Preparation method of hollow FeCo2O4-coated CuCo2O4 Z-type heterostructure photoelectric catalyst and application of hollow FeCo2O4-coated CuCo2O4 Z-type heterostructure photoelectric catalyst in photoelectric NH3 production

Abstract

The invention belongs to the technical field of production of high value-added chemicals and catalysts, and particularly relates to a preparation method of a hollow FeCo2O4-coated CuCo2O4 Z type heterostructure photoelectric catalyst and application of the hollow FeCo2O4-coated CuCo2O4 Z type heterostructure photoelectric catalyst in photoelectric NH3 production. The preparation method comprises the following steps: dispersing ZIF-67 in ethanol, adding K3 [Fe (CN) 6], obtaining a precursor through an ion exchange method, dispersing the precursor in ethanol, adding a Cu (CH3COO) 2 aqueous solution, stirring in a water bath, centrifuging, collecting a product, drying the obtained product, and calcining to obtain a target product. The yield of NH3 catalytically synthesized by the photoelectric catalyst prepared by the preparation method disclosed by the invention within 60 minutes is up to 26.124 mg under the irradiation of visible light and the action of specific additional bias voltage. The prepared photoelectric catalyst has the characteristics of high efficiency, low cost and good nitrate adsorption performance, and can be applied to the field of preparation of NH3 through photoelectric catalysis.

Description

Technical Field

[0001] The invention belongs to the technical field of high value-added chemicals and catalyst production, and specifically relates to a preparation method of a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst and its application in photoelectric NH3 production. Background Art

[0002] As an indispensable component of fertilizer, NH3 plays a vital role in modern agricultural production. In addition, due to its high hydrogen content and easy storage, NH3 is also considered a promising energy carrier. The current industrial method for producing NH3 is mainly the Haber-Bosch method, which consumes a lot of energy and emits a lot of greenhouse gases. Therefore, it is particularly important to find an environmentally friendly and green method for synthesizing NH3. Photoelectrocatalytic nitrate reduction is the most promising method for green synthesis of NH3 reported so far. This technology directly uses light to convert NO3 - The conversion into NH3 minimizes energy consumption. In addition, nitrate is one of the most common pollutants, which is potentially harmful to human health and ecosystems. Therefore, the photoelectrocatalytic nitrate reduction method can not only produce valuable NH3, but also effectively treat nitrate wastewater.

[0003] An effective strategy to improve the performance of photoelectrocatalysis is to couple semiconductors with matching energy band structures to construct a Z-type heterojunction. The Z-type heterojunction is expected to improve the separation of carriers and enhance the redox ability, thereby improving the catalytic activity of the photoelectrocatalyst. However, in most current heterojunctions, there is often a small gap between the two semiconductors, which significantly affects the transfer of photogenerated carriers. Therefore, it is a major challenge to construct an atomic-level interface to overcome the "obstacle" and ensure effective carrier transport. Another promising strategy to improve the performance of photoelectrocatalysis is to design hollow nanostructures. On the one hand, the hollow structure is conducive to light reflection and improves light absorption efficiency. On the other hand, it can increase the specific surface area of ​​the catalyst. In addition, the hollow structure can enhance the adsorption and enrichment of nitrates. Therefore, the present invention designs a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst with an atomic-level interface, which is used for photoelectrocatalytic preparation of NH3. Summary of the invention

[0004] One of the purposes of the present invention is to provide a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst having visible light response and capable of effectively separating photogenerated electrons and holes and a preparation method thereof.

[0005] The second object of the present invention is to provide a method for photoelectrocatalytically preparing NH3 using a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst.

[0006] The technical solution adopted by the present invention is:

[0007] A hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst is prepared. First, ZIF-67 is synthesized by a solvothermal method using Co(NO3)2·6H2O and 2-methylimidazole. Then, part of ZIF-67 is converted into PBA by an ion exchange method to obtain ZIF@PBA. ZIF@PBA is dissolved in ethanol and a Cu(CH3COO)2 aqueous solution is added to obtain LDH@PBA by a hydrothermal method. Finally, LDH@PBA is calcined to obtain the target product.

[0008] The method for preparing the above-mentioned hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst comprises the following steps:

[0009] 1) Dissolve Co(NO3)2·6H2O and 2-methylimidazole in methanol, stir to react, collect the product by centrifugation, wash with ethanol, and dry at 60°C to obtain ZIF-67;

[0010] 2) dispersing the ZIF-67 prepared in step 1) in ethanol, adding an aqueous solution of K3[Fe(CN)6] thereto, stirring for reaction, collecting by centrifugation, washing with deionized water and ethanol, and drying at 60° C. to obtain ZIF@PBA;

[0011] 3) dispersing the ZIF@PBA prepared in step 2) in ethanol, and adding an aqueous solution of Cu(CH3COO)2·H2O thereto, reacting in a water bath, collecting the product by centrifugation, washing with ethanol, and drying at 60°C to obtain LDH@PBA;

[0012] 4) Calcine the LDH@PBA prepared in step 3) to obtain a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst.

[0013] Furthermore, in the above-mentioned preparation method, in step 1), the mass ratio of Co(NO3)2·6H2O to 2-methylimidazole is 1:1.12; and the stirring reaction condition is magnetic stirring reaction at room temperature for 6 hours.

[0014] Furthermore, in the above-mentioned preparation method, in step 2), the mass ratio of ZIF-67 and K3[Fe(CN)6] is 4:3; and the stirring reaction conditions are magnetic stirring reaction at room temperature for 2 hours.

[0015] Furthermore, in the above preparation method, in step 3), the mass ratio of ZIF@PBA and Cu(CH3COO)2·H2O is 1:1; and the water bath reaction conditions are magnetic stirring in a 40°C water bath for 30 minutes.

[0016] Furthermore, in the above preparation method, in step 4), the calcination conditions are in air, with a heating rate of 2°C / min and maintained at 350°C for 2 hours.

[0017] The above-mentioned hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst is used in the photoelectrocatalytic production of NH3.

[0018] Further, the above application method is as follows: a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst is grown on carbon felt as a working electrode, a platinum sheet is used as a counter electrode, and a silver / silver chloride electrode is used as a reference electrode, which is placed in an H-type reactor to form a three-electrode system, and the cathode electrolyte is 0.5M sodium sulfate and 0.05M sodium nitrate. The reaction is carried out under an applied voltage and simulated sunlight to catalyze the synthesis of NH3.

[0019] Preferably, the applied voltage is -1.403 V vs. NHE.

[0020] Preferably, the simulated sunlight irradiation uses a 300W xenon lamp as a light source, and the xenon lamp λ≥420nm.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention synthesizes a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst by an ion exchange method, further improving the light response, inhibiting the recombination of electron-hole pairs, increasing the utilization rate of electron holes, and improving the photocatalytic activity.

[0023] 2. Under visible light irradiation and specific additional bias voltage, the catalytic production of NH3 reached 26.124 mg within 60 minutes, providing a green synthesis route and sustainable technology for the production of NH3.

[0024] 3. The present invention is simple, efficient and low-cost. The prepared hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst has the characteristics of large specific surface area, good conductivity, good nitrate adsorption effect and high catalytic activity, and has good visible light absorption performance and good stability. The separation efficiency of photogenerated electron-hole pairs is high, the interfacial charge transfer efficiency is fast, and the NH3 production output is high. It can be applied to the field of photoelectric catalytic production of NH3. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Scanning electron microscopy (SEM) images of ZIF-67 (a), ZIF@PBA (b), LDH@PBA (c) and FeCo2O4@CuCo2O4 (d).

[0026] Figure 2This is the transmission electron microscope (TEM) image of FeCo2O4@CuCo2O4.

[0027] Figure 3 These are the XRD patterns of ZIF-67, ZIF@PBA, LDH@PBA and FeCo2O4@CuCo2O4.

[0028] Figure 4 The transient photocurrent curves (a) and impedance curves (b) of FeCo2O4, CuCo2O4 and FeCo2O4@CuCo2O4.

[0029] Figure 5 This is a graph showing the yield of NH3 synthesized by photoelectrocatalysis of FeCo2O4, CuCo2O4 and FeCo2O4@CuCo2O4 at different voltages. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments.

[0031] Example 1 Preparation of hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst

[0032] (I) Preparation of ZIF-67

[0033] 1.108 g Co(NO3)2·6H2O was dissolved in 50 mL methanol as solution A, and 1.244 g 2-methylimidazole was dissolved in 50 mL methanol as solution B, then solution A was quickly added to solution B at room temperature and magnetically stirred for 6 h. The mixture was collected by centrifugation, washed several times with ethanol, and dried at 60 °C to obtain ZIF-67.

[0034] (II) Preparation of ZIF@PBA

[0035] 0.4 g ZIF-67 polyhedron was dispersed in 350 mL ethanol as solution A, and 0.3 g K3[Fe(CN)]6 was dissolved in 50 mL deionized water as solution B. Then solution B was added to solution A and magnetically stirred at room temperature for 2 h. The mixture was collected by centrifugation, washed with ethanol and deionized water, and dried at 60 °C to obtain ZIF@PBA.

[0036] (III) Preparation of LDH@PBA

[0037] 0.15 g ZIF@PBA was dispersed in 200 mL ethanol as solution A, and 0.15 g Cu(CH3COO)2·H2O was dissolved in 50 mL deionized water as solution B. Then solution B was added to solution A and magnetically stirred in a 40°C water bath for 30 min. The mixture was collected by centrifugation, washed with ethanol, and dried at 60°C to obtain LDH@PBA.

[0038] (IV) Preparation of hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst

[0039] LDH@PBA was calcined in a muffle furnace (2°C / min, 350°C, 2h) to obtain a hollow FeCo2O4@CuCo2O4Z-type heterostructure photoelectrocatalyst.

[0040] (V) Testing

[0041] 1. If Figure 1 As shown in the figure, (a)-(d) are the morphologies of ZIF-67, ZIF@PBA, LDH@PBA and FeCo2O4@CuCo2O4, respectively. It can be observed that ZIF-67 is a typical 12-sided cube with an average grain size of 300-500nm. ZIF@PBA, LDH@PBA and FeCo2O4@CuCo2O4 continue to maintain a 12-sided structure, but the surface is rougher. In addition, FeCo2O4@CuCo2O4 can be seen to have openings.

[0042] 2. If Figure 2 As shown, TEM proved that FeCo2O4@CuCo2O4 has a hollow structure.

[0043] 3. If Figure 3 As shown, the crystal structures of ZIF-67, ZIF@PBA, LDH@PBA and FeCo2O4@CuCo2O4 were determined by XRD, proving that the materials were successfully synthesized.

[0044] 4. If Figure 4 As shown, from (a) the transient photocurrent curve, it can be seen that under illumination conditions, the transient photocurrent increases rapidly, and the transient photocurrent of FeCo2O4@CuCo2O4 is larger than that of FeCo2O4 and CuCo2O4, indicating that the FeCo2O4@CuCo2O4 heterojunction has a better photoelectric response; from (b) the impedance curve, it can be seen that the arc radius of FeCo2O4@CuCo2O4 is smaller than that of FeCo2O4 and CuCo2O4, indicating that the carriers are effectively transferred and separated.

[0045] Example 2 Photoelectrocatalytic production of NH3

[0046] (I) The method is as follows:

[0047] 1) The hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst was grown on carbon felt as the working electrode, the platinum sheet as the counter electrode, and the silver / silver chloride electrode as the reference electrode, which were placed in an H-type reactor to form a three-electrode system.

[0048] 2) The cathode electrolyte was 0.5M sodium sulfate + 0.05M sodium nitrate; argon was introduced into the cathode liquid for 30 minutes before the reaction; a photoelectrocatalytic experiment was conducted under the conditions of -1.403V vs. NHE bias and an ambient temperature of 25°C, using a 300W xenon lamp to simulate sunlight irradiation, with the xenon lamp λ≥420nm. After 60 minutes of reaction, 0.5mL of the cathode liquid was taken, diluted to 10mL with water, and 0.2ml of 10M sodium hydroxide solution was added, and the NH3 concentration was detected with a gas-sensitive electrode.

[0049] (II) Effect of different voltages on NH3 generation

[0050] Photoelectrocatalytic experiments were carried out at applied potentials of -1.003, -1.203, -1.403 and -1.603 V vs. NHE. The results are shown in Figure 5 shown.

[0051] As the voltage gradually increases, the production of NH3 gradually increases and reaches the highest at -1.403 V. However, further increasing the voltage will lead to an increase in competitive side reactions, resulting in a decrease in production. Therefore, -1.403 V was selected as the optimal applied voltage.

Claims

1. A hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst, characterized in that: The hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst is firstly prepared by solvothermal method using Co(NO3)2·6H2O and 2-methylimidazole to synthesize ZIF-67; then, part of ZIF-67 is converted into PBA by ion exchange method to obtain ZIF@PBA; then, ZIF@PBA is dissolved in ethanol and Cu(CH3COO)2 aqueous solution is added to obtain LDH@PBA by hydrothermal method; finally, LDH@PBA is calcined to obtain the target product.

2. The method for preparing a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst according to claim 1, characterized in that: The following steps are involved: 1) Dissolve Co(NO3)2·6H2O and 2-methylimidazole in methanol, stir to react, collect the product by centrifugation, wash with ethanol, and dry at 60°C to obtain ZIF-67; 2) dispersing the ZIF-67 prepared in step 1) in ethanol, adding an aqueous solution of K3[Fe(CN)6] thereto, stirring for reaction, collecting by centrifugation, washing with deionized water and ethanol, and drying at 60° C. to obtain ZIF@PBA; 3) dispersing the ZIF@PBA prepared in step 2) in ethanol, and adding an aqueous solution of Cu(CH3COO)2·H2O thereto, reacting in a water bath, collecting the product by centrifugation, washing with ethanol, and drying at 60°C to obtain LDH@PBA; 4) Calcine the LDH@PBA prepared in step 3) to obtain a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst.

3. The preparation method according to claim 2, characterized in that: In step 1), the mass ratio of Co(NO3)2·6H2O to 2-methylimidazole is 1:1.12; and the stirring reaction condition is magnetic stirring reaction at room temperature for 6 hours.

4. The preparation method according to claim 2, characterized in that: In step 2), the mass ratio of ZIF-67 to K3[Fe(CN)6] is 4:3; and the stirring reaction condition is magnetic stirring reaction at room temperature for 2 hours.

5. The preparation method according to claim 2, characterized in that: In step 3), the mass ratio of ZIF@PBA and Cu(CH3COO)2·H2O is 1:1; and the water bath reaction conditions are magnetic stirring in a 40°C water bath for 30 minutes.

6. The preparation method according to claim 2, characterized in that: In step 4), the calcination conditions are in air, with a heating rate of 2°C / min and maintained at 350°C for 2 hours.

7. Use of the hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectrocatalyst according to claim 1 in photoelectrocatalytic production of NH3.

8. The use according to claim 7, characterized in that: The method is as follows: a hollow FeCo2O4@CuCo2O4 Z-type heterostructure photoelectric catalyst is grown on carbon felt as a working electrode, a platinum sheet is used as a counter electrode, and a silver / silver chloride electrode is used as a reference electrode. It is placed in an H-type reactor to form a three-electrode system. The cathode electrolyte is 0.5M sodium sulfate and 0.05M sodium nitrate. The reaction is carried out under an applied voltage and simulated sunlight to catalyze the synthesis of NH3.

9. The use according to claim 8, characterized in that: The applied voltage is -1.403 V vs. NHE.

10. The use according to claim 8, characterized in that: The simulated sunlight irradiation adopts a 300W xenon lamp as a light source, and the xenon lamp λ≥420nm.

Images