Hierarchical pore particle electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of sewage treatment, in particular to a hierarchical pore particle electrode and a preparation method and application thereof. According to the hierarchical pore particle electrode, carbonized cellulose doped with nitrogen and boron serves as a carrier, metal nickel nanoparticles are loaded on the carrier, the hierarchical pore particle electrode provided by the invention has excellent electrocatalytic activity and catalytic stability, and meanwhile, the service life is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a multi-level porous particle electrode, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the development of modern industry, the amount of industrial wastewater discharged is increasing day by day, and its composition is becoming more and more complex. The treatment of industrial wastewater containing recalcitrant organic pollutants has always been a difficult problem.

[0004] Electrochemical oxidation technology, as an advanced oxidation technology, has attracted increasing attention due to its advantages such as being able to be carried out at room temperature, requiring little space, being easy to automate, and producing complete degradation without secondary pollution. Electrochemical oxidation mainly includes the two-dimensional plate electrode method and the three-dimensional particle electrode method. In the traditional two-dimensional plate electrode method, the area of ​​the plate electrode to the solution surface is relatively small, resulting in a small throughput per unit electrolytic cell and low current efficiency. The three-dimensional electrode method involves filling granular or other fragmented working electrode materials between the plate electrodes of the two-dimensional electrolytic cell as a third electrode. This charges the surface of the particle electrode material, causing an electrochemical reaction to occur on the particle electrode surface. Compared to the two-dimensional electrode, the three-dimensional electrode has a larger specific surface area, and because of the smaller particle spacing, the mass transfer effect is improved, expanding the reaction zone and increasing the ability to generate hydroxyl radicals, thus resulting in higher current efficiency.

[0005] The core of a three-dimensional particle electrode system is the particle electrode itself, which is generally divided into supported particle electrodes and composite material particle electrodes. Commonly used supports for supported particle electrodes include metallic conductors, carbon materials, alumina, and ceramics. These materials have high density and strong adsorption capacity, meaning that a large portion of the removal is actually physical adsorption without degradation of the pollutants. Furthermore, these particle electrodes suffer from problems such as long preparation cycles, complex processes, easy detachment of the supported coating affecting catalytic activity, and poor catalytic stability. Summary of the Invention

[0006] To overcome the above problems, the present invention provides a multi-level porous particle electrode, its preparation method and application.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a hierarchical porous particle electrode, which uses nitrogen- and boron-doped carbonized cellulose as a carrier and loads nickel nanoparticles. The total specific surface area of ​​the hierarchical porous particle electrode is 810~880 m².2 / g, with a microporous specific surface area of ​​230~250 m² 2 / g, mesoporous specific surface area is 510~550 m² 2 / g, the specific surface area of ​​the macropores is 75~90 m² 2 / g, with an average pore size of 3.5~4.2 nm.

[0008] A second aspect of the present invention provides a method for preparing the hierarchical porous particle electrode described in the first aspect, comprising the following steps: (1) Add alkali lignin, yeast powder, boric acid and surfactant to sodium hydroxide solution, mix evenly and adjust pH to 9.5~10.5 to obtain composite impregnation solution; (2) The polyurethane foam is impregnated in a composite impregnation solution and vacuum impregnated. After curing, the precursor is obtained. (3) The precursor is subjected to a first heat treatment in an oxygen-free environment to obtain carbonized cellulose doped with nitrogen and boron; (4) Nitrogen- and boron-doped carbonized cellulose is immersed in a nickel salt solution, dried, and then subjected to a second heat treatment to obtain a multi-level porous particle electrode.

[0009] In one or more embodiments, in step (1), the mass ratio of alkali lignin, yeast powder and boric acid is 1:(0.05~0.15):(0.12~0.18).

[0010] In one or more embodiments, in step (1), the surfactant is sodium dodecyl sulfate; Preferably, the mass fraction of sodium dodecyl sulfate is 0.8-1.2%, more preferably 1%.

[0011] Adding surfactants ensures uniform penetration and loading of the composite impregnation solution.

[0012] In one or more embodiments, in step (1), the concentration of the sodium hydroxide solution is 0.8~1.2 mol / L, preferably 1 mol / L.

[0013] In one or more embodiments, step (2) of the vacuum impregnation method includes: Maintain immersion under negative pressure conditions of -0.05 MPa to -0.1 MPa for 20 min to 40 min; Then, the immersion was maintained under a positive pressure of 0.3 MPa to 0.8 MPa for 15 min to 30 min. Repeat the soaking process 3 to 5 times.

[0014] In one or more embodiments, in step (2), after vacuum impregnation, the mixture is left to stand at room temperature for 2 to 6 hours to improve the uniformity of the impregnation.

[0015] In one or more embodiments, the curing method in step (2) includes: First curing at 65℃~80℃ for 1~2 hours; Second curing at 85℃~100℃ for 1~3 hours; A third curing process is performed at 120℃~150℃ for 2~5 hours; The material was cured for the fourth time at 160 ℃~200 ℃ for 1~4 h.

[0016] Multiple-stage curing processes enable gradient dehydration and structural stabilization, suppressing cracking and deformation during subsequent heat treatment and regulating the gradual development of pores. Gradient dehydration and structural stabilization are achieved through several key steps: the initial low-temperature curing removes residual moisture and low-boiling-point impurities, preventing cracking during subsequent high-temperature carbonization due to vigorous volatilization. As the temperature increases, functional groups such as hydroxyl and carboxyl groups in the organic components are gradually removed, promoting the cross-linking and recombination of lignin molecular chains to form a stable three-dimensional network framework. The final high-temperature curing promotes the graphitization of the carbon framework while fixing the positions of dopant elements, enhancing the material's mechanical strength and electrical conductivity.

[0017] Suppressing volume shrinkage and crack formation: Single-stage rapid curing can easily lead to thermal stress concentration due to internal and external temperature differences, resulting in sample deformation or microcrack propagation. A four-stage stepped heating method ensures uniform heating of all parts of the material, gradually releasing internal stress and guaranteeing the dimensional accuracy and integrity of the finished product.

[0018] Regulating pore development and specific surface area: Yeast powder, as a pore-forming agent, decomposes to produce gas in different temperature ranges. Combined with staged curing, the ratio of mesopores to macropores can be precisely controlled, ultimately achieving a balance between high specific surface area and suitable pore size distribution.

[0019] The key reason for limiting different heating rates: Following the time-temperature equivalence principle, the mobility of polymer chain segments depends on the combined effect of temperature and time. A faster heating rate forces the chain segments to activate their mobility at higher temperatures, causing a deviation in the measured glass transition temperature, and vice versa. Therefore, a slower rate is used in the initial curing stage to facilitate sufficient molecular rearrangement, while a faster heating rate is used during deep carbonization to overcome the reaction barrier.

[0020] Thermal conductivity characteristics of the compatible materials: Polyurethane foam substrate is a poor conductor. If the temperature is raised at high speed throughout the process, the surface will harden prematurely, hindering the diffusion of the internal solvent and forming closed bubbles. Therefore, low-speed operation is required in the early stage to ensure smooth mass transfer, and the speed can be increased later to improve production efficiency.

[0021] Matching the requirements of chemical reaction kinetics: In the nickel salt reduction step, the heating rate under a hydrogen atmosphere directly affects the nucleation rate of metal nanoparticles. Too fast a rate leads to severe particle agglomeration, while too slow a rate prolongs the production cycle. Experiments have verified that setting a specific rate can achieve the optimal solution between crystallization quality and economic benefits.

[0022] In one or more embodiments, the method for the first heat treatment in step (3) includes: The first carbonization was carried out at 300 ℃~500 ℃ for 0.5~2 h; Second carbonization at 700 ℃~800 ℃ for 2~4 h; The third carbonization was carried out at 800 ℃~1000 ℃ for 1~3 h.

[0023] The purpose of the multiple heating carbonization is to achieve the mild decomposition and inheritance of the precursor structure, the graphitization and B / N atom doping of the carbon skeleton, and the deep ordering and micropore activation in stages, thereby synergistically optimizing the conductivity, specific surface area and chemical stability of the carbon support.

[0024] The multi-stage, stepped heating carbonization process aims to achieve synergistic optimization of the structure and performance of the carbon support by controlling the pyrolysis kinetics in stages. Low temperature range (~400℃) - structural inheritance: mild pyrolysis causes the organic precursor to decompose in an orderly manner, retaining the macroporous framework of the three-dimensional foam template and forming the initial carbon network.

[0025] Mid-temperature range (~750℃) - graphitization and doping: promotes carbon atom rearrangement to form graphite microcrystals and improves intrinsic conductivity; simultaneously achieves stable doping of B / N atoms into the carbon lattice and constructs an active interface.

[0026] High-temperature section (~900℃) - deep ordering and activation: further improve the degree of graphitization to enhance stability; generate abundant micropores through high-temperature self-etching to construct a complete multi-level pore system.

[0027] By precisely matching temperature and time parameters, the synergistic effects of morphology preservation, conductive network construction, heteroatomic doping, and fine-tuning of pores were achieved step by step. This is the key to obtaining carbon supports with high conductivity, high specific surface area, and stable active interfaces.

[0028] In one or more embodiments, in step (4), the nickel salt includes one or more of nickel sulfate, nickel nitrate or nickel acetate.

[0029] In one or more embodiments, in step (4), the impregnation method is equal volume impregnation.

[0030] In one or more embodiments, in step (4), the atmosphere during the second heat treatment is an oxygen-free atmosphere, which is a mixture of hydrogen and argon. Preferably, the volume percentage of hydrogen is 5% to 25%.

[0031] In one or more embodiments, in step (4), the temperature of the second heat treatment is 400~600 ℃ and the heat treatment time is 2~4 h.

[0032] A third aspect of the present invention provides the application of the hierarchical porous particle electrode described in the first aspect or the preparation method described in the second aspect in the electrocatalytic degradation of pollutants in industrial wastewater.

[0033] A fourth aspect of the present invention provides a method for electrocatalytic degradation of pollutants in industrial wastewater, comprising the following steps: A three-dimensional electrocatalytic oxidation system is constructed in an electrolytic cell, the system comprising an anode, a cathode, an electrolyte solution, and a particle electrode suspended in the electrolyte solution; the particle electrode is a hierarchical porous particle electrode as described in the first aspect or a hierarchical porous particle electrode prepared by the preparation method described in the second aspect.

[0034] The beneficial effects of this invention are as follows: (1) This invention provides a hierarchical porous particle electrode, which uses nitrogen- and boron-doped carbonized cellulose as a carrier and loads metallic nickel nanoparticles. The hierarchical porous particle electrode provided by this invention has excellent electrocatalytic activity and catalytic stability, while significantly improving its service life. Specifically, regarding electrocatalytic activity: the hierarchical pores in the hierarchical porous particle electrode provide an ideal channel for rapid mass transfer and enrichment of pollutants and efficient electron transfer. The highly dispersed and firmly anchored nickel nanoparticles serve as active centers. The boron / nitrogen co-doping interface can regulate the electron density of the adjacent nickel active centers, reduce the interfacial charge transfer resistance, and thus exhibit excellent single-metal catalytic performance, significantly improving the generation efficiency of active species such as hydroxyl radicals (·OH), thereby showing a strong electrocatalytic oxidation degradation ability for recalcitrant organic matter. Regarding the significantly enhanced catalytic stability and service life: the synergistic doping of boron / nitrogen atoms constructs a stable three-dimensional conductive network in the carbon framework and introduces a large number of strong anchoring sites. The strong electronic interaction formed between these sites and the nickel active components is like an "atomic-level lock," which can effectively inhibit the aggregation, shedding, and ion dissolution of nickel nanoparticles. Meanwhile, the increased graphitization of the carbon framework through boron and nitrogen doping enhances the intrinsic chemical stability of the material, jointly ensuring the structural integrity and long-term performance of the electrode under complex water quality conditions and during long-term electrochemical operation. Furthermore, a hierarchical porous structure was synergistically prepared through the pyrolysis of polyurethane foam and yeast powder as a pore-forming agent. This not only significantly improves mass transfer efficiency and pollutant enrichment capacity, but also achieves an optimized hydrophobic-hydrophilic balance on the boron / nitrogen-doped carbon surface. This effectively reduces the non-selective strong adsorption of impurities such as natural organic matter in the water at the active sites, thereby endowing the electrode with excellent anti-poisoning properties, and further improving catalytic stability and service life.

[0035] (2) Nitrogen- and boron-doped carbonized cellulose in the hierarchical porous particle electrode possesses excellent physical adsorption properties, while the supported nickel active sites endow it with powerful catalytic function. This structure realizes a synergistic mechanism of "enrichment followed by degradation": pollutant molecules are first efficiently adsorbed and enriched on the huge hierarchical pore surface and within the pores, and then rapidly electrocatalytically degraded at the adjacent nickel active sites. This tight spatial coupling significantly improves the local concentration and contact efficiency of pollutants, thereby greatly improving the overall removal efficiency and energy utilization efficiency. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 This is a comparison of the electrocatalytic degradation effects of the particle electrodes prepared in Example 1 and Comparative Examples 1-4 of the present invention on N,N-dimethylformamide (DMF) pollutants. Figure 2 This is a comparison of the electrocatalytic degradation effects of the particle electrodes prepared in Example 1 and Comparative Examples 1-4 of the present invention on dimethyl sulfoxide (DMSO) pollutants. Figure 3 This is a comparison of the electrocatalytic degradation effects of the particle electrodes prepared in Example 1 and Comparative Examples 1-4 of the present invention on pyrrolidone pollutants; Figure 4 This is a comparison chart showing the electrocatalytic degradation effect of the particle electrodes prepared in Example 1 and Comparative Examples 1-4 of the present invention on mixed pollutants of benzene and phenol. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] In this invention, a hierarchical porous structure is prepared by synergistic pore-forming through the pyrolysis of polyurethane foam and yeast powder as a pore-forming agent. This not only greatly improves the mass transfer efficiency and pollutant enrichment capacity, but also achieves an optimized hydrophobic-hydrophilic balance on the carbon surface modified by boron / nitrogen doping. This effectively reduces the non-selective strong adsorption of impurities such as natural organic matter in water at the active sites, thereby endowing the electrode with excellent anti-poisoning properties.

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0042] Example 1 (1) A 1 cm × 1 cm × 0.5 cm polyurethane foam was ultrasonically cleaned with acetone and anhydrous ethanol for 25 min respectively, and then dried in a vacuum drying oven at 60℃ for 10 h to obtain a clean polyurethane foam template.

[0043] (2) Disperse 10 g alkali lignin, 1 g dry yeast powder, 1.5 g boric acid and 0.33 g sodium dodecyl sulfate together in 200 mL of NaOH solution with a concentration of 1 mol / L, mechanically stir for 60 min in a water bath at 70 ℃, and then sonicate for 25 min to adjust the pH to about 10 to form a homogeneous composite impregnation solution.

[0044] (3) The polyurethane foam was completely impregnated in the composite impregnation solution and placed in a vacuum impregnation device. First, the impregnation was maintained under a negative pressure of -0.08 MPa for 30 min, and then under a positive pressure of 0.5 MPa for 20 min. The impregnation was repeated 4 times. After impregnation, the foam was left to stand at room temperature for 4 h.

[0045] The sample was then placed in a temperature-controlled drying oven and heated to 70 °C at a rate of 2 °C / min for the first curing for 1.5 h; heated to 90 °C at a rate of 5 °C / min for the second curing for 2 h; heated to 130 °C at a rate of 2 °C / min for the third curing for 3 h; and heated to 180 °C at a rate of 1 °C / min for the fourth curing for 2 h, thus obtaining the precursor.

[0046] (4) The precursor was placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection. The first carbonization was carried out for 1 h. The first carbonization was carried out at 750°C at 3°C / min, and the second carbonization was carried out for 3 h. The first carbonization was carried out at 900°C at 3°C / min, and the third carbonization was carried out for 2 h, to obtain carbonized cellulose (BN-CF-1) doped with nitrogen and boron.

[0047] (5) A 0.3 mol / L nickel nitrate solution was loaded onto nitrogen- and boron-doped carbonized cellulose (BN-CF-1) using an equal-volume impregnation method. After aging at room temperature for 8 h, the sample was dried at 100 ℃ for 8 h. The dried sample was then heat-treated in a mixed atmosphere of hydrogen and argon (hydrogen volume percentage 15%) to 500 ℃ at a heating rate of 3 ℃ / min for 3 h to obtain a hierarchical porous particle electrode.

[0048] The specific surface area and pore size of nitrogen- and boron-doped carbonized cellulose (BN-CF-1) and hierarchical porous particle electrodes were analyzed using nitrogen adsorption-desorption isotherms.

[0049] Nitrogen- and boron-doped carbonized cellulose (BN-CF-1) possesses a rich hierarchical porous structure with a total specific surface area of ​​920 m². 2 / g, of which the microporous specific surface area is 300 m² 2 / g, mesoporous specific surface area is 560 m² 2 / g, macroporous specific surface area 60m²2 / g, with an average pore size of 3.8 nm.

[0050] Hierarchical porous particle electrode (after Ni loading): Total specific surface area is 850 m² 2 / g, of which the microporous specific surface area is 240m² 2 / g, mesoporous specific surface area is 530 m² 2 / g, macroporous specific surface area 80 m² 2 / g, with an average pore size of 4.0 nm.

[0051] The results show that loading nickel nanoparticles resulted in a favorable change in the internal pore structure of the material, as designed. The nickel particles primarily entered and were fixed within the tiny micropores, efficiently utilizing their high surface area and creating numerous catalytically active sites. Simultaneously, the overall framework structure of mesopores and macropores, serving as the main mass transport channels, was well preserved.

[0052] Comparative Example 1 Compared with Example 1, boric acid is not added in step (2).

[0053] Comparative Example 2 Compared with Example 1, no dry yeast powder was added in step (2), and the remaining steps and conditions were the same. The resulting particle electrode was denoted as Ni / BN-CF-2.

[0054] The pore structure of Ni / BN-CF-2 was analyzed using nitrogen adsorption-desorption isotherms: the total specific surface area is 310 m². 2 / g, microporous specific surface area 90 m² 2 / g, mesoporous specific surface area 35 m² 2 / g, macroporous specific surface area 185 m² 2 / g, average pore size >50 nm.

[0055] Therefore, it can be seen that without yeast powder, the material cannot form an effective hierarchical porous structure. Its pores mainly inherit from the macroporous framework of the polyurethane template, severely lacking small and medium-sized mesopores that play a crucial role in mass transfer. This structural defect directly creates a mass transfer bottleneck, resulting in inefficient diffusion of reactants and products, which is completely consistent with the significant decrease in catalytic performance observed in the experiment (e.g., COD removal rate decreased from 98.5% to 62.3%). This result directly proves that yeast powder is an indispensable key component for constructing the efficient mesoporous mass transfer channels of this invention.

[0056] Comparative Example 3 Compared with Example 1, no surfactant is added in step (2).

[0057] Comparative Example 4 Compared with Example 1, the nickel loading in step (5) is not performed, and the particle electrode is carbonized cellulose doped with nitrogen and boron.

[0058] Experimental Example 1 The particles prepared in Example 1 and Comparative Examples 1-4 were used as particle electrodes for electrocatalytic degradation of pollutants. Two pairs of working electrodes (two anodes and three cathodes) were used. The cathodes were made of titanium plates, and the anodes were made of DSA ruthenium-iridium electrodes. The power supply was a DC regulated power supply. A three-dimensional electrocatalytic oxidation system was assembled and electrochemical catalytic oxidation tests were conducted.

[0059] (1) Using N,N-dimethylformamide (DMF) as the target pollutant, experimental water with a COD of 2000 mg / L was prepared, Na2SO4 with an electrolyte of 20 mmol / L was used, the amount of particle electrode added was 1.2 g / L, the electrode spacing was 2.5 cm, and the current density of the electrocatalytic oxidation system was adjusted to 20 mA / cm. 2 The reaction time is 2 hours.

[0060] The degradation effects of the particles prepared in Example 1 and Comparative Examples 1-4 are as follows: Figure 1 As shown.

[0061] (2) Using dimethyl sulfoxide (DMSO) as the target pollutant, experimental water with a COD of 1500 mg / L was prepared, Na2SO4 with an electrolyte of 20 mmol / L was used, the amount of particle electrode added was 1.2 g / L, the electrode spacing was 2.5 cm, and the current density of the electrocatalytic oxidation system was adjusted to 20 mA / cm. 2 The reaction time is 2 hours.

[0062] The degradation effects of the particles prepared in Example 1 and Comparative Examples 1-4 are as follows: Figure 2 As shown.

[0063] (3) Using pyrrolidone as the target pollutant, experimental water with a COD of 1000 mg / L was prepared, Na2SO4 with an electrolyte of 20 mmol / L was used, the amount of particle electrode added was 1.2 g / L, the electrode spacing was 2.5 cm, and the current density of the electrocatalytic oxidation system was adjusted to 20 mA / cm. 2 The reaction time is 2 hours.

[0064] The degradation effects of the particles prepared in Example 1 and Comparative Examples 1-4 are as follows: Figure 3 As shown.

[0065] (4) Using benzene and phenol as target pollutants, prepare experimental water with a COD of 2000 mg / L, electrolyte of 20 mmol / L Na2SO4, particle electrode dosage of 1.2 g / L, electrode spacing of 2.5 cm, and adjust the current density of the electrocatalytic oxidation system to 20 mA / cm. 2 The reaction time is 2 hours.

[0066] The degradation effects of the particles prepared in Example 1 and Comparative Examples 1-4 are as follows: Figure 4 As shown.

[0067] comprehensive Figure 1 and Figure 4 As can be seen, the hierarchical porous particle electrode (Ni / BN-CF-1) provided by this invention exhibits excellent and stable electrocatalytic oxidation performance for a variety of typical recalcitrant organic pollutants. Systematic comparative experiments demonstrate that boron / nitrogen co-doping, the hierarchical porous structure formed by yeast powder pore creation, the uniform loading promoted by surfactants, and the active centers of nickel nanoparticles are four key and indispensable technical features of this invention. These features collectively achieve a synergistic effect of "adsorption-enrichment-catalysis," thereby significantly improving degradation efficiency and current efficiency. The significantly deteriorated performance of Comparative Example 2 (without yeast powder) and Comparative Example 4 (without nickel) strongly confirms the core role of the hierarchical porous mass transfer channels and the metal active centers. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-level porous particle electrode, characterized in that, It uses nitrogen- and boron-doped carbonized cellulose as a carrier to load metallic nickel nanoparticles. The total specific surface area of ​​the hierarchical porous particle electrode is 810~880 m². 2 / g, with a microporous specific surface area of ​​230~250 m² 2 / g, mesoporous specific surface area is 510~550 m² 2 / g, the specific surface area of ​​the macropores is 75~90 m² 2 / g, with an average pore size of 3.5~4.2 nm.

2. The method for preparing the multi-level porous particle electrode according to claim 1, characterized in that, Includes the following steps: (1) Add alkali lignin, yeast powder, boric acid and surfactant to sodium hydroxide solution, mix evenly to obtain composite impregnation solution; (2) The polyurethane foam is impregnated in a composite impregnation solution and vacuum impregnated. After curing, the precursor is obtained. (3) The precursor is subjected to a first heat treatment in an oxygen-free environment to obtain carbonized cellulose doped with nitrogen and boron; (4) Nitrogen- and boron-doped carbonized cellulose is immersed in a nickel salt solution, dried, and then subjected to a second heat treatment to obtain a multi-level porous particle electrode.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of alkali lignin, yeast powder, and boric acid is 1:(0.05~0.15):(0.12~0.18). Alternatively, in step (1), the surfactant is sodium dodecyl sulfate; Preferably, the mass fraction of sodium dodecyl sulfate is 0.8-1.2%, more preferably 1%.

4. The preparation method according to claim 2, characterized in that, In step (1), the pH value of the sodium hydroxide solution is 9~11, preferably 10.

5. The preparation method according to claim 2, characterized in that, In step (2), the vacuum impregnation method includes: Maintain immersion under negative pressure conditions of -0.05 MPa to -0.1 MPa for 20 min to 40 min; Then, the immersion was maintained under a positive pressure of 0.3 MPa to 0.8 MPa for 15 min to 30 min. Repeat the soaking process 3-5 times; Alternatively, in step (2), after vacuum impregnation, the mixture is left to stand at room temperature for 2-6 hours to improve the uniformity of the impregnation.

6. The preparation method according to claim 2, characterized in that, In step (2), the curing method includes: First curing at 65℃~80℃ for 1~2 hours; Second curing at 85℃~100℃ for 1~3 hours; A third curing process is performed at 120℃~150℃ for 2~5 hours; The material was cured for the fourth time at 160 ℃~200 ℃ for 1~4 h.

7. The preparation method according to claim 2, characterized in that, In step (3), the method for the first heat treatment includes: The first carbonization was carried out at 300 ℃~500 ℃ for 0.5~2 h; Second carbonization at 700 ℃~800 ℃ for 2~4 h; The third carbonization was carried out at 800 ℃~1000 ℃ for 1~3 h.

8. The preparation method according to claim 2, characterized in that, In step (4), the nickel salt includes one or more of nickel sulfate, nickel nitrate, or nickel acetate; Alternatively, in step (4), the impregnation method is equal-volume impregnation; Alternatively, in step (4), the atmosphere during the second heat treatment is an oxygen-free atmosphere, which is a mixture of hydrogen and argon. Preferably, the volume percentage of hydrogen is 5% to 25%. Alternatively, in step (4), the temperature of the second heat treatment is 400~600 ℃ and the heat treatment time is 2~4 h.

9. The application of the multi-level porous particle electrode according to claim 1 or the preparation method according to any one of claims 2 to 8 in the electrocatalytic degradation of pollutants in industrial wastewater.

10. A method for electrocatalytic degradation of pollutants in industrial wastewater, characterized in that, Includes the following steps: A three-dimensional electrocatalytic oxidation system is constructed in an electrolytic cell, the system comprising an anode, a cathode, an electrolyte solution, and a particle electrode suspended in the electrolyte solution; the particle electrode is the hierarchical porous particle electrode as described in claim 1 or a hierarchical porous particle electrode prepared by any one of claims 2 to 8.

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