High entropy catalysts for fluid purification systems

Abstract

The present invention relates to a water treatment system comprising: a vessel, wherein the vessel contains a catalytic material and a porous inorganic medium; wherein the catalytic material comprises a multi-metal oxide and is dispersed in the porous inorganic medium. The present invention also relates to a water treatment method comprising the steps of: providing an aqueous sample comprising an organic pollutant; adding one or more peroxide precursors to the aqueous sample; and contacting the aqueous sample with a catalytic material comprising a metal oxide; wherein the catalytic material is dispersed in a porous inorganic medium.

Description

[0001] Attorney Docket No. 047162-5399-00WO

[0002] TITLE

[0003] High Entropy Catalysts for Fluid Purification Systems

[0004] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U. S. Provisional Application No. 63 / 776,466, filed March 24, 2025, which is incorporated by reference herein in its entirety.

[0005] BACKGROUND OF THE INVENTION

[0006] Heterogeneous advanced oxidation processes (AOPs) generate reactive oxygen species (ROS) on catalyst surfaces to degrade organic contaminants. While AOPs have attracted significant research interest in wastewater treatment applications, their long-term stability in practical water environments, such as in groundwater and seawater, remains a challenge. This instability is partially due to surface deactivation mechanisms of catalysts, including metal leaching under oxidative conditions and surface fouling by polymeric byproducts, both of which deteriorate catalytic performance over time. Thus, the development of heterogeneous AOP catalysts with enhanced structural stability and reduced surface adsorption is essential. These processes are mainly driven by Fenton or Fenton-like reactions, in which oxidants such as hydrogen peroxide and persulfates are activated to generate hydroxyl (’OH) or sulfate radicals (SOT") with high oxidation potential. Among various catalysts, 3d transition metal-based oxides are widely recognized fortheir effectiveness in AOPs (Zhang, S. et al., Nat. Water. 2023, 1, 666-681; Miklos, D. B et al., Water Res. 2018, 139, 118-131; Hodges, B. C. et al., Nat. Nanotechnol.

[0007] 2018, 13, 642-650; Wang, Y. et al., Adv. Mater. 2024, 36, 2402935; Zhou, Q. et al., Proc. Natl. Acad. Sci. U. S. A. 2023, 120, e2300085120; Duan, P.-J. et al., Nat. Water. 2025, 3, 178-190; Xiong, Yu et al., Adv. Mater. 2022, 34, 2110653; Yun, Q. et al., Angew. Chem. Int. Ed. 2021, 60, 17155-17163; Lee, J. et al., Environ. Sci. Technol. 2020, 54, 3064-3081; Xu, J. et al., Nat. Sustain. 2021, 4, 233-241).

[0008] Heterogeneous advanced oxidation processes (AOPs) have been widely applied for the degradation of persistent organic contaminants in wastewater, wherein the reactive oxygen species (ROS) are generated at solid-water interfaces (Zhang et al., Proc. Natl. Acad. Sci. USA, 2023, 120, e2302407120; Chen et al., Nat. Commun., 2025, 16, 3789). Recent studies have revealed that at these interfaces, the overall contaminant transformation is indeed governedAttorney Docket No. 047162-5399-00WO

[0009] by non-radical oxidants rather than by bulk-phase radical pathways, with high-valent metal-oxo (HVMO) species on the solid surface, such as MnIV, FeIV, CoIV, and CuIII, facilitating selective oxidative coupling and polymerization through direct electron transfer (Zhang et al., Nat.

[0010] Commun., 2022, 13, 3005; Gao et al., Nat. Commun., 2024, 15, 2808; Zhang et al., Nat. Water, 2024, 2, 770; Liu et al., Nat. Commun., 2024, 15, 2327). Notably, such surface-confined HVMO species exhibit longer lifetimes, reduced susceptibility to water-matrix interferences (e.g., CL, HCO3, NO3, and natural organic matter), and distinct activity at near-neutral pH conditions, which are collectively desirable for practical long-term operation (Yan et al., Environ. Sci.

[0011] Technol., 2023, 57, 12153). Among the heterogeneous catalysts developed to date, Cu-based oxides are of particular interest for this approach due to their favorable oxidation potential of surface CuIIIHVMO species (E0(CuIII / CuII) = 2.3 V vs NHE in the solid state) and strong selectivity for the oxidative coupling of aromatic substrates (Wei et al., 2022, Environ. Sci.

[0012] Technol., 56, 8984; Huang et al., 2021, Environ. Sci. Technol., 55, 15361; Cho et al., ACS Nano, 2025, 19, 30137). Nonetheless, the ‘oxo-wall’ rule, wherein excessive d-orbital filling in late 3d-transition metals destabilizes metal-oxo bonds, results in a significant energetic barrier to CuIIIHVMO generation, leaving these species inherently transient and difficult to sustain (Larson et al., Nat. Rev. Chem., 2020, 4, 404). This electronic instability is further compounded by the weak lattice and coordination stability of Cu-based oxides, which promotes severe oxidative leaching of Cu during catalysis.

[0013] In this context, to simultaneously modulate the structural stability and catalytic reactivity of Cu-based oxides, incorporating Cu into multimetallic oxides has been explored (Huang et al., Proc. Natl. Acad. Sci. USA, 2022, 119, e2202682119; Huang et al., Angew. Chem. Int. Ed., 2025, 64, e202508754), and recently extended to high-entropy oxide (HEO) frameworks, which accommodate five or more elements within a single-phase lattice (Shi et al., ACS Catal., 2024, 14, 14796; Mo et al., ACS Catal., 2025, 15, 5928; Jin et al., Adv. Funct.

[0014] Mater., 2025, e20146; Yu et al., Small, 2025, 21, 2410819). Increased lattice disorder and distortion in HEO systems induce sluggish cation diffusion that suppresses metal dissolution, while multimetallic coordination environments facilitate electron delocalization across neighboring metal centers, lowering the energetic barrier for CuIIIHVMO generation. These attributes make HEOs a highly promising platform for overcoming the limitations of Cu-based catalysts (Aamlid et al., J. Am. Chem. Soc., 2023, 145, 5991). Despite these advantages,Attorney Docket No. 047162-5399-00WO

[0015] achieving more stable single-phase HEOs necessitates higher synthesis temperatures, which rigidifies the coordination environment around the Cu sites. This structural rigidification compromises both the adsorption affinity toward organic substrates and oxidants and the redox flexibility of Cu sites, thus ultimately hindering the generation of CuIIIHVMO species (Zhang et al., Chem. Eng. J., 2024, 488, 150826). Moreover, such high-temperature conditions promote phase separation, further destabilizing the single-phase lattice. Consequently, rational design strategies that preserve the entropic features of HEOs while mitigating limitations in high-temperature synthesis are essential for the sustainable operation of Cu-incorporating HEOs in heterogeneous AOPs.

[0016] Thus, there is a need in the art for methods of oxidative containment degradation. The present invention satisfies this unmet need.

[0017] SUMMARY OF THE INVENTION

[0018] In one aspect, the present invention relates to a water treatment system comprising: a vessel, wherein the vessel contains a catalytic material and a porous inorganic medium; wherein the catalytic material comprises a multi-metal oxide and is dispersed in the porous inorganic medium; wherein the multi-metal oxide is a compound of Formula (I), which is (M1)a(M2)b(M3)c(M4)d(M5)e(M6)fAl2O4, wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); and wherein a to f represent the molar ratio of each of M1, M2, M3, M4, M5, and M6, and a to f each has a value of 0.0 to 1.0, provided that the sum of a to f is 1.0.

[0019] In some examples, a to f each have a value of 0.167. In some examples, a is 1.0. In some examples, a and b are each 0.5. In some examples, a >b > c > d > e > f. In some examples, each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). In some examples, each ofAttorney Docket No. 047162-5399-00WO

[0020] M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). In some examples, the multi-metal oxide has the formula (Mn)0.167(Fe)0.167(Co)0.167(Ni)0.167(Cu)0.167(Zn)0.167Al2O4.

[0021] In some examples, the multi-metal oxide is hydrophobic. In some examples, the multi-metal oxide has a spinel crystal structure. In some examples, the multi-metal oxide is in the shape of a non-spherical particle. In some examples, the non-spherical particle has an average diameter of less than 10 mm. In some examples, the porous inorganic medium is selected from the list consisting of a packed media such as silica (SiO2), sand, glass media, ceramic media, membranes and filters, microfiltration and ultrafiltration membranes, fiber filters, metallic membrane and filters, and combinations thereof.

[0022] In one aspect, the present invention relates to a water treatment method comprising the steps of: providing an aqueous sample comprising an organic pollutant; adding one or more peroxide precursors to the aqueous sample; and contacting the aqueous sample with a catalytic material comprising a metal oxide; wherein the catalytic material is dispersed in a porous inorganic medium; wherein the multi -metal oxide is a compound of Formula (I), which is (M1)a(M2)b(M3)c(M4)d(M5)e(M6)fAl2O4; wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); and wherein a to f represent the molar ratio of each of M1, M2, M3, M4, M5, and M6, and a to f each has a value of 0.0 to 1.0, provided that the sum of a to f is 1.0.

[0023] In some examples, the method further comprises the step of adding a bicarbonate salt to the aqueous sample. In some examples, the bicarbonate salt has a concentration greater than 0.1 mM. In some examples, the multi-metal oxide is in an amount greater than 0.1 g / L of aqueous sample. In some examples, the method further comprises the step of filtering the aqueous sample before contacting with the catalytic material. In some examples, the methodAttorney Docket No. 047162-5399-00WO

[0024] further comprises the steps of oxidizing the organic pollutant to form an organic pollutant byproduct; and removing the organic pollutant byproduct from the aqueous sample.

[0025] In one aspect, the present invention relates to a catalytic material comprising a multi-metal oxide, wherein the multi-metal oxide has the formula

[0026] (Mn)0.167(Fe)0.167(Co)0.167(Ni)0.167(Cu)0.167(Zn)0.167Al2O4.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following detailed description of various embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings illustrative embodiments. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

[0029] Figure 1 depicts an X-ray diffraction (XRD) pattern of synthesized metal aluminate (Mno.i67Feo.i67Coo.i67Nio.i67Cuo.i67Zno.i67A1204; denoted as M6Al2O4hereafter)

[0030] Figure 2 depicts a scanning electron microscopy (SEM) image of M6Al2O4. Figure 3 depicts a scanning transmission electron microscopy (STEM) and high-angle annular dark-field STEM energy-dispersive spectroscopy (STEM-HAADF-EDS) elemental mapping of M6Al2O4(scale bar indicates 1 μm).

[0031] Figure 4 depicts an EDS spectrum of M6Al2O4.

[0032] Figure 5 depicts a chart displaying phenol degradation kinetics under different concentrations of bicarbonates.

[0033] Figure 6 depicts a chart displaying phenol degradation kinetics under different quenching agents.

[0034] Figure 7 depicts a chart displaying methyl phenyl sulfoxide (PMSO) degradation and methyl phenyl sulfone (PMSO2) generation kinetics.

[0035] Figure 8 depicts electron paramagnetic resonance (EPR) measurements using 5,5-Dimethyl-1 -pyrroline N-oxide (DMPO) as a spin-trapping agent under the bicarbonate concentration of 0 mM.

[0036] Figure 9 depicts EPR measurements using DMPO as a spin-trapping agent under the bicarbonate concentration of 1 mM.Attorney Docket No. 047162-5399-00WO

[0037] Figure 10 depicts EPR measurements using DMPO as a spin-trapping agent under the bicarbonate concentration of 10 mM. Experimental conditions for Figures 5 through Figure 10: [phenol]o = 100 pM, [PMS]o = 1 mM, and [catalyst]o = 0.5 g L1.

[0038] Figure 11 depicts a chart with chronoamperometry test (CA) measurements using a M6AhO4-loaded glassy carbon electrode (GCE) as working electrode. 100 mM of Na2SO4was used as electrolyte and the potential was +0.8 V vs. Ag / AgCl.

[0039] Figure 12 depicts a chart displaying long-term phenol degradation and total organic carbon (TOC) removal performance using M6AhO4 as a pack-bed column. Experimental condition: [phenol]o = 500 pM, [PMS]o = 1 mM, [NaHCO3] = 10 mM, and 10 g of catalyst. Water flow rate was 1 mL min which corresponds to the retention time of 500 s (-120 L m2h1).

[0040] Figure 13 depicts a chart displaying gel permeation chromatography (GPC) data of product which adsorbed on the surface of M6Al2O4after 120 h of operation under continuous water flow. The product was obtained after washing with methanol and toluene.

[0041] Figure 14 depicts a schematic illustration of the dual-functional mechanism of high-entropy spinel aluminate (MAl2O4) for bicarbonate-mediated CuIIIHVMO generation. Function I: Strong Al-0 bonding reinforces the lattice to suppress metal leaching. Function II: Surface Al sites enrich bicarbonate ions, enabling their coordination to neighboring Cu sites for effective CuIIIHVMO activation.

[0042] Figure 15, comprising Fig. 15A through Fig. 15G, depicts synthesis and structural characterization of the (MnFeCoNiCuZn)Al2O4catalyst. Fig. 15A depicts a schematic illustration of the preparation of (MnFeCoNiCuZn)Al2O4. Fig. 15B depicts representative XRD patterns of the Al2O3microfiber and (MnFeCoNiCuZn)Al2O4; α-Al2O3(#01-075-1862) and CuAl2O4(#01-075-4264) references were taken from the ICDD database. Fig. 15C depicts representative HAADF-STEM images. Fig. 15D depicts corresponding EDS elemental mapping images. Fig. 15E depicts a representative EDS spectrum of (MnFeCoNiCuZn)Al2O4. The insets of Fig. 15C and Fig. 15E show the particle size distribution and atomic percentages of transition metals, respectively. Fig. 15F depicts a representative HRTEM image of the interface region of Al2O3and (MnFeCoNiCuZn)Al2O4. Fig. 15G depicts representative Cu K-edge XANES spectra of (MnFeCoNiCuZn)Al2O4with Cu-based references. The inset shows the magnified pre-edge region.Attorney Docket No. 047162-5399-00WO

[0043] Figure 16 comprises Figure 16A through Figure 16D. Figure 16A depicts an SEM image of Al2O3microfibers. Figure 16B depicts an XRD pattern of Al2O3microfibers. Figure 16C depicts length distribution of Al2O3microfibers. Figure 16D depicts diameter distribution of Al2O3microfibers. α-Al2O3(#01-075-1862) references taken from the ICDD database.

[0044] Figure 17 depicts UV-Vis absorption spectra of metal nitrate precursor mixture (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) and its complexes with citric acid. For comparison, sodium nitrate (NaNO3) and citric acid were also measured.

[0045] Figure 18, comprising Figure 18A through Figure 18F, depicts individual UV-Vis absorption spectra of constituent metal nitrates and their citrate complexes. Comparison of Mn2+(Figure 18A), Fe3+(Figure 18B), Co2+(Figure 18C), Ni2+(Figure 18D), Cu2+(Figure 18E), and Zn2+(Figure 18F) nitrates and after the addition of citric acid. The final concentrations in the measured samples were 5 mM for both the metal nitrates and citric acid, except for Fe3+, which was prepared at 250 pM.

[0046] Figure 19 comprises Figure 19A and Figure 19B. Figure 19A depicts HAADF-STEM image and corresponding EDS elemental mapping images for Mn, Fe, Co, Ni, Cu, Zn, and C (scale bar indicates 500 nm). Figure 19B depicts an EDS spectrum after deposition of the metal-citrate complex on AI2O3 microfibers. The uniform distribution of transition metals and carbon in (a) confirms the formation of a homogeneous metal-citrate complex coating on AI2O3 microfibers. The EDS-determined atomic ratio between transition metals was Mn / Fe / Co / Ni / Cu / Zn = 16.0 / 14.8 / 17.0 / 16.2 / 18.4 / 17.7, which is well aligned with the equimolar initial precursor feed ratio. The Au signal was from the TEM grid.

[0047] Figure 20 comprises Figure 20A through Figure 20C. Figure 20A depicts a representative XRD pattern of the (MnFeCoNiCuZn)xOyon Al2O3fibers. Figure 20B depicts a representative HRTEM image of the (MnFeCoNiCuZn)xOyon Al2O3fibers. Figure 20C depicts a representative HAADF-STEM image with corresponding EDS elemental mapping images of the (MnFeCoNiCuZn)xOy on AI2O3 fibers. The XRD pattern in Figure 20A shows only the characteristic peaks of the AI2O3 substrate (01-AI2O3, see also Figure 16A), and the HRTEM image in Figure 16B reveals an amorphous layer coating on the AI2O3 fiber, both indicating the formation of an amorphous multi-metal oxide layer following the chemical combustion of the metal-citrate complex at 200 °C. In addition, the EDS elemental mapping analysis in Figure 20C demonstrates that this amorphous layer consists of uniformly distributed transition metals. TheseAttorney Docket No. 047162-5399-00WO

[0048] results confirm that the (MnFeCoNiCuZn)xOycoating remains as a distinct amorphous phase on the Al2O3surface without significant Al3+interdiffusion across the interfaces at this stage.

[0049] Figure 21 depicts magnified Cu K-edge XANES spectra at the pre-edge region for the (MnFeCoNiCuZn)Al2O4catalyst and Cu-based references. The pre-edge peak at 8978.6 eV denotes the 1s → 3d transition of CuII, and the peak intensity reflects the structural asymmetry of Cu sites, as observed in Cu2CO3(OH)2references, which demonstrates the high-entropy lattice disorder and the asymmetric environment of Cu in (MnFeCoNiCuZn)Al2O4(Uchikoshi, Struct. Chem., 2019, 30, 61; Klokishner et al., J. Phys. Chem. A, 2011, 115, 9954).

[0050] Figure 22, comprising Figure 22A through Figure 22H, depicts data from a bicarbonate-enhanced catalytic performance and mechanistic investigation. Figure 22A depicts phenol degradation kinetics of (MnFeCoNiCuZn)Al2O4at various initial bicarbonate concentrations ([NaHCO3] = 0, 1, and 10 mM). Figure 22B and Figure 22C depict mass-normalized rate constants (knorm) and concentration of leached Cu ions after the reaction for CuO, Q1AI2O4, and (MnFeCoNiCuZn)A12O4. The knorm values were obtained by normalizing the apparent rate constant to the total mass of transition metals ( TM). The inset in Figure 22C shows the magnified leaching data for (MnFeCoNiCuZn)AhO4at [NaHCO3] = 10 mM. Figure 22D depicts the effect of scavengers (MeOH, tert-BuOH, and TEMP) on phenol degradation. Figure 22E depicts EPR spectra of the reaction system in the presence of DMPO as a spin-trapping agent at different time intervals. Figure 22F depicts concentration profiles of phenol, PMSO, and PMSO2 during the competitive oxidation of a 1:1 mixture of phenol and PMSO. Figure 22G depicts long-term continuous flow performance for phenol removal and the corresponding leached Cu ion concentration over 336 h. The inset illustrates the configuration of the pack-bed reactor. Figure 22H depicts GPC analysis of the reaction products extracted by THF after 336 h of column test. Experimental conditions: [catalyst]o = 0.1 g L1, [PMS]o = 1 mM, and [phenol]o = 100 pM, and [NaHCO3] = 10 mM (unless otherwise specified).

[0051] Figure 23 comprises Figure 23 A and Figure 23B. Figure 23 A depicts XRD patterns of the CuAl2O4(green) and CuO (purple) supported on Al2O3microfibers. The orange and yellow stars denote the characteristic peaks corresponding to the spinel CUAI2O4 and monoclinic CuO phases, respectively. References were taken from the ICDD database (01-AI2O3: 01-075-1862, CUAI2O4: 01-075-4264, and CuO: 01-070-6831). Figure 23B depicts HAADF-STEM images and the corresponding EDS elemental mapping images for the CUAI2O4 (top) andAttorney Docket No. 047162-5399-00WO

[0052] CuO (bottom) catalysts. For the synthesis of CuAl2O4and CuO supported on Al2O3microfibers, the input amount of metal precursors was stoichiometrically adjusted to ensure that the total molar concentration of transition metals consisted of that of the (MnFeCoNiCuZn)Al2O4catalyst. Specifically, 12.0 mL of an aqueous copper nitrate solution (40 mM) was used for CuAl2O4, while 120 mM was employed for CuO.

[0053] Figure 24 comprises Figure 24 A and Figure 24B. Figure 24 A and Figure 24B depict degradation kinetics of phenol and concentrations of leached metal ions determined by ICP-MS after the reaction in the unbuffered condition for (MnFeCoNiCuZn)Al2O4, CuAl2O4, and CuO. Experimental conditions: [catalyst]o = 0.5 g L \ [PMS]o = 1 mM, [phenol]o = 0.1 mM, initial pH = 3.5, and room temperature.

[0054] Figure 25 depicts phenol degradation kinetics of (MnFeCoNiCuZn)Al2O4under standard conditions and with D2O solvent exchange.

[0055] Figure 26 depicts phenol degradation kinetics of (MnFeCoNiCuZn)Al2O4under standard conditions and with the addition of DMSO.

[0056] Figure 27 depicts time-dependent UV-Vis absorption spectra after the addition of sodium periodate as a selective CuIITquencher during the catalytic reaction in the (MnFeCoNiCuZn)AbO4 system.

[0057] Figure 28 depicts phenol degradation kinetics for (MnFeCoNiCuZn)Al2O4and derivative different composition catalysts: (MnFeCoNiCu)Al2O4, (MnFeCoNi)Al2O4, and (MnFeCo)Al2O4.

[0058] Figure 29 depicts phenol degradation kinetics for (MnFeCoNiCuZn)Al2O4with different buffer conditions.

[0059] Figure 30, comprising Figure 30A through Figure 30D, depicts in situ spectroscopic investigation of the bicarbonate-facilitated Cumactivation mechanism. Figure 30A depicts ATR-FTIR difference spectra of (MnFeCoNiCuZn)Al2O4and reference catalysts in the bicarbonate solution. Figure 30B depicts in situ Cu K-edge XANES spectra displaying the energy shift from Cu2+(8976.8 eV) to Cu3+(8980.3 eV). Figure 30C depicts FT-EXAFS spectra and (inset) coordination numbers (CN) of the Cu-0 shell showing the increase from 3.1 to 4.58. Figure 30D depicts a schematic illustration for the bicarbonate-facilitated CuIIIHVMO generation on the (MnFeCoNiCuZn)AbO4 surface.Attorney Docket No. 047162-5399-00WO

[0060] Figure 31 depicts HAADF-STEM image and corresponding EDS elemental mapping for (MnFeCoNiCuZn)Al2O4after 336 h of continuous water flow operation. The uniform distribution of constituent elements and the prominent carbon signal confirm the anchoring of organic matter on the catalyst surface during the reaction.

[0061] Figure 32 depicts a representative LC-MS spectrum of the reaction product after retrieved from THF washing of the (MnFeCoNiCuZn)Al2O4catalyst after 336 h of continuous water flow operation.

[0062] DETAILED DESCRIPTION

[0063] It is to be understood that the Figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements used in fluid purification. Those of ordinary skill in the art may recognize that other elements and / or steps are desirable and / or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.

[0064] As used herein, each of the following terms have the meanings associated with it as specified below. Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0065] The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0066] As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.Attorney Docket No. 047162-5399-00WO

[0067] Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

[0068]

[0069] The present invention relates to water treatment systems comprising catalytic processes, materials, and methods of use thereof. In some examples, the catalytic process comprises the generation of high-valent oxo (HVMO) species. In some examples, the catalytic process comprises a non-radical oxidation pathway. In some examples, the catalytic process demonstrates an unexpected and unique synergistic effect, wherein bicarbonate ions in natural water systems accelerate degradation kinetics and stabilize the HVMO species on a catalyst interface.

[0070] Water Treatment Systems

[0071] In one aspect, the present invention relates to a water treatment system comprising a vessel, wherein said vessel contains a catalytic material and a porous inorganic medium; wherein the catalytic material comprises a multi-metal oxide and is dispersed in the porous inorganic medium.

[0072] In some examples, the vessel is selected from the list of, but not limited to, a packed bed reactor, a pressurized membrane reactor, a batch reactor, a semi-batch reactor, a pulsed bed reactor, a fixed-bed reactor, a plug flow reactor, and a packed bed column. In some examples, the vessel includes a means for agitation, selected from the list of but not limited to, an agitator, a baffle, an impellor and combinations thereof. In some examples, the system is a portable self-contained unit or incorporated into a non-portable structure.Attorney Docket No. 047162-5399-00WO

[0073] A flow of water through the system may be controlled by a valve and the rate of flow may be monitored and varied using the valve or similar mechanism. The system may further include a monitoring device located downstream of the outlet. In some examples the system has a replaceable module, wherein the catalytic material and / porous inorganic medium may be located in, or may be part of a multiple modular system to facilitate maintenance of the catalytic material while maintaining constant flow and remediation of the wastewater.

[0074] Additionally, multiple modules and / or systems may be used in series and / or parallel. The flow rate of the wastewater and amount of catalyst and other components described herein may be determined by the desired amount of oxidation and the composition of the wastewater.

[0075] In some examples, the catalytic material is dispersed in a porous inorganic medium including, but are limited to, packed media such as silica (SiO2), sand, glass media, ceramic media, membranes and filters, microfiltration and ultrafiltration membranes, fiber filters, metallic membranes and filters, and the like. In some examples, the catalytic material is dispersed within the interspatial space of the porous inorganic media, wherein the size of the interstitial space may be used to exclude colloids, particles, microorganisms, and organic matter that are present in water to be treated, thereby reducing the quantity of material that contacts the catalytic material. In some examples, the catalytic material is supported on carbon or graphene oxide.

[0076] In some examples, the system comprises a microfiltration membrane or an ultrafiltration membrane. In some examples, the micro- or ultrafiltration membrane comprises ZrO₂ and TiO₂. In some examples, the micro- or ultrafiltration membrane has a pore diameter between 1 nm and 1000 nm.

[0077] In some examples, the system comprises a peroxide precursor or peroxide including but not limited to peroxy-monosulfate, peroxy di sulfate, peracetic acid, percarbonic acid, ozone, and hydrogen peroxide. In some examples, the system comprises a bicarbonate salt including, but not limited to, sodium bicarbonate, potassium bicarbonate, and calcium bicarbonate. In some examples, the system comprises a borate salt including, but not limited to, sodium metaborate, sodium tetraborate, sodium borate, calcium borate, potassium borate, and the like.

[0078] In some examples, the multi-metal oxide comprises a metal selected from the list of, but not limited to, aluminum (Al), boron (B), gallium (Ga), indium (In), zirconium (Zr),Attorney Docket No. 047162-5399-00WO

[0079] hafnium (Hf), niobium (Nb), vanadium (V), chromium (Cr), strontium (Sr), calcium (Ca), barium (Ba), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), yttrium (Y), thallium (Tl), scandium (Sc), titanium (Ti), magnesium (Mg), zinc (Zn), copper (Cu), lead (Pb), iron (Fe), nickel (Ni), tin (Sn), cobalt (Co), manganese (Mn), combinations thereof, oxides thereof, and any oxidation state thereof. In some examples, the multi-metal oxide has high configurational entropy. In some examples, the multi-metal oxide has a high number of oxygen vacancies. In some examples, the multi-metal oxide possesses an active catalytic center. In some examples, the multi-metal oxide is nanostructured. In some examples, the multi-metal oxide is hydrophobic. In some examples, the multi-metal oxide has a spinel crystal structure.

[0080] In some examples, the multi-metal oxide contains between 1 and 10 metals M1-M10and is a compound of the following formula: (M1)a(M2)b(M3)c(M4)d(M5)e(M6)f (M7)g(M8)h(M9)i(M10)jA12O4 wherein each of M1, M2, M3, M4, M5, M6, M7, M8, M9, and M10independently represents a metal selected from the list including, but not limited to, scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); wherein a-j represent the molar ratio of each metal M1-M10, and a-j each have a value of 0 to 1.0, wherein at least one of a to j is not 0, such that a+b+c+d+e+f+g+h+i+j is 1.

[0081] In some examples, a is 1 and the multi-metal oxide is a compound is of the formula (M¹)₁.₀Al₂O₄. In some examples, a is 0.5 and b is 0.5, and the multi-metal oxide is a compound is of the formula (M¹)₀.₅(M²)₀.₅Al₂O₄. In some examples, a is 0.33, b is 0.33, and c is 0.33, and the multi-metal oxide is a compound is of the formula (M¹)₀.₃₃(M²)₀.₃₃(M³)₀.₃₃Al₂O₄. In some examples, a is 0.25, b is 0.25, c is 0.25, and d is 0.25, and the multi-metal oxide is a compound is of the formula (M¹)₀.₂₅(M²)₀.₂₅(M³)₀.₂₅(M⁴)₀.₂₅Al₂O₄. In some examples, a is 0.2, b is 0.2, c is 0.2, d is 0.2, and e is 0.2, and the multi-metal oxide is a compound is of the formula (M¹)₀.₂(M²)₀.₂(M³)₀.₂(M⁴)₀.₂(M⁵)₀.₂Al₂O₄. In some examples, a is 0.167, b is 0.167, c is 0.167, d isAttorney Docket No. 047162-5399-00WO

[0082] 0.167, e is 0.167, and f is 0.167 and the multi-metal oxide is a compound is of the formula (M¹)₀.₁₆₇(M²)₀.₁₆₇(M³)₀.₁₆₇(M⁴)₀.₁₆₇(M⁵)₀.₁₆₇(M⁶)₀.₁₆₇Al₂O₄. In some examples, a is 0.142, b is 0.142, c is 0.142, d is 0.142, e is 0.142, f is 0.142, g is 0.142 and the multi-metal oxide is a compound is of the formula (M¹)₀.₁₄₂(M²)₀.₁₄₂(M³)₀.₁₄₂(M⁴)₀.₁₄₂(M⁵)₀.₁₄₂(M⁶)₀.₁₄₂(M⁷)₀.₁₄₂Al₂O₄. In some examples, a is 0.125, b is 0.125, c is 0.125, d is 0.125, e is 0.125, f is 0.125, g is 0.125, and h is 0.125, and the multi-metal oxide is a compound is of the formula (M¹)₀.₁₂₅(M²)₀.₁₂₅(M³)₀.₁₂₅(M⁴)₀.₁₂₅(M⁵)₀.₁₂₅(M⁶)₀.₁₂₅(M⁷)₀.₁₂₅(M⁸)₀.₁₂₅Al₂O₄. In some examples, a is 0.111, b is 0.111, c is 0.111, d is 0.111, e is 0.111, f is 0.111, g is 0.111, h is 0.111, and i is 0.111, and the multi-metal oxide is a compound is of the formula (M¹)₀.₁₁₁(M²)₀.₁₁₁(M³)₀.₁₁₁(M⁴)₀.₁₁₁(M⁵)₀.₁₁₁(M⁶)₀.₁₁₁(M⁷)₀.₁₁₁(M⁸)₀.₁₁₁(M⁹)₀.₁₁₁Al₂O₄. In some examples, a is 0.1, b is 0.1, c is 0.1, d is 0.1, e is 0.1, f is 0.1, g is 0.1, h is 0.1, and i is 0.1, andj is 0.1, and the multi-metal oxide is a compound is of the formula (M¹)₀.₁(M²)₀.₁(M³)₀.₁(M⁴)₀.₁(M⁵)₀.₁(M⁶)₀.₁(M⁷)₀.₁(M⁸)₀.₁(M⁹)₀.₁(M¹⁰)₀.₁Al₂O₄.

[0083] In some examples, M¹-M10represent 3d transition metals selected from the list of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).

[0084] In some examples, the multi-metal oxide is a compound of the following formulas, but is not limited to (Fe)a(Co)b(Ni)c(Mn)d(Zn)eAl₂O₄, (Fe)a(Co)b(Ni)c(Cu)d(Zn)eAl₂O₄, (Ti)a(V)b(Cr)c(Mn)d(Fe)eAl₂O₄, (Cu)a(Zn)b(Ni)c(Co)d(Fe)eCu₂O₄, (Ti)a(Fe)b(Co)c(Ni)d(Zn)eFe2O4, (Mn)a(Fe)b(Co)c(Ni)d(Zn)eFe2O4, (Mg)a(Fe)b(Co)c(Ni)d(Zn)eMg₂O₄, and (Cr)a(Fe)b(Co)c(Ni)d(Zn)eCr₂O₄.

[0085] In some examples, the multi-metal oxide is a compound of Formula (I): (M¹)a(M²)b(M³)c(M⁴)d(M⁵)e(M⁶)fAl₂O₄, wherein at least one of a to f is not 0, such that a+b+c+d+e+f = 1. In some examples, the multi-metal oxide is a compound of the following formulas, but is not limited to, (M¹)a(M²)b(M³)c(M⁴)d(M⁵)eAl₂O₄, (M¹)a(M²)b(M³)c(M⁴)dAl₂O₄, (M¹)a(M²)b(M³)cAl₂O₄, (M¹)a(M²)bAl₂O₄, and (M¹)aAl₂O₄.

[0086] In some examples, the molar the ratio of a:b:c:d:e:f is about 1:1:1:1:1:1. In some examples, the ratio of a:b:c:d:e:f is about 2:1:1:1:1:1. In some examples, the ratio of a:b:c:d:e:f is about 1:2:1: 1:1:1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1:2: 1: 1: 1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1: 1:2: 1: 1. In some examples, the ratio of a:b:c:d:e:f is about 1:1:1:1:2:1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1: 1: 1: 1:2. In someAttorney Docket No. 047162-5399-00WO

[0087] examples, the ratio of a:b:c:d:e:f is about 2:2: 1: 1: 1: 1. Tn some examples, the ratio of a:b:c:d:e:f is about 1:2:2: 1:1:1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1:2:2: 1:1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1: 1:2:2: 1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1: 1: 1:2:2. In some examples, the ratio of a:b:c:d:e:f is about 2: 1: 1: 1:2: 1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:2: 1: 1: 1. In some examples, the ratio of a:b:c:d:e:f is about 1:2:2:2: 1: 1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1:2:2:2: 1. In some examples, the ratio of a:b:c:d:e:f is about 1:2:2:2: 1: 1. In some examples, the ratio of a:b:c:d:e:f is about 1: 1: 1:2:2:2. In some examples, the ratio of a:b:c:d:e:f is about 2:1:1:2:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:1: 1:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:2:2:1:1. In some examples, the ratio of a:b:c:d:e:f is about 1:2:2:2:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2: 1:2:2:2: 1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:1:2:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:2: 1:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:1:2:2:1. In some examples, the ratio of a:b:c:d:e:f is about 2:2:2: 1:1:2. In some examples, a> b > c > d > e > f.

[0088] In some examples, the multi-metal oxide can take the morphology of any 3-dimensionally shaped particle, which includes but is not limited to, a non-spherical particle with a random and indistinguishable shape, an angular particle with sharp edges and corners, a rodlike particle, a platelet-like particle, a sheet-like particle, a rough or granular particle, a spherical particle which can optionally agglomerate into a larger spherical cluster of particles, a dendritic-like particle where particles grow with a central trunk and branching arms, and any combination thereof.

[0089] In some examples, the multi-metal oxide is of the shape of a non-spherical particle with an average diameter greater than about 1 nanometer (nm), greater than about 10 nm, greater than about 50 nm, greater than about 100 nm, greater than about 200 nm, greater than about 300 nm, greater than about 400 nm, greater than about 500 nm, greater than about 600 nm, greater than about 700 nm, greater than about 800 nm, greater than about 900 nm, greater than about 1 micrometer (pm), greater than about 5 pm, greater than about 10 pm, greater than about 20 pm, greater than about 30 pm, greater than about 40 pm, greater than about 50 pm, greater than about 60 pm, greater than about 70 pm, greater than about 80 pm, greater than about 90 pm, greater than about 100 pm, greater than about 150 pm, greater than about 200 pm, greater than about 250 pm, greater than about 300 pm, greater than about 350 pm, greater than aboutAttorney Docket No. 047162-5399-00WO

[0090] 400 gm, greater than about 450 gm, greater than about 500 gm, greater than about 1 millimeter (mm), greater than about 5 mm, greater than about 10 mm, or greater than about 100 mm.

[0091] In some examples, the multi-metal oxide is of the shape of a non-spherical particle with an average diameter of less than about 1 nanometer (nm), less than about 10 nm, less than about 50 nm, less than about 100 nm, less than about 200 nm, less than about 300 nm, less than about 400 nm, less than about 500 nm, less than about 600 nm, less than about 700 nm, less than about 800 nm, less than about 900 nm, less than about 1 micrometer (pm), less than about 5 gm, less than about 10 gm, less than about 20 gm, less than about 30 gm, less than about 40 gm, less than about 50 gm, less than about 60 gm, less than about 70 gm, less than about 80 gm, less than about 90 gm, less than about 100 gm, less than about 150 gm, less than about 200 gm, less than about 250 gm, less than about 300 gm, less than about 350 gm, less than about 400 gm, less than about 450 gm, less than about 500 gm, less than about 1 millimeter (mm), less than about 5 millimeters, less than about 10 millimeters, or less than about 100 mm(mm).

[0092] In some examples, the multi-metal oxide is of the shape of a non-spherical particle with an average diameter of about 1 nanometer (nm), about 10 nm, about 50 nm, about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 1 micrometer (gm), about 5 gm, about 10 gm, about 20 gm, about 30 gm, about 40 gm, about 50 gm, about 60 gm, about 70 gm, about 80 gm, about 90 gm, about 100 gm, about 150 gm, about 200 gm, about 250 gm, about 300 gm, about 350 gm, about 400 gm, about 450 gm, about 500 gm, about 1 millimeter, about 2 millimeters, about 5 millimeters, or about 10 millimeters (mm).

[0093] In some examples, catalytic material is made through a method comprising the steps of: dispersing a metal nitrate in a solvent; adding an acid to the solution and heating the solution to create a gel; and heating the gel to create the catalytic material. In some examples, the catalytic material comprises a multi-metal oxide. The catalytic material is further described elsewhere in the instant invention.

[0094] In some examples, the metal nitrate comprises a metal, including but not limited to, any metal described in the instant invention. In some examples, the acid is selected from the list of, but not limited to, citric acid, tartaric acid, malic acid, lactic acid, fumaric acid, acetic acid, oxalic acid, succinic acid, glutaric acid, ascorbic acid, pyruvic acid, hydrochloric acid, sulfuric acid, and the like. In some embodiments, the solvent is aqueous or / and organic.Attorney Docket No. 047162-5399-00WO

[0095] In some examples, the gel is heated to a temperature greater than 10 °C, greater than 20 °C, greater than 30 °C, greater than 40 °C, greater than 50 °C, greater than 60 °C, greater than 70 °C, or greater than 80 °C. In some embodiments, the gel is heated to a temperature of about 70 °C, of about 80°C, or of about 90°C.

[0096] In some examples, the step of heating the gel further comprises the step of grinding the gel in a mortar and combusting the gel in the mortar at a temperature of greater than 100 °C to create an intermediate product. In some examples, the gel is combusted at a temperature of greater than 100 °C, greater than 120 °C, greater than 130 °C, greater than 140 °C, greater than 150 °C, greater than 160 °C, greater than 170 °C, greater than 180 °C, greater than 190 °C, or greater than 200 °C. In some examples, the gel is combusted at a temperature of about 100 °C, of about 200 °C, or of about 300 °C.

[0097] In some examples, the step of grinding the gel in a mortar and combusting at a temperature of greater than 100 °C to create an intermediate product, further comprises the step of transferring the intermediate product to a crucible and heating the crucible with the intermediate product to create the catalytic material. In some examples, step of heating the crucible with the intermediate product is done at a temperature of greater than 500 °C. In some examples, step of heating the crucible with the intermediate product is done at a temperature of greater than 500 °C induces calcination of the intermediate product.

[0098] In some examples, step of heating the crucible with the intermediate product is done at a temperature of greater than 500 °C, greater than 600 °C, greater than 700 °C, greater than 800 °C, or greater than 900 °C. In some examples, step of heating the crucible with the intermediate product is done at a temperature of about 700 °C, of about 800 °C, of about 900 °C, or about 1000 °C.

[0099] In some examples, once a desired temperature is reached in any part of the method, said desired temperature may be maintained for a period of time.

[0100] Water Treatment Methods

[0101] In one aspect, the present invention relates in part to a water treatment method comprising the steps of: providing an aqueous sample comprising an organic pollutant; adding one or more peroxide precursors to the aqueous sample; and contacting the aqueous sample with a catalytic material comprising a multi-metal oxide; wherein the catalytic material is dispersed inAttorney Docket No. 047162-5399-00WO

[0102] a porous inorganic medium. In some examples, the multi-metal oxide contains between 1 and 10 metals M¹-M10and is a compound of the following formula: (M1)a(M2)b(M3)c(M4)d(M3)e(M6)f (M7)g(M8)h(M9)i(M10)jA12O4. In some examples, the multi-metal oxide is a compound of Formula (I): (M¹)a(M²)b(M³)c(M⁴)d(M⁵)e(M⁶)fAl₂O₄; wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); and wherein a to f each has a value of 0.0 to 0.3, provided that the sum of a to f is 1.0. Further examples of the catalytic material and the inorganic porous medium are described elsewhere in the instant invention.

[0103] In some examples, the step of contacting the aqueous sample with a catalytic material comprising a multi-metal oxide further comprises the step of contacting the peroxide precursor with the multi-metal oxide. In some examples, the step of contacting the peroxide precursor with the multi-metal oxide further comprises the step of absorption of the peroxide precursor onto the multi-metal oxide. In some examples, the step of absorption of the peroxide precursor onto the multi-metal oxide promotes an electron transfer process between the peroxide precursor and the organic pollutant in the aqueous sample. In some examples, the electron transfer process between the peroxide precursor and the organic pollutant in the aqueous sample induces the formation of an organic pollutant radical. In some examples, the formation of the organic pollutant radical induces degradation of the organic pollutant to form a pollutant byproduct. In some examples, the pollutant byproduct is polymeric. In some examples, the polymeric byproduct does not adhere to the catalytic material, preserving active sites and maintaining catalytic efficiency. This is in part due to the hydrophobic nature of the multi-metal oxide.

[0104] In some examples, the step of contacting the aqueous sample with a catalytic material comprising a multi-metal oxide further comprises the step of removing the organic pollutant byproduct. In some examples, the pollutant byproduct may be removed at any part of the method to ensure stable and continuous long-term operation. In some examples, the step ofAttorney Docket No. 047162-5399-00WO

[0105] removing the organic pollutant byproduct comprises washing the catalytic material with organic solvents known in the art. In some examples, the step of removing the organic pollutant byproduct comprises heating the catalytic material. In some examples, the step of removing the organic pollutant byproduct comprises applying an electric current to catalytic material. In some examples, the step of contacting the aqueous sample with a catalytic material comprising a multimetal oxide further comprises the step of filtering the aqueous sample before contacting the aqueous sample with the catalytic material. The filtering step may remove any waste, sediments, and / or objects which may hinder the performance of the catalytic material.

[0106] As described above, the multi-metal oxide may effectively activate peroxides for pollutant degradation through an electron transfer process, wherein peroxides absorb to the catalyst surface and transfer electrons to target pollutants, which leads to the formation of pollutant radicals and their degradation. Peroxide molecules or peroxide precursor molecules include but are not limited to peroxymonosulfate, peroxydisulfate, peracetic acid, percarbonic acid, percarbonate salts, hydrogen peroxide, ozone, potassium persulfate, calcium peroxide, sodium peroxide, magnesium peroxide, and combinations thereof. In some examples, pollutants include but are not limited to, phenols, carboxylic acid, aromatic hydrocarbons, pesticides, nitroaromatic compounds, azo-dyes, perfluorinated compounds, and the like. In some examples, no residual peroxide exists at the end of the electron transfer process, or residual peroxide concentration at the end of the electron transfer process is less than the detection limit, or the residual peroxide concentration at the end of the electron transfer process is less than 10 ppm, or less than 5 ppm, or less than 3 ppm, or less than 1 ppm. In some examples, the electron transfer process degrades organic pollutants in aqueous sources.

[0107] In some examples, the step of contacting the peroxide precursor with the catalytic material does not involve the production of reactive radicals. In some examples, the electron transfer process described above occurs along with the production of reactive radicals.

[0108] In some examples, the step of contacting the aqueous source with a catalytic material comprising a multi-metal oxide further comprises the step of adding a bicarbonate salt and / or a borate salt to the aqueous sample. In some examples, the aqueous sample is already rich in bicarbonate salts and / or borate salts, such as in most natural water environments. In some examples, the bicarbonate salt and / or borate salt accelerates the organic pollutant degradation, compared to when there is a decreased amount or no bicarbonate salt is involved in the methodAttorney Docket No. 047162-5399-00WO

[0109] described herein. In some examples, the bicarbonate salt and / or borate salt suppresses metal leaching in the catalytic material. In some examples, the bicarbonate salt and / or borate salt acts as a pH buffer. Bicarbonate salts include, but are not limited to, sodium bicarbonate, potassium bicarbonate, and calcium bicarbonate. Borate salts include, but are not limited to, sodium metaborate, sodium tetraborate, sodium borate, calcium borate, potassium borate, and the like.

[0110] In some examples, the aqueous sample is selected from the list of, but not limited to, municipal wastewater, industrial wastewater, ground water, and surface water. In some examples, organic pollutants include but are not limited to, phenols, carboxylic acid, aromatic hydrocarbons, pesticides, nitroaromatic compounds, azo-dyes, perfluorinated compounds, and the like.

[0111] In some examples, the concentration of the peroxide precursors is greater than 0.1 mM, greater than 0.5 mM, greater than 1.0 mM, greater than 2.0 mM, greater than 5.0 mM, greater than 10.0 mM, greater than 25.0 mM, greater than 50.0 mM, greater than 100 mM, greater than 500.0 mM, or greater than 1 M. In some examples, the concentration of peroxide precursors is less than 0.1 mM, less than 0.5 mM, less than 1.0 mM, less than 2.0 mM, less than 5.0 mM, less than 10.0 mM, less than 25.0 mM, less than 50.0 mM, less than 100 mM, less than 500.0 mM, or less than 1 M. In some examples, the concentration of peroxide precursors is about 0.1 mM, about 0.5 mM, about 1.0 mM, about 2.0 mM, about 5.0 mM, about 10.0 mM, about 25.0 mM, about 50.0 mM, about 100 mM, about 500.0 mM, or about 1 M.

[0112] In some examples, the concentration of the bicarbonate salt in the sample after the addition of bicarbonate salt is greater than 0.1 mM, greater than 0.5 mM, greater than 1.0 mM, greater than 2.0 mM, greater than 5.0 mM, greater than 10.0 mM, greater than 25.0 mM, greater than 50.0 mM, greater than 100 mM, greater than 500.0 mM, or greater than 1 M. In some examples, the concentration of the bicarbonate salt in the sample after the addition of bicarbonate salt is less than 0.1 mM, less than 0.5 mM, less than 1.0 mM, less than 2.0 mM, less than 5.0 mM, less than 10.0 mM, less than 25.0 mM, less than 50.0 mM, less than 100 mM, less than 500.0 mM, or less than 1 M. In some examples, the concentration of the bicarbonate salt in the sample after the addition of bicarbonate salt is about 0.1 mM, about 0.5 mM, about 1.0 mM, about 2.0 mM, about 5.0 mM, about 10.0 mM, about 25.0 mM, about 50.0 mM, about 100 mM, about 500.0 mM, or about 1 M.Attorney Docket No. 047162-5399-00WO

[0113] In some examples, the multi-metal oxide is any amount necessary to effectively oxidize and / or degrade the organic pollutants. In some examples, the multi-metal oxide is in an amount of greater than 0.1 g / L of aqueous sample, greater than 0.2 g / L of aqueous sample, greater than 0.3 g / L of aqueous sample, greater than 0.4 g / L of aqueous sample, greater than 0.5 g / L of aqueous sample, greater than 0.7 g / L of aqueous sample, greater than 1 g / L of aqueous sample, greater than 2 g / L of aqueous sample, greater than 5 g / L of aqueous sample, or greater than 10 g / L of aqueous sample. In some examples, the multi-metal oxide is in an amount of less than 0.1 g / L of aqueous sample, less than 0.2 g / L of aqueous sample, less than 0.3 g / L of aqueous sample, less than 0.4 g / L of aqueous sample, less than 0.5 g / L of aqueous sample, less than 0.7 g / L of aqueous sample, less than 1 g / L of aqueous sample, less than 2 g / L of aqueous sample, less than 5 g / L of aqueous sample, or less than 10 g / L of aqueous sample.

[0114] In some examples, the step of contacting the aqueous sample with the catalytic material is done with a flow rate of at least 1 μL / min, at least 5 μL / min, at least 25 μL / min, at least 100 μL / min, at least 500 μL / min, at least 1 mL / min, at least 5 mL / min, at least 50 mL / min, at least 100 mL / min, at least 250 mL / min, at least 500 mL / min, at least 1 L / min, or at least 5 L / min. In some examples, the step of contacting the aqueous sample with the catalytic material is done with a flow rate of less than 1 μL / min, less than 5 μL / min, less than 25 μL / min, less than 100 μL / min, less than 500 μL / min, less than 1 mL / min, less than 5 mL / min, less than 50 mL / min, less than 100 mL / min, less than 250 mL / min, less than 500 mL / min, less than 1 L / min, or less than 5 L / min.

[0115] EXPERIMENTAL EXAMPLES

[0116] The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

[0117] Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the materials, devices, and kits of the present invention and practice the claimed methods. TheAttorney Docket No. 047162-5399-00WO

[0118] following working examples, therefore, specifically point out exemplary embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

[0119] Example 1: Advanced Oxidation Processes

[0120] High-entropy oxides (HEOs) have attracted great attention as promising heterogeneous catalysts for advanced oxidation processes (AOPs) due to their exceptional structural stability and tunable electronic properties. Herein is reported a synthesis of a transition metal aluminate-based HEO and its application in peroxymonosulfate (PMS) activation for phenol degradation. The catalyst exhibited minimal transition metal leaching and enhanced degradation efficiency in the presence of bicarbonate, a common pH-buffering ions in natural water systems. Mechanistic investigations, including radical quenching tests, electron paramagnetic resonance (EPR) analysis, and electrochemical measurements, confirmed that phenol degradation proceeds predominantly via an electron transfer process (ETP) rather than a radical pathway. A packed-bed column test under continuous water flow further demonstrated the long-term stability of catalyst, maintaining over than 70% phenol degradation over 72 hours.

[0121] Heterogeneous advanced oxidation processes (AOPs) benefit from multi-metallic compositions by enhancing catalytic activity and durability compared to their monometallic counterparts. This is partially due to synergistic metal interactions and electronic structure modulation. This effect can be further optimized in high-entropy oxides (HEOs), where five or more different elements are randomly distributed across specific lattice sites to form a singlephase crystal structure. Such atomic-scale mixing endows unique physicochemical properties, including exceptional thermodynamic stability and tunable surface characteristics that improve catalytic performance. For example, the surface of HEOs can shift ROS formation mechanism from radical-based to non-radical pathways, such as high-valent metal-oxo species (HVMO) or direct electron transfer to target pollutants. Therefore, to better understand the deactivation mechanisms of structurally robust HEO catalysts in heterogeneous AOPs, it is critical to elucidate how the non-radical pathways influence catalytic surface properties and long-term reactivity. (Wang, P. et al., Adv. Funct. Mater. 2024, 34, 2316542; Zhao, Z et al., Environ. Sci. Technol. 2023, 57, 4556-4567; Shi, Z. et al., ACS Catal. 2024, 14, 14796-14806; Yao, Y. et al.,Attorney Docket No. 047162-5399-00WO

[0122] J. Mater. Chem. A 2024, 12, 10081-10089; Yao, Z. et al., Nat. Commun. 2025, 16, 148; Zhang, Y.-J. et al., Nat. Commun. 2022, 13, 3005; Zhang, Y.-J. et al., Nat. Water. 2024, 2, 770-781) Recent studies have demonstrated that when the non-radical pathways dominate on the surface of the catalysts, particularly during the degradation of electron-rich aromatic compounds such as phenol, an alternative deactivation mechanism emerges from the adsorption of stable alkyl radicals onto the catalyst surface. This phenomenon facilitates the formation of oxidative coupling products, including polymeric byproducts, which gradually accumulate and block active sites. Moreover, the formation of alkyl radicals can be further accelerated in bicarbonate-containing water systems, where bicarbonate (HCO₃⁻), a major ion in groundwater and seawater, directly interacts with oxidants such as persulfate (eq. (1)) to generate radicals. This interaction is followed by the quenching of sulfate radicals, leading to the formation of secondary carbonate radicals (CO₃•⁻) as the dominant reactive species (eq. (2)), which exhibit lower oxidation potential and contribute to the persistence of alkyl radicals, ultimately driving oxidative coupling reactions (eq. (3)). Consequently, in water systems where bicarbonate and other coexisting ions are abundant, oxidative coupling reactions are further promoted, increasing the catalyst fouling and accelerating deactivation. Taken together, a rational design of HEO catalysts that minimizes the accumulation of oxidative coupling products is highly desirable for achieving long-term stability in heterogeneous AOPs. (Wen, Y. et al., ACS EST Water 2022, 2, 635-643; Meyerstein, D., Nat. Rev. Chem. 2021, 5, 595-597; Vijay, A. K. et al., Angew. Chem. Int. Ed. 2023, 62, e20230947; Buhl, M. et al., J. Am. Chem. Soc. 2015, 137, 16153-16162; Liu, Y.-Q. et al., Environ. Sci. Technol. 2025, 59, 880-891)

[0123] HSOs + HCO3 SOT + CO32+ H2O eq. (1) SOT + HCO3 SO42+ CO3’ eq. (2) CO3’ + R R‘ + CO32eq. (3 )

[0124] Herein is reported a high-entropy oxide (HEO) catalyst designed for enhanced stability in the oxidative environment of AOP catalysis. Among various HEOs, metal aluminates (MAl₂O₄, where M represents a transition metal) with spinel structures exhibit superior stability compared to conventional metal oxides due to the strong Al-0 bond strength. Additionally, incorporating multiple metals at the M site enhances electronic conductivity by narrowing theAttorney Docket No. 047162-5399-00WO

[0125] band gap. Building on these insights, metal aluminate-based HEOs were synthesized and applied to phenol degradation in an AOP system using peroxymonosulfate (PMS) as an oxidant. The catalyst exhibited minimal transition metal leaching, attributed to its stable catalytic surface. ROS quenching, electron paramagnetic resonance (EPR), and electrochemical measurements confirmed that the dominant ROS mechanism is not radical-driven but rather an electron transfer process facilitated by PMS adsorption. This mechanism promoted phenol radical formation, leading to oxidative coupling rather than complete mineralization. Notably, despite the formation of coupling products, the hydrophobic catalyst surface prevented their adsorption compared to conventional hydrophilic HEOs, preserving active sites and maintaining catalytic efficiency. In a continuous water flow system using a packed bed column, the catalyst maintained high consistent degradation performance under accelerated condition, highlighting its potential for commercialization. (Wu, T. et al., Nat. Catal. 2019, 2, 763-772; Wu, T. et al., Nat. Catal. 2019, 2, 763-772)

[0126] A high-entropy oxide catalyst was synthesized by uniformly incorporating six 3d transition metals into the M site of metal aluminate in an equimolar ratio (Mno.i67Feo.i67Coo.i67Nio.i67Cuo.i67Zno.i67A1204, denoted asM6Al2O4hereafter). The citric-gel combustion method was employed, using citric acid as a complexing agent and metal nitrates in a stoichiometric ratio (see Methods for details). The X-ray diffraction (XRD) patterns of the synthesized M⁶Al₂O₄ (Figure 1A) confirm the formation of a single-phase spinel structure, with characteristic diffraction peaks matching well with reported metal aluminates (CoAl₂O₄).

[0127] Scanning electron microscopy (SEM) analysis revealed that the synthesized oxides formed irregular microparticles (Figure 1B). Scanning transmission electron microscopy (STEM) and high-angle annular dark-field STEM energy-dispersive spectroscopy (STEM-HAADF-EDS) elemental mapping confirmed the homogeneous distribution of all transition metals and aluminum without segregation (Figure 1C). Additionally, EDS-determined elemental ratios matched the intended stoichiometry (Figure ID).

[0128] The catalytic performance of the synthesized M⁶Al₂O₄ in heterogeneous AOP was evaluated through PMS activation for phenol degradation as a model reaction. As shown in Figure 5, in an ideal water system without bicarbonate, only -17% of phenol was degraded after 1 hour, likely due to the high stability of the HEO surface. Even in the absence of a buffering system, transition metal leaching remained minimal, with a maximum concentration of 300 ppb,Attorney Docket No. 047162-5399-00WO

[0129] indicating strong structural stability (Table 1). Notably, the addition of bicarbonate, a ubiquitous component in natural water systems, significantly accelerated phenol degradation as its concentration increased. Furthermore, increasing bicarbonate concentration not only suppressed transition metal leaching through its pH-buffering role but also significantly enhanced reaction kinetics. This result implies that dominant ROS mechanism in our catalysts is facilitated with bicarbonate which likely due to the formation of carbonate radicals, demonstrating that our catalyst can operate more effectively in real water environments.

[0130] Table 1. Inductively coupled plasma mass spectrometry (ICP-MS) determined concentration of transition metal ions in the solution after reaction.

[0131] Concentration of Metal leaching (μg L⁻¹, ppb)

[0132] NaHCO₃ (mM) Mn Fe Co Ni Cu Zn

[0133] 0 112.56 54.21 68.26 59.11 303.21 110.39 1 4.06 4.78 15.97 41.57 11.70 48.98 10 1.30 2.89 15.10 6.53 3.63 1.22

[0134] To elucidate the ROS formation mechanism of the catalyst, radical probe experiments were conducted. First, the addition of methanol or tert-butanol (TBA), which are effective quenchers of ’OH and SOT radicals typically generated through PMS activation via a radical mechanism, had negligible impact on the reaction rate (Figure 6). This suggests that the dominant ROS in the catalytic system is not radical-based. Additionally, when methyl phenyl sulfoxide (PMSO) was used as a probe molecule instead of phenol, it was fully converted to methyl phenyl sulfone (PMSO₂), confirming the absence of radical formation during the reaction (Figure 7). Consistently, as shown in Figures 8-10, electron paramagnetic resonance (EPR) measurements using 5,5-Dimethyl-l-pyrroline N-oxide (DMPO) as a spin trapper exhibited no noticeable ’OH and SO4' radical signals. (Zong, Y. et al., Environ. Sci. Technol. 2020, 54, 16231-16239; Wu, Q.-Y. et al., Proc. Natl. Acad. Sci. U. S. A. 2023, 120, e2219923120)

[0135] Recent studies have demonstrated that the electron transfer process (ETP) is the dominant mechanism on the stable HEO catalyst surface, where electrons are transferred from HVMO species or surface-adsorbed-PMS complexes, to the phenol, leading to the generation ofAttorney Docket No. 047162-5399-00WO

[0136] phenoxyl radicals. To verify this, electrochemical tests were conducted to monitor electron flow upon PMS and phenol addition. As shown in the chronoamperometry (CA) test (Figure 3), PMS introduction to the catalyst-coated electrode resulted in electron absorption from the catalyst surface. Subsequently, phenol addition induced electron loss, leading to its oxidation. These results demonstrate that the degradation mechanism of our catalyst is an ETP, where PMS adsorbed on the catalyst surface transfers electrons to phenol, which leads to the formation of phenolic radicals. Through this mechanism, catalytic performance is not diminished but rather enhanced, particularly in realistic environments where bicarbonate is present.

[0137] To evaluate the feasibility of large-scale application, phenol degradation was investigated in a packed-bed column under continuous water flow using M⁶Al₂O₄ catalysts. To assess stability under accelerated conditions, phenol and bicarbonate concentrations were set at 500 pM and 10 mM, respectively. As a result, both phenol degradation and total organic concentration (TOC) removal exceeded 70% between 12 and 72 hours of operation; however, rapid deactivation occurred gradually until 120 hours (Figure 12). This was not attributed to surface deformation, as indicated by the low metal leaching concentration (Table 2). Instead, since the primary ROS mechanism of the catalyst was ETP, oxidative coupling of phenol was enhanced on the catalyst surface, leading to the formation of polymeric products, particularly under the high phenol concentration of 500 pM. To confirm this, the adsorbed products in the column were washed with methanol and toluene, followed by gel permeation chromatography (GPC) analysis (Figure 13).

[0138] Table 2. ICP-MS-determined concentration of transition metal ions during longterm operation. ’Concentration was below detection level

[0139] Metal leaching (μg L⁻¹, ppb)

[0140] Operation hour (h)

[0141]

[0142] Mn Fe Co Ni Cu Zn* 1 19.125 0.332 0.259 0.761 0.525

[0143] 2 88.905 0.020 0.675 1.926 0.372

[0144] 3 108.484 0.077 1.793 2.498 0.273

[0145] 4 112.177 0.125 2.737 3.004 0.747Attorney Docket No. 047162-5399-00WO

[0146] 130.705 0.155 2.426 2.719 2.912

[0147] 6 148.380 0.104 2.532 2.953 5.676

[0148] 12 161.294 0.037 2.070 2.341 10.172

[0149] 24 72.060 0.087 1.226 1.188 9.204

[0150] 36 32.871 0.060 0.570 0.824 6.993

[0151] 48 9.640 0.137 0.263 0.592 5.159

[0152] 60 3.940 0.184 0.181 0.608 5.081

[0153] 120 0.031 0.753 0.027 0.111 0.429

[0154] The result revealed the presence of polymers with average molecular weight of 1,371, confirming that surface blocking due to their accumulation is a major deactivation mechanism in long-term accelerated operation. Therefore, further designing catalysts or implementing engineering strategies to effectively remove these products in-situ or post-reaction is crucial for achieving stable and continuous long-term operation.

[0155] Materials synthesis

[0156] For the preparation of high entropy oxide micro powder, the citrate-gel combustion method was employed using metal nitrates as precursors and citrate acid as a complexing agent. In a typical synthesis of M⁶Al₂O₄, metal nitrates in a stoichiometric molar ratio (5 mmol of total transition metals and 10 mmol for aluminum) were dissolved in a water / ethanol mixture (3:1) and stirred for 1 h at room temperature. Subsequently, 10 mmol of citric acid was added, and the solution was heated to 80 °C until complete solvent evaporation, followed by the formation of a homogeneous metal nitrate-citrate gel. The gel was gently ground in a mortar and combusted at 200 °C for 1 h. Finally, the resulting material was transferred to an alumina crucible and calcined in a muffle furnace at 900 °C for 12 h.

[0157] Material characterization

[0158] SEM images were collected using a Hitachi SU-70 operated at 2 kV. STEM, and HAADF-STEM-EDS measurements were conducted with an FEI Tecnai Osiris operated at 200Attorney Docket No. 047162-5399-00WO

[0159] kV. XRD patterns were obtained with a Rigaku SmartLab X-ray diffractometer. X-ray photoelectron spectroscopy (XPS) measurements were performed using a PHI VersaProbe III AD Scanning XPS Microprobe, and the signals were calibrated to the adventitious carbon Is peak (C-C bond, 284.8 eV).

[0160] Catalytic performance evaluation

[0161] A typical batch experiment was conducted using 50 mL of an aqueous solution containing the catalyst (0.5 g L⁻¹), phenol (100 μM), and peroxymonosulfate (PMS, 1 mM). Sodium bicarbonate (0-10 mM) was also added to simulate the natural buffering conditions of seawater. At predetermined time intervals, a 0.5 mL aliquot was withdrawn from the reaction solution and quenched by adding 0.5 mL of methanol. The sample was then immediately centrifuged at 13,000 rpm for 3 min to remove particulates, followed by filtration through a 0.22 μm polyethersulfone (PES) membrane before product analysis for high-performance liquid chromatography (HPLC). For the total organic concentration (TOC) measurements, 10 mL of aliquot was withdrawn after the reaction and quenched by adding 20 mM NaNO₂, and the particulates were removed by centrifugation and filtration.

[0162] Oxidation product characterization

[0163] Phenol concentration was measured using HPLC (Agilent 1260 infinity). A 50 pL liquid sample was injected into a C18 column (ZORBAX Eclipse XDB-C18, 4.6 × 150 mm, 5 μm) with a flow rate of 1 mL min ’. The mobile phase consisted of 80% water containing 0.1% phosphoric acid and 20% acetonitrile. Detection was performed using a diode array detector (DAD) at a wavelength of 270 nm. The column temperature was maintained at 30 °C. For the evaluation of phenol oxidation products, liquid chromatography-mass spectrometry (LC-MS) was conducted using an Agilent 6550A Q-TOF system. TOC measurements were performed using a Shimadzu TOC-L analyzer. EPR signals were performed with a Bruker Magnettech ESR5000 spectrometer. Metal leaching after the reaction was quantified by inductively coupled plasma mass spectrometry (ICP-MS) using a PerkinElmer NexION 5000.

[0164] Electrochemical testAttorney Docket No. 047162-5399-00WO

[0165] Electrochemical measurements were performed in a three-electrode system using a BioLogic potentiostat at room temperature. A platinum (Pt) wire, a Ag / AgCl electrode (in 3 M KC1), and a drop-cast film of catalysts on a glassy carbon electrode (GCE, diameter = 3 mm) were employed as the counter, reference, and working electrodes, respectively. For the preparation of catalysts ink, 2 mg of M⁶Al₂O₄ powder was vigorously sonicated with in the solution mixture of 380 μL of water, 100 μL of isopropanol, and 20 μL of 5% Nafion perfluorinated resin (Ion Power, Inc.). Then, the 5 μL of the catalyst ink was drop-casted onto a GCE and dried under infrared light irradiation for prepare working electrode. Electrolyte solutions were purged with 99.999% Ar gas for 30 min before use.

[0166] Continuous water flow system

[0167] To construct a packed-bed column for continuous water flow testing, 10 g of M₆Al₂O₄ powder was loaded into the column (Kimble Chromaflex, inner diameter = 2.5 cm), with 40 g of SiO₂ (sea sand, 50–70 mesh) placed both above and below the catalyst layer to ensure uniform water flow. After washing the column interior with water (10 mL min⁻¹ for 30 min), phenol, bicarbonate, and PMS feed stock solutions were simultaneously injected into the column to initiate reaction.

[0168] 2: Bicarbonate-facilitated CuIIIformation in hi

[0169]

[0170] aluminates for efficient oxidative polymerization of water contaminants

[0171] Surface modulation of heterogeneous catalysts with interfacial ligands is a promising strategy to overcome the trade-off between catalytic activity and structural stability. However, achieving high activity in complex multimetallic systems, such as high-entropy oxides (HEOs), remains a challenge because their rigid coordination environments hinder the generation of reactive intermediates. The present example presents an Al-incorporated HEO catalyst ((MnFeCoNiCuZn)Al₂O₄), where the Al sites reinforce the lattice framework and simultaneously act as selective anchors for bicarbonate ions at the solid-water interface. This system exhibited high catalytic activity and exceptional durability in the oxidative polymerization of water contaminants over 336 h of continuous operation. Mechanistic studies revealed that the interfacial bicarbonate coordinates with neighboring Cu sites to facilitate the formation of high-valent CuIIIintermediates, which serve as the primary reactive species. Accordingly, theAttorney Docket No. 047162-5399-00WO

[0172] coordination of bicarbonate effectively lowers the energetic barrier for CuIIIgeneration that is otherwise hindered by the rigid HEO lattice. This synergy between the multimetallic framework and the interfacial ligand enables the HEO to decouple catalytic reactivity from structural stability, ensuring sustained high performance for realistic water treatment applications.

[0173] Bicarbonate ions (HCO3 ), ubiquitous in natural water matrices (typically 1-10 mM) (Chou et al., Environ. Sci.: Nano, 2025, 12, 3047), can coordinate with transition metals to stabilize HVMO generation, a ligand-mediated pathway demonstrated in homogeneous catalysis (Patra et al., Acc. Chem. Res., 2020, 53, 2189; Vijay et al., Angew. Chem. Int. Ed., 2023, 62, e202309472). Yet, this ligand-mediated strategy remains largely overlooked in heterogeneous catalysis, especially for HEO systems, due to the weak coordination affinity of surface metal sites. In this study, we propose a surface-regulation strategy by designing high-entropy spinel aluminate (MAI2O4, where M = Mn, Fe, Co, Ni, Cu, and Zn) in which bicarbonate ions serve as a selective surface activator for the generation of CuIIIHVMO species. The coordination challenge is addressed by introducing Al into the HEO spinel lattice, which serves a dual function (Figure 14). The strong Al-0 bond (dissociation energy of 511 kJ mol1) compared to M-0 bonds (269-403 kJ mol1) enhances the overall lattice network to suppress metal leaching under oxidative conditions (Haynes, CRC Handbook of Chemistry and Physics, 2014). While such structural reinforcement typically compromises catalytic reactivity, surface Al sites simultaneously serve a critical second function: they act as selective anchors that enrich bicarbonate ions at the solidwater interface (Lund et al., Chem. Mater., 2022, 34, 3893). This interfacial enrichment enables bicarbonate to coordinate with neighboring Cu sites, forming a bicarbonate-Cu11intermediate that lowers the energetic barrier for CuIIIHVMO generation and stabilizes these transient species. As a result, this Al-incorporated HEO system, mediated by interfacial bicarbonate, decouples structural stability from catalytic reactivity, enabling sustained and selective oxidative coupling of organic contaminants in heterogeneous AOPs.

[0174] Results

[0175] The high-entropy MAl₂O₄ was synthesized on Al₂O₃ via a sol–gel assisted solid-state diffusion strategy (see Methods for the details). As illustrated in the synthetic schematic (Figure 15 A), Al₂O₃ microfiber with an average length of 5.42 ± 1.3 μm were first prepared and served as a structural support (Figure 16), followed by the deposition of a homogeneous metal-Attorney Docket No. 047162-5399-00WO

[0176] citrate complex gel with equimolar concentrations of transition metal precursors (Mn, Fe, Co, Ni, Cu, and Zn) and citric acid (Figure 17) (Burroughs et al., J. Phys. Chem. C, 2015, 119, 12138). This allowed the atomic-scale mixing of multiple metals, which is essential for achieving a homogeneous HEO configuration. Then, thermal treatment at 200 °C initiated the chemical combustion of this complex to produce an amorphous multi-metal oxide layer (MnFeCoNiCuZn)xOyon the Al2O3fiber surface (Figure 18). The final crystallization into a single-phase (MnFeCoNiCuZn)A12C>4 spinel structure is driven by the interfacial solid-state diffusion of Al3+from the AI2O3 support into the (MnFeCoNiCuZn)xOymatrix during high-temperature calcination at 900 °C (Zhang et al., Environ. Sci. Technol., 2025, 59, 6863).

[0177] Red arrows denote the coordination-induced change in absorbance, indicating the formation of metal-citrate complexes. In particular, Fe3+and Cu2+exhibit prominent ligand-to-metal charge transfer (LMCT) with citric acid, which are clearly discernible within the UV-Vis wavelength range without interference from the strong nitrate peak. Detailed measurements for each individual metal constituent are provided in Figure 18.

[0178] All UV-Vis measurements were conducted using a 1-cm path-length quartz cuvette with DI water as the baseline. Reference solutions (NaNO3and citric acid) were prepared at 10 mM. For the metal nitrate precursor mixture, stock solutions of 10 mM (Mn2+, Co2+, Ni2+, Cu2+, and Zn2+) and 500 μM (Fe3+) were used. Due to its higher molar absorption coefficient (e), the Fe concentration was reduced to ensure an appropriate spectral comparison within an absorbance range. Equal volumes (2 mL each) of these stock solutions were mixed and further diluted with either DI water or 10 mM citric acid to a total volume of 24 mL. The final concentrations in the measured samples were 0.833 mM for Mn2+, Co2+, Ni2+, Cu2+, and Zn2+, and 41.67 μM for Fe3+. The final concentration of citric acid was 5 mM for the complexes.

[0179] The powder X-ray diffraction (XRD) pattern confirmed the formation of a singlephase spinel structure coexisting with the α-Al2O3support (Figure 15B). The characteristic peaks are well associated with the copper aluminate spinel structure (CuAhCL), which indicates the diffusion of Al3+successfully integrated the multiple cations into a single lattice without phase segregation, such as individual metal oxides. High-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM) image revealed that uniform nanoparticles with an average size of 6.52 ± 1.19 nm were anchored onto the Al2O3surface (Figure 15C). HAADF-STEM-energy-dispersive X-ray spectroscopy (EDS) elemental mapping demonstrates that allAttorney Docket No. 047162-5399-00WO

[0180] constituent transition metals are homogeneously distributed across the nanoparticle domains without any observable segregation (Figure 15C), and corresponding quantitative EDS analysis confirmed a near-equimolar atomic ratio of transition metals (Mn / Fe / Co / Ni / Cu / Zn = 16.1 / 15.7 / 15.9 / 15.7 / 18.2 / 18.3), corroborating the formation of the stoichiometry of (Mni / 6Fei / 6Coi / 6Nii / 6Cui / 6Znt / 6)A12O4 (Figure 15E). High-resolution TEM (HRTEM) analysis elucidates the intimate interface between the (MnFeCoNiCuZn)AhO4 and the Al2O3support (Figure 15F). Lattice fringes with d-spacings of 4.62 A and 2.48 A were identified at the nanoparticle-fiber interfaces, corresponding to the (111) plane of the (MnFeCoNiCuZn)AhO4 and (104) planes of α-Al2O3, respectively.

[0181] Lattice calculation for (MnFeCoNiCuZn)AhO4 via Vegard’s Law.

[0182] To validate the phase identity of (MnFeCoNiCuZn)AhO4 nanoparticles, the experimental tZ-spacing was compared with theoretical values derived from Vegard’s law (Vegard, Z. Phys., 1921, 5, 17). The theoretical d111spacing (dcalc) was estimated using the actual atomic fractions ( ) obtained from EDS elemental analysis (Figure 15E, Mn / Fe / Co / Ni / Cu / Zn = 16.1 / 15.7 / 15.9 / 15.7 / 18.2 / 18.3):

[0183] dcalc= (Σxidi) / (Σxi)

[0184] u-calc v1..

[0185]

[0186] 2J

[0187] where direpresents the (111) d-spacing of each constituent metal aluminate taken from the ICDD database: MnAl2O4(4.730 Å, #00-029-0880), FeAl2O4(4.708 Å, #01-082-3023), CoAl2O4(4.680 Å, #01-07

[0188]

[0189] 5-6033), NiAl2O4(4.650 Å, #00-010-0339), CuAl2O4(4.692 Å, #01-075-4264), and ZnAl2O4(4.671 Å, #01-070-8181). The calculated theoretical value of dcalc= 4.69 Å is consistent with the experimental observation of 4.62 Å (Figure 15F). The slight deviation is attributed to the lattice distortion within the high-entropy configuration, which results from the lattice mismatch in ionic radii of the multiple metal constituents in HEOs.

[0190] Following the structural analysis, Cu K-edge X-ray absorption near-edge Structure (XANES) and X-ray photoelectron spectroscopy (XPS) confirm the Cu2+oxidation state, and the 1 → 3 transition at 8978.6 eV in XANES reveals the coordination distortion characteristic of the HEO structure, with a peak position and intensity comparable to those of the Cu2CO3(OH)2reference (Figure 15G and Figure 19) (Uchikoshi, Struct. Chem., 2019, 30, 61).Attorney Docket No. 047162-5399-00WO

[0191] Collectively, these results demonstrate the successful integration of the Al-incorporated high-entropy spinel oxide, providing a well-defined platform to investigate surface-regulated AOP mechanisms.

[0192] To explore the catalytic properties of Al-incorporated HEO, the catalytic performance and stability of (MnFeCoNiCuZn)AhO4was evaluated for peroxymonosulfate (PMS)-activated phenol degradation as a representative heterogeneous AOP. For comparative analysis, Cu-based aluminate (CUAI2O4) and conventional Cu oxide (CuO) were also synthesized on the surface of Al2O3microfibers by adjusting the initial metal precursor stoichiometry (Figure 20) and tested under identical conditions. In unbuffered conditions (initial pH = 3.5), the control samples (CuO and CUAI2O4) exhibited relatively higher removal efficiencies of 84.9% and 46.2%, respectively, within 60 min; however, this apparent activity was accompanied by significant structural instability. As shown in Figure 11B, inductively coupled plasma-mass spectrometry (ICP-MS) analysis revealed substantial Cu leaching for CuO (19.2 mg L1) and Q1AI2O4 (15.5 mg L ’), indicating their severe structural instability under the reaction conditions, with far exceeding the US Environmental Protection Agency (EPA) regulation limit for drinking water (1.3 mg L−1). Given the negligible contribution of dissolved Cu to the reaction, this high efficiency resulted from rapid surface corrosion (Figure 21). In contrast, the (MnFeCoNiCuZn)A12O4 catalysts demonstrated significantly reduced Cu leaching (0.36 mg L ’), confirming the exceptional lattice rigidity provided by the synergy between the Al-based spinel structure and the high-entropy configuration (Table 3). Nevertheless, this robust confinement of active sites resulted in lower catalytic activity (7.8% removal), illustrating the intrinsic activitystability trade-off in heterogeneous catalysis.

[0193] Table 3. Concentrations of leached metal ions determined by ICP-MS after the reaction.

[0194] Catalyst Mn Fe Co Ni Cu Zn

[0195]

[0196] (MnFeCoNiCuZn)Al2O4 0.06 N. D 0.02 0.01 0.36 0.05 CuAl2O4- - - - 15.47

[0197] CuO - 19.19

[0198] To overcome the activity-stability trade-off observed under conventional unbuffered conditions, the introduction of bicarbonate was exploited as a cocatalyst to trigger aAttorney Docket No. 047162-5399-00WO

[0199] ligand-facilitated activation mechanism for CuIIIHVMO species. This strategy leverages the high affinity of the Al sites for bicarbonate; specifically, surface Al sites in (MnFeCoNiCuZn)AhO4 serve as anchors that accumulate bicarbonate, and thus provide a local environment that promotes the formation of surface-bound Cu-bicarbonate complexes. As shown in Figure 22, the phenol degradation kinetics exhibited a strong dependence on the initial bicarbonate concentration. The (MnFeCoNiCuZn)AhO4 catalyst showed almost negligible removal in the absence of bicarbonate; however, the introduction of even 1 mM of bicarbonate significantly triggered the catalytic process, and increasing the concentration to 10 mM resulted in complete phenol degradation and total organic carbon (TOC) removal within 20 min, a performance that outperforms both CuO and CuAhO4 catalysts (Figure 21). To quantitatively evaluate the intrinsic catalytic efficiency, we compared the mass-normalized rate constants (knorm) across all samples (Figure 22B). As a result, (MnFeCoNiCuZn)Al2O4achieved the highest knormof 3.02 min−1gTM−1at 10 mM of bicarbonate, representing a 75.5-fold enhancement compared to the bicarbonate-free condition, which is more prominent than those of CuO (x2.31) and CuAl2O4(×6.31). Notably, this promotion factor for bicarbonate-mediated activation was more pronounced in the Al-containing catalysts (CUAI2O4 and (MnFeCoNiCuZn)AhO4) than in the Al-free CuO, strongly supporting the hypothesis that surface Al-sites act as pivotal anchors for capturing and utilizing bicarbonate ions to facilitate catalysis. The structural integrity of the Al-based catalyst was simultaneously verified by monitoring metal leaching after the reaction (Figure 22C). Despite its superior activity, (MnFeCoNiCuZn)AhO4 exhibited exceptional stability with negligible Cu ion leaching of only 1.1 μg L−1at 10 mM bicarbonate (Table 3). Overall, the Al-incorporated framework allows the HEO catalyst to decouple the traditional activity-stability trade-off, as the Al sites provide both structural integrity and a platform for bicarbonate-induced activation (Figure 14).

[0200] It is worth noting that this bicarbonate-facilitated enhancement suggests that the reaction does not follow a conventional radical-based pathway, given that bicarbonate ions are typically regarded as radical scavengers in AOPs. To identify the dominant ROS and the underlying mechanism of (MnFeCoNiCuZn)AhO4, we performed a series of ROS scavenger experiments. For quenching the free radical species, the addition of tert-butanol (tert-BuOH, 'OH scavenger) and methanol (MeOH, both ’OH and SO4’ scavenger) in the solution exerted minimal effects on phenol degradation (Figure 22D) (Anipsitakis, Environ. Sci. Technol., 2004,Attorney Docket No. 047162-5399-00WO

[0201] 38, 3705). Corroborating these results, electron paramagnetic resonance (EPR) spectroscopy using 5,5-dimethyl-l -pyrroline N-oxide (DMPO) as a spin-trapping agent revealed no detectable signals for 'OH or SOf adducts (Figure 22E), collectively excluding these radical species as dominant ROS. The contribution of singlet oxygen (

[0202]

[0203] 'Ch) was also ruled out, as the addition of 2,2,6,6-tetramethylpiperidine (TEMP, a selective '02 quencher) and the use of D2O solvent exchange, which prolongs the lifetime of ’02, did not noticeably affect the reaction rate (Figure 23). In contrast, phenol degradation was significantly suppressed by methyl phenyl sulfoxide (PMSO), a diagnostic probe that reacts with HVMO species via an oxygen-transfer process. The stoichiometric conversion of PMSO to methyl phenyl sulfone (PMSO2) directly correlates with the disappearance of phenol, confirming that surface-bound HVMO species, rather than diffusible radicals, serve as the dominant oxidants (Figure 22F and Figure 24) (Zong et al., Environ. Sci. Technol., 2020, 54, 16231). To specifically identify the active metal center among high-entropy components, we employed sodium periodate (NaIO4) as a selective quencher for CuIII. The addition of NalCh effectively inhibited the reaction, and the formation of the specific Cuni-periodate complex was confirmed by UV-Vis analysis (Figure 25). Furthermore, a control experiment using a Cu-free HEO composition showed decreased performance, confirming that Cu sites serve as the essential active centers for generating these HVMO species (Figure 26). Finally, comparative tests with NaOH and other buffers confirmed that this CuIIIactivation is exclusively driven by the specific ligand effect of bicarbonate rather than a simple pH increase (Figure 27) (Wang et al., Environ. Sci. Technol., 2020, 54, 16231).

[0204] Having established the CuIIIHVMO species as the primary oxidant, its impact on long-term catalyst stability and the phenol transformation pathway was further investigated. To demonstrate the practical feasibility, a continuous-flow packed-bed column test was conducted under a bicarbonate concentration of 10 mM (Figure 22G). The (MnFeCoNiCuZn)AhO4 catlyst sustained near-complete phenol removal (>99%) over 336 h of continuous operation without any noticeable decline in performance. Throughout this period, the Cu ion concentration in the effluent remained consistently below 5 μg L−1, highlighting the exceptional lattice rigidity of the Al-stabilized structure under realistic flow conditions. Following the 336-h operation, the catalyst was collected and analyzed to characterize the reaction products. TEM and STEM-EDS elemental mapping analyses confirmed the presence of organic matter anchored to the catalyst surface (Figure 28). Subsequent extraction with tetrahydrofuran (THF) followed by GPCAttorney Docket No. 047162-5399-00WO

[0205] measurements revealed that these products consist of highly uniform oligomers (Mn= 1,302 Da, PDI = 1.05) (Figure 22H). This selective transformation was further corroborated by LC-MS analysis (Figure 29), which identified specific dimeric and trimeric intermediates. Collectively, the Cuni-mediated pathway promotes the selective formation of uniform phenol oligomers rather than non-selective fragments, providing a sustainable and practical platform that maintains reactivity over extended periods for advanced water treatment.

[0206] To elucidate the molecular mechanism underlying this bicarbonate-facilitated Cu3+HVMO activation, in situ attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR) was employed to probe the surface adsorption behavior of bicarbonate species. To minimize spectral interference from the aqueous solvent, difference spectra were obtained by subtracting the pure water background (see Methods).

[0207] As shown in Figure 30A, both the bulk solution and Al-free CuO catalyst exhibited a dominant band at ~1361 cm−1corresponding to the symmetric stretching mode (νs) of free or weakly physisorbed bicarbonate (Kock et al., J. Phys. Chem. C, 2013, 117, 17666). In contrast, the Al-containing catalysts (CuAhO4 and (MnFeCoNiCuZn)A12C>4) displayed distinct spectral features, characterized by the emergence of an asymmetric stretching band (νas) at ~1624 cm−1. The appearance of these bands confirms the chemical adsorption of bicarbonate on surface Al sites. Furthermore, the (MnFeCoNiCuZn)AhO4 catalysts exhibited a prominent C-OH stretching band at ~1064 cm−1alongside the most intense νaspeak. The distinctive characteristic peak of bicarbonate indicates successful stabilization of the bicarbonate species at the surface. These results suggest that the high-entropy structure not only enhances adsorption capacity but also provides an optimal geometric or electronic configuration for anchoring the bicarbonate ligand, which is critical for the subsequent activation cycle of neighboring Cu sites, potentially lowering the energy barrier to HVMO species formation. To directly capture the electronic and structural evolution during this process, in situ XANES was conducted (Figure 30B and Figure 30C). The Cu K-edge XANES spectra for the (MnFeCoNiCuZn)AhO4 catalyst initially exhibited a feature at 8976.8 eV, characteristic of Cu11(Figure 17G and Figure 30B). Upon the addition of both bicarbonate and PMS, a distinct blue shift toward higher energy was observed during reaction, appearing in a peak at 8980.3 eV, which corresponds to CuIIIHVMO species as the primary active intermediates during the reaction.33This electronic transition was also supported by the Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) analysisAttorney Docket No. 047162-5399-00WO

[0208] (Figure 30C). The intensity of the first Cu-0 shell increased significantly in the presence of both bicarbonate and PMS, with the coordination number (CN) increasing from 3.1 to 4.58 (Figure 31 and Table 4).

[0209] Table 4. The structural parameters of various conditions obtained by fitting the EXAFS spectra shown in Figure 15 A.

[0210] R factor Conditions Shell NaR(Å)b<r

[0211] (eV)

[0212]

[0213] Water Cu–O 2.17 1.97 0.0005 4.14 0.0038 NaHCO3Cu–O 1.55 1.99 0.0006 4.45 0.0037 NaHCO3+PMS Cu–O

[0214] PMS Cu-0

[0215] This increase in CN directly reflects the formation of the Cuni-oxo bond, where the oxygen atom derived from PMS is incorporated into the Cu coordination sphere. In contrast, no meaningful change in coordination (CN = 3.08) or energy shift was observed when only PMS was introduced, nor were these changes detected for the CuO or CuAhO4 references even in the presence of bicarbonate (Figure 32). As a result, clear contrast demonstrates that while bicarbonate adsorption is a necessary step, as seen in the ATR-FTIR results for CuAhCh (Figure 30A), only the high-entropy configuration provides the specific electronic environment required to stabilize and generate the resulting CuIIIintermediates, which confirms that the synergy between the multimetallic lattice and the bicarbonate adsorption is a prerequisite for driving the unique Cun / Cuinredox cycle (Figure 30D).

[0216] Conclusions

[0217] In summary, the present example presents an Al-incorporated high-entropy oxide (HEO) catalyst, (MnFeCoNiCuZn)A12C>4, which successfully overcomes the activity-stability trade-off in heterogeneous advanced oxidation. Through the strategic integration of Al into the spinel framework, the lattice structural integrity was reinforced while surface Al sites simultaneously provided a chemical platform for interfacial bicarbonate adsorption. Detailed mechanistic studies, including in situ XANES and EXAFS, revealed that this interaction is aAttorney Docket No. 047162-5399-00WO

[0218] prerequisite for the generation of high-valent CuIIIspecies, as the coordination of bicarbonate effectively lowers the energetic barrier for CuIIIHVMO intermediate formation, otherwise hindered by the rigid HEO lattice. As a result, the (MnFeCoNiCuZn)AhO4 exhibited exceptional catalytic activity and superior durability over 336 h of continuous operation with minimal metal loss (<5 pg L '), facilitating the selective oxidative coupling of phenol into uniform oligomers. The present work demonstrates that the exploitation of ligand-mediated surface regulation in HEO systems is highly desirable to decouple catalytic reactivity from structural stability for heterogeneous oxidation platforms.

[0219] Methods

[0220] Chemicals and Materials. Manganese(II) nitrate tetrahydrate (>99.9%), iron(III) nitrate nonahydrate (>98%), cobalt(II) nitrate hexahydrate (>98%), nickel(II) nitrate hexahydrate (>97%), copper(II) nitrate trihydrate (>98%), zinc(II) nitrate hexahydrate (>99%), aluminum nitrate nonahydrate (>98%), Pluronic F127 (average Mn= 12,500), urea (>99.5%, pellet) were purchased from Sigma-Aldrich. Citric acid monohydrate and THF were purchased from J. T. Baker.

[0221] Synthesis of Al2O3microfiber. Al2O3microfibers were synthesized through a copolymer-templated hydrothermal method with slight modifications from a previous report. In a typical synthesis, 2.51 g of Pluronic F127 was dissolved in 65 mL of water under stirring for 30 min to form a transparent solution. Then, aluminum nitrate nonahydrate (40 mmol) and urea (35 mmol) were added, followed by continuous stirring for an additional 30 min. The resulting solution was transferred into a PPL-lined autoclave and heated at 100 °C for 24 h. After cooling naturally to room temperature, the precipitate was collected by centrifugation (6000 rpm for 10 min), washed 3 times with water, and dried at 80 °C overnight. Finally, the dried precursor was then calcined at 1300 °C for 2 h with a ramping rate of 1 °C min1to yield crystalline Al2O3microfibers.

[0222] Synthesis of (MnFeCoNiCuZn)Al2O4. The high-entropy spinel aluminate was synthesized on Al2O3microfibers via a citrate-gel combustion method using transition metal nitrates as precursors and citric acid as a complexing agent. In a typical procedure for (MnFeCoNiCuZn)A12O4, 400 mg of Al2O3microfibers were dispersed in 100 mL of ethanol with vigorous sonication. Then, 2.0 mL of an aqueous solution of metal nitrates (40 mM) for eachAttorney Docket No. 047162-5399-00WO

[0223] transition metal (Mn, Fe, Co, Ni, Cu, and Zn) and citric acid (1.0 mmol) were added to the suspension. The mixture was then stirred for 1 h and heated at 80 °C until complete solvent evaporation. The resulting precursor-coated fibers were gently ground in a mortar and subjected to combustion at 200 °C for 1 h. Finally, the obtained powder was calcined in a muffle furnace at 900 °C for 12 h with a ramping rate of 5 °C min '.

[0224] Material Characterizations. The morphologies of the synthesized catalysts were characterized by scanning electron microscopy (SEM) using a Hitachi SU-70 operated at 2 kV. TEM, HAADF-STEM, and HAADF-STEM-EDS elemental mapping were conducted with an FEI Tecnai Osiris operated at 200 kV. XRD patterns were obtained with a Rigaku SmartLab X-ray diffractometer. XPS measurements were performed using a PHI VersaProbe III AD Scanning XPS Microprobe, and the signals were calibrated to the adventitious carbon Is peak (C-C bond, 284.8 eV).

[0225] Catalytic performance evaluation. A typical batch experiment was conducted using 50 mL of an aqueous solution containing the catalyst (0.5 g L−1), phenol (100 pM), and peroxymonosulfate (PMS, 1 mM). Sodium bicarbonate (0-10 mM) was also added to simulate the natural buffering conditions. At predetermined time intervals, a 0.5 mL aliquot was withdrawn from the reaction solution and quenched by adding 0.5 mL of methanol. The sample was then immediately centrifuged at 13,000 rpm for 3 min to remove particulates, followed by filtration through a 0.22 pm polyethersulfone (PES) membrane, and then analyzed by high-performance liquid chromatography (HPLC). For the total organic concentration (TOC) measurements, 10 mL of an aliquot was withdrawn after the reaction and quenched by adding 20 mM NaNO2. The particulates were then removed by centrifugation and filtration.

[0226] Product characterization. Phenol concentration was measured using HPLC (Agilent 1260 Infinity). A 50 pL liquid sample was injected into a C18 column (ZORBAX Eclipse XDB-C18, 4.6 x 150 mm, 5 pm) with a flow rate of 1 mL min−1. The mobile phase consisted of 80% water containing 0.1% phosphoric acid and 20% acetonitrile. Detection was performed using a diode array detector (DAD) at a wavelength of 270 nm. The column temperature was maintained at 30 °C. For the evaluation of phenol oxidation products, LC-MS was conducted using an Agilent 6550A Q-TOF system. Analytic GPC measurements were performed using a concentration range of 0.1 to 1.0 mg mL1in HPLC-grade THF on an HLC-8320GPC EcoSEC (TOSOH Bioscience) equipped with a differential refractive index detectorAttorney Docket No. 047162-5399-00WO

[0227] and TSKgel GMHhr-M column. The GPC analysis was run at a flow rate of 1 mf min1at 40 °C, and the instrument was calibrated using linear polystyrene standards. TOC measurements were performed using a Shimadzu TOC-L analyzer. EPR signals were performed with a Bruker Magnettech ESR5000 spectrometer. Metal leaching after the reaction was quantified by inductively coupled plasma mass spectrometry (ICP-MS) using a PerkinElmer NexION 5000.

[0228] XAS measurements. XAS were conducted at Inner Shell Spectroscopy (ISS, 8-ID) beamline of the National Synchrotron Light Source II (Brookhaven National Laboratory, USA). For ex-situ analysis, powder samples were mixed with polyethylene glycol (PEG), pressed into pellets, and sealed with Kapton tape. For in-situ experiments, 5 mg of the sample was dispersed in a mixture of 750 pL of ethanol and 15 pL of 5% Nafton solution and drop-cast onto carbon paper (1*1 cm2). The catalyst-coated carbon paper was mounted against the hole in the custom-built cell wall, which was then sealed with Kapton tape to create an X-ray transparent window. The cell was filled with the solution, and XAS data were collected at l-min intervals. All XAS spectra were calibrated using a Cu foil reference and recorded in fluorescence mode using a passivated implanted planar silicon (PIPS) detector. The data were processed and analyzed using the Larix software to obtain XANES and EXAFS spectra.

[0229] Continuous water flow operation. To construct a packed-bed column for continuous water flow testing, 1 g of (MnFeCoNiCuZn)AhO4 powder was loaded into the column (Kimble Chromaflex, inner diameter = 2.5 cm), with 40 g of SiO2(sea sand, 50-70 mesh) placed both above and below the catalyst layer to ensure uniform water flow. After washing the column interior with water (10 mL min1for 30 min), phenol, bicarbonate, and PMS feed stock solutions were simultaneously injected into the column to initiate the reaction.

[0230] The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

Claims

Attorney Docket No. 047162-5399-00WOCLAIMSWe claim:

1. A water treatment system comprising:a vessel, wherein the vessel comprises a catalytic material and a porous inorganic medium;wherein the catalytic material comprises a multi-metal oxide and is dispersed in the porous inorganic medium;wherein the multi-metal oxide is a compound of Formula (I)(M1)a(M2)b(M3)c(M4)d(M5)e(M6)fAl2O4Formula (I)wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); and wherein a to f represent the molar ratio of each of M1, M2, M3, M4, M5, and M6, and a to f each has a value of 0.0 to 1.0, provided that the sum of a to f is 1.0.

2. The system of claim 1, wherein a to f each have a value of 0.167.

3. The system of claim 1, wherein a is 1.0.

4. The system of claim 1, wherein a and b are each 0.5.

5. The system of claim 1, wherein a >b > c > d > e > f.

6. The system of claim 1, wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadiumAttorney Docket No. 047162-5399-00WO(V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).

7. The system of claim 1, wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).

8. The system of claim 1, wherein the multi-metal oxide has the formula (Mn)0.167(Fe)0.167(Co)0.167(Ni)0.167(Cu)0.167(Zn)0.167Al2O4.

9. The system of claim 1, wherein the multi-metal oxide is hydrophobic.

10. The system of claim 1, wherein the multi-metal oxide has a spinel crystal structure.

11. The system of claim 1, wherein the multi-metal oxide is in the shape of a non-spherical particle.

12. The system of claim 10, wherein the non-spherical particle has an average diameter of less than 10 mm.

13. The system of claim 1, wherein the porous inorganic medium is selected from the list consisting of a packed media such as silica (SiO2), sand, glass media, ceramic media, membranes and filters, microfiltration and ultrafiltration membranes, fiber filters, metallic membrane and filters, and combinations thereof.

14. A water treatment method comprising the steps of:providing an aqueous sample comprising an organic pollutant;adding one or more peroxide precursors to the aqueous sample; andcontacting the aqueous sample with a catalytic material comprising a metal oxide; wherein the catalytic material is dispersed in a porous inorganic medium;wherein the multi-metal oxide is a compound of Formula (I)Attorney Docket No. 047162-5399-00WO(M1)a(M2)b(M3)c(M4)d(M5)e(M6)fAl2O4Formula (I)wherein each of M1, M2, M3, M4, M5, and M6independently represents a metal selected from the group consisting of scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and gadolinium (Gd); and wherein a to f represent the molar ratio of each of M1, M2, M3, M4, M5, and M6, and a to f each has a value of 0.0 to 1.0, provided that the sum of a to f is 1.0.

15. The method of claim 14, further comprising the step of adding a bicarbonate salt to the aqueous sample.

16. The method of claim 15, wherein the bicarbonate salt has a concentration greater than 0.1 mM.

17. The method of claim 14, wherein the multi-metal oxide is in an amount greater than 0.1 g / L of aqueous sample.

18. The method of claim 14, wherein the method further comprises the step of filtering the aqueous sample before contacting with the catalytic material.

19. The method of claim 14, wherein the method further comprises the steps of oxidizing the organic pollutant to form an organic pollutant byproduct; andremoving the organic pollutant byproduct from the aqueous sample.

20. A catalytic material comprising a multi-metal oxide, wherein the multi-metal oxide has the formula (Mn)0.167(Fe)0.167(Co)0.167(Ni)0.167(Cu)0.167(Zn)0.167Al2O4.

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