coordination membrane, according to one or more embodiments of the invention.

[0011] FIG. 3 is a flowchart describing a method of using a metal-polymer coordination membrane according to one or more embodiments of the present disclosure, to separate and/or recover one or more chemical species present in a mixture (e.g., an organic feed stream comprising solvents, catalysts, dyes, biofuels, and/or active pharmaceutical agents).

[0012] FIGS. 4A-B illustrate one of the differences between: (A) a membrane having metal-polymer coordination on the surface, leaving the uncoordinated polymer susceptible to dissolution by polar aprotic solvents, such as DMSO, according to US 10,696,025B; and (B) a solvent-resistant membrane characterized by homogenous metal-polymer coordination, which is stable in polar aprotic solvents, according to one or more embodiments of the present disclosure.

[0013] FIG. 5 shows X-ray photoelectron spectroscopy (XPS) spectra of membrane M0 (uncrosslinked PBI membrane) and membrane M3, a metal-polymer coordination membrane, according to one or more embodiments of the present disclosure.

[0014] FIG. 6 shows a SEM cross-section of M3, a metal-polymer coordination membrane, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

[0015] The present disclosure describes methods of treating polymeric membranes to confer enhanced properties for use in a variety of applications, including applications involving one or more harsh conditions (e.g., OSN). In some cases, the method includes crosslinking polymer chains of pre-formed membranes with a polymer coordinating agent. For example, the polymer coordinating agent may include a metal that is capable of associating with a heterocycle of the polymer chains to form crosslinks between the polymer chains via non- covalent interactions. Examples of the one or more enhanced properties include, without limitation: mechanical stability, such as membrane hardness, elastic, plastic, viscoelastic, fracture and toughness properties; chemical stability, such as stability against the detrimental effects of organic solvents, acids, bases and/or oxidizing agents; and wettability (e.g., lower water contact angle). The membranes of the present disclosure may also include crosslinks that are reversible such that at least one of the polymer and the polymer coordinating agent may be recovered and/or recycled. Additional advantages of the present invention include a simple fabrication method, greater control over membrane properties, homogeneous distributions of metals in the surface and bulk membrane portions, among other advantages described herein. [0016] The term “metal-polymer coordination membrane” refers to a polymeric membrane with coordination complexes between one or more ligand functional groups or atoms anchored to a polymer matrix and a metal ion, in which the metal ion is attached to the polymeric ligand(s) by a coordination bond. The ligand functional group or atom (e.g., O, N, P or S) can be present in the polymer backbone or on a pendant group. The membrane can include various types of coordination structures including pendant, inter- and/or intramolecular bridged complexes.

[0017] The term “pre-formed” as used herein, means that the object is manufactured into a form having a predetermined shape and size, wherein the object (e.g., polymeric membrane) may be removed from any associated packaging without further preparative steps by the user. [0018] As used herein, “casting” refers to disposing a material on, in, or around an object or mold, among other things. For example, casting may refer to disposing a pourable composition of a material (e.g., polymer) dissolved in a solvent on an object or mold. Casting may include, but is not limited to, one or more of depositing, pouring, dipping, coating, and applying.

[0019] As used herein, “contacting” refers to an act of touching, making contact, or of bringing to close or immediate proximity. Contacting may refer to bringing two or more components in proximity, such as close physical proximity. Mixing is an example of contacting.

[0020] As used herein, “dissolving” refers to providing one or more of a uniform, somewhat uniform, and substantially uniform distribution. For example, dissolving may refer to dissolution of a first chemical species or solute (e.g., polymer, metal salt, dye, or active pharmaceutical ingredient) in a solvent forming a solution of the first chemical species in the original solvent. Dissolving may generally refer to disassociating, disentangling, solvating polymer chains, blocks, or segments.

[0021] “Heterocycle” or “heterocyclic” refers to a stable 3- to 14-membered aromatic or non-aromatic ring radical comprising 2 to 10 carbon atoms and from one to 4 heteroatoms (e.g., nitrogen, oxygen, and sulfur). The heteroatom(s) may be oxidized, and nitrogen atom may be quaternized. The heterocycle can be monocyclic or polycyclic. The heterocycle can be partially or fully saturated. Examples of heterocyclic groups include pyridyl, pyrazolyl, benzoxazolyl, benzimidazolyl, benzothiazolyl, imidazolyl, oxazolyl, thiazolyl, morpholinyl, thiomorpholinyl, furyl, piperazinyl, piperidinyl, pyranyl, pyrrolidinyl, tetrahydropyranyl, tetrahydrofuranyl, and 1,3-dioxanyl.

[0022] The term “heteroalkyl” as used herein, refers to an alkyl group in which one or more of the constituent carbon atoms have been replaced by nitrogen, oxygen, or sulfur. In some embodiments, the heteroalkyl group can be further substituted with 1, 2, 3, or 4 substituent groups. Examples of heteroalkyl groups are an “alkoxy” which, as used herein, refers alkyl-0 — (e.g., methoxy and ethoxy). A heteroalkylene is a divalent heteroalkyl group. The alkyl group can be a branched or straight-chain monovalent saturated aliphatic hydrocarbon radical of 1 to 20 carbon atoms (e.g., 1 to 16 carbon atoms, 1 to 10 carbon atoms, or 1 to 6 carbon atoms). An alkylene is a divalent alkyl group.

[0023] The term “heteroalkenyl,” as used herein, refers to an alkenyl group in which one or more of the constituent carbon atoms have been replaced by nitrogen, oxygen, or sulfur. In some embodiments, the heteroalkenyl group can be further substituted with 1, 2, 3, or 4 substituent groups. Examples of heteroalkenyl groups are an “alkenoxy” which, as used herein, refers alkenyl-0 — . A heteroalkenylene is a divalent heteroalkenyl group. The alkenyl group can be a straight-chain or branched hydrocarbon residue having a carbon-carbon double bond and having 2 to 20 carbon atoms (e.g., 2 to 16 carbon atoms, 2 to 10 carbon atoms, 2 to 6, or 2 carbon atoms).

[0024] The term “heteroalkynyl,” as used herein, refers to an alkynyl group, as defined herein, in which one or more of the constituent carbon atoms have been replaced by nitrogen, oxygen, or sulfur. In some embodiments, the heteroalkynyl group can be further substituted with 1, 2, 3, or 4 substituent groups as described herein for alkynyl groups. Examples of heteroalkynyl groups are an “alkynoxy” which, as used herein, refers alkynyl-0 — . A heteroalkynylene is a divalent heteroalkynyl group. The alkynyl group can be a straight-chain or branched hydrocarbon residue having a carbon-carbon triple bond and having 2 to 20 carbon atoms (e.g., 2 to 16 carbon atoms, 2 to 10 carbon atoms, 2 to 6, or 2 carbon atoms).

[0025] Generally, “immersing” refers to positioning an object in a solution sufficient for the solution to contact the object or a part thereof. The object may be partially immersed or completely immersed. An example of immersing may include submerging.

[0026] As used herein, the term “non-solvent” refers to a liquid that, at processing temperatures, dissolves no more than trace amounts of a given heterocycle-containing polymer when used alone.

[0027] Ah percentages, parts and ratios are based upon the total weight of the compositions of the present invention, unless otherwise specified. Ah measurements are conducted at 25° C. unless otherwise specified. Certain materials, compounds, compositions, and components described herein can be obtained commercially or readily synthesized using techniques generally known to those of skill in the art. [0028] The present disclosure describes an efficient approach for fabricating solvent- resistant membranes based on metal-polymer coordination between heterocyclic polymer and a metal derivative, such as coordination between a N-heterocyclic polymer and a metal salt (i.e., a chelating method). The heterocyclic polymer can be polybenzimidazole which contains imida ole moieties. The obtained membranes demonstrate excellent stability in organic solvents and improved mechanical properties, which is advantageous for operating at high pressure. This chelating method and membranes made thereby can be applied to different industries, including organic solvent nanofiltration (OSN), membrane-based gas separation, fuel cell, catalysis, sensors for trace substance detection, electronic industry, pharmaceutical applications, and in the development of composite materials.

A. METHODS OF MAKING METAL-POLYMER COORDINATION MEMBRANES [0029] FIG. 1 provides a schematic summary of the chelating method for fabricating highly solvent-resistant membranes by crosslinking polymer chains containing building blocks A and B through coordination with metal derivative MX, a polymer coordination agent comprising a metal M. Building blocks A and B can be selected from the same or different monomers. Building blocks A and B can be connected linearly (single stranded) or as a ladder like connection (double stranded). At least one of A and B can be an aromatic ring containing heterocyclic structure (Z), such as but not limited to nitrogen, oxygen, sulfur (e.g., optionally phosphorous). Ri, R ₂ , and R ₃ represent optional substituents connected to A and/or B building blocks, each independently selected from the group consisting of aryl (e.g., substituted and unsubstituted phenyl), carbocyclyl (e.g., substituted and unsubstituted cycloalkyl), halogen (e.g., fluoro), hydroxyl, heteroalkyl (e.g., substituted and unsubstituted methoxy, ethoxy, or thioalkoxy), heterocyclyl, amino (e.g., NH ₂ or mono- or dialkyl amino), azido, cyano, nitro, or thiol. The aryl, carbocyclyl (e.g., cycloalkyl), and heterocyclyl groups may also be substituted with alkyl (unsubstituted and substituted, such as arylalkyl (e.g., substituted and unsubstituted benzyl)). Building blocks A and B can have none, one, or multi substituents with same or diverse types. The polymer chain can include one or more heterocyclic units selected from the group consisting of 3-atom rings, 4-atom rings, 5-atom rings, and 6-atom rings. The coordination between the polymers through the metal can be governed by the heterocyclic atom (Z), an aromatic ring (A and/or B), the substituents (Ri, R ₂ , and/or R ₃ ), or combinations thereof. [0030] The heterocycle of the polymer chain is selected from heterocycles of the polymer backbone, heterocyclic pendant groups, and combinations thereof. The heterocycle can have one or more N atoms as well as other heteroatoms in the ring, e.g. S, P, O. The heterocycle can be commercial or synthetic whether derived from natural source or not. The heterocycle can be aromatic, aliphatic, and with or without double bonds and triple bonds. Non-limiting examples of suitable heterocycles in the polymer structures include the subunits below:

[0031] The polymer coordinating agent MX of FIG. 1 is selected from metal derivatives such as, but not limited to, metal oxides, metal salts, and metal complexes. M can be any metal capable of coordinating with the heteroatom of the heterocycle and/or an aromatic or aliphatic ring to form a cross-link. In some cases, M is a metal cation selected from the group consisting of copper, silver, zinc, iron, and aluminum and X is a corresponding anion selected from the group consisting of halogen, sulfate, oxide, nitrate, and anionic complexes. Non-limiting examples include metal halides (e.g., Cul, CuBr, CuCl, FeCb, AuCh, AgBr, and TiCU); metal sulfates (e.g., CuSCb, FeSCb, CdSCb, and ZnSCb); metal nitrates (e.g., Cu(NC>3)2, Fe(NC>3)3, and Zh(N(¾)2); and metal oxides (e.g., ZnO, CuO, NiO, and ZrC ). In some cases, the polymer coordinating agent is a metal derivative other than FeCb, a copper(II)-containing polymer coordinating agent or Ag ⁺ -containing polymer coordinating agents. The polymer coordinating agent can have the formula MX _a , where: M is a metal cation selected from the group consisting of Cu ⁺ , Cu ²⁺ , Ag ⁺ , Zn ²⁺ , Fe ²⁺ , Fe ³⁺ , Ni ²⁺ , Co ²⁺ , Mn ²⁺ , Cr ²⁺ , and Al ³⁺ ; X is an anion selected from the group consisting of Br, Cl, F, I, SO4, NO3, O, O2, and combinations thereof; and a is from 1 to 4.

[0032] Fig. 2 describes method 100 for preparing a metal-polymer coordination membrane. Step 101 includes obtaining a pre-formed membrane prepared from a heterocyclic- containing polymer. The pre-formed membrane may need stabilization (e.g., an uncrosslinked or partially crosslinked polymeric membrane). The form of the membrane can be selected based on a desired application. The pre-formed membrane can have symmetric or asymmetric architecture, can be porous or dense, and supported or freestanding, in any combination. In some cases, the pre-formed membrane does not have a porous support layer or a support layer. The pre-formed membrane can be a spiral wound, hollow fiber, tubular or flat sheet membrane. [0033] The pre-formed membrane can be prepared by any suitable process for membrane fabrication of the selected heterocyclic polymer (e.g., a polymer described above having building blocks A and B). For example, the pre-formed membrane can be made by casting, evaporation, phase inversion, spin coating, dip coating, interfacial polymerization, or other membrane preparation techniques.

[0034] In step 106, the pre-formed membrane is immersed in a crosslinking bath that contains one or more non-solvents with respect to the polymer and a polymer coordinating agent (e.g., MX and MX„, as defined above for Scheme 1). The polymer coordinating agent can be selected from the group consisting of metal oxides, metal salts, metal complexes, and combinations thereof; such as metal halides, metal sulfates, metal nitrates, metal oxides, and combinations thereof. The polymer coordinating agent can be at least partially dissolved in the crosslinking bath. The non-solvent can be selected to favor permeation of MX or the metal ion through the membrane. For example, the non-solvent can be selected based on polarity and/or the extent to which the polymer swells. In some cases, the non-solvent can be acetonitrile. The polymer coordination agent can be present in any suitable concentration up to the limit of solubility of the selected polymer coordination agent(s) in the selected non-solvent, such as at least about 1 ppm to 10,000 ppm, about 5 ppm to about 5,000 ppm, about 10 ppm to about 2,000 ppm, about 10 ppm to about 1000 ppm or about 100 ppm to about 500 ppm, or any value within these ranges. Step 106 can be performed at room temperature or elevated temperature. The duration for immersion can vary from about 2 hours to about 24 hours. The type of non solvent, temperature and duration can be selected to achieve a desired degree of crosslinking. [0035] In some cases, method 100 includes one or more steps for fabricating the pre formed membrane. For example, the method can include step 102 to obtain a cast membrane by casting a solution containing dissolved chains of a heterocyclic polymer (e.g., a dope solution). Step 102 can further include a step of preparing the dope solution by dissolving the heterocyclic polymer in a suitable solvent at the necessary temperature, and optionally agitating the mixture. In some cases, the polymer solution includes a solvent selected from the group consisting of dimethyl sulfoxide (DMSO), N-Methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA or DMAc), acetonitrile (MeCN) and mixtures thereof. The polymer solution can include about 1% to about 99%, about 1% to about 50%, about 5% to about 45%, about 10% to about 40% or about 15% to about 35% by weight polymer chains. The heterocyclic polymer can be contacted with the solvent(s) and the mixture can be agitated and/or heated until a viscous solution is obtained. The solution can include one or more co-solvents, porogens, or other additives. In some cases, the solution is coated on a substrate (e.g., a thin-film composite ). A suitable substrate can be selected on the application of the membrane.

[0036] For step 104, the pre-formed membrane is coagulated (or precipitated) by immersing the cast membrane in a suitable non-solvent for the polymer (i.e., a coagulation bath containing at least one non-solvent). Step 104 can be free of any compound that could be used as a polymer coordinating agent. The non-solvent(s) of the coagulation bath can be the same or different than the non-solvent(s) of the crosslinking bath. The non-solvent(s) can be selected based on a desired membrane architecture. For example, the non-solvent(s) can be selected to promote formation of a porous microstructure, a integrally dense layer, macro-voids, uniform interconnected pores, etc., as according to known methods. In some cases, the non-solvent coagulation bath comprises one or more of water, methanol, ethanol and isopropanol. The pre formed membrane can be an integrally skinned asymmetric membrane.

[0037] Although a non-solvent induced phase separation process is described, step 104 is not limited to this method of membrane fabrication. After polymeric film formation, the pre formed membrane can be dried (e.g., at room temperature and/or in a heated vacuum oven), stored an aqueous organic solution (e.g., 1% acetonitrile and distilled water) or can be immediately treated according to step 106 described above. B . METAL-POLYMER COORDINATION MEMBRANES

[0038] A metal-polymer coordination membrane of the present disclosure can possess one or more improved properties as compared to a non-crosslinked membrane. For example, a membrane made according to method 100 may exhibit at least one of the following: (a) increased hardness; (b) lower contact angle; (c) increased roughness; (d) reduced plasticization; and (e) increased stability in at least one of «-heptane, toluene, ethanol, methanol, tetrahydrofuran (THF), acetone, acetonitrile (MeCN), N,N-Dimethylacetamide (DMA or DMAc), N,N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and an alkaline solution (such as a solution having a pH of greater than 7 to about 12), compared with the pre formed membrane. In some cases, the metal-polymer coordination membrane possesses catalytic activity imparted by the metal (e.g., copper-based catalysis) and/or exhibits a lower molecular weight cut-off because of crosslinking. The metal-polymer coordination membranes of the present disclosure can exhibit improved mechanical stability without loss of flexibility. In some cases, the mechanical properties allow scale-up and rolling of flat sheet membranes into industrially applicable spiral-wound membrane modules (SWMM).

[0039] A metal-polymer coordination membrane of the present disclosure can be characterized by the distribution of polymer coordinating agent, crosslinks and/or crosslink density. In some cases, the crosslinking is uniform or substantially uniform throughout the bulk membrane, e.g., due to diffusion of the polymer coordinating agent throughout the membrane matrix. The membrane thickness, , composition, immersion time, temperature, and polymer coordinating agent concentration can be manipulated to promote uniform crosslinking. In some embodiments, the metal-polymer coordination membrane does not include a layer of polymeric membrane that lacks crosslinks.

[0040] The preformed membrane and/or metal-polymer coordination membrane of method 100 can have a thickness of about 1 nm to about 10 nm, about 1 nm to about 50 nm, about 1 nm to about 75 nm, about 1 nm to about 100 nm, about 1 nm to about 150 nm, about 1 nm to about 200 nm, about 1 nm to about 250 nm, about 1 nm to about 500 nm, about 1 nm to about 750 nm, about 1 nm to about 1,000 nm, about 1 nm to about 2,500 nm, about 1 nm to about 5,000 nm, about 1 nm to about 10,000 nm, about 10 nm to about 50 nm, about 10 nm to about 75 nm, about 10 nm to about 100 nm, about 10 nm to about 150 nm, about 10 nm to about 200 nm, about 10 nm to about 250 nm, about 10 nm to about 500 nm, about 10 nm to about 750 nm, about 10 nm to about 1,000 nm, about 10 nm to about 2,500 nm, about 10 nm to about 5,000 nm, about 10 nm to about 10,000 nm, about 50 nm to about 75 nm, about 50 nm to about 100 nm, about 50 nm to about 150 nm, about 50 nm to about 200 nm, about 50 nm to about 250 nm, about 50 nm to about 500 nm, about 50 nm to about 750 nm, about 50 nm to about 1,000 nm, about 50 nm to about 2,500 nm, about 50 nm to about 5,000 nm, about 50 nm to about 10,000 nm, about 75 nm to about 100 nm, about 75 nm to about 150 nm, about 75 nm to about 200 nm, about 75 nm to about 250 nm, about 75 nm to about 500 nm, about 75 nm to about 750 nm, about 75 nm to about 1,000 nm, about 75 nm to about 2,500 nm, about 75 nm to about 5,000 nm, about 75 nm to about 10,000 nm, about 100 nm to about 150 nm, about 100 nm to about 200 nm, about 100 nm to about 250 nm, about 100 nm to about 500 nm, about 100 nm to about 750 nm, about 100 nm to about 1,000 nm, about 100 nm to about 2,500 nm, about 100 nm to about 5,000 nm, about 100 nm to about 10,000 nm, about 150 nm to about 200 nm, about 150 nm to about 250 nm, about 150 nm to about 500 nm, about 150 nm to about 750 nm, about 150 nm to about 1,000 nm, about 150 nm to about 2,500 nm, about 150 nm to about 5,000 nm, about 150 nm to about 10,000 nm, about 200 nm to about 250 nm, about 200 nm to about 500 nm, about 200 nm to about 750 nm, about 200 nm to about 1,000 nm, about 200 nm to about 2,500 nm, about 200 nm to about 5,000 nm, about 200 nm to about 10,000 nm, about 250 nm to about 500 nm, about 250 nm to about 750 nm, about 250 nm to about 1,000 nm, about 250 nm to about 2,500 nm, about 250 nm to about 5,000 nm, about 250 nm to about 10,000 nm, about 500 nm to about 750 nm, about 500 nm to about 1,000 nm, about 500 nm to about 1,000 nm, about 500 nm to about 2,500 nm, about 500 nm to about 5,000 nm, about 500 nm to about 10,000, about 750 nm to about 1,000 nm, about 750 nm to about 2,500 nm, about 750 nm to about 5,000 nm, about 750 nm to about 10,000, about 1,000 nm to about 2,500 nm, about 1,000 nm to about 5,000 nm, about 1,000 nm to about 10,000, about 2,500 nm to about 5,000 nm, about 2,500 nm to about 10,000 nm, or about 5,000 to about 10,000 nm.

[0041] In some embodiments, the preformed membrane and/or metal-polymer coordination membrane has a thickness of about 1 nm, about 2 nm, about 5 nm, about 10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, about 50 nm, about 55 nm, about 60 nm, about 65 nm, about 70 nm, about 75 nm, about 80 nm, about 85 nm, about 90 nm, about 95 nm, about 100 nm, about 110 nm, about 120 nm, about 130 nm, about 140 nm, about 150 nm, about 160 nm, about 170 nm, about 180 nm, about 190 nm, about 200 nm, about 210 nm, about 220 nm, about 230 nm, about 240 nm, about 250 nm, about 260 nm, about 270 nm, about 280 nm, about 290 nm, about 300 nm, about 310 nm, about 320 nm, about 330 nm, about 340 nm, about 350 nm, about 360 nm, about 370 nm, about 380 nm, about 390 nm, about 400 nm, about 410 nm, about 420 nm, about 430 nm, about 440 nm, about 450 nm, about 460 nm, about 470 nm, about 480 nm, about 490 nm, about 500 nm, about 510 nm, about 520 nm, about 530 nm, about 540 nm, about 550 nm, about 560 nm, about 570 nm, about 580 nm, about 590 nm, about 600 nm, about 610 nm, about 620 nm, about 630 nm, about 640 nm, about 650 nm, about 660 nm, about 670 nm, about 680 nm, about 690 nm, about 700 nm, about 710 nm, about 720 nm, about 730 nm, about 740 nm, about 750 nm, about 760 nm, about 770 nm, about 780 nm, about 790 nm, about 800 nm, about 810 nm, about 820 nm, about 830 nm, about 840 nm, about 850 nm, about 860 nm, about 870 nm, about 880 nm, about 890 nm, about 900 nm, about 910 nm, about 920 nm, about 930 nm, about 940 nm, about 950 nm, about 960 nm, about 970 nm, about 980 nm, about 990 nm, about 1000 nm, about 1150 nm, about 1300 nm, about 1,450 nm, about 1,600 nm, about 2,000 nm, about 2,500 nm, about 3,000 nm, about 3,500 nm, about 4,000 nm, about 4,500 nm, about 5,000 nm, about 5,500 nm, about 6,000 nm, about 6,500 nm, about 7,000 nm, about 7,500 nm, about 8,000 nm, about 8,500 nm, about 9,000 nm, about 9,500 nm, or about 10,000 nm.

C. METHODS OF USING METAL-POLYMER COORDINATION MEMBRANES [0042] The present disclosure includes methods of using a metal-polymer coordination membrane for the recovery and recycling of homogenous catalysts from organic solvents; solvent and oil exchange, recovery, and purification; solute (including pharma API) purification and enrichment; impurity removal; membrane-assisted crystallization and evaporation; and more. The metal-polymer coordination membranes based on heterocyclic containing polymer can be used for organic solvent nanofiltration (also called as solvent- resistant nanofiltration, and organophilic nanofiltration), ultrafiltration and microfiltration under harsh conditions, water and wastewater treatment. These materials can also be used for liquid separation, pharmaceutical, fuel cell applications, membrane catalysis, and composite materials.

[0043] In one or more embodiments of the present disclosure, the metal-polymer coordination membrane can be used for separating one or more chemical species. In FIG. 3, method 200 illustrates a flow chart for separation and/or recovery of one or more chemical species present in a liquid feed stream (e.g., a mixture such as an organic feed stream comprising solvents, dyes, catalyst, biofuels and/or active pharmaceutical agents). The process includes contacting a metal-polymer coordination membrane 204 with a liquid feed stream 202 comprising a first solute and a first solvent to separate 206 the first solute or the first solvent from liquid feed stream. The metal-polymer coordination membrane 204 can be a membrane made by method 100. Contacting can be ultrafiltration, nanofiltration, or microfiltration. Contacting can be performed under an operating pressure higher than 10 bar. For example, the operating pressure can be higher than 10 bar up to about 100 bar. Contacting can be performed at any suitable temperature (e.g., heated or cooled conditions). In some cases, the operating temperature is within the range of cooled conditions up to 100 °C.

[0044] The liquid feed stream 202 can be an aqueous liquid, an organic liquid, or a combination thereof. The liquid feed stream 202 can be wastewater. The first solute can be selected from the group consisting of sugars, salts, amino acids, flavors, genotoxins, colorants, dyes, pigments, catalysts, peptides, antibiotics, proteins, enzymes, and active pharmaceutical ingredients. Separating 206 can include dead end filtration or cross-flow filtration. Separating 206 can includes concentrating the first solute, recovering the first solvent or a combination thereof. In some cases, liquid feed stream 202 includes at least two solvents and the method includes solvent exchange. Additionally or alternatively, liquid feed stream 202 includes at least two solutes, and the method further includes purifying the first solute of the at least two solutes. Liquid feed stream 202 can include a first solvent is selected from the group consisting of alcohols, methanol, ethanol, isopropanol, butanol, acetone, alkanes, pentane, n-hexane, n- heptane, cyclohexane, alkyl acetates, butyl acetate, ethyl acetate, ethers, methyl ethyl ketone, diethyl ether dichloroethane, chloroform, trichloroethane, methyl isobutyl ketone, formaldehyde, ethylene glycol, propylene oxide, methylene chloride, nitrobenzene, tetrahydrofuran, toluene, diethyl ether, acetonitrile, carbon tetrachloride, xylene, dioxane, dimethyl sulfoxide, dimethylformamide, N-methyl pyrrolidone, and dimethylacetamide. Method 200 can include a subsequent step (not shown) including contacting at least one additional membrane with a filtered feed stream comprising the separated first solute or the separated first solvent.

[0045] The present disclosure includes methods of recycling the metal-polymer coordination membrane. The metal-coordination crosslinked heterocyclic polymer chains can exhibit a recyclable behavior. The crosslinked membrane can be recycled by reversibly breaking the non-covalent bonds with an acidic solution rendering the membrane susceptible to dissolution. Metals and polymers can be recovered. The recycled membrane solution can be directly utilized to cast a new pre-formed membrane, which can be cross-linked at least one more time. In some cases, this process is repeatable for at least two times. Thus, the cross- linking process described herein provides a promising strategy for enhancing membrane properties, and also reducing the impact of membrane polymers on the environment, by reducing solid waste.

[0046] Method 200 optionally further includes recycling 210 the metal-polymer coordination membrane by reversing the crosslinks and recovering the polymer coordinating agent, the metal of the polymer coordinating agent, the uncrosslinked membrane, a solution of dissolved membrane. Recycling can include step 208 to treat the membrane with an aqueous acid solution. Recycling can include dissolving the acid-treated membrane in DMSO, NMP, DMF, DMAc, or a mixture thereof. In some cases, the solution of dissolved membrane can be recast to form a pre-formed membrane.

EXAMPLES

[0047] These Examples demonstrate facile crosslinking of N-heterocyclic containing polymer (polybenzimidazole (PBI)) membranes through coordination with metal salts (copper (I) iodide) for OSN:

Metal coordination resulted in solvent-resistant and stable PBI membranes or materials.

While previous reports described crosslinidng of commercial polybenzimidazole (PBI) to enhance the membrane stability and performance, none of these describe the use of metal salts to crosslink the PBI. Previous reports describing the use of metal salts in membrane fabrication use solvents that can dissolve the polymer and, therefore, only deposit the metal film on the outer surface of the membrane resulting in solubility of the membrane in particular solvents.

[0048] Three membranes were prepared using polybenzimidazole (PBI) as polymer and copper(I) iodide (Cul) as polymer coordinating agent, with different concentrations of Cul. The obtained membranes exhibited high stability in organic solvents. Prior to metal treatment, a PBI membrane was found to be soluble in /V, /V- D i m e th y I ac c ta m i dc (DM Ac), N,N- Dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Following Cul treatment, the metal-coordinated/crosslinked PBI membrane exhibited no solubility in either of N,N- Dimethylacetamide (DMAc), /V, /V- D i m c th y I fo r m a m i dc (DMF), or dimethyl sulfoxide (DMSO). The metal-coordinated/crosslinked PBI membrane was also insoluble in n-heptane, toluene, ethanol, methanol, tetrahydrofuran, acetone, and acetonitrile.

EXAMPLE 1

Ml Membrane - PBI and 10 ppm Cul

[0049] The Ml membrane was prepared by coordinating PBI membrane (made from 20 wt% dope solution) with 10 ppm copper(I) iodide, in acetonitrile at 25 °C for 24 hours. The membrane was then washed with acetonitrile and water a few times before being stored in distilled water with 1% (v/v) of acetonitrile. The membrane demonstrated excellent solvent- resistant property and was insoluble in n-heptane, toluene, ethanol, methanol, tetrahydrofuran, acetone, and acetonitrile. The Ml membrane had a roughness of 1.61 nm, a contact angle of 78°, and a hardness of 0.07 GPa. The molecular sieving effect of the membranes was tested in a cross-flow nanofiltration system. According to polystyrene standard rejection in acetone solvent at 30 bar pressure, the Ml membrane exhibited a molecular weight cut-off (MWCO) of 689 g mol ¹ . The Ml membrane had a flux of acetone of 50 L m ² h ¹ at 10 bar pressure, 141 L m ² h ¹ at 20 bar pressure, 211 L m ² h ¹ at 30 bar pressure, and 294 L m ² h ¹ at 40 bar pressure.

COMPARATIVE EXAMPLE

[0050] As illustrated in FIGS. 4A-4B, the method of 10,696,025B produces a layered membrane that is not fully solvent-resistant, unlike the membranes of the present disclosure. Specifically, the prior art method is configured to provide a membrane having metal-rich dense layer and a porous support layer formed of polymer chains substantially, if not completely, lacking the presence of metal ions. As a result, the porous support layer is unstable in DMSO, a polar aprotic solvent employed in OSN, leaving only the metal-rich dense layer after dissolution (FIG. 4A). The membrane of the present method is characterized by homogeneous crosslinking and/or metal-polymer coordination, which is completely stable in DMSO (FIG. 4B), and other polar aprotic solvents.

EXAMPLE 2

M2 Membrane - PBI and 100 ppm Cul

[0051] The M2 membrane was prepared by coordinating PBI membrane (made from 20 wt% dope solution) with 100 ppm copper(I) iodide, in acetonitrile at 25 °C for 24 hours. The membrane was then washed with acetonitrile and water a few times before being stored in distilled water with 1% (v/v) of acetonitrile. The membrane demonstrated excellent solvent- resistant property and was insoluble in n-heptane, toluene, ethanol, methanol, tetrahydrofuran, acetone, and acetonitrile. The M2 membrane had a roughness of 2.3 nm, a contact angle of 12°, and a hardness of 0.11 GPa. The molecular sieving effect of the membranes was tested in a cross-flow nanofiltration system. According to polystyrene standard rejection in acetone solvent at 30 bar pressure, the M2 membrane exhibited a molecular weight cut-off (MWCO) of 549 g mol ¹ . The M2 membrane had a flux of acetone of 39 L m ² h ¹ at 10 bar pressure, 103 L m ² h ¹ at 20 bar pressure, 158 L m ² h ¹ at 30 bar pressure, and 202 L m ² h ¹ at 40 bar pressure. EXAMPLE 3

M3 Membrane - PBI and 1000 ppm Cul

[0052] The M3 membrane was prepared by coordinating PBI membrane (made from 20 wt% dope solution) with 1000 ppm copper(I) iodide, in acetonitrile at 25 °C for 24 hours. The membrane was then washed with acetonitrile and water a few times before being stored in distilled water with 1 % (v/v) of acetonitrile. M3 Membrane morphology is shown in FIG. 6. [0053] The membrane demonstrated excellent solvent-resistant property and was insoluble in n-heptane, toluene, ethanol, methanol, tetrahydrofuran, acetone, acetonitrile, N,N- Dimethylacetamide (DMAc), /V, /V-Di mcthylf rmam idc (DMF), and dimethyl sulfoxide (DMSO). The M3 membrane had a roughness of 2.6 nm, a contact angle of 62°, and a hardness of 0.16 GPa.

[0054] The molecular sieving effect of the membranes was tested in a cross-flow nanofiltration system. According to polystyrene standard rejection in acetone solvent at 30 bar pressure, the M3 membrane exhibited a molecular weight cut-off (MWCO) of 357 g mol ¹ . The M3 membrane acetone flux increased as pressure increased from 10 to 40 bar. Specifically, M3 exhibited acetone flux of 19 L m ^~2 h ^_1 at 10 bar, acetone flux of 47 L m ^~2 h ^_1 at 20 bar, acetone flux of 72 L m ^~2 h ^_1 at 30 bar, and acetone flux of 92 L m ^~2 h ^_1 at 40 bar. These results are summarized in TABLE 1.

Table 1: Relationship between Acetone Flux and Pressure

[0055] As shown in FIG. 5, the metal-polymer coordination is evident from the comparison of the X-ray photoelectron spectroscopy (XPS) spectra of M0 (uncrosslinked PBI membrane) and M3, where the intensity of the peak corresponding to =N- in the PBI decreases after coordinating with Cul.

EXAMPLE 4 Separation Performance of M3 Membrane

[0056] The separation performance of the M3 membrane was further tested for the separation of five active pharmaceutical ingredients (APIs) and three dye molecules. The APIs included estradiol, losartan, valsartan, oleuropein, and roxithromycin. The three dye molecules included methyl orange, acid fuchsin, and rose bengal. The M3 membrane exhibited a rejection of 91% towards Estradiol, a rejection of 91% towards methyl orange, a rejection of 94% towards losartan, a rejection of 94% towards valsartan, a rejection of 97% towards oleuropein, a rejection of 99% towards acid fuchsin, a rejection of 100% towards roxithromycin, and a rejection of 100% towards rose Bengal.

[0057] The M3 membrane exhibited a stable flux over a long-term stability in 13 days continuous filtration test at 30 bar. The M3 membrane exhibited acetone flux of 72 L m ^~2 h ^_1 at day 7 of the continuous filtration test, acetone flux of 72.8 L m ^~2 h ^_1 at day 7 of the continuous filtration test, acetone flux of 72.3 L m ^~2 h ^_1 at day 8 of the continuous filtration test, acetone flux of 72.3 L m ^~2 h ^_1 at day 9 of the continuous filtration test, acetone flux of 71.5 L m ^~2 h ^_1 at day 10 of the continuous filtration test, acetone flux of 71 L m ^~2 h ^_1 at day 11 of the continuous filtration test, acetone flux of 71 L m ^~2 h ^_1 at day 12 of the continuous filtration test, acetone flux of 71 L m ^~2 h ^_1 at day 13 of the continuous filtration test. These results are summarized in TABLE 2.

Table 2: Acetone flux over 13 days continuous filtration

[0058] The M3 membrane exhibited stable rejections of Rose Bengal, acid fuchsin, and methyl orange over a long-term stability in 13 days continuous filtration test at 30 bar. The M3 membrane exhibited a rejection of 100% towards Rose Bengal at day 7 of the continuous filtration test, a rejection of 100% towards Rose Bengal at day 8 of the continuous filtration test, a rejection of 100% towards Rose Bengal at day 9 of the continuous filtration test, a rejection of 100% towards Rose Bengal at day 10 of the continuous filtration test, a rejection of 100% towards Rose Bengal at day 11 of the continuous filtration test, a rejection of 100% towards Rose Bengal at day 12 of the continuous filtration test, and a rejection of 100% towards Rose Bengal at day 13 of the continuous filtration test. The M3 membrane exhibited a rejection of 99% towards Acid fuchsin at day 7 of the continuous filtration test, a rejection of 99% towards Acid fuchsin at day 8 of the continuous filtration test, a rejection of 99% towards Acid fuchsin at day 9 of the continuous filtration test, a rejection of 99% towards Acid fuchsin at day 10 of the continuous filtration test, a rejection of 99% towards Acid fuchsin at day 11 of the continuous filtration test, a rejection of 99% towards Acid fuchsin at day 12 of the continuous filtration test, and a rejection of 99% towards Acid fuchsin at day 13 of the continuous filtration test. The M3 membrane exhibited a rejection of 91% towards Methyl orange at day 7 of the continuous filtration test, a rejection of 91% towards Methyl orange at day 8 of the continuous filtration test, a rejection of 91% towards Methyl orange at day 9 of the continuous filtration test, a rejection of 91% towards Methyl orange at day 10 of the continuous filtration test, a rejection of 91% towards Methyl orange at day 11 of the continuous filtration test, a rejection of 91% towards Methyl orange at day 12 of the continuous filtration test, and a rejection of 91% towards Methyl orange at day 13 of the continuous filtration test. These results are summarized in TABLE 3.

Table 3: Dye rejection over 13 days continuous filtration

[0059] The foregoing description of various preferred embodiments of the disclosure have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise embodiments. The example embodiments, as described above, were chosen and described in order to best explain the principles of the disclosure and its practical application to thereby enable others skilled in the art to best utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto.