A bifunctional catalyst, its preparation method and use
By using a porous carbon layer to coat noble metal nanoparticles, the problem of noble metal catalysts being easily poisoned and deactivated is solved, achieving highly efficient electrocatalytic reduction of nitrates and oxidation of sulfides. The preparation process is simple and controllable, making it suitable as a bifunctional catalyst for wastewater treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 天津仁爱学院
- Filing Date
- 2026-02-09
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies struggle to achieve efficient electrocatalytic nitrate reduction and sulfide oxidation in a single system. Noble metal catalysts are prone to poisoning and deactivation, and existing preparation methods struggle to control the carbon layer structure, resulting in limited improvements in catalytic performance.
A bifunctional catalyst was prepared by using a structure in which a porous carbon layer is coated with noble metal nanoparticles, the noble metals being selected from Pd, Rh, and Ru. The specific surface area of the porous carbon layer is 150-1000 m2/g, the pore size is 0.1-5 nm, and the nanoparticles are doped with transition metal elements Co, Fe, Ni, Ce, and Zr. The catalyst was prepared by solvothermal and calcination treatment.
The catalyst achieves high stability and high activity in sulfur-containing environments, and can simultaneously reduce nitrate to ammonia and oxidize sulfides to elemental sulfur, thus simultaneously removing pollutants and recovering resources. This simplifies the preparation process and has the potential for large-scale production.
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Figure CN121669216B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wastewater treatment technology, and in particular to a bifunctional catalyst, its preparation method, and its application. Background Technology
[0002] Nitrates (NO3) in water - ) and sulfide ions (S 2- These pollutants mainly originate from agricultural runoff, industrial wastewater, and domestic sewage. They easily lead to eutrophication of water bodies and increase toxicity to aquatic organisms. Currently, common treatment technologies for wastewater containing these pollutants include reverse osmosis, ion exchange, and biological denitrification. However, these methods generally have limitations such as low treatment efficiency, high operating costs, and the potential for secondary pollution, making it difficult to simultaneously meet the dual requirements of sustainable water treatment and resource recovery.
[0003] Electrochemical catalysis, particularly the coupled system of electrocatalytic nitrate reduction (ENRR) and sulfide oxidation (SOR), offers a promising solution for the simultaneous removal of pollutants and the conversion and recovery of high-value resources such as ammonia and elemental sulfur. However, the practical application of this technology still faces a series of key challenges. First, the efficient catalysts for the ENRR process typically rely on noble metals (such as Pd, Pt, and Ru), whose high cost limits their large-scale application. More importantly, these noble metal catalysts are highly susceptible to poisoning and deactivation in the anodic SOR environment due to the strong adsorption of sulfur species, leading to a sharp decline in catalytic stability. Second, to regulate the reaction microenvironment or improve stability, researchers have attempted to use a configuration of carbon-coated noble metal particles. However, existing preparation methods often struggle to precisely control the pore structure, thickness, and specific surface area of the carbon layer, resulting in low accessibility of active sites, hindered mass transfer, and limited improvement in catalytic performance. Furthermore, existing research focuses on single reaction systems and lacks bifunctional catalysts that can simultaneously adapt to anode and cathode reactions and possess high activity, high stability, and resistance to poisoning. This leads to complex coupling system design, increased costs, and difficulty in achieving efficient synergy and engineering applications.
[0004] Therefore, developing a bifunctional catalyst with controllable structure, stable performance, and the ability to simultaneously and efficiently drive ENRR and SOR has become a key bottleneck in promoting the development of electrocatalytic resource utilization technology for nitrogen- and sulfur-containing wastewater. Summary of the Invention
[0005] The purpose of this invention is to address the problems existing in the prior art by providing a bifunctional catalyst, its preparation method, and its application. Through the unique structure of porous carbon layer-coated noble metal nanoparticles, it achieves "two uses in one material," possessing both excellent cathode electrocatalytic nitrate reduction activity and anodic sulfide oxidation stability.
[0006] To achieve the above objectives, the present invention provides a bifunctional catalyst, the catalyst comprising noble metal nanoparticles and a porous carbon layer coated on the surface of the noble metal nanoparticles;
[0007] The precious metal is selected from one or more of Pd, Rh, and Ru;
[0008] The specific surface area of porous carbon layers is 150-1000 m². 2 / g, with a pore size distribution of 0.1-5nm;
[0009] The porous carbon layer is doped with transition metal elements.
[0010] Preferably, the particle size of the noble metal nanoparticles is ≤100nm.
[0011] Preferably, the transition metal element is selected from one or more of Co, Fe, Ni, Ce, and Zr.
[0012] The present invention also provides a method for preparing the aforementioned bifunctional catalyst, comprising the following steps:
[0013] S1. Mix the noble metal salt solution and the reducing agent solution, and react to obtain noble metal nanoparticles;
[0014] S2. Mix noble metal nanoparticles, carbon source precursor, transition metal salt solution and water to obtain a mixture;
[0015] S3. The mixture is subjected to a solvothermal reaction and calcination treatment in sequence to obtain the precursor;
[0016] S4. The precursor is acid-washed to obtain a bifunctional catalyst.
[0017] Preferably, in S1, the noble metal salt is selected from one or more of PdCl2, RhCl3, and RuCl3; the reducing agent is selected from sodium borohydride; and the mass ratio of the noble metal salt to the reducing agent is 0.1-2.5:1.
[0018] Preferably, in S1, the reaction temperature is 20-30℃ and the time is 5-10h.
[0019] Preferably, in S2, the carbon source precursor is selected from chitosan; the transition metal salt is selected from one or more of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl2, Ni(NO3)2, Ce(NO3)3, and ZrCl2; the mass-volume ratio of noble metal nanoparticles, carbon source precursor, transition metal salt solution and water is 0.3-2g:0.3-1g:10-100mL:70-90mL.
[0020] Preferably, in S3, the temperature of the solvothermal reaction is 80-180℃ and the time is 2-8h; the temperature of the calcination treatment is 600-800℃ and the time is 1.5-2.5h.
[0021] Preferably, in step S4, an acid solution with a concentration of 0.1-3 mol / L is used for acid washing, and the acid washing time is 3-5 hours.
[0022] The present invention also provides the application of the aforementioned bifunctional catalyst in the electrocatalytic treatment of nitrogen- and sulfur-containing wastewater.
[0023] The beneficial effects of this invention are as follows:
[0024] 1. This invention provides a bifunctional catalyst, comprising noble metal nanoparticles and a porous carbon layer coated on the surface of the noble metal nanoparticles; the noble metal is selected from one or more of Pd, Rh, and Ru; the specific surface area of the porous carbon layer is 150-1000 m². 2 The catalyst has a pore size distribution of 0.1-5 nm and is composed of porous carbon layers doped with transition metal elements. Through the unique structure of the porous carbon layer coating noble metal nanoparticles, a dual-purpose material is achieved, exhibiting both excellent cathodic electrocatalytic nitrate reduction (ENRR) activity and anodic sulfide oxidation (SOR) stability. This catalyst can simultaneously construct an electrocatalytic system coupling ENRR and SOR, efficiently reducing nitrates in wastewater to high-value ammonia and oxidizing sulfides to elemental sulfur in a single system, thus simultaneously achieving pollutant removal and valuable resource recovery.
[0025] On the one hand, the porous carbon layer coating the surface of the noble metal plays a dual role of physical barrier and chemical protection, effectively preventing sulfur species generated during the SOR process from directly poisoning the active sites of the noble metal. This significantly improves the catalyst's resistance to poisoning and long-term operational stability in sulfur-containing environments, solving the key problem of the easy deactivation of noble metals in the presence of sulfur. On the other hand, this porous carbon layer can construct a localized alkaline microenvironment around the active sites of the noble metal, promoting water dissociation and providing more active hydrogen for the ENRR reaction, thereby greatly improving the rate and selectivity of nitrate reduction to ammonia.
[0026] 2. The preparation process of this invention is simple and controllable, and the process flow is mature. It shows good repeatability and potential for large-scale production, laying a solid foundation for practical industrial applications. Attached Figure Description
[0027] Figure 1 This is a scanning electron microscope (SEM) characterization image of the bifunctional catalyst in Example 1 of this invention;
[0028] Figure 2 This is the isothermal adsorption-desorption curve of the bifunctional catalyst in Example 1 of this invention;
[0029] Figure 3 These are schematic diagrams showing the pore sizes of the porous carbon layers in Embodiments 1 and 6-7 of the present invention;
[0030] Figure 4 This is a pore size distribution diagram of the Pd nanoparticles in Example 1 of the present invention;
[0031] Figure 5 This is a comparison diagram of the stability of the bifunctional catalyst in Example 1 and the catalyst in Comparative Example 1 in the sulfide oxidation reaction (SOR).
[0032] Figure 6 This is a comparison diagram of the activities of the bifunctional catalyst in Example 1 and the catalyst in Comparative Example 1 in the electrocatalytic reduction reaction (ENRR) of nitrate;
[0033] Figure 7 This is a comparison chart of the activity of the bifunctional catalysts in Examples 1-5 of the present invention in the electrocatalytic reduction reaction (ENRR) of nitrate. Detailed Implementation
[0034] This invention provides a bifunctional catalyst, which includes noble metal nanoparticles and a porous carbon layer coated on the surface of the noble metal nanoparticles.
[0035] The precious metal is selected from one or more of Pd, Rh, and Ru;
[0036] The specific surface area of porous carbon layers is 150-1000 m². 2 / g, with a pore size distribution of 0.1-5nm;
[0037] The porous carbon layer is doped with transition metal elements.
[0038] In this invention, the particle size of the noble metal nanoparticles is ≤100nm.
[0039] In this invention, the transition metal element is selected from one or more of Co, Fe, Ni, Ce, and Zr.
[0040] The present invention also provides a method for preparing the aforementioned bifunctional catalyst, comprising the following steps:
[0041] S1. Mix the noble metal salt solution and the reducing agent solution, and react to obtain noble metal nanoparticles;
[0042] S2. Mix noble metal nanoparticles, carbon source precursor, transition metal salt solution and water to obtain a mixture;
[0043] S3. The mixture is subjected to a solvothermal reaction and calcination treatment in sequence to obtain the precursor;
[0044] S4. The precursor is acid-washed to obtain a bifunctional catalyst.
[0045] In this invention, in S1, the noble metal salt is selected from one or more of PdCl2, RhCl3, and RuCl3, the solvent of the noble metal salt solution is selected from ethylene glycol, and the concentration of the noble metal salt solution is 0.05-0.5 mol / L.
[0046] In this invention, in S1, the reducing agent is selected from sodium borohydride, and the solvent of the reducing agent solution is selected from water; the concentration of the reducing agent in the reducing agent solution is 0.1-0.5 mol / L.
[0047] In this invention, in S1, the mass ratio of the noble metal salt to the reducing agent is 0.1-2.5:1.
[0048] In this invention, in S1, the reaction temperature is 20-30℃ and the time is 5-10h.
[0049] In this invention, in step S1, after the reaction is completed, the mixture is centrifuged for 3-7 minutes, the precipitate is collected, and then washed with water and ethanol in sequence, wherein the number of water washings is ≥2 times and the number of ethanol washings is ≥2 times. Finally, it is vacuum dried for 8-12 hours to obtain noble metal nanoparticles.
[0050] In this invention, in S2, the carbon source precursor is selected from chitosan, and the molecular weight of chitosan is 50,000-100,000.
[0051] In this invention, in S2, the transition metal salt is selected from one or more of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl2, Ni(NO3)2, Ce(NO3)3, and ZrCl2.
[0052] In this invention, in S2, the solvent for the transition metal salt solution is selected from water, and the concentration of the transition metal salt solution is 0.5-2 mol / L; the mass-volume ratio of noble metal nanoparticles, carbon source precursor, transition metal salt solution and water is 0.3-2 g: 0.3-1 g: 10-100 mL: 70-90 mL.
[0053] In this invention, in S2, the mixing is performed by ultrasonic dispersion at 40-60 kHz for 30-60 min.
[0054] In this invention, in step S3, the temperature of the solvothermal reaction is 80-180℃ and the time is 2-8h. After the solvothermal reaction is completed, the product is naturally cooled to room temperature, filtered and collected, washed with water until neutral, vacuum dried for 8-12h, and then calcined under an inert atmosphere. The inert atmosphere is selected from argon, and the calcination temperature is 600-800℃ and the time is 1.5-2.5h.
[0055] In this invention, in step S4, an acid solution with a concentration of 0.1-3 mol / L is used for acid washing. The acid solution is selected from hydrochloric acid solution, sulfuric acid solution or nitric acid solution, and the acid washing time is 3-5 hours.
[0056] In this invention, in step S4, after the acid washing treatment is completed, the solid is collected by centrifugation, washed with water until the filtrate is neutral, and then vacuum dried for 8-12 hours to obtain a bifunctional catalyst.
[0057] The present invention also provides the application of the aforementioned bifunctional catalyst in the electrocatalytic treatment of nitrogen- and sulfur-containing wastewater.
[0058] In this invention, a bifunctional catalyst is used for cathode electrocatalytic nitrate reduction and / or anodic electrocatalytic sulfide oxidation, enabling simultaneous ammonia production from nitrate reduction and elemental sulfur production from sulfide oxidation.
[0059] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.
[0060] Example 1
[0061] This embodiment provides a method for preparing a bifunctional catalyst, comprising the following steps:
[0062] A 0.2 mol / L PdCl2 solution (using ethylene glycol as the solvent) was mixed with a 0.2 mol / L sodium borohydride solution (using water as the solvent), with a mass ratio of noble metal salt to sodium borohydride of 2.5:1. The mixture was reacted at 25 °C for 6 h. After the reaction was completed, the mixture was centrifuged for 5 min, the precipitate was collected, washed three times with water, then washed three times with ethanol, and finally dried under vacuum for 10 h to obtain Pd nanoparticles.
[0063] 0.5 g of Pd nanoparticles, 0.5 g of chitosan (molecular weight 80000), 20 mL of 0.5 mol / L Co(NO3)2 solution (solvent is water) and 80 mL of deionized water were mixed and ultrasonically dispersed at a frequency of 50 kHz for 60 min to make them uniformly mixed to obtain a mixture.
[0064] The mixture was solvothermal reacted at 120℃ for 5 h. After the reaction was completed, it was naturally cooled to room temperature, the solid product was collected by filtration, washed with deionized water until neutral, dried under vacuum for 10 h, and calcined at 600℃ for 2 h under argon atmosphere to obtain the precursor.
[0065] The precursor was immersed in a 0.1 mol / L hydrochloric acid solution and magnetically stirred at room temperature for 5 h. After acid washing, the solid was collected by centrifugation, washed with deionized water until the filtrate was neutral, and vacuum dried for 10 h to obtain the bifunctional catalyst.
[0066] Example 2
[0067] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the mass ratio of noble metal salt and sodium borohydride is modified to 1.5:1.
[0068] Example 3
[0069] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the mass ratio of noble metal salt and sodium borohydride is modified to 1:1.
[0070] Example 4
[0071] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the mass ratio of noble metal salt and sodium borohydride is modified to 0.5:1.
[0072] Example 5
[0073] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the mass ratio of the noble metal salt and sodium borohydride is modified to 0.1:1.
[0074] Example 6
[0075] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the concentration of the Co(NO3)2 solution is modified to 1 mol / L.
[0076] Example 7
[0077] This embodiment provides a method for preparing a bifunctional catalyst, which differs from Example 1 in that the concentration of the Co(NO3)2 solution is modified to 2 mol / L.
[0078] Comparative Example 1
[0079] This comparative example provides a method for preparing a catalyst, comprising the following steps:
[0080] A 0.2 mol / L PdCl2 solution (using ethylene glycol as the solvent) was mixed with a 0.2 mol / L sodium borohydride solution (using water as the solvent), with a mass ratio of noble metal salt to sodium borohydride of 2.5:1. The mixture was reacted at 25 °C for 6 h. After the reaction was completed, the mixture was centrifuged for 5 min, the precipitate was collected, washed three times with water, then washed three times with ethanol, and finally dried under vacuum for 10 h to obtain Pd nanoparticles, which were used as the catalyst.
[0081] Experimental Example 1
[0082] The bifunctional catalyst prepared in Example 1 was analyzed by scanning electron microscopy (SEM), and the SEM characterization image of the bifunctional catalyst in Example 1 was obtained, as shown below. Figure 1 As shown. From Figure 1 As can be seen, the catalyst has a uniformly dispersed nanoparticle morphology.
[0083] The pore structure was further analyzed by N2 isothermal adsorption-desorption testing, and the isothermal adsorption-desorption curves of the bifunctional catalyst in Example 1 were obtained, as shown in the figure. Figure 2 As shown. Figure 2 The material is confirmed to possess a rich mesoporous structure. The specific surface area of the porous carbon layer in the catalyst, calculated from this curve, is approximately 678.449 m². 2 / g.
[0084] Based on the adsorption data, the pore size distribution was plotted to obtain the pore size of the porous carbon layer of the catalyst in Example 1. The same method was used to test Examples 6 and 7, resulting in schematic diagrams of the pore size of the porous carbon layers in Examples 1 and Examples 6-7, as shown below. Figure 3 As shown. Figure 3 The results show that the pore size of the porous carbon layer in Example 1 is concentrated at about 0.5 nm, while the pore size in Examples 6 and 7 increases to about 1.0 nm and 2.3 nm, respectively, indicating that the concentration of transition metal salt has a regulatory effect on the pore size of the carbon layer.
[0085] Furthermore, particle size analysis was performed on the Pd nanoparticles prepared in Example 1, and the pore size distribution map of the Pd nanoparticles in Example 1 was obtained, as shown below. Figure 4 As shown. From Figure 4 It can be seen that the Pd nanoparticles have a uniform particle size distribution, mainly distributed between 20-60 nm.
[0086] Experimental Example 2
[0087] The electrocatalytic performance of the bifunctional catalyst in Example 1 and the catalyst in Comparative Example 1 were tested. The test conditions for the nitrate reduction reaction (ENRR) were as follows: the electrolyte was a mixed solution of NaOH and NaNO3 (the concentration of NaOH in the mixed solution was 1 mol / L, and the concentration of NaNO3 was 1 mol / L); the working electrode was the prepared catalyst; the counter electrode was a graphite rod; and the reference electrode was a Hg / HgO electrode. The test conditions for the sulfide oxidation reaction (SOR) were as follows: the electrolyte was a mixed solution of NaOH and Na2S (the concentration of NaOH in the mixed solution was 1 mol / L, and the concentration of Na2S was 1 mol / L); and the working electrode, counter electrode, and reference electrode system were the same as those for ENRR.
[0088] The stability comparison diagram of the bifunctional catalyst in Example 1 and the catalyst in Comparative Example 1 in the sulfide oxidation reaction (SOR) was obtained from the test, as shown in the figure. Figure 5 As shown; a comparison of the activities of the bifunctional catalyst in Example 1 and the catalyst in Comparative Example 1 in the electrocatalytic reduction of nitrate (ENRR) is presented. Figure 6 As shown in the figure. The test results show that in the SOR stability comparison, the bifunctional catalyst of Example 1 exhibits significant resistance to sulfur poisoning, and its stability is much higher than that of Comparative Example 1. Meanwhile, in the ENRR activity evaluation, the catalyst of Example 1 is significantly superior to Comparative Example 1 in terms of Faraday efficiency. These results fully demonstrate that the porous carbon layer coating structure designed in this invention not only effectively improves the stability of the catalyst in harsh anolyte environments but also simultaneously enhances its catalytic activity in cathodic reduction reactions.
[0089] Experimental Example 3
[0090] The bifunctional catalysts in Examples 1-5 were subjected to performance tests in the electrocatalytic reduction reaction (ENRR) of nitrate (the test method was the same as in Experiment 2, with the potential set to -0.2 V vs. RHE). The resulting comparison chart of the activities of the bifunctional catalysts in Examples 1-5 in the electrocatalytic reduction reaction (ENRR) of nitrate was obtained, as shown below. Figure 7 As shown. From Figure 7 It can be seen that the ENRR performance of the catalyst changes regularly with the change of the ratio of noble metal salt to reducing agent, which further illustrates the regulatory role of preparation parameters on the final catalytic activity and provides a basis for process optimization.
[0091] Therefore, this invention employs the aforementioned bifunctional catalyst, utilizing a unique structure of porous carbon layers coating noble metal nanoparticles to achieve "dual-purpose use of a single material," possessing both excellent cathodic electrocatalytic nitrate reduction (ENRR) activity and anodic sulfide oxidation (SOR) stability. This catalyst can simultaneously construct an electrocatalytic system coupling ENRR and SOR, efficiently reducing nitrates in wastewater to high-value ammonia and oxidizing sulfides to elemental sulfur in a single system, thereby simultaneously achieving pollutant removal and valuable resource recovery, meeting the requirements of green chemistry and a circular economy.
[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. A bifunctional catalyst, characterized in that, The catalyst includes noble metal nanoparticles and a porous carbon layer coated on the surface of the noble metal nanoparticles. The precious metal is selected from one or more of Pd, Rh, and Ru; The specific surface area of porous carbon layers is 150-1000 m². 2 / g, with a pore size distribution of 0.1-5nm; The porous carbon layer is doped with a transition metal element; the transition metal element is selected from one or more of Co, Fe, and Ni; The bifunctional catalyst possesses both the activity of cathode electrocatalytic nitrate reduction and the stability of anodic electrocatalytic sulfide oxidation.
2. The bifunctional catalyst according to claim 1, characterized in that, The particle size of the noble metal nanoparticles is ≤100nm.
3. The method for preparing the bifunctional catalyst according to claim 1 or 2, characterized in that, Includes the following steps: S1. Mix the noble metal salt solution and the reducing agent solution, and react to obtain noble metal nanoparticles; S2. Mix noble metal nanoparticles, carbon source precursor, transition metal salt solution and water to obtain a mixture; S3. The mixture is subjected to a solvothermal reaction and calcination treatment in sequence to obtain the precursor; S4. The precursor is acid-washed to obtain a bifunctional catalyst.
4. The method for preparing the bifunctional catalyst according to claim 3, characterized in that, In S1, the noble metal salt is selected from one or more of PdCl2, RhCl3, and RuCl3; the reducing agent is selected from sodium borohydride; the mass ratio of the noble metal salt to the reducing agent is 0.1-2.5:
1.
5. The method for preparing the bifunctional catalyst according to claim 3, characterized in that, In S1, the reaction temperature is 20-30℃ and the time is 5-10h.
6. The method for preparing the bifunctional catalyst according to claim 3, characterized in that, In S2, the carbon source precursor is selected from chitosan; the transition metal salt is selected from one or more of CoCl2, Co(NO3)2, FeCl3, Fe(NO3)3, NiCl2, and Ni(NO3)2; the mass-volume ratio of noble metal nanoparticles, carbon source precursor, transition metal salt solution and water is 0.3-2g:0.3-1g:10-100mL:70-90mL.
7. The method for preparing the bifunctional catalyst according to claim 3, characterized in that, In S3, the temperature of the solvothermal reaction is 80-180℃ and the time is 2-8h; the temperature of the calcination treatment is 600-800℃ and the time is 1.5-2.5h.
8. The method for preparing the bifunctional catalyst according to claim 5, characterized in that, In S4, an acid solution with a concentration of 0.1-3 mol / L is used for acid washing, and the acid washing time is 3-5 hours.
9. The application of the bifunctional catalyst according to claim 1 or 2 in the electrocatalytic treatment of nitrogen- and sulfur-containing wastewater.