A method for preparing a transition metal sulfide nanosheet catalytic electrode and its application in nitrate electrocatalysis.

Abstract

To overcome the problems of complex preparation processes and limited loading control of existing nitrate electrocatalytic reduction raw materials, this invention provides a method for preparing a transition metal sulfide nanosheet catalytic electrode, comprising the following steps: dissolving a transition metal salt and a sulfur source to form a solution; immersing a pre-acidified self-supporting electrode support in the solution; and depositing transition metal sulfide nanosheets MxS on the self-supporting electrode support as a cathode using a constant current method to obtain the transition metal sulfide nanosheet catalytic electrode. This invention also discloses the application of the above-mentioned transition metal sulfide nanosheet catalytic electrode in nitrate electrocatalysis. The transition metal sulfide nanosheet catalytic electrode provided by this invention is a novel nitrate electrocatalytic reduction raw material with advantages such as short preparation process, high cycle stability, high nitrogen selectivity, and high catalytic activity, and is easy to scale up for production and application.

Description

Technical Field

[0001] This invention relates to a method for preparing a transition metal sulfide nanosheet catalytic electrode and its application in nitrate electrocatalysis. Background Technology

[0002] With the rapid development of industry, agriculture, and aquaculture, nitrates have become one of the most common pollutants in surface water and groundwater, severely disrupting the natural nitrogen cycle. As a non-ligand-formed oxygen anion, nitrates are highly mobile and readily soluble in water, making them a significant indicator of eutrophication and impact on drinking water quality. According to the relevant provisions of the National Standard for Drinking Water Quality GB5749-2006, the limit for nitrates (calculated as nitrogen) is 10 mg / L, and for groundwater sources, it is 20 mg / L. Therefore, effectively addressing nitrate pollution has become a global concern.

[0003] Among various methods for removing nitrates, electrochemical denitrification, represented by electrocatalytic reduction, has advantages such as high efficiency, simple operation, and environmental friendliness, and is considered one of the effective ways to solve nitrate pollution in the future. Electrocatalytic reduction mainly uses an external current to load a material with specific catalytic activity onto the cathode to achieve the degradation and conversion of nitrates, leaving virtually no harmful residues after treatment. Factors affecting the performance of electrocatalytic nitrate reduction technology mainly include cathode material, applied potential, electrolyte solution, and pH value, among which the cathode material is one of the most critical factors, directly affecting the nitrate reaction efficiency.

[0004] Currently used metal electrode materials, such as Pb, Pt, Au, Ru, and Cu, exhibit good hydrogen adsorption capacity and superior activity in the indirect reduction of nitrates. However, their poor chemical stability, especially in high-chloride ion systems (seawater aquaculture tailwater), greatly limits their application. Transition metal oxides, such as Co3O4, are widely used in electrochemical hydrogen production, and their catalytic activity and electrochemical durability make them ideal cathode electrode materials. However, the weak conductivity and limited number of catalytic active sites of transition metal oxides hinder their nitrate reduction performance. Heteroatom doping can regulate the electronic structure and adsorption capacity of metal oxides, effectively improving the electrocatalytic reduction activity of nitrates. Gao et al. prepared a three-dimensional P-doped Co3O4 electrode using a hydrothermal coupled high-temperature phosphating method for the electrocatalytic reduction of nitrates. The results showed that the introduction of P increased the Co... 3+The percentage of P-doped Co3O4 significantly improves its nitrate reduction activity due to its higher electrochemical active area and lower interfacial impedance. Furthermore, compared to transition metal oxides, transition metal sulfides possess superior electronic conductivity and high hydrogen evolution activity, potentially offering greater application prospects in the electrocatalytic reduction of nitrates. Currently, there are no reports on the use of transition metal sulfides as electrode materials for electrocatalytic nitrate reduction. The main synthesis methods for transition metal sulfides include hydrothermal methods and high-temperature pyrolysis methods. The hydrothermal and high-temperature pyrolysis methods for preparing transition metal sulfides are complex, require relatively stringent control conditions, and are difficult to control in terms of loading. Summary of the Invention

[0005] To address the problems of complex raw material preparation processes and limited loading control in existing nitrate electrocatalytic reduction methods, this invention provides a method for preparing transition metal sulfide nanosheet catalytic electrodes and their application in nitrate electrocatalysis.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] This invention provides a method for preparing a transition metal sulfide nanosheet catalytic electrode, comprising the following steps:

[0008] Dissolve the transition metal salt and sulfur source to form a solution;

[0009] The pre-acidified self-supporting electrode carrier is immersed in the above solution;

[0010] Using a self-supporting electrode carrier as the cathode, transition metal sulfide nanosheets MxS were deposited on the self-supporting electrode carrier in a constant current manner, where M is a transition metal. After deposition, the nanosheets were removed, washed, and dried to obtain a transition metal sulfide nanosheet catalytic electrode.

[0011] Furthermore, the transition metal salt is selected from one or more of the sulfates, chlorides, and acetates of nickel, cobalt, iron, and copper.

[0012] Furthermore, the sulfur source is selected from one or more of thiourea, sodium thiosulfate, and thioacetamide, and the concentration of the sulfur source in the solution is 0.6–1.2 mol / L.

[0013] Furthermore, the molar ratio of the transition metal salt to the sulfur source is 1:10 to 1:50.

[0014] Furthermore, the self-supporting electrode carrier is selected from one or more of nickel foam, copper foam, carbon cloth, carbon paper, and carbon foam, and the acid used in the pre-acidification treatment of the self-supporting electrode carrier is one or more of hydrochloric acid, acetic acid, phosphoric acid, and citric acid.

[0015] Furthermore, the cathode deposition current is 0.6mA to 0.9mA, the deposition time is 20 to 60 min, and the deposition temperature is 10 to 60℃.

[0016] The present invention also provides the application of the transition metal sulfide nanosheet catalytic electrode prepared by the preparation method described above in nitrate electrocatalysis, wherein the transition metal sulfide nanosheet catalytic electrode is used as the cathode and the DSA electrode is used as the anode to treat nitrate wastewater in a two-electrode system.

[0017] Furthermore, the operating conditions of the two-electrode system are: operating current of 2–4 mA / cm². 2 The initial nitrate concentration was 10–500 mg / L, and the chloride ion concentration was 0–30 g / L.

[0018] The transition metal sulfide nanosheet catalytic electrode provided by this invention is a novel transition metal sulfide electrode material with high efficiency in nitrate catalysis and resistance to chloride ion corrosion, developed based on a constant current deposition method. Compared with the commonly used hydrothermal method, the constant current deposition method can accurately control the growth rate of transition metal sulfides and obtain uniformly distributed electrocatalytic materials. The preparation process of the transition metal sulfide nanosheet catalytic electrode is simple, energy-efficient, and relatively environmentally friendly, and it is easy to achieve large-scale production and application. When used as a catalyst for nitrate electrocatalytic reduction, it exhibits high nitrate removal rate, high N2 selectivity, low reaction byproducts, and good stability, and can provide some theoretical reference for the design of novel electrochemical nitrate reduction catalysts. Attached Figure Description

[0019] Figure 1 This is a SEM image of the NiCo2S4 nanosheets provided in Example 1 of this invention;

[0020] Figure 2 These are (a) XRD and (b) Raman images of the NiCo2S4 nanosheets provided in Example 1 of this invention;

[0021] Figure 3 This is a comparison of the nitrate removal performance of the NiCo2S4 / NF electrode (a) and NF electrode (b) prepared in Example 1;

[0022] Figure 4 This is a graph showing the effect of Cl- concentration on nitrate removal by the NiCo2S4 / NF electrode in Example 1.

[0023] Figure 5 This is a graph showing the reusability of the NiCo2S4 / NF electrode prepared in Example 1. Detailed Implementation

[0024] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the invention.

[0025] Example 1

[0026] This embodiment provides a method for preparing and applying a nickel-cobalt-based sulfide nitrate electrocatalyst, including the following steps:

[0027] The selected nickel foam mesh (NF) was cut into 2*2cm pieces and ultrasonically washed for 20 min with acetone, anhydrous ethanol, 0.5 mol / L hydrochloric acid, and deionized water. It was then dried in a vacuum oven at 50°C to obtain a pretreated nickel mesh, which served as the sulfide deposition substrate. Using the pretreated nickel mesh as the working electrode, a Pt sheet electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the mesh was placed in a 100 mL mixed solution of nickel nitrate, cobalt nitrate, and thiourea. The nickel nitrate concentration was 20 mmol / L, the cobalt nitrate concentration was 25 mol / L, and the thiourea concentration was 0.8 mol / L. Deposition was carried out at room temperature for 30 min at a current of 0.7 mA. The nickel mesh with NiCo2S4 nanosheets (NiCo2S4 / NF) was then washed repeatedly with deionized water and anhydrous ethanol, and dried in a vacuum oven at 50°C for later use. The NiCo2S4 / NF prepared in Example 1 was observed by electron microscopy, and the SEM images are shown below. Figure 1 As shown, the NiCo2S4 is in the form of nanosheets with a large specific surface area, which is beneficial to improving its catalytic effect. Figure 2 The images show (a) XRD and (b) Raman spectroscopy patterns of NiCo2S4. The electrochemical catalytic performance of NiCo2S4 / NF was tested, and the results are as follows. Figures 3-5 As shown. By Figure 3 The test results show that, compared with a simple nickel mesh (NF), the NiCo2S4 / NF provided in Example 1 can effectively improve the removal rate of nitrate in the treated sample, while exhibiting high N2 selectivity during the removal process. Figure 4 The test results show that the NiCo2S4 / NF provided in Example 1 still exhibits good electrocatalytic removal effect of nitrate even under the condition of chloride ion interference (10 g / L). Figure 5 The test results show that the NiCo2S4 / NF provided in Example 1 has good cycle stability and can be used continuously multiple times.

[0028] Comparative Example 1

[0029] This comparative example provides a method for preparing and applying a nickel-cobalt-based sulfide nitrate electrocatalyst, including the following steps:

[0030] Weigh out 5 mmol of nickel nitrate, 10 mmol of cobalt nitrate and 20 mmol of urea and dissolve them in 100 mL of deionized water. After stirring evenly, transfer the mixture to a polytetrafluoroethylene reactor and immerse the pretreated nickel mesh in the reaction solution. React at 120 °C for 4 h. After cooling and washing, obtain a nickel mesh loaded with pink Ni-Co precursor. Then place the above nickel mesh in 100 mL of 0.05 mol / L sodium sulfide aqueous solution and keep it at 170 °C for 8 h. After cooling, washing and drying, obtain the NiCo2S4 / NF-SR electrode sample.

[0031] Performance testing

[0032] The NiCo2S4 / NF electrode or NiCo2S4 / NF-SR electrode prepared in Example 1 and Comparative Example 1 were used as cathodes and the DSA electrode as anodes, respectively, and placed in a 100 mL mixed solution of nitrate and sodium sulfate, wherein the nitrate concentration was 20 mg / L (calculated as N) and the sodium sulfate concentration was 0.05 mol / L (as supporting electrolyte), and the reaction was carried out at a working current of 4.0 mA for 180 min; the test results are shown in Table 1:

[0033] Table 1

[0034]

[0035] As shown in Table 1, the NiCo2S4 / NF electrode in Example 1 achieved a nitrate removal rate of 85.3% and an N2 selectivity as high as 94.5%. Even after five cycles of reuse, the NiCo2S4 / NF electrode maintained high nitrate removal rates and N2 selectivity (82.4% and 92.2%, respectively). In contrast, the NiCo2S4 / NF-SR electrode prepared by hydrothermal coupling sulfidation in Comparative Example 1, with a NiCo2S4 catalyst amount six times that of electrodeposition, only achieved a nitrate removal rate of 78.9% and a corresponding N2 selectivity of only 86.1% after 180 minutes of reaction at a working current of 4.0 mA. After five cycles, the nitrate removal rate decreased to 68.7%, and the N2 selectivity remained at 78.3%, indirectly demonstrating the superiority of the electrodeposition method for preparing MxS.

[0036] Example 2

[0037] This embodiment provides a method for preparing and applying a nickel-based sulfide nitrate electrocatalyst, including the following steps:

[0038] (1) The selected nickel foam mesh was cut into 2*2cm pieces and ultrasonically washed with acetone, anhydrous ethanol, 0.5mol / L acetic acid, and deionized water for 20 min. Then, it was dried in a vacuum drying oven at 50℃ to obtain a pretreated nickel mesh as a sulfide deposition substrate. Using the above pretreated nickel mesh as the working electrode, Pt sheet electrode as the counter electrode, and Ag / AgCl electrode as the reference electrode, it was placed in 100mL of a mixed solution of nickel sulfate and sodium thiosulfate, in which the concentration of nickel chloride was 30mmol / L and the concentration of thiourea was 1.0mol / L. Deposition was carried out at a current of 0.6mA and 30℃ for 20 min. Then, the nickel mesh (NixS / NF) with NixS nanosheets was washed repeatedly with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 50℃ for later use.

[0039] (2) Using the NixS / NF electrode prepared above as the cathode and the DSA electrode as the anode, the electrode was placed in a 100 mL mixed solution of nitrate and sodium sulfate, wherein the nitrate concentration was 20 mg / L (calculated as N), the sodium sulfate concentration was 0.05 mol / L (as a supporting electrolyte), and the chloride ion concentration was 15 g / L. The reaction was carried out at a working current of 4.0 mA for 180 min. The nitrate removal rate was 82.1%, and the N2 selectivity was as high as 92.1%. After the NixS / NF electrode was reused 5 times, it still had a high nitrate removal rate and N2 selectivity (80.2% and 90.3%, respectively).

[0040] Example 3

[0041] This embodiment provides a method for preparing and applying a cobalt-based sulfide nitrate electrocatalyst, including the following steps:

[0042] (1) The selected copper foam was cut into 2*2cm pieces and ultrasonically washed with acetone, anhydrous ethanol, 0.5mol / L hydrochloric acid, and deionized water for 20 min. Then it was dried in a vacuum drying oven at 50℃ to obtain a pretreated nickel mesh as a sulfide deposition substrate. Using the above pretreated copper foam as the working electrode, Pt sheet electrode as the counter electrode, and Ag / AgCl electrode as the reference electrode, it was placed in 100mL of a mixed solution of cobalt acetate and thioacetamide, where the concentration of cobalt acetate was 30mmol / L and the concentration of thiourea was 0.7mol / L. It was deposited at room temperature for 30 min at a current of 0.8mA. Then the copper foam (CoxS / CF) with CoxS nanosheets was washed repeatedly with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 50℃ for later use.

[0043] (2) Using the CoxS / CF electrode prepared above as the cathode and the DSA electrode as the anode, the electrode was placed in a 100 mL mixed solution of nitrate and sodium sulfate, wherein the nitrate concentration was 10 mg / L (as N), the sodium sulfate concentration was 0.05 mol / L (as a supporting electrolyte), and the chloride ion concentration was 30 g / L. The reaction was carried out at a working current of 3.0 mA for 180 min. The nitrate removal rate was 87.1%, and the N2 selectivity was as high as 93.7%. After the CoxS / CF electrode was reused 5 times, it still had a high nitrate removal rate and N2 selectivity (83.2% and 91.5%, respectively).

[0044] Example 4

[0045] This embodiment provides a method for preparing and applying a copper-based sulfide nitrate electrocatalyst, including the following steps:

[0046] (1) The selected carbon cloth was cut into 2*2cm pieces and ultrasonically washed with anhydrous ethanol, 0.5mol / L phosphoric acid, and deionized water for 20min. Then it was dried in a vacuum drying oven at 50℃ to obtain pretreated carbon cloth as a sulfide deposition substrate. Using the above pretreated carbon cloth as the working electrode, Pt sheet electrode as the counter electrode, and Ag / AgCl electrode as the reference electrode, it was placed in 100mL of a mixed solution of copper acetate and thioacetamide, where the concentration of copper acetate was 20mmol / L and the concentration of thiourea was 0.8mol / L. Deposition was carried out at a deposition current of 0.9mA and an ambient temperature of 50℃ for 30min. Then the carbon cloth with CuxS nanosheets (CuxS / CC) was washed repeatedly with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 50℃ for later use.

[0047] (2) Using the CuxS / CC electrode prepared above as the cathode and the DSA electrode as the anode, the electrode was placed in a 100 mL mixed solution of nitrate and sodium sulfate, wherein the nitrate concentration was 50 mg / L (as N), the sodium sulfate concentration was 0.05 mol / L (as a supporting electrolyte), and the chloride ion concentration was 20 g / L. The reaction was carried out at a working current of 5.0 mA for 240 min. The nitrate removal rate was 85.1%, and the N2 selectivity was as high as 91.7%. After the CuxS / NF electrode was reused 5 times, it still had a high nitrate removal rate and N2 selectivity (82.2% and 90.1%, respectively).

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The application of transition metal sulfide nanosheet catalytic electrode in nitrate electrocatalysis, characterized in that, Using the transition metal sulfide nanosheet catalytic electrode as the cathode and the DSA electrode as the anode, nitrate wastewater is treated in a two-electrode system to generate nitrogen gas. The preparation method of the transition metal sulfide nanosheet catalytic electrode includes the following steps: A solution is formed by dissolving a transition metal salt and a sulfur source; the transition metal salt is selected from one or more of the sulfates, chlorides, and acetates of nickel, cobalt, iron, and copper; the sulfur source is selected from one or more of thiourea, sodium thiosulfate, and thioacetamide; the concentration of the sulfur source in the solution is 0.6~1.2 mol / L; the molar ratio of the transition metal salt to the sulfur source is 1:10~1:

50. The pre-acidified self-supporting electrode carrier is immersed in the above solution; Using a self-supporting electrode carrier as the cathode, transition metal sulfide nanosheets MxS were deposited on the self-supporting electrode carrier in a constant current manner, where M is a transition metal, the cathode deposition current was 0.6mA~0.9mA, the deposition time was 20~60min, and the deposition temperature was 10~60℃. After deposition, the material is removed, washed, and dried to obtain a transition metal sulfide nanosheet catalytic electrode.

2. The application of the transition metal sulfide nanosheet catalytic electrode according to claim 1, characterized in that, The self-supporting electrode carrier is selected from one or more of nickel foam, copper foam, carbon cloth, carbon paper, and carbon foam. The acid used in the pre-acidification treatment of the self-supporting electrode carrier is one or more of hydrochloric acid, acetic acid, phosphoric acid, and citric acid.

3. The application of the transition metal sulfide nanosheet catalytic electrode according to claim 1, characterized in that, The operating conditions for the two-electrode system are: operating current of 2~4mA / cm. 2 The initial nitrate concentration is 10~500 mg / L, and the chloride ion concentration is 0~30 g / L.

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