Plasmon-enhanced photocatalyst and method of using the same for the degradation of halogenated organics in aqueous solutions

Abstract

A plasmon-enhanced photocatalyst comprising: (a) a support substrate; and (b) a surface plasma resonance (SPR) metal coupled to / loaded on the support substrate and a method of making the same are described. The SPR metal is a plasmonic metal and is coupled to / loaded on the support substrate by embedding the SPR metal into and onto surfaces of the support substrate. A method of using plasmon-enhanced photocatalysis for the degradation of halogenated organic molecules and compounds in an aqueous solution is also described.

Description

PLASMON-ENHANCED PHOTOCATALYST AND METHOD OF USING THE SAME FOR THE DEGRADATION OF HALOGENATED ORGANICS IN AQUEOUS SOLUTIONSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. provisional application Serial No. 63 / 658,069, filed on June 10, 2024, the subject matter of which is herein incorporated by reference in its entirety.FIELD OF THE INVENTION

[0002] The present invention relates generally to a plasmon-enhanced photocatalyst, a method of making the plasmon-enhanced photocatalyst, and a method of using the same for the degradation of halogenated organics in aqueous solutions.BACKGROUND OF THE INVENTION

[0003] Polyfluoroalkyl and perfluoroalkyl substances (PFAS) represent a broad class of synthetic, organic chemicals that contain a hydrophobic fluorinated carbon chain and a polar end group, consisting of sulfonate, carboxylate, alcohol, or sulfonamide. Due to their amphiphilic properties and high stability, PFAS have been extensively used as surface coatings in textiles and apparel, packaging, and aqueous film-forming foams (AFFF) for fire suppression, among other broad applications. Based on the highly recalcitrant nature of PFAS (from the strength of C-F covalent bonds (-485 kj / mol)) and the large number of potential PFAS molecular structures (-15,000) occurring at low environmental concentrations with documented human health risks, effective PFAS management remains a significant and urgent global health need.

[0004] To put the scale of impact in perspective, at least 57,412 sites of presumptive PFAS contamination in the United States (alone) have been identified, including 49,145 industrial facilities, 4,255 wastewater treatment plants (WWTPs), 3,493 military sites, and 519 major airports (see Salvatore et al., Presumptive contamination: a new approach to PFAS contamination based on likely sources. Environmental Science & Technology Letters 2022, 9, (11), 983-990).

[0005] Further, it has been estimated that “ 18-80 million people in the U.S. receive tap water with 10 ng / L or greater concentration of perfluorooctanoic acid (PFOA) andperfluorooctanesulfonate (PFOS) combined, and over 200 million people likely receive water with a PFOA (and PFOS concentration at or above 1 ng / L” (Andrews et al., Population-wide exposure to per-and polyfluoroalkyl substances from drinking water in the United States. Environmental Science & Technology Letters 2020, 7, (12), 931-936).

[0006] Five common PFAS molecules are currently regulated by the United States Environmental Protection Agency (EP A), including PFOA, PFOS, perfluoro-nonanoic acid (PFNA), perfluoro-hexane sulfonate (PFHxS), and hexafluoropropylene oxide dimer acid (HFPO-DA).

[0007] Maximum PFAS contaminant levels (MCL) in drinking water for PFOA and PFOS as individual contaminants is 4 ng / L (ppt), while the MCL in drinking water for PFHxS, PFNA, and HFPO-DA is 10 ng / L (10 ppt). Additionally, as of 2024, PFOA and PFOS are categorized as Hazardous Materials under U.S. CERCLA-based regulations.

[0008] There have been several treatment options proposed to address PFAS contamination. For PFAS destruction (i.e., ultimate treatment), current options are highly intense (e.g., energy, economical) chemical / thermal processes or limited (i.e., slow) biological-driven transformations. Transformation technologies can be generally categorized as chemical / catalytic, thermal, plasma-based, and bio-based. Among these, chemical / catalytic transformation processes have proven effective for PFAS degradation via chemical oxidation and reduction, photocatalysis, electrocatalysis, and sonolysis based pathways. However, despite considerable progress, there remains significant room for improvement in terms of overall process efficiencies and product outcomes, especially for preferred reductive defluorination pathways. Additionally, there is a lack of data regarding long-term catalyst performance / stability, which is a key life cycle component.

[0009] From a sustainability perspective, photocatalysis provides inherent advantages in terms of energy and chemical reactant inputs. In particular, plasmon-enhanced photocatalysis, which is an emerging field focused on enabling / enhancing chemical reactions through specific light-matter interactions, has been demonstrated to catalyze reactions with relatively high activation energies under ambient conditions. Generally, surface plasmon resonance (SPR) phenomena is based on the excitation of free electrons in the conduction band (of metal nanostructures) by incident photons, as shown, for example, in Fig. 1.

[0010] SPR typically occurs in very thin layered metal surfaces, including metallic mono-layered single atoms and quantum-sized metallic clusters (typically ranging from approximately 0.5 to 8 nm, depending on the material, as shown in Fig. 2). When incident light interacts with such substrates, photons undergo total internal reflection at angles higher than the critical angle.Under such conditions, photon propagates parallel to the metal surface and transfers its energy to the oscillating free electrons of the surface metal layer which leads to the SPR effect. The specified critical angle that induces SPR depends on the refractive index of the penetrated medium. At the SPR critical angle, the energy of the photon is transferred into the oscillating surface free electrons and subsequently, excites a resonance mode which can be identified with a sharp dip in the reflected light intensity. As a result, surface free electrons exhibit a collective oscillation when the interaction is phase-matched to the surface plasmon resonance at the incident photon frequency. This leads to the formation of highly energetic electrons (or hot holes), heat dissipation, and a strong electromagnetic field on the surface of metal nanostructures.

[0011] Numerous studies have explored the use of SPR metals as catalysts across a diverse array of reaction pathways. These pathways encompass a broad spectrum, including, but not limited, to ammonia synthesis, CO oxidation, H2 dissociation, electrochemical oxygen production, hydrogen production via ammonia or ammonia borane decomposition, methanol production, nitrobenzene hydrogenation, among others. SPR-based reactions have also been demonstrated for environmental applications such as water splitting, CO2 reduction, water purification, and degradation of organic molecules.

[0012] However, despite the clear potential, this approach has not previously been successfully applied for PF AS treatment.SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to provide a plasmon-enhanced photocatalyst.

[0014] It is another object of the present invention to provide a method of making the plasmon- enhanced photocatalyst.

[0015] It is still another object of the present invention to provide a method of using the plasmon-enhanced photocatalyst for the degradation of halogenated organics in aqueous solutions.

[0016] It is still another object of the present invention to provide a method of using the plasmon-enhanced photocatalyst for the degradation and defluorination of polyfluoroalkyl and perfluoroalkyl substances (PF AS).

[0017] It is still another object of the present invention to provide a method of using the plasmon-enhanced photocatalyst for high-efficiency PFAS defluorination and the degradation of other halogenated organic compounds.

[0018] To that end, in one embodiment, the present invention relates generally to a plasmon- enhanced photocatalyst comprising: a. a support substrate; and b. a surface plasma resonance (SPR) metal coupled to / loaded on the support substrate.

[0019] Also described is a method of making the plasmon-enhanced photocatalyst and a method of using the plasmon-enhanced photocatalyst for the degradation of halogenated organic compounds in aqueous solutions.BRIEF DESCRIPTION OF THE FIGURES

[0020] Fig. 1 depicts a schematic overview of surface plasmon resonance (SPR) phenomena.

[0021] Fig. 2 depicts digital images of SPR metals. The top row depicts digital images (bright field- and dark field-scanning transmission electron micrographs (BF-STEM, ADF-STEM, and scanning electron micrograph) of SPR metals (MSPR = Pd, 1-2 nm monodispersed) embedded in / on mesoporous silica nanoparticles. The bottom row shows energy dispersive X-ray (EDX) mapping analysis of SPR metals (MSPR = Au (left), Pd (middle), and Pt (right), 102 nm monodispersed) embedded in / on mesoporous silica nanoparticles.

[0022] Fig. 3 depicts a map showing contamination at thousands of test sites across the country where PFAS has been found.

[0023] Fig. 4 depicts representative digital micrograph images (Bright field- and Dark fieldscanning transmission electron micrographs (BF-STEM, ADF-STEM), and scanning electron micrograph) of SPR metals (here as MSPR = Pt, 4% by weight) embedded in / on mesoporous silica nanoparticle supports.

[0024] Figs. 5(a)-(e) depict digital images of diverse SPR metals (Palladium (Pd), Platinum (Pt), and Gold (Au)) embedded in Mesoporous Silica Nanoparticles or carbon-based substrates. Fig.5(a) depicts MSN-Pd, Fig. 5(b) depicts MSN-Pt, Fig. 5(c) depicts MSN-Au, Fig. 5(d) depicts MWCNT-Pd, and Fig. 5(e) depicts GO.

[0025] Figs. 6(a) and 6(b) depict PFOA (Fig. 6(a)) and PFOS (Fig. 6(b)) destruction as a function of SPR metal type (Palladium (Pd), and Platinum (Pt) and supports, as mesoporous silica nanoparticles (MSN), graphene oxide (GO), and multiwalled carbon nanotubes (MWCNT)) under UVC irradiation.

[0026] Fig. 7 depicts PFOA Degradation utilizing SPR metal (Palladium (Pd) on Mesoporous Silica nanoparticles (MSN)) under UVC irradiation.

[0027] Fig. 8(a) and (b) depict UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis (Fig. 8(a)) and H2 production detection through thermal conductivity detector (TCD) of gas chromatography technique for SPR metal Palladium (Pd) on Mesoporous Silica nanoparticles (MSN).

[0028] Fig. 9 depicts fluoride evolution during PFOA and PFOS degradation utilizing Pd-loaded Mesoporous Silica Nanoparticles (MSN-Pd, %Pd= 4% by weight). Fluoride concentration was monitored using iron chromatography (IC) until complete degradation was achieved (over 74 hours).

[0029] Fig. 10 depicts fluoride evolution during PFOA and PFOS degradation utilizing Pt-loaded Mesoporous Silica Nanoparticles (MSN-Pt, %Pt= 4% by weight). Fluoride concentration was monitored using iron chromatography (IC) until complete degradation was achieved (over 74 hours).

[0030] Fig. 11 depicts pH-dependent PFOA degradation utilizing palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVC irradiation at pH 4.2-4.5 (CO2 buffer; red data points), pH 7 (N2 purging; pink data points), and pH 9.2 (bicarbonate buffer; orange data points). Active catalysts here are similar to, or what is shown, in Figs. 2, 4, and 5(a)-(e).

[0031] Fig. 12 depicts PFOA degradation utilizing palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVA and UVC.

[0032] Fig. 13 depicts PFOS degradation using palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVA and UVC .

[0033] Fig. 14 depicts PFOA degradation using platinum-loaded mesoporous silica nanoparticles (MSN-Pt) under UVA and UVC.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] The present invention describes new materials and material combinations along with successful application for high-efficiency PFAS defluorination and the degradation of other halogenated organic compounds.

[0035] As discussed above, there is an urgent and widespread need for rapid yet sustainable PFAS treatment technologies as contamination is extensive in the United States and beyond. Fig. 3 is a map that shows contamination at thousands of test sites across the United States where PFAS has been found.

[0036] EPA regulations require treatment of PFAS in drinking water (via EPA 2024 PFAS National Primary Drinking Water Regulation). In addition, on April 19, 2024, the EPA also announced that it was designating two types of PFAS, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), as CERCLA hazardous substances, which necessitate extensive environmental remediation.

[0037] There have been a number of approaches explored to destroy (transform) PFAS in water and other aqueous solutions. These include photocatalysis, electrochemical oxidation, surface radical-based advanced redox processes, thermal destruction, and other oxidative or reductive techniques. Among these, photochemical routes using photocatalysts have not received as much attention as other methods due to their drawbacks, including slow PFAS degradation rates, incomplete PFAS decomposition, and challenges associated with reusing / recycling the photocatalyst.

[0038] The inventors have determined that the engineered nanocatalysts as described herein exhibit enhanced PFAS degradation, in terms of the reaction rate and %removal, at neutral (i.e., pH 7) as well as mildly acidic conditions (i.e., pH 4.2-4.5). Thus, one clear advantage of the use of the materials and processes described herein is the complete degradation of PFOA and PFOS at neutral as well under mildly acidic conditions. Such degradation occurred in the presence ofnanocrystalline Pd (catalysts) embedded in mesoporous silica nanoparticles (MSN-Pd) under UV-C irradiation with controlled reaction conditions, including a 2% methanol as a hole scavenger, without the need for applied hydrogen gas. MSN-Pd, as a multifunctional SPR metal, possesses both SPR properties and the ability to generate hydrogen gas. Notably, such rapid degradation rates (0.34 hour1for PFOA and 0.26 hour1for PFOS) achieved in the complete degradation of PFAS, including PFOA and PFOS have not been reported previously for SPR- based (reductive) photochemical pathways specifically for PFAS treatment.

[0039] Further, the complete degradation of PFOA and PFOS is attainable for a range of pH values, including circumneutral, which is likely a more sustainable / green approach. Reactions at neutral pH hold promise for providing transferable, low input technical advantages for scaling up the production process.

[0040] One of the key factors in initiating / proceeding with PFAS degradation using SPR metals (Pd and Pt) embedded in stable substrates in water under illumination is having sufficient energy to excite SPR metals and generate surface plasmon resonance. This electromagnetic surface wave triggers the dissociation of hydrogen molecules (produced by water dissociation) adsorbed on the surface of SPR metals, thereby enhancing the reductive degradation of PFAS molecules. The SPR effect has been observed in thin metallic substances, such as, quantum sized Pd and Pt nanocatalysts (with average diameters below 10 nm) when excited by light energy (including both UVA and UVC), as shown in Figs. 12 and 13.

[0041] As described herein, the inventors of the present invention have developed a highly novel PFAS degradation pathway that utilizes surface plasmon resonance generated in quantum-sized metallic crystals (SPR metals) embedded in and on chemically and environmentally stable substrates under various illumination conditions, such as UV-A / B / C or visible light irradiation.

[0042] As used herein, “a,” “an,” and “the” refer to both singular and plural referents unless the context clearly dictates otherwise.

[0043] As used herein, the term “about” refers to a measurable value such as a parameter, an amount, a temporal duration, and the like and is meant to include variations of + / -15% or less, preferably variations of + / -10% or less, more preferably variations of + / -5% or less, even more preferably variations of + / -1% or less, and still more preferably variations of + / -0.1% or less of and from the particularly recited value, in so far as such variations are appropriate to perform inthe invention described herein. Furthermore, it is also to be understood that the value to which the modifier “about” refers is itself specifically disclosed herein.

[0044] As used herein, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “front,” “back,” and the like, are used for ease of description to describe one element or feature's relationship to another element(s) or feature(s). It is further understood that the terms “front” and “back” are not intended to be limiting and are intended to be interchangeable where appropriate.

[0045] As used herein, the terms “comprises” and / or “comprising,” specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0046] In one embodiment, the present invention relates generally to a plasmon-enhanced photocatalyst comprising: a. a support substrate; and b. a surface plasma resonance (SPR) metal coupled to / loaded on the support substrate.

[0047] In one preferred embodiment, the support substrates comprises silica- and / or carbonbased substrates (e.g., silica nanospheres, mesoporous silica nanoparticles (MSN), single-wall carbon nanotubes, multi -walled carbon nanotubes (MWCNT), graphene and graphene oxides (GO)). In one embodiment, the support substrate is selected from the group consisting of silica nanospheres, mesoporous silica nanoparticles, multiwalled carbon nanotubes, graphene, and graphene oxides, preferably wherein the graphene oxide is highly oxidized, and combinations of the foregoing.

[0048] These support substrates serve to stabilize and protect SPR metals from catalyst poisoning / aging (including, for example, etching, dissolution, transformation, aging, and agglomeration). This extends the lifespan and durability of the applied SPR metals, allowing for multiple uses, recycling, and higher turnover rates.

[0049] The observed reaction pathway via H / F exchange on the SPR metals, can be applied to a wide range of PFAS compounds (and other halogenated organic molecules) regardless of theirchain length and functional head groups as shown in Figs. 4, 5(a)-(e), 6(a) and (b), 7, and 8(a) and (b). The wt.% of the SPR metal coupled to / loaded on the support substrate is in the range of about 1 to about 10 wt.%, more preferably about 1 to about 7 wt.%.

[0050] In one embodiment, surfaces of the support substrate are amine-functionalized or coated with amine-functionalized polymer. For example, in one embodiment, the amine may be selected from the group consisting of primary amines, secondary amines, tertiary amines, and quaternary amines. The amine may comprise one or more of aminosilanes, branched / linear polyethyleneimines, and aminated cellulose.

[0051] In one embodiment, the amine may comprise any aminosilane that is easily bound to a silica-based substrates. Examples of suitable aminosilanes include, but are not limited to (3- aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, N-(2-aminoethyl)-3- aminopropyltrimethoxysilane, and 2-[2-(3-Trimethoxysilylpropylamino)ethylamino]ethylamine.

[0052] In one embodiment, the amine comprises polyethyleneimine and both linear and branched polyethyleneimines may be used with various molecular weights ranging from 600 to 70,000 g / mol.

[0053] In one embodiment, an aminated cellulose may be used, such as chitosan or trimethyl chitosan.

[0054] As described herein primary, secondary, and / or tertiary amines may be used (functional groups) associated with various support materials include silica, mesoporous silica (MSN), MWNT, SWNT, graphene, graphene oxides, cellulose, hemicellulose, and lignin. Such support materials can be aminated through a variety of ways both directly and by being coated with aminated polymers such as polyethyleneimines.

[0055] In one embodiment, the SPR metal is coupled to / loaded on the support substrate by embedding the SPR metal into and onto surfaces of the support substrate. In one embodiment, the SPR metal is a plasmonic metal selected from the group consisting of gold, silver, copper, aluminum, magnesium, platinum, palladium, ruthenium and combinations of one or more of the foregoing.

[0056] In one embodiment, the SPR metal has a maximum diameter of less than about 10 nm, preferably less than about 8 nm, preferably less than about 6 nm, or less than about 5 nm or lessthan about 4 nm or less than about 3 nm or less than about 2 nm or less than about 1 nm or less than about 0.5 nm. In one embodiment, the SPR metal has an average diameter in the range of about 0.1 to about 8 nm, more preferably in the range of about 0.2 to about 5 nm.

[0057] In one embodiment, the wt.% of the SPR metal coupled to / loaded on the support substrate is in the range of about 1 to about 10 wt.%, more preferably about 1 to about 7 wt.%.

[0058] In one embodiment the support substrate has a BET surface area between about 500 to about 800 m2 / g and pore sizes ranging from about 0.5 to about 7.5 nm. This porosity is tuned / controlled by using pore sizes ranging from about 3.5 to about 7.5 nm, as determined by small-angle X-ray scattering (SAXS) measurements. These properties can be achieved through synthetic processes as further described herein.

[0059] In one embodiment, the present invention also relates generally to a method of making a plasmon-enhanced photocatalyst, the method comprising a) functionalizing a silicon or carbon-based material with an amine to provide an amine functionalized support substrate; b) nucleating and growing a plasmonic metal on the amine functionalized silicon or carbon-based material in an aqueous solution; c) precipitating the resulting plasmon-enhanced photocatalyst; and d) separating the plasmon-enhanced photocatalyst from the aqueous solution.

[0060] In one embodiment, the method further comprises the step of purifying the photocatalyst prior to separating the plasmon-enhanced photocatalyst from the aqueous solution.

[0061] In one embodiment, the resulting plasmon-enhanced photocatalyst comprises about 1 to about 10 wt.%, more preferably about 2 to about 8 wt.%, more preferably about 3 to about 6 wt.% of the plasmonic metal.

[0062] In one embodiment, the present invention also relates generally to a method of using plasmon-enhanced photocatalysis for the degradation of halogenated organic molecules / compounds in an aqueous solution, the method comprising the steps of: a. providing a plasmon-enhance photocatalyst as further described herein;b. mixing the plasmon-enhanced photocatalyst, a hole scavenger, and the aqueous solution containing halogenated organic molecules / compounds in a reaction vessel to form a reaction suspension; c. bubbling carbon dioxide into the reaction vessel; d. irradiating the reaction suspension with a source of irradiation for a period of time to degrade and reduce the halogenated organic molecules / compounds to less toxic product compounds, preferably wherein the less toxic product compounds comprise non-fluorinated product compounds.

[0063] In one embodiment, the halogenated organic molecules / compounds comprise polyfluoroalkyl and perfluoroalkyl compounds.

[0064] In one embodiment, the SPR metal generates hydrogen molecules through water dissociation under the source of UV radiation.

[0065] In one embodiment, the hole scavenger is added to the reaction suspension at a concentration within the range of about 1 to about 4 wt.%, more preferably about 2 to about 3 wt.%. In one embodiment, the hole scavenger is selected from the group consisting of methanol, ethanol, isopropanol, tert-butyl alcohol, triethylamine, ascorbic acid, ammonium formate, mercaptopropionic acid, sodium borohydride, ethylenediaminetetraacetic acid EDTA sodium sulfite, and combinations of the foregoing.

[0066] In one embodiment, the source of irradiation operates at a wavelength, or spectrum of wavelengths, within the range of UV-A, UV-B, or UV-C or visible light. As described herein, nanocatalysts embedded in / on a variety of stable substrates processed surface plasmon resonance-driven PFAS degradation in a wide range of UV irradiation from UV-A to UV-C. UV region covers the wavelength range 100-400 nm and is divided into three bands: UV-A (315-400 nm) UV-B (280-315 nm) UV-C (100-280 nm).

[0067] In one embodiment, hydrogen molecules generated during the photocatalytic reaction are bound to the surface of the SPR metal and dissociate into hydrogen atoms and / or hydrogen radicals due to surface plasmon resonance generated by excited electron clouds on the surface of the SPR metal under UV irradiation.

[0068] In one embodiment, in situ produced hydrogen generated through water dissociation is used to regenerate the spent SPR metal.

[0069] In one embodiment, the period of time the reaction suspension is irradiated is until complete degradation of the halogenated organic molecules / compounds is achieved.

[0070] In one embodiment, the reaction is conducted at a pH in the range of 4 to 8, more preferably about 4.1 to about 7, more preferably about 4.2 to 5.

[0071] In one embodiment, the method further comprises the step of periodically purging carbon dioxide from the reaction vessel.

[0072] In one embodiment, the step of irradiating the reaction suspension with a source of irradiation is accomplished without applying external hydrogen gas.

[0073] The advanced photocatalysis technique described herein employs the novel nanocatalyst platform incorporating the SPR metals with average diameters as described herein, leading to enhanced PFAS degradation that significantly outperforms traditional photochemical reactions in terms of overall efficiencies.

[0074] The invention will now be described with reference to the following non-limiting examples:Examples:Materials:

[0075] Cetyltrimethylammonium bromide (CTAB, >99.0%), tetraethyl orthosilicate (TEOS, 98%) triethanol amine (TEA, >99.0%), (aminopropyl)triethoxysilane (APTES, 99%), chloroplatinic acid hydrate (H2PtCU xH2O, 99.9%), Sodium tetrachloropalladate (Na2PdC14, 99.99%), Gold chloride trihydrate (AuC13'3H2O, 99.9%), trisodium citrate dihydrate (US Pharmacopeia grade), sodium borohydride (NaBHi, 99%), pure methanol (MeOH, 99.95%) and pure ethanol (EtOH, 200 proof, anhydrous, 99.5%) were all sourced from Sigma Aldrich.

[0076] All experiments were conducted in Milli-Q water (MQ water, >18 MQ cm)Material Synthesis:Mesoporous silica nanoparticle (MSN).

[0077] CTAB (5.72 g, 15.69 mmol) was dissolved in ethanol (18 g, 0.39 mol) and water (129.6 g, 7.2 mol) under stirring (at 750 rpm) at room temperature (RT) for 30 min. In the CTAB micelle containing solution, TEA (0.568 g, 3.81 mmol) was added at RT and agitated for additional 30 min and the final pH was 9.0 at RT. The mixture was then heated to 70°C (ramp rate = 10°C / min) under the vigorous agitation (at 750 rpm). TEOS (66.28 mmol) was injected to the solution at 70°C (the injection rate was 1000 uL / min) and the whole reaction mixture was continuously stirred at 750 rpm at 70 °C for 2 h under N2 flow. 4000 mg of MSN was homogenously dispersed in HC1 containing ethanol (120 mL) at pH below 1.0 (typically 2 wt.% HC1 in ethanol) and agitated at 70°C for 3 h. The purified MSN was cooled and separated by centrifugation (13,751 ref for 40 min). The CTAB removal process was repeated 3 times.APTES coating on MSN (MSN-NH2).

[0078] Primary amine functionalization on MSN was processed by APTES addition to MSN containing solution. Before the reaction, MSN samples were purified under acidic condition to remove CTAB and TEA in each pore (channel) of MSN)) as described above. APTES (6 mL, 25.64 mmol) was added to the purified MSN (1000 mg) containing ethanol / water (120 mL I 60 mL) co-solvent at RT under vigorous agitation (at 750 rpm) and heated to 70°C (ramp rate = 10°C / min). The reaction mixture was stirred at 70 °C for 2 h under N2 flow. The resulting cloudy solution was purified using ethanol and separated by centrifugation (at 13,750 ref for 25 min) and kept in an amber bottle.Palladium nanoparticles embedded in MSN (MSN-NH2-Pd).

[0079] Palladium nanoparticles were nucleated and grown on primary amine functionalized MSN (MSN-NH2) in aqueous media at 83 °C. All synthetic conditions were processed using palladium and citrate stock solutions; palladium stock solution was 51205.47 ppm of Pd concentration (in MQ-water, measured by ICP-MS) and citrate stock solution was 105 mol / L (in water). The stock solutions were prepared 1 day before the reaction and stored in the refrigerator (3-5 °C). Typically, to synthesize 5% Pd loaded MSN-NH2-Pd, 400 mg of MSN-NH2 was dispersed in DI water (100 mL) at RT and stirred at 750 rpm under N2 flow over 30 min. Homogeneously mixed MSN-NH2 solution was then agitated with palladium stock solution (0.377 mL, 19.30 mg of Pd) and sodium citrate stock solution (8.8 mL, 0.924 mmol) at RT. The reaction temperature of the reaction was then, heated to 83 °C (ramp rate = 10°C / min) and kept at that temperature for a desired time (25, 60, and 120 min) under N2 flow. After the reaction at83 °C, the reaction vessel was cooled immediately in an ice bath to stop growing Pd nanoparticles. The resulting brown (or gray / black, depending on Pd nanoparticle size and / or concentration) precipitates were purified using ethanol and water and separated by centrifugation (at 13,750 ref for 25 min). The purified MSN-Ntb-Pd was dried under vacuum overnight and kept in an amber vial.Platinum nanoparticles embedded in MSN (MSN-NHi-Pt).

[0080] Platinum nanoparticles were nucleated and grown on primary amine functionalized MSN (MSN-NH2) in aqueous media at 90°C. All synthetic conditions were processed using platinum and citrate stock solutions; platinum stock solution was 43379.50 ppm of Pt concentration (in MQ-water, measured by ICP-MS) and the citrate stock solution was 105 mol / L (in water). The stock solutions were made 1 day before the reaction and stored in the refrigerator (3-5 °C).Typically, to make 3.7% Pt loaded MSN-NEk-Pt, 400 mg of MSN-NH2 was dispersed in DI water (100 mL) at RT and stirred at 750 rpm under N2 flow over 30 min. Homogeneously mixed MSN-NH2 solution was then agitated with platinum stock solution (0.715 mL, 31.00 mg of Pt) and sodium citrate stock solution (6.6 mL, 0.693 mmol) at RT. The reaction temperature of the reaction was then, heated to 95°C (ramp rate = 10°C / min) and kept at that temperature for a desired time (25, 60, and 120 min) under N2 flow. After the reaction at 90°C, the reaction vessel was cooled immediately in an ice bath to stop growing Pt nanoparticles. The resulting yellow (or gray / black, depending on Pt nanoparticle size and / or concentration) precipitates were purified using ethanol and water and separated by centrifugation (at 13,750 ref for 25 min). The purified MSN-NH2-Pt was dried under vacuum overnight and kept in an amber vial.Materials Characterization:

[0081] Nanomaterials engineered in these examples were characterized through established and standard methods including Transmission Electron Microscopy (TEM), High-Resolution X-ray Diffractometer (XRD), X-ray Photoelectron Spectroscopy (XPS), inductively coupled plasmamass spectroscopy (ICP-MS), and Brunauer-Emmett-Teller (BET) Surface Area Analyzer. For details, the size and shape of the engineered nanomaterials was characterized through FEI Tecnai Osiris 200 KV TEM. TEM samples (10 mg of the sample in 10 mL of ethanol) were bath sonicated for a couple of minutes and one drop of the dispersed sample was placed on the TEM grid, and dried at room temperature in the air, overnight. The crystal structure analysis of theengineered nanomaterials was performed on XRD using Cu Kot radiation (X = 1.54 A). The X- ray was generated at 44 mA and 40 KV and the scan rate was 10 degree per min. Oxidation state of the engineered materials was evaluated via XPS(PHI VersaProbe II Scanning XPS Microprobe). The elemental composition analysis of the nanomaterials was examined by ICP-MS (NexION 5000, Perkin Elmer). The analytical samples were digested in the boiling acid solution (typically 3:1 v / v ratio of HCI HNO3 at 100°C for 4h). BET specific surface area of the engineered nanomaterials was analyzed using BET spectrometer (Micrometritics ASAP 2460 Surface Area and Porosity Analyzer) by N2 adsorption isotherm at liquid nitrogen temperature (77 K). Before BET measurement, the sample was degassed at 110°C over 15 hours under nitrogen flow using the sample degas system (Micrometritics FlowPrep 060).Photochemical Reactions:

[0082] Photocatalytic experiments were conducted under constant UV irradiation at a wavelength of 254 nm or 370 nm in a 100 ml quartz vial. The reaction suspension consisted of 400 mg / L of catalyst, 10 mg / L of PFOA and 2.5 ml of methanol. Prior to UV irradiation, a quartz vial containing a reaction suspension was sealed and bubbled with CO2 and H2 gasses for 30 min. Samples were collected at different reaction times (hourly for the first 4 hours and then every two hours until the 8thhour) and analyzed accordingly for PFAS and fluoride concentration. The concentration of PFOA and corresponding byproducts were measured by using liquid chromatography coupled with mass spectroscopy (LC-MS, Shimadzu LCMS TQ 8060) while fluoride concentration was determined by ion chromatography (IC). The concentrations of PFOA and catalyst were kept constant in each scavenger experiment. Carbonate-bicarbonate buffer was used as the weak basic buffer in the pH study.PFAS (LC-MS) Measurements:

[0083] Mass spectrometric measurements were performed with a Shimadzu Scientific Instruments 8060 Triple-Quad LC-MS system, equipped with a Nexera LC-40D xs UHPLC, consisting of a CBM-40 Lite system controller, a DGU-405 Degasser Unit, two LC-40D XS UHPLC pumps, a SIL-40C XS autosampler and a Column Oven CTO-40S. UV data was collected with a Shimadzu Nexera HPLC / UHPLC Photodiode Array Detector SPD M-40 in the range of 190 - 800nm. Massspectra were subsequently recorded with the triple quadrupole (TQ) 8060 mass spectrometer. The samples were held at 20°C in the autosampler compartment. luL of each sample were injected into a sample loop and separated on a Shimadzu Velox PFPP column, 1.8um, 2.1x100mm, equilibrated at 40°C in a column oven. A binary gradient was used during the measurements, respectively, Solvent A (Water, HPLC grade Chromasolv, with 0.1% Formic Acid) and Solvent B (Methanol, HPLC grade Chromasolv).

[0084] Figs. 6(a) and (b) and 7 depict normalized concentrations (C / Co) where Co is the initial concentration at t = 0 and C is the concentration at time t versus reaction time (t) for different samples tested.

[0085] Fig. 8(a) and (b) depict UV-Vis Diffuse Reflectance Spectroscopy (DRS) analysis (Fig. 8(a)) and H2 production detection through thermal conductivity detector (TCD) of gas chromatography technique for SPR metal Palladium (Pd) on Mesoporous Silica nanoparticles (MSN).

[0086] Fig. 9 depicts fluoride evolution during PFOA and PFOS degradation utilizing Pd-loaded Mesoporous Silica Nanoparticles (MSN-Pd, %Pd= 4% by weight). Fluoride concentration was monitored using iron chromatography (IC) until complete degradation was achieved (over 74 hours).

[0087] Fig. 10 depicts fluoride evolution during PFOA and PFOS degradation utilizing Pt-loaded Mesoporous Silica Nanoparticles (MSN-Pt, %Pt= 4% by weight). Fluoride concentration was monitored using iron chromatography (IC) until complete degradation was achieved (over 74 hours).

[0088] Fig. 11 depicts pH-dependent PFOA degradation utilizing palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVC irradiation at pH 4.2-4.5 (CO2 buffer), pH 7 (N2 purging), and pH 9.2 (bicarbonate buffer). Active catalysts here are similar to, or what is shown, in Figs. 2, 4, and 5(a)-(e).

[0089] Fig. 12 depicts PFOA degradation utilizing palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVA and UVC.

[0090] Fig. 13 depicts PFOS degradation using palladium-loaded mesoporous silica nanoparticles (MSN-Pd) under UVA and UVC.

[0091] Fig. 14 depicts PFOA degradation using platinum-loaded mesoporous silica nanoparticles (MSN-Pt) under UVA (blue data points) and UVC (purple data points).

[0092] The experiments depicted in Figs. 6(a) and (b), 7, 8(a) and (b), 9, 10 and 12-14 were conducted at pH 4.2-4.5 (CO2 buffer) in the presence of methanol (2.5%) in DI water under CO2 purging (with no applied hydrogen gas (H2)). Active catalysts were similar to, or what is shown, in Figs. 2, 4, and 5(a)-(e).

[0093] Thus it can be seen that the engineered nanocatalyst platform described herein shows rapid and complete PFAS degradation and required hydrogen generation in water under various illuminations. No applied hydrogen is necessary and complete defluorination is observed.

[0094] The inventors of the present invention of have demonstrated the use of SPR metals with average diameters below 10 nm, including palladium and platinum, supported on chemically stable silica- and carbon-based substrates as photocatalysts for effective PFAS degradation via reductive defluorination in water under UV irradiation.

[0095] This approach differs from traditional photocatalysis, which typically follow oxidation (or mixed oxidation and reduction) pathways assisted by reactive oxygen species (ROS), such as hydroxyl radical and superoxide anion, generated by photochemical reactions under UV irradiation. The reductive defluorination of PFAS, often referred to as the H / F exchange reaction, proceeds through the (PFAS)C-F / H2 exchange, resulting in a conversion to (PFAS)C-H / H-F and forming less toxic, less or non-fluorinated product compounds.

[0096] The underlying theory for the reductive pathway to defluorinate PFAS described herein involves the presence of SPR metals, hydrogen molecules, a hole accepter (ROS scavenger), and suitable light sources, such as UV-A / B / C or visible light, to excite SPR metals. As set forth herein, the inventors of the present invention have describe the synthesis and application of extremely small and highly monodispersed SPR metals, including, for example, Pd and Pt nanocrystals with average diameters below 2 nm on silica- and carbon-based substrates, which are also capable of generating hydrogen through water dissociation under the appropriate light sources as illustrated in Fig. 7.

[0097] The newly generated hydrogen molecules, during the photochemical reaction, are bound to the surface of the engineered SPR metals and subsequently dissociated into hydrogen atoms or hydrogen radicals due to the surface plasmon resonance generated by excited electron clouds on the surface of the SPR metals under UV irradiation. This promotes the complete (100%)defluorination of PFAS by H / F exchange reaction on the surface of SPR metals, as shown in Figs. 9 and 10. Furthermore, the in situ produced hydrogen, generated through water dissociation, as shown in Figs. 7 and 8, can also be utilized to regenerate SPR metals, a process for prolonging catalytic activity. This enhances the potential for multiple uses of the catalysts in a turnover cycle, provided the catalysts do not undergo transformation processes such as aging, dissociation, or agglomeration.

[0098] Regenerating used SPR metals involves reducing or reactivating them. Under UV irradiation, SPR metals in water become oxidized. Supporting hydrogen is a well-known method to reactivate these metals. In the reaction system described herein, there is no need for an additional hydrogen supply because hydrogen is generated in situ and can be used for self-healing and regeneration. SPR also directly produces hydrogen via water splitting which in turn has high reducing potential that maintains the SPR metals, keeping them in their active state (non-oxidized). The inventors have observed SPR-based co-production (simultaneously) of hydrogen directly as shown in Figs. 8(a) and (b).

[0099] As set forth in the Examples, exceptional PFAS degradation was observed under both UV-C and UV-A irradiation. Most notably, achieving complete PFAS degradation under UV-A assisted photocatalytic reaction with a comparable reaction rate of 0.052 hour'1has never been reported before. Further developments and improvements of the materials library developed for use in the present invention are also expected for complete and efficient PFAS degradation under visible lights, which can be applicable in real environmental conditions (i.e., without a photoreactor).

[0100] High-performance SPR metals on carbon-based substrate also performed similarly in the case of efficient PFAS degradation.

[0101] SPR metals were successfully deposited on the surfaces of multiwalled carbon nanotubes (MWCNT) and graphene oxides (GO), both of which are chemically stable carbon-based substrates. These materials exhibited outstanding PFAS degradation properties, with a comparable reaction rate of 0.096 hour1for MWCNT-Pd and 0.085 min'1for GO-Pd, respectively, as seen in Fig. 6(a). it is believed that the slightly faster PFAS degradation observed with quantum-sized Pd embedded in MWCNT and GO could be attributed to the higher electron conductivity of carbon materials compared to silica-based substrates. This enhanced electron conductivity allows the electron magnetic energy generated by the applied light source, here UV-C, to be efficiently provided and transferred to the target molecules such as hydrogen molecules and PFAS adsorbed on the surface of these conductive carbon-based substrates.

[0102] As described herein, the use of SPR metals embedded in silica- and carbon-based substrates show not only outstanding performance for broad PFAS treatment in water under appropriate light sources. But also require very low energy inputs. From a materials development perspective, the inventors of the present invention constructed and demonstrated a range of materials libraries incorporating SPR metals (Pt, Pd, Au) and stable substrates (nanocrystalline silica, mesoporous silica nanoparticles, multi-walled carbon nanotubes, and highly oxidized graphene oxides) as provided below in Table 1. By functionalizing the surface of the substrate with carboxyl, amine, epoxy, and hydroxyl groups, finely deposited or nucleated / grown SPR metals on the applied substrates can be achieved with controllable / tunable size and composition.

[0103] Due to the simplicity and potential for scale-up through chemical process development, the synthesis technique of the instant invention is highly transferable to production development ensuring consistency in quality and high reactivity / productivity. Particle synthesis technologies, including substrates and SPR metals embedded in substrates are feasible within existing classical / fundamental high-temperature chemical reactor or pilot designs.

[0104] Beyond materials development, the present invention introduces a photochemical method for PFAS removal in water, which will undoubtedly gamer significant attention in the fields of chemistry, environmental science, and biology. In particular, achieving rapid PFAS degradation rate under UV-A (mimicking sunlight) at neutral pH without the need for applied hydrogen represents a highly feasible process condition(s), which is scalable, and which is likely to draw significant commercial interest. Furthermore, the reaction process, using the catalyst libraries and methodology described herein, can be applied to the degradation via reduction of various other compounds (including both inorganic pollutants such as bromate, chlorate, and iodate, and volatile organic carbon compounds. Dehalogenation of halogenated phenols has also been demonstrated.

[0105] In addition, the present invention also realizes economic advantages due to its production simplicity. According to current cost calculations of products in chemical manufacturing, raw materials account for over 50-60% of the total price, while the remainder covers expenses related to reactor design / usage, product transfer / storage, purification, electricity, waste treatment, packaging, and labor. A preliminary cost analysis using Sigma- Aldrich database estimated thatthe raw materials cost for producing Pd embedded in silica nanoparticles is about $11.29 / gram. While raw material costs can vary significantly depending on vendors worldwide, a decrease in these costs is estimated over time. Additionally, if the synthetic technology described herein is integrated into existing chemical reactor pilot systems, there will be no need for new reactor installations. Based thereon, the total cost of the product (Pd embedded in silica substrates, containing 4% Pd by weight) is expected to be well below $22 / gram. Thus, it is believed that the simplicity of materials synthesis developed by the invention described herein promises significant cost savings for current manufacturing processes.

[0106] With these economic advantages in materials synthesis, the process developed for PFAS degradation is poised to gain substantial attention within the chemical, environmental, and process engineering communities. The stability and durability of the nanocatalyst design on stable substrates (SPR metals deposited silica- and carbon-based substrates) will reduce the costs associated with PFAS treatment. Highly efficient PFAS degradation capacity (12500 mg- PFAS / gram-Pd; 10 mg PFAS per 0.8 mg Pd in system) with rapid degradation rates at neutral pH and reusability under UVA without the need for applied hydrogen gas offer extraordinary advantages in terms of usage rate of the catalysts. Based on these advantages, the proposed materials and combine technique using SPR metals on stable silica- and carbon-based substrates can significantly reduce the cost of process for PFAS degradation than other methods, currently utilized, including thermal treatment, chemical redox process, and electrochemical reactions, which requires high energy inputs as well as materials / chemical costs.

[0107] A non-exhaustive list of materials that may be used in the practice of the invention is provided below in Table 1.Table 1. Materials usable in the invention

Claims

WHAT IS CLAIMED IS:

1. A plasmon-enhanced photocatalyst comprising: a. a support substrate; and b. a surface plasma resonance (SPR) metal coupled to / loaded on the support substrate.

2. The photocatalyst according to claim 1, wherein the support substrate comprises a silica or carbon-based substrate.

3. The photocatalyst according to claim 1, wherein the support substrate is selected from the group consisting of silica nanospheres, mesoporous silica nanoparticles, multiwalled carbon nanotubes, graphene, and graphene oxides, preferably wherein the graphene oxide is highly oxidized.

4. The photocatalyst according to any of claims 1 to 3, wherein surfaces of the support substrate are amine-functionalized or coated with amine-functionalized polymer.

5. The photocatalyst according to claim 4, wherein the amine is selected from the group consisting of primary amines, secondary amines, tertiary amines, and quaternary amines.

6. The photocatalyst according to any of claims 1 to 3, wherein the SPR metal is coupled to / loaded on the support substrate by embedding the SPR metal into and onto surfaces of the support substrate.

7. The photocatalyst according to claim 6, wherein the SPR metal is a plasmonic metal selected from the group consisting of gold, silver, copper, aluminum, magnesium, platinum, palladium, ruthenium and combinations of one or more of the foregoing.

8. The photocatalyst according to claim 6, wherein the SPR metal has a maximum diameter of less than about 10 nm, preferably less than about 8 nm, preferably less than about 6nm, or less than about 5 nm or less than about 4 nm or less than about 3 nm or less than about 2 nm or less than about 1 nm or less than about 0.5 nm.

9. The photocatalyst according to claim 6, wherein the SPR metal has an average diameter in the range of about 0.1 to about 8 nm, more preferably in the range of about 0.2 to about 5 nm.

10. The photocatalyst according to any of claims 1 to 3, wherein a wt.% of the SPR metal coupled to / loaded on the support substrate is in the range of about 1 to about 10 wt.%, more preferably about 1 to about 7 wt.%.

11. The photocatalyst according to any of claims 1 to 3, wherein the support substrate has a BET surface area between about 500 to about 800 m2 / g and pore sizes ranging from about 0.5 to about 7.5 nm.

12. A method of making a plasmon-enhanced photocatalyst, the method comprising a) functionalizing a silicon or carbon-based material with an amine to provide an amine functionalized support substrate; b) nucleating and growing a plasmonic metal on the amine functionalized silicon or carbon-based material in an aqueous solution; c) precipitating the resulting plasmon-enhanced photocatalyst; and d) separating the plasmon-enhanced photocatalyst from the aqueous solution.

13. The method according to claim 12, further comprising the step of purifying the photocatalyst prior to separating the plasmon-enhanced photocatalyst from the aqueous solution.

14. The method according to claim 12, wherein the silicon or carbon-based material is selected from the group consisting of silica nanospheres, mesoporous silica nanoparticles,multiwalled carbon nanotubes, graphene, and graphene oxides, preferably wherein the graphene oxide is highly oxidized.

15. The method according to any of claims 12 to 14, wherein the amine is selected from the group consisting of primary amines, secondary amines, tertiary amines, and quaternary amines.

16. The method according to claim 15, wherein the amine comprises one or more of aminosilanes, branched / linear polyethyleneimines, and aminated cellulose.

17. The method according to any of claims 12 to 14, wherein the plasmonic metal is selected from the group consisting of gold, silver, copper, aluminum, magnesium, platinum, palladium, ruthenium and combinations of one or more of the foregoing.

18. The method according to claim 17, wherein the plasmonic metal has a maximum diameter of less than about 10 nm, preferably less than about 8 nm, preferably less than about 6 nm, or less than about 5 nm or less than about 4 nm or less than about 3 nm or less than about 2 nm or less than about 1 nm or less than about 0.5 nm.

19. The method according to claim 17, wherein the plasmonic metal has an average diameter in the range of about 0.1 to about 8 nm, more preferably in the range of about 0.2 to about 5 nm.

20. The method according to any of claims 12 to 14, wherein the resulting plasmon-enhanced photocatalyst comprises about 1 to about 10 wt.%, more preferably about 2 to about 8 wt.%, more preferably about 3 to about 6 wt.% of the plasmonic metal.

21. A method of using plasmon-enhanced photocatalysis for the degradation of halogenated organic molecules / compounds in an aqueous solution, the method comprising the steps of:a. providing a plasmon-enhance photocatalyst according to any one of claims 1 to H; b. mixing the plasmon-enhanced photocatalyst, a hole scavenger, and the aqueous solution containing halogenated organic molecules / compounds in a reaction vessel to form a reaction suspension; c. bubbling carbon dioxide into the reaction vessel; d. irradiating the reaction suspension with a source of irradiation for a period of time to degrade and reduce the halogenated organic molecules / compounds to less toxic product compounds, preferably wherein the less toxic product compounds comprise non-fluorinated product compounds.

22. The method according to claim 21, wherein the halogenated organic molecules / compounds comprise polyfluoroalkyl and perfluoroalkyl compounds.

23. The method according to claim 21, wherein the SPR metal generates hydrogen molecules through water dissociation under the source of UV radiation.

24. The method according to claim 21, wherein the hole scavenger is selected from the group consisting of methanol, ethanol, isopropanol, tert-butyl alcohol, triethylamine, ascorbic acid, ammonium formate, mercaptopropionic acid, sodium borohydride, ethylenediaminetetraacetic acid (EDTA), sodium sulfite, and combinations of the foregoing.

25. The method according to claim 24, wherein the hole scavenger is added to the reaction suspension at a concentration within the range of about 1 to about 4 wt.%, more preferably about 2 to about 3 wt.%.

26. The method according to claim 21, wherein the source of irradiation operates at a wavelength, or spectrum of wavelengths, within the range of UV-A, UV-B, or UV-C or visible light.

27. The method according to claim 21, wherein hydrogen molecules generated during the photocatalytic reaction are bound to the surface of the SPR metal and dissociate into hydrogen atoms and / or hydrogen radicals due to surface plasmon resonance generated by excited electron clouds on the surface of the SPR metal under UV irradiation.

28. The method according to claim 27, wherein in situ produced hydrogen generated through water dissociation is used to regenerate the spent SPR metal.

29. The method according to claim 21, wherein the period of time the reaction suspension is irradiated is until complete degradation of the halogenated organic molecules / compounds is achieved.

30. The method according to claim 21, wherein the reaction is conducted at a pH in the range of 4 to 8, more preferably about 4.1 to about 7, more preferably about 4.2 to about 5.

31. The method according to claim 21, further comprising the step of periodically purging carbon dioxide from the reaction vessel.

32. The method according to claim 21, wherein the step of irradiating the reaction suspension with a source of irradiation is accomplished without applying external hydrogen gas.

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