Patent Application
20250043032
Per- and polyfluoroalkyl substances (PFASs) are fluorinated surfactants1-4 applied in industrial processes5-7 (e.g., pesticide formulations, waterproofing textiles, and oil production) and consumer products8-9 (e.g., cosmetics, firefighting foams and food packaging). Their manufacture and use have contaminated water resources around the world, and their bioaccumulative nature, toxicity at low levels of chronic exposure, and environmental persistence motivate efforts to prevent and remediate PFAS contamination.4, 10-12 Anionic perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs) are the most widely detected classes of anionic PFASs, whose structures include long-chain derivatives, such as the eight carbon perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), and short-chain derivatives, such as the four-carbon-containing perfluorobutanoic acid (PFBA) and perfluorobutanesulfonic acid (PFBS). The short-chain PFASs are now also widespread and are more mobile in the environment, and more resistant to degradation or removal efforts than long-chain PFASs.3 Conventional adsorbents, such as activated carbons (ACs),13-15 ion exchange resins,15-16 and inorganic minerals17-19 have been widely studied and applied for PFAS removal. However, these adsorbents generally suffer from shortcomings, such as moderate or low affinity for long- and short-chain PFASs, and fouling by dissolved natural organic matters and inorganic constituents found in natural and engineered water systems.20-23 As a result, there exists a need for new polymeric material as efficient adsorbents for per- and polyfluoroalkyl substances (PFASs).
Disclosed herein are mesoporous polymeric materials and methods for preparing and using the same. One aspect of the invention provides for a mesoporous polymeric material comprising a network of cyclodextrin moieties crosslinked by a plurality of crosslinks. The network comprises
or any combination thereof. A is an unsubstituted or substituted aryl or unsubstituted or substituted heteroaryl. R1 and R2 are independently —C(═O)OR4, an unsubstituted or substituted alkyl, an unsubstituted or substituted aryl, an unsubstituted or substituted heteroaryl, or hydrogen. R3 is independently selected from hydrogen, alkyl, hydroxyalkyl, alkanoyl, or carboxyalkyl. R4 is a substituted or unsubstituted alkyl,
Another aspect of the invention provides for purifying a fluid sample comprising one or more pollutants. The method comprises contacting the fluid sample with the mesoporous polymeric material as described herein. The methods disclosed herein may be used to adsorb at least 50 wt % of the total amount of the one or more pollutants in the fluid sample.
Another aspect of the invention provides for a method of preparing a mesoporous polymeric material comprising a network of cyclodextrin moieties crosslinked by a plurality of crosslinks. The method comprises contacting a functionalized cyclodextrin monomer with a comonomer in the presence of a free radical initiator under conditions sufficient to prepare the network of cyclodextrin moieties crosslinked by a plurality of crosslinks. The functionalized cyclodextrin monomer comprises
or any combination thereof. The comonomer comprises a formula of
A is an unsubstituted or substituted aryl or unsubstituted or substituted heteroaryl. R1 and R2 are independently —C(═O)OR4, an unsubstituted or substituted alkyl, an unsubstituted or substituted aryl, an unsubstituted or substituted heteroaryl, or hydrogen. R3 is independently selected from hydrogen, alkyl, hydroxyalkyl, alkanoyl, or carboxyalkyl. R4 is a substituted or unsubstituted alkyl,
These and other aspects and embodiments of the invention will be further described herein.
Non-limiting embodiments of the present invention 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. 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 invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
Disclosed herein are functionalized cyclodextrin monomers and polymers prepared from the same for water remediation. The present technology provides for a modular, permanently porous, and crosslinked functionalized CD polymers with a controllable binding environment and tunable compositions of comonomers to remove PFASs of different chain lengths and other micropollutants from water. The modularity of this platform and reliability of radical polymerization enabled a broad range of comonomers to be incorporated. This structural versatility in turn enables performance trends to be studied as a function of the adsorbent structure and water matrix.
As demonstrated in the Examples, the polymers achieved exceptional removal efficiencies of PFCAs and PFSAs at an adsorbent loading as low as 1 mg L−1. The Examples also demonstrated that removal of shorter chain PFASs that are conventionally difficult to remove. These results demonstrate that functionalized CD polymers are useful adsorbents for the remediation of anionic PFAS. Furthermore, the unprecedented control afforded by the platform allows the polymers to be tailored to target other organic micropollutants, including cationic and neutral PFAS by varying the comonomer structures.
One aspect of the technology is a mesoporous polymeric material. The term “mesoporous polymeric material” refers to porous cyclodextrin polymeric materials (P-CDPs). The P-CDPs are comprised of insoluble polymers of cyclodextrin. Cyclodextrins are macrocycles that may be inexpensively and sustainably produced from glucose. The polymers of cyclodextrin are comprised of cyclodextrin moieties that are derived from cyclodextrins. The cyclodextrin moiety(s) can be derived from naturally occurring cyclodextrins (e.g., alpha-, beta-, and gamma-, comprising 6, 7, and 8 glucose units, respectively) or synthetic cyclodextrins. The cyclodextrin moiety has at least one —O— bond derived from an OH group on the cyclodextrin from which it is derived. The cyclodextrin moieties can comprise 3-20 glucose units, including 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 glucose units, inclusive of all ranges therebetween. In many embodiments, the cyclodextrin moieties are derived from starch, and comprise 6-9 glucose units. The polymeric materials may comprise two or more different cyclodextrin moieties. In particular embodiments, the P-CDP is comprised of insoluble polymers of beta-cyclodextrin (beta-CD).
The P-CDP can also comprise cyclodextrin derivatives or modified cyclodextrins. The derivatives of cyclodextrin consist mainly of molecules wherein some of the OH groups are converted to OR groups. The cyclodextrin derivatives can, for example, have one or more additional moieties that provide additional functionality, such as desirable solubility behavior and affinity characteristics. Examples of suitable cyclodextrin derivative materials include methylated cyclodextrins (e.g., RAMEB, randomly methylated beta-cyclodextrins), hydroxyalkylated cyclodextrins (e.g., hydroxypropyl-cyclodextrin and hydroxypropyl-gamma-cyclodextrin), acetylated cyclodextrins (e.g., acetyl-gamma-cyclodextrin), reactive cyclodextrins (e.g., chlorotriazinyl-CD), branched cyclodextrins (e.g., glucosyl-beta-cyclodextrin and maltosyl-cyclodextrin), sulfobutyl-cyclodextrin, and sulfated cyclodextrins. For example, the cyclodextrin moiety further comprises a moiety that binds (e.g., with specificity) a metal such as arsenic, cadmium, copper, or lead.
The P-CDP can also comprise cyclodextrin derivatives as disclosed in U.S. Pat. No. 6,881,712 including, e.g., cyclodextrin derivatives with short chain alkyl groups such as methylated cyclodextrins, and ethylated cyclodextrins, wherein R is a methyl or an ethyl group; those with hydroxyalkyl substituted groups, such as hydroxypropyl cyclodextrins and/or hydroxyethyl cyclodextrins, wherein R is a CH2—CH(OH) CH3 or a XH2CH2—OH group; branched cyclodextrins such as maltose-bonded cyclodextrins; cationic cyclodextrins such as those containing 2-hydroxy-3-(dimethylamino)propyl ether, wherein R is CH2—CH(OH)—CH2N(CH3)2 which is cationic at low pH; quaternary ammonium, e.g., 2-hydroxy-3-(trimethylammonio)propyl ether chloride groups, wherein R is CH2—CH(OH) CH2N+ (CH3)3Cl−; anionic cyclodextrins such as carboxymethyl cyclodextrins, cyclodextrin sulfates, and cyclodextrin succinylates; amphoteric cyclodextrins such as carboxymethyl/quaternary ammonium cyclodextrins; cyclodextrins wherein at least one glucopyranose unit has a 3-6-anhydro-cyclomaltostructure, e.g., the mono-3-6-anhydrocyclodextrins, as disclosed in “Optimal Performances with Minimal Chemical Modification of Cyclodextrins”, F. Diedaini-Pilard and B. Perly, The 7th International Cyclodextrin Symposium Abstracts, April 1994, p. 49 said references being incorporated herein by reference; and mixtures thereof. Other cyclodextrin derivatives are disclosed in U.S. Pat. No. 3,426,011, Parmerter et al., issued Feb. 4, 1969; U.S. Pat. Nos. 3,453,257; 3,453,258; 3,453,259; and 3,453,260, all in the names of Parmerter et al., and all issued Jul. 1, 1969; U.S. Pat. No. 3,459,731, Gramera et al., issued Aug. 5, 1969; U.S. Pat. No. 3,553,191, Parmerter et al., issued Jan. 5, 1971; U.S. Pat. No. 3,565,887, Parmerter et al., issued Feb. 23, 1971; U.S. Pat. No. 4,535,152, Szejtli et al., issued Aug. 13, 1985; U.S. Pat. No. 4,616,008, Hirai et al., issued Oct. 7, 1986; U.S. Pat. No. 4,678,598, Ogino et al., issued Jul. 7, 1987; U.S. Pat. No. 4,638,058, Brandt et al., issued Jan. 20, 1987; and U.S. Pat. No. 4,746,734, Tsuchiyama et al., issued May 24, 1988; all of said patents being incorporated herein by reference.
The term cyclodextrin may refer to any of the known cyclodextrins such as unsubstituted cyclodextrins containing from six to twelve glucose units, especially, alpha cyclodextrin, beta-cyclodextrin, gamma-cyclodextrin and/or their derivatives and/or mixtures thereof. The alpha-cyclodextrin consists of six glucose units, the beta-cyclodextrin consists of seven glucose units, and the gamma-cyclodextrin consists of eight glucose units arranged in donut-shaped rings. The specific coupling and conformation of the glucose units give the cyclodextrins rigid, conical molecular structures with hollow interiors of specific volumes. The “lining” of each internal cavity is formed by hydrogen atoms and glycosidic bridging oxygen atoms; therefore, this surface is fairly hydrophobic. The unique shape and physical chemical properties of the cavity enable the cyclodextrin molecules to absorb (form inclusion complexes with) organic molecules or parts of organic molecules which can fit into the cavity.
As used herein, the term “beta-cyclodextrin” refers to a cyclic oligosaccharide consisting of seven glucose subunits joined by α-(1,4)glycosidic bonds forming a truncated conical structure. Beta-cyclodextrin has a molecular structure of:
Each R may be independently selected from hydrogen, alkyl, hydroxyalkyl, alkanoyl, carboxyalkyl, or moiety capable of reacting to prepare the mesoporous polymeric material. In some embodiments, the moiety capable of reacting to prepare the mesoporous polymeric material is a stryenic double bond.
The terms “crosslink” refers to a monomer capable of forming a covalent linkage between one or more cyclodextrins or polymers. For example, if the crosslinker reacts at the end of the polymer it may covalently react with one cyclodextrin moiety of the polymer (e.g., via the styrenic double bond of the functionalized cyclodextrin described herein). The crosslink may or may not further react with other monomers or cyclodextrin units or polymers. For example, the crosslink may be bound to 1, 2, 3, or 4+ monomers or functionalized cyclodextrin units or polymers.
The mesoporous polymeric material comprises a network of cyclodextrin moieties crosslinked by a plurality of crosslinks. The network comprises
or any combination thereof. The wavy lines surrounding the glucose subunit of the cyclodextrin moiety indicate the points where the cyclodextrin moiety is repeated to form the CD moiety. Each of the glucose subunits may be independently functionalized. Suitably some or all of the glucose subunits may be functionalized with one or more reactive moieties for forming the network. The wavy lines surrounding the ethylene having pendant groups extending therefrom indicate the points where a polymeric unit may be repeated.
In some embodiments, A is an unsubstituted or substituted aryl or unsubstituted or substituted heteroaryl. In some embodiments, A is phenyl.
In some embodiments, R1 and R2 are independently —C(═O)OR4 an unsubstituted or substituted alkyl, an unsubstituted or substituted aryl, an unsubstituted or substituted heteroaryl, or hydrogen. R4 may be a substituted or unsubstituted alkyl. Optionally, R4 may be substituted with an amine or ammonium moiety. In some embodiments, R1 and R2 are independently selected from ethyltrimethylammonium, methyl, phenyl, or hydrogen. In some embodiments, R1 and R2 are methyl and —C(═O)OCH2CH2N(CH3)3. In some embodiments, R1 and R2 are methyl and —C(═O)OCH3. In some embodiments, R1 and R2 are hydrogen and phenyl.
In some embodiments, R3 is independently selected from hydrogen, alkyl, hydroxyalkyl, or alkanoyl. In some embodiments, R3 is hydrogen.
The term “aryl” refers to cyclic, aromatic hydrocarbon groups that have 1 to 3 aromatic rings, including monocyclic or bicyclic groups such as phenyl, biphenyl or naphthyl. Where containing two aromatic rings (bicyclic, etc.), the aromatic rings of the aryl group may be joined at a single point (e.g., biphenyl), or fused (e.g., naphthyl). The aryl group may be optionally substituted by one or more substituents, e.g., 1 to 5 substituents, at any point of attachment. The substituents can themselves be optionally substituted. Furthermore, when containing two fused rings the aryl groups herein defined may have an unsaturated or partially saturated ring fused with a fully saturated ring. Exemplary ring systems of these aryl groups include, but are not limited to, phenyl, biphenyl, naphthyl, anthracenyl, phenalenyl, phenanthrenyl, indanyl, indenyl, tetrahydronaphthalenyl, tetrahydrobenzoannulenyl, and the like.
The term “heteroaryl” refers to a monovalent monocyclic or polycyclic aromatic radical of 5 to 18 ring atoms or a polycyclic aromatic radical, containing one or more ring heteroatoms selected from N, O, or S, the remaining ring atoms being C. Heteroaryl as herein defined also means a polycyclic (e.g., bicyclic) heteroaromatic group wherein the heteroatom is selected from N, O, or S. The aromatic radical is optionally substituted independently with one or more substituents described herein. The substituents can themselves be optionally substituted. Examples include, but are not limited to, benzothiophene, furyl, thienyl, pyrrolyl, pyridyl, pyrazinyl, pyrazolyl, pyridazinyl, pyrimidinyl, imidazolyl, isoxazolyl, oxazolyl, oxadiazolyl, pyrazinyl, indolyl, thiophen-2-yl, quinolyl, benzopyranyl, isothiazolyl, thiazolyl, thiadiazolyl, thieno[3,2-b]thiophene, triazolyl, triazinyl, imidazo[1,2-b]pyrazolyl, furo[2,3-c]pyridinyl, imidazo[1,2-a]pyridinyl, indazolyl, pyrrolo[2,3-c]pyridinyl, pyrrolo[3,2-c]pyridinyl, pyrazolo[3,4-c]pyridinyl, benzoimidazolyl, thieno[3,2-c]pyridinyl, thieno[2,3-c]pyridinyl, thieno[2,3-b]pyridinyl, benzothiazolyl, indolyl, indolinyl, indolinonyl, dihydrobenzothiophenyl, dihydrobenzofuranyl, benzofuran, chromanyl, thiochromanyl, tetrahydroquinolinyl, dihydrobenzothiazine, dihydrobenzoxanyl, quinolinyl, isoquinolinyl, 1,6-naphthyridinyl, benzo[de]isoquinolinyl, pyrido[4,3-b][1,6]naphthyridinyl, thieno[2,3-b]pyrazinyl, quinazolinyl, tetrazolo[1,5-a]pyridinyl, [1,2,4]triazolo[4,3-a]pyridinyl, isoindolyl, pyrrolo[2,3-b]pyridinyl, pyrrolo[3,4-b]pyridinyl, pyrrolo[3,2-b]pyridinyl, imidazo[5,4-b]pyridinyl, pyrrolo[1,2-a]pyrimidinyl, tetrahydropyrrolo[1,2-a]pyrimidinyl, 3,4-dihydro-2H-1/v-pyrrolo[2,1-bjpyrimidine, dibenzo[b,d]thiophene, pyridin-2-one, furo[3,2-c]pyridinyl, furo[2,3-c]pyridinyl, 1H-pyrido[3,4-b][1,4]thiazinyl, benzooxazolyl, benzoisoxazolyl, furo[2,3-b]pyridinyl, benzothiophenyl, 1,5-naphthyridinyl, furo[3,2-b]pyridine, [1,2,4]triazolo[1,5-a]pyridinyl, benzo[1,2,3]triazolyl, imidazo[1,2-a]pyrimidinyl, [1,2,4]triazolo[4,3-b]pyridazinyl, benzo[c][1,2,5]thiadiazolyl, benzo[c][1,2,5]oxadiazole, 1,3-dihydro-2H-benzo[d]imidazol-2-one, 3,4-dihydro-2H-pyrazolo[1,5-b][1,2]oxazinyl, 4,5,6,7-tetrahydropyrazolo[1,5-ajpyridinyl, thiazolo[5,4-d]thiazolyl, imidazo[2,1-b][1,3,4]thiadiazolyl, thieno[2,3-b]pyrrolyl, 3H-indolyl, and derivatives thereof. Furthermore, when containing two fused rings the heteroaryl groups herein defined may have an unsaturated or partially saturated ring fused with a fully saturated ring.
The term “alkyl” refers to a straight chain or branched saturated chain having from 1 to 10 carbon atoms. Representative saturated alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, butyl, isobutyl, t-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl and the like, and longer alkyl groups, such as heptyl, and octyl and the like. An alkyl group can be unsubstituted or substituted. Alkyl groups containing three or more carbon atoms may be straight or branched. As used herein, “lower alkyl” means an alkyl having from 1 to 6 carbon atoms.
As used herein, the term “—C(═O)OR4” refers to a structural moiety of
As used herein, the term “ethyltrimethylammonium” refers to a structural moiety of
As used herein, the term “hydroxyalkyl” refers to a hydroxy derivative of an alkylene group (-alkylene-OH).
The term “alkylene” or “alkylenyl” refers to a divalent radical derived from a straight or branched, saturated alkyl chain, for example, of 1 to 10 carbon atoms or of 1 to 6 carbon atoms (C1-C6 alkylenyl) or of 1 to 4 carbon atoms or of 1 to 3 carbon atoms (C1-C3 alkylenyl) or of 2 to 6 carbon atoms (C2-C6 alkylenyl). Examples of C1-C6 alkylenyl include, but are not limited to, —CH2—, —CH2CH2—, —C(CH3)2CH2CH2CH2—, —C(CH3)2CH2CH2—, —CH2CH2CH2CH2—, and —CH2CH(CH3)CH2—.
As used herein, the term “alkanoyl” refers to a moiety having a structure of —C(═O)—R, wherein R group is an alkyl.
As used herein, the term “carboxyalkyl” refers to a carboxyl derivative of an alkylene group (-alkylene-C(═O)OH).
In some embodiments, the mesoporous polymeric material has a BET surface area greater than 200 m2 g−1. In some embodiments, the mesoporous polymeric material has a BET surface area greater than 210 m2 g−1, greater than 220 m2 g−1, greater than 230 m2 g−1, greater than 240 m2 g−1, greater than 250 m2 g−1, greater than 260 m2 g−1, greater than 270 m2 g−1, greater than 280 m2 g−1, greater than 290 m2 g−1, or greater than 3000 m2 g−1.
As used herein, the term “BET surface area” refers to the specific surface area of a material evaluated by the BET (Brunauer, Emmett and Teller) theory. The specific surface area is expressed in units of area per mass of sample (m2/g). The specific surface area of a material is determined by the physical adsorption of a gas (typically nitrogen, krypton, or argon) onto the surface of the sample at cryogenic temperatures (typically liquid nitrogen or liquid argon temperatures). The choice of gas to be used is dependent on the expected surface area and the properties of the sample. Once the amount of adsorbate gas has been measured (either by a volumetric or continuous flow technique), calculations which assume a monomolecular layer of the known gas are applied. BET surface area analysis must be done in the linear region of the BET plot, which could be systematically evaluated using the Rouquerol transform.
In some embodiments, the mesoporous polymeric material is prepared from a functionalized cyclodextrin monomer comprising
or any combination thereof and comonomer comprising
In some embodiments, the comonomer and functionalized cyclodextrin monomer are incorporated into the mesoporous polymeric material in a ratio of 1:1 to 4:1. In some embodiments, the comonomer and functionalized cyclodextrin monomer are incorporated in a ratio of 1.2:1 to 3.8:1, 1.4:1 to 3.6:1, 1.6:1 to 3.4:1, 1.8:1 to 3.2:1, 2:1 to 3:1, 2.2:1 to 2.8:1, or 2.4:1 to 2.6:1.
Another aspect of the technology is to provide a method of purifying a fluid sample comprising one or more pollutants. The method comprises contacting the fluid sample with the mesoporous polymeric material described herein. The methods allow for at least 50 wt % of the total amount of the one or more pollutants in the fluid sample is adsorbed by the mesoporous polymeric material. In some embodiments, at least 55 wt %, at least 60 wt %, at least 65 wt %, at least 70 wt %, at least 75 wt %, at least 80 wt %, at least 85 wt %, at least 90 wt %, or at least 95 wt % of the total amount of the one or more pollutants in the fluid sample is adsorbed by the mesoporous polymeric material.
As used herein, the term “adsorbent” refers to solid polymeric materials as described herein which remove contaminants or pollutants, typically but not exclusively organic molecules, from a fluid medium such as a liquid (e.g., water) or a gas (e.g., air or other commercially useful gases such as nitrogen, argon, helium, carbon dioxide, anesthesia gases, etc.). Such terms do not imply any specific physical mechanism (e.g., adsorption vs. absorption).
As used herein, the term “fluid sample” refers to liquid sample such as drinking water, wastewater, ground water, aqueous extract from contaminated soil, or landfill leachate.
In some embodiments, the pollutant is an anionic micropollutant. In some embodiments, the anionic micropollutant is a perfluorinated alkyl compound. In some embodiments, the perfluorinated alkyl compound is selected from PFCA, PFSA, or combinations thereof.
As used herein, the term “micropollutant” refers to chemicals present in water resources at ng L−1 to μg L−1 concentrations as a consequence of human activities. Concerns about their negative effects on human health and the environment motivate the development of technologies that remove MPs more effectively. Micropollutants encompass a range of organic and inorganic pollutants of anthropogenic origin. Micropollutants occur above natural background levels due to human activity and may persistent in the environment for decades or centuries do to slow degradation. Micropollutants may be characterized by their use or chemical characteristics. Micropollutants may include industrial chemicals (such as flame retardants or surfactants, per- and polyfluoroalkyl substances (PFAS)), pharmaceuticals, food and beverage additives, or agricultural chemicals. Micropollutant (MP) span a wide variety of physiochemical properties including surface charge, size, and chemical functionality. Charged MPs can be cationic, anionic, or zwitterionic and are typically difficult to remove in the presence of complex matrix constituents like natural organic matter (NOM) using conventional adsorption materials like activated carbon.
As used herein, the term “PFAS” refers to per- and polyfluoroalkyl substances. PFAS are a group of chemicals used to make fluoropolymer coatings and products that resist heat, oil, stains, grease, and water. Fluoropolymer coatings can be in a variety of products. These include clothing, furniture, adhesives, food packaging, heat-resistant non-stick cooking surfaces, and the insulation of electrical wire. PFAS are also used in many other consumer, commercial, and industrial products, including aqueous film forming foam (AFFF), which is used to extinguish fires. Many PFAS are a concern because they do not break down in the environment, can move through soils and contaminate drinking water sources, build up (bioaccumulate) in fish and wildlife. PFAS have been found in rivers and lakes and in many types of animals on land and in the water.
Anionic PFASs present a particular environmental problem because of their resistance to biodegradation or chemical transformation and correlation to negative health effects. PFASs have been used in the formulations of thousands of consumer goods and are present in aqueous film-forming foam (AFFF) formulations used to suppress aviation fires in training scenarios. As a result, they have contaminated surface and ground waters near thousands of airports and military installations. In 2018, the Environmental Working Group reported that over 110 million people in the United states were exposed to drinking water with PFAS concentrations above 2.5 ng L−1. PFASs have been linked to cancers, liver damage, thyroid disease and other health problems.
As used herein, the term “PFCA” refers to perfluorinated carboxylic acids (PFCAs), or perfluoroalkylcarboxylic acids. PFCAs are compounds of the formula CnF(2n+1)CO2H. The simplest example is trifluoroacetic acid. These compounds are organofluorine analogues of ordinary carboxylic acids, but they are stronger by several pKa units and they exhibit great hydrophobic character.
As used herein, the term “PFSA” refers to perfluorosulfonic acids and are chemical compounds of the formula CnF(2n+1)SO3H. The simplest example of a perfluorosulfonic acid is the trifluoromethanesulfonic acid.
Another aspect of the technology is to provide a method of preparing a mesoporous polymeric material comprising a network of cyclodextrin moieties crosslinked by a plurality of cyclodextrin branch units. The method comprises contacting a functionalized cyclodextrin monomer with a comonomer in the presence of a free radical initiator under conditions sufficient to prepare the network of cyclodextrin moieties crosslinked by a plurality of cyclodextrin branch units, wherein the network comprises Formula I.
In some embodiments, the free radical initiator is AIBN. AIBN is the chemical azobisisobutyronitrile and has a CAS No. of 78-67-1. Other examples of suitable free radical initiators for the methods of preparing the mesoporous polymeric material described herein include, but are not limited to, AMBN, ADVN, ACVA, dimethyl 2,2′-azobis(2-methylpropionate), AAPH, 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, TBIHP, α,α-Dimethylbenzyl hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, BPO, dicyandiamide, cyclohexyl tosylate, diphenyl(methyl)sulfonium tetrafluoroborate, benzyl(4-hydroxyphenyl)-methylsulfonium hexafluoroantimonate, (4-hydroxyphenyl)methyl-(2-methylbenzyl)sulfonium hexafluoroantimonate, the atom transfer radical polymerization catalysts and initiators described in Chem. Rev. 2001, 101, 9, 2921-2990, the xanthate chain transfer agent/initiator described in Macromolecules 2017, 50, 19, 7433-7447, and nitroxide-based initiators described in pChem Record, 2005, 5, 27-35 and p Polymer Reviews, 2011, 51, 2, 104-137.
In some embodiments, the molar ratio of the functionalized cyclodextrin monomer to the comonomer is from 1:10 to 2:1. In some embodiments, the molar ratio of the functionalized cyclodextrin monomer to the comonomer is from 1:9 to 1:1, from 1:8 to 1:1, from 1:7 to 1:1, from 1:6 to 1:1, from 1:5 to 1:1, from 1:4 to 1:1, from 1:3 to 1:1, or from 1:2 to 1:1.
In some embodiments, the conditions comprise a reaction temperature from 40° C. to 100° C. In some embodiments, the conditions comprise a reaction temperature from 60° C. to 100° C., 70° C. to 90° C., or from 75° C. to 85° C.
In some embodiments, the conditions comprise a reaction time of less than 1.5 hours, or less than 1.3 hours, or less than 1.1 hours.
In some embodiments, the conditions comprise a reaction solvent selected from dimethylformamide. Other examples of suitable solvents for the methods of preparing the mesoporous polymeric material described herein include, but are not limited to, water, toluene, benzene, acetonitrile, acetone, ethyl acetate, methanol, N-methyl-2-pyrrolidinone, and tetrahydrofuran.
In some embodiments, the network of cyclodextrin moieties crosslinked by a plurality of crosslinks is produced in a yield of greater than 90%. In some embodiments, the network of cyclodextrin moieties crosslinked by a plurality of crosslinks is produced in a yield of greater than 92%, greater than 94%, greater than 96%, greater than 98%, or greater than 99%.
In some embodiments, the method further comprises extraction of the network of cyclodextrin moieties crosslinked by a plurality of crosslinks in methanol. In some embodiments, the method further comprises activation of the network of cyclodextrin moieties crosslinked by a plurality of crosslinks by supercritical carbon dioxide. In some embodiments, activation happens after extraction. As used herein, the term “supercritical carbon dioxide” refers to the fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.
Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”
As used herein, “about”, “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus ≤10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.
As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising.” The terms “comprise” and “comprising” should be interpreted as being “open” transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms “consist” and “consisting of” should be interpreted as being “closed” transitional terms that do not permit the inclusion additional components other than the components recited in the claims. The term “consisting essentially of” should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
E.; Dichtel, W. R., Cross-linker Chemistry Determines the Uptake Potential of Perfluorinated Alkyl Substances by β-Cyclodextrin Polymers. Macromolecules 2019, 52 (10), 3747-3752.
Disclosed herein is a CD polymer platform in which styrene groups are covalently attached to β-CD to form a discrete monomer that is amenable to radical polymerization. A β-CD polymer copolymerized with a methacrylic monomer bearing a cationic functional group achieved nearly 100% removal for eight anionic PFASs at an exceedingly low adsorbent loading of 1 mg L−1, which is at least an order of magnitude lower than what has been explored in previous studies. Furthermore, when the adsorbents were studied in a challenging salt matrix, it was observed that long-chain PFAS adsorption was controlled by a complementary interplay of hydrophobic and electrostatic interactions, whereas short-chain PFASs primarily relied on electrostatic interactions. These materials allow for anionic PFAS removal, and new compositions can be tailored using the versatility of radical polymerization to simultaneously target PFAS and other classes of micropollutants in the future.
The Example demonstrates a structurally well-defined and tunable approach to access porous β-CD polymers that offers superior PFAS removal performance as well as insight into the interactions that drive short- and long-chain PFAS removal. The approach involves copolymerizing a styrene-functionalized β-CD derivative with various styrenic or methacrylic comonomers to give permanently porous, crosslinked molecules with a more uniform β-CD binding environments and easily tunable compositions of hydrophobic or charged comonomers. The first polymers based on these design principles were evaluated for their ability to bind seven PFCAs and four PFSAs of different chain lengths and in different water matrices to elucidate the relative importance of the β-CD interactions, conventionally thought to be hydrophobic, and electrostatic interactions between anionic PFASs and cations embedded in one of the polymer networks. These Examples demonstrate that a β-CD adsorbent containing a cationic functional group exhibits exceptional removal of PFASs with different chain length from nanopure water at an exceedingly low adsorbent loading of 1 mg L−1 which is at least an order of magnitude lower than what has been explored in previous studies. The changes in removal efficiency for both long- and short-chain PFASs as a function of salt concentration provided insight into the combined roles of charge and β-CD binding sites for PFAS binding. These studies establish the styrene-functionalized β-CD monomer as a highly promising building block for β-CD adsorbents.
Seven styrene groups were installed at the 6′ position of each β-CD subunit, effectively replacing primary alcohol groups (C-6) using approaches modified from Rojas and coworkers.41 First, the primary alcohols were selectively substituted with iodines following established protocols, yielding 1 (
The 1H NMR spectrum of 3 indicated the successful installation of styrene groups, based on the appearance of resonances in the 5.0-7.5 ppm region as well as the disappearance of thiol S—H resonance at 2.16 ppm.41 The integrations of the aromatic resonances (7.0-7.5 ppm) relative to the β-CD resonance at 5.0 ppm was consistent with seven styrene groups per β-CD (
The styrene groups of 3 are potentially compatible with hundreds of commercially available vinyl comonomers as well as many radical polymerization methods. This versatility will be advantageous in targeting a broad scope of micropollutants in the future.24, 43 For this study, we polymerized 3 using azobisisobutyronitrile (AIBN) as a free radical initiator. We used these conditions to prepare three polymers based on 3: a styrene copolymer 4, a methyl methacrylate copolymer 5, and a cationic methacrylate copolymer 6. Polymers 4, 5, and 6 were synthesized using similar procedures by heating 3, the comonomer, and AIBN in DMF for 1 h, with increased viscosity of the solution developing within 15 min. The crosslinked polymer was subjected to continuous liquid/solid extraction in methanol for approximately 14 h. Following extraction, the polymers were activated by supercritical CO2 washing and isolated in high yields at multigram scales (
Polymers 4, 5, and 6 formed porous and crosslinked networks with permanent surface charge. Solid-state cross-polarization magic angle spinning 13C NMR spectroscopy confirmed the incorporation of comonomers in 4, 5, and 6 (
We first evaluated the removal performances of polymers 4, 5, and 6 at an adsorbent loading of 10 mg L−1 for 4-10 carbon PFCAs (initial concentration of 1 μg L−1 for each compound) in a nanopure (NP) water matrix and in a 1 mM Na2SO4 (SS) matrix (
The removal of four carbon PFBA by 6 was inhibited substantially from 99% to 21% in SS matrix, suggesting that electrostatic interactions play a significant role in short-chain PFCA removal. We attribute the interference to either direct-site competition in which inorganic anions compete with anionic PFCAs for adsorption sites, or the increased screening that attenuates electrostatic interactions at increased electrolyte concentrations.17, 19, 31 Notably, the removal of 6-10 carbon PFCAs was less inhibited in the SS matrix than that of shorter chain derivatives. The removal of six carbon PFHxA decreased from 99% to 87%, and the removal of 8-10 carbon PFCAs were nearly unaffected. The decreased sensitivity of longer chain PFCAs to ionic strength suggests that hydrophobic interactions between the perfluoroalkyl tails, the hydrophobic portions of the polymer, and the β-CD inner cavity, play a relatively large role in longer chain PFCA removal. Alternatively, it is possible that these hydrophobic interactions increase in energy at higher ionic strength as PFCA and electrostatic interactions are attenuated. On the other hand, the performance of adsorbents 4 and 5 was significantly enhanced for most PFCAs, except four carbon PFBA, with longer chain PFCAs experiencing more profound enhancement. For instance, the removal of ten carbon PFDA increased from 7% to 34% by 4 and from 1% to 39% by 5. We attribute this enhancement to a screening effect that reduces the repulsion between negatively charged surfaces of 4 or 5, and the anionic PFCAs.17, 19, 31 Additionally, this enhancement may also result from a salting out effect, in which the presence of inorganic ions decreased the solubility of organic molecules and increased hydrophobic interactions for adsorbents 4 and 5 and long-chain PFCAs.1, 47
To better investigate the magnitude of inhibitory or enhancement effects for the same concentration of PFCA in NP and SS matrices, adsorbent 6 loading was adjusted from 10 mg L−1 to 1 mg L−1 (
The inhibitory effect of inorganic ions on short-chain PFCAs and PFSA is apparent at a lower adsorbent 6 loading in SS matrix, with decreased removal performance as a function of decreasing fluoroalkyl chain length for both PFCAs and PFSAs. The removal of shorter chain PFCAs and PFSAs experienced significantly greater removal interference from inorganic ions than longer-chain analogues. The removal of four carbon PFBA decreased from 57% to 1% and five carbon PFPeA decreased from 84% to 12%. The virtually complete inhibition of adsorbent 6 implies that the removal of shorter-chain PFCAs relies heavily on electrostatic interactions. Four carbon and five carbon PFSA removals were less inhibited, with removals decreasing from 94% to 38% and 97% to 64%, respectively. The removal of longer-chain PFCAs and PFSAs were weakly inhibited. The removal of eight carbon PFOS decreased from 97% to 79% and the removal of ten carbon PFDA decreased from 97% to 65%. As noted previously, the uptake of longer-chain PFAS was less attenuated because of the more pronounced hydrophobic interaction with the β-CD cavities. Assuming that electrostatic attraction is rendered ineffective in the SS matrix, such as the case of four carbon PFBA, hydrophobic interactions become the primary interactions for removal. In NP matrix, 96% of PFOA was removed by adsorbent 6, whereas the removal decreased to 48% in SS matrix. This difference of approximately 50% in removal performance hints at a complementary nature of electrostatic and hydrophobic interactions.
Monovalent and divalent inorganic ions were evaluated to further explore the importance of observed adsorption inhibition. We selected the following salts and concentrations: 1 mM Na2SO4 (SS), 2 mM NaCl (SC), and 1 mM CaCl2) (CC) in order to generate comparable data with 2 mM of monovalent sodium or chloride ions and 1 mM of divalent sulfate or calcium ions (
In summary, a modular, permanently porous, and crosslinked styrene-functionalized β-CD polymers with a controllable binding environment and tunable compositions of comonomers is used to remove PFASs of different chain lengths from water. The modularity of this platform and reliability of radical polymerization enabled a broad range of comonomers to be incorporated. This structural versatility in turn enables performance trends to be studied as a function of the adsorbent structure and water matrix. Adsorbent 6, with its cationic comonomer, achieved exceptional removal efficiencies of PFCAs and PFSAs at an adsorbent loading as low as 1 mg L−1. The inhibition effect observed in SS matrix revealed a complementary interplay of hydrophobic and electrostatic interactions between the adsorbent and PFASs as a function of fluorocarbon chain lengths. We demonstrated that removal of shorter chain PFASs that are conventionally difficult to remove relies most strongly on electrostatic interactions, which are disrupted when salts are present in the matrix. The removal of longer chain PFASs is achieved through both hydrophobic and electrostatic interactions. These results demonstrate that styrene-functionalized β-CD polymers are promising adsorbents for the remediation of anionic PFAS. Furthermore, the materials might be tailored to target other organic micropollutants, including cationic and neutral PFAS by varying the comonomer structures.
β-Cyclodextrin (97%) was provided by Wacker Chemical and dried at 80° C. under high vacuum prior to monomer synthesis. Iodine (>99.8%), triphenylphosphine (99%), styrene (>99%), [2-(Methacryloyloxy)ethyl]trimethylammonium chloride solution (MATMA, 80% in H2O), 2,2′-Azobis(2-methylpropionitrile) (AIBN, 98%), sodium sulfate, and calcium chloride were purchased from Sigma Aldrich. Sodium chloride was purchased from Fisher Scientific. The chemicals were stored at room temperature and used as received. Two PFAS mixtures of anionic PFASs (PFC-MXA and PFS-MXA) and one mixture of PFAS isotope-labelled internal standards (ILISs) (MPFAC-MXA) were purchased from Wellington Laboratories, Inc. See PFAS and Internal Standards (Section F, Table 5) for a detailed list of the two PFAS mixtures and internal standards. For PFAS mixture preparation, see descriptions in that section.
Critical Point Dryer: Activation of polymers by supercritical CO2 washing was performed on a Leica EM CPD 300. The polymer samples were stored in teabags for both Soxhlet extraction and supercritical CO2 washing. After 14 h of Soxhlet extraction in methanol, the polymer samples were immediately transferred to the drying chamber of the critical point dryer (samples contain residual methanol). The drying chamber was cooled to 15° C. and filled with CO2 at the “slow” setting with 120 s delay. After the delay, CO2 exchange occurred at the speed setting of “5” for 20 cycles. The samples were then cooled to 40° C. on the “slow” setting and the pressure in the chamber was also relieved on the “slow 50%” setting.
Nuclear Magnetic Resonance (NMR) Spectroscopy: Solution 1H and 13C NMR spectra were acquired on a Bruker AvanceIII-500 MHz spectrometer with a TXO 5 mm Prodigy probe w/Z-Gradient, or a Bruker AdvanceIII-500 MHz spectrometer with a CryoProbe 5 mm DCH w/Z-Gradient. All solution spectra were recorded at 25° C., and calibrated using DMSO-d6 as an internal reference, 2.50 ppm for 1H NMR and 39.52 ppm for 13C NMR. 1H NMR data are reported as follows: chemical shift, multiplicity (d=doublet, dd=doublet of doublets, m=multiplet), and integration.
Solid-State Cross-Polarization Mass Angle Spinning 13C NMR spectra were acquired on a Bruker AvanceIII HD 400 MHz spectrometer with a 4 mm HX probe w/Z-Gradient. All solid-state NMR spectra were recorded at 25° C., and calibrated using adamantane as an external reference at 38.3 ppm for 13C NMR. The reference was converted to tetramethylsilane at 0.00 ppm. The sample spinning rate was controlled by a Bruker pneumatic MAS unit at 10 kHz, and 2048 scans were collected for each sample.
Fourier-Transform Infrared (FTIR) Spectroscopy: FTIR data were collected at room temperature on a Bruker Tensor 37 FTIR Spectrometer equipped with a Mid IR detector and KBr beam splitter. The spectrum was collected in attenuated total reflectance mode in the range of 3600 to 600 cm1. The data were averaged over 32 scans. The OPUS software was used for the data acquisition.
High-Resolution Mass Spectroscopy (HRMS): High-resolution mass spectrum was acquired on an Agilent 6545 Q-TOF Mass Spectrometer, with Electrospray Ionization (ESI) as an ion source. The instrument is equipped with an Agilent 1200 Series HPLC binary pump and autosampler. Analysis was performed with direct injection with methanol as solvent. Data acquisition and analysis were done using Agilent MassHunter Data Workstation and Qualitative Analysis software.
Batch adsorption experiments were quantified using a ThermoFisher Scientific QExactive high-resolution quadrupole-orbitrap mass spectrometer coupled to a high performance liquid chromatography system. The trap column, a Hypersil Gold dC18 12 μm 2.1×20 mm, was purchased from Fischer Scientific. The analytical column, an Atlantis® dC18 5 μm 2.1×150 mm, was purchased from Waters. See Analytical Methods (Section E) for a detailed description of sample preparation and data collection and analysis.
Surface Area Analysis: The polymer porosity and Brunauer-Emmett-Teller surface areas (SBET) were collected on a Micromeritics ASAP 2420 Accelerated Surface Area and Porosity Analyzer. Approximately 40 mg of polymer was used for each analysis. The polymers were degassed at 100° C. for 24 h until the off-gas rate was constantly reading less than 0.2 μmHg/min. N2 isotherms were generated by incremental exposure to ultrahigh purity nitrogen up to 1 atm in a liquid nitrogen bath at 77K. The SBET were calculated using the linear region (P/P0 of 0.05-0.1) of the isotherm using adsorption models included in the instrument software (Micromeritics ASAP-2420 V4.00).
Elemental Analysis of C, H, N, and S: Elemental analysis was performed by Robertson Microlit Laboratories. Combustion analysis was used for carbon, hydrogen, and nitrogen on a Perkin-Elmer Model 2400 CHN Analyzer, and titration was used for sulfur. For monomer, the elemental analysis result was compared to calculated values. For polymers, see the Polymer Characterization (Section D, V. Elemental Analysis) for a detailed analysis for determining the ratio of comonomers with respect to monomers.
Synthesis of 1 (Heptakis-(6-deoxy-6-iodo)-β-Cyclodextrin): Literature procedures1,2 were followed to replace the primary alcohol at 6′ position with iodine with the following modifications: Soxhlet in methanol was not carried out, because the large scale of products rendered Soxhlet ineffective. Instead the product was suspended in methanol for several days and filtered until filtrate ran clean. Note: Solvents do not need to be dried or degassed. (Yield 91%)
Synthesis of 2 (Heptakis-(6-deoxy-6-mercapto)-β-Cyclodextrin): Literature porcedures1, 2 were followed to convert the iodines to thiols with the following modifications: After NaHSO4 precipitation and filtration, the product was suspended in methanol and filtered twice. The solid was then subjected to a rotary evaporation at 30° C. for 3 h before being placed on a high vacuum line for 48 h at room temperature. Note: Solvents during synthesis must be degassed and the product must be stored away from light in a freezer. (Yield 92%)
Synthesis of 3 (Heptakis-(6-deoxy-6-vinylbenzyl)-β-Cyclodextrin): 2 (17.591 g, 14.102 mmol) was dissolved in DMSO (170 mL) and degassed with nitrogen sparging for 30 min. Potassium carbonate (6.8213 g, 49.357 mmol) was added and the solution was stirred for an additional 30 min. 4-vinylbenzyl chloride (14.11 mL, 100.123 mmol) was then added dropwise to the solution under N2 pressure. The solution was stirred at room temperature. After 24-32 h the solution was precipitated into water (1500 mL) and stirred for an additional 10 min before filtering. The filtrate was wash with copious amounts of methanol, superficially dried, then resuspended in methanol (600 mL). After 30 min, the solution was filtered again, and the filter cake was resuspended in methanol (600 mL). After 30 min, the solution was filtered again, superficially dried and transferred to a drying flask and subjected to rotary evaporation for an additional 3 h at 35° C. The powder was then transferred onto a high vacuum line and dried at room temperature for 24-48 h. Note: Powder is not bench stable for long periods of time (>30 days); store in freezer away from light. (Yield 89%)
1H NMR (500 MHz, DMSO-d6) δ 7.24 (d, 14H), 7.14 (d, 14H), 6.62 (dd, 7H), 5.95 (d, 7H), 5.90 (d, 7H), 5.71 (dd, 7H), 5.20 (dd, 7H), 4.92 (d, 7H), 3.75 (m, 7H), 3.58 (m, 14H), 3.35 (m, 14H), 3.11 (d, 7H), 3.81 (dd, 7H) ppm.
13C NMR (126 MHz, DMSO-d6): δ 138.64, 136.60, 135.89, 129.62, 126.26, 114.26, 102.36, 85.54, 72.90, 72.65, 72.44, 36.92, 33.48 ppm.
ESI HRMS m z calculated for C105H126O28S7([M-H]−) 2059.65; found 2058.6437.
Elemental Analysis (%) calculated for C105H126O28S7: C, 61.20; H, 6.18; 0, 21.74; S, 10.89. Found C, 58.84; H, 5.99; 0, 10.73; S, 24.28.
General Polymerization for 4, 5, and 6: Synthesis of 4, 5, and 6 is shown in
Monomer 3 (0.600 g, 0.291 mmol) and AIBN (0.019 g, 0.116 mmol) were dissolved in DMF (2 mL). Two equivalence of comonomer (0.582 mmol) were added as a liquid; comonomers consisted of styrene, methyl methacrylate, or MATMA (aqueous 80%). Note: Two equivalents was determined to be optimal equivalency, see Optimal Comonomer Equivalency Test (Section H). The monomer solution was transferred into a dry Schlenk flask, subjected to 3 freeze-pump-thaw cycles and heated to 80° C. for 1 h. Polymer gelled after 15 min and was heated for an additional 45 mins. After 1 h total reaction time, the solid gel was broken apart with a metal spatula, suspended in methanol, transferred to a teabag, and sealed with staples. This teabag was subjected to a Soxhlet extractor with methanol for 14 h before activating the polymer with supercritical CO2 (80 cycles, 4 h). The polymer was then crushed into a fine powder and isolated. (yields: 89-97%)
See 13C ssNMR spectra of (4), (5), and (6) below.
SBET: (4) 402 m2 g−1, (5) 392 m2 g−1 and (6) 237 m2 g−1.
Elemental Analysis was used to calculate comonomer:β-CD ratio: (4) 1.76, (5) 1.21, and (6) 1.99. See Section D, V for a sample calculation.
Functionalized CD monomer was characterized by 1H and 13C NMR as shown in
HRMS of 3 in chloroform as also performed. The most abundant adduct is 2058.6437, corresponding to [M-H]− (calculated 2059.65). Other peaks correspond to the isotopic masses of 3 (
Solid state 13C NMR spectra for 4, 5, and 6 are shown in
FT-IR spectra for 3, 4, 5, and 6 are shown in
N2 isotherms for 4, 5, and 6 are shown in
aN content for 4 and 5 is below the instrument threshold.
bThe Comonomer:β-CD ratio was calculated from a system of equations. The following sample calculation was for 4, but 5 and 6 were calculated with the same analysis.
The system of equations was set up such that,
Polymer 4 consists of two components: modified β-CD and the comonomer styrene. The molecular formula of modified β-CD is C105H126O28S7, and the molecular of the comonomer styrene is C8H8. The total mol of C, H, or S follows,
We converted the raw % elemental analysis data (Table 3) to mol for each element by arbitrarily assuming a 1 g of the sample and dividing it by the element's molar mass. The converted mol amount of each element was used in the system of equations equation:
where resulting b is the mol of the comonomer in 4. The comonomer:β-CD ratio was determined by diving a into b.
Quantification of target PFCAs or PFSAs after Batch Equilibrium Adsorption Experiments (Section G) was conducted using a HPLC coupled with HRMS (QExactive, quadrupole-orbitrap, ThermoFischer Scientific) using an established parallel reaction monitoring (PRM) method optimized for PFAS quantification.3 Previously established methods were also used for HPLC parameters.4-6 HPLC-MS was operated with electrospray ionization in negative polarity mode for all PFAS measurements. A detailed list of analytical information is provided in Table 4, and a summary of PFAS mixtures and their isotope-labeled internal standards (ILISs) is provided in Table 5. Matrix-matched calibration standards (n=9) were prepared with concentrations ranging between 0 ng L−1 to 1000 ng L−1. Analytes were quantified from the calibration standards (spiked with same concentration of ILISs) based on the PFAS target-to-ILIS peak area ratio responses of the designated quantitation product ion by linear least-squares regression. Calibration curves were run at the beginning of the analytical sequence. Instrument blanks and quality control (QC) samples were run before and after the calibration curve to ensure minimal carryover and adequate MS performance (QC tolerance set at +30%). PFAS spike controls were used to determine the PFAS recovery rate during analysis; recovery rate threshold was set at +50% for reach PFAS to be considered as reliable data.
The mobile phase consisted of (A) LC-MS grade water amended with 20 mM ammonium acetate and (B) LC-MS grade methanol. Samples were injected at 5 mL volumes onto a Hypersil Gold dC18 12 μm 2.1×20 mm trap column (Fisher Scientific) at room temperature using an isocratic mobile phase of 99% (A), pumped at 1 mL·min−1 via a low-pressure loading pump. Elution from the trap column and subsequent separation of analytes on an Atlantis® dC18 5 μm 2.1×150 mm analytical column (Waters) at 25° C. was achieved using an initial mobile phase of 60% (A), pumped at 0.3 mL·min−1 via a high-pressure elution pump. The isocratic mobile phase delivered from the loading pump changed to 2% (A) at 37.3 minutes to rinse the trap column and returned to 99% (A) at 41.3 minutes to prepare for the next sample injection. The mobile phase gradient delivered from the loading pump remained at 60% (A) until 6.1 minutes and then increased linearly to 10% (A) at 30.1 minutes. The mobile phase was held at 10% (A) until 37.1 minutes before it returned to 60% (A) to prepare for the next sample. The chromatography program had a total duration of 42.1 minutes.
The PFC-MXA mixture contains eleven PFCAs (C4 through C14) dissolved in methanol each at a concentration of 2 mg L−1. The PFS-MXA mixture contains five PFSAs (C4, C6-C8, and C10) dissolved in methanol each at a concentration of 2 mg L−1. The MPFAC-MXA mixture contains seven isotope-labelled PFCAs (C4, C6, C8-C12) and two isotope-labelled PFSAs (C6 and C8) dissolved in methanol each at a concentration of 2 mg L−1. The PFAS standard spike mixtures were diluted from the stock mixtures (PFC-MXA and PFS-MXA) using nanopure water to yield a concentration of 1 mg L1. The ILIS spike mixture was diluted from MPFAC-MXA using nanopure water to yield a concentration of 250 μg L−1. The stock mixtures and the spike mixtures were stored at −20° C. and 4° C., respectively.
Adsorption experiments (also referred to as removal experiments) were conducted in 15 mL polypropylene centrifuge tubes (Corning) with either 10 mL of nanopure water or salt-amended nanopure water, with the following concentrations: 1 mM Na2SO4, 2 mM NaCl, or 1 mM CaCl2 as previously described.4-6 All adsorption experiments were conducted with either the PFCA or the PFSA mixture (Table 4) at an initial concentration of 1 μg L−1 at pH of 5.5 to 6, and adsorbent loadings at 1 mg L−1, 10 mg L−1, or 100 mg L−1 in triplicate. Prepared centrifuge tubes were placed on a tube revolver and rotated at 40 rpm at 23° C. for 48 h to reach equilibrium in adsorption. After rotating, samples were filtered through 0.45 m cellulose acetate filters (Restek) and transferred into 10 mL glass LC-MS vials (Fischer Scientific). All triplicate samples were spiked with ILISs and stored at 4° C. until analysis. Control experiments were conducted in triplicate using the same procedure, but without adsorbents. The average and the standard deviation of PFAS removal efficiency were calculated based on the triplicate concentrations of each PFAS in the experimental group and the control group. The PFAS removal efficiency (%) by adsorbents were determined using Eq. S2:
where C0 (g L−1) and Cf (μg L−1) are the initial and residual concentration at 48 h of PFAS, respectively. The initial concentration C0 was obtained from the average concentration of control samples to account for the loss of PFAS from experimental conditions.
The optimal equivalency of the comonomer for polymerization was determined. Polymer formulations of 0.5, 1, 4, or 10 equivalencies of comonomer MMA, with respect to 3, were synthesized in the same condition as 5, which all resulted in high yields (90-93%) and high SBET(150-300 m2 g−1) [denoted as 5_0.5, 5_1, 5_4, and 5_10]. Note, 5 contains two equivalents of comonomer MMA. Each polymer was subjected to the same equilibrium adsorption experiment as previously described (see Section G). Specifically, the polymers were loaded at 40 mg L−1 to remove PFOA with an initial concentration of 40 mg L−1 in nanopure water (NP) or 1 mM NaSO4 (SS) matrix (
Adsorbent loadings of 4 and 5 were adjusted from 10 mg L−1 to 100 mg L−1 to better probe the magnitude of the enhanced adsorptions of PFCAs and PFSAs observed in SS matrix (
The experiments with the mixture of PFSAs (
A β-CD polymer bearing quaternary ammonium groups was synthesized through free radical polymerization. The polymer was evaluated for the removal efficiencies of 13 trace organic contaminants (TrOCs) that were spiked into nanopure water and municipal wastewater, and benchmarked to two commercial adsorbents: a regenerable granular activated carbon Filtrasorb 600 and a single-use anion exchange resin Amberlite PSR2+. Batch adsorption experiments and rapid small-scale column tests offered important insights into the performance of the β-CD polymer for removal of 13 TrOCs under environmentally relevant conditions in this complex water matrix. The β-CD polymer exhibited superior TrOCs removal performance and resisted fouling by wastewater constituents most effectively compared to the benchmarks. The β-CD polymer can readily be regenerated and, when packed in a fix-bed column, demonstrated late breakthroughs, indicating high adsorbent capacities, rapid adsorption kinetics and narrow mass transfer zones. Together, these studies further demonstrate β-CD polymer as promising adsorbents for practical wastewater remediation.
To prepare StyDex monomers, styrene groups were installed at the hydroxyl groups at the 2′, 3′ and 6′ positions of β-CD via direct etherification reactions with 4-vinylbenzyl chloride as the electrophile (
The styrene groups of StyDex monomers are potentially compatible with hundreds of commercially available vinyl comonomers and different radical polymerization methods. This versatility is advantageous in targeting a broad scope of TrOCs. For this study, we prepared a polymer based on the StyDex monomer and a cationic methacrylate monomer bearing quaternary ammonium groups, which were copolymerized using azobisisobutyronitrile (AIBN) in DMF at 80° C., with an isolated yield of 95% after 15 h Soxhlet extraction in methanol and activation by supercritical CO2 washing. Cationic StyDex formed porous and cross-linked polymer network with permanent surface charge. The polymer was characterized using solid-state cross-polarization magic angle spinning 13C NMR spectroscopy, N2 porosimetry, FTIR spectroscopy, combustion elemental analysis and (potentials. Solid state 13C NMR spectroscopy confirmed the successful incorporation of the comonomers. The resonance corresponding to the vinyl carbons (113 ppm) of StyDex monomer was not detected, indicating a high degree of cross-linking of the styrene groups. The resonances corresponding to the polymer backbone were detected in the broadened alkane regions (20-55 ppm). Carbonyl carbons of the comonomers were detected around 180 ppm. Furthermore, the characteristic N-methyl carbons (55 ppm) were detected in spectrum of Cationic StyDex. The porosity and Brunauer-Emmett-Teller surface area (SBET) of Cationic StyDex, F600 and PSR2+ were characterized by N2 porosimetry. Cationic StyDex exhibited permanent porosity and high SBET of 260 m2 g−1, with the most abundant pore width around 22 Å. F600 exhibited a SBET of 840 m2 g−1, with the most abundant pore width around xx A. PSR2+ was not porous under these conditions. Cationic StyDex was found to have strongly positive surface charge, corresponding to a (potential of 10 mV, and consistent with the incorporation of free cations into the polymer. Combustion elemental analysis and FTIR of Cationic StyDex was consistent with its expected structures. This characterization confirmed the porous and cross-linked nature of Cationic StyDex, which was used to remove TrOCs from nanopure water and municipal wastewater.
Given the trace analysis nature of this study and a diverse list of TrOCs (
Municipal wastewater effluents were acquired from the Terrance O'Brien Water Reclamation Plant in Skokie, Illinois, which treats an average of 230 Mgal per day of influents from the northeastern areas of Chicago. All effluents collected received primary and secondary treatments at the plant, but not tertiary ultraviolet (UV) disinfection treatment. Therefore, the effluents contained various concentrations of microbes, as well as background concentrations of TrOCs, which are reported in
The wastewater was also characterized for general water quality parameters including pH, DOC concentration, TDS concentration, and the concentrations of target inorganic ions. The pH of wastewater effluents ranged between 7.1 and 7.6, which is consistent with pH measurements reported by Terrance O'Brien Water Reclamation Plant.
We first evaluated the equilibrium removal efficiencies of 100 mg L−1 Cationic StyDex, F600, and PSR2+ for 13 TrOCs (spiked 500 ng L−1 each) in nanopure water and Pre-UV disinfected municipal wastewater following a 24 h contact time at room temperature. This contact time was sufficient to reach equilibrium removal, based on similar removal efficiencies observed in samples with 48 h contact times. In nanopure water, Cationic StyDex performed effectively, with near 100% removal of PFOA, PFOS, PFHxA, PFHxS, BEZ, and DCF (
The fouling of conventional adsorbents by DOM and inorganic constituents in complex water matrices remains a serious material drawback and limit wider implementations of these adsorbents. Different degrees of reduced uptake, which we associate with fouling, were observed for Cationic StyDex, F600 and PSR2+ in wastewater (
Regeneration is a critical factor when considering adsorbents for practical applications. The spent adsorbent should be readily regenerable using technically and economically feasible methods (e.g., washing with organic solvents) in contrast to the highly energy intensive and degradative regeneration method used for GACs or the single use of PSR2+. The regenerability and reuse of 100 mg L−1 Cationic StyDex in wastewater over four cycles was evaluated using either methanol, ethanol or 10% NaCl brine as the regenerating media. Methanol (
This application claims benefit of priority to U.S. Patent Application Ser. No. 63/265,022, filed Dec. 6, 2021, the contents of which is incorporated by reference in its entirety.
This invention was made with government support under Grant No. ER18-1026 awarded by the Department of Defense. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/081043 | 12/6/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63265022 | Dec 2021 | US |
