Method for preparing cathode catalyst by treating dye wastewater based on ZIF-8 material

Abstract

The invention provides a method for preparing a cathode catalyst by treating dye wastewater based on a ZIF-8 material, and relates to the field of dye wastewater treatment.The method comprises the steps that firstly, an adsorbent is prepared; step 2, dye adsorption to obtain a dye-loaded adsorption material; 3, iron doping is carried out, and an iron-doped dye loading material is obtained; and 4, performing high-temperature calcination to obtain the cathode catalyst. According to the method, azo dye wastewater is adsorbed and recycled, wastewater treatment is achieved, meanwhile, further metal doping is utilized, preparation of a functional material is completed, full utilization of the material is achieved, and secondary pollution of solid waste is avoided; in addition, through wastewater treatment and secondary doping, the electrochemical performance of the cathode catalyst is effectively improved, and collaborative development of wastewater treatment and clean energy production is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of dye wastewater treatment, and in particular to a method for preparing a cathode catalyst by treating dye wastewater based on a ZIF-8 material. Background Art

[0002] Azo dyes are the most diverse type of synthetic dye and are widely used in industries such as textiles, leather, and rubber. The production, use, and processing of azo dyes releases industrial wastewater containing pollutants such as undegraded dyes, intermediates, and chemical additives. Due to the complex structure and high chemical stability of azo dyes, these wastewaters are difficult to effectively degrade using traditional treatment methods. Currently, approximately 10% to 15% of the world's annual industrial wastewater is azo dye wastewater. Typical azo dyes such as Congo Red and Acid Red 66 are highly toxic and potentially carcinogenic due to their presence of benzene rings and sulfonic acid groups. Once these wastewaters enter water bodies, they not only damage aquatic ecosystems but also accumulate through the food chain, threatening human health. Furthermore, elements such as sulfur and nitrogen in azo dye molecules can be further converted into harmful substances such as nitrite and hydrogen sulfide, exacerbating the risk of environmental pollution.

[0003] Currently, treatment methods for azo dye wastewater primarily include chemical oxidation, biodegradation, membrane separation, and adsorption. Adsorption, in particular, has attracted significant attention due to its simplicity, low cost, and high efficiency. Compared to chemical oxidation, which is prone to secondary pollution and biodegradation's poor adaptability to high dye concentrations, adsorption allows for the targeted removal of pollutants and the recycling of adsorbents through the design of functionalized adsorbents, achieving the resource-based "waste treatment" principle. However, there is currently a lack of technical solutions that couple dye wastewater treatment with functional material regeneration and energy recovery. This, coupled with the lack of synergy between wastewater treatment and clean energy regeneration, hinders the development of efficient and sustainable wastewater treatment technologies. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing cathode catalysts by treating dye wastewater based on ZIF-8 materials. This method realizes wastewater treatment by adsorbing and recovering azo dye wastewater. At the same time, by further doping and completing the preparation of functional materials, the full utilization of materials is achieved and secondary pollution of solid waste is avoided.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material, comprising: Step 1: Preparation of adsorbent: Dissolve zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in ethanol to form solution A; dissolve mixed ligand powder in ethanol to form solution B; then slowly pour solution A into solution B, stir, centrifuge, wash, and dry to obtain an adsorbent; Step 2: Dye adsorption: Add the adsorbent to the azo dye wastewater, adjust the pH to 6-8, and obtain the dye-loaded adsorption material after vibration adsorption, filtration separation, and drying; Step 3, iron doping: The dye-loaded adsorbent material is dispersed in an ethanol solution to form a suspension solution C; ferric chloride hexahydrate (FeCl3·6H2O) and sodium citrate are dissolved in the ethanol solution to form a solution D; under stirring, the solution D is poured into the suspension solution C, and the stirring is continued for a period of time, followed by centrifugation and drying to obtain an iron-doped dye-loaded material; Step 4: High-temperature calcination: placing the iron-doped dye-loaded material in a tube furnace and calcining it under a mixed atmosphere, cooling and grinding it after calcination to obtain a cathode catalyst.

[0006] Based on further optimization of the above scheme, the concentration of solution A in step 1 is 0.05-0.2 mol / L; the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid, and 2-(4-hydroxyphenyl)imidazole; the concentration of solution B is 20-40 times that of solution A, and the amount of ethanol used in the preparation of solutions A and B is the same.

[0007] Based on further optimization of the above scheme, the usage ratio of the 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole is 7.8-8.2:0.6-0.8:0.6-0.8:0.5-0.7.

[0008] During the preparation process of the adsorbent, the present invention can effectively improve the adsorption of the adsorbent on azo dye wastewater through the synergistic effect of multiple functional groups (amino groups form strong electrostatic attraction with sulfonic acid groups, carboxyl groups, etc. in the dye, the thiol groups of the polar groups enhance the affinity for polar dyes, and the phenyl groups can form a π-π stacking effect with the aromatic rings of the dyes, etc.); at the same time, the co-coordination of the multiple functional groups is utilized to broaden the pore size distribution of the adsorbent (amino groups, thiol groups, etc. increase the polarity of the pore surface, making the material easier to disperse in the azo dye wastewater, that is, the aqueous phase, and increasing the contact area), thereby forming a multi-level pore structure, thereby significantly increasing the adsorption capacity of the adsorbent for azo dye wastewater (preventing problems such as large molecular azo dyes from diffusing into the pores and causing pore blockage). At the same time, the multiple functional groups can also act as strong coordinating groups, stabilizing and fixing the subsequently doped iron ions through chelation and forming coordination bonds. This not only prevents the direct replacement of zinc ions in the adsorbent by trivalent iron ions, which can lead to defects such as framework distortion or collapse (zinc ions and imidazole ligands bind in a tetrahedral manner, while trivalent iron ions tend to coordinate in an octahedral or planar manner. If trivalent iron ions directly replace zinc ions, defects such as framework distortion and collapse are inevitable). It also ensures that the iron ions are evenly distributed on the framework, preventing iron agglomeration during high-temperature calcination, thereby improving catalytic activity. In addition, through the coordination of multiple functional groups, the anchoring of Fe, S, and N is achieved, preventing the volatilization of catalytically active elements during high-temperature calcination and ensuring the formation and uniform distribution of Fe-Nx-S active sites.

[0009] Based on further optimization of the above scheme, in step 1, stirring is carried out at room temperature (i.e., 25±2°C) for 11 to 13 hours at a stirring rate of 500 to 800 rpm; centrifugation is carried out at a speed of 8000 to 10000 rpm for 5 to 10 minutes, and the precipitate is collected; washing is carried out by a mixed washing method of methanol and ethanol solution, and the precipitate is washed 3 to 5 times; and drying is carried out by freeze drying.

[0010] Based on further optimization of the above scheme, the azo dye wastewater contains at least one of Congo red and acid red 66; the concentration of the azo dye wastewater is 380-420 mg / L.

[0011] Based on further optimization of the above scheme, the oscillating adsorption in step 2 is carried out at room temperature (ie, 25±2° C.) for 0.8 to 1.2 h at an oscillation speed of 100 to 200 rpm; and freeze drying is used for drying.

[0012] Based on further optimization of the above scheme, step three is specifically as follows: first, 400 mg of the dye-loaded adsorbent material is dispersed in 20 mL of ethanol solution to form a C suspension solution; then, 2 mmol of ferric chloride hexahydrate and sodium citrate are dissolved in 20 mL of ethanol solution, wherein the molar ratio of ferric chloride hexahydrate to sodium citrate is 1:0.5-1; the stirring rate is 500-800 rpm, the stirring time is 11-13 h, and the stirring temperature is room temperature (i.e., 25±2°C); the centrifugation conditions are the same as those in step one; and the drying is performed in a vacuum oven at a temperature of 40°C to 60°C for 12-24 h.

[0013] Based on further optimization of the above scheme, the mixed atmosphere in step 4 is a mixed gas composed of nitrogen and hydrogen, wherein the volume ratio of hydrogen is 5% to 8%.

[0014] By combining ferric chloride hexahydrate with sodium citrate and utilizing weakly coordinating ligands to complex divalent iron ions, the framework distortion and collapse problems caused by direct replacement of zinc ions by trivalent iron ions are further avoided. Guided by multifunctional groups, divalent iron ions enter the framework interstices rather than directly replacing zinc ions, forming a "site coexistence" structure that ensures the stability of the entire framework while also exposing more active sites. Ligand anchoring effectively inhibits the migration and aggregation of iron during calcination, while promoting the fixation of sulfur in the form of thiophene-S around the Fe-Nx active sites. This modulates the electronic structure of the active sites, enhancing their catalytic activity and stability. This prevents the sulfur released during high-temperature calcination and carbonization from reacting with iron to form Fe-S compounds, ensuring the generation and exposure of more Fe-Nx-S active sites and improving the activity of the entire catalyst.

[0015] Based on further optimization of the above scheme, the steps of high-temperature calcination in step 4 are specifically as follows: first, the temperature is raised to 250-300°C at a rate of 8-10°C / min, and pre-calcined for 30-50 minutes, and then the temperature is raised to 800-900°C at a rate of 4-6°C / min, and high-temperature calcined for 50-70 minutes.

[0016] The following are the technical effects of the solution of the present invention: This method prepares an adsorbent using a mixed ligand powder composed of zinc nitrate hexahydrate and 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid, and 2-(4-hydroxyphenyl)imidazole. This adsorbent is then used to treat azo dye wastewater, adsorbing harmful azo dye molecules and anchoring sulfur and nitrogen in situ. Iron ligands are then introduced to form an iron-doped dye-loaded material. High-temperature calcination is then used to achieve confined co-doping of iron, nitrogen, and sulfur, effectively forming catalytic active sites. This results in a high-performance Fe-S-NC cathode catalyst. This not only establishes a closed-loop system of "waste treatment-element regeneration-energy conversion," achieving wastewater treatment and energy recovery, but also yields a high-performance catalytic material (the Fe-Nx active sites and sulfur doping synergistically enhance oxygen reduction reaction activity). Compared to existing fuel cell cathode catalysts, the catalyst prepared by this method significantly improves both electron transfer efficiency and power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an electron microscope image (2 μm) of the oxygen reduction catalyst constructed for resource recycling of azo dye wastewater in an embodiment of the present invention.

[0018] Figure 2 This is an electron microscope image (1 μm) of the oxygen reduction catalyst constructed for resource recycling of azo dye wastewater in an embodiment of the present invention.

[0019] Figure 3 This is an electron microscope image (500 nm) of the oxygen reduction catalyst constructed for resource recycling of azo dye wastewater in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0021] Example 1: A method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material, comprising: Step 1. Preparation of adsorbent: dissolve zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in ethanol solution to form solution A, the concentration of solution A is 0.05 mol / L; dissolve mixed ligand powder in ethanol solution to form solution B, wherein: the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole, and the usage ratio therebetween is 7.8:0.6:0.6:0.5, the concentration of solution B is 20 times that of solution A, and the amount of ethanol used in the preparation process of solution A and solution B is the same; then slowly pour solution A into solution B, and after stirring, centrifugation, washing and drying, obtain the adsorbent.

[0022] Among them, stirring is carried out at room temperature (i.e., 25±2°C) for 13 hours at a stirring rate of 500 rpm; centrifugation is carried out at a speed of 8000 rpm for 10 minutes, and the precipitate is collected; washing is carried out by using a mixed washing method of methanol and ethanol solution, and the precipitate is washed 3 times (i.e., methanol-ethanol-methanol washing method); drying is carried out by freeze drying (specifically: first pre-freeze in a freeze drying box at -60°C for 2 hours; then, under a vacuum degree of 10 Pa, heat to -10°C at a rate of 0.5°C / min, and keep warm for 12 hours; finally, maintain the vacuum degree unchanged, heat to 20°C at a rate of 1°C / min, and keep warm for 4 hours).

[0023] Step 2: Dye Adsorption: Add the adsorbent to azo dye wastewater (containing at least one of Congo Red and Acid Red 66) at a concentration of 380 mg / L. Adjust the pH to 6-8. After adsorption by oscillation, separation by filtration, and drying, the dye-loaded adsorbent material (i.e., ZIF-8@CR and ZIF-8@AR66) is obtained. The oscillation adsorption is carried out at room temperature (i.e., 25±2°C) for 1.2 hours at a shaking speed of 100 rpm. Drying is performed by freeze drying (specifically, pre-freezing in a -60°C freeze-drying oven for 2 hours; then, under a vacuum of 10 Pa, heating to -10°C at a rate of 0.5°C / min and holding for 12 hours; finally, maintaining the vacuum, heating to 20°C at a rate of 1°C / min and holding for 4 hours).

[0024] Step 3, iron doping: 400 mg of the dye-loaded adsorbent material was dispersed in 20 mL of ethanol solution to form a suspension solution C; 2 mmol of ferric chloride hexahydrate (FeCl3·6H2O) and 1 mmol of sodium citrate were dissolved in 20 mL of ethanol solution to form a solution D; under stirring conditions, a stirring rate of 500 rpm, and a stirring temperature of room temperature (i.e., 25±2°C), the D solution was poured into the C suspension solution for 13 h (the stirring rate was the same as above), and after centrifugation (the centrifugation was the same as the centrifugation process in step 1) and drying, the iron-doped dye-loaded material (i.e., Fe / ZIF-8@CR, Fe / ZIF-8@AR66) was obtained by drying in a vacuum oven at a temperature of 40°C for 24 h.

[0025] Step 4: High-temperature calcination: Place the iron-doped dye-loaded material in a tube furnace and calcine it under a mixed atmosphere, wherein the mixed atmosphere is composed of nitrogen and hydrogen, with the volume proportion of hydrogen being 5% (the flow rate of the mixed gas is 10 mL / min); the calcination steps are as follows: first, heat to 250°C at a rate of 8°C / min, pre-calcine for 30 minutes, then heat to 800°C at a rate of 4°C / min, and calcine at high temperature for 70 minutes. After calcination, cool and grind to obtain the cathode catalyst (i.e., Fe-S CR -NC, Fe-S AR66 -NC).

[0026] Example 2: A method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material, comprising: Step 1. Preparation of adsorbent: dissolve zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in ethanol solution to form solution A, the concentration of solution A is 0.1 mol / L; dissolve mixed ligand powder in ethanol solution to form solution B, wherein: the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole, and the usage ratio between them is 8:0.7:0.7:0.6, the concentration of solution B is 30 times that of solution A, and the amount of ethanol used in the preparation process of solution A and solution B is the same; then slowly pour solution A into solution B, and after stirring, centrifugation, washing and drying, obtain the adsorbent.

[0027] Among them, stirring is carried out at room temperature (i.e., 25±2°C) for 12 hours at a stirring rate of 650 rpm; centrifugation is carried out at a speed of 9000 rpm for 7.5 minutes, and the precipitate is collected; washing is carried out by using a mixed washing method of methanol and ethanol solution, and the precipitate is washed 4 times (i.e., methanol-ethanol-methanol-ethanol washing method); drying is carried out by freeze drying (specifically: first pre-freeze in a freeze drying box at -50°C for 3 hours; then, under a vacuum degree of 20 Pa, heat to -5°C at a rate of 0.7°C / min, and keep warm for 14 hours; finally, maintain the vacuum degree unchanged, heat to 25°C at a rate of 1.5°C / min, and keep warm for 5 hours).

[0028] Step 2: Dye Adsorption: Add the adsorbent to azo dye wastewater (containing at least one of Congo Red and Acid Red 66) at a concentration of 400 mg / L. Adjust the pH to 6-8. After adsorption by oscillation, separation by filtration, and drying, the dye-loaded adsorbent material (i.e., ZIF-8@CR, ZIF-8@AR66) is obtained. The oscillation adsorption is carried out at room temperature (i.e., 25±2°C) for 1 hour at a shaking speed of 150 rpm. Drying is performed by freeze drying (specifically, pre-freezing in a -50°C freeze-drying oven for 3 hours; then, under a vacuum of 20 Pa, heating to -5°C at a rate of 0.7°C / min and holding for 14 hours; finally, maintaining the vacuum, heating to 25°C at a rate of 1.5°C / min and holding for 5 hours).

[0029] Step 3, iron doping: 400 mg of the dye-loaded adsorbent material was dispersed in 20 mL of ethanol solution to form a C suspension solution; 2 mmol of ferric chloride hexahydrate (FeCl3·6H2O) and 1.5 mmol of sodium citrate were dissolved in 20 mL of ethanol solution to form a D solution; under stirring conditions, a stirring rate of 650 rpm, and a stirring temperature of room temperature (i.e., 25±2°C), the D solution was poured into the C suspension solution for 12 h. After centrifugation (the centrifugation process was the same as in step 1) and drying, the iron-doped dye-loaded material (i.e., Fe / ZIF-8@CR, Fe / ZIF-8@AR66) was obtained by drying in a vacuum oven at a temperature of 500°C for 18 h.

[0030] Step 4: High-temperature calcination: Place the iron-doped dye-loaded material in a tube furnace and calcine it under a mixed atmosphere, wherein the mixed atmosphere is composed of nitrogen and hydrogen, with the volume proportion of hydrogen being 6.5% (the flow rate of the mixed gas is 10 mL / min); the calcination steps are as follows: first, heat to 275°C at a rate of 9°C / min, pre-calcine for 40 minutes, then heat to 850°C at a rate of 5°C / min, and calcine at high temperature for 60 minutes. After calcination, cool and grind to obtain the cathode catalyst (i.e., Fe-S CR-NC, Fe-S AR66 -NC).

[0031] Example 3: A method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material, comprising: Step 1. Preparation of adsorbent: Dissolve zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in ethanol solution to form solution A, the concentration of solution A is 0.2 mol / L; dissolve mixed ligand powder in ethanol solution to form solution B, wherein: the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole, and the usage ratio therebetween is 8.2:0.8:0.8:0.7, the concentration of solution B is 40 times that of solution A, and the amount of ethanol used in the preparation process of solution A and solution B is the same; then slowly pour solution A into solution B, and after stirring, centrifugation, washing and drying, obtain the adsorbent.

[0032] Among them, stirring is carried out at room temperature (i.e., 25±2°C) for 11 hours at a stirring rate of 800 rpm; centrifugation is carried out at a speed of 10,000 rpm for 5 minutes, and the precipitate is collected; washing is carried out by using a mixed washing method of methanol and ethanol solution, and the precipitate is washed 5 times (i.e., a washing method of methanol-ethanol-methanol-ethanol-methanol); drying is carried out by freeze drying (specifically: first pre-freeze in a freeze drying box at -40°C for 4 hours; then, under a vacuum degree of 30 Pa, heat to 0°C at a rate of 1°C / min, and keep warm for 16 hours; finally, maintain the vacuum degree unchanged, heat to 30°C at a rate of 2°C / min, and keep warm for 6 hours).

[0033] Step 2: Dye Adsorption: Add the adsorbent to azo dye wastewater (containing at least one of Congo Red and Acid Red 66) at a concentration of 420 mg / L. Adjust the pH to 6-8. After adsorption by oscillation, separation by filtration, and drying, the dye-loaded adsorbent material (i.e., ZIF-8@CR, ZIF-8@AR66) is obtained. The oscillation adsorption is carried out at room temperature (i.e., 25±2°C) for 0.8 h at a shaking speed of 200 rpm. Drying is performed by freeze drying (specifically, pre-freezing in a -40°C freeze-drying oven for 4 h; then, under a vacuum of 30 Pa, heating to 0°C at a rate of 1°C / min and holding for 16 h; finally, maintaining the vacuum, heating to 30°C at a rate of 2°C / min and holding for 6 h).

[0034] Step 3, iron doping: 400 mg of the dye-loaded adsorbent material was dispersed in 20 mL of ethanol solution to form a suspension solution C; 2 mmol of ferric chloride hexahydrate (FeCl3·6H2O) and 2 mmol of sodium citrate were dissolved in 20 mL of ethanol solution to form a solution D; under stirring conditions, a stirring rate of 800 rpm, and a stirring temperature of room temperature (i.e., 25±2°C), the D solution was poured into the C suspension solution for 11 hours. After centrifugation (the centrifugation process was consistent with the centrifugation process in step 1) and drying, the iron-doped dye-loaded material (i.e., Fe / ZIF-8@CR, Fe / ZIF-8@AR66) was obtained by drying in a vacuum oven at a temperature of 60°C for 12 hours.

[0035] Step 4: High-temperature calcination: The iron-doped dye-loaded material is placed in a tube furnace and calcined under a mixed atmosphere, wherein the mixed atmosphere is composed of nitrogen and hydrogen, with the volume proportion of hydrogen being 8% (the flow rate of the mixed gas is 10 mL / min); the calcination steps are as follows: first, the temperature is raised to 300°C at a rate of 10°C / min, pre-calcined for 50 minutes, then the temperature is raised to 900°C at a rate of 6°C / min, and high-temperature calcined for 50 minutes. After calcination, the material is cooled and ground to obtain the cathode catalyst (i.e., Fe-S CR -NC, Fe-S AR66 -NC).

[0036] Example 4: An electrochemical performance test material prepared based on dye wastewater, using any cathode catalyst in Examples 1 to 3 (i.e., Fe-S CR -NC, Fe-S AR66 -NC), specifically: the prepared Fe-S CR -NC or Fe-S AR66 -NC materials are mixed with conductive carbon black and Nafion emulsion to prepare ink, Fe-S CR -NC or Fe-S AR66 The mass volume ratio of -NC material, conductive carbon black, and Nafion emulsion (5%) is 10 mg:2 mg:100 μL. Drop the ink on the polished glassy carbon electrode and let it dry naturally to obtain the test electrode.

[0037] Example 5: A fuel cell cathode material prepared based on dye wastewater, using any cathode catalyst in Examples 1 to 3 (i.e., Fe-S CR -NC, Fe-S AR66 -NC), specifically: the prepared Fe-S CR -NC or Fe-S AR66 -NC material is mixed with conductive carbon black and polytetrafluoroethylene emulsion, Fe-S CR-NC or Fe-S AR66 The mass ratio of -NC material to conductive carbon black and polytetrafluoroethylene emulsion (60%) is 10:4:5, which is coated on the surface of titanium mesh and used as the MFC cathode.

[0038] Comparative Example 1: A method for preparing a cathode catalyst, comprising: Step 1, preparation of adsorbent: dissolving zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in an ethanol solution to form a solution A, the concentration of solution A being 0.1 mol / L; dissolving a mixed ligand powder in an ethanol solution to form a solution B, wherein the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole and 2-(4-hydroxyphenyl)imidazole, and the amount ratio thereof is 8:0.7:0.6, the concentration of solution B is 30 times that of solution A, and the amount of ethanol used in the preparation process of solution A and solution B is the same; then slowly pouring solution A into solution B, stirring, centrifuging, washing, and drying to obtain an adsorbent (wherein, stirring, centrifuging, washing, and drying are consistent with the steps in Example 2).

[0039] Step 2: Dye adsorption: the same as step 2 in Example 2.

[0040] Step 3: Iron doping: the same as step 3 in Example 2.

[0041] Step 4: High-temperature calcination: the same as step 4 in Example 2.

[0042] The prepared cathode catalyst was prepared into a cathode for electrochemical performance testing using the method of Example 4.

[0043] Comparative Example 2: A method for preparing a cathode catalyst, comprising: Step 1, preparation of adsorbent: dissolving zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in an ethanol solution to form a solution A, the concentration of solution A being 0.1 mol / L; dissolving a mixed ligand powder in an ethanol solution to form a solution B, wherein the mixed ligand powder includes 2-methylimidazole, 4-aminoimidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole, and the amount ratio thereof is 8:0.7:0.7:0.6, the concentration of solution B is 30 times that of solution A, and the amount of ethanol used in the preparation process of solution A and solution B is the same; then slowly pouring solution A into solution B, stirring, centrifuging, washing, and drying to obtain an adsorbent (wherein, stirring, centrifuging, washing, and drying are consistent with the steps in Example 2).

[0044] Step 2: Dye adsorption: the same as step 2 in Example 2.

[0045] Step 3: Iron doping: the same as step 3 in Example 2.

[0046] Step 4: High-temperature calcination: the same as step 4 in Example 2.

[0047] The prepared cathode catalyst was prepared into a cathode for electrochemical performance testing using the method of Example 4.

[0048] Comparative Example 3: A method for preparing a cathode catalyst, comprising: Step 1, preparation of adsorbent: dissolving zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O) in an ethanol solution to form a solution A, the concentration of solution A being 0.1 mol / L; dissolving a mixed ligand powder in an ethanol solution to form a solution B, wherein the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole and 3-mercaptopropionic acid, and the amount ratio thereof is 8:0.7:0.7, the concentration of solution B is 30 times that of solution A, and the amount of ethanol used in the preparation of solution A and solution B is the same; then slowly pouring solution A into solution B, stirring, centrifuging, washing, and drying to obtain an adsorbent (wherein, stirring, centrifuging, washing, and drying are consistent with the steps in Example 2).

[0049] Step 2: Dye adsorption: the same as step 2 in Example 2.

[0050] Step 3: Iron doping: the same as step 3 in Example 2.

[0051] Step 4: High-temperature calcination: the same as step 4 in Example 2.

[0052] The prepared cathode catalyst was prepared into a cathode for electrochemical performance testing using the method of Example 4.

[0053] Comparative Example 4: A method for preparing a cathode catalyst, comprising: Step 1: Preparation of adsorbent: Same as step 1 in Example 2.

[0054] Step 2: Dye adsorption: the same as step 2 in Example 2.

[0055] Step 3, iron doping: 400 mg of the dye-loaded adsorbent material was dispersed in 20 mL of ethanol solution to form a C suspension solution; 2 mmol of ferric chloride hexahydrate (FeCl3·6H2O) and 1.5 mmol of sodium acetate were dissolved in 20 mL of ethanol solution to form a D solution; under stirring conditions, the stirring rate was 650 rpm, and the stirring temperature was room temperature (i.e., 25±2°C), the D solution was poured into the C solution, and the stirring time was 12 h. After centrifugation (the centrifugation process was consistent with the centrifugation process in step 1) and drying, the iron-doped dye-loaded material (i.e., Fe / ZIF-8@CR, Fe / ZIF-8@AR66) was obtained by drying in a vacuum oven at a temperature of 500°C for 18 h.

[0056] Step 4: High-temperature calcination: the same as step 4 in Example 2.

[0057] The prepared cathode catalyst was prepared into a cathode for electrochemical performance testing using the method of Example 4.

[0058] Comparative Example 5: A method for preparing a cathode catalyst, comprising: Step 1: Preparation of adsorbent: Same as step 1 in Example 2.

[0059] Step 2: Dye adsorption: the same as step 2 in Example 2.

[0060] Step 3: Iron doping: the same as step 3 in Example 2.

[0061] Step 4: High-temperature calcination: The iron-doped dye-loaded material is placed in a tube furnace and calcined under a mixed atmosphere, wherein the mixed atmosphere is composed of nitrogen and argon, with the volume proportion of argon being 6.5% (the flow rate of the mixed gas is 10 mL / min); the calcination step is specifically as follows: heating to 850°C at a rate of 5°C / min and calcining at high temperature for 1 hour. After calcination, cooling and grinding are performed to obtain the cathode catalyst (i.e., Fe-S CR -NC, Fe-S AR66 -NC).

[0062] The prepared cathode catalyst was prepared into a cathode for electrochemical performance testing using the method of Example 4.

[0063] The electrochemical performance of the test cathodes prepared from the cathode catalysts of Examples 1 to 3 and Comparative Examples 1 to 5 was tested by cyclic voltammetry using an electrochemical workstation. The test results are shown in the following table:

[0064] It can be clearly seen from the above table that the cathode catalyst prepared by the method of the present invention can expose more active sites, has better catalytic performance, and the assembled MFC has better conductive properties.

Claims

1. A method for preparing cathode catalyst by treating dye wastewater based on ZIF-8 material, characterized in that: include: Step 1: Preparation of adsorbent: Dissolve zinc nitrate hexahydrate in ethanol solution to form solution A; The mixed ligand powder is dissolved in an ethanol solution to form a B solution; the A solution is then slowly poured into the B solution, and after stirring, centrifugation, washing, and drying, an adsorbent is obtained; Step 2: Dye adsorption: Add the adsorbent to the azo dye wastewater, adjust the pH to 6-8, and obtain the dye-loaded adsorption material after vibration adsorption, filtration separation, and drying; Step 3, iron doping: dispersing the dye-loaded adsorbent material in an ethanol solution to form a C suspension solution; Dissolve ferric chloride hexahydrate and sodium citrate in ethanol solution to form solution D; Under stirring conditions, solution D is poured into solution C, and after continuous stirring for a period of time, the mixture is centrifuged and dried to obtain an iron-doped dye-loaded material; Step 4: High-temperature calcination: The iron-doped dye-loaded material is placed in a tube furnace and calcined under a mixed atmosphere. After calcination, the material is cooled and ground to obtain a cathode catalyst.

2. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1, characterized in that: In step 1, the concentration of solution A is 0.05 to 0.2 mol / L; the mixed ligand powder includes 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid, and 2-(4-hydroxyphenyl)imidazole; the concentration of solution B is 20 to 40 times that of solution A, and the amount of ethanol used in the preparation of solutions A and B is the same.

3. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1 or 2, characterized in that: The usage ratio of the 2-methylimidazole, 2-(3-aminopropyl)imidazole, 3-mercaptopropionic acid and 2-(4-hydroxyphenyl)imidazole is 7.8-8.2:0.6-0.8:0.6-0.8:0.5-0.

7.

4. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1 or 3, characterized in that: In the step 1, stirring is performed at room temperature for 11 to 13 hours at a stirring rate of 500 to 800 rpm; centrifugation is performed at a speed of 8000 to 10000 rpm for 5 to 10 minutes, and the precipitate is collected; The precipitate is washed 3 to 5 times using a mixed solution of methanol and ethanol; and is dried using freeze-drying.

5. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1, characterized in that: The azo dye wastewater contains at least one of Congo red and acid red 66; the concentration of the azo dye wastewater is 380-420 mg / L.

6. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1, characterized in that: The oscillation adsorption in the step 2 is carried out at room temperature for 0.8 to 1.2 hours at an oscillation speed of 100 to 200 rpm; and freeze drying is used for drying.

7. The method for preparing a cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1, characterized in that: The step three is specifically as follows: first, 400 mg of the dye-loaded adsorbent material is dissolved in 20 mL of ethanol solution to form solution C; then, 2 mmol of ferric chloride hexahydrate and sodium citrate are dissolved in 20 mL of ethanol solution, wherein the molar ratio of ferric chloride hexahydrate to sodium citrate is 1:0.5-1; the stirring rate is 500-800 rpm, the stirring time is 11-13 hours, and the stirring temperature is room temperature; the centrifugation conditions are the same as those in step one; and the drying is carried out in a vacuum oven at a temperature of 40°C to 60°C for 12-24 hours.

8. The method for preparing cathode catalyst by treating dye wastewater based on ZIF-8 material according to claim 1, characterized in that: The mixed atmosphere in step 4 is a mixed gas composed of nitrogen and hydrogen, wherein the volume ratio of hydrogen is 5% to 8%.

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