Method for preparing homojunction Cd-ZnIn2S4 photoelectric catalyst by in-situ cation doping

Abstract

The invention discloses a method for preparing a homojunction Cd-ZnIn2S4 photoelectric catalyst through in-situ cation doping. The method comprises the following steps: ultrasonically dissolving cadmium nitrate, zinc chloride, indium chloride and thiourea in deionized water to form a precursor solution, and then carrying out hydrothermal reaction to prepare the ultrathin folded nanosheet homojunction Cd-ZnIn2S4 photoelectric catalyst. The method disclosed by the invention is simple, the homojunction Cd-ZnIn2S4 is formed by doping Cd < 2 + > in the hydrothermal reaction, and the prepared photoanode has relatively high photoelectrocatalytic performance and stability.

Description

Technical Field

[0001] The invention relates to a method for preparing a homojunction Cd-ZnIn2S4 photoelectric catalyst by in-situ cation doping, and belongs to the field of nano material preparation. Background Art

[0002] Hydrogen is a high energy density, storable, ideal clean energy, but the current development and utilization of hydrogen energy is seriously insufficient. Photoelectrochemistry driven by solar energy can convert solar energy into hydrogen energy, which is an important way to solve the energy problem. The water oxidation reaction involved in PEC water splitting is the rate-limiting reaction and the decisive step in water decomposition. Since TiO2 photocatalysts were proven to achieve water decomposition in 1972, the rational design of high-performance photoanodes has become a research hotspot.

[0003] The ideal photoelectrode semiconductor material should have a band gap greater than 1.6eV to decompose water, and should also have a band gap less than 2.4eV to obtain a wide range of solar light absorption spectra. Metal sulfides have always been the focus of research in the field of photoelectrocatalysis because of their appropriate electronic band gap, exposed active sites, and diverse and adjustable chemical structures. ZnIn2S4, as a two-dimensional layered sulfide with a high specific surface area, has the advantages of adjustable band gap and short carrier migration path, but severe body recombination and slow transport of photogenerated carrier migration have become its biggest problems. Constructing a heterojunction is a common strategy for optimizing the performance of ZnIn2S4. However, the common methods for constructing heterojunctions require a two-step method to achieve, and lattice mismatch and defects are prone to occur at the interface. Wang et al. first prepared hexagonal ZnIn2S4 microspheres as an ideal matrix by a solvothermal method, and then used a hydrothermal growth method to decorate the surface of the hexagonal ZnIn2S4 microspheres with cubic ZnIn2S4 quantum dots to form a heterojunction. The heterojunction formed by this method is not only complex in process, but also has a certain imbalance in the lattice matching at the interface between the two phases. These problems will limit its catalytic activity (Wang, Y. Chen, W. Zhou, et al, Cubic quantum dot / hexagonal microsphere ZnIn2S4 heterophase junctions for exceptional visible-light-driven photocatalytic H2 evolution, J. Mater. Chem. A, 2017, 5, 8451-8460). Mamta Devi Sharma et al. first synthesized ZnIn by a hydrothermal method 2.2 S y Nanosheets, and then Cd element was introduced into ZnIn by cation exchange method. 2.2 S y, Cd-ZnIn is synthesized 2.2 S y Nanosheets increase light absorption and carrier density, but this method has many steps, and the introduced Cd element is only used as an impurity to adjust the energy level of ZnIn 2.2 S y The band structure of (Mamta Devi Sharma, Chavi Mahala, and Mrinmoyee Basu, Vertically Grown Cd-ZnIn2.2Sy, Nanosheets for Photoelectrochemical Water Splitting, ACS Appl. Nano Mater. 2021, 4, 3013-3021). Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing homojunction Cd-ZnIn2S4 (CZIS) photoelectric catalyst by in-situ cation doping. The method introduces Cd element during the in-situ growth of ZnIn2S4 nanosheets by a one-step hydrothermal method, which can control the phase transformation of ZnIn2S4 nanosheets and synthesize ZnIn2S4 nanosheets with coexistence of rhombohedral phase and hexagonal phase.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] The method for preparing homojunction Cd-ZnIn2S4 photoelectric catalyst by in-situ cation doping comprises the following steps:

[0007] According to the molar ratio of cadmium nitrate to zinc chloride of 5:100, cadmium nitrate, zinc chloride, indium chloride and thiourea were ultrasonically dissolved in deionized water to obtain a precursor solution, which was then poured into a polytetrafluoroethylene hydrothermal autoclave, and clean conductive glass was placed therein to carry out a hydrothermal reaction at 160-180°C. After the reaction was completed, the homojunction Cd-ZnIn2S4 photoelectric catalyst was obtained by washing and drying.

[0008] Preferably, the conductive glass is FTO conductive glass.

[0009] Preferably, the conductive glass is cleaned with acetone, ethanol and water for 15 to 20 minutes respectively, and then dried at 60±10° C. to obtain clean conductive glass.

[0010] Preferably, in the precursor solution, the concentration of zinc chloride is 0.01 mol / L, the concentration of indium chloride is 0.02 mol / L, the concentration of thiourea is 0.04 mol / L, and the concentration of cadmium nitrate is 0.0005 mol / L.

[0011] Preferably, the hydrothermal reaction time is 6±2h.

[0012] Preferably, the washing method is to wash twice with ethanol and water in sequence.

[0013] Preferably, the drying temperature is 60±10° C. and the drying time is 12±2 h.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) The technical route of the present invention is simple, the synthesis conditions are easy to achieve, and only one step of hydrothermal synthesis is used, which reduces the experimental cost and improves the repeatability of the experiment.

[0016] (2) Different from conventional metal doping, the present invention introduces metal atom cadmium and simultaneously regulates the molar ratio of cadmium nitrate and zinc chloride, so as to regulate the phase change during the in-situ growth of the material, directionally regulate the phase transition of ZnIn2S4, and guide the formation of a homojunction, thereby improving the separation and migration efficiency of carriers.

[0017] (3) The homojunction Cd-ZnIn2S4 photocatalyst prepared by the present invention has the morphology of wrinkled ultra-thin nanosheets, which is conducive to light capture and carrier transport, and has better lattice matching, improving the problems of serious electron-hole recombination, slow carrier migration and severe photocorrosion in traditional indium zinc sulfide. It can reach 2.6mA / cm under the condition of 1.23V vs RHE. 2 The photocurrent density is as high as 0.017 V, and the stability at low current is also significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the method for preparing homojunction C-ZnIn2S4 photoelectrocatalysts by in situ cation doping.

[0019] Figure 2 This is the XRD spectrum of C-ZIS in Example 1.

[0020] Figure 3 This is the SEM image of C-ZIS in Example 1.

[0021] Figure 4 This is the solid UV DRS spectrum of C-ZIS in Example 1.

[0022] Figure 5 This is a graph showing the LSV performance test results of C-ZIS in Example 1.

[0023] Figure 6 This is a graph showing the stability test results of C-ZIS in Example 1.

[0024] Figure 7This is the XRD spectrum of ZIS in Comparative Example 1.

[0025] Figure 8 This is the SEM image of ZIS in Comparative Example 1.

[0026] Fig. 9 This is the solid UV DRS spectrum of ZIS in Comparative Example 1.

[0027] Fig.10 This is a graph showing the LSV performance test results of the ZIS in Comparative Example 1.

[0028] Fig.11 This is a graph showing the stability test results of ZIS in Comparative Example 1.

[0029] Fig.12 This is the XRD spectrum of C1-ZIS in Comparative Example 2.

[0030] Fig.13 This is the SEM image of C1-ZIS in Comparative Example 2.

[0031] Fig.14 This is the solid UV DRS spectrum of C1-ZIS in Comparative Example 2.

[0032] Fig.15 This is a graph showing the LSV performance test results of C1-ZIS in Comparative Example 2.

[0033] Fig.16 This is the XRD spectrum of C10-ZIS in Comparative Example 3.

[0034] Fig.17 This is the SEM image of C10-ZIS in Comparative Example 3.

[0035] Fig.18 This is the solid UV DRS spectrum of C10-ZIS in Comparative Example 3.

[0036] Fig.19 This is a graph showing the LSV performance test results of C10-ZIS in Comparative Example 3.

[0037] Fig. 20 This is the XRD spectrum of C20-ZIS in Comparative Example 4.

[0038] Fig.21 This is a graph showing the LSV performance test results of C20-ZIS in Comparative Example 4.

[0039] Fig. 22 This is the XRD spectrum of CZIS-140℃ in Comparative Example 5.

[0040] Fig.23 This is the XRD spectrum of CZIS-180℃ in Comparative Example 6.

[0041] Fig.24 This is the XRD spectrum of 1C-ZIS in Comparative Example 7.

[0042] Fig.25 This is a graph showing the LSV performance test results of 1C-ZIS in Comparative Example 7.

[0043] Fig.26 This is the XRD spectrum of 6C-ZIS in Comparative Example 8. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with specific embodiments and accompanying drawings.

[0045] Example 1

[0046] Step 1, according to the molar ratio of cadmium nitrate to zinc chloride of 5:100, weigh 0.0125mmol of cadmium nitrate, 0.25mmol of zinc chloride, 0.5mmol of indium chloride and 1mmol of thiourea in a beaker containing 25mL of deionized water, and dissolve them uniformly by ultrasonication to obtain a precursor solution. The FTO conductive glass was washed with acetone, ethanol and water for 20min respectively and dried.

[0047] Step 2: Place the cleaned FTO conductive glass with the conductive surface facing downward into a polytetrafluoroethylene kettle, and then place the precursor solution in a polytetrafluoroethylene hydrothermal reactor for hydrothermal reaction at 160°C for 6 hours; wash the hydrothermal product three times with ethanol and deionized water respectively, and then dry it in a vacuum oven at 60°C for 12 hours to obtain a homojunction Cd-ZnIn2S4 photoelectric catalyst, named C-ZIS.

[0048] Figure 2 is the XRD spectrum of C-ZIS, where the (009), (104) and (018) crystal planes correspond to the rhombohedral phase ZnIn2S4, and the (102) and (104) crystal planes correspond to the hexagonal phase ZnIn2S4, respectively. Figure 3 The SEM image shows that C-ZIS is an ultrathin nanosheet with wrinkles. Figure 4 The solid-state UV DRS spectrum shown indicates that C-ZIS has a narrower band gap and stronger light absorption ability.

[0049] The light source of the photoelectrocatalytic test is a solar simulator, and the electrochemical workstation is a Princeton electrochemical workstation. The tests are all conducted using a three-electrode system, with 0.5M sodium sulfate as the electrolyte, a Pt sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a conductive glass as the working electrode. The test voltage is 0 to 1.23 V vs RHE.

[0050] Figure 5This is the linear sweep voltammetry (LSV) test of C-ZIS. It can be seen that at 1.23 V vs RHE, the photocurrent density can reach 2.6 mA / cm 2 The initial potential is only 0.017 V. This shows that CZIS has good photoelectrocatalytic activity. The stability test curve of C-ZIS is shown in Figure 2. Figure 6 As shown in the figure, after 1500s of change, the photocurrent density can still retain 73% of the initial value. The above results show that C-ZIS has good chemical stability at low voltage.

[0051] Comparative Example 1

[0052] This comparative example is substantially the same as Example 1, except that cadmium nitrate is not added, and the obtained product is named ZIS.

[0053] exist Figure 7 The XRD spectrum shown, where the (009), (104) and (018) crystal planes correspond to the rhombohedral phase ZnIn2S4. Figure 8 The SEM image of ZIS is shown, indicating that it has the morphology of ultrathin nanoarrays. Fig. 9 It is the solid-state UV DRS diagram of ZIS, showing the absorbance and band gap of ZIS.

[0054] Fig.10 This is the linear sweep voltammetry (LSV) test of ZIS. It can be seen that at 1.23 V vs RHE, the photocurrent density is 0.4 mA / cm 2 The results show that the photoelectric activity of the catalyst is much lower than that of C-ZIS. The stability test curve of ZIS is shown in Fig.11 As shown in Figure 2, after 1500s of change, the photocurrent density can only retain 42% of the initial value. The above results show that ZIS has poor stability.

[0055] Comparative Example 2

[0056] This comparative example is substantially the same as Example 1, except that the amount of cadmium nitrate added is 0.0025 mmol, that is, the molar ratio of cadmium nitrate to zinc chloride is 1:100, and the obtained product is named C1-ZIS.

[0057] Fig.12 It is the XRD spectrum of C1-ZIS, indicating that C1-ZIS is still in rhombohedral phase. Fig.13 Shown is the SEM image of C1-ZIS, showing the morphology of ultrathin nanoarrays. Fig.14 This is the solid-state UV DRS image of C1-ZIS, showing the absorbance and band gap of 1CZIS. Fig.15This is the linear sweep voltammetry (LSV) test of C1-ZIS. It can be seen that at 1.23 V vs RHE, the photocurrent density is 1 mA / cm 2 The results show that the photoelectric activity of the catalyst is higher than that of ZIS not doped with Cd, but much lower than that of C-ZIS prepared in Example 1.

[0058] Comparative Example 3

[0059] This comparative example is substantially the same as Example 1, except that the amount of cadmium nitrate added is 0.025 mmol, that is, the molar ratio of cadmium nitrate to zinc chloride is 10:100, and the obtained product is named C10-ZIS.

[0060] Fig.16 The XRD pattern shown shows that C10-ZIS is a hexagonal phase of ZnIn2S4. Fig.17 The SEM image of C10-ZIS is shown, showing the morphology of agglomerated nanoflowers. Fig.18 It is the solid UV DRS image of C10-ZIS, showing the absorbance and band gap of C10-ZIS. Fig.19 This is the linear sweep voltammetry (LSV) test of C10-ZIS. It can be seen that at 1.23V vs RHE, the photocurrent density is 1.6mA / cm 2 The results show that the photoelectric activity of the catalyst is higher than that of ZIS not doped with Cd, but lower than that of C-ZIS prepared in Example 1.

[0061] Comparative Example 4

[0062] This comparative example is substantially the same as Example 1, except that the amount of cadmium nitrate added is 0.05 mmol, that is, the molar ratio of cadmium nitrate to zinc chloride is 20:100, and the obtained product is named C20-ZIS.

[0063] Fig. 20 The XRD pattern shown shows that C20-ZIS contains not only the hexagonal phase ZnIn2S4, but also the crystal form corresponding to CdS. Fig.21 This is the linear sweep voltammetry (LSV) test of C20-ZIS. It can be seen that at 1.23 V vs RHE, the photocurrent density is 1.6 mA / cm 2 This result indicates that the photoelectric activity of this catalyst is lower than that of C-ZIS.

[0064] Comparative Example 5

[0065] This comparative example is substantially the same as Example 1, except that the hydrothermal reaction is carried out at 140°C, and the obtained product is named CZIS-140°C.

[0066] Fig. 22This is the XRD pattern of CZIS-140℃, which shows that the synthesis temperature is not enough to generate any crystalline phase of ZnIn2S4.

[0067] Comparative Example 6

[0068] This comparative example is substantially the same as Example 1, except that the hydrothermal reaction is carried out at 180°C, and the obtained product is named CZIS-180°C.

[0069] Fig.23 This is the XRD spectrum of CZIS-180℃, which shows that CZIS-180℃ contains both hexagonal ZnIn2S4 and rhombohedral ZnIn2S4. Compared with C-ZIS, the intensity of the characteristic peak corresponding to the hexagonal phase is enhanced, while the intensity of the characteristic peak corresponding to the rhombohedral phase is weakened.

[0070] Comparative Example 7

[0071] Weigh 0.25mmol of zinc chloride, 0.5mmol of indium chloride and 1mmol of thiourea in a beaker containing 25mL of deionized water, dissolve them evenly by ultrasonication, and obtain a precursor solution. Wash FTO with acetone, ethanol and water for 20min respectively and dry them. Place the washed FTO conductive surface downward in a polytetrafluoroethylene kettle, and then place the precursor solution in a polytetrafluoroethylene hydrothermal reactor for hydrothermal reaction at 160℃ for 6h; wash the hydrothermal product with ethanol and deionized water three times respectively, and then dry it in a vacuum oven at 60℃ for 12h to obtain a photoelectric catalyst, and the obtained product is named ZIS. Weigh 5mmol of cadmium nitrate in a beaker, add 50ml of deionized water, dissolve them evenly by ultrasonication, place ZIS in the solution, react in an oven at 60℃ for 1h, wash the obtained product with ethanol and deionized water three times respectively, and then dry it in a vacuum oven at 60℃ for 12h to obtain a photoelectric catalyst, and the obtained product is named 1C-ZIS.

[0072] Fig.24 This is the XRD pattern of 1C-ZIS, showing that only rhombohedral phase ZnIn2S4 exists in 1C-ZIS. Fig.25 This is the linear sweep voltammetry (LSV) test of 1C-ZIS. It can be seen that at 1.23V vs RHE, the photocurrent density is 1mA / cm 2 , and the current shows a trend of first increasing and then decreasing. This result shows that the photoelectric activity of the catalyst is much lower than that of C-ZIS in Example 1, and its stability is very poor.

[0073] Comparative Example 8

[0074] This comparative example is substantially the same as comparative example 7, except that the reaction was carried out in an oven at 60° C. for 6 h. The obtained product was named 6C-ZIS.

[0075] Fig.26 The XRD spectrum of 6C-ZIS shows that 6C-ZIS contains not only the characteristic peaks of the rhombohedral phase ZnIn2S4, but also the characteristic peaks of other substances, which indicates that it is impossible to complete the phase transformation under this method.

Claims

1. A method for preparing homojunction Cd-ZnIn2S4 photoelectrocatalyst by in-situ cation doping, characterized in that: The following steps are involved: According to the molar ratio of cadmium nitrate to zinc chloride of 5:100, cadmium nitrate, zinc chloride, indium chloride and thiourea were ultrasonically dissolved in deionized water to obtain a precursor solution, which was then poured into a polytetrafluoroethylene hydrothermal autoclave, and clean conductive glass was placed therein to carry out a hydrothermal reaction at 160-180°C. After the reaction was completed, the homojunction Cd-ZnIn2S4 photoelectric catalyst was obtained by washing and drying.

2. The method according to claim 1, characterized in that The conductive glass is FTO conductive glass.

3. The method according to claim 1, characterized in that The conductive glass was cleaned with acetone, ethanol and water for 15-20 min each, and then dried at 60±10 ℃ to obtain clean conductive glass.

4. The method according to claim 1, characterized in that In the precursor solution, the concentration of zinc chloride is 0.01 mol / L, the concentration of indium chloride is 0.02 mol / L, the concentration of thiourea is 0.04 mol / L, and the concentration of cadmium nitrate is 0.0005 mol / L.

5. The method according to claim 1, characterized in that The hydrothermal reaction time was 6±2 h.

6. The method according to claim 1, characterized in that The washing method is to wash twice with ethanol and water in sequence.

7. The method according to claim 1, characterized in that The drying temperature is 60±10 ℃ and the drying time is 12±2h.

Images