Cu monatomic loaded TiO2 electrode material as well as preparation method and application thereof

Abstract

The invention discloses a Cu monatomic loaded TiO2 electrode material (called monatomic Cu-TiO2 for short), and a preparation method and application thereof. The preparation method comprises the following steps: hydrothermally synthesizing a substrate TiO2, doping monatomic Cu by a molten salt method, and calcining in an inert atmosphere. The prepared material is used for electrochemical nitrate reduction, can be used as a cathode and an anode, and realizes seawater denitrification under a high salinity condition. The preparation method provided by the invention is simple in process, low in consumption, environment-friendly, green and efficient, and the prepared material has good performance on electro-catalysis nitrate reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis and relates to a single-atom Cu-TiO 2 The invention relates to a preparation method of the material and its application in treating nitrate wastewater. Background Art

[0002] As people's daily demand for aquatic products increases, the aquaculture industry is in a period of rapid development. The resulting environmental problem is that the nitrogen content in the aquaculture tailwater exceeds the standard, and the nitrate concentration is much higher than the 10 mg / L specified in the environmental standard. If the aquaculture tailwater is discharged at will without treatment, it will not only endanger the survival of aquatic organisms, but also deteriorate the surrounding water environment and affect human life. Therefore, selectively reducing nitrate to harmless nitrogen gas (N 2 ) is vital to the ecological environment and human health.

[0003] Due to the stability, high solubility and poor adsorption performance of nitrates, it is extremely challenging to remove nitrates from wastewater. Current conventional treatment methods include physical, biological and chemical methods. Physical methods are methods of removing nitrates from water through physical processes, including adsorption, distillation, ion exchange, reverse osmosis, electrodialysis, etc. Among them, modified adsorption materials can improve adsorption capacity, but require a large amount of materials; ion exchange method also requires a large amount of regeneration agent, and the effluent needs to be treated before discharge; distillation method has high energy consumption and is only suitable for treating a small amount of water; reverse osmosis and electrodialysis methods have good nitrate removal effects, but the cost is high, and subsequent wastewater is difficult to treat. The biological process is to convert nitrates into nitrogen through microbial denitrification to remove nitrate pollution. It has low cost and little impact on the environment, but it also has disadvantages such as the operating environment and microbial growth are easily affected. In contrast, the electrochemical reduction method has its significant advantages: it can make full use of green energy, does not require additional reagents, and is easy to equipment.

[0004] Electrocatalytic reduction is a proton-coupled electron transfer process, involving complex transformations of nitrogen-containing intermediates. First, nitrate is adsorbed by the catalyst and reduced to nitrite, which is dominated by the catalyst's promotion site; followed by the reduction of nitrite, which may generate nitrogen through a 5-electron pathway or ammonia through an 8-electron pathway, which is dominated by the catalyst's selective site. Titanium dioxide materials can reduce the overpotential of nitrate reduction reactions due to their high Fermi level and electrochemical durability. Currently, a large number of studies have been conducted on their modification for use in the field of electrocatalysis, such as constructing heterojunctions, creating oxygen vacancies, and doping single atoms. (Energy Environ. Sci., 2021,14, 3938-3944)(ACS Cata. 2020, 10, 3533-3540) In addition, metal Cu is considered to be the most effective metal for nitrate adsorption (Angew. Chem. Int. Ed.2022,61,e202202556)(Journal of Energy Chemistry 78 (2023) 211–221). Therefore, the rational design of electrocatalysts with multiple active sites is extremely critical to improving the performance of electrocatalytic nitrate reduction. Summary of the invention

[0005] The purpose of the present invention is to provide a Cu single atom loaded TiO 2 Electrode materials, preparation methods and applications, CuCl 2· 2H 2 O as a copper source by controlling the substrate TiO 2 The loading amount of single-atom Cu on the substrate can achieve better catalytic effect and be used for the electrocatalytic reduction of nitrate.

[0006] The specific technical solution for achieving the purpose of the present invention is:

[0007] A Cu single atom-loaded TiO 2 A method for preparing an electrode material, the method comprising the following steps:

[0008] Step 1: Measure a certain amount of hydrofluoric acid (HF), slowly add it dropwise into tetrabutyl titanate (TBOT) solution, and stir to form a uniform solution; wherein the molar ratio of hydrofluoric acid to tetrabutyl titanate is 3:1, and the stirring time is 30 min;

[0009] Step 2: Transfer the solution in step 1 to a reactor and place it in an oven at 180°C for hydrothermal reaction for 24 hours;

[0010] Step 3: The material obtained in step 2 was washed with deionized water and ethanol for 5 times respectively; then placed in a sodium hydroxide solution and stirred for 8 hours to wash away the F adsorbed on the surface. - ;

[0011] Step 4: Place the material obtained in step 3 into a freeze dryer and dry for 12 hours to obtain a substrate TiO 2 ;

[0012] Step 5: Place the material obtained in step 4 into a mortar and add CuCl 2 ·2H 2 O, LiCl, and KCl were fully ground to uniformity, transferred to a porcelain boat and placed in a tube furnace, pyrolyzed under argon protection, heated to 500°C at a heating rate of 8°C / min, and pyrolyzed for 2 hours to obtain the Cu single atom-loaded TiO 2 Electrode material is Cu-TiO 2 Materials; wherein the mass ratio of the substrate TiO2, LiCl, and KCl is 1:1:1, and CuCl 2 ·2H 2 O is the substrate TiO 2 The grinding time was at least 30 min.

[0013] A Cu single atom-loaded TiO prepared by the above method 2 Electrode material.

[0014] A use of the material in electrocatalytic reduction of nitrate.

[0015] Further, the application is: the obtained Cu-TiO2 material is configured into ink and dripped onto carbon paper to make Cu-TiO 2 The electrodes are used as cathode and anode respectively, saturated calomel electrode is used as reference electrode, and a mixed solution of sodium sulfate and sodium chloride is used as electrolyte. A light source is introduced into the nitrate-containing wastewater, and the light source irradiates the anode (cathode is at the bottom, anode is at the top, and two electrode sheets are placed horizontally). Then, an electrochemical workstation is connected, and a chronoamperometry is used to pass a constant voltage for electrocatalytic reduction. The reaction time is set to 4 hours; the nitrate in the reaction system is converted into nitrogen. The ink formula is: Cu-TiO 2 The molar ratio of materials, Nafion solution, anhydrous ethanol and deionized water is 5600:1:190:580.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the present invention prepares for the first time a bifunctional single-atom Cu / TiO 2 The electrode can more effectively and quickly electrocatalyze the reduction of nitrate to nitrogen, reducing the pollution of nitrate to the environment. The electrode has high stability and good reproducibility, and is suitable for the removal of nitrate in natural water and sewage without pH adjustment. It is green, mild, environmentally friendly, simple, low-cost, easy to operate, and has a wide source of raw materials and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The single-atom Cu-TiO 2 X-ray diffraction (XRD) pattern of materials;

[0018] Figure 2 The single-atom Cu-TiO 2 Material spherical aberration electron microscope (HAADF-STEM) image;

[0019] Figure 3 The single-atom Cu-TiO obtained in Example 1 2 The reduction performance diagram of the material in nitrate wastewater with different chloride ion concentrations;

[0020] Figure 4 The single-atom Cu-TiO obtained in Example 1 2 Nitrate reduction performance diagram of the material at different current densities;

[0021] Figure 5 The single-atom Cu-TiO obtained in Example 1 2 The rendering of the device where the material is actually applied to nitrate reduction and denitrification in seawater. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] (1) Single-atom Cu-TiO 2 Powder preparation

[0025] Accurately measure 3 ml of hydrofluoric acid and slowly add it to 20 ml of tetrabutyl titanate solution, stir for 30 min until a uniform solution is formed; transfer it to a reactor, put it in an oven at 180°C for 24 hours, and naturally cool it to room temperature; wash the obtained material with deionized water and ethanol for 5 times respectively; place it in 0.1 M sodium hydroxide solution and stir for 8 hours, then put it in a freeze dryer and dry it for 12 hours to obtain the substrate TiO 2 Weigh 1 g TiO 2 Put it in a mortar and add 3 wt% CuCl 2 ·2H 2 O, 1 g LiCl, and 1 g KCl were fully ground for more than 30 min, transferred to a porcelain boat and placed in a tube furnace. Under argon protection, the mixture was heated to 500 °C at a rate of 8 °C / min and pyrolyzed for 2 h. Single-atom Cu / TiO 2 Material. Figure 1 In this embodiment, Cu-TiO 2 X-ray diffraction (XRD) pattern of materials; Figure 2For example, single-atom Cu-TiO 2 Spherical aberration electron microscopy (HAADF-STEM) image of the material.

[0026] (2) Pretreatment of carbon substrate

[0027] Carbon paper needs to undergo a series of pretreatments, including cutting, acid washing and ultrasonic water washing. Use a blade or other tool to cut into 2*2.5cm rectangles; mix 10ml of concentrated hydrochloric acid and 30ml of water, and soak the carbon paper in the mixed solution for 3 hours; use deionized water to ultrasonically rinse until the pH value of the carbon paper surface is neutral, ensuring that there is no residual hydrochloric acid.

[0028] (3) Single-atom Cu-TiO 2 Preparation of electrodes

[0029] Accurately weigh 10 mg of the Cu / TiO prepared in step (1). 2 Powder, add 10 μL Nafion solution, 250 μL ethanol and 230 μL water, ultrasonicate the mixture for 1 hour, use a pipette to draw the mixture evenly onto the carbon paper in step (2), and dry it naturally for 12 hours.

[0030] Example 2

[0031] In this embodiment, a three-electrode system is used, including a cathode, an anode and a reference electrode. 2 The electrodes were used as cathode and anode, saturated calomel was used as reference electrode, 0.1 M sodium sulfate solution and sodium chloride solution of different concentrations were used as electrolyte, and 100 mg NL -1 Sodium nitrate was the target pollutant, and a 300 W xenon lamp with an AM1.5 filter was used as a simulated solar light source. The light source was irradiated on the anode and connected to an electrochemical workstation. A constant voltage of -1 V vs. RHE was used for electrocatalytic reaction. The system size was 30 ml. After 4 hours of continuous reaction, the nitrate reduction rate in the water could reach 98.7±0.7%, and the nitrogen selectivity could reach 100%. Figure 3 The single-atom Cu / TiO obtained in Example 1 2 The reduction performance diagram of the material in nitrate wastewater with different chloride ion concentrations; Figure A shows the change in nitrate concentration during the reaction; Figure B shows the removal efficiency of nitrate and total nitrogen (TN) in the reaction system at different chloride ion concentrations; Figure C shows the nitrogen selectivity of the reaction system at different chloride ion concentrations.

[0032] Example 3

[0033] In this embodiment, direct current is used as the power source to prepare a single-atom Cu / TiO2 The electrodes were used as cathode and anode; 0.1 M sodium sulfate solution and 0.5 M sodium chloride solution were used as electrolytes, and 100 mg NL -1 Sodium nitrate is the target pollutant, and a 300 W xenon lamp with an AM1.5 filter is used as a simulated solar light source. The light source is irradiated on the anode and connected to a DC power supply. Electrocatalytic reactions are carried out using different current densities. The system size is 500 ml. After 8 hours of continuous reaction, the nitrate reduction rate in water can reach 96.9±1.3%, and the nitrogen selectivity can reach 100%. Figure 3 The single-atom Cu-TiO obtained in Example 1 2 The nitrate reduction performance diagram of the material at different current densities; Figure A shows the change in nitrate concentration during the reaction; Figure B shows the nitrate and total nitrogen removal efficiency of the reaction system at different current densities; Figure C shows the nitrogen selectivity of the reaction system at different current densities.

[0034] Example 4

[0035] In this embodiment, a 19 V 10 W solar photovoltaic panel with a length and width of 310*210 mm was used as a power source. 2 The electrodes act as cathode and anode; real seawater is used as the electrolyte, where the chloride concentration is about 19.77 g / L-27.39 g / L and the nitrate concentration is 20 mg NL -1 The system size was 1000 ml, the reaction lasted for 2 days, and the total illumination time was 12 hours. The nitrate reduction rate in the water could reach 54.5±4.7%, the nitrogen selectivity could reach 100%, and the terminal nitrate concentration was less than the tailwater discharge standard value of 10 mg NL. -1 . Figure 5 Figure A shows the single-atom Cu-TiO obtained in Example 1. 2 Figure B shows the effect of the material being actually applied to the device for nitrate reduction and denitrification of seawater; Figure B shows the change in nitrate concentration in the reaction device over two days.

Claims

1. A method for preparing a Cu single atom-loaded TiO2 electrode material, characterized in that: The method comprises the following steps: Step 1: Measure a certain amount of hydrofluoric acid, slowly add it dropwise into the tetrabutyl titanate solution, and stir and mix until a uniform solution is formed; wherein the molar ratio of hydrofluoric acid to tetrabutyl titanate is 3:1, and the stirring time is 30 min; Step 2: Transfer the solution in step 1 to a reactor and place it in an oven at 180°C for hydrothermal reaction for 24 hours; Step 3: The material obtained in step 2 was washed with deionized water and ethanol for 5 times respectively; then placed in a sodium hydroxide solution and stirred for 8 hours to wash away the F adsorbed on the surface. - ; Step 4: Place the material obtained in step 3 into a freeze dryer and dry for 12 hours to obtain a substrate TiO2; Step 5: Put the material obtained in step 4 into a mortar, add CuCl2·2H2O, LiCl, and KCl, grind thoroughly until uniform, transfer to a porcelain boat and put into a tube furnace, pyrolyze under argon protection, heat to 500°C at a heating rate of 8°C / min, and pyrolyze for 2 hours to obtain the Cu single atom-loaded TiO2 electrode material, i.e., Cu-TiO2 material; wherein the mass ratio of the substrate TiO2, LiCl, and KCl is 1:1:1, CuCl2·2H2O is 3 wt% of the substrate TiO2, and the grinding time is at least 30 min.

2. A Cu single atom loaded TiO2 electrode material prepared by the method of claim 1.

3. Use of the material according to claim 2 in electrocatalytic reduction of nitrates.

4. The use according to claim 3, characterized in that: The obtained Cu-TiO2 material is configured into ink and dropped onto carbon paper to make Cu-TiO2 electrodes, which are used as cathode and anode respectively, a saturated calomel electrode is used as a reference electrode, and a mixed solution of sodium sulfate and sodium chloride is used as an electrolyte. A light source is introduced into the nitrate-containing wastewater to irradiate the anode, with the cathode at the bottom and the anode at the top. The two electrode sheets are placed horizontally and then connected to an electrochemical workstation. The chronoamperometry is used to pass a constant voltage for electrocatalytic reduction, and the reaction time is set to 4 hours; the conversion of nitrate in the reaction system into nitrogen is achieved, wherein the ink formula is: Cu-TiO2 material, Nafion solution, anhydrous ethanol and deionized water, and the molar ratio thereof is 5600:1:190:580.

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