A ternary heterojunction catalyst electrode and its preparation method and its application in the electrocatalytic degradation of dyes

Abstract

This invention relates to a ternary heterojunction catalyst electrode, its preparation method, and its application in the electrocatalytic degradation of dyes. The preparation method of the ternary heterojunction catalyst electrode of this invention involves: dissolving a sulfur source in an MXene dispersion, heating and stirring to obtain a first mixture; dissolving a molybdenum source in the first mixture, heating and stirring to obtain a second mixture; immersing nickel foam in the second mixture and placing it in a reactor for heating and reaction to obtain the ternary heterojunction catalyst electrode. The ternary heterojunction catalyst electrode uses nickel foam as a substrate, the surface of which is coated with MXene, and the surface of the MXene is supported with intercalated molybdenum disulfide; wherein the MXene and molybdenum disulfide are bonded through Ti-O-Mo bonds. This invention, by constructing a heterojunction and utilizing interface engineering to synergistically optimize the electronic structure, can effectively enhance the electron transfer rate, achieving a highly efficient electrocatalytic activity of "1+1>2".

Description

Technical Field

[0001] This invention relates to the technical field of catalytic materials, and in particular to a ternary heterojunction catalyst electrode, its preparation method, and its application in the electrocatalytic degradation of dyes. Background Technology

[0002] Dyes are widely used chemical substances in our daily lives, and their production and use generate large amounts of wastewater. This wastewater contains complex components, mostly recalcitrant colored dyes, and their discharge causes serious pollution to water bodies, soil, and ecosystems. Dye removal methods mainly include physical, chemical, biological, and electrochemical methods. Physical methods primarily use porous materials such as activated carbon to adsorb and remove dyes. While low-cost and simple to operate, they face challenges such as low separation efficiency and difficulty in recycling adsorbents. Chemical methods remove dyes by reacting chemical reagents with pollutant molecules. Although highly efficient, they also face problems such as high cost and the potential for secondary pollution. Biological methods utilize microorganisms to degrade pollutants, offering advantages such as low energy consumption and good treatment effects, but they also face the challenge of requiring highly trained microorganisms. Electrocatalytic degradation technology, due to its high efficiency, environmental friendliness, and strong controllability, shows great potential in dye wastewater treatment. This technology uses electron transfer processes on the catalyst surface to decompose organic dye molecules into harmless small molecules, thereby achieving effective pollutant removal.

[0003] Currently, various catalysts have been prepared for the electrocatalytic degradation of pollutants. These include commercially available rare metal oxide electrodes such as Ti / RuO2 and Ti / IrO2. While these exhibit catalytic activity, their high cost hinders practical engineering applications. Furthermore, numerous single-electrode catalytic electrodes are also used for pollutant degradation; however, their active sites are often limited, resulting in slow electron transfer rates and consequently poor degradation performance. Therefore, it is essential to develop a simple, low-cost, and environmentally friendly method for preparing high-performance ternary heterojunction catalytic electrodes. Based on this, compared to the drop-coating method, hydrothermal in-situ growth is employed, allowing the catalyst to adhere more firmly to the substrate and avoiding the poor stability issues faced by many current electrocatalysts. Summary of the Invention

[0004] To address the technical problems of insufficient catalytic performance, slow reaction kinetics, and poor stability of existing catalysts under neutral or weakly acidic conditions, resulting in low catalytic efficiency, easy activity decline during long-term operation, and high cost that limits large-scale application, this invention provides a ternary heterojunction catalyst electrode, its preparation method, and its application in the electrocatalytic degradation of dyes.

[0005] The first objective of this invention is to provide a method for preparing a ternary heterojunction catalyst electrode, comprising the following steps:

[0006] Provide an MXene dispersion;

[0007] The sulfur source was dissolved in the MXene dispersion, and the mixture was heated and stirred to obtain the first mixture.

[0008] The molybdenum source is dissolved in the first mixture, heated and stirred to obtain the second mixture;

[0009] Nickel foam is immersed in the second mixture and placed in a reactor for heating to obtain a ternary heterojunction catalyst electrode.

[0010] In some embodiments of the present invention, the concentration of the MXene dispersion is 0.1~0.33 mg / mL.

[0011] In some embodiments of the present invention, the sulfur source is selected from thiourea and / or thioacetamide.

[0012] In some embodiments of the present invention, the heating and stirring temperature is 40~60°C and the time is 2~5h.

[0013] In some embodiments of the present invention, the molybdenum source is selected from ammonium molybdate and / or sodium molybdate.

[0014] In some embodiments of the present invention, the heating reaction temperature is 180~200°C and the time is 12~24h.

[0015] In some embodiments of the present invention, the mass ratio of the sulfur source, MXene and molybdenum source is (3.6~7.2):1:(8~16).

[0016] In some embodiments of the present invention, the nickel foam is pretreated as follows: cut into 1cm×1cm sizes, ultrasonically treated in acetone, 1M hydrochloric acid, water, and ethanol for 20 minutes respectively, and then soaked in ethanol for storage.

[0017] The second objective of this invention is to provide a ternary heterojunction catalyst electrode prepared by the aforementioned method. The ternary heterojunction catalyst electrode uses nickel foam as a substrate and sequentially forms a multi-level structure of nickel sulfide, molybdenum disulfide, and MXene. Both sides of the MXene are loaded with intercalated molybdenum disulfide. The MXene and molybdenum disulfide are bonded through Ti-O-Mo bonds, which constitutes a sandwich structure.

[0018] A third objective of this invention is to provide the application of the ternary heterojunction catalyst electrode in the electrocatalytic degradation of dyes.

[0019] In some embodiments of the present invention, the dye includes one or more of methylene blue, rhodamine B, and acid orange.

[0020] The technical solution of the present invention has the following advantages compared with the prior art:

[0021] 1) The preparation method of the present invention is simple to operate, low in cost, reproducible and universal;

[0022] 2) This invention uses a hydrothermal method to grow the catalyst in situ. Compared with the "drop coating method" for electrode preparation, the catalyst can be stably fixed on the substrate, effectively avoiding the problems of catalyst shedding and difficulty in powder recovery.

[0023] 3) This invention, by constructing a heterojunction and utilizing interface engineering to synergistically optimize the electronic structure, can effectively enhance the electron transfer rate. The ternary heterojunction promotes electron transfer, with electrons moving from nickel sulfide to molybdenum disulfide and then to MXene, achieving a highly efficient electrocatalytic activity of "1+1>2". Oxygen gains electrons at the cathode to generate hydroxyl radicals, which can attack the conjugated double bonds in methylene blue, ultimately mineralizing it into carbon dioxide and water. The reaction of this invention is: O2 + 2H⁺ + + 2e - → H2O2, H2O2 + e - → ·OH + OH - . Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0025] Figure 1 These are microscopic morphology images of the ternary heterojunction catalyst electrode obtained in Example 1 of the present invention; wherein, (a) is a 100 μm SEM scanning electron microscope image, (b) is a 50 μm SEM scanning electron microscope image, (c) is a 1 μm SEM scanning electron microscope image, and (d) is a 20 μm SEM scanning electron microscope image.

[0026] Figure 2 This is the Raman spectrum of the ternary heterojunction catalyst electrode obtained in Example 1 of the present invention;

[0027] Figure 3 This is the Fourier transform infrared spectrum of the ternary heterojunction catalyst electrode obtained in Example 1 of the present invention;

[0028] Figure 4 These are the effect diagrams of the electrochemical degradation of methylene blue by the catalyst electrodes obtained in Example 1 and Comparative Examples 1-2 of the present invention;

[0029] Figure 5These are the stability test results of the ternary heterojunction catalyst electrode obtained in Example 1 of this invention;

[0030] Figure 6 These are the electrochemical impedance spectra of the catalyst electrodes obtained in Example 1 and Comparative Examples 1-2 of this invention;

[0031] Figure 7 These are cyclic voltammograms of the catalyst electrodes obtained in Example 1 and Comparative Examples 1-2 of this invention;

[0032] Figure 8 These are Tafel diagrams of the catalyst electrodes obtained in Example 1 and Comparative Examples 1-2 of this invention;

[0033] Figure 9 These are X-ray photoelectron spectra of the catalyst electrodes obtained in Example 1 and Comparative Examples 1-2 of the present invention; wherein, (1) is the fine spectrum of the 2p orbitals of Ni; (2) is the fine spectrum of the 3d orbitals of Mo; (3) is the fine spectrum of the 2p orbitals of Ti; and (4) is the fine spectrum of the 1s orbitals of O. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] Example 1

[0036] This embodiment provides a method for preparing a ternary heterojunction catalytic electrode, including the following steps:

[0037] 1) Dissolve 5 mg MXene in 30 ml of deionized water and sonicate at a frequency of 400 W and a power of 40 kHz for 30 min to form a uniform dispersion.

[0038] 2) Dissolve 36 mg of thiourea in the dispersion of step 1), and stir at 800 rpm for 3 hours in a constant temperature sand bath at 60°C until it is completely dissolved to obtain the first mixture.

[0039] 3) Dissolve 80 mg of ammonium molybdate in the first mixture of step 2), and stir at 800 rpm for 2 hours in a constant temperature sand bath at 60°C until it is completely dissolved to obtain the second mixture.

[0040] 4) Transfer the second mixture from step 3) to a 50ml polytetrafluoroethylene reactor and mix it with the pretreated (pretreatment: cut the nickel foam into 1*1cm pieces) 2 Square shapes were ultrasonicated in acetone, 1M HCl, water, and ethanol for 20 min respectively, and nickel foam was reacted at 200℃ for 12 h.

[0041] 5) After cooling to room temperature, the electrode was washed several times with ethanol and water, and then dried in a vacuum drying oven at 50°C to obtain a ternary heterojunction catalytic electrode. The obtained ternary heterojunction catalytic electrode was characterized structurally, and the results are as follows: Figures 1-2 As shown:

[0042] Figure 1 The image shows the microstructure of the ternary heterojunction. It can be seen that MXene grows uniformly on the nickel foam substrate, and the surface of MXene is covered with intercalated molybdenum disulfide.

[0043] Figure 2 The Raman spectrum of the ternary heterojunction is shown. Figure 3 The Fourier transform infrared spectrum of the ternary heterojunction shows that MXene, molybdenum disulfide, and nickel sulfide form a composite structure.

[0044] Comparative Example 1 (compared to Example 1, the difference being that step 1 is missing)

[0045] This comparative example provides a method for preparing a binary heterojunction catalytic electrode, including the following steps:

[0046] 1) Dissolve 36 mg of thiourea in 30 ml of deionized water and stir at 800 rpm for 3 h in a constant temperature sand bath at 60 °C until it is completely dissolved to obtain a solution.

[0047] 2) Dissolve 80 mg of ammonium molybdate in the solution from step 1), and stir at 800 rpm for 2 hours in a constant temperature sand bath at 60°C until it is completely dissolved to obtain a mixture.

[0048] 3) Transfer the mixture from step 2) to a 50 ml polytetrafluoroethylene reactor and react it with the pretreated nickel foam at 200 °C for 12 h;

[0049] 4) After cooling to room temperature, wash several times with ethanol and water, and then dry in a vacuum drying oven at 50°C to obtain a binary heterojunction catalytic electrode.

[0050] Comparative Example 2 (compared to Example 1, except that step 1 is missing) and 2)

[0051] This comparative example provides a method for preparing a molybdenum disulfide catalytic electrode, including the following steps:

[0052] 1) Dissolve 36mg of thiourea in 30ml of deionized water and stir at 800rpm for 3 hours in a constant temperature sand bath at 60℃ until it is completely dissolved.

[0053] 2) Transfer the solution from step 1) to a 50 ml polytetrafluoroethylene reactor and react it with the pretreated nickel foam at 200 degrees Celsius for 12 h;

[0054] 3) After cooling to room temperature, wash several times with ethanol and water, and then dry in a vacuum drying oven at 50°C to obtain a molybdenum disulfide catalytic electrode.

[0055] Performance test examples

[0056] The catalyst electrodes prepared in Examples 1 and Comparative Examples 1-2 were tested for electrocatalytic degradation of methylene blue. The specific steps included: first, preparing a 30 mg / L MB solution using 0.1 M sodium sulfate as the electrolyte; then, adding 50 ml of the pollutant to a 100 ml electrolytic cell at room temperature. Using the catalyst electrodes prepared in the examples and comparative examples as cathodes and the graphite electrode as anode, air was bubbled in at a flow rate of 3 L / min, and the degradation experiment was conducted for 60 min under a constant current of 0.026 A. After the reaction started, 0.7 ml of the reaction solution was pipetted at predetermined time points and quenched with methanol at a ratio of 7:3. After thorough mixing, the mixture was poured into a microcuvette (1 ml), and the sample was detected at a wavelength of 664 nm using a UV-Vis spectrophotometer. The experimental results are shown in [Figure number missing]. Figure 4 .

[0057] Depend on Figure 4 It can be seen that all three catalysts can degrade methylene blue at a concentration of 30 mg / L and a constant current of 0.026 A. Among them, the degradation effect of the MXene@MoS2@Ni3S2 ternary heterojunction is greatly improved, and about 90% of the pollutant can be degraded within 60 min.

[0058] Performance Test Example 2

[0059] The stability test of the ternary heterojunction catalyst prepared in Example 1 was carried out. The specific steps included: after the catalyst was subjected to the steps of Performance Test Example 1, the electrode was recovered, rinsed with ethanol and deionized water, soaked in ethanol overnight, and the steps of Performance Test Example 1 were continued. This process was repeated seven times.

[0060] Depend on Figure 5 It is known that the ternary heterojunction catalytic electrode prepared by the present invention can still maintain the degradation performance of the first use after being reused 7 times.

[0061] Performance Test Example 3

[0062] The electrochemical performance of the catalyst electrodes prepared in Example 1 and Comparative Examples 1-2 was tested. The specific steps included: using the prepared electrodes as working electrodes, a platinum sheet as the counter electrode, and Ag / AgCl as the reference electrode, the tests were conducted using a Chenhua electrochemical workstation. Electrochemical impedance spectroscopy (EIS) was performed using 0.1M sodium sulfate as the electrolyte; cyclic voltammetry (CV) was performed using 1M potassium hydroxide as the electrolyte, with an initial voltage of -0.1V, a termination voltage of 0.6V, and a scan rate of 5mV / s; Tafel voltammetry was performed using 1M potassium hydroxide as the electrolyte. The experimental results are shown in […]. Figures 6-8 .

[0063] Depend on Figure 6 It can be seen that the prepared ternary heterojunction catalyst has lower resistance and faster electron transfer rate. From Figure 7 It can be seen that the prepared ternary heterojunction catalyst has higher redox activity. Figure 8 It can be seen that the prepared ternary heterojunction catalyst has the lowest Tafel slope, that is, it has the best catalytic activity or reaction efficiency.

[0064] Performance Test Example 4

[0065] The mechanism of the composite material was investigated, and the XPS spectra of the catalytic electrode materials synthesized in Example 1 and Comparative Examples 1-2 were tested.

[0066] Depend on Figure 9 It is evident that the addition of MXene increases the binding energies of both Mo and Ni, indicating that molybdenum disulfide and nickel sulfide lose electrons; conversely, the binding energy of Ti decreases, indicating that MXene gains electrons. This suggests the formation of an electron transport channel at the interface between the three components, reducing resistance, which may be the primary reason for the accelerated catalytic reaction efficiency. Furthermore, analysis of the fine O-matrix of the ternary heterostructure reveals the possible formation of Ti-O-Mo bonds between MXene and molybdenum disulfide, which could serve as the electron transport channel.

[0067] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. The application of a ternary heterojunction catalyst electrode in the electrocatalytic degradation of dyes, characterized in that, The ternary heterojunction catalyst electrode uses nickel foam as a substrate and sequentially forms a multi-level structure of nickel sulfide, molybdenum disulfide and MXene. Both sides of the MXene are loaded with intercalated molybdenum disulfide. The MXene and molybdenum disulfide are bonded together through Ti-O-Mo bonds. The preparation method of the ternary heterojunction catalyst electrode includes the following steps: Provide an MXene dispersion; The sulfur source was dissolved in the MXene dispersion, and the mixture was heated and stirred to obtain the first mixture. The molybdenum source is dissolved in the first mixture, heated and stirred to obtain the second mixture; Nickel foam is immersed in the second mixture and placed in a reactor for heating to obtain a ternary heterojunction catalyst electrode.

2. The application according to claim 1, characterized in that, The concentration of MXene dispersion is 0.1~0.33 mg / mL.

3. The application according to claim 1, characterized in that, The sulfur source is selected from thiourea and / or thioacetamide.

4. The application according to claim 1, characterized in that, The heating and stirring temperature is 40~60℃, and the time is 2~5h.

5. The application according to claim 1, characterized in that, The molybdenum source is selected from ammonium molybdate and / or ammonium molybdate.

6. The application according to claim 1, characterized in that, The heating reaction is carried out at a temperature of 180~200℃ for 12~24 hours.

7. The application according to claim 1, characterized in that, The mass ratio of the sulfur source, MXene, and molybdenum source is (3.6~7.2):1:(8~16).

8. The application according to claim 1, characterized in that, The dyes include one or more of methylene blue, rhodamine B, and acid orange.

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