Method for preparing polyacid-based surface micro-electric field catalyst and application thereof in industrial wastewater

Abstract

This invention discloses a method for preparing a polyacid-based surface micro-electric field catalyst and its application in industrial wastewater treatment. Using reduced graphene oxide as a support, phosphomolybdenum-vanadium heteropolyacids are immobilized on its surface via a hydrothermal method, forming a composite structure with a significant electronic polarization distribution. The catalyst surface is constructed with Mo / V electron-rich microregions and rGO electron-poor π microregions, forming a strong surface micro-electric field through cation interactions, effectively promoting electron transfer and oxygen activation. This method offers a simple catalyst preparation process, stable structure, and recyclability. It is suitable for treating industrial wastewater containing lignin and other recalcitrant organic compounds, and features high catalytic efficiency, mild reaction conditions, and good product selectivity. It achieves highly efficient catalytic oxidation degradation of lignin, a typical recalcitrant aromatic organic compound in wastewater, and simultaneously converts it into high-value-added aromatic chemicals.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource utilization technology, and in particular to a method for preparing a polyacid-based surface micro-electric field catalyst and its application in industrial wastewater. Background Technology

[0002] Industrial papermaking wastewater is typically characterized by foul odor, deep color, low biodegradability, high organic load, and high suspended solids content. The large amounts of lignin, lignin derivatives, and other unsaturated aromatic compounds in this wastewater represent important organic carbon resources. Failure to efficiently degrade these components or convert them into high-value-added chemicals will not only cause severe environmental pollution but also result in a huge waste of resources. While conventional treatment methods for industrial papermaking wastewater can generally achieve discharge standards, they commonly suffer from problems such as the instability of treatment processes being easily affected by fluctuations in raw material prices, limited removal efficiency for large molecular organic compounds like lignin, and difficulty in resource recovery.

[0003] Phosphomolybdenum-vanadium heteropolyacids (such as H5PMo) 10 V2O 40 Homogeneous heteropolyacids are considered to have catalytic oxidation activity for lignin model compounds. However, their direct application to real-world systems has significant drawbacks: First, the high solubility of homogeneous heteropolyacids in water makes catalyst recovery and recycling difficult, easily causing secondary pollution and increasing costs; second, their limited specific surface area leads to easy aggregation of active sites, resulting in insufficient intrinsic catalytic efficiency; third, their adsorption and activation capacity for complex lignin macromolecules is limited, and the selective control of depolymerization products is often unsatisfactory, making directional conversion difficult. Moreover, simple physical mixing or loading often results in weak interfacial bonding, leading to easy loss of active components. Therefore, current technologies still lack a stable composite catalyst that can significantly enhance electron transfer efficiency, oxygen activation capacity, and directional catalytic performance for lignin by constructing a surface micro-electric field through strong interfacial coupling.

[0004] In summary, existing technologies still have shortcomings in terms of catalyst recovery convenience, catalytic efficiency, product selectivity, and cost-effectiveness when treating high-concentration, recalcitrant industrial organic wastewater. Therefore, it is necessary to prepare a targeted catalyst and apply it to industrial wastewater treatment. Summary of the Invention

[0005] This invention provides a method for preparing a polyacid-based surface micro-electric field catalyst and its application in industrial wastewater, in order to solve the technical problems that existing technologies still have shortcomings in terms of catalyst recovery convenience, catalytic efficiency, product selectivity and cost-effectiveness when treating high-concentration, recalcitrant industrial organic wastewater.

[0006] A composite catalyst with high catalytic activity, good stability, easy sedimentation and recovery, and the ability to directionally convert lignin into high-value chemicals such as vanillin and p-hydroxybenzaldehyde. To achieve the above objectives, the present invention adopts the following technical solution: In the preparation method of polyacid-based surface micro-electric field catalyst, the polyacid-based surface micro-electric field catalyst is composed of phosphomolybdenum vanadium heteropolyacid supported on reduced graphene oxide, forming a surface micro-electric field structure with cation-π interaction, which promotes electron transfer and oxygen activation, and is used for catalytic degradation of organic matter in industrial wastewater; The phospomolybdenum vanadium heteropolyacid is H5PMo. 10 V2O 40 , denoted as PMoV2; the reduced graphene oxide is obtained by heat treatment of graphene oxide; The specific steps are as follows: Step 1: Preparation of reduced graphene oxide, denoted as rGO: Graphene oxide is prepared from graphite using a modified Hummers method, and then obtained by high-temperature thermal reduction. Step 2: Preparation of phosphomolybdenum-vanadium heteropolyacid: PMoV2 is obtained by hydrothermal synthesis and extraction purification using inorganic salts containing phosphorus, molybdenum, and vanadium as raw materials. Step 3: Preparation of composite catalyst PMoV2-rGO(n): The rGO obtained in Step 1, the PMoV2 obtained in Step 2, and thiourea are uniformly dispersed in water. After hydrothermal reaction, filtration, washing, and drying, the polyacid-based surface micro-electric field catalyst PMoV2-rGO(n) is obtained; where n represents the mass percentage of phosphomolybdenum-vanadium heteropolyacid in the composite catalyst, n=10, 20, 30, 40, 50, 60.

[0007] Further, graphite powder was added to pre-cooled concentrated sulfuric acid, and sodium nitrate and potassium permanganate were added sequentially under ice bath conditions, with stirring to induce a reaction. The temperature was then raised to 35-38℃ to continue the reaction, followed by the slow addition of deionized water and a further increase in temperature to 95-98℃ for holding. After the reaction was completed, hydrogen peroxide solution was added to terminate the reaction. The resulting product was repeatedly washed with dilute hydrochloric acid and deionized water until neutral, and then dried to obtain graphene oxide. The obtained graphene oxide was placed in a sealed crucible and heated to 300-400℃ in a muffle furnace at a programmed rate of 3-10℃ / min, and held for 0.5-2 hours to obtain reduced graphene oxide.

[0008] Furthermore, in step two, sodium molybdate and disodium hydrogen phosphate are dissolved separately in deionized water, mixed evenly, heated to boiling and kept under reflux for 20-40 minutes; then sodium metavanadate solution is added, and the reaction is continued at 85-95℃ for 20-40 minutes with stirring. After the reaction was completed, the pH of the reaction solution was adjusted to 1.5-2.5 with sulfuric acid. After cooling to room temperature, the orange-red oily polyacid-ether adduct was separated by ether extraction. The ether was removed by evaporation in a fume hood, and the resulting solid was recrystallized and dried to obtain purified phosphomolybdic vanadium heteropolyacid.

[0009] Furthermore, after mixing in step three, the mixture is ultrasonically treated for 20-60 minutes to ensure uniform dispersion. Then, the suspension is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, with the filling degree controlled at 60-80%, and reacted at 180-220℃ for 18-24 hours. After the reaction is completed, the product is naturally cooled to room temperature. The resulting solid product is then vacuum filtered and washed 3-5 times alternately with deionized water and anhydrous ethanol. Finally, the washed solid is vacuum dried at 60-80℃ for 12-24 hours and then ground to obtain the phosphomolybdenum-vanadium heteropolyacid / reduced graphene oxide composite catalyst. Furthermore, the mass ratio of the thiourea to the phosphomolybdate-vanadium heteropoly acid is 0.5-1.5:1.

[0010] Furthermore, the polyacid-based surface micro-electric field catalyst is composed of a reduced graphene oxide support and Keggin-type phosphomolybdenum vanadium heteropolyacid nanospheres supported thereon through chemical bonding. The heteropolyacid nanospheres and rGO are connected by sulfur bridges CS-Mo bonds generated by thiourea pyrolysis, forming a surface micro-electric field on the catalyst surface composed of Mo / V electron-rich microregions and π electron-poor microregions of rGO. The surface micro-electric field structure efficiently promotes the transfer of electrons from the adsorbed lignin aromatic rings to the catalyst active sites.

[0011] Furthermore, electrons enriched at Mo / V sites continuously activate oxygen molecules, efficiently converting them into singlet oxygen and superoxide radicals, key reactive oxygen species, thereby enhancing oxygen activation efficiency and the selective breaking dynamics of key bonds in organic matter.

[0012] Furthermore, the polyacid-based surface micro-electric field catalyst is applied to the catalytic degradation of organic matter in industrial wastewater, which is papermaking wastewater, and the organic matter is lignin or its derivatives.

[0013] Furthermore, the polyacid-based surface micro-electric field catalyst, in the presence of oxygen, reacts at 120-150℃ and 0.5-2 MPa oxygen partial pressure for 2-12 h to achieve the oxidative degradation of lignin-like organic matter and convert it into high-value-added aromatic chemicals; the mass ratio of the catalyst dosage to lignin is 0.5:1 to 1.5:1; after use, the catalyst is recovered and recycled through filtration, washing, drying, and can be recycled more than 10 times while maintaining good activity. 10. The application of the polyacid-based surface micro-electric field catalyst in industrial wastewater according to claim 8, characterized in that the specific steps of PMoV2-rGO catalytic oxidation and decomposition of lignin-like organic matter are as follows: S1. Adsorption and pre-activation: Hydrophobic lignin macromolecules preferentially adsorb onto the hydrophobic rGO region of the PMoV2-rGO catalyst through π-π interactions; this interaction leads to a decrease in the electron cloud density on the lignin aromatic ring, pre-activating the Cα-OH and β-O-4 bonds attached to it. S2, Interfacial Electron Transfer: Driven by the electron-rich Mo / V and electron-poor rGO in the surface micro-electric field, electrons are directionally transferred from the adsorbed lignin molecules to the electron-deficient π system of rGO, and further rapidly conducted to the Mo / V active center of PMoV2 through the CS-Mo chemical bridge, making it in an electron-rich state; lignin is oxidized and activated by losing electrons. S3, Oxygen Activation: A large number of electrons enriched in the Mo / V active center are rapidly transferred to the adsorbed O2 (Oxygenmolecule, O2) molecules, activating them into reactive oxygen species mainly composed of singlet oxygen and superoxide radicals. S4. Selective attack and bond breaking: The generated ROS (Reactive Oxygen Species) selectively attack the weakest link in the electron-activated lignin molecule—the Cα site of the side chain—oxidizing it to Cα=O; greatly weakening the β-O-4 bond, leading to its breakage; S5. Fragmentation and Product Generation: The free radical fragments generated by the fracture undergo subsequent reactions to eventually generate small molecule chemicals such as p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate; O2 also acts as a terminal oxidant to re-oxidize the low-valence metal centers after the catalyst reduction, thus completing the catalytic cycle.

[0014] The beneficial effects of this invention are reflected in: 1) This invention constructs a phosphomolybdenum-vanadium heteropolyacid / reduced graphene oxide composite catalyst, forming a surface micro-electric field composed of electron-rich microregions of Mo / V metal centers and electron-poor microregions of the rGO support π system. This micro-electric field structure can efficiently promote the transfer of electrons from the adsorbed lignin aromatic rings to the catalyst active sites; simultaneously, electrons enriched at the Mo / V sites can continuously activate oxygen molecules, efficiently converting them into singlet oxygen (…). 1 O2) and superoxide radicals (•O2) - Key reactive oxygen species such as β-O-4 and β-5 in organic matter are significantly improved, thereby enhancing oxygen activation efficiency and selective breaking kinetics of key bonds such as β-O-4 and β-5 in organic matter.

[0015] 2) This invention demonstrates excellent catalytic oxidation activity of composite materials on lignin in papermaking wastewater. Under mild conditions, the organic matter conversion rate can reach more than 88%, and it can selectively convert it into high-value-added aromatic chemicals such as p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate, thus achieving synergy between pollution control and resource recovery.

[0016] 3) This invention utilizes phosphomolybdenum-vanadium heteropolyacids, which are chemically anchored on the rGO support, making them difficult to dissolve or leak. The catalyst is in solid powder form, and after the reaction, it can be rapidly separated and recovered through simple filtration and washing. Experiments show that after 10 cycles, its catalytic activity and product selectivity remain at a high level, demonstrating good potential for practical application.

[0017] 4) This invention utilizes inexpensive and readily available raw materials such as graphite, sodium molybdate, and sodium metavanadate. The preparation process requires no expensive equipment or complex procedures, employing a one-step hydrothermal synthesis method. This is environmentally friendly and suitable for large-scale production. Furthermore, it uses oxygen as a green oxidant, resulting in relatively mild reaction conditions. This technology not only achieves efficient removal of pollutants but also transforms them into valuable chemicals, embodying the green chemistry concept of "turning waste into treasure" and providing a new strategy for the deep treatment and resource recovery of industrial wastewater.

[0018] Therefore, this application solves the technical problems that still exist in terms of catalyst recovery convenience, catalytic efficiency, product selectivity, and cost-effectiveness. Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention; the main objects and other advantages of the invention can be realized and obtained by means of the methods particularly pointed out in the description. Attached Figure Description

[0019] Figure 1 A scanning electron microscope image of the PMoV2-rGO(50) composite catalyst prepared in Example 1; Among them, (a)-(c) are scanning electron microscope images of the PMoV2-rGO(50) composite catalyst prepared in Example 1 at different magnifications; (d) is an elemental mapping diagram of PMoV2-rGO(50) and Mo, V, P, O, C, S and N thereon. Figure 2 X-ray diffraction patterns of rGO, PMoV2, PMoV2-rGO (50) prepared in Example 1, and rGO; Figure 3 X-ray photoelectron spectroscopy analysis results of PMoV2-rGO(50) prepared in Example 1; Figure 4 Infrared spectra of rGO, PMoV2, and PMoV2-rGO(50); Figure 5 Cyclic voltammetry curves for rGO, NS-rGO, PMoV2, and PMoV2-rGO(n) with different loadings are shown. Figure 6 Malvern particle size distribution diagrams for different catalysts; Figure 7 Solid PMoV2 and PMoV2-rGO(50) 31 p-NMR spectrum; Figure 8 The electrostatic potential distribution of the PMoV2-rGO(50) optimization model obtained based on DFT calculation is shown. Figure 9 A comparison of the activities of different catalysts in the oxidative degradation of high-boiling-point lignin; Figure 10 The reaction kinetic fitting curves and apparent activation energies of lignin degradation under PMoV2-rGO(50) catalyst and no catalyst conditions are shown in the figure. Figure 11 Figure 1 shows the effect of reaction temperature, time, oxygen pressure and catalyst dosage on the catalytic oxidation performance of PMoV2-rGO(50) prepared in Experiment 1 on lignin. Figure 12 The typical product of PMoV2-rGO(50) catalytic degradation of lignin prepared for Example 1 is shown in the gas chromatography-mass spectrometry total ion chromatogram. Figure 13 Cyclic stability test results of the PMoV2-rGO(50) catalyst prepared for Example 1; Figure 14 The results show the effects of different free radical quenchers on the degradation of lignin in the PMoV2-rGO(50) catalytic system. Figure 15 The electron paramagnetic resonance spectrum of the PMoV2-rGO(50) catalyst in the reaction system; Figure 16 Electrochemical impedance spectroscopy for PMoV2, PMoV2-NS, rGO and PMoV2-rGO(50); Figure 17 This is a schematic diagram of the interfacial reaction mechanism of PMoV2-rGO(50) catalytic oxidation and depolymerization of lignin, proposed based on experimental and theoretical calculations. Detailed Implementation

[0020] The technical solutions of the present invention will be described in detail below through embodiments. The following embodiments are merely exemplary and can only be used to explain and illustrate the technical solutions of the present invention, and should not be construed as limiting the technical solutions of the present invention.

[0021] This embodiment details the preparation method of the phosphomolybdenum vanadium heteropolyacid / reduced graphene oxide composite catalyst (PMoV2-rGO(50)) and provides a systematic physicochemical characterization to confirm its successful composite structure and unique surface electronic properties. The preparation method of the PMoV2-rGO(50) catalyst includes the following steps: Step 1: Preparation of Reduced Graphene Oxide (rGO) The specific steps are as follows: 1.0 g of graphite powder is placed in 23 mL of concentrated sulfuric acid (H2SO4) cooled in an ice bath. 5.0 g of sodium nitrate (NaNO3) and 3.0 g of potassium permanganate (KMnO4) are added sequentially at 0-5℃, and the mixture is stirred for 30 minutes. The temperature is then raised to 38℃ and the reaction continues for another 30 minutes. 50 mL of deionized water is slowly added, and the temperature is raised to 95℃ and maintained for 1 hour. After the reaction is complete, 10 mL of 30 wt% hydrogen peroxide (H2O2) solution is added to terminate the reaction. The obtained product is repeatedly washed with dilute hydrochloric acid (HCl) solution and deionized water, centrifuged until neutral, and dried at 70℃ to obtain graphene oxide (GO). GO powder is placed in a sealed crucible and heat-treated in air at a programmed heating rate of 5℃ / min to 350℃ for 1 hour to obtain reduced graphene oxide (rGO). In this step, specific heat treatment temperature and time are key to controlling the defect density and conductivity of rGO sheets.

[0022] Step 2: Synthesis of phosphomolybdic-vanadium heteropolyacid (PMoV2): 7.16 g of disodium hydrogen phosphate dodecahydrate (Na2HPO4•12H2O) (solution A) and 48.4 g of sodium molybdate dihydrate (Na2MoO4•2H2O) (solution B) were dissolved separately in 130 mL of deionized water. After mixing, the mixture was heated to boiling and refluxed for 30 minutes. Subsequently, 4.88 g of sodium metavanadate (NaVO3) solution was added, and the reaction was continued at 90℃ for 30 minutes. The pH of the reaction solution was adjusted to 2.0 with concentrated H2SO4. After cooling, the orange-red oily polyacid-ether adduct was separated by ether extraction. After evaporation of the ether in a fume hood, recrystallization, and drying, H5PMo was obtained. 10 V2O 40 Pure product.

[0023] Step 3: Construction of PMoV2-rGO(50) composite catalyst: Accurately weigh 0.12 g of rGO obtained in step (1), 2.64 g of PMoV2 obtained in step (2) and 2.52 g of thiourea, disperse them together in 120 mL of deionized water, and sonicate for 30 minutes to form a uniform suspension. Transfer the suspension to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and react at 200 °C for 24 hours. After the reaction is completed, cool naturally, filter the product under vacuum, and wash it several times with deionized water and anhydrous ethanol. Finally, dry it under vacuum at 70 °C for 24 hours to obtain a black powder PMoV2-rGO(50) catalyst. By changing the amount of PMoV2 added and repeating the above steps, catalysts PMoV2-rGO(n) with different mass fractions can be prepared (n = 10, 20, 30, 40, 50, 60, where n is the mass fraction of PMoV2). The synthesis methods for NS-rGO and PMoV2-NS are the same as those described above, except that the former does not contain PMoV2 and the latter does not contain rGO. In subsequent practical applications, PMoV2-rGO(50) performed the best, so PMoV2-rGO(50) will be used as the main characterization object in subsequent examples.

[0024] In this step, the introduction of thiourea and its specific mass ratio (approximately 1:1) to PMoV2 are key aspects of this invention. Thiourea plays a triple role in this process: as a sulfur source, it decomposes under high-temperature hydrothermal conditions to produce sulfur. 2- The rGO reacts with Mo in PMoV2 to form a crucial CS-Mo chemical bridge bond, which is the core of achieving a strong chemical bond (rather than physical adsorption) between PMoV2 and rGO. As a structure-directing agent, it guides PMoV2 to grow into uniform nanospheres (PMoV2-NS) and anchor them on rGO, preventing disordered aggregation. The mass ratio of rGO, PMoV2, and thiourea is 1:22:21, a golden ratio determined through extensive condition optimization experiments. At this ratio, the resulting catalyst exhibits the strongest surface micro-electric field (calculated potential difference of approximately 560.92 kJ / mol) and the optimal Brønsted acid content (0.75 mmol / g), thus achieving optimization of subsequent catalytic activity and selectivity.

[0025] In this embodiment, the morphology and structure of the obtained catalyst were characterized: Scanning electron microscopy (SEM) analysis showed that ( Figure 1 Scanning electron microscopy (SEM) analysis showed that ( Figure 1In the PMoV2-rGO(50) composite material, PMoV2 is uniformly embedded in the wrinkled surface of rGO as three-dimensional nanospheres with uniform size and exquisite structure (PMoV2-NS). The two form a tight heterogeneous composite structure rather than a simple physical mixture. Elemental distribution mapping confirmed the uniform dispersion of Mo, V, P, O, C, S and N elements in the composite material, indicating that PMoV2 and thiourea are uniformly combined during the preparation process, and the PMoV2-NS nanospheres are uniformly embedded in the rGO nanosheets.

[0026] This embodiment uses X-ray diffraction (XRD) patterns to display ( Figure 2 The diffraction spectrum of the composite material simultaneously retained the broadened (002) peak of rGO and the characteristic diffraction peak (8.9°) of PMoV2. Notably, compared to pure rGO, the intensity of the rGO (002) peak in the composite material was significantly weakened, while the full width at half maximum (FWHM) increased. This indicates that the introduction of PMoV2 disrupted the ordered stacking of rGO, increasing its structural disorder. Literature suggests that the greater the degree of disorder in rGO, the better its adsorption and activation performance. This provides the catalyst with more exposed edges and defect sites, which is beneficial for the adsorption and activation of reactants.

[0027] This embodiment further reveals the chemical state and electronic interactions of the composite interface through X-ray photoelectron spectroscopy (XPS) analysis. Figure 3 The orbital labels "S 2p / C1s / Mo 3d / V 2p" in the figure refer to the X-ray photoelectron spectral peaks of the 2p orbital of sulfur, the 1s orbital of carbon, the 3d orbital of molybdenum, and the 2p orbital of vanadium, respectively; among them, 2p... 3 / 2 2p 1 / 2 3D 5 / 2 3D 3 / 2 These are the spin-orbit splitting peaks corresponding to the orbitals; the elemental valence states in the figure mainly include "V(V) / V(IV)" which refer to +5 vanadium and +4 vanadium, respectively, and "Mo(VI) / Mo(V)" which refer to +6 molybdenum and +5 molybdenum, respectively; the bond type / functional group part mainly includes CC / C=C which refers to carbon-carbon single / double bonds, CS which refers to carbon-sulfur bonds, and C=O / OC-OH which refers to carbonyl / hydroxyl ester bonds; the peak markings are mainly A / B, which are different component peaks of the corresponding elemental orbitals (e.g., S 2p). 3 / 2 A is the A-group peak of the 2p3 / 2 orbital of sulfur.

[0028] Full spectrum ( Figure 3a) Confirmed the presence of the elements C, O, Mo, V, P, S, and N. Mo3d fine spectrum ( Figure 3 d), except Mo 6+ In addition to the characteristic peaks, a peak at an even lower binding energy appears at a point at which the characteristic peaks attributable to Mo appear. 4+ New peak; V 2p fine spectrum ( Figure 3 e) Also displays V 5+ With V 4+ The coexistence of C1s spectrum. Figure 3 In c), a characteristic peak of the CS bond appeared at 285.1 eV. These results strongly demonstrate that PMoV2 and rGO formed a chemical bond through a sulfur bridge (CS-Mo) and underwent significant electron transfer, leading to partial reduction of the metal center (Mo, V), and preliminarily confirming the existence of surface electronic polarization distribution.

[0029] These results strongly demonstrate that: the chemical bonding was successful, the presence of the CS bond confirms that a chemical bond was formed between PMoV2 and rGO through a sulfur bridge (CS-Mo); and there was significant electron transfer, Mo 4+ The presence of V4+ and S4- indicates that electron transfer from rGO to PMoV2 occurred during recombination, leading to partial reduction of the metal centers. This charge redistribution is direct evidence for the formation of surface micro-electric fields.

[0030] This embodiment uses Fourier Transform Infrared Spectroscopy (FT-IR) results to show ( Figure 4 PMoV2-rGO(50) retained the four characteristic absorption peaks of the Keggin structure PMoV2 in the range of 700-1100 cm-1, but showed a significant red shift compared to pure PMoV2. This is attributed to the formation of CS-Mo bonds altering the coordination environment of Mo. Meanwhile, the signals of oxygen-containing functional groups such as carboxyl groups on rGO were weakened, indicating enhanced hydrophobicity of the composite surface.

[0031] This embodiment demonstrates through cyclic voltammetry (CV) testing that ( Figure 5 PMoV2-rGO(50) exhibits four pairs of reversible redox peaks, attributed to the redox processes of Mo and V, with a half-wave potential (E) 1 / 2 The positive shift is compared to pure PMoV2, and as the PMoV2 loading increases to 50%, E... 1 / 2 The result of 0.191 V (Table 3-2) indicates that the electron transfer capability and conductivity of the composite material have been significantly improved.

[0032] This embodiment shows through particle size distribution analysis ( Figure 6 The average particle size of the PMoV2-rGO composite (approximately 110-150 nm) is much smaller than that of pure rGO (approximately 425 nm), confirming that the introduction of PMoV2 effectively inhibits the aggregation of rGO sheets and increases the specific surface area.

[0033] This embodiment uses solid-state 31P nuclear magnetic resonance spectroscopy (… Figure 7 The results showed that after PMoV2 bound to rGO, its characteristic 31P chemical shift shifted by 0.5 ppm, directly confirming at the molecular level that PMoV2 and the rGO support formed a stable hybrid structure through chemical bonds.

[0034] In this embodiment, an optimized model of PMoV2-rGO(50) was constructed by density functional theory calculation and its electrostatic potential distribution was plotted. Figure 8 The calculation results visually demonstrate that there is significant electronic polarization on the catalyst surface: the Mo and V metal site regions exhibit negative potential, while the aromatic ring π system region of rGO exhibits positive potential, with a surface potential difference of up to approximately 560.92 kJ / mol. This theoretically confirms the built-in micro-electric field on the surface induced by strong cation-π interactions.

[0035] This embodiment provides an evaluation of the catalytic performance of the PMoV2-rGO(50) catalyst in the catalytic oxidative degradation of lignin, showcasing its application and performance in the catalytic oxidative degradation of high-boiling-point lignin, a model pollutant in industrial wastewater. High-boiling-point lignin extracted from corn stalks was used as the target pollutant to simulate the recalcitrant lignin components in papermaking wastewater.

[0036] (1) Specific experimental steps and conditions: Accurately weigh 0.25 g of high-boiling-point lignin and 0.1875 g of the PMoV2-rGO(50) catalyst prepared in Example 1, and place them in a 25 mL stainless steel high-pressure reactor with a polytetrafluoroethylene liner. Add 10 mL of a mixed solvent of ethanol and water (volume ratio 1:1). After sealing the reactor, purge it with high-purity oxygen to replace the air, and adjust the initial oxygen pressure to 1.0 MPa. Place the reactor in a preheated oil bath and magnetically stir at 500 rpm at 130 °C for 10 hours.

[0037] After the reaction was completed, the reactor was cooled to room temperature to release residual pressure. The reaction liquid was collected, and the solid catalyst was recovered by centrifugation. The liquid product was subjected to rotary evaporation to remove most of the solvent, then extracted with dichloromethane. The extract was dried with anhydrous sodium sulfate and then subjected to gas chromatography-mass spectrometry (GC-MS) for qualitative analysis and gas chromatography (GC) for quantitative analysis to calculate the lignin conversion rate and the yield of the major product. Multiple control experiments were set up, including: no catalyst, rGO only, PMoV2 only, and a physically mixed PMoV2 and rGO (denoted as PMoV2-Mix), to highlight the synergistic effect of the composite catalyst.

[0038] This embodiment uses catalytic activity comparison and synergistic effect analysis: the catalytic activity comparison results are as follows: Figure 9 As shown, under catalyst-free conditions, the lignin conversion rate was 80.2%, while the yields of p-hydroxybenzaldehyde and vanillin were extremely low (1.2% and 0.8%, respectively). Using rGO or PMoV2 alone resulted in limited improvement in catalytic activity (conversion rates of 81-90%, but low selectivity for the target products). PMoV2-rGO (50) exhibited the best overall performance: a lignin conversion rate of 88.3%, and yields of p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate of up to 8.3%, 2.4%, and 7.8%, respectively. The total selectivity for the three high-value products reached approximately 20%, significantly higher than all control catalysts. Particularly noteworthy is its performance, which is also far superior to physically mixed PMoV2-Mix. This excludes the possibility of synergistic effects from simple physical contact, confirming the crucial role of chemical bonding and micro-field construction described in Example 1.

[0039] This significant "1+1>2" synergistic effect can be attributed to the coupling of multiple mechanisms: Adsorption-catalysis spatial proximity effect: The hydrophobic surface of rGO efficiently adsorbs lignin macromolecules and reduces the electron cloud density of its aromatic rings through π-π interactions, pre-activating adjacent CO / CC bonds (such as β-O-4 bonds). Since the active center of PMoV2 is chemically anchored to rGO, the adsorbed and activated lignin can immediately contact the active center, greatly improving the reaction efficiency. The micro-electric field constructed on the catalyst surface (Mo / V electron-rich, rGO electron-poor) drives electrons to flow rapidly and directionally from the adsorbed lignin molecules to the Mo / V active center of PMoV2, achieving efficient intrinsic electron transfer. The large number of electrons enriched in the Mo / V active center efficiently activates the adsorbed O2 molecules into singlet oxygen (…). 1 O2) and superoxide radicals (•O2) -The active oxygen species (ROS) are mainly composed of α- and β-hydroxyl groups. These ROS have moderate oxidation potentials and good selectivity, and can precisely attack specific weak bonds in pre-activated lignin molecules, thereby achieving selective depolymerization rather than random mineralization.

[0040] This embodiment further confirms the catalyst's effectiveness through reaction kinetics and activation energy analysis. Figure 10 Lignin degradation experiments were conducted at different temperatures (110, 120, 130, 140, 150 °C) under both PMoV2-rGO(50) and catalyst-free conditions, and the lignin concentration was monitored over time. The study found that the degradation process under both conditions conformed to a pseudo-first-order reaction kinetic model. Figure (a) shows the first-order kinetic fit of the PMoV2-rGO(50) catalytic system and Figure (b) shows the catalyst-free system, indicating that the reaction rate constant k1 under catalytic conditions was 0.08 h⁻¹. -1 Without a catalyst, k2 is only 0.02 h. -1 The former is four times that of the latter, and the goodness of fit between the two is R. 2 All values ​​are greater than 0.98, indicating a high degree of agreement between the data and the first-order kinetic model. Figure (c) shows that the apparent activation energy of the PMoV2-rGO(50) catalytic system, calculated based on the Arrhenius equation, is 35.79 kJ / mol, which is significantly lower than the 58.86 kJ / mol of the uncatalyzed system. This demonstrates that the PMoV2-rGO(50) catalyst can effectively reduce the reaction energy barrier and significantly increase the depolymerization rate of lignin.

[0041] This embodiment systematically investigated the effects of key parameters such as reaction temperature, time, oxygen pressure, and catalyst dosage on the catalytic oxidation performance of PMoV2-rGO(50) of lignin to determine the optimal reaction conditions. The results are summarized in […]. Figure 11 .

[0042] (a) Effect of reaction temperature: Experiments were conducted at 110, 120, 130, 140, and 150 °C (other conditions were kept constant: catalyst / lignin = 0.75:1, 1 MPa O2, 10 h). The lignin conversion rate increased monotonically with increasing temperature, reaching a peak at 140 °C (90.6%). However, the yields of the target aromatic aldehydes (p-hydroxybenzaldehyde, vanillin) reached their maximum at 130 °C (e.g., 8.3% for p-hydroxybenzaldehyde).

[0043] Increased temperature accelerates molecular motion and reaction kinetics, promoting bond breaking. However, above 130°C, the rate increase brought about by the Arrhenius effect is offset by the exacerbation of side reactions: aldehyde products themselves are unstable at high temperatures and are easily over-oxidized into acids or CO2; this may lead to the re-polymerization of depolymerization intermediates. Therefore, 130°C is the optimal temperature point for balancing reaction rate and product selectivity.

[0044] (b) Effect of reaction time: Different reaction times were investigated at 130℃ and 1 MPa O2. The lignin conversion rate increased rapidly within 10 hours, and the growth slowed down after 10 hours. The yields of key products (p-hydroxybenzaldehyde and vanillin) reached a plateau around 10 hours, and the yields decreased slightly when extended to 12-24 hours.

[0045] In the early stages of the reaction, the catalyst primarily attacks weak bonds in lignin (such as β-O-4) to generate monomer products. In the later stages of the reaction, secondary reactions of the monomer products (such as excessive oxidation and polymerization) gradually become dominant, leading to a decrease in net yield. 10 hours is considered the optimal reaction time to obtain the maximum monomer yield.

[0046] (c) Effect of oxygen pressure: Different initial oxygen pressures were investigated at 130℃ for 10 h. The lignin conversion rate increased significantly with increasing oxygen pressure, approaching complete depolymerization at 2 MPa. However, the yield of the key product was optimal at 1.0 MPa. Crucially, even under anaerobic conditions (0 MPa), the lignin conversion rate could still reach 42.1% relying solely on the redox capacity of the catalyst, with the generation of a small amount of aromatic aldehydes.

[0047] Oxygen, as a green oxidant, has three functions: (1) Terminal electron acceptor: It receives electrons transferred from lignin through the catalyst and regenerates the oxidation state of the catalyst (such as V). 5+ / Mo 6+ (1) Maintaining the catalytic cycle; (2) Direct reactants: After activation, ROS is generated and participates in the attack of lignin; (3) Pressure effect: Increasing the oxygen partial pressure increases its concentration and mass transfer rate in the solvent. The activity under anaerobic conditions confirms that the catalyst has a unique "hydrogen extraction" or direct electron transfer oxidation ability that does not depend on external O2. Although excessively high oxygen pressure (>1 MPa) increases the conversion rate, it may lead to over-oxidation of the product, so 1.0 MPa is the optimal oxygen pressure.

[0048] (d) Effect of catalyst dosage: With a fixed amount of lignin (0.25 g), the catalyst dosage was varied. The lignin conversion rate increased with increasing catalyst dosage, reaching its maximum at a ratio of 1:1. However, the efficiency of producing the target product per unit catalyst (i.e., product yield / catalyst dosage) peaked at a ratio of 0.75:1. Further increases in catalyst dosage resulted in minimal increase in product yield.

[0049] When the catalyst dosage is insufficient, the number of active sites is limited. When the ratio reaches 0.75:1, the active sites are sufficient to efficiently catalyze lignin in the system. Excessive catalyst may lead to: (1) excessively high local ROS concentration, causing non-selective oxidation; (2) increased probability of secondary adsorption and reaction of the product, which may reduce selectivity. Therefore, 0.75:1 is the optimal catalyst dosage ratio that balances economy and efficiency.

[0050] (e) Effect of solvent system: The experiment compared pure water, pure ethanol, and ethanol-water mixtures with different ratios. It was found that the 1:1 (v / v) ethanol-water mixture had the best effect. Water provides a polar environment and proton source, which is beneficial to certain hydrolysis steps; ethanol acts as a co-solvent and reaction participant: (1) significantly improves the solubility of hydrophobic lignin; (2) acts as an extractant to remove the product from the catalyst surface in time and avoid over-reaction; (3) undergoes esterification with the generated carboxylic acid to generate more stable ester products (such as ethyl p-hydroxycinnamate), which is both a product protection mechanism and enhances the product value.

[0051] Summary of optimal conditions: Based on the above systematic study, the optimal process parameters for the catalytic oxidation degradation of lignin by PMoV2-rGO(50) were determined to be: reaction temperature 130℃, reaction time 10 hours, initial oxygen pressure 1.0 MPa, catalyst to lignin mass ratio 0.75:1, and solvent 1:1 (v / v) ethanol-water mixture. Under these conditions, the lignin conversion rate was >88%, and the total yield of the target high-value chemicals (p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate) was >18%, demonstrating a perfect combination of efficient degradation and high-value conversion.

[0052] This embodiment analyzes the liquid product obtained under optimized conditions using GC-MS, and its total ion chromatogram is shown below. Figure 12 As shown, the main products identified are: p-hydroxybenzaldehyde, vanillin, ethyl p-hydroxybenzoate, ethyl vanillate, ethyl p-hydroxycinnamate, and other aromatic aldehydes and esters, all of which are basic chemicals with high added value.

[0053] Combined with the study of lignin structure before and after the reaction using two-dimensional nuclear magnetic resonance (2D-HSQC NMR), it was found that the signals of key linkages such as β-O-4 and β-5 in lignin almost completely disappeared after the reaction. Based on the product distribution and structural changes, the possible pathway of PMoV2-rGO(50) catalyzed oxidation and depolymerization of lignin was deduced: the catalyst first activates O2 to attack the C of the lignin side chain. α-OH groups are oxidized to ketone groups, thereby weakening and breaking the β-O-4 bond; the resulting lignin monomer fragments are further oxidized, through C... α -C β key or C β -C γ Through pathways such as bond breaking, the various aromatic aldehydes and esters detected are ultimately formed.

[0054] This embodiment evaluated the recycling performance of PMoV2-rGO(50). The reaction conditions were the same as the optimal conditions in Example 2. After the reaction, the catalyst was recovered by centrifugation, thoroughly washed with ethanol and hot 1,4-butanediol solution to remove surface-adsorbed organic matter, and dried for use in the next cycle experiment. The cycle test results are as follows: Figure 13 As shown, after 10 consecutive uses, the lignin conversion rate of the catalyst decreased slightly from 88.3% initially to 81.8%, and the total yield of p-hydroxybenzaldehyde and vanillin decreased from 10.7% to 9.1%, while the activity remained good. FT-IR and XPS characterization of the recycled catalyst showed that its spectra were basically consistent with those of the fresh catalyst, indicating that the catalyst's chemical structure and surface properties were stable, with no significant loss of active components or structural damage, demonstrating excellent potential for repeated use.

[0055] To elucidate the reaction mechanism of the PMoV2-rGO(50) / O2 catalytic system, this embodiment identifies key active species in the reaction and reveals the crucial role of lignin as an electron donor through radical quenching experiments and electron paramagnetic resonance (EPR) technology. The results of the radical quenching experiments are as follows: Figure 14 As shown. In the optimal reaction system, specific quenchers for different reactive oxygen species were added: sodium azide (NaN3, which efficiently quenches singlet oxygen). 1 O2), p-benzoquinone (BQ, a highly efficient superoxide radical quencher •O2) - The catalyst was treated with potassium iodide (KI, which is highly efficient at quenching hydroxyl radicals •OH) and potassium iodide (KI, which is highly efficient at quenching hydroxyl radicals •OH). The amount of quencher added was 10% of the catalyst mass. By comparing the changes in the degradation efficiency of lignin and the yield of the target product before and after the addition of the quencher, it was determined which active species played a dominant role.

[0056] The addition of NaN3 and BQ strongly inhibited the degradation efficiency of lignin and the yield of aromatic aldehyde products (inhibition rate > 60%). However, the addition of KI significantly reduced the inhibition (inhibition rate < 20%). This definitively proves that in the PMoV2-rGO(50) / O2 catalytic degradation system of lignin, singlet oxygen ( 1 O2) and superoxide radicals (•O2) -O2 is the dominant reactive oxygen species, while the role of hydroxyl radicals (•OH) is relatively minor. This differs from many systems based on transition metals and carbon materials for O2 activation, highlighting the unique oxygen activation pathway of this catalyst.

[0057] This embodiment utilizes in-situ EPR detection to directly capture and confirm the presence of reactive oxygen species. Figure 15 The PMoV2-rGO(50) catalyst, lignin, and ethanol aqueous solvent were placed in a reaction vessel and reacted at 1 MPa O2 and 130℃ for 1 hour, followed by rapid quenching in an ice bath. The reaction solution was then taken and added separately... 1 O2 specific scavengers TEMP and •O2 - The specific capture agent DMPO was shaken well and an EPR test was performed immediately.

[0058] In the reaction system where PMoV2-rGO(50) is present, the EPR spectrum clearly shows the TEMP-1:1:1 triplet characteristic. 1 DMPO-•O2 with O2 adduct signal and 1:1:1:1 quartet characteristic - adduct signal ( Figure 15 In control experiments without catalysts or O2, these signals were extremely weak or completely absent.

[0059] This result directly confirms that the PMoV2-rGO(50) catalyst can indeed efficiently activate O2 under the reaction conditions. 1 O2 and •O2 - The two ROS have moderate oxidation potentials and good chemoselectivity, which explains why this system can achieve selective oxidative depolymerization of lignin rather than complete mineralization.

[0060] Simultaneously, two reaction systems were designed: System A: catalyst + O2, and System B: catalyst + O2 + lignin. This key comparison reveals the core mechanism: lignin is not only the substrate of the reaction but also a crucial electron donor. During the reaction, lignin molecules transfer electrons to the catalyst (through π-π interactions and surface micro-electric fields), and these electrons greatly promote the catalyst's reduction and activation process of O2. In other words, the oxidation of lignin (loss of electrons) and the reduction of O2 (gain of electrons) are coupled through the catalyst, forming a self-electron-donating enhanced catalytic cycle. This perfectly explains why the system exhibits such high oxygen activation efficiency and reaction rate in the presence of lignin.

[0061] The electron transfer capability of a catalyst is the core factor determining its catalytic performance. In this embodiment, it was studied using electrochemical impedance spectroscopy (EIS) and electron paramagnetic resonance (EPR). Based on all experimental and theoretical calculation results, a complete interfacial reaction mechanism model for the catalytic oxidation and depolymerization of lignin by PMoV2-rGO(50) was constructed.

[0062] EIS test results are as follows Figure 16 As shown, the Nyquist plot of PMoV2-rGO(50) shows the smallest radius of curvature, indicating that it has the lowest interfacial charge transfer resistance and the strongest electron transport capability, which is due to the strong promotion of electron transfer by its surface micro-electric field.

[0063] EPR spectra further revealed the electronic properties of the catalyst. Fresh PMoV2-rGO(50) showed a significant sulfur defect signal at g=2.0, indicating that the material surface has abundant unpaired electrons and unsaturated sites, which is conducive to electron capture and transfer. The enhanced EPR signal of the catalyst after the reaction indicates that a significant electron transfer cycle occurred between the catalyst, lignin, and O2 during the reaction: lignin, as an electron donor, transferred electrons to the electron-deficient region (rGO) of the catalyst, and the electrons were rapidly transferred to the electron-rich Mo / V sites through the surface micro-electric field, and then transferred these electrons to the adsorbed O2 molecules, activating them into molybdenum. 1 O2 / •O2 - Based on the above experimental and theoretical calculation results, a complete interfacial reaction mechanism model for the catalytic oxidation and depolymerization of lignin by PMoV2-rGO(50) is proposed. Figure 17 ).

[0064] S1: Adsorption and Pre-activation: Hydrophobic lignin macromolecules preferentially adsorb onto the hydrophobic rGO region of the PMoV2-rGO catalyst via π-π interactions. This interaction leads to a decrease in the electron cloud density on the aromatic ring of lignin, pre-activating the Cα-OH and β-O-4 bonds attached to it.

[0065] S2: Interfacial Electron Transfer: Driven by the surface micro-electric field (Mo / V electron-rich, rGO electron-poor), electrons are directionally transferred from the adsorbed lignin molecules to the electron-deficient π system of rGO, and further rapidly conducted to the Mo / V active centers of PMoV2 through the CS-Mo chemical bridge, placing them in an electron-rich state. Lignin is then oxidized and activated by losing electrons. S3: Oxygen Activation: The large number of electrons enriched in the Mo / V active centers are rapidly transferred to the adsorbed O2 molecules, activating them into oxygen molecules. 1 O2 and •O2 -The dominant reactive oxygen species (ROS) were identified; EPR and quenching experiments confirmed this step.

[0066] S4: Selective Attacks and Bond Breaking: Generated ROS (especially) 1 O2 selectively attacks the weakest link in an electronically activated lignin molecule—typically the Cα site on the side chain—oxidizing it to Cα=O. This significantly weakens the β-O-4 bond, causing it to break.

[0067] S5: Fragmentation and Product Generation: The free radical fragments generated by the fracture undergo a series of subsequent reactions (such as Cα-Cβ cleavage, Cβ-O cleavage, oxidation, esterification, etc.) to ultimately generate small molecule chemicals such as p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate. O2 also acts as a terminal oxidant, re-oxidizing the low-valence metal centers after catalyst reduction, thus completing the catalytic cycle.

[0068] It not only describes the process of catalyst activation to generate free radicals from O2, but also fully elucidates the entire series of processes from "lignin adsorption pre-activation" to "interfacial electron directional transfer," then to "highly efficient oxygen activation" and "selective chemical bond breaking," profoundly revealing the essence of how the PMoV2-rGO(50) catalyst achieves efficient and highly selective resource conversion of lignin by constructing an integrated micro-reaction environment of "adsorption sites-electron channels-active centers." This mechanism provides a clear theoretical blueprint for designing similar highly efficient catalytic materials.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyacid-based surface micro-electric field catalyst, characterized in that, The polyacid-based surface micro-electric field catalyst is composed of phosphomolybdenum-vanadium heteropolyacid supported on reduced graphene oxide, forming a surface micro-electric field structure with cation-π interaction, which promotes electron transfer and oxygen activation, and is used for catalytic degradation of organic matter in industrial wastewater. The phospomolybdenum vanadium heteropolyacid is H5PMo. 10 V2O 40 , denoted as PMoV2; the reduced graphene oxide is obtained by heat treatment of graphene oxide; The specific steps are as follows: Step 1: Preparation of reduced graphene oxide, denoted as rGO: Graphene oxide is prepared from graphite using a modified Hummers method, and then obtained by high-temperature thermal reduction. Step 2: Preparation of phosphomolybdenum-vanadium heteropolyacid: PMoV2 is obtained by hydrothermal synthesis and extraction purification using inorganic salts containing phosphorus, molybdenum, and vanadium as raw materials. Step 3: Preparation of composite catalyst PMoV2-rGO(n): The rGO obtained in Step 1, the PMoV2 obtained in Step 2, and thiourea are uniformly dispersed in water. After hydrothermal reaction, filtration, washing, and drying, the polyacid-based surface micro-electric field catalyst PMoV2-rGO(n) is obtained; where n represents the mass percentage of phosphomolybdenum-vanadium heteropolyacid in the composite catalyst, n=10, 20, 30, 40, 50, 60.

2. The method for preparing a multi-acid-based surface micro-electric field catalyst as described in claim 1, characterized in that, In step one, graphite powder is added to pre-cooled concentrated sulfuric acid, and sodium nitrate and potassium permanganate are added sequentially under ice bath conditions, with stirring to react. Then, the temperature is raised to 35-38℃ to continue the reaction, and deionized water is slowly added while the temperature is raised to 95-98℃ and held for further reaction. After the reaction is completed, hydrogen peroxide solution is added to terminate the reaction. The resulting product is repeatedly washed with dilute hydrochloric acid and deionized water until neutral, and dried to obtain graphene oxide. The obtained graphene oxide is placed in a sealed crucible and heated to 300-400℃ in a muffle furnace at a programmed rate of 3-10℃ / min, and held for heat treatment for 0.5-2 hours to obtain reduced graphene oxide.

3. The method for preparing a polyacid-based surface micro-electric field catalyst as described in claim 2, characterized in that, In step two, sodium molybdate and disodium hydrogen phosphate are dissolved separately in deionized water, mixed evenly, heated to boiling and kept under reflux for 20-40 minutes; then sodium metavanadate solution is added, and the reaction is continued at 85-95℃ for 20-40 minutes with stirring. After the reaction was completed, the pH of the reaction solution was adjusted to 1.5-2.5 with sulfuric acid. After cooling to room temperature, the orange-red oily polyacid-ether adduct was separated by ether extraction. The ether was removed by evaporation in a fume hood, and the resulting solid was recrystallized and dried to obtain purified phosphomolybdic vanadium heteropolyacid.

4. The method for preparing a polyacid-based surface micro-electric field catalyst as described in claim 3, characterized in that, After mixing in step three, the mixture is ultrasonically treated for 20-60 minutes to ensure uniform dispersion. Then, the suspension is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, with the filling degree controlled at 60-80%, and reacted at 180-220℃ for 18-24 hours. After the reaction is completed, the product is naturally cooled to room temperature. The resulting solid product is then vacuum filtered and washed 3-5 times alternately with deionized water and anhydrous ethanol. Finally, the washed solid is vacuum dried at 60-80℃ for 12-24 hours and then ground to obtain the phosphomolybdenum-vanadium heteropolyacid / reduced graphene oxide composite catalyst.

5. The method for preparing a polyacid-based surface micro-electric field catalyst as described in claim 4, characterized in that, The mass ratio of thiourea to phosphomolybdicavanadium heteropolyacid is 0.5-1.5:

1.

6. The method for preparing a polyacid-based surface micro-electric field catalyst as described in claim 4, characterized in that, The polyacid-based surface micro-electric field catalyst is composed of a reduced graphene oxide support and Keggin-type phosphomolybdenum vanadium heteropolyacid nanospheres supported thereon through chemical bonding. The heteropolyacid nanospheres and rGO are connected by sulfur bridges CS-Mo bonds generated by thiourea pyrolysis, forming a surface micro-electric field on the catalyst surface composed of Mo / V electron-rich microregions and π electron-poor microregions of rGO. The surface micro-electric field structure efficiently promotes the transfer of electrons from the adsorbed lignin aromatic rings to the active sites of the catalyst.

7. The method for preparing a polyacid-based surface micro-electric field catalyst as described in claim 6, characterized in that, Electrons enriched at Mo / V sites continuously activate oxygen molecules, efficiently converting them into singlet oxygen and superoxide radicals, key reactive oxygen species, thereby enhancing oxygen activation efficiency and the selective breaking dynamics of key bonds in organic matter.

8. The application of the polyacid-based surface micro-electric field catalyst as described in any one of claims 1 to 7 in industrial wastewater, characterized in that, A polyacid-based surface micro-electric field catalyst is used to catalytically degrade organic matter in industrial wastewater, which is papermaking wastewater, and the organic matter is lignin or its derivatives.

9. The application of the polyacid-based surface micro-electric field catalyst according to claim 8 in industrial wastewater, characterized in that, The polyacid-based surface micro-electric field catalyst, in the presence of oxygen, reacts at 120-150℃ and 0.5-2MPa oxygen partial pressure for 2-12 h to achieve the oxidative degradation of lignin-based organic matter and convert it into high-value-added aromatic chemicals. The mass ratio of the catalyst dosage to lignin is 0.5:1 to 1.5:

1. After use, the catalyst is recovered and recycled through filtration, washing, and drying, and can be recycled more than 10 times while maintaining good activity.

10. The application of the polyacid-based surface micro-electric field catalyst according to claim 8 in industrial wastewater, characterized in that, The specific steps of PMoV2-rGO catalytic oxidation and hydrolysis of lignin-based organic compounds are as follows: S1. Adsorption and pre-activation: Hydrophobic lignin macromolecules preferentially adsorb onto the hydrophobic rGO region of the PMoV2-rGO catalyst through π-π interactions; this interaction leads to a decrease in the electron cloud density on the lignin aromatic ring, pre-activating the Cα-OH and β-O-4 bonds attached to it. S2, Interfacial Electron Transfer: Driven by the electron-rich Mo / V and electron-poor rGO in the surface micro-electric field, electrons are directionally transferred from the adsorbed lignin molecules to the electron-deficient π system of rGO, and further rapidly conducted to the Mo / V active center of PMoV2 through the CS-Mo chemical bridge, making it in an electron-rich state; lignin is oxidized and activated by losing electrons. S3, Oxygen Activation: A large number of electrons enriched in the Mo / V active center are rapidly transferred to the adsorbed O2 (Oxygenmolecule, O2) molecules, activating them into reactive oxygen species mainly composed of singlet oxygen and superoxide radicals. S4. Selective attack and bond breaking: The generated reactive oxygen species (ROS) selectively attack the weakest link in the electron-activated lignin molecule—the Cα site on the side chain—oxidizing it to Cα=O; greatly weakening the β-O-4 bond, leading to its breakage; S5. Fragmentation and Product Generation: The free radical fragments generated by the fracture undergo subsequent reactions to eventually generate small molecule chemicals such as p-hydroxybenzaldehyde, vanillin, and ethyl p-hydroxycinnamate; O2 also acts as a terminal oxidant to re-oxidize the low-valence metal centers after the catalyst reduction, thus completing the catalytic cycle.

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