A hydrogel-based heterogeneous catalyst

Abstract

Hydrogel-based heterogenous catalysts, e.g., for oxidation of organic molecules, and related articles, systems, and methods, are generally described herein.

Description

[0001] A HYDROGEL-BASED HETEROGENEOUS CATALYST

[0002] RELATED APPLICATIONS

[0003] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 600,591, filed November 17, 2023, and entitled “A HYDROGEL-BASED HETEROGENEOUS CATALYST,” which is incorporated herein by reference in its entirety for all purposes.

[0004] TECHNICAL FIELD

[0005] Hydrogel-based heterogenous catalysts, e.g., for oxidation of organic molecules, and related articles, systems, and methods, are generally described herein.

[0006] BACKGROUND

[0007] Persistent organic pollutants (POPs), such as xenoestrogens and per- or polyfluoroalkyl substances (PFAS), pose a global challenge requiring immediate action. Fenton oxidation, catalyzed by iron ions, has been extensively studied for its potential to degrade recalcitrant organic contaminants using low-cost reagents, but has limitations, including the need for acid addition, continuous loss of catalyst material, and disposal issues. Attempts to make long-lasting heterogenous Fenton catalysts for practical applications have so far been unable to simultaneously eliminate the need for acid addition, maintain fast kinetics, and effectively retain iron using a minimal number of unit operations.

[0008] SUMMARY

[0009] Described herein are hydrogel-based heterogeneous catalysts, e.g., for oxidation of organic molecules, and related articles, systems, and methods. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0010] According to some embodiments, a hydrogel is described. In some embodiments, the hydrogel comprises: a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged; and one or metal ions, at least some of which are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel. According to some embodiments, the hydrogel is resistant to degradation: (i) at a pH greater than or equal to 4; and / or (ii) in the presence of hydrogen peroxide, ultraviolet (UV) light, the one or more metals ions, and / or one or more metal ions that are not incorporated within the volume of the hydrogel.

[0011] According to certain embodiments, a method of oxidizing one or more organic molecules is described. In some embodiments, the method comprises exposing a hydrogel to the one or more organic molecules, wherein the hydrogel is resistant to degradation in the presence of hydrogen peroxide. In certain embodiments, the hydrogel comprises: a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged; and one or more metal ions, at least some of which are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel. In some embodiments, the method comprises oxidizing the one or more organic molecules.

[0012] According to some embodiments, an article is described. In some embodiments, the article comprises a hydrogel, wherein the hydrogel comprises: a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged; and one or metal ions, at least some of which are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel. According to some embodiments, the hydrogel is resistant to degradation: (i) at a pH greater than or equal to 4; and / or (ii) in the presence of hydrogen peroxide, UV light, the one or more metals ions, and / or one or more metal ions that are not incorporated within the volume of the hydrogel.

[0013] Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0015] FIG. 1A shows a cross-sectional schematic diagram of a hydrogel in the form of a particle, in accordance with certain embodiments.

[0016] FIG. IB shows a cross-sectional schematic diagram of a hydrogel in the form of a plurality of particles, in accordance with certain embodiments.

[0017] FIG. 2A shows a cross-sectional schematic diagram representing a method comprising exposing a hydrogel to a solution comprising one or more organic molecules, in accordance with certain embodiments.

[0018] FIG. 2B shows a cross-sectional schematic diagram representing a method comprising absorbing one or more organic molecules from a solution into a hydrogel, in accordance with certain embodiments.

[0019] FIG. 3A shows a schematic diagram of a bed reactor, in accordance with certain embodiments.

[0020] FIG. 3B shows a schematic diagram of a tank reactor, in accordance with certain embodiments.

[0021] FIG. 4A shows: (i) a schematic diagram showing a monomer solution being pinched off using mineral oil to prepare droplets in a microfluidic device, wherein the droplets are photo-polymerized into microparticles using UV light, soaked in iron to functionalize them, and subsequently used to catalyze Fenton oxidation in a stirred tank; and (ii) hydrogel microparticles constructed using a zwitterionic monomer (PSB) and crosslinker (BIS), in accordance with certain embodiments.

[0022] FIG. 4B shows microparticles that are optically transparent and 800 ± 100 pm in size, in accordance with certain embodiments.

[0023] FIG. 4C shows clear microparticles obtained after polymerization (left), which become yellow after iron functionalization (center), and dark orange after being used to catalyze Fenton oxidation in the absence of UV light (right), in accordance with certain embodiments.

[0024] FIG. 4D shows a scanning electron microscopy (SEM) micrograph (left) and corresponding energy dispersive spectroscopy (EDS) map of iron (right), showing uniform distribution, in accordance with certain embodiments.

[0025] FIG. 4E shows an X-ray diffraction (XRD) spectrum (top) obtained from iron- functionalized microparticles, and the pair correlation function g(r) obtained therefrom (bottom), in accordance with certain embodiments.

[0026] FIG. 5A shows pictures before and after the rapid degradation of methylene blue dye in a stirred vial containing hydrogel microparticles at neutral pH, in accordance with certain embodiments.

[0027] FIG. 5B shows the kinetics of the process in shown in FIG. 5A compared to the same process with an equal concentration of free iron ions in solution, measured as the change in the hue of the solution over time, in accordance with certain embodiments.

[0028] FIG. 5C shows the total organic carbon content in water obtained after a Fenton reaction in the absence of POPs catalyzed by iron-functionalized hydrogels, in accordance with certain embodiments.

[0029] FIG. 5D shows the concentration of iron measured in the supernatant after the reactions described in FIG. 5C, in accordance with certain embodiments.

[0030] FIG. 6A shows structures and elimination of three POPs at equilibrium, in accordance with certain embodiments.

[0031] FIG. 6B shows kinetics and equilibrium elimination of EDOL by UV light, by the classical Fenton reaction using hydrogel microparticles, and by the UV-Fenton reaction using hydrogel microparticles, in accordance with certain embodiments.

[0032] FIG. 6C shows kinetics and equilibrium elimination of EDOL with varying initial concentration, using the same amount of hydrogen peroxide and iron-functionalized hydrogel, in accordance with certain embodiments.

[0033] FIG. 6D shows kinetics and equilibrium elimination of EDOL with varying initial hydrogen peroxide concentration, in accordance with certain embodiments.

[0034] FIG. 6E shows kinetics and equilibrium elimination of DCP with varying initial hydrogen peroxide concentration, in accordance with certain embodiments. FIG. 6F shows kinetics and equilibrium elimination of PFOA with varying initial hydrogen peroxide concentration, in accordance with certain embodiments.

[0035] FIG. 7A shows the simultaneous consumption and regeneration of Fe(II) ions within a hydrogel when operated in a UV-Fenton process, in accordance with certain embodiments.

[0036] FIG. 7B shows the kinetics of EDOL degradation over multiple cycles of use, in accordance with certain embodiments.

[0037] FIG. 7C shows equilibrium elimination of EDOL over multiple cycles of use, in accordance with certain embodiments.

[0038] FIG. 7D shows equilibrium elimination of DCP over multiple cycles of use, in accordance with certain embodiments.

[0039] FIG. 7E shows equilibrium elimination of PFOA over multiple cycles of use, in accordance with certain embodiments.

[0040] FIG. 8 shows a polymerization schematic in which a free-radical chain-growth polymerization reaction converts dissolved PSB and BIS molecules into a cross-linked hydrogel, in accordance with certain embodiments.

[0041] FIGS. 9A-9B show measurement of Young’s modulus from two different hydrogel samples, in accordance with certain embodiments.

[0042] FIG. 10 shows thermogravimetric analysis of PSB hydrogels containing iron compared to those without iron, wherein the difference yields the iron content, in accordance with certain embodiments.

[0043] FIGS. 11A-1 IB show control experiments for methylene blue degradation, in accordance with certain embodiments.

[0044] FIGS. 12A-12C show POP degradation in a UV-Fenton batch process, compared to degradation solely due to UV light, in accordance with certain embodiments.

[0045] FIG. 13 shows defluorination of PFOA, in accordance with certain embodiments.

[0046] FIG. 14 shows elemental maps of hydrogel constituents, showing homogeneous structure, in accordance with certain embodiments.

[0047] FIG. 15 shows conversion in GMA-IDA synthesis, measured using 1H-NMR spectroscopy, in accordance with certain embodiments. DETAILED DESCRIPTION

[0048] Described herein are hydrogel-based heterogeneous catalysts, e.g., for oxidation of organic molecules, and related articles, systems, and methods. In certain embodiments, a composition comprising a hydrogel is described. The term “hydrogel” is used herein in a manner consistent with its ordinary meaning in the art and generally refers to a material comprising a mixture of: (i) at least one porous and permeable solid; and (ii) at least 10% by weight or volume of an interstitial fluid, i.e., water or a waterbased fluid mixture. The hydrogel may comprise: (i) a charged (e.g., positively charged, negatively charged, or positively and negatively charged, i.e., zwitterionic) hydrophilic crosslinked polymer; and (ii) one or more metal ions (e.g., transition metal ions) coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel. In certain embodiments, the hydrogel is configured to absorb water and / or an aqueous solution (e.g., comprising one or more organic molecules), i.e., the hydrogel is configured to swell.

[0049] The hydrogel is advantageously robust such that it is resistant to degradation under a variety of conditions. In some embodiments, for example, the hydrogel is resistant to degradation at a pH greater than or equal to 3 in the presence of hydrogen peroxide, in the presence of UV light, in the presence of the one or more metal atoms incorporated within the volume of the hydrogel, and / or in the presence of one or more metal atoms not incorporated within the volume of the hydrogel (e.g., one or more metal ions that are external to the volume of the hydrogel). For example, the hydrogel may be configured such that it loses a substantially low weight percentage when exposed to any of the previously described conditions for a period of at least 24 hours (e.g., 36 hours, 48 hours, 60 hours, or more). In some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% when exposed to any of the previously described conditions for a period of 24 hours.

[0050] The hydrogel may be used as a heterogeneous catalyst, e.g., to catalyze the oxidation of one or more organic molecules. In some embodiments, for example, the hydrogel is a heterogeneous Fenton oxidation catalyst comprising iron ions (e.g., iron(II) ions) incorporated within a volume of the hydrogel. The Fenton reaction, shown below in Equation 1, is conventionally used to oxidize organic molecules by dissolving iron(II) ions and hydrogen peroxide in aqueous solutions comprising the target organic molecules. y +

[0051] Fe2++ H202-> Fe3++ OH" + OH' (1)

[0052] Such conventional techniques require separation of the iron ions in order to obtain clean water, and due to the presence of other contaminants, the formation of sludge, and the considerations of cost, the separated iron cannot be used. Furthermore, conventional Fenton oxidation reactions optimally occur at a pH of 3, which necessitates the addition of acid, which significantly adds to process complexity and cost. For example, base addition is often used to neutralize the added acid. In certain embodiments, the hydrogels described herein advantageously incorporate iron ions (e.g., iron(II) ions) within a volume of the hydrogel such that the iron ions can be retained and reused for the oxidation of organic molecules in water without undesirable and costly separation techniques or the addition of acid and / or base.

[0053] The hydrogel is highly porous and facilitates the absorption of one or more organic molecules within a volume of the hydrogel such that the one or more organic molecules are oxidized by the one or more metal ions incorporated within a volume of the hydrogel. A wide variety of organic molecules may be oxidized using the hydrogel, including, for example, persistent organic pollutants (POPs) (e.g., xenoestrogens, PFAS, pesticides), drugs (e.g., antibiotics), dyes, and / or surfactants).

[0054] In some embodiments, articles and / or systems comprising the hydrogel are described herein. The article and / or system may be a bed reactor (e.g., a packed bed reactor, a fluidized bed reactor), in accordance with certain embodiments. For example, the article and / or system may comprise a packed or fluidized bed of the hydrogel that is configured to be exposed to a treatable aqueous solution comprising one or more target organic molecules. In some embodiments, the article and / or system is a tank reactor (e.g., a stirred tank reactor) comprising the hydrogel at least partially dissolved and / or suspended in a treatable aqueous solution comprising one or more target organic molecules. In certain embodiments, the hydrogel in the reactor (e.g., bed reactor, tank reactor) absorbs the aqueous solution and / or the one or more target organic molecules within a volume of the hydrogel, i.e., the hydrogel swells. Upon absorption of the target organic molecule, the one or more metal ions incorporated within a volume of the hydrogel are configured to oxidize the one or more organic molecules.

[0055] According to certain embodiments, methods of oxidizing one or more organic molecules are described. In some embodiments, a method comprises exposing a hydrogel to one or more organic molecules, absorbing the one or more organic molecules into the hydrogel, and oxidizing the one or more organic molecules. Advantageously, the hydrogel may be continuously used for such oxidation processes over certain periods of time (e.g., at least 24 hours) without experiencing degradation.

[0056] According to some embodiments, the hydrogel comprises a crosslinked polymer. In some embodiments, for example, the crosslinked polymer comprises a physical or chemical bond that connects one or more functional groups of a first portion of the crosslinked polymer (e.g., a first monomer, a first polymer chain, etc.) to one or more functional groups of a second portion of the crosslinked polymer (e.g., a second monomer, a second polymer chain, etc.) via covalent bonding and / or supramolecular interactions such as ionic bonding and / or hydrogen bonding.

[0057] In some embodiments, the crosslinked polymer is hydrophilic. For example, in certain embodiments, the hydrogel can absorb and / or otherwise interact with water (e.g., via hydrogen bonding interactions).

[0058] In some embodiments, at least a portion of the hydrophilic crosslinked polymer is charged. In certain embodiments, for example, at least a portion of the hydrophilic crosslinked polymer is positively charged. In some embodiments, at least a portion of the hydrophilic crosslinked polymer is negatively charged. According to some embodiments, at least a first portion (e.g., a first moiety) of the hydrophilic crosslinked polymer is positively charged and at least a second portion (e.g., a second moiety) of the hydrophilic crosslinked polymer is negatively charged, wherein the first portion of the hydrophilic crosslinked polymer and the second portion of the hydrophilic crosslinked polymer are different. In certain embodiments, for example, at least a portion of the hydrophilic crosslinked polymer is zwitterionic. In some embodiments, at least a portion of the hydrophilic crosslinked polymer is polar. For example, in certain embodiments, at least a portion of the hydrophilic crosslinked polymer has a separation of electric charge leading to the portion of the hydrophilic crosslinked polymer having an electric dipole moment with a positively charged end and a negatively charged end. The hydrophilic crosslinked polymer may be a crosslinked reaction product between one or more monomer precursors. Any of a variety of suitable monomer precursors may be used to form the hydrophilic crosslinked polymer. In certain embodiments, for example, the hydrophilic crosslinked polymer comprises a crosslinked reaction product between [2-(methacryloyloxy)ethyl]dimethyl-(3- sulfopropyl)ammonium hydroxide (PSB) and N,N’-methylenebis(acrylamide) (BIS). In some such embodiments, PSB comprises charged groups that render the hydrogel hydrophilic and increase its ability to absorb water, and BIS crosslinks the PSB polymer chains and stabilizes the hydrogel structure. In certain embodiments, the hydrophilic crosslinked polymer comprises 3-sulfopropyl methacrylate and / or a crosslinked reaction product between 3-sulfopropyl methacrylate and one or more monomer precursors. Other monomer precursors are also possible.

[0059] The hydrogel may comprise the hydrophilic crosslinked polymer in any of a variety of suitable weight percentages versus a total weight of the hydrogel. In some embodiments, for example, the hydrogel comprises the hydrophilic crosslinked polymer in an amount greater than or equal to 10 weight percent (wt%), greater than or equal to 20 wt%, greater than or equal to 30 wt%, greater than or equal to 40 wt%, greater than or equal to 50 wt%, greater than or equal to 60 wt%, greater than or equal to 70 wt%, or greater than or equal to 80 wt% versus a total weight of the hydrogel. In certain embodiments, the hydrogel comprises the hydrophilic crosslinked polymer in an amount less than or equal to 90 wt%, less than or equal to 80 wt%, less than or equal to 70 wt%, less than or equal to 60 wt%, less than or equal to 50 wt%, less than or equal to 40 wt%, less than or equal to 30 wt.%, or less than or equal to 20 wt% versus a total weight of the hydrogel. Combinations of the above recited ranges are possible (e.g., the hydrogel comprises the hydrophilic crosslinked polymer in an amount greater than or equal to 10 wt% and less than or equal to 90 wt% versus a total weight of the hydrogel, the hydrogel comprises the hydrophilic crosslinked polymer in an amount greater than or equal to 40 wt% and less than or equal to 60 wt% versus a total weight of the hydrogel). Other ranges are also possible. The amount of the hydrophilic crosslinked polymer in the hydrogel may be determined by thermogravimetric analysis (TGA).

[0060] In certain embodiments, the hydrogel comprises one or metal ions. In some embodiments, at least some of the metal ions are coordinated to the hydrophilic crosslinked polymer. According to certain embodiments, each of the metal ions are coordinated to the hydrophilic crosslinked polymer. For example, in some embodiments, each of the one or more metal ions are individually coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel. The coordination between the metal ions and the hydrophilic crosslinked polymer may be any of a variety of suitable interactions (e.g., bonding interactions). In some embodiments, for example, the coordination between the metal ions and the hydrophilic crosslinked polymer is a covalent bonding interaction or an ionic bonding interaction. In certain embodiments, the coordination between the metal ions and the hydrophilic crosslinked polymer is a non-covalent interaction (e.g., an electrostatic interaction, a van der Waals interaction, etc.). According to some embodiments, at least a portion of the positively charged metal ions are coordinated to a portion of the hydrophilic crosslinked polymer that is negatively charged (e.g., one or more negatively charged oxygen atoms, such as one or more negatively charged oxygen atoms in PSB).

[0061] In some embodiments, the one or more metal ions comprise a cluster of metal ions. In certain embodiments for example, at least a portion of the metal ions may interact with each other (e.g., via one or more bonding interactions). The cluster of metal ions may comprise any of a variety of suitable number of metal ions. In certain embodiments, for example, the cluster of metal ions comprises less than or equal to 100,000 metal ions, less than or equal to 50,000 metal ions, less than or equal to 20,000 metal ions, less than or equal to 10,000 metal ions, less than or equal to 5,000 metal ions, less than or equal to 2,000 metal ions, less than or equal to 1,000 metal ions, less than or equal to 500 metal ions, less than or equal to 200 metal ions, less than or equal to 100 metal ions, or less than or equal to 50 metal ions. In some embodiments, the cluster of metal ions comprises greater than or equal to 3 metal ions, greater than or equal to 50 metal ions, greater than or equal to 100 metal ions, greater than or equal to 200 metal ions, greater than or equal to 500 metal ions, greater than or equal to 1,000 metal ions, greater than or equal to 2,000 metal ions, greater than or equal to 5,000 metal ions, greater than or equal to 10,000 metal ions, greater than or equal to 20,000 metal ions, or greater than or equal to 50,000 metal ions. Combinations of the above recited ranges are possible (e.g., the cluster of metal ions comprises less than or equal to 100,000 metal ions and greater than or equal to 3 metal ions, the cluster of metal ions comprises less than or equal to 2,000 metal ions and greater than or equal to 1,000 metal ions). Other ranges are also possible. The number of metal ions in the cluster of metal ions may be determined by X-ray diffraction or EDS.

[0062] The one or more metal ions may be or comprise any of a variety of suitable metal ions. In some embodiments, for example, the one or more metal ions are or comprise a transition metal ion. Suitable metal ions (e.g., transition metal ions) include, but are not limited to, iron, copper, cobalt, manganese, cerium, silver, chromium, ruthenium, tungsten, molybdenum, vanadium, titanium, nickel, and / or combinations thereof. Other metal ions are also possible.

[0063] The hydrogel may comprise the one or more metal ions in any of a variety of suitable weight percentages versus a total weight of the hydrogel. In some embodiments, for example, the hydrogel comprises the one or more metal ions in an amount greater than or equal to 0.01 wt%, greater than or equal to 0.02 wt%, greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel. In certain embodiments, the hydrogel comprises the one or more metal ions in an amount less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 2 wt%, less than or equal to 0.1 wt%, less than or equal to 0.05 wt.%, or less than or equal to 0.02 wt% versus a total weight of the hydrogel. Combinations of the above recited ranges are possible (e.g., the hydrogel comprises the one or more metal ions in an amount greater than or equal to 0.01 wt% and less than or equal to 5 wt% versus a total weight of the hydrogel, the hydrogel comprises the one or more metal ions in an amount greater than or equal to 0.02 wt% and less than or equal to 0.5 wt% versus a total weight of the hydrogel). Other ranges are also possible. The amount of metal ions in the hydrogel may be determined by thermogravimetric analysis.

[0064] According to certain embodiments, the hydrogel is resistant to degradation at any of a variety of suitable pH values. In some embodiments, for example, the hydrogel is resistant to degradation at a pH greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, or greater than or equal to 9. In certain embodiments, the hydrogel is resistant to degradation a pH less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, less than or equal to 5, or less than or equal to 4. Combinations of the above recited ranges are possible (e.g., the hydrogel is resistant to degradation at a pH greater than or equal to 3 and less than or equal to 10, the hydrogel is resistant to degradation a pH greater than or equal to 6 and less than or equal to 7). Other ranges are also possible.

[0065] The hydrogel may be resistant to degradation at a pH greater than or equal to 3 such that the hydrogel is configured to lose a substantially low weight percentage versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 for a certain period of time. For example, the hydrogel may be configured such that it loses any of a variety of suitable weight percentages versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 (e.g., a pH greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, or more) for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0066] In certain embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.2 wt%, or less than or equal to 0.1 wt% versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 for a period of at least 24 hours. In some embodiments, the hydrogel is configured such that it loses greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 for a period of at least 24 hours. Combinations of the above recited ranges are possible (e.g., the hydrogel is configured such that is loses less than or equal to 5 wt% and greater than or equal to 0.05 wt% when exposed to a pH greater than or equal to 3 for a period of at least 24 hours, the hydrogel is configured such that it loses less than or equal to 0.5 wt% and greater than or equal to 0.2 wt% when exposed to a pH greater than or equal to 3 for a period of at least 24 hours). Other ranges are also possible. The loss of weight percent of the hydrogel when exposed to a pH greater than or equal to 3 for a period of at least 24 hours may be determined by total organic carbon (TOC) analysis or by comparing the weight of the hydrogel prior to being exposed to a pH greater than or equal to 3 for a period of at least 24 hours to the weight of the hydrogel after being exposed to the pH greater than or equal to 3 for a period of at least 24 hours.

[0067] In some embodiments, the hydrogel is resistant to degradation in the presence of hydrogen peroxide. The hydrogel may be resistant to degradation in the presence of hydrogen peroxide such that the hydrogel is configured to lose a substantially low weight percentage versus a total weight of the hydrogel when exposed to hydrogen peroxide for a certain period of time. For example, the hydrogel may be configured such that it loses any of a variety of suitable weight percentages versus a total weight of the hydrogel when exposed to hydrogen peroxide for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0068] In certain embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.2 wt%, or less than or equal to 0.1 wt% versus a total weight of the hydrogel when exposed to hydrogen peroxide for a period of at least 24 hours. In some embodiments, the hydrogel is configured such that it loses greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel when exposed to hydrogen peroxide for a period of at least 24 hours. Combinations of the above recited ranges are possible (e.g., the hydrogel is configured such that is loses less than or equal to 5 wt% and greater than or equal to 0.05 wt% when exposed to hydrogen peroxide for a period of at least 24 hours, the hydrogel is configured such that it loses less than or equal to 0.5 wt% and greater than or equal to 0.2 wt% when exposed to hydrogen peroxide for a period of at least 24 hours). Other ranges are also possible. The loss of weight percent of the hydrogel in the presence of hydrogen peroxide for a period of at least 24 hours may be determined by TOC analysis or by comparing the weight of the hydrogel prior to being exposed to hydrogen peroxide for a period of at least 24 hours to the weight of the hydrogel after being exposed to hydrogen peroxide for a period of at least 24 hours.

[0069] In certain embodiments, the hydrogel is resistant to degradation in the presence of UV light. As used herein, UV light refers to electromagnetic radiation having a wavelength in a range of 100 nm to 400 nm. The hydrogel may be resistant to degradation in the presence of UV light such that the hydroigel is configured to lose a substantially low weight percentage versus a total weight of the hydrogel when exposed to UV light for a certain period of time. For example, the hydrogel may be configured such that it loses any of a variety of suitable weight percentages versus a total weight of the hydrogel when exposed to UV light for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0070] In certain embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.2 wt%, or less than or equal to 0.1 wt% versus a total weight of the hydrogel when exposed to UV light for a period of at least 24 hours. In some embodiments, the hydrogel is configured such that it loses greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel when exposed to UV light for a period of at least 24 hours. Combinations of the above recited ranges are possible (e.g., the hydrogel is configured such that is loses less than or equal to 5 wt% and greater than or equal to 0.05 wt% when exposed to UV light for a period of at least 24 hours, the hydrogel is configured such that it loses less than or equal to 0.5 wt% and greater than or equal to 0.2 wt% when exposed to UV light for a period of at least 24 hours). Other ranges are also possible. The loss of weight percent of the hydrogel in the presence of UV light for a period of at least 24 hours may be determined by TOC analysis or by comparing the weight of the hydrogel prior to being exposed to UV light for a period of at least 24 hours to the weight of the hydrogel after being exposed to UV light for a period of at least 24 hours.

[0071] In some embodiments, the hydrogel is resistant to degradation in the presence of one or more metals ions that are incorporated within a volume of the hydrogel. The hydrogel may be resistant to degradation in the presence of one or more metals ions that are incorporated within a volume of the hydrogel such that the hydrogel is configured to lose a substantially low weight percentage versus a total weight of the hydrogel when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a certain period of time. For example, the hydrogel may be configured such that it loses any of a variety of suitable weight percentages versus a total weight of the hydrogel when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0072] In certain embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.2 wt%, or less than or equal to 0.1 wt% versus a total weight of the hydrogel when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours. In some embodiments, the hydrogel is configured such that it loses greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours. Combinations of the above recited ranges are possible (e.g., the hydrogel is configured such that is loses less than or equal to 5 wt% and greater than or equal to 0.05 wt% when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours, the hydrogel is configured such that it loses less than or equal to 0.5 wt% and greater than or equal to 0.2 wt% when exposed to one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours). Other ranges are also possible. The loss of weight percent of the hydrogel in the presence of one or more metals ions that are incorporated within a volume of the hydrogel for a period of at least 24 hours may be determined by inductively coupled plasma mass spectroscopy (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) .

[0073] In some embodiments, the hydrogel is resistant to degradation in the presence of one or more metal ions that are not incorporated within a volume of the hydrogel (e.g., one or more metal ions that are external to the volume of the hydrogel). The hydrogel may be resistant to degradation in the presence of one or more metal ions that are not incorporated within a volume of the hydrogel such that the hydrogel is configured to lose a substantially low weight percentage versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a certain period of time. For example, the hydrogel may be configured such that it loses any of a variety of suitable weight percentages versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0074] In certain embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt%, less than or equal to 2 wt%, less than or equal to 1 wt%, less than or equal to 0.5 wt%, less than or equal to 0.2 wt%, or less than or equal to 0.1 wt% versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours. In some embodiments, the hydrogel is configured such that it loses greater than or equal to 0.05 wt%, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, or greater than or equal to 2 wt% versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours. Combinations of the above recited ranges are possible (e.g., the hydrogel is configured such that is loses less than or equal to 5 wt% and greater than or equal to 0.05 wt% when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours, the hydrogel is configured such that it loses less than or equal to 0.5 wt% and greater than or equal to 0.2 wt% when exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours). Other ranges are also possible. The loss of weight percent of the hydrogel in the presence of one or more metals ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours may be determined by TOC analysis or by comparing the weight of the hydrogel prior to being exposed to one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours to the weight of the hydrogel after being exposed to the one or more metal ions that are not incorporated within a volume of the hydrogel for a period of at least 24 hours. In certain embodiments, the TOC analysis or the weight comparison may be corrected for uptake or loss of one or more metal ions incorporated within a volume of the hydrogel using ICP-MS or ICP-OES.

[0075] The hydrogel may have any of a variety of suitable mesh sizes. As used herein, the term “mesh size” refers to an average distance between two neighboring network junctions that are connected by a polymer chain in a hydrogel. A hydrogel that has a relatively large mesh size may advantageously facilitate the absorption, rate of transport through the hydrogel, and oxidation of one or more organic molecules, as described elsewhere herein in greater detail.

[0076] The mesh size of the hydrogel may be advantageously large. In some embodiments, the hydrogel has a mesh size of at least 1 nanometer, at least 2 nanometers, at least 5 nanometers, at least 10 nanometers, at least 20 nanometers, at least 30 nanometers, at least 40 nanometers, at least 50 nanometers, at least 60 nanometers, at least 70 nanometers, at least 80 nanometers, or at least 90 nanometers. In certain embodiments, the hydrogel has a mesh size of less than or equal to 100 nanometers, less than or equal to 90 nanometers, less than or equal to 80 nanometers, less than or equal to 70 nanometers, less than or equal to 60 nanometers, less than or equal to 50 nanometers, less than or equal to 40 nanometers, less than or equal to 30 nanometers, less than or equal to 20 nanometers, less than or equal to 10 nanometers, less than or equal to 5 nanometers, or less than or equal to 1 nanometer. Combinations of the above recited ranges are possible (e.g., the hydrogel has a mesh size of at least 1 nanometer and less than or equal to 100 nanometers, the hydrogel has a mesh size of at least 40 nanometers and less than or equal to 50 nanometers). Other ranges are also possible. The mesh size of the hydrogel may be determined by swelling studies.

[0077] According to certain embodiments, the hydrogel is in the form of a particle. FIG. 1A shows a cross-sectional schematic diagram of hydrogel 102a in the form particle 104, in accordance with certain embodiments. In some embodiments, the hydrogel is in the form of a plurality of particles. FIG. IB shows a cross-sectional schematic diagram of hydrogel 102b in the form of a plurality of particles 104, in accordance with certain embodiments. Although particle(s) 104 in FIGS. 1A-1B are shown as spherical particles, the particles may have any of a variety of suitable shapes, as the disclosure is not meant to be limiting in this regard.

[0078] In some embodiments, the particle is a microparticle. For example, referring to FIG. 1A, particle 104 is a microparticle. The term “microparticle” is used herein in a manner consistent with its ordinary meaning in the art. A microparticle is a particle having a maximum characteristic dimension (e.g., a maximum diameter) from 1 micrometer to 1 millimeter. The maximum characteristic dimension of a particle generally refers to the longest dimension from a first surface of the particle to a second surface of the particle that is substantially opposite the first surface of the particle. As one illustrative example, referring to FIG. 1A, particle 104 has maximum characteristic dimension 106. According to some embodiments, the maximum characteristic dimension of the microparticle is from 1 micrometer to 10 micrometers, 10 micrometers to 20 micrometers, 20 micrometers to 30 micrometers, 30 micrometers to 50 micrometers, 50 micrometers to 70 micrometers, or 70 micrometers to 1 millimeter. Combinations of the above recited ranges are possible (e.g., 30 micrometers to 70 micrometers, or 20 micrometers to 1 millimeter). Other ranges are also possible. The maximum characteristic dimension of the particle may be determined by electron microscopy techniques (e.g., SEM and / or transmission electron microscopy (TEM)).

[0079] The particle may have any of a variety of suitable average characteristic dimensions (e.g., average diameters). The average characteristic dimension of a particle generally refers to an average of at least two dimensional measurements from a first surface of the particle to a second surface of the particle that is substantially opposite the first surface of the particle. In some embodiments, the particle has an average characteristic dimension greater than or equal to 1 micrometer, greater than or equal to 2 micrometers, greater than or equal to 5 micrometers, greater than or equal to 10 micrometers, greater than or equal to 20 micrometers, greater than or equal to 50 micrometers, greater than or equal to 100 micrometers, greater than or equal to 200 micrometers, or greater than or equal to 500 micrometers. In certain embodiments, the particle has an average characteristic dimension less than or equal to 1 millimeter, less than or equal to 500 micrometers, less than or equal to 200 micrometers, less than or equal to 100 micrometers, less than or equal to 50 micrometers, less than or equal to 20 micrometers, less than or equal to 10 micrometers, less than or equal to 5 micrometers, or less than or equal to 2 micrometers. Combinations of the above recited ranges are possible (e.g., the particle has an average characteristic dimension greater than or equal to 1 micrometer and less than or equal to 1 millimeter, the particle has an average characteristic dimension greater than or equal to 20 micrometers and less than or equal to 50 micrometers). Other ranges are also possible. The average characteristic dimension of the particle may be determined by electron microscopy techniques (e.g., SEM and / or TEM). According to some embodiments, the hydrogel (e.g., hydrogel particle) is substantially optically transparent. A hydrogel that is substantially optically transparent may advantageously allow light to substantially pass through the hydrogel, thereby facilitating the oxidation of one or more organic molecules absorbed by the hydrogel, as described elsewhere herein in greater detail. In certain embodiments, a water content of the hydrogel facilitates the optical transparency of the hydrogel. Suitable wavelengths of light (e.g., electromagnetic radiation) that substantially pass through the hydrogel include visible light having a wavelength greater than or equal to 400 nm and less than or equal to 700 nm, UV-A light having a wavelength greater than or equal to 315 nm and less than 400 nm, UV-B light having a wavelength greater than or equal to 280 nm and less than 315 nm, and / or UV-C light having a wavelength greater than or equal to 100 nm and less than 280 nm.

[0080] In certain embodiments, the particle (e.g., having an average characteristic dimension less than or equal to 1 millimeter) has an optical transparency greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, greater than or equal to 95%, greater than or equal to 98%, greater than or equal to 99%, greater than or equal to 99.5%, greater than or equal to 99.8%, or greater than or equal to 99.9% when the particle is placed 1 centimeter from a 100 W light source. In some embodiments, the particle has an optical transparency less than or equal to 99.99%, less than or equal to 99.9%, less than or equal to 99.8%, less than or equal to 99.5%, less than or equal to 99%, less than or equal to 98%, less than or equal to 95%, less than or equal to 90%, less than or equal to 85%, or less than or equal to 80% when the particle is placed 1 centimeter from a 100 W light source. Combinations of the above recited ranges are possible (e.g., the particle has an optical transparency greater than or equal to 75% and less than or equal to 99.9% when the particle is placed 1 centimeter from a 100 W light source, the particle has an optical transparency greater than or equal to 98% and less than or equal to 99% when the particle is placed 1 centimeter from a 100 W light source). Other combinations are also possible. The percent optical transparency of the particle when the particle is placed 1 centimeter from a 100 W light source may be determined by UV-vis absorbance spectroscopy.

[0081] A loss of light intensity through the particle (e.g., having an average characteristic dimension less than or equal to 1 millimeter) may be any of a variety of suitable percentages when the particle is placed 1 centimeter from a 100 W light source. In some embodiments, for example, a loss of light intensity through the particle is less than or equal to 25%, less than or equal to 20%, less than or equal to 15%, less than or equal to 10%, less than or equal to 5%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.5%, less than or equal to 0.2%, or less than or equal to 0.1% when the particle is placed 1 centimeter from a 100 W light source. In certain embodiments, a loss of light intensity through the particle is greater than or equal to 0.05%, greater than or equal to 0.1%, greater than or equal to 0.2%, greater than or equal to 0.5%, greater than or equal to 1%, greater than or equal to 2%, greater than or equal to 5%, greater than or equal to 10%, greater than or equal to 15%, or greater than or equal to 20% when the particle is placed 1 centimeter from a 100 W light source. Combinations of the above recited ranges are possible (e.g., a loss of light intensity through the particle is less than or equal to 25% and greater than or equal to 0.05% when the particle is placed 1 centimeter from a 100 W light source, a loss of light intensity through the particle is less than or equal to 1% and greater than or equal to 0.5% when the particle is placed 1 centimeter from a 100 W light source). Other ranges are also possible. The loss of light intensity through the particle when the particle is placed 1 centimeter from a 100 W light source may be determined by UV-vis absorbance spectroscopy.

[0082] According to certain embodiments, the hydrogel (e.g., hydrogel particle) may be synthesized via any of a variety of suitable methods. In some embodiments, for example, a solution (e.g., aqueous solution) comprising one or more monomer precursors and a photoinitiator is processed in a micro fluidic device to provide one or more droplets of the solution. In certain embodiments, the one or more droplets are exposed to UV light, thereby triggering the formation of free radicals from the photoinitiator. In some embodiments, the free radicals react with the one or more monomer precursors via a polymerization reaction (e.g., chain-growth polymerization) to convert the droplets into hydrogel particles. According to certain embodiments, the hydrogel particles are disposed in a metal-ion containing solution, thereby resulting in one or more metal ions coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel.

[0083] According to certain embodiments, an article and / or system is described. In some embodiments, the article and / or system comprises a hydrogel. In some embodiments, the hydrogel comprises a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged (e.g., positively charged, negatively charged, or positively charged and negatively charged, i.e., zwitterionic). In certain embodiments, the hydrogel comprises one or more metal ions, at least some of which (e.g., each of which) are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel.

[0084] In certain embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation at a pH greater than or equal to 3 (e.g., greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, or more). For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0085] In some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of hydrogen peroxide. In certain embodiments, for example, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to hydrogen peroxide for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0086] In some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of UV light. For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to UV light for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0087] According to some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of one or more metal ions incorporated within a volume of the hydrogel. In certain embodiments, for example, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to one or more metal ions incorporated within a volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more). In certain embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of one or more metal ions that are not incorporated within the volume of the hydrogel (e.g., one or more metal ions that are external to the volume of the hydrogel). For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within the volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0088] The article and / or system may be any of a variety of suitable articles and / or systems. In some embodiments, for example, the article and / or system is a bed reactor. FIG. 3A shows a schematic diagram of bed reactor 302a, in accordance with certain embodiments. In some embodiments, as shown in FIG. 3A, bed reactor 302a comprises fluid inlet 304a configured to flow fluid 308a (e.g., a solution, such as an aqueous solution) comprising one or more organic molecules into bed reactor 302a, through bed 310 comprising hydrogel 104, and to fluid outlet 306a. In certain embodiments, hydrogel 104 is exposed to fluid 308a comprising the one or more organic molecules as fluid 308a flows through bed 308 comprising hydrogel 104. In some embodiments, hydrogel 104 absorbs the one or more organic molecules from fluid 308a as fluid 308a flows through bed 310 comprising hydrogel 104. In certain embodiments, hydrogel 104 oxidizes the one or more absorbed organic molecules. According to some embodiments, fluid 308b comprising one or more reaction products from the oxidation of the one or more absorbed organic molecules (e.g., CO2, H2O) flows out of bed reactor 302a via fluid outlet 306a. Suitable bed reactors include, but are not limited to, a packed bed reactor (e.g., comprising a packed bed of the hydrogel) and / or a fluidized bed reactor (e.g., comprising a fluidized bed of the hydrogel). Other bed reactors are also possible.

[0089] In certain embodiments, the article and / or system is a tank reactor. FIG. 3B shows a schematic diagram of tank reactor 302b, in accordance with certain embodiments. In some embodiments, as shown in FIG. 3B, tank reactor 302b comprises fluid inlet 304b configured to flow fluid 308a (e.g., a solution, such as an aqueous solution) comprising one or more organic molecules into tank reactor 302b comprising hydrogel 104 and to fluid outlet 306b. In certain embodiments, hydrogel 104 is exposed to fluid 308a comprising the one or more organic molecules as fluid 308a flows into tank reactor 302b comprising hydrogel 104. In some embodiments, hydrogel 104 absorbs the one or more organic molecules from fluid 308a as fluid 308a flows into tank reactor 302b comprising hydrogel 104. In certain embodiments, hydrogel 104 oxidizes the one or more absorbed organic molecules. According to some embodiments, fluid 308b comprising one or more reaction products from the oxidation of the one or more absorbed organic molecules (e.g., CO2, H2O) flows out of tank reactor 302b via fluid outlet 306b. In certain embodiments, tank reactor 302b comprises one or more impellers 312 or other agitating device to mix fluid 308 and hydrogel 104. Suitable tank reactors include, but are not limited to, a stirred tank reactor. Other tank reactors are also possible.

[0090] Although not shown in the figures, the article and / or system (e.g., bed reactor, tank reactor) may comprise one or more pumps, sensors, and / or controls.

[0091] According to certain embodiments, a method of oxidizing one or more organic molecules is described. In some embodiments, the method comprises exposing a hydrogel to the one or more organic molecules. Suitable organic molecules are described elsewhere herein in greater detail.

[0092] In some embodiments, the hydrogel comprises a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged (e.g., positively charged, negatively charged, or positively charged and negatively charged, i.e., zwitterionic). In certain embodiments, the hydrogel comprises one or more metal ions, at least some of which (e.g., each of which) are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel.

[0093] In certain embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation at a pH greater than or equal to 3 (e.g., greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, or more). For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to a pH greater than or equal to 3 for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0094] In some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of hydrogen peroxide. In certain embodiments, for example, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to hydrogen peroxide for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0095] In some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of UV light. For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to UV light for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0096] According to some embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of one or more metal ions incorporated within a volume of the hydrogel. In certain embodiments, for example, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to one or more metal ions incorporated within a volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0097] In certain embodiments, as described elsewhere herein in greater detail, the hydrogel is resistant to degradation in the presence of one or more metal ions that are not incorporated within the volume of the hydrogel (e.g., one or more metal ions that are external to the volume of the hydrogel). For example, in some embodiments, the hydrogel is configured such that it loses less than or equal to 5 wt% versus a total weight of the hydrogel when exposed to one or more metal ions that are not incorporated within the volume of the hydrogel for a period of at least 24 hours (e.g., at least 36 hours, at least 48 hours, or more).

[0098] According to certain embodiments, the exposing comprises exposing the hydrogel to a solution (e.g., an aqueous solution) comprising the one or more organic molecules. In some embodiments, the one or more organic molecules are dissolved and / or suspended in the solution (e.g., aqueous solution). FIG. 2A shows a cross- sectional schematic diagram representing a method comprising exposing hydrogel 102 to solution 202 comprising one or more organic molecules 206, in accordance with certain embodiments. In certain embodiments, referring to FIG. 2A, the exposing comprises disposing (e.g., at least partially submerging, fully submerging) hydrogel 102 in solution 202 comprising one or more organic molecules 206. In some embodiments, as shown in FIG. 2A, solution 202 comprising one or more organic molecules 206 is contained within container 204.

[0099] Although not shown in the figures, other methods of exposing the hydrogel to the solution comprising the one or more organic molecules are also possible. In some embodiments, for example, the exposing comprises flowing a solution comprising one or more organic molecules over the hydrogel such that the solution comprising the one or more organic molecules contacts a surface of the hydrogel.

[0100] In some embodiments, the exposing comprises absorbing the one or more organic molecules from the solution (e.g., aqueous solution) into the hydrogel (e.g., within a volume of the hydrogel). FIG. 2B shows a cross-sectional schematic diagram representing a method comprising absorbing one or more organic molecules 206 from solution 202 into hydrogel 102, in accordance with certain embodiments. According to some embodiments, the exposing comprises absorbing the solution (e.g., aqueous solution) comprising the one or more organic molecules into the hydrogel, i.e., the exposing results in swelling of the hydrogel.

[0101] According to some embodiments, the method comprises oxidizing the one or more organic molecules. In some embodiments, for example, the hydrogel advantageously facilitates the catalytic oxidation of the one or more organic molecules. In certain embodiments, the oxidizing the one or more organic molecules comprises producing carbon dioxide (CO2) and / or water (H2O) as reaction products.

[0102] In some embodiments, the oxidizing the one or more organic molecules is performed in the presence of hydrogen peroxide. The hydrogen peroxide may, in some embodiments, advantageously facilitate the catalytic oxidation of the one or more organic molecules. In certain embodiments, the oxidizing the one or more organic molecules is performed in the presence of UV light. The UV light may, in some embodiments, advantageously facilitate the catalytic oxidation of the one or more organic molecules.

[0103] The oxidizing may be performed at any of a variety of suitable pH values (e.g., of the solution comprising the one or more organic molecules). In some embodiments, for example, the oxidizing is performed at a pH greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, or greater than or equal to 9. In certain embodiments, the oxidizing is performed at a pH less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, or less than or equal to 5. Combinations of the above recited ranges are possible (e.g., the oxidizing is performed at a pH greater than or equal to 3 and less than or equal to 10, the oxidizing is performed at a pH greater than or equal to 6 and less than or equal to 7). Other ranges are also possible.

[0104] According to some embodiments, the hydrogel is capable of being reused to oxidize one or more organic molecules. Advantageously, the hydrogel may be capable of continuously regenerating itself without the need for additional processing. In certain embodiments, for example, the hydrogel is capable of being reused to oxidize one or more organic molecules without addition of one or more external acids and / or one or more metal ions that are not incorporated within a volume of the hydrogel.

[0105] The hydrogel may be capable of being reused to oxidize one or more organic molecules any of a variety of a suitable number of times without losing less than or equal to 10% of its reactivity. In certain embodiments, for example, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times, more than 10 times, more than 50 times, more than 100 times, more than 200 times, more than 300 times, more than 400 times, more than 500 times, or more, without losing less than or equal to 10% of its reactivity. In some embodiments, the hydrogel is capable of being reused to oxidize one or more organic molecules less than 1000 times, less than 500 times, less than 400 times, less than 300 times, less than 200 times, less than 100 times, less than 50 times, or less than 10 times without losing 10% of its reactivity. Combinations of the above recited ranges are possible (e.g., the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times and less than 1000 times without losing less than or equal to 10% of its reactivity, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 200 times and less than 300 times without losing less than or equal to 10% of its reactivity). Other ranges are also possible.

[0106] The hydrogel may be capable of being reused to oxidize one or more organic molecules any of a variety of a suitable number of times without losing less than or equal to 5% of its reactivity. In certain embodiments, for example, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times, more than 10 times, more than 50 times, more than 100 times, more than 200 times, more than 300 times, more than 400 times, more than 500 times, or more, without losing less than or equal to 5% of its reactivity. In some embodiments, the hydrogel is capable of being reused to oxidize one or more organic molecules less than 1000 times, less than 500 times, less than 400 times, less than 300 times, less than 200 times, less than 100 times, less than 50 times, or less than 10 times without losing 5% of its reactivity.

[0107] Combinations of the above recited ranges are possible (e.g., the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times and less than 1000 times without losing less than or equal to 5% of its reactivity, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 200 times and less than 300 times without losing less than or equal to 5% of its reactivity). Other ranges are also possible.

[0108] The hydrogel may be capable of being reused to oxidize one or more organic molecules any of a variety of a suitable number of times without losing less than or equal to 1% of its reactivity. In certain embodiments, for example, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times, more than 10 times, more than 50 times, more than 100 times, more than 200 times, more than 300 times, more than 400 times, more than 500 times, or more, without losing less than or equal to 1% of its reactivity. In some embodiments, the hydrogel is capable of being reused to oxidize one or more organic molecules less than 1000 times, less than 500 times, less than 400 times, less than 300 times, less than 200 times, less than 100 times, less than 50 times, or less than 10 times without losing 1% of its reactivity. Combinations of the above recited ranges are possible (e.g., the hydrogel is capable of being reused to oxidize one or more organic molecules more than 5 times and less than 1000 times without losing less than or equal to 1% of its reactivity, the hydrogel is capable of being reused to oxidize one or more organic molecules more than 200 times and less than 300 times without losing less than or equal to 1% of its reactivity). Other ranges are also possible.

[0109] The hydrogel may lose a substantially low amount of the one or more metal ions incorporated within a volume of the hydrogel after using the catalyst for the oxidation of one or more organic molecules over a period of time. In some embodiments for example, the hydrogel loses less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less, of the total amount the one or more metal ions after using the catalyst for the oxidation of one or more organic molecules over a period of at least 24 hours (e.g., 36 hours, 48 hours, or more).

[0110] The one or more organic molecules may be or comprise any of a variety of suitable organic molecules. In some embodiments, for example, the one or more organic molecules is or comprises a persistent organic pollutant (POP). The POP may be or comprise any of a variety of suitable POPs. In certain embodiments, for example, the POP is or comprises a xenoestrogen, a pesticide, and / or a per- or polyfluoroalkyl substance (PFAS). Other POPs are also possible.

[0111] The xenoestrogen may be or comprise any of a variety of suitable xenoestrogens. In some embodiments, for example, the xenoestrogen is or comprises ethinyl estradiol. Other xenoestrogens are also possible.

[0112] The pesticide may be or comprise any of a variety of suitable pesticides. In certain embodiments, for example, the pesticide is or comprises a chlorinated pesticide. In some embodiments, the pesticide is or comprises 2,4-dichlorophenol, diclofenac, and / or combinations thereof. Other pesticides are also possible.

[0113] The PFAS may be or comprise any of a variety of suitable PFAS. In some embodiments, for example, the PFAS is or comprises perfluorooctanoic acid (PFOA), perfluorooctanesulphonic acid (PFOS), perfluorobutanoic acid (PFBA), perfluorobutanesulphonic acid (PFBS), perfluorohexanesulphonic acid (PFHxS), a sodium salt thereof, a potassium salt thereof, and / or an ammonium salt thereof, hexafluoropropylene oxide (HFPO), and / or combinations thereof. Other PFAS are also possible.

[0114] According to some embodiments, the one or more organic molecules is or comprises a drug. The drug may be or comprise any of a variety of suitable drugs. In some embodiments, for example, the drug is or comprises aspirin, ibuprofen, and / or combinations thereof.

[0115] In certain embodiments, the drug is or comprises an antibiotic. The antibiotic may be or comprise any of a variety of suitable antibiotics. In some embodiments, for example, the antibiotic is or comprises tetracycline, ciprofloxacin, cefixime, amoxicillin, penicillin, streptomycin, and / or combinations thereof. Other drugs and / or antibiotics are also possible.

[0116] According to some embodiments, the one or more organic molecules is or comprises a dye. The dye may be any of a variety of suitable dyes. In certain embodiments, for example, the dye is methylene blue, fluorescein, an azo dye, indigo, methyl orange, congo red, tyrian purple, an anthraquinone dye, a sulfur dye, a Sudan dye, malachite green, Allura Red AC, Amaranth, Sunset Yellow FCF, fuchsine, carmine, a triarylmethane dye, a xanthene, acridine, a carotenoid dye, a diazo dye, and / or combinations thereof. Other dyes are also possible.

[0117] According to certain embodiments, the one or more organic molecules is or comprises a surfactant. The surfactant may be any of a variety of suitable surfactants. In some embodiments, for example, the surfactant is a Span surfactant, a Tween surfactant, a Pluronic surfactant, and / or combinations thereof. Other surfactants are also possible.

[0118] In some embodiments, the one or more organic molecules is or comprises a polypeptide, a protein, and / or combinations thereof.

[0119] Other organic molecules are also possible.

[0120] The following application is incorporated herein by reference, in its entirety, for all purposes: U.S. Provisional Patent Application No. 63 / 600,591, filed November 17, 2023, and entitled “A HYDROGEL-BASED HETEROGENEOUS CATALST”.

[0121] EXAMPLE

[0122] This example describes a heterogeneous Fenton catalyst utilizing a zwitterionic hydrogel. Containing individually complexed iron ions in a highly porous scaffold, the hydrogel catalyst has a large effective surface area and exhibits kinetics comparable to homogeneous Fenton degradation. The complexed ions can initiate Fenton degradation at neutral pH, eliminating acid additions. Simultaneously, the zwitterionic hydrogel scaffold is specifically selected to be resistant to Fenton oxidation and strongly bind to the iron ions, enabling repeated long-term use. Distinguishing itself from existing designs, the zwitterionic hydrogel-based Fenton catalyst is compatible with UV-Fenton processes and achieves rapid self-regeneration during operation, presenting a promising solution for the efficient and scalable degradation of persistent organic pollutants. The rapid degradation of three structurally disparate contaminants of major concern, including a xenoestrogen, a pesticide, and a model PFAS, is showcased over multiple cycles of use at trace concentrations.

[0123] POPs are organic pollutants that undergo natural degradation in the environment only over several years or decades. POPs include chemically diverse materials such as organic solvents, chemical intermediates, industrial surfactants, lubricants, detergents, disinfectants, antibiotics and other medications, food additives, and flavoring agents. Though they typically occur at low concentrations (pg / L), the tendency of POPs to accumulate inside the body and the environment over these long-time scales makes them subjects of significant environmental concern. POPs are ubiquitous in the environment and can have significant adverse effects on the ecosystem (including cancer in humans and animals, and the increased prevalence of antibiotic -resistant diseases). Though the Stockholm Convention on Persistent Organic Pollutants imposed restrictions on the manufacture and use of specific POPs, these still persist in the environment where they continue to have negative impacts on the ecosystem, and are expected to do so for several decades. At the same time, newer ‘designer’ POPs continue to be manufactured, sometimes as industrial substitutes for restricted substances. Among other POPs, the US Environmental Protection Agency (USEPA) and the European Chemicals Agency (ECHA) are currently in the process of imposing ever-stricter limits on PFAS in the environment, increasing the urgency of the need for technologies to remove POPs from water. Such technologies will also be essential to meet the targets of United Nations Sustainable Development Goal (UNSDG) 6.

[0124] Addressing the POP problem requires a combination of techniques for the sequestration and destruction of POP molecules. Destructive methods are necessary to accelerate the slow natural degradation of POPs in water and waste streams, including those in concentrated streams produced by sequestration technologies like reverse osmosis or adsorption. Advanced oxidation processes (AOPs) use ozone or hydrogen peroxide in combination with a catalyst to produce reactive hydroxyl ions to attack POPs in situ. One such advanced oxidation process, the Fenton reaction, uses Fe(II) ions as the underlying catalyst. The Fenton reaction, shown in Equation 1, has found substantial interest in academia and industry due to its ability to destroy chemically diverse POPs efficiently, including those known to be difficult to degrade using other AOPs. The low cost of materials required to implement the process also make a Fenton AOP promising for use in real world scenarios.

[0125] It must be noted, as shown in Equation 1, that the Fe(II) ions in a classical Fenton reaction are not true catalysts since they are continuously converted into Fe(III) ions that have a limited ability to degrade contaminants. Further, the Fe(II) ions are dissolved in the water to be treated, so subsequent separation steps are necessary to eliminate the iron and obtain clean water. Due to the presence of other contaminants, formation of sludge, and considerations of cost, any recovered iron is disposed of as toxic chemical waste and cannot be reused. Fenton oxidation optimally occurs at a pH close to 3.0, necessitating acid addition to degrade POPs on the short timescales encountered in real- world water treatment processes, significantly adding to process complexity and cost. A treatment process based on the classical Fenton reaction typically requires at least four unit operations with multiple pumps, sensors, and controls, alongside continuous acid, iron, hydrogen peroxide, and base addition (for neutralizing acids). To operate a more practical and cost-effective process based on the Fenton reaction, it is necessary to retain and reuse the iron within the unit operation by immobilizing it in a heterogenous catalyst, while also eliminating the need to add acid.

[0126] Previous attempts to retain iron have included preparing iron or iron oxide nanoparticles that are immobilized on a traditional adsorbent like activated carbon, other substrates, or inside a polymer such as chitosan. Adding acid to such a system is still necessary to achieve rapid Fenton oxidation, but acid addition can dissolve nanoparticles and significantly reduces catalyst life. Reaction kinetics are significantly slowed in the absence of acid addition (due to the increase in Fe(III) ions relative to Fe(II) ions, Fe(III) ions reacting much more slowly), or if nanoparticles are replaced with bulk iron or iron oxide (due to reduction in active surface area). Current approaches to retain iron are therefore not amenable to the elimination of acid addition.

[0127] On the other hand, approaches to eliminate acid addition while maintaining rapid kinetics focus on preparing soluble complexes of iron, in which the ligands change the effective work function of the Fe(II) ion to allow oxidation at higher pH. Since these complexes are water-soluble, it is not possible to effectively retain the iron. Further, the performance of these iron complexes is sensitive to pH, and iron ions may be released from the complexes with change in oxidation state during the Fenton reaction. Current approaches to eliminate acid addition are therefore not amenable to iron retention.

[0128] There are also additional challenges associated with current approaches; primarily, Fenton oxidation degrades not only the target POPs, but also many of the encapsulating polymers, ligands, and associated substrates that are used to improve the classical Fenton reaction. In general, AOP performance may be further boosted by the simultaneous use of UV light, which can degrade molecules directly (photolysis) or by accelerating the production of hydroxyl ions from hydrogen peroxide to degrade POPs. Though UV-Fenton processes have been explored and show great promise for POP elimination, they make the design of a heterogenous catalyst more challenging, requiring it to be transparent, and any complexing ligand to be UV-resistant.

[0129] In sum, a practical and efficient Fenton process to eliminate POPs requires the development of (1) a heterogenous catalyst that retains iron while (2) eliminating the need for acid addition, (3) is highly porous and has a large effective surface area to preserve efficacy, (4) is optically transparent and (5) resistant to degradation by UV light, hydrogen peroxide, and the Fenton reaction itself, (6) preferably does not use nanoparticles which may pose a threat to the environment if they escape the catalyst, and (7) can be regenerated rapidly and reused in a facile way. This example introduces a zwitterionic hydrogel catalyst containing chelated iron to simultaneously satisfy all these criteria, and demonstrates its use by showcasing the degradation of ethinyl estradiol (EDOL; a xenoestrogen), perfluorooctanoic acid (PFOA; a model for PFAS, fluorinated POPs, and industrial surfactants), and 2,4-dichlorophenol (DCP; a model for pesticides and chlorinated aromatics). All three molecules are of significant global concern and there is an urgent need for strategies to eliminate each of them.

[0130] There is significant interest in applying hydrogels to solve problems in water treatment due to the several unique advantages they offer. First, hydrogels can be prepared from a vast library of mutually compatible and commercially available molecules, allowing the facile design of structures with specific functional groups and chemical properties. Chemical flexibility allows the creation of a polymeric hydrogel structure containing ligand-like groups that can bind individual iron ions to hold them within the gel, while simultaneously changing the work function of iron ions to enable Fenton oxidation at neutral pH. As described in this example, appropriate precursor materials can be used to prepare hydrogels that are optically transparent and resist oxidation. Further, the affinity of hydrogel backbones to water and their tendency to swell when wet leads to architectures with high microporosity and water content, facilitating the passage of contaminants into hydrogel structures. In prior work, functionalized hydrogels were used to absorb contaminants from water by leveraging these features to prepare materials that exhibited high mass transfer coefficients and imposed minimal transport limitations on contaminant molecules. The inherent kinetic advantages of binding individual iron ions (rather than nanoparticles), combined with rapid mass transport, makes hydrogels ideal scaffolds for supporting fast POP degradation. The synthesis of the hydrogel catalyst is a facile and scalable process, requiring off-the-shelf equipment that operates at room temperature and does not use hazardous chemicals. Finally, it is shown that a catalyst structured in this manner and operated in a UV-Fenton process can continuously regenerate itself and be reused, without the need for any additional processing, making the catalysts promising solutions to degrade POPs.

[0131] Strategy and synthesis'. Hydrogels were synthesized from monomer solutions as described herein and shown in FIG. 4A. In brief, a monomer solution consisting of precursors and a photoinitiator (PI) dissolved in water was processed into monodisperse droplets using an off-the-shelf microfluidic device (micro-cross) that operates by pinching off the monomer solution using an immiscible mineral oil phase (FIG. 4A). There are well-known methods of scaling up the production of these devices to produce large quantities of hydrogels for commercial use. The droplets were then exposed to UV light, triggering the formation of free-radicals from the PI molecules. These free-radicals attack the terminal double bonds in the hydrogel precursor molecules in a chain-growth polymerization reaction that converts the droplets into solid hydrogel microparticles containing water (FIG. 8). A picture of these hydrogel microparticles, washed with water after synthesis to remove unreacted molecules, is shown in FIG. 4B. The microparticles have a uniform size of 800 ± 100 m, which was large enough to separate them from water by simple gravitational settling for a few seconds (to enable retention within a unit operation without additional separation steps), but small enough to limit the length scales on which POP molecules need to be transported inside the hydrogel, leading to faster kinetics. Creating hydrogels in the form of microparticles also enabled limiting the extinction of UV light as it passes through and is absorbed by the hydrogels in a UV-Fenton process.

[0132] Using [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PSB) and N,N’-methylenebis(acrylamide) (BIS) as the hydrogel precursors allows several advantages. PSB forms the bulk of the hydrogel, while BIS acts to cross-link PSB chains and stabilize the entire structure. Hydrogel microparticles prepared using this method were mechanically robust (FIGS. 9A-9B). At the same time, PSB also contains charged groups (FIG. 4A) that make it superhydrophilic, increase its solubility, and limit polymerization-induced phase separation (PIPS) during the synthesis process. As such, microparticles made from PSB-BIS are internally homogenous and have a very high water content, making them optically transparent to support the passage of UV light. The superhydrophilicity of PSB hydrogels leads to greater swelling than other conventional hydrogels, increasing mesh size and increasing the rate of POP transport. Though the hydrogel is swollen, the negatively charged terminal oxygen atoms on the PSB molecule serve to strongly bind Fe(II) and Fe(III) ions through the formation of coordinate bonds. As such, the hydrogel microparticles can be made to bind Fe(II) ions simply by soaking them in a saturated solution of ferrous sulfate as described in experimental methods. Finally, a synthesis based on PSB and BIS does not consume any hazardous chemicals, and since the bound iron ions are left in a solvated state (rather than sintering, as in other catalysts), the entire process can be operated at room temperature.

[0133] The presence of bound iron within the microparticles may be confirmed by visual inspection, after the soaked microparticles are washed extensively with water to remove any free iron ions. As shown in FIG. 4C, the once clear microparticles are seen to turn yellow after being used to bind iron. Though Fe(II) ions are blue-green, the microparticles look yellow due to a combination of (1) a changed work- function due to the formation of coordinate bonds, affecting the absorbance spectrum of the ions, and (2) the formation of trace quantities of yellow-brown Fe(III) ions due to exposure to atmospheric oxygen. The hydrogel microparticles containing bound iron may then be used to catalyze Fenton oxidation as shown in FIG. 4A, with Fe(II) ions within the hydrogel being oxidized to Fe(III) ions while hydrogen peroxide is converted to hydroxyl radicals. The absence of UV light and using limited quantities of hydrogen peroxide suppress reverse reactions that convert Fe(III) ions to Fe(II) ions, and the microparticles can be seen to change color from yellow to orange-brown as the relative concentration of Fe(III) ions increases (FIG. 4C).

[0134] To maximize the rate of Fenton oxidation, the loading of iron ions within the hydrogel microparticles should be maximized, and these ions should be well-dispersed within the hydrogel to increase the effective surface area of the reaction. Soaking the hydrogels microparticles in a saturated solution of ferrous sulfate enables us to achieve an internal iron concentration of 0.023% (w / w) or 233 ppm (parts-per-million), determined using thermogravimetric analysis (FIG. 10). Data in FIG. 10 is normalized to dry hydrogel mass. As can be seen from FIG. 10, the presence of iron accelerates iron loss by replacing water-PSB hydrogen bonds with stronger iron-PSB coordinate bonds. The curves are seen to rise after a minimum close to 600 °C due to the oxidation of iron in air to iron oxide. Classical homogenous Fenton reactions effective in degrading POPs have been previously reported with iron concentrations as low as 0.1 pM or 0.0005% (w / w), which is two orders of magnitude lower than within the microparticles described herein. Further, iron ions avoid forming clusters within the hydrogel due to the presence of repelling positive charges on each ion. The absence of clusters is confirmed using elemental mapping (FIG. 4D), indicating the absence of clusters at the pm scale, and using XRD to study clustering at the nm scale (FIG. 4E). The XRD spectrum of microparticles containing bound iron captures information solely about iron-iron correlations due to the significantly larger form factor of iron ions compared to other elements in the hydrogel. The absence of sharp or tall peaks in the XRD spectrum indicates the absence of crystallites, and the shape of the spectrum indicates an amorphous distribution. The XRD spectrum may be used to calculate a pair correlation function indicating the spatial distribution of ions relative to each other (FIG. 4E). The pair correlation function has a characteristic liquid-like shape, indicating that the iron ions are well-dispersed inside the hydrogel.

[0135] As a result of these design choices, hydrogel microparticles containing bound iron ions can catalyze the Fenton degradation of organic molecules on time scales similar to classical Fenton degradation by free iron ions in water. FIG. 5A shows the degradation of methylene blue dye in a batch experiment using catalytic hydrogel microparticles that have a total mass approximately one-tenth that of the solution. Methylene blue is a model organic pollutant commonly used to study the efficacy of Fenton degradation. Interestingly, the hydrogel microparticles were able to catalyze dye degradation at low concentrations, and at neutral pH in the absence of added acid. Dye degradation was rapid and complete in about 10 seconds. The progress of the reaction was tracked by measuring the hue of a representative cross-section. Dye degradation kinetics for a neutral pH process catalyzed by hydrogel microparticles were compared to a classical Fenton process at pH 3.0 using the same quantity of dissolved iron (FIG. 5B). In control experiments, it was verified that the classical Fenton process was unable to degrade methylene blue in the absence of acid or hydrogen peroxide addition (FIGS. 11A-1 IB). Degradation was attempted in a 2 mL reaction mixture containing 0.008 M H2O2 (only in FIG. 11A), 0.002 M Fe(II) ions (only in FIG. 11B), 0.001 M H2SO4, and 30 mg / 1 methylene blue. The control experiments show that classical Fenton oxidation in the methylene blue system is not possible in the absence of either hydrogen peroxide or acid. These data can be used to calculate first-order reaction time constants which have the same order of magnitude (2.54 seconds for hydrogel-chelated iron, and 0.82 seconds for free iron in a classical Fenton process), indicating only a minimal loss in kinetics due to mixing restrictions imposed by binding the iron to the hydrogel microparticles.

[0136] It is important not only to maintain rapid kinetics at neutral pH, but also to effectively retain the iron within a heterogenous catalyst resistant to oxidation to enable a more practical Fenton process. Iron retention requires that the catalyst material be stable under conditions of UV-Fenton oxidation. FIG. 5C shows the TOC content measured in DI water when it is used as the medium for a UV-Fenton batch reaction for 24 hours in the absence of POPs. Control data (< 1 ppm) indicates the observed concentration in the absence of any bound or free iron, i.e., purely due to the addition of hydrogen peroxide and exposure to UV light. As such, the measured TOC reflects the amount of organic material released into the supernatant due to hydrogel degradation. Iron-laden PSB hydrogels were compared to two other iron-laden hydrogels: (1) poly (ethylene glycol) diacrylate (PEGDA, a commonly used hydrogel scaffold in other application areas) copolymer with iminodiacetic acid (IDA, a commonly used chelating agent), and (2) a PSB hydrogel copolymer also containing chemically bound IDA. Chelating agents often act as the functional moieties in ion-exchange resins and have previously been explored to bind iron for performing Fenton degradation at neutral pH. Copolymerizing hydrogels with chelating agents adds functional sites to bind additional iron ions, significantly increasing capacity. FIG. 5C shows that both iron-laden PEGDA+IDA and PSB+IDA hydrogels undergo significant degradation due to the UV-Fenton process while ironladen PSB hydrogels do not, underscoring the need to pick an appropriate scaffold that resists oxidation. An extensive literature review indicates that Fenton-resistant polymers share two features: (1) an absence of heteroatoms along the polymerized backbone, and (2) electron- withdrawing side-groups with heteroatoms that are in a high oxidation state. PSB hydrogels satisfy both criteria (FIG. 4A), since bonds along the PSB polymer chain contain only carbon atoms, the ester linkage is electron- withdrawing, and nitrogen and sulfur atoms within PSB are in a high-oxidation state. The supernatant TOC concentration is measured to be about 2 ppm, corresponding to iron-laden PSB hydrogel microparticles losing only 0.0002% of their mass during each Fenton cycle. Selecting an appropriate chemistry not only enables regeneration and reuse, but also prevents secondary contamination of the water being treated, due to degradation by-products. Such secondary contamination may otherwise require additional treatment steps to eliminate.

[0137] In addition to structural stability, strong chemical bonds between the hydrogel and iron ions are important to retain iron. FIG. 5D shows the amount of iron released from iron-laden hydrogels when they are used to catalyze UV-Fenton reactions in the absence of POPs. It should be noted that these values, measured using ICP-MS analysis, only capture dissolved iron, and not the loss of iron that remains associated to large residues (>200 nm) produced by hydrogel degradation described in FIG. 5C. From FIG. 5D, it may be noted that PSB-containing hydrogels, which possess a large number of moieties to bind iron as a result of negatively charged oxygen atoms in FIG. 4A, have a greater affinity for iron than classical hydrogel materials. This greater affinity, combined with the higher affinity of PSB-IDA hydrogels to bind iron is consistent with prior work that used these hydrogels as absorbents to remove metals from water. Finally, the loss of iron from iron-laden PSB hydrogels per 24h UV-Fenton cycle is about 2.1% of the total iron content of the hydrogel, indicating that the substantial majority of iron is effectively retained within the catalyst. The inherent flexibility of chains within the hydrogel enables the motion of PSB chains to bind to or unbind from iron ions bound to the hydrogel even as the iron ions undergo oxidative or reductive changes (shown using PSB molecules in FIG. 4A), enabling significant iron retention during the Fenton reaction. Any lost iron can be made up by soaking the PSB hydrogels in ferrous sulfate solution as previously described.

[0138] POP elimination kinetics and. reusability: Catalytic hydrogel microparticles were used to showcase the destruction of three model POPs of significant environmental concern (EDOL, DCP, and PFOA) whose structures are shown in FIG. 6A. Prior work that uses Fenton reactions has demonstrated the successful degradation of these molecules. It is important to demonstrate the degradation of small molecule POPs such as these on practical time scales and at environmentally relevant concentrations, since the degradation of dyes is accelerated by electron-transfer effects. PSB hydrogel microparticles containing chelated iron ions can effectively eliminate these recalcitrant POPs by catalyzing a UV-Fenton batch process in a stirred vessel continuously exposed to UV light as described in the experimental section. The initial POP concentration is 1 ppm, and sufficient hydrogen peroxide is added at the beginning of the reaction to yield an initial concentration of 0.07% (w / w). Final POP concentrations are measured after 24 hours using liquid chromatography-mass spectroscopy (LC-MS), and indicate complete elimination of EDOL and DCP, and significant elimination of PFOA. The elimination achieved using our heterogenous UV-Fenton process is similar to elimination observed in prior work, and demonstrates the ability of the catalytic hydrogel microparticles to degrade POPs at trace levels.

[0139] The Fenton process was operated in the presence of UV light due to the faster kinetics and higher equilibrium elimination achieved in the UV-Fenton process compared to a Fenton process without UV light, or solely by the action of UV light (shown for EDOL in FIG. 6B). It was verified that the degradation of all model POPs was due to the UV-Fenton process, and not simply due to the presence of UV light (FIGS. 12A-12C). The kinetics of UV-Fenton degradation are also dependent on the initial concentration of the POP to be degraded. As shown in FIG. 6C, it was observed that lowering the initial POP concentration increased the fractional elimination at equilibrium but reduced the speed of elimination. Since the initial concentration of hydrogen peroxide, bound iron, and the intensity of UV light were kept constant in these experiments, it may be assumed that the UV-Fenton reaction that produces hydroxyl radicals (FIG. 4A) does so at a rate that is identical over time across all three systems in FIG. 6C. As such, the concentration of hydroxyl ions is independent of the initial POP concentration over time. As we lower the POP concentration, the number of hydroxyl ions relative to the number of POP molecules increases, leading to an increase in equilibrium elimination. However, since the POP molecules have a lower concentration, the kinetics of the degradation reactions are slower, leading to a decrease in the rate of elimination.

[0140] The rate of UV-Fenton degradation and equilibrium elimination also depend on the initial concentration of hydrogen peroxide loaded into the reaction mixture, as shown in FIGS. 6D-6F. Interestingly, the data shows that POP degradation first increases and then decreases as the initial concentration of hydrogen peroxide is increased. For PFOA, it is as important to defluorinate the reaction by-products as it is to degrade the target molecule for environmental applications. The defluorination of PFOA was measured as a function of initial hydrogen peroxide concentration using ion chromatography experiments, observing the same non-linear trend (FIG. 13), with 0.07% hydrogen peroxide leading to greater defluorination than a higher and lower concentration. Note that defluorination is lower than total PFOA degradation, consistent with prior work using homogeneous UV-Fenton reactions. Though this effect has not been observed in classical Fenton degradation experiments, it has previously been reported in heterogenous Fenton degradation experiments. As the concentration of hydrogen peroxide increases, the rate of production of hydroxyl ions close to the iron ions within the hydrogels also increases. These hydroxyl ions then diffuse outwards and react with POP molecules that are continuously diffusing into the hydrogel microparticles, thereby degrading the POP. However, as shown in prior work, when the initial concentration of hydrogen peroxide is increased beyond a critical value, the concentration of hydroxyl ions close to the catalytic sites (here, the iron ions) increases significantly enough that reactions between hydrogen peroxide molecules and the hydroxyl ions to produce hydroperoxy radicals occur faster than the outward diffusion of hydroxyl ions. These radicals have the same capacity to degrade POPs as hydroxyl radicals, but require greater quantities of hydrogen peroxide to make. As such, the normalized degradation capacity of each hydrogen peroxide molecule is reduced, and POP degradation decreases above the critical threshold of initial hydrogen peroxide concentration. The value of this threshold is set by competition between the mass transport of hydroxyl radicals (affected by the size of the hydrogel microparticles and mixing within the reaction setup) and the rate of formation of hydroperoxy radicals (affected by the concentration of hydrogen peroxide, bound iron, and the intensity of UV light), and is therefore independent of the POP being degraded (FIGS. 6D-6F).

[0141] Regenerating Fenton catalysts requires the use of the reverse-Fenton reactions shown in FIG. 7A. In commercial classical Fenton processes, it is not possible to regenerate and reuse the catalyst because: (1) the catalyst is not retained separately from the water to be treated, requiring additional separation steps to recover the iron, adding significant cost; (2) Fe(III) ions have a tendency to form a sludge if the pH is not tightly controlled to be between 3.0 and 4.0; (3) the reverse Fenton reactions are suppressed by the presence of excess protons in these acidic environments; (4) the reverse-Fenton reactions proceed two to three orders of magnitude more slowly than the forward Fenton reaction in the absence of UV light. The materials described herein overcome these challenges due to their innate ability to strongly bind and retain iron, and to operate at neutral pH as described in previous sections. Further, if the catalytic microparticles are used in a UV-Fenton process to accelerate POP degradation (FIG. 6B), the same UV light can drive the reverse-Fenton reactions simultaneously with the forward Fenton reaction. As shown in FIG. 7A, the simultaneity of the forward and reverse Fenton reactions obviates the need for a separate regeneration step, and catalytic hydrogel microparticles may continuously be reused if fresh hydrogen peroxide is added to drive reactions in both directions. As an aside, the reverse-Fenton reactions also produce hydroxyl radicals that can attack POPs, and are one of the reasons why the UV-Fenton process is more effective than the Fenton process without UV (FIG. 6B).

[0142] Batch experiments were performed by loading a solution of hydrogen peroxide (0.07% (w / w)) and a single POP at an environmentally relevant concentration (1 ppm) into a stirred vessel containing previously used catalytic hydrogel microparticles, to assess their ability to degrade POPs after prior use without an intervening regeneration step (see experimental section). As shown in FIG. 7B, reusing the catalytic hydrogels in this manner in day-long batch experiments did not affect the kinetics of EDOL degradation over at least 3 cycles of use. Similarly, when batch experiments were performed by loading fresh hydrogen peroxide and a POP into a stirred vessel containing used hydrogel microparticles every 3 hours, no loss of performance was observed in elimination at the end of each 3 hour cycle for all three POPs (FIGS. 7C-7E).

[0143] A zwitterionic hydrogel-based heterogenous UV-Fenton catalyst has been developed that satisfies all design requirements for a low-cost, efficient, and sustainable UV-Fenton process. Consisting of individual iron ions strongly bound to a charged and swollen hydrogel structure, the catalyst has a high effective surface and rapid mass transport properties, allowing Fenton degradation of POPs on time scales that are within an order of magnitude of classical homogenous Fenton reactions. Resistance to Fenton degradation, high retention of iron, optical transparency, and self-regeneration without loss in performance make the catalyst compatible with more efficient UV-Fenton processes and allow long-term usage. The hydrogel catalyst efficiently degraded ethinyl estradiol, a xenoestrogenic endocrine disruptor, 2,4-dichlorophenol, a chlorinated pesticide of concern, and PFOA, a model for PFAS contamination. More significantly, these high levels of degradation can be achieved using a single unit operation with minimal controls. A facile and scalable synthesis, combined with high levels of POP degradation over multiple cycles of use, make the hydrogel catalyst a promising solution to urgent problems in the elimination of recalcitrant POPs from wastewater, raw water streams, and water bodies.

[0144] Chemicals'. N,N’-methylenebis(acrylamide) (BIS), [2- (Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PSB), poly(ethylene glycol) diacrylate (PEGDA; MW 700), 2-hydroxy-2-methylpropiophenone (PI), iminodiacetic acid (IDA), glycidyl methacrylate (GMA), ferrous sulfate heptahydrate, water (HPLC-grade), acetonitrile (HPLC-grade), methanol (HPLC-grade), formic acid (LC-MS grade; LiChropur), ammonium acetate (LC-MS grade), ethinyl estradiol (EDOL), 2,4-dichlorophenol (DCP), perfluorooctanoic acid (PFOA), mineral oil, methylene blue dye (MB), and fluorescein sodium salt were purchased from Sigma- Aldrich, and used as obtained.

[0145] Synthesis of hydrogel microparticles'. First, 5.65 g of PSB, 0.25 g of BIS, and 0.5 mL of PI (photoinitiator) were dissolved in 9.5 mL of water to produce the aqueous monomer solution (FIG. 4A). This solution was processed into microparticles through an off-the-shelf microcross setup, which forms monodisperse monomer droplets of approximately 800 ± 100 pm in diameter by pinching off the flow of monomer solution using a mineral oil phase (FIG. 4A). The monomer droplets were exposed to UV light, triggering a free-radical chain-growth polymerization reaction to form hydrogel microparticles (FIG. 8).

[0146] These polymerized microparticles were then washed in deionized water to remove unreacted monomers, oligomers, and residual mineral oil. The washed microparticles were subsequently soaked in saturated ferrous sulfate heptahydrate solution (1.08M or 60% (w / w)) for 6 hours to incorporate ferrous ions into the zwitterionic structure through complexation with PSB (FIG. 4A). The iron-incorporated microparticles then undergo a final wash using deionized water to remove any free, excess iron ions that may still be present in the gel matrix; this prevents iron contamination of POP solutions used in degradation studies.

[0147] Methylene blue decomposition experiments'. To qualitatively determine the kinetics and efficacy of the hydrogel catalyst, test runs utilizing dilute methylene blue solutions were run to visually observe decomposition behavior. 600 mg of the iron-laden hydrogel was added to 5 mL of 0.05 mM (0.016 g / L) methylene blue solution and stirred continuously (FIG. 5A). Then 150 pl of 1% (w / w) hydrogen peroxide solution was injected into the reaction mixture, resulting in a 0.03% (w / w) effective hydrogen peroxide concentration in the reaction mixture. No acid was added to the reaction mixture to ensure a neutral pH of around 7 ; Fenton reactions utilizing free iron required the addition of sulfuric acid, shifting the pH closer to 3, due to the precipitation of free iron at higher pH. After approximately 10 seconds of mixing, the reaction mixture turned colorless, indicating fast and efficient MB decomposition by the Fenton catalyst (FIG. 5A).

[0148] The reaction mixture was filmed with a OnePlus 9 smartphone camera for approximately a minute. Individual frames were then extracted from the video using MATLAB and an appropriate cross-section that remained stationary within the frames and did not contain hydrogel microparticles was identified. The RGB values corresponding to each pixel are converted to HSV, and the average hue within the crosssection of interest is calculated and used to track the progress of the reaction. MATLAB code was used for video processing (process_vid.m) to obtain the kinetics data shown in FIG. 5B. Scanning electron microscopy & elemental mapping'. Samples were coated with a 5 nm Au / Pd conductive layer prior to imaging. Scanning electron microscopy images were recorded using a Zeiss Merlin High-resolution SEM with an EDX probe. Energy- dispersive X-ray spectroscopy for elemental mapping was performed at 12kV and elemental peaks were fit using the APEX software. Maps of other elements are shown in FIG. 14.

[0149] X-Ray Diffraction'. A Rigaku Smartlab X-ray diffractometer equipped with a 45 kV, 200 nA, Cu Ka source ( = 1.5406A) was used in Bragg-Brentano geometry to analyze wet Fe ion-laden hydrogels from which free water was removed under a vacuum. Tests were performed with a scan range (29) of 3°-80°, a step size of 0.1°, and at a rate of 27min. XRD data was analyzed to obtain a pair correlation function.

[0150] Synthesis of GMA-IDA: GMA-IDA was synthesized as described previously. In brief, 6.055 g IDA was dissolved in 50 mL 2M sodium hydroxide solution in water. 6.821 mL GMA was added drop wise, and the mixture was allowed to react with constant stirring in the dark at room temperature for 6 hours. The reaction was confirmed using 1H-NMR spectroscopy (FIG. 15). The appearance of peaks c,d indicates conversion. The reaction product was diluted to obtain a 0.5M solution of GMA-IDA in water and stored in the dark at 4 °C.

[0151] Synthesis of PEGDA-1DA and PSB-IDA hydrogel microparticles'. PEGDA-IDA and PSB-IDA particles were synthesized using the previously described microfluidics setup operated in the same manner. To make PEGDA-IDA microparticles, the monomer solution was obtained by mixing 1 mL PEGDA with 8.5 mL GMA-IDA solution (prepared as previously described) and 0.5 mL PI. To make PSB-IDA microparticles, the monomer solution was obtained by dissolving 5.65 g of PSB, 0.25 g of BIS, and 0.5 mL of PI in 9.5 mL GMA-IDA solution. Microparticles obtained from the microfluidics setup are washed and soaked in iron as previously described before use.

[0152] Hydrogel degradation and iron leaching'. Hydrogel degradation and iron leaching was measured using 4 g hydrogel suspended in 40 mL deionized water. 3.01 mL 1% (w / w) hydrogen peroxide was then added to obtain a 0.07% (w / w) solution that was placed in a UV-enclosure for 24 hours, thereby exposing the hydrogel to a UV-Fenton reaction in the absence of POP. At the end of the experiment, 3 mL of the supernatant was extracted for ICP-MS analysis to measure the amount of leached iron as described later. The remaining quantity of supernatant was measured and diluted to 80 mL and shipped to an external third-party facility (SimpleLab, USA) for TOC measurement to study hydrogel degradation.

[0153] 1CP-MS analysis of iron leaching'. Supernatant concentrations were measured in iron leachate samples using ICP-MS (Agilent 7900 in He mode) for metals. Prior to ICP-MS analysis, samples were filtered using a 0.2 pm syringe filter, digested for 24 hours in an equal volume of 70% nitric acid (to destroy organic matter), and the pH of overall mixture was subsequently increased with 75% of the equivalent amount of sodium hydroxide pellets. Finally, a volume of 200 ppb erbium solution in 4% nitric acid equal to the digested sample was added as an internal standard. In samples not containing organics, the internal standard was added as described without prior digestion in nitric acid. Linear least-squares calibrations were prepared using known standards and used to quantify iron concentrations.

[0154] Kinetics experiments and. reuse: 1 g of hydrogel catalyst was continuously stirred in a 50 mL POP solution with known initial concentration in a beaker at 500 rpm. Varying volumes of 1% (w / w) hydrogen peroxide solution in water were added to achieve the desired overall hydrogen peroxide concentration in the reaction mixture. The sample was then immediately placed in a UV-enclosure with the UV lamp on and continued stirring. A ThorLabs M365LP1 - 365 nm, 1350 mW (min), 1700 mA mounted LED at the maximum power setting was used as the UV source. 2 mL samples were drawn from the reaction mixture supernatant at regular intervals and stored in the dark before analysis.

[0155] No processing was required before the hydrogel catalyst was reused. The reaction vessel was emptied and the vessel and catalyst were washed with deionized water to remove any residual POP, fresh contaminant solution and hydrogen peroxide are added, and kinetics measurements were conducted as previously described.

[0156] Quantification of POP concentrations: Supernatant organic micropollutant concentrations were measured using an HPLC-MS (Agilent 1100 Series LC coupled to and Agilent 6410 Triple Quadrupole MS), adapting a previously described method. The triple quadrupole MS was operated in full scan mode to detect ions with a mass-to- charge ratio in the range 100 to 1000, and chromatograms corresponding to the micropollutants of interest were extracted during post-processing. The limit of detection of each micropollutant was the lowest concentration at which the height of the peak corresponding to that micropollutant was twice the background level.

[0157] EDOL was analyzed in positive polarization mode, and samples were injected in 100 pl volumes into an Kinetex (Phenomenex Inc.) C18 column (particle size 2.6 pm, pore size 100 A, 100 x 4.6 mm) using a gradient pump delivering 300 pl min of a water and methanol mobile phase, each containing 0.1% formic acid. The gradient, retention times, and linear least-squares calibration curves were developed using known standards.

[0158] DCP and PFOA-containing samples were analyzed in negative polarization mode, and injected in 50 pl volumes into a Zorbax eclipse XDB (Agilent Technnologies) C18 column (particle size 3.5 pm, pore size 80 A, 100 x 2.1 mm). For DCP quantification, isocratic mode was operated with a pump delivering 500 pl min'1of a 60% methanol / 40% water buffer. For PFOA quantification, a gradient pump was used delivering 150 pl min'1of a 0.2 g / E ammonium acetate in water, and 100% acetonitrile mobile phase. The gradient, retention times, and linear least-squares calibration curves were developed using known standards.

[0159] Swelling ratios'. To study the effect of using zwitterionic monomers on hydrogel mesh size, two monomer solutions were prepared:

[0160] (1) Zwitterionic hydrogel: 5.65 g PSB, 0.25 g BIS, 9.5 mF water, and 0.5 mF PI

[0161] (2) Non-zwitterionic hydrogel: 1 mF PEGDA 700, 8.5 mF water, and 0.5 mF PI The compositions of these solutions were selected so that the zwitterionic and non-zwitterionic hydrogel have the same average chain length between crosslinks, allowing for comparison on a uniform basis. The monomer solutions were poured into Petri dishes and exposed to UV light (365 nm) for 5 minutes to prepare two cylindrical hydrogel tablets, 3.5 cm in diameter, and 6 mm in height. The original mass of these tablets was recorded and they were immersed in excess deionized water for 24 hours, followed by a second immersion in fresh deionized water for another 24 hours to allow them to reach a swollen equilibrium. Dimensions and masses of the swollen state were recorded. The hydrogel tablets were subsequently dried in an oven, first at 70 °C for 6 hours, then at 70 °C under a vacuum for 6 hours, and finally at 105 °C for 36 hours. The dimensions and masses of the dry state were also recorded. All dimensions and masses are shown in Table 1 and are used to calculate the swelling ratio, which is a proxy for the mesh size of these hydrogels.

[0162] Table 1: Dimensions and masses of cylindrical non-zwitterionic and zwitterionic hydrogel tablets in various states of hydration.

[0163] Using these values, two swelling ratios were computed, which are shown in Table 2.

[0164] (1.1.1)

[0165] (1.1.2)

[0166] Table 2: Swelling ratios of non-zwitterionic and zwitterionic hydrogels.

[0167] It was observed that when non-zwitterionic and zwitterionic hydrogels tablets were synthesized to have the same cross-linking density and degree of polymerization between junctions at synthesis, the zwitterionic hydrogel tablet reached a higher degree of swelling than the non-zwitterionic hydrogel. The greater swelling implies that the zwitterionic hydrogel must have a larger mesh size than the non-zwitterionic hydrogel.

[0168] Mesh size'. Two approaches were sed to estimate the mesh size of non- zwitterionic (PEGDA) and zwitterionic (PSB) hydrogels. The classical Canal-Peppas theory evaluates mesh size as: (1.2.1)

[0169] Equation 1.2.2 corrects for the effects of junction functionality:

[0170] As can be seen in Table 3, the mesh size of zwitterionic hydrogels was estimated to be significantly larger than the non-zwitterionic hydrogels. It may also be noted that the zwitterionic hydrogel mesh size estimate is more significantly affected by the junction functionality correction due to its larger characteristic ratio Cm.

[0171] Table 3: Estimated mesh sizes of non-zwitterionic and zwitterionic hydrogels. Polymer search:

[0172] Table 4: Polymers that are and are not degraded by Fenton oxidation (*only with excess H2O2). Estimation ofPSB molecules per chelated iron ion'. The mass or number of moles of PSB added to make 16 mL of monomer solution was determined (5.65 g or 2.02 X 10"2mol). The conversion in the polymerization process is not perfect, and the added quantity should be corrected by this yield. To correct for these effects and obtain the functional moles reacted, the added amount is scaled by p1?the yield of the polymerization reaction. In prior work, it has been shown that for similar hydrogels using the same reaction setup, = 0.968 . After scaling by to obtain the number of reacted active molecules, these are then scaled down for losses during the washing process (18.8%). The concentration of PSB molecules in the hydrogel was obtained to be 9.923 X 10'4mol / mL. Due to the minimal swelling of hydrogels after synthesis, dividing by the density (2.82 g / mL) yields the moles of PSB per gram of hydrogel: 3.52 X IO"4mol / g.

[0173] The concentration of iron within the hydrogel was 0.0233% by thermogravimetric analysis, yielding the moles of iron per gram of hydrogel: 4.18 X 10'6mol / g.

[0174] Therefore, the hydrogel catalyst contains 1 iron atom for every 84.6 molecules of PSB at saturation, supporting the substantial separation between iron ions and the ability of the hydrogel to add or remove binding groups as the oxidation state of the iron changes during the Fenton and reverse-Fenton reactions.

[0175] Measurement of Young’s modulus'. 2 g of hydrogel microparticles (5.65 g PSB, 0.25 g BIS, 9.5 mL water, and 0.5 mL PI) were prepared using an off-the-shelf microcross. A TA instruments DHR-3 rheometer with parallel plate geometry (20 mm Peltier steel plate) was used in axial compression mode to axially strain the particles up to a maximum axial force / loading of 1.5 N. Care was taken to ensure that the particles formed a tightly packed monolayer between the plates, completely filling the gap, and all fluid was drained using a wipe immediately prior to measurement. Rapid measurement and the use of a solvent trap ensures that the hydrogel microparticles are fully hydrated during measurement. The force and gap between the rheometer plate and stage were recorded at equal intervals over multiple compression-relaxation cycles at equilibrium, and used to obtain the stress-strain plots shown in FIGS. 9A-9B. The Young’s modulus of the monolayer was obtained as the slope of the best-fit lines in FIGS. 9A-9B (45.19 kPa). Performing the measurement over multiple cycles mimics practical operation in a packed bed, and using multiple samples allows us to capture variation across batches. The measured modulus was much greater than the pressure experienced by a single particle in typical packed bed operation (~O(1 Pa)) .

[0176] Thermo gravimetric analysis'. TGA experiments were performed on iron-laden and iron-free PB hydrogel microparticles using a TA Instruments Thermogravimetric Analyzer 550 with a ramp rate of 2 °C / min from room temperature to 1000 °C in air. Data were normalized by the weight of the sample at 230 °C to correct for the initial weight of free and bound water in the sample and obtain iron loadings relative to the dry hydrogel mass (FIG. 10). The difference between the minimum values of the TGA curves of iron-laden and iron-free PB hydrogel microparticles yield the mass of iron per mass of dry hydrogel, accounting for the presence of impurities in the PSB samples. These minimum values were seen to occur below 1000 °C, at which point the iron is oxidized to ferric oxide. The iron concentration so obtained was then renormalized to obtain the mass of iron per mass of wet hydrogel by using the swelling data in supporting information 1.1, yielding an iron concentration of 0.023% or 233 ppm.

[0177] Analysis ofXRD data and the pair correlation function'. XRD data was collected as described previously The hydrogels contain multiple elements: C, N, O, S, H, and Fe. Of these, iron ions (Fe(II) and Fe(III)) have the largest X-ray form factor, and the XRD spectrum may be assumed to arise entirely from iron-iron scattering. Using XRD data, the pair correlation function was calculated as previously described. First, shifting to reciprocal space:

[0178] Here, 2 is the wavelength of source X-rays. The XRD data, 5(0) is transformed into reciprocal space and normalized so that S(q) -> 1 as q -> +oo (since we use a fixed wavelength source, it is not possible to access data as q -> +oo, and normalization is done as 26 -> -). The pair distribution function (r) is obtained as the Fourier transform (or inverse Fourier transform) of S(q). The constant p0is set so that (r) -> 0 as r -> 0, and normalized to obtain the pair correlation function g(r) so that ^(r) -> 1 as r -> +oo. The pair correlation function is shown in FIG. 4E.

[0179] Protocol information for LC-MS

[0180] Quantification of EDOL'. Ethinyl estradiol (EDOL) was analyzed in positive polarization mode (+3800V), and samples were injected at 100 pl volumes into an Kinetex (Phenomenex Inc.) C18 column (particle size 2.6 pm, pore size 100 A, 100 x 4.6 mm) using a gradient pump delivering 300 pl / min. A gradient was used combining water (A) and methanol (B), each containing 0.1% formic acid. The gradient is shown below in Table 5. The mass spectrum between 100 and 500 Dalton was recorded, and the extracted ion chromatogram with m / z of 297.2 was used for EDOL quantification. The peak retention time was 29.3 min.

[0181] Table 5: HPLC-MS mobile phase gradient to detect EDOL.

[0182] Quantification of PEOA'. Perfluorooctanoic acid (PFOA) was analyzed in negative polarization mode (-4500V), and injected in 50 pl volumes into a Zorbax eclipse XDB (Agilent Technnologies) C18 column (particle size 3.5 pm, pore size 80 A, 100 x 2.1 mm). A gradient pump was used delivering 150 pl / min of a 0.2 g / L ammonium acetate in water (A), and 100% acetonitrile (B) mobile phase. The gradient is shown below in Table 6. The mass spectrum between 100 and 600 Dalton was recorded, and the extracted ion chromatogram with m / z of 413.0 was used for PFOA quantification. The peak retention time is 2.5 min.

[0183] Table 6: HPLC-MS mobile phase gradient to detect PFOA.

[0184] Quantification of DCP'. DCP was analyzed in negative polarization mode (- 3500V), and injected in 50 pl volumes into a Zorbax eclipse XDB (Agilent Technnologies) C18 column (particle size 3.5 pm, pore size 80 A, 100 x 2.1 mm). For DCP quantification, isocratic mode was used with a pump delivering 500 pl / min of a 60% methanol in water buffer. The mass spectrum between 100 and 600 Dalton was recorded, and the extracted ion chromatogram with m / z of 413.0 was used for PFOA quantification. The peak retention time is 2.5 min.

[0185] Ion chromatography of fluoride ions: Fluorine ion concentrations were measured in supernatants containing PFOA degradation products using a Dionex Integrion high pressure ion-chromatography (HPIC) system (Thermo Scientific), adapting a previously described method. The system was equipped with an lonPac AG11-HC (4 x 50 mm) guard column and an lonPac AS 11-HC (4 x 250 mm) separation column. A 30 mmol / L KOH in water eluent was pumped through the system at 1 mL / min. A suppressor current of 75 mA was used, and the injection volume was 5 mL. A linear least-squares calibration was developed using known calibration samples produced by diluting Fluoride Standard for IC TraceCERT 1000 mg / 1 (SigmaAldrich, USA), and used to measure unknown concentrations in analyte samples. Measured fluorine concentrations were normalized by the total fluorine content of PFOA molecules initially loaded into the batch reactions to obtain a defluorination efficiency, shown in FIG. 13.

[0186] While several embodiments of the present disclosure have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present disclosure. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present disclosure is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the disclosure may be practiced otherwise than as specifically described and claimed. The present disclosure is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

[0187] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0188] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0189] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0190] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0191] As used herein, “wt%” is an abbreviation of weight percentage. As used herein, “at%” is an abbreviation of atomic percentage.

[0192] Some embodiments may be embodied as a method, of which various examples have been described. The acts performed as part of the methods may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include different (e.g., more or less) acts than those that are described, and / or that may involve performing some acts simultaneously, even though the acts are shown as being performed sequentially in the embodiments specifically described above.

[0193] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0194] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03

Claims

CLAIMSWhat is claimed is:

1. A hydrogel, comprising: a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged; and one or metal ions, at least some of which are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel, wherein the hydrogel is resistant to degradation: (i) at a pH greater than or equal to 3; and / or (ii) in the presence of hydrogen peroxide, UV light, the one or more metals ions, and / or one or more metal ions that are not incorporated within the volume of the hydrogel.

2. The hydrogel of claim 1, wherein the hydrogel has a mesh size of at least 1 nanometer and less than or equal to 100 nanometers.

3. The hydrogel of any one of claims 1-2, wherein at least a portion of the hydrophilic crosslinked polymer is positively charged.

4. The hydrogel of any one of claims 1-2, wherein at least a portion of the hydrophilic crosslinked polymer is negatively charged.

5. The hydrogel of any one of claims 1-2, wherein at least a portion of the hydrophilic crosslinked polymer is zwitterionic.

6. The hydrogel of any one of claims 1-2, wherein at least a portion of the hydrophilic crosslinked polymer is polar.

7. The hydrogel of any one of claims 1-6, wherein the hydrogel is in the form of a particle.

8. The hydrogel of claim 7, wherein the particle has an average characteristic dimension greater than or equal to 1 micrometer and less than or equal to 1 millimeter.

9. The hydrogel of claim 8, wherein the particle has a percent optical transmittance greater than or equal to 90% when the particle is placed 1 centimeter from a 100 W light source.

10. The hydrogel of claim 9, wherein the percent optical transmittance of the particle is greater than or equal to 95% when the particle is placed 1 centimeter from the 100 W light source.

11. The hydrogel of any one of claims 9-10, wherein the percent optical transmittance of the particle is greater than or equal to 99% when the particle is placed 1 centimeter from the 100 W light source.

12. The hydrogel of any one of claims 9-11, wherein the percent optical transmittance of the particle is greater than or equal to 99.9% when the particle is placed 1 centimeter from the 100 W light source.

13. The hydrogel of any one of claims 1-12, wherein the one or more metal ions comprise a transition metal ion.

14. The hydrogel of any one of claims 1-13, wherein the one or more metal ions comprise iron, copper, cobalt, manganese, cerium, silver, chromium, ruthenium, tungsten, molybdenum, vanadium, titanium, nickel, and / or combinations thereof.

15. The hydrogel of any one of claims 1-14, wherein the one or more metal ions comprise a cluster of metal ions.

16. The hydrogel of claim 15, wherein the cluster of metal ions comprises less than or equal to 100,000 metal ions.

17. The hydrogel of any one of claims 15-16, wherein the cluster of metal ions comprises less than or equal to 100 metal ions.

18. The hydrogel of any one of claims 1-17, wherein each of the one or metal ions are coordinated to the hydrophilic crosslinked polymer.

19. The hydrogel of any one of claims 1-18, wherein each of the one or more metal ions are individually coordinated to the hydrophilic crosslinked polymer.

20. The hydrogel of any one of claims 1-19, wherein the hydrogel is configured such that it loses less than or equal to 5 weight percent (wt.%) versus a total weight of the hydrogel when: (i) exposed to the pH greater than or equal to 3 for a period of at least 24 hours; and / or (ii) in the presence of the hydrogen peroxide, the UV light, the one or more metals ions, and / or the one or more metal ions that are not incorporated within the volume of the hydrogel for a period of 24 hours.

21. The hydrogel of any one of claims 1-20, wherein the hydrogel is configured such that it loses less than or equal to 1 wt.% versus a total weight of the hydrogel when: (i) exposed to the pH greater than or equal to 3 for the period of at least 24 hours; and / or (ii) in the presence of the hydrogen peroxide, the UV light, the one or more metals ions, and / or the one or more metal ions that are not incorporated within the volume of the hydrogel for the period of at least 24 hours.

22. The hydrogel of any one of claims 1-21, wherein the hydrogel is configured such that it loses less than or equal to 0.1 wt.% versus a total weight of the hydrogel when: (i) exposed to the pH greater than or equal to 3 for a period of at least 24 hours; and / or (ii) in the presence of the hydrogen peroxide, the UV light, the one or more metals ions, and / or the one or more metal ions that are not incorporated within the volume of the hydrogel for a period of 24 hours.

23. The hydrogel of any one of claims 1-22, wherein the hydrogel is configured to oxidize one or more organic molecules.

24. A method of oxidizing one or more organic molecules, comprising: exposing a hydrogel to the one or more organic molecules, wherein the hydrogel is resistant to degradation in the presence of hydrogen peroxide, and wherein the hydrogel comprises: a hydrophilic crosslinked polymer, wherein at least a portion of the hydrophilic crosslinked polymer is charged; and one or more metal ions, at least some of which are coordinated to the hydrophilic crosslinked polymer such that the one or more metal ions are incorporated within a volume of the hydrogel; and oxidizing the one or more organic molecules.

25. The method of claim 24, wherein the hydrogel is resistant to degradation: (i) at a pH greater than or equal to 3; and / or (ii) in the presence of UV light, the one or more metals ions, and / or one or more metal ions that are not incorporated within the volume of the hydrogel.

26. The method of any one of claims 24-25, wherein the one or more organic molecules comprise a persistent organic pollutant (POP).

27. The method of claim 26, wherein the POP is a xenoestrogen, a pesticide, and / or a per- or polyfluoroalkyl substance (PFAS).

28. The method of claim 27, wherein the xenoestrogen is ethinyl estradiol.

29. The method of any one of claims 27-28, wherein the pesticide is a chlorinated pesticide.

30. The method of any one of claims 27-29, wherein the pesticide is 2,4-dichlorophenol, diclofenac, and / or combinations thereof.

31. The method of any one of claims 27-30, wherein the PFAS is perfluorooctanoic acid (PFOA), perfluorooctanesulphonic acid (PFOS), perfluorobutanoic acid (PFBA), perfhiorobutanesulphonic acid (PFBS), perfluorohexanesulphonic acid (PFHxS), a sodium,potassium, and / or ammonium salt thereof, hexafluoropropylene oxide (HFPO), and / or combinations thereof.

32. The method of any one of claims 24-31, wherein the one or more organic molecules comprise a drug.

33. The method of claim 32, wherein the drug is aspirin, ibuprofen, and / or combinations thereof.

34. The method of claim 32, wherein the drug is an antibiotic.

35. The method of claim 34, wherein the antibiotic is tetracycline, ciprofloxacin, cefixime, amoxicillin, penicillin, streptomycin, and / or combinations thereof.

36. The method of any one of claims 24-35, wherein the one or more organic molecules comprise a dye.

37. The method of claim 36, wherein the dye is methylene blue, fluorescein, an azo dye, indigo, methyl orange, congo red, tyrian purple, an anthraquinone dye, a sulfur dye, a Sudan dye, malachite green, Allura Red AC, Amaranth, Sunset Yellow FCF, fuchsine, carmine, a triarylmethane dye, a xanthene, acridine, a carotenoid dye, a diazo dye, and / or combinations thereof.

38. The method of any one of claims 24-37, wherein the one or more organic molecules comprise a surfactant.

39. The method of any claim 38, wherein the surfactant is a Span surfactant, a Tween surfactant, a Pluronic surfactant, and / or combinations thereof.

40. The method of any one of claims 24-39, wherein the one or more organic molecules comprise a polypeptide, a protein, and / or combinations thereof.

41. The method of any one of claims 24-40, wherein the exposing comprises exposing the hydrogel to an aqueous solution comprising the one or more organic molecules.

42. The method of any one of claims 24-41, wherein the exposing comprises absorbing the one or more organic molecules from the aqueous solution into the hydrogel.

43. The method of any one of claims 24-42, wherein the oxidizing the one or more organic molecules is performed in the presence of hydrogen peroxide.

44. The method of any one of claims 24-43, wherein the oxidizing the one or more organic molecules is performed in the presence of UV light.

45. The method of any one of claims 24-44, wherein the oxidizing is performed at pH greater than or equal to 3.

46. The method of any one of claims 24-45, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 5 times without losing less than or equal to 10% of its reactivity.

47. The method of any one of claims 24-46, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 50 times without losing less than or equal to 10% of its reactivity.

48. The method of any one of claims 24-47, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 100 times without losing less than or equal to 10% of its reactivity.

49. The method of any one of claims 24-48, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 5 times without losing less than or equal50. The method of any one of claims 24-49, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 50 times without losing less than or equal to 5% of its reactivity.

51. The method of any one of claims 24-50, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules more than 100 times without losing less than or equal to 5% of its reactivity.

52. The method of any one of claims 24-51, wherein the hydrogel is capable of being reused to oxidize the one or more organic molecules without addition of one or more external acids and / or one or more metal ions that are not incorporated within a volume of the hydrogel.

53. The method of any one of claims 24-52, wherein the oxidizing the one or more organic molecules comprises producing carbon dioxide and / or water.

54. An article, comprising: the hydrogel of any one of claims 1-23.

55. The article of claim 54, wherein the article is a bed reactor.

56. The article of any one of claims 54-55, wherein the article is a packed bed reactor.

57. The article of any one of claims 54-55, wherein the article is a fluidized bed reactor.

58. The article of claim 54, wherein the article is a tank reactor.

59. The article of any one of claims 54 or 58, wherein the article is a stirred tank reactor.

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