A method for microchannel electrode flow-through electrodeposition loading of controllable nanostructured metal catalysts

Abstract

The present invention belongs to the technical field of loaded catalyst preparation, and discloses a method for loading a controllable nanostructured metal catalyst by flow-through electroplating on a microchannel electrode, comprising the following steps: first, pre-treating the microchannel electrode to remove the substrate oxide film and oil stains; then, flow-through alkali etching to increase the active sites and surface area in the microchannel; second, loading the metal catalyst in the microchannel, using a step-by-step pressure increase and two-way circulation technology to control the catalyst loading size and distribution; and finally, post-processing the electroplating solution. The catalyst loaded inside the prepared microchannel electrode is nanostructured and has the advantages of uniform distribution, and controllable loading amount and particle size. The present invention is simple to operate, has an easily controllable loading rate, and a stable coating, and has broad application prospects in various fields such as wastewater treatment, carbon dioxide recovery, and nitrate removal.

Description

Technical Field

[0001] The invention belongs to the technical field of supported catalyst preparation, and particularly relates to a method for loading a controllable nanostructured metal catalyst using flow-through electrodeposition on a microchannel electrode. Background Art

[0002] Microchannel structures are currently a frontier and hot research topic in chemistry, materials, and environmental sciences. The channel pore size can be regulated according to actual application needs. Conductive microchannel electrodes, with their high surface area and void volume, abundant active sites, and excellent conductivity, have broad application potential in electrochemistry, catalysis, adsorption, and sample preparation.

[0003] The loading of catalysts can enhance the efficiency of various chemical reactions. For non-conductive substrates, the most widely used method of catalyst loading is the impregnation method, in which the catalyst is loaded on the substrate through long-term impregnation. However, the impregnation method has defects such as long reaction time, high concentration of impregnation liquid, and the need to clean the waste liquid after impregnation, thereby increasing the cost of the impregnation method. The Chinese invention patent with patent application number 202310538050.4 discloses a method for preparing an alumina-based catalyst for propane dehydrogenation to propylene. The Pt catalyst is loaded on the alumina substrate by the impregnation method. Because the alumina substrate is not conductive, the catalyst can only be loaded by the impregnation method. The concentration of chloroplatinic acid catalyst used in this method is as high as 60g / L, but the final Pt loading amount on the alumina substrate is only 0.3wt%. There is still a large amount of chloroplatinic acid in the impregnation waste liquid, which causes waste. The Chinese invention patent application number 202310375878.2 discloses a catalyst for the photocatalytic reduction of carbon dioxide to produce methane and its preparation method. Manganese oxide is loaded on a copper mesh substrate by an impregnation method. The attached figure in the specification shows that a large number of manganese oxide clusters are loaded on the copper mesh. However, due to the limited surface area of ​​the copper mesh, the manganese oxide clusters are densely distributed, and the effective catalytic area during the reaction is reduced.

[0004] For conductive substrates, electrodeposition becomes a better choice. The electrodeposition method has a simple operation process, does not rely on production equipment, can work on large-area and complex-shaped substrates, and is carried out at room temperature, which can avoid thermal diffusion between layers and thus obtain a single component with a certain composition. However, traditional electrodeposition is to immerse the substrate in an electroplating bath and energize it. The concentration of the plating solution in the electroplating bath is high, and the loading effect on the inside of the carbon electrode pores is not obvious. The Chinese invention patent application number 201810227908.4 discloses a method for electroplating preparation of metal-supported cobalt oxide catalysts, in which the constant voltage static electroplating time is as long as 2 hours. Not only is the electroplating time long, but it also causes catalyst particles to agglomerate, affecting the effective area of ​​catalytic activity. In addition, the metal content of the electroplating solution is high, and the tail liquid is difficult to handle. Therefore, the development of an electroplating method with high electron transfer efficiency, adjustment of intrinsic structural activity, increase of reaction area, and energy saving is of great significance to the development of catalyst loading. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a simple and efficient electro-deposition preparation method for loading adjustable nanostructured metal catalysts on microchannel electrodes. In the present invention, we propose a flow-through electro-deposition method for the electro-deposition preparation of loaded metal microchannel electrodes, in which a metal salt solution is loaded into the microchannel of the electrode under a flow state, and explore the quantitative relationship between step-by-step pressure increase, electro-deposition solution concentration and flow-through flow rate, and utilize the abundant micro- and mesopores in the channel to improve the loading firmness and loading rate of the catalyst. The present invention successfully loads nanostructured catalysts on the electrode surface using the method of electro-deposition under a flow state, and the catalyst particle size, catalyst loading type and distribution density can be adjusted, effectively increasing the catalytic performance. The synthesized catalyst can be used in a variety of electrochemical applications and has a flexible range of use. In addition, when the electrode is used as a cathode, the catalyst activity can be guaranteed, and the heat generated during use can further activate the catalyst.

[0006] The technical solution of the present invention:

[0007] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode comprises the following steps:

[0008] (1) Microchannel electrode pretreatment: Prepare an acid solution and pass it into the microchannel in a flow-through electrodeposition device to remove the oxide film in the channel; then, pass a 30% NaOH solution heated to 70-100°C into the microchannel for 20-50 minutes to remove the oil stains in the microchannel;

[0009] (2) Flow-through alkali etching: prepare an alkali solution, and pass the alkali solution into the microchannel at a flow rate of 0.2-2.5 mL / min in a flow-through electrodeposition device for 8-12 hours for etching. Then, calcine the electrode at 400-1200°C under a nitrogen atmosphere for 5-24 hours. After taking it out, neutralize the residual alkali solution on the surface and set it aside for use.

[0010] (3) Metal catalyst loading in microchannels: In a flow-through electrodeposition device, an alkaline-etched microchannel electrode is used as the cathode, and a ternary metal electrode of ruthenium, iridium, and titanium is used as the anode. A metal salt electrodeposition solution of a certain concentration is prepared and flows from the water inlet to the water outlet of the microchannel electrode at a certain flow rate. This process is carried out under step-by-step pressure increase conditions, and the step-by-step pressure increase time is set to 5 to 60 minutes. Afterwards, the metal salt electrodeposition solution flows from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electrodeposition reaction is carried out under the same conditions.

[0011] (4) Post-treatment of the electroplating solution: In the flow-through electroplating device, the voltage is adjusted to form hydroxide precipitation of excess metal in the electroplating solution, which is then discharged and dried and calcined.

[0012] In step (1), the volume ratio of hydrofluoric acid, 65-68% nitric acid, and high-purity water in the mixed acid solution is 0.5-10:2-14:3.6-17. The volume of the mixed acid required is 1-60 mL / cm 2 The time of mixed acid treatment is 10 to 60 s. If the mixed acid treatment time is too long, the morphology of the microchannel electrode will be destroyed. If the mixed acid treatment time is too short, the oxide film of the microchannel electrode will not be completely removed.

[0013] In step (2), the solution is a mixture of an alkali solution, ammonium acetate, and an alcohol solution having no more than three carbon atoms, with a mass ratio of 10-65:0.5-20:1-30. The amount of alkali used is related to the effective reaction area of ​​the microchannel electrode and is 0.2-3 kg / m 2 After the alkaline treatment, the electrode needs to be soaked in acid to neutralize the alkaline substances remaining on the surface. The purpose of alkaline etching is to enhance the bonding force between the substrate and the metal catalyst particles, thereby facilitating the loading of the metal catalyst, improving the conductivity, and extending the service life of the electrode. After alkaline etching, the inner and outer surfaces of the microchannel electrode will show a certain rough surface state. If the etching time is too short, the binding force of the metal catalyst is insufficient. If the etching time is too long, the more depressions formed by etching will affect the service life of the electrode. At the same time, during the alkaline etching process, a layer of organic phase can be loaded inside the microchannel, enhancing the controllability of the electrodeposition process.

[0014] In step (3), the metal salt is one or more of copper, iron, cobalt, palladium, titanium, nickel, gold, silver, platinum, rhodium, molybdenum, ruthenium, and manganese salts. The materials of the microchannel cathode structure include but are not limited to foam metal, porous carbon, and carbon nanotubes with an equivalent diameter of 0.001 to 2 mm. The use of step-by-step voltage-boosting electrodeposition is a major breakthrough in improvement. The reason is that the concentration of the electrodeposition solution, the flow rate, the microchannel pore volume, and the voltage are all related to the size and distribution of the catalyst load. Therefore, first, the microchannel electrode unit pore volume (cm 3 ) Control the concentration of the metal electrodeposition solution to be 5-500mg / L; then control the water inlet flow rate to be 0.01~7.5mL / min according to the unit concentration of the electrodeposition solution (mg / L); finally, control the voltage of the step-by-step boost to be -0.1~-1.2V according to the unit flow rate (mL / min), ensure that the voltage is within the range of -1~-75V, and step-by-step boost the voltage by -0.1~-1.2V per minute, and perform electrodeposition for 5~60min, then reverse the water inlet direction and perform electrodeposition under the same conditions. The ring-related electrodeposition conditions and the process of two-way flow make the size of the nano-metal catalyst particles deposited in the microchannel controllable and the catalyst evenly distributed. If the concentration, flow rate, voltage and other conditions are too large, the metal particles will agglomerate, reduce the specific surface area of ​​the catalyst, and it will be difficult to adhere to the microchannel; if the concentration, flow rate, voltage and other conditions are too small, the catalyst loading will be insufficient, resulting in reduced catalytic performance.

[0015] In step (4), water is electrolyzed using a voltage of -1 to -95 V to generate an alkaline environment for 1 to 120 minutes, so that excess metal ions in the electrodeposition solution are precipitated as hydroxides, thereby reducing the cost of subsequent secondary treatment of the electrodeposition solution.

[0016] Beneficial effects of the present invention:

[0017] (1) The flow-through method of the present invention prepares a metal catalyst-loaded microchannel electrode. The microchannel substrate is used as the electrodeposition target. First, a pretreatment is performed to remove oxides and oil stains on the inner and outer surfaces of the microchannel electrode. Then, an alkaline etching step is performed to increase the effective reaction area and active sites inside the microchannel, thereby increasing the contact area between the metal catalyst and the microchannel and enhancing the mass transfer effect. By utilizing the advantages of the microchannel and using the flow-through electrodeposition method, the reaction is confined to the interior of the channel, shortening the mass transfer distance, improving the electrode reaction efficiency and the utilization rate of the metal catalyst in the electrodeposition solution.

[0018] (2) The flow-through preparation of the metal catalyst-loaded microchannel electrode of the present invention utilizes an electrodeposition process, quantitatively controlling reaction conditions such as microchannel volume, step-by-step pressure increase, electrodeposition solution concentration, and flow velocity. The optimized preparation process is simple, and the use of flow-through electrodeposition significantly increases the metal catalyst loading and electrode service life. It fully utilizes the characteristics of the microchannel electrode and ensures stable operating performance of the metal catalyst-loaded microchannel electrode. The entire process requires minimal equipment, has low production costs, is simple to operate, and easily enables large-scale preparation and batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a scanning electron microscope image of a microchannel carbon electrode without metal catalyst loading in the present invention.

[0020] Figure 2 This is a scanning electron microscope image of Example 1 of a flow-through preparation method for a microchannel carbon electrode loaded with a nanostructured metal catalyst according to the present invention.

[0021] Figure 3 This is a scanning electron microscope image of Example 2 of a flow-through preparation method for a microchannel carbon electrode loaded with a nanostructured metal catalyst according to the present invention.

[0022] Figure 4 This is a scanning electron microscope image of Example 3 of a flow-through preparation method for a microchannel carbon electrode loaded with a nanostructured metal catalyst according to the present invention.

[0023] Figure 5 This is a scanning electron microscope image of Example 4 of a flow-through preparation of a microchannel carbon electrode loaded with a nanostructured metal catalyst according to the present invention.

[0024] Figure 6 This is a scanning electron microscope image of Example 5 of a flow-through preparation of a microchannel carbon electrode loaded with nanostructured metal catalysts according to the present invention.

[0025] Figure 7 It is a preparation flow chart of the present invention. DETAILED DESCRIPTION

[0026] In order to further illustrate the present invention, the present invention is described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1

[0028] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, the preparation steps of which are as follows:

[0029] (1) Pretreatment of microchannel carbon electrodes: Place the microchannel carbon electrodes in a mixed acid solution containing hydrofluoric acid, nitric acid, and high-purity water for 10 seconds to remove the surface oxide film; the volume ratio of hydrofluoric acid, nitric acid, and high-purity water in the mixed acid solution is 1:4:5. Then, in a constant temperature water bath at 90°C, pass a 30% mass fraction NaOH solution through the electrodes for 30 minutes to remove oil stains on the microchannel electrodes.

[0030] (2) Flow-through alkaline etching: A mixed solution of potassium hydroxide solution, ammonium acetate, and ethanol was prepared in a mass ratio of 30:2.5:10. The alkaline solution was passed into the microchannel in a flow-through electrodeposition device for etching. The electrode was then calcined at 900 °C for 6 h under a nitrogen atmosphere. After removal, the residual alkaline solution on the surface was neutralized and set aside for use.

[0031] (3) Metal catalyst loading in microchannels: In a flow-through electroplating device, an alkaline-etched microchannel electrode was used as the cathode. A 100 mg / L CuSO4 electroplating solution was prepared and flowed from the water inlet to the water outlet of the microchannel electrode at a flow rate of 3.3 mL / min. The process was carried out under the conditions of an initial voltage of -1 V and a step-by-step voltage increase of -0.75 V per minute. The step-by-step voltage increase time was set to 10 minutes. Afterwards, the CuSO4 electroplating solution was flowed from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electroplating reaction was carried out under the same conditions.

[0032] (4) Post-treatment of the electrolytic solution: Adjust the voltage to -10V and perform a 15-minute water electrolysis process. By decomposing water, an alkaline environment is generated, so that the Cu that has not been successfully deposited in the microchannel is precipitated as Cu(OH)2 and discharged, thereby avoiding secondary contamination of the electrolytic solution. The microchannel electrode that has been successfully loaded with the catalyst is dried at 100°C for 4 hours. The preparation process of the microchannel carbon electrode loaded with nano-copper catalyst is realized. The scanning electron micrograph of the electrode without the catalyst is shown in FIG. Figure 1 , the scanning electron microscopy image of the electrode after loading the catalyst is shown in Figure 2 .

[0033] Example 2

[0034] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, the preparation steps of which are as follows:

[0035] (1) Pretreatment of microchannel carbon electrodes: Place the microchannel carbon electrodes in a mixed acid solution containing hydrofluoric acid, nitric acid, and high-purity water for 10 seconds to remove the surface oxide film; the volume ratio of hydrofluoric acid, nitric acid, and high-purity water in the mixed acid solution is 1:5:7. Then, in a constant temperature water bath at 90°C, pass a 30% mass fraction NaOH solution through the electrodes for 30 minutes to remove oil stains on the microchannel electrodes.

[0036] (2) Flow-through alkaline etching: A mixed solution of potassium hydroxide solution, ammonium acetate, and ethanol was prepared in a mass ratio of 10:1:7. The alkaline solution was passed into the microchannel in a flow-through electrodeposition device for etching. The electrode was then calcined at 900 °C for 6 h under a nitrogen atmosphere. After removal, the residual alkaline solution on the surface was neutralized and set aside for use.

[0037] (3) Metal catalyst loading in microchannels: In a flow-through electroplating device, an alkaline-etched microchannel electrode was used as the cathode. A 20 mg / L CuSO4 electroplating solution was prepared and flowed from the water inlet to the water outlet of the microchannel electrode at a flow rate of 7 mL / min. The process was carried out under the conditions of an initial voltage of -1 V and a step-by-step voltage increase of -1 V per minute. The step-by-step voltage increase time was set to 10 minutes. Afterwards, the CuSO4 electroplating solution was flowed from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electroplating reaction was carried out under the same conditions.

[0038] (4) Post-treatment of the electrolytic solution: Adjust the voltage to -10V and perform a 15-minute water electrolysis process. By decomposing water, an alkaline environment is generated, so that the Cu that has not been successfully deposited in the microchannel is formed into Cu(OH)2 precipitation and discharged, thereby avoiding secondary contamination of the electrolytic solution. The microchannel electrode that has successfully loaded the catalyst is dried at 100°C for 4 hours. The scanning electron microscope image of the electrode after loading the catalyst is shown in the preparation process of the microchannel carbon electrode loaded with nano-copper catalyst. Figure 3 .

[0039] Example 3

[0040] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, the preparation steps of which are as follows:

[0041] (1) Pretreatment of microchannel carbon electrodes: Place the microchannel carbon electrodes in a mixed acid solution containing hydrofluoric acid, nitric acid, and high-purity water for 10 seconds to remove the surface oxide film; the volume ratio of hydrofluoric acid, nitric acid, and high-purity water in the mixed acid solution is 1:5:7. Then, in a constant temperature water bath at 90°C, pass a 30% mass fraction NaOH solution through the electrodes for 30 minutes to remove oil stains on the microchannel electrodes.

[0042] (2) Flow-through alkaline etching: A mixed solution of potassium hydroxide solution, ammonium acetate, and ethanol was prepared in a mass ratio of 10:1:7. The alkaline solution was passed into the microchannel in a flow-through electrodeposition device for etching. The electrode was then calcined at 900 °C for 6 h under a nitrogen atmosphere. After removal, the residual alkaline solution on the surface was neutralized and set aside for use.

[0043] (3) Metal catalyst loading in microchannels: In a flow-through electroplating device, an alkaline-etched microchannel electrode was used as the cathode. A 500 mg / L CuSO4 electroplating solution was prepared and flowed from the water inlet to the water outlet of the microchannel electrode at a flow rate of 5 mL / min. The process was carried out under the conditions of an initial voltage of -1 V and a step-by-step voltage increase of -2 V per minute. The step-by-step voltage increase time was set to 30 minutes. Afterwards, the CuSO4 electroplating solution was flowed from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electroplating reaction was carried out under the same conditions.

[0044] (4) Post-treatment of the electrolytic solution: Adjust the voltage to -20V and perform a 30-min electrolysis process. By decomposing water, an alkaline environment is generated, so that the Cu that has not been successfully deposited in the microchannel is precipitated as Cu(OH)2 and discharged, thereby avoiding secondary contamination of the electrolytic solution. The microchannel electrode that has successfully loaded the catalyst is dried at 100°C for 4 hours. The scanning electron microscope image of the electrode after loading the catalyst is shown in the preparation process of the microchannel carbon electrode loaded with nano-copper catalyst. Figure 4 .

[0045] Comparative Example 1

[0046] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, the preparation steps of which are as follows:

[0047] (1) Pretreatment of microchannel carbon electrodes: Place the microchannel carbon electrodes in a mixed acid solution containing hydrofluoric acid, nitric acid, and high-purity water for 10 seconds to remove the surface oxide film; the volume ratio of hydrofluoric acid, nitric acid, and high-purity water in the mixed acid solution is 1:5:7. Then, in a constant temperature water bath at 90°C, pass a 30% mass fraction NaOH solution through the electrodes for 30 minutes to remove oil stains on the microchannel electrodes.

[0048] (2) Flow-through alkaline etching: A mixed solution of potassium hydroxide solution, ammonium acetate, and ethanol was prepared in a mass ratio of 10:1:7. The alkaline solution was passed into the microchannel in a flow-through electrodeposition device for etching. The electrode was then calcined at 900 °C for 6 h under a nitrogen atmosphere. After removal, the residual alkaline solution on the surface was neutralized and set aside for use.

[0049] (3) Metal catalyst loading in microchannels: In a flow-through electroplating device, an alkaline-etched microchannel electrode was used as the cathode. A 0.1 mg / L CuSO4 electroplating solution was prepared and flowed from the water inlet to the water outlet of the microchannel electrode at a flow rate of 3.5 mL / min. The process was carried out under the conditions of an initial voltage of -1 V and a step-by-step voltage increase of -0.2 V per minute. The step-by-step voltage increase time was set to 15 minutes. Afterwards, the CuSO4 electroplating solution was flowed from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electroplating reaction was carried out under the same conditions;

[0050] (4) Post-treatment of the electroplating solution: The voltage was adjusted to -3 V, and the electrolysis process was carried out for 10 minutes. By decomposing water to create an alkaline environment, the Cu that was not successfully deposited in the microchannel was precipitated as Cu(OH)2 and discharged, thus avoiding secondary contamination of the electroplating solution. The microchannel electrode with the successful catalyst loading was dried at 100°C for 4 hours. The scanning electron micrograph of the electrode after loading of the catalyst is shown in Figure 5. The metal salt concentration of the electroplating solution was too low, resulting in the failure of the metal catalyst to be successfully loaded inside the microchannel.

[0051] Comparative Example 2

[0052] A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, the preparation steps of which are as follows:

[0053] (1) Pretreatment of microchannel carbon electrodes: Place the microchannel carbon electrodes in a mixed acid solution containing hydrofluoric acid, nitric acid, and high-purity water for 10 seconds to remove the surface oxide film; the volume ratio of hydrofluoric acid, nitric acid, and high-purity water in the mixed acid solution is 1:5:7. Then, in a constant temperature water bath at 90°C, pass a 30% mass fraction NaOH solution through the electrodes for 30 minutes to remove oil stains on the microchannel electrodes.

[0054] (2) Flow-through alkaline etching: A mixed solution of potassium hydroxide solution, ammonium acetate, and ethanol was prepared in a mass ratio of 10:1:7. The alkaline solution was passed into the microchannel in a flow-through electrodeposition device for etching. The electrode was then calcined at 900 °C for 6 h under a nitrogen atmosphere. After removal, the residual alkaline solution on the surface was neutralized and set aside for use.

[0055] (3) Metal catalyst loading in microchannels: In a flow-through electroplating device, an alkaline-etched microchannel electrode was used as the cathode. A 10 g / L CuSO4 electroplating solution was prepared and flowed from the water inlet to the water outlet of the microchannel electrode at a flow rate of 2.3 mL / min. The process was carried out under the conditions of an initial voltage of -1 V and a step-by-step voltage increase of -0.2 V per minute. The step-by-step voltage increase time was set to 15 minutes. Afterwards, the CuSO4 electroplating solution was flowed from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electroplating reaction was carried out under the same conditions;

[0056] (4) Post-treatment of the electroplating solution: The voltage was adjusted to -12 V, and the electrolysis process was carried out for 25 minutes. By decomposing water to create an alkaline environment, the Cu that was not successfully deposited in the microchannel was precipitated as Cu(OH)2 and discharged, thus avoiding secondary contamination of the electroplating solution. The microchannel electrode with the successful catalyst loading was dried at 100°C for 4 hours. The scanning electron micrograph of the electrode after loading of the catalyst is shown in Figure 6. Due to the high concentration of metal salts in the electroplating solution, the loaded Cu aggregated over a large area in the channel, affecting the catalytic performance.

[0057] Application Examples

[0058] Comparison of the nitrate ion removal performance of the unloaded copper catalyst microchannel carbon electrode with the loaded copper catalyst microchannel carbon electrode prepared in the examples and comparative examples:

[0059] The preparation steps of the copper catalyst-loaded microchannel carbon electrode are respectively as follows: Examples 1, 2, and 3, and Comparative Examples 1 and 2; the preparation steps of another copper catalyst-unloaded microchannel electrode are as follows: Steps 1 and 2 in Example 1.

[0060] The prepared microchannel electrode was used to remove nitrate ion concentration of 20 mg / L wastewater prepared in the laboratory, with an operating voltage of -3V, and was treated in a flow-through electrochemical filter for 30 minutes. The copper ion concentration in the inlet and outlet water of the preparation process and the nitrate ion removal effect of the treatment process are shown in Table 1. The catalyst in the copper catalyst-loaded microchannel carbon electrode prepared in Examples 1, 2, and 3 is evenly distributed, with a large number of active sites, and the removal effect of nitrate ions is greatly improved compared to the log electrode. Comparative Example 1 has a weak catalytic effect due to the low content of the loaded copper catalyst; Comparative Example 2 has a caking phenomenon due to the loaded catalyst, which leads to a reduction in the effective reaction area of ​​the electrode and a decrease in the reaction performance. Therefore, the removal effect of nitrate ions in Comparative Examples 1 and 2 is not significantly improved compared to the log.

[0061] Table 1 is a performance comparison table of nitrate removal effects of various embodiments and comparative examples of the present invention.

[0062]

Claims

1. A method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode, characterized in that: Here are the steps: (1) Microchannel electrode pretreatment: prepare an acid solution and pass it into the microchannel in a flow-through electrodeposition device to remove the oxide film in the channel; then, a NaOH solution heated to 70-100 °C with a mass fraction of 30% is passed into the microchannel for 20-50 min to remove the oil stains in the microchannel; (2) Flow-through alkaline etching: Prepare the solution and pass it into the microchannel at a flow rate of 0.2-2.5 mL / min in a flow-through electrodeposition device for 8-12 h for etching. Then, calcine the electrode at 400-1200 °C in a nitrogen atmosphere for 5-24 h. After taking it out, neutralize the residual alkaline solution on the surface and set aside for use. (3) Metal catalyst loading in microchannels: In a flow-through electrodeposition device, an alkaline-etched microchannel electrode is used as the cathode, and a ternary metal electrode of ruthenium, iridium, and titanium is used as the anode. A metal salt electrodeposition solution is prepared and flows from the water inlet to the water outlet of the microchannel electrode. The process is carried out under step-by-step pressure increase conditions, and the step-by-step pressure increase time is set to 5-60 min. Afterwards, the metal salt electrodeposition solution flows from the water outlet to the water inlet of the microchannel electrode at the same flow rate, and the electrodeposition reaction is carried out under the same conditions. The step-by-step voltage-boosting electroplating is as follows: First, the unit pore volume of the microchannel electrode is cm 3 The concentration of the metal salt electrodeposition solution is controlled to be 5-500 mg / L; the water inlet flow rate of the metal salt electrodeposition solution is then controlled to be 0.01-7.5 mL / min according to the unit concentration of the electrodeposition solution mg / L; finally, the voltage of the step-by-step voltage is controlled to be -0.1--1.2 V / min according to the unit flow rate mL / min, ensuring that the voltage is within the range of -1--75 V, and the voltage is stepped up in steps of -0.1--1.2 V per minute for 5-60 minutes of electrodeposition; (4) Post-treatment of the electroplating solution: In the flow-through electroplating device, the voltage is adjusted to allow the excess metal in the electroplating solution to form hydroxide precipitation and be discharged, and the microchannel electrode loaded with the catalyst is dried.

2. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (1), the volume ratio of hydrofluoric acid, 65-68 wt.% nitric acid and water in the acid solution is 0.5-10:2-14:3.6-17.

3. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (1), the volume of the acid solution is related to the effective reaction area of ​​the microchannel electrode in the range of 1 to 60 mL / cm 2 The acid solution treatment time is 10~60 s.

4. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (2), the solution is prepared by mixing an alkali solution, ammonium acetate, and an alcohol solution having no more than three carbon atoms, and the mass ratio of the three is 10~65:0.5~20:1~30.

5. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (2), the relationship between the amount of base used and the effective reaction area of ​​the microchannel electrode is 0.2~3 kg / m 2 After the alkaline treatment, the electrode needs to be soaked in acid to neutralize the alkaline substances remaining on the surface.

6. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (3), the metal salt is one or a mixture of two or more of copper, iron, cobalt, palladium, titanium, nickel, gold, silver, platinum, rhodium, molybdenum, ruthenium, and manganese salts.

7. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (3), the material of the microchannel cathode includes foam metal and porous carbon.

8. The method for loading a controllable nanostructured metal catalyst by flow-through electrodeposition on a microchannel electrode according to claim 1, characterized in that: In step (4), water is electrolyzed using a voltage of -1 to -95 V to generate an alkaline environment reaction for 1 to 120 minutes, so that excess metal ions in the electrodeposition solution are precipitated as hydroxides, thereby reducing the cost of subsequent secondary treatment of the electrodeposition solution.

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