A preparation method of a sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode

Abstract

The application relates to a preparation method of a sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode. First, biocarbon is modified by nitrogen doping; then, the nitrogen-doped biocarbon is compounded with MnO2 with high pseudo-capacitance. On this basis, a sulfonated polypyrrole film is further deposited on the surface of the biocarbon / MnO2 electrode by electro-deposition to serve as an ion exchange film, so as to construct the sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode. Therefore, the specific capacitance, hydrophilicity and ion exchange film selective permeability of the electrode are significantly improved, and the desalination performance of the MCDI in treating low-concentration uranium-containing wastewater is improved. The sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode prepared by the application has the advantages of high specific capacitance, good conductivity and easy preparation. The sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode prepared under the optimal conditions is used for treating uranium-containing wastewater by membrane capacitive deionization, the membrane permeation flux is 0.021 m 3 / (m 2 .h), the adsorption equilibrium time is 60 min, the uranium removal rate reaches 92%, and the uranium removal capacity is 460 mg / g.

Description

Technical Field

[0001] This invention relates to the field of chemical separation, specifically to a method for preparing an integrated electrode of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2. Background Technology

[0002] Large quantities of uranium-containing wastewater are generated during uranium mining and metallurgy, uranium tailings accumulation, uranium separation and enrichment, and spent fuel reprocessing. The resulting radioactive pollution seriously endangers the environment and human health. Effective separation of uranium from uranium-containing wastewater is of great significance, as it not only effectively recovers uranium resources to meet the urgent demand for uranium fuel in nuclear power development but also reduces radioactive pollution from wastewater discharge. Traditional methods such as evaporation, precipitation, membrane separation, and reverse osmosis are costly and may generate secondary pollution, especially for treating low-concentration uranium-containing wastewater. Membrane capacitive deionization (MCDI), a novel separation technology developed in recent years, offers advantages such as energy efficiency, ease of operation, and environmental friendliness in treating low-concentration uranium-containing wastewater. Electroadsorption utilizes an external electric field to induce the rapid insertion / extraction of ions in solution within the pores of a porous electrode (such as a carbon electrode), resulting in an adsorption capacity far exceeding that of conventional adsorption. MCDI involves placing reverse ion exchange membranes before the electrodes, specifically cation exchange membranes before the cathode and anion exchange membranes before the anode. MCDI ion exchange membranes can act as selective barriers to ion permeation, improve the distribution of adsorbed ions, reduce electrode side reactions, and enhance desalination performance.

[0003] The key to treating low-concentration uranium-containing wastewater using MCDI lies in constructing high-performance electrode and membrane materials. Good electrode materials should possess high specific capacitance, good conductivity, hydrophilicity, and membrane permeability. Currently, commonly used carbon electrode materials for MCDI have low specific capacitance and poor hydrophilicity. Furthermore, the ion exchange membranes used in MCDI devices are separated from the electrode materials, and commercially available ion exchange membranes are relatively thick, have high osmotic resistance, poor conductivity, and are prone to scaling and clogging. These factors severely affect the uranium separation performance of MCDI. Therefore, improving the specific capacitance and hydrophilicity of MCDI electrode materials, as well as enhancing membrane permeability and conductivity, are problems that need to be addressed when treating low-concentration uranium-containing wastewater using MCDI. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing an integrated electrode of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing an integrated sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 electrode includes the following steps:

[0007] S1. Preparation of nitrogen-doped biocarbon:

[0008] Take 10g of sugarcane bagasse, wash and chop it. Then mix the biomass with 0.5g of polyethyleneimine aqueous solution and dry it at 105℃. Place the sample in the middle of a tube furnace and heat it at 700℃ in a N2 + water vapor + CO2 mixed atmosphere with a volume ratio of 1:1:1 for 2h. The obtained solid product is washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground and sieved to obtain biochar.

[0009] S2, Nitrogen-doped bio-carbon / MnO2 preparation:

[0010] Dissolve 1.2g KMnO4 in 60mL of deionized water, then add 1.72g MnSO4 to the solution and stir the mixture for 1h to obtain a homogeneous solution.

[0011] Add the nitrogen-doped biochar prepared above according to a certain ratio, ultrasonically disperse for 30 min, then transfer the mixture solution to a polytetrafluoroethylene-lined autoclave, transfer the mixture to a reaction vessel, heat at 180℃ for 24 h, wash the obtained product thoroughly with deionized water and ethanol, and then vacuum dry at 80℃ to obtain nitrogen-doped biochar / MnO2.

[0012] S3, Preparation of nitrogen-doped bio-carbon / MnO2 electrode:

[0013] The nitrogen-doped biocarbon / MnO2 electrode material, conductive additives, and polyvinyl alcohol prepared above were mixed in a mass ratio of 8:1:1, and epichlorohydrin (ECH) crosslinking agent was added. The mixture was thoroughly mixed, coated onto the current collector, and vacuum dried at 70°C.

[0014] S4. Fabrication of an integrated electrode of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2:

[0015] A three-electrode system was adopted, with nitrogen-doped bio-carbon / MnO2 electrode as the working electrode, Pt as the counter electrode, and Ag / AgCl electrode as the reference electrode.

[0016] The reaction system contains a certain concentration of pyrrole, pyrrole-2-sulfonic acid and 0.1M NaCl O4. Before the reaction, nitrogen is bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential is controlled at 0.8V and the polymerization time is 300s. After the reaction is completed, a sulfonated conductive polymer film is formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby producing a sulfonated polypyrrole / nitrogen-doped biochar / MnO2 integrated electrode.

[0017] The electrochemical polymerization reaction for the formation of sulfonated polypyrrole is as follows:

[0018]

[0019] Furthermore, in S1, nitrogen-doped biocarbon is prepared using sugarcane bagasse as a carbon source and polyethyleneimine as a nitrogen dopant, and an activator is used with a mixture of N2 + water vapor + CO2 for 2 hours.

[0020] Furthermore, in step S2, the amount of nitrogen-doped biocarbon added is 1.0-2.0g.

[0021] Furthermore, in step S4, the concentrations of pyrrole and pyrrole-2-sulfonic acid are the same, both being 0.1-0.3M.

[0022] Furthermore, in step S3, the conductive additive is conductive graphite, the polyvinyl alcohol is a mixture of PVA aqueous solution and binder, and the crosslinking agent is epichlorohydrin, which accounts for 1 wt.% of the PVA aqueous solution.

[0023] Furthermore, in S3, the current collector is a foamed titanium substrate.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention utilizes nitrogen doping to modify bio-carbon, thereby improving the conductivity and hydrophilicity of carbon materials, increasing pseudocapacitance, and thus enhancing the hydrophilicity of carbon materials; by combining nitrogen-doped bio-carbon with MnO2, which has high pseudocapacitance, the specific capacitance of the electrode material can be significantly improved.

[0026] 2. This invention utilizes electrochemical deposition to modify the surface of a biochar / MnO2 electrode with a sulfonated polypyrrole membrane as an ion exchange membrane, constructing an electrode-membrane integrated electrode, which can significantly improve the electrode specific capacitance, hydrophilicity, and selective permeability of the ion exchange membrane, thereby improving the desalination performance of MCDI in treating low-concentration uranium-containing wastewater.

[0027] 3. This invention utilizes a mixture of N2 + water vapor + CO2 (volume ratio 1:1:1) to activate biochar, which is beneficial for forming a well-developed mesoporous structure, improving pore size distribution, and avoiding the problem of equipment corrosion caused by traditional chemical activation.

[0028] 4. This invention uses a hydrophilic PVA binder instead of a traditional hydrophobic binder (such as polyvinylidene fluoride), which can effectively improve the hydrophilicity of the electrode material;

[0029] 5. The sulfonated conductive polymer film formed by electrochemical deposition on the surface of nitrogen-doped bio-carbon / MnO2 electrode of the present invention has both good ion exchange performance and conductivity, and the film thickness is easy to control, thereby improving the film conductivity and ion selective permeability. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0031] like Figure 1 As shown, a method for preparing an integrated sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 electrode includes the following steps:

[0032] S1. Preparation of nitrogen-doped biocarbon:

[0033] Take 10g of sugarcane bagasse, wash and chop it. Then mix the biomass with 0.5g of polyethyleneimine aqueous solution and dry it at 105℃. Place the sample in the middle of a tube furnace and heat it at 700℃ in a N2 + water vapor + CO2 mixed atmosphere with a volume ratio of 1:1:1 for 2h. The obtained solid product is washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground and sieved to obtain biochar.

[0034] S2, Nitrogen-doped bio-carbon / MnO2 preparation:

[0035] Dissolve 1.2g KMnO4 in 60mL of deionized water, then add 1.72g MnSO4 to the solution and stir the mixture for 1h to obtain a homogeneous solution.

[0036] Add the nitrogen-doped biochar prepared above according to a certain ratio, ultrasonically disperse for 30 min, then transfer the mixture solution to a polytetrafluoroethylene-lined autoclave, transfer the mixture to a reaction vessel, heat at 180℃ for 24 h, wash the obtained product thoroughly with deionized water and ethanol, and then vacuum dry at 80℃ to obtain nitrogen-doped biochar / MnO2.

[0037] S3, Preparation of nitrogen-doped bio-carbon / MnO2 electrode:

[0038] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive additives, and polyvinyl alcohol prepared above were mixed in a mass ratio of 8:1:1, and ECH crosslinking agent was added. The mixture was thoroughly mixed, coated onto the current collector, and vacuum dried at 70°C.

[0039] S4. Fabrication of an integrated electrode of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2:

[0040] A three-electrode system was adopted, with nitrogen-doped bio-carbon / MnO2 electrode as the working electrode, Pt as the counter electrode, and Ag / AgCl electrode as the reference electrode.

[0041] The reaction system contains a certain concentration of pyrrole, pyrrole-2-sulfonic acid and 0.1M NaCl O4. Before the reaction, nitrogen is bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential is controlled at 0.8V and the polymerization time is 300s. After the reaction is completed, a sulfonated conductive polymer film is formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby producing a sulfonated polypyrrole / nitrogen-doped biochar / MnO2 integrated electrode.

[0042] The electrochemical polymerization reaction for the formation of sulfonated polypyrrole is as follows:

[0043]

[0044] In S1, nitrogen-doped biochar is prepared using sugarcane bagasse as a carbon source and polyethyleneimine as a nitrogen dopant, with a N2 + water vapor + CO2 mixture as an activator and an activation time of 2 hours; in S2, the amount of nitrogen-doped biochar added is 1.0-2.0 g.

[0045] In S3, the conductive additive is conductive graphite, the polyvinyl alcohol is a mixture of PVA aqueous solution and binder, the ECH crosslinking agent is epichlorohydrin, and the proportion of the ECH crosslinking agent is 1 wt.% of the PVA aqueous solution; in S3, the current collector is a foamed titanium substrate; in S4, the concentrations of pyrrole and pyrrole-2-sulfonic acid are the same, both being 0.1-0.3M.

[0046] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0047] Example 1

[0048] Step 1: Preparation of nitrogen-doped biochar

[0049] 10g of sugarcane bagasse was washed, chopped, and then mixed with 0.5g of polyethyleneimine aqueous solution. The mixture was dried at 105℃. The sample was placed in the middle of a tube furnace and activated at 700℃ under a mixed atmosphere of N2 + water vapor + CO2 with a volume ratio of 1:1:1 for 2 hours. The resulting solid product was washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground, and sieved to obtain biochar.

[0050] Step 2: Preparation of nitrogen-doped bio-carbon / MnO2

[0051] 1.2 g KMnO4 was dissolved in 60 mL of deionized water, and then 1.72 g MnSO4 was added to the solution. The mixture was stirred for 1 h to obtain a homogeneous solution. 1.0 g of the nitrogen-doped biochar prepared above was added, and the mixture was ultrasonically dispersed for 30 min. The mixture solution was then transferred to a polytetrafluoroethylene-lined autoclave, and the mixture was transferred to a reaction vessel and heated at 180 °C for 24 h. The resulting product was thoroughly washed with deionized water and ethanol, and then vacuum dried at 80 °C to obtain nitrogen-doped biochar / MnO2.

[0052] Step 3: Preparation of nitrogen-doped bio-carbon / MnO2 electrode

[0053] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive graphite (conductive additive), and polyvinyl alcohol (PVA aqueous solution, binder) prepared above were mixed in a mass ratio of 8:1:1, and a small amount of epichlorohydrin (ECH crosslinking agent, about 1 wt.% of PVA) was added and mixed thoroughly. The mixture was then coated onto a foamed titanium substrate (current collector) and vacuum dried at 70°C (while simultaneously crosslinking the PVA).

[0054] Step 4: Fabrication of an integrated electrode made of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2

[0055] A three-electrode system was employed, with a nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction system contained 0.2 M pyrrole, 0.2 M pyrrole-2-sulfonic acid, and 0.1 M NaClO4 (to increase solution conductivity). Before the reaction, nitrogen was bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential was controlled at 0.8 V, and the polymerization time was 300 s. After the reaction was completed, a sulfonated conductive polymer film was formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby fabricating an integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode.

[0056] The performance of the above-mentioned sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 integrated electrode was tested, showing that its specific capacitance is 137 F / g and its contact angle in aqueous solution is 41°.

[0057] Using the aforementioned integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode as parallel electrodes (20 mg of active material), it was applied to the membrane capacitive deionization treatment of 1 L of uranium-containing wastewater with a concentration of 10 mg / L. The results showed a membrane permeation flux of 0.015 m... 3 / (m 2 (h). The adsorption equilibrium time was 60 min, the uranium removal rate reached 70%, and the uranium removal capacity was 350 mg / g.

[0058] Example 2

[0059] Step 1: Preparation of nitrogen-doped biochar

[0060] 10g of sugarcane bagasse was washed, chopped, and then mixed with 0.5g of polyethyleneimine aqueous solution. The mixture was dried at 105℃. The sample was placed in the middle of a tube furnace and activated at 700℃ under a mixed atmosphere of N2 + water vapor + CO2 with a volume ratio of 1:1:1 for 2 hours. The resulting solid product was washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground, and sieved to obtain biochar.

[0061] Step 2: Preparation of nitrogen-doped bio-carbon / MnO2

[0062] 1.2 g of KMnO4 was dissolved in 60 mL of deionized water, and then 1.72 g of MnSO4 was added to the solution. The mixture was stirred for 1 h to obtain a homogeneous solution. 1.5 g of the nitrogen-doped biochar prepared above was added, and the mixture was ultrasonically dispersed for 30 min. The mixture solution was then transferred to a polytetrafluoroethylene-lined autoclave, and the mixture was transferred to a reaction vessel and heated at 180 °C for 24 h. The resulting product was thoroughly washed with deionized water and ethanol, and then vacuum dried at 80 °C to obtain nitrogen-doped biochar / MnO2.

[0063] Step 3: Preparation of nitrogen-doped bio-carbon / MnO2 electrode

[0064] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive graphite (conductive additive), and polyvinyl alcohol (PVA aqueous solution, binder) prepared above were mixed in a mass ratio of 8:1:1, and a small amount of epichlorohydrin (ECH crosslinking agent, about 1 wt.% of PVA) was added and mixed thoroughly. The mixture was then coated onto a foamed titanium substrate (current collector) and vacuum dried at 70°C (while simultaneously crosslinking the PVA).

[0065] Step 4: Fabrication of an integrated electrode made of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2

[0066] A three-electrode system was employed, with a nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction system contained 0.2 M pyrrole, 0.2 M pyrrole-2-sulfonic acid, and 0.1 M NaClO4 (to increase solution conductivity). Before the reaction, nitrogen was bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential was controlled at 0.8 V, and the polymerization time was 300 s. After the reaction was completed, a sulfonated conductive polymer film was formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby fabricating an integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode.

[0067] The performance of the above-mentioned sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 integrated electrode was tested, showing that its specific capacitance is 156 F / g and its contact angle in aqueous solution is 32°.

[0068] Using the aforementioned integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode as parallel electrodes (20 mg of active material), it was applied to the membrane capacitive deionization treatment of 1 L of uranium-containing wastewater with a concentration of 10 mg / L. The results showed a membrane permeation flux of 0.021 m... 3 / (m 2 (h). The adsorption equilibrium time was 60 min, the uranium removal rate reached 92%, and the uranium removal capacity was 460 mg / g.

[0069] Example 3

[0070] Step 1: Preparation of nitrogen-doped biochar

[0071] 10g of sugarcane bagasse was washed, chopped, and then mixed with 0.5g of polyethyleneimine aqueous solution. The mixture was dried at 105℃. The sample was placed in the middle of a tube furnace and activated at 700℃ under a mixed atmosphere of N2 + water vapor + CO2 with a volume ratio of 1:1:1 for 2 hours. The resulting solid product was washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground, and sieved to obtain biochar.

[0072] Step 2: Preparation of nitrogen-doped bio-carbon / MnO2

[0073] 1.2 g of KMnO4 was dissolved in 60 mL of deionized water, and then 1.72 g of MnSO4 was added to the solution. The mixture was stirred for 1 h to obtain a homogeneous solution. 2.0 g of the nitrogen-doped biochar prepared above was added, and the mixture was ultrasonically dispersed for 30 min. The mixture solution was then transferred to a polytetrafluoroethylene-lined autoclave, and the mixture was transferred to a reaction vessel and heated at 180 °C for 24 h. The resulting product was thoroughly washed with deionized water and ethanol, and then vacuum dried at 80 °C to obtain nitrogen-doped biochar / MnO2.

[0074] Step 3: Preparation of nitrogen-doped bio-carbon / MnO2 electrode

[0075] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive graphite (conductive additive), and polyvinyl alcohol (PVA aqueous solution, binder) prepared above were mixed in a mass ratio of 8:1:1, and a small amount of epichlorohydrin (ECH crosslinking agent, about 1 wt.% of PVA) was added and mixed thoroughly. The mixture was then coated onto a foamed titanium substrate (current collector) and vacuum dried at 70°C (while simultaneously crosslinking the PVA).

[0076] Step 4: Fabrication of an integrated electrode made of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2

[0077] A three-electrode system was employed, with a nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction system contained 0.2 M pyrrole, 0.2 M pyrrole-2-sulfonic acid, and 0.1 M NaClO4 (to increase solution conductivity). Before the reaction, nitrogen was bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential was controlled at 0.8 V, and the polymerization time was 300 s. After the reaction was completed, a sulfonated conductive polymer film was formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby fabricating an integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode.

[0078] The performance of the above-mentioned sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 integrated electrode was tested, showing that its specific capacitance is 124 F / g and its contact angle in aqueous solution is 38°.

[0079] Using the aforementioned integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode as parallel electrodes (20 mg of active material), it was applied to the membrane capacitive deionization treatment of 1 L of uranium-containing wastewater with a concentration of 10 mg / L. The results showed a membrane permeation flux of 0.018 m... 3 / (m 2 (h). The adsorption equilibrium time was 70 min, the uranium removal rate reached 62%, and the uranium removal capacity was 310 mg / g.

[0080] Example 4

[0081] Step 1: Preparation of nitrogen-doped biochar

[0082] 10g of sugarcane bagasse was washed, chopped, and then mixed with 0.5g of polyethyleneimine aqueous solution. The mixture was dried at 105℃. The sample was placed in the middle of a tube furnace and activated at 700℃ under a mixed atmosphere of N2 + water vapor + CO2 with a volume ratio of 1:1:1 for 2 hours. The resulting solid product was washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground, and sieved to obtain biochar.

[0083] Step 2: Preparation of nitrogen-doped bio-carbon / MnO2

[0084] 1.2 g of KMnO4 was dissolved in 60 mL of deionized water, and then 1.72 g of MnSO4 was added to the solution. The mixture was stirred for 1 h to obtain a homogeneous solution. 1.5 g of the nitrogen-doped biochar prepared above was added, and the mixture was ultrasonically dispersed for 30 min. The mixture solution was then transferred to a polytetrafluoroethylene-lined autoclave, and the mixture was transferred to a reaction vessel and heated at 180 °C for 24 h. The resulting product was thoroughly washed with deionized water and ethanol, and then vacuum dried at 80 °C to obtain nitrogen-doped biochar / MnO2.

[0085] Step 3: Preparation of nitrogen-doped bio-carbon / MnO2 electrode

[0086] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive graphite (conductive additive), and polyvinyl alcohol (PVA aqueous solution, binder) prepared above were mixed in a mass ratio of 8:1:1, and a small amount of epichlorohydrin (ECH crosslinking agent, about 1 wt.% of PVA) was added and mixed thoroughly. The mixture was then coated onto a foamed titanium substrate (current collector) and vacuum dried at 70°C (while simultaneously crosslinking the PVA).

[0087] Step 4: Fabrication of an integrated electrode made of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2

[0088] A three-electrode system was employed, with a nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction system contained 0.1 M pyrrole, 0.1 M pyrrole-2-sulfonic acid, and 0.1 M NaClO4 (to increase solution conductivity). Before the reaction, nitrogen was bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential was controlled at 0.8 V, and the polymerization time was 300 s. After the reaction was completed, a sulfonated conductive polymer film was formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby fabricating an integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode.

[0089] The performance of the above-mentioned sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode was tested, showing that its specific capacitance is 98 F / g and its contact angle in aqueous solution is 45°.

[0090] Using the aforementioned integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode as parallel electrodes (20 mg of active material), it was applied to the membrane capacitive deionization treatment of 1 L of uranium-containing wastewater with a concentration of 10 mg / L. The results showed a membrane permeation flux of 0.016 m... 3 / (m 2 (h). Adsorption equilibrium time: 80 min; uranium removal rate: 52%; uranium removal capacity: 260 mg / g.

[0091] Example 5

[0092] Step 1: Preparation of nitrogen-doped biochar

[0093] 10g of sugarcane bagasse was washed, chopped, and then mixed with 0.5g of polyethyleneimine aqueous solution. The mixture was dried at 105℃. The sample was placed in the middle of a tube furnace and activated at 700℃ under a mixed atmosphere of N2 + water vapor + CO2 with a volume ratio of 1:1:1 for 2 hours. The resulting solid product was washed with 1.0M HNO3 to remove impurities, washed with water until neutral, and then dried, ground, and sieved to obtain biochar.

[0094] Step 2: Preparation of nitrogen-doped bio-carbon / MnO2

[0095] 1.2 g of KMnO4 was dissolved in 60 mL of deionized water, and then 1.72 g of MnSO4 was added to the solution. The mixture was stirred for 1 h to obtain a homogeneous solution. 1.5 g of the nitrogen-doped biochar prepared above was added, and the mixture was ultrasonically dispersed for 30 min. The mixture solution was then transferred to a polytetrafluoroethylene-lined autoclave, and the mixture was transferred to a reaction vessel and heated at 180 °C for 24 h. The resulting product was thoroughly washed with deionized water and ethanol, and then vacuum dried at 80 °C to obtain nitrogen-doped biochar / MnO2.

[0096] Step 3: Preparation of nitrogen-doped bio-carbon / MnO2 electrode

[0097] The nitrogen-doped bio-carbon / MnO2 electrode material, conductive graphite (conductive additive), and polyvinyl alcohol (PVA aqueous solution, binder) prepared above were mixed in a mass ratio of 8:1:1, and a small amount of epichlorohydrin (ECH crosslinking agent, about 1 wt.% of PVA) was added and mixed thoroughly. The mixture was then coated onto a foamed titanium substrate (current collector) and vacuum dried at 70°C (while simultaneously crosslinking the PVA).

[0098] Step 4: Fabrication of an integrated electrode made of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2

[0099] A three-electrode system was employed, with a nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The reaction system contained 0.1 M pyrrole, 0.1 M pyrrole-2-sulfonic acid, and 0.1 M NaClO4 (to increase solution conductivity). Before the reaction, nitrogen was bubbled into the reaction system for 30 min to remove oxygen. The polymerization potential was controlled at 0.8 V, and the polymerization time was 300 s. After the reaction was completed, a sulfonated conductive polymer film was formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thereby fabricating an integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode.

[0100] The performance of the above-mentioned sulfonated polypyrrole / nitrogen-doped biocarbon / MnO2 integrated electrode was tested, showing that its specific capacitance is 142 F / g and its contact angle in aqueous solution is 35°.

[0101] Using the aforementioned integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode as parallel electrodes (20 mg of active material), it was applied to the membrane capacitive deionization treatment of 1 L of uranium-containing wastewater with a concentration of 10 mg / L. The results showed a membrane permeation flux of 0.019 m... 3 / (m 2 (h). Adsorption equilibrium time: 70 min; uranium removal rate: 74%; uranium removal capacity: 370 mg / g.

[0102] The experimental results of treating 1L of uranium-containing wastewater with a concentration of 10mg / L using membrane capacitive deionization (MCDI) in Examples 1 to 5 show that Example 2 (implemented according to the method of adding 1.5g of nitrogen-doped biochar in step 2 and 0.2M concentration of pyrrole and pyrrole-2-sulfonic acid in step 4) has the best wastewater treatment effect, with a membrane permeation flux of 0.021m. 3 / (m 2(h). The adsorption equilibrium time was 60 min, the uranium removal rate reached 92%, and the uranium removal capacity was 460 mg / g. With increasing monomer concentration, the loading of sulfonated polypyrrole increased, which improved the electrode specific capacitance. However, excessive loading would clog the electrode pore structure, thus worsening the MCDI performance. By adjusting the amount of nitrogen-doped biochar and the concentrations of the polymerized monomers pyrrole and pyrrole-2-sulfonic acid, the nitrogen-doped biochar content and the loading of sulfonated polypyrrole in the integrated sulfonated polypyrrole / nitrogen-doped biochar / MnO2 electrode could be optimized. This allowed the pore structure of the nitrogen-doped biochar to match the pseudocapacitance provided by the sulfonated polypyrrole, resulting in synergy and optimal MCDI desalination performance.

[0103] In summary, this invention utilizes nitrogen doping to modify biochar, thereby improving the conductivity and hydrophilicity of the carbon material, increasing pseudocapacitance, and thus enhancing its hydrophilicity. Combining nitrogen-doped biochar with MnO2, which has high pseudocapacitance, significantly improves the specific capacitance of the electrode material. Electrochemically depositing a sulfonated polypyrrole membrane onto the surface of the biochar / MnO2 electrode as an ion exchange membrane to construct an integrated electrode-membrane electrode significantly improves the electrode's specific capacitance, hydrophilicity, and selective permeability of the ion exchange membrane, thereby enhancing the desalination performance of MCDI in treating low-concentration uranium-containing wastewater. Furthermore, in step 1, the activation of biochar using a mixture of N2 + water vapor + CO2 (volume ratio 1:1:1) facilitates the formation of a well-developed mesoporous structure, improves pore size distribution, and avoids the problem of equipment corrosion associated with traditional chemical activation. In step 3, replacing traditional hydrophobic binders (such as polyvinylidene fluoride) with a hydrophilic PVA binder effectively improves the hydrophilicity of the electrode material. In step 4 of this invention, the sulfonated conductive polymer film formed by electrochemical deposition on the surface of nitrogen-doped bio-carbon / MnO2 electrode has both good ion exchange performance and conductivity, and the film thickness is easy to control, thereby improving the film conductivity and ion selective permeability.

[0104] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an integrated electrode of sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2, characterized in that, It comprises the following steps: S1, preparation of nitrogen-doped biochar: Take 10 g of washed sugarcane residue, cut it into small pieces, and then mix the biomass with 0.5 g of polyethyleneimine aqueous solution. Dry the mixture at 105°C, place the sample in the middle of a tube furnace, and heat it at 700°C under a mixed gas atmosphere of N2+water vapor+CO2 at a volume ratio of 1:1:1 for 2 hours. Wash the obtained solid product with 1.0 M HNO3 to remove impurities, wash with water until neutral, and then dry, grind, and sieve to obtain biochar; S2, preparation of nitrogen-doped biochar / MnO2: Dissolve 1.2 g of KMnO4 in 60 mL of deionized water, then add 1.72 g of MnSO4 to the solution, and stir the mixture for 1 hour to obtain a uniform solution; The nitrogen-doped biocarbon prepared above was added in a certain ratio, ultrasonically dispersed for 30 min, and then the mixture solution was transferred into a polytetrafluoroethylene-lined high-pressure kettle. The mixture was transferred into the reaction kettle, heated at 180 o C for 24 h, and the obtained product was washed with deionized water and ethanol, vacuum dried at 80 o C for 24 h, and the obtained product was washed with deionized water and ethanol, vacuum dried at 80 S3, preparation of nitrogen-doped biochar / MnO2 electrode: The nitrogen-doped biocarbon / MnO2 electrode material prepared above, a conductive additive, and polyvinyl alcohol are mixed in a mass ratio of 8:1:1, an ECH crosslinking agent is added, and the mixture is mixed thoroughly, coated on a current collector, and vacuum dried at 70°C under N2for 12 hours to obtain a nitrogen-doped biocarbon / MnO2 electrode material. o C under vacuum; S4, preparation of sulfonated polypyrrole / nitrogen-doped biochar / MnO2 integrated electrode: A three-electrode system is used, with the nitrogen-doped biochar / MnO2 electrode as the working electrode, Pt as the counter electrode, and Ag / AgCl electrode as the reference electrode; The reaction system contains a certain concentration of pyrrole, pyrrole-2-sulfonic acid, and 0.1 M NaClO4. Before the reaction, the reaction system is purged with nitrogen for 30 minutes to remove oxygen. The polymerization potential is controlled at 0.8 V, and the polymerization time is 300 seconds. After the reaction is completed, a sulfonated conductive polymer film is formed on the surface of the nitrogen-doped biochar / MnO2 electrode, thus forming a sulfonated polypyrrole / nitrogen-doped biochar / MnO2 integrated electrode.

2. The method according to claim 1, wherein the method is characterized by, In S1, sugarcane residue is used as the carbon source, and polyethyleneimine is used as the nitrogen dopant to prepare nitrogen-doped biochar. N2+water vapor+CO2 mixed gas is used as the activator, and the activation time is 2 hours.

3. The method according to claim 1, wherein the method is characterized by, In S2, the amount of nitrogen-doped biochar added is 1.0-2.0 g.

4. The method according to claim 1, wherein the method is characterized by, In S3, the conductive additive is conductive graphite, the polyvinyl alcohol is a mixture of PVA aqueous solution and binder, and the ECH crosslinking agent is epichlorohydrin. The ECH crosslinking agent accounts for 1 wt.% of the PVA aqueous solution.

5. The method for preparing an integrated sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 electrode according to claim 1, characterized in that, In S3, the current collector is a foam titanium substrate.

6. The method for preparing an integrated sulfonated polypyrrole / nitrogen-doped bio-carbon / MnO2 electrode according to claim 1, characterized in that, In S4, the concentrations of pyrrole and pyrrole-2-sulfonic acid are the same, both being 0.1-0.3 M.

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