Preparation method and application of heterojunction structure adjustable composite material

Abstract

The invention discloses a preparation method and application of a heterojunction structure adjustable composite material, and belongs to the field of photochemical energy conversion and energy band engineering. The invention aims to solve the problem of improving the photochemical energy conversion efficiency by optimizing and improving a heterojunction photocatalyst and adjusting the type of a heterojunction. The method comprises the following steps: 1, dispersing titanium dioxide, strontium nitrate and potassium hydroxide in water for hydrothermal reaction, cooling, washing and drying to obtain STO powder; and 2, dispersing the STO, cadmium acetate dehydrate and thioacetamide in water for water bath reaction, cooling, washing and drying to obtain the I-type heterojunction composite material CSTO-I. And 3, adding iron nitrate nonahydrate on the basis of the step 1 to obtain FSTO powder. And 4, replacing STO with FSTO on the basis of the step 2 to obtain the II-type heterojunction composite material CFSTO-II. And 5, adding zinc acetate on the basis of the step 4 to obtain the S-type heterojunction composite material ZCFSTO-S.

Description

Technical Field

[0001] The invention belongs to the field of photochemical energy conversion and energy band engineering. Background Art

[0002] In recent years, the method of improving the performance of photocatalysts by constructing heterojunctions has attracted the attention of many researchers. The construction of appropriate heterojunctions can significantly improve the separation efficiency of photogenerated carriers, thereby enhancing the redox ability of photocatalysts. The understanding and development of heterojunction materials in the field of photocatalysis has gone through the following stages. (1) Type I heterojunction photocatalysts: The CB (conduction band) and VB (valence band) of PSⅠ (relatively high Fermi level) are higher and lower than the conduction band and valence band of PSⅡ (relatively low Fermi level), respectively. Under photoexcitation, electrons and holes accumulate on the CB and VB of PSⅡ, respectively. Both electrons and holes accumulate on the same semiconductor, and electron-hole pairs cannot be effectively separated. (2) Type II heterojunction photocatalysts: The CB and VB energy levels of PSⅠ are higher than the corresponding energy levels of PSⅡ. Under photoexcitation, photogenerated electrons transfer to PSⅡ, while photogenerated holes migrate to PSⅠ under light irradiation, resulting in the spatial separation of electron-hole pairs. (3) S-scheme heterojunction photocatalyst: The CB and VB energy levels of PS I are higher than the corresponding energy levels of PS II, and the direction of the built-in electric field formed is opposite to that of the II-type heterojunction. Under light excitation, the electrons in the conduction band of PS II transfer to the valence band of PS I, promoting the recombination of carriers with lower redox potentials, thereby leaving photogenerated electrons and photogenerated holes with higher redox potentials on PS I and PS II, respectively. Obviously, the S-type heterojunction can maximize the redox thermodynamic potential of the catalyst, is the most optimized heterojunction structure, and is also the artificial photosynthetic structure that researchers have focused on developing in recent years. Limited by the strict band structure requirements of the S-type heterojunction for the two semiconductor materials, the construction and optimization of this type of catalyst is still very difficult, and has become a major research hotspot in the field of catalysis at this stage.

[0003] Among many semiconductor photocatalytic materials, strontium titanate (SrTiO3) is a typical perovskite structure n-type semiconductor with advantages such as excellent thermal stability, high dielectric constant and low dielectric loss. Therefore, it has a wide range of applications in electronics, mechanics, ceramics, catalysis and many other fields. However, due to its wide bandgap of 3.2eV, it only responds to ultraviolet light and has a low utilization rate of the solar spectrum, which limits its application. Cadmium sulfide (CdS) is a typical narrow bandgap semiconductor with a bandgap of about 2.4eV. It has wide solar spectrum light-harvesting characteristics and excellent photocatalytic activity, and is the most active target for catalyst modification and heterostructure construction. Coincidentally, the band structure and Fermi level relative position of CdS and SrTiO3 conform to the type I heterojunction type. Therefore, the present invention will transform the heterojunction type based on the type I CdS / SrTiO3 heterojunction composite material by using the band engineering principle and element doping technology, and obtain the type II CdS / Fe-SrTiO3 heterojunction composite material and the S-type Zn-CdS / Fe-SrTiO3 heterojunction composite material respectively. The patent of this invention provides a heterojunction modulation optimization strategy and feasible method, providing new ideas for the development of new high-efficiency solar energy conversion materials. Summary of the invention

[0004] The present invention relates to the optimization and improvement of heterojunction photocatalysts, and thus proposes a method for adjusting the heterojunction type through a band engineering doping strategy. To solve the above problems, a preparation method of a heterojunction structure adjustable composite material and its application in the present invention are completed by the following steps.

[0005] Step 1: Disperse titanium dioxide, strontium nitrate and potassium hydroxide in deionized water, stir thoroughly and transfer to a reactor for hydrothermal reaction, cool to room temperature and wash and dry to obtain SrTiO3 solid powder, recorded as STO.

[0006] Step 2: Disperse the STO, cadmium acetate dihydrate and thioacetamide prepared in step 1 in deionized water for water bath reaction, cool to room temperature, wash and dry to obtain a type I heterojunction composite material CdS / SrTiO3, recorded as CSTO-I.

[0007] Step 3: Disperse titanium dioxide, strontium nitrate, potassium hydroxide and ferric nitrate nonahydrate in deionized water, stir thoroughly and transfer to a reactor for hydrothermal reaction, cool to room temperature and wash and dry to obtain Fe-doped SrTiO3 (Fe-SrTiO3) solid powder, recorded as FSTO.

[0008] Step 4: Disperse the FSTO, cadmium acetate dihydrate and thioacetamide prepared in step 3 in deionized water for water bath reaction, cool to room temperature, wash and dry to obtain a type II heterojunction composite material CdS / Fe-SrTiO3, recorded as CFSTO-II.

[0009] Step 5: Disperse the FSTO, cadmium acetate dihydrate, zinc acetate and thioacetamide prepared in step 3 in deionized water for water bath reaction, cool to room temperature, wash and dry to obtain an S-type heterojunction composite material Zn-CdS / Fe-SrTiO3, recorded as ZCFSTO-S.

[0010] It is further defined that in step 1, 750-850 mg of titanium dioxide, 2.5-3.0 g of strontium nitrate, and 1.5-2.0 g of potassium hydroxide are dissolved in 20-40 ml of deionized water.

[0011] It is further defined that the hydrothermal reaction temperature in step 1 is 180-220° C., and the hydrothermal reaction time is 10-14 h.

[0012] It is further defined that the washing conditions in step 1 are washing with deionized water and ethanol at room temperature three times each, and the drying conditions are keeping warm at 60° C. in a vacuum drying oven for 12 hours.

[0013] It is further defined that in step 2, 80-120 mg of STO, 350-400 mg of cadmium acetate dihydrate, and 110-120 mg of thioacetamide are added to 40-60 ml of deionized water in sequence.

[0014] It is further defined that in step 2, the water bath reaction temperature is 60-90° C., the water bath reaction time is 2-4 hours, and the washing and drying conditions are the same as those in step 1.

[0015] It is further defined that in step three, 750-850 mg of titanium dioxide, 2.5-3.0 g of strontium nitrate, 1.5-2.0 g of potassium hydroxide, and 150-170 mg of ferric nitrate nonahydrate are dissolved in 20-40 ml of deionized water, and the hydrothermal reaction, washing, and drying conditions are the same as those in step one.

[0016] Further defined, in step 4, 80-120 mg of FSTO, 350-400 mg of cadmium acetate dihydrate, and 110-120 mg of thioacetamide are added to 40-60 ml of deionized water, the water bath reaction conditions are the same as those in step 2, and the washing and drying conditions are the same as those in step 1.

[0017] Further defined, in step five, 80-120 mg of FSTO, 35-40 mg of cadmium acetate dihydrate, 240-260 mg of zinc acetate, and 110-120 mg of thioacetamide are added to 50 ml of deionized water, the water bath reaction conditions are the same as those in step two, and the washing and drying conditions are the same as those in step one.

[0018] The CSTO-I heterojunction catalyst prepared by the method of the present invention is a type I heterojunction, the CFSTO-II heterojunction catalyst prepared by iron doping strontium titanate is a type II heterojunction, and the ZCFSTO-S prepared by adding zinc to CdS to form a zinc-cadmium solid solution is an S-type heterojunction. The present invention provides a technical method for adjusting the heterojunction type through a band engineering doping strategy, thereby improving the application performance of the photocatalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the XRD pattern of STO, FSTO, CSTO-Ⅰ, CFSTO-Ⅱ and ZCFSTO-S; Figure 2 These are SEM photos of STO, FSTO, CSTO-Ⅰ, CFSTO-Ⅱ, and ZCFSTO-S, and the upper right illustration is the actual picture; Figure 3 It is the XPS spectra of STO, FSTO, CSTO-Ⅰ, CFSTO-Ⅱ and ZCFSTO-S; Figure 4 It is the Mott-Schottky spectrum of STO, FSTO, CSTO-Ⅰ, CFSTO-Ⅱ, and ZCFSTO-S; Figure 5 It is the SPV spectrum of CdS, CSTO-Ⅰ, CFSTO-Ⅱ, and ZCFSTO-S; Figure 6 These are the photocatalytic reduction degradation curves of STO, FSTO, CSTO-Ⅰ, CFSTO-Ⅱ and ZCFSTO-S to potassium dichromate indicator solution. DETAILED DESCRIPTION

[0020] Step 1: Disperse 800 mg titanium dioxide, 2.6 g strontium nitrate, and 1.7 g potassium hydroxide in 30 ml deionized water, stir thoroughly, transfer to a 50 ml reactor, and react at 200°C for 12 hours. Wash the product with deionized water and ethanol three times each, and dry it in a vacuum drying oven at 60°C for 12 hours to obtain SrTiO3 solid powder, recorded as STO.

[0021] Step 2: Disperse 100 mg STO, 392 mg cadmium acetate dihydrate and 110 mg thioacetamide prepared in step 1 in 50 ml deionized water, stir for 30 min to fully disperse, heat to 80 ° C and continue stirring for 3 h. Wash the product with deionized water and ethanol three times each, dry it in a vacuum drying oven at 60 ° C for 12 h, and obtain a type I heterojunction composite material CdS / SrTiO3, recorded as CSTO-I.

[0022] Step 3: Disperse 800 mg titanium dioxide, 2.6 g strontium nitrate, 1.7 g potassium hydroxide, and 162 mg ferric nitrate nonahydrate in 30 ml deionized water, transfer to a 50 ml reactor after sufficient stirring, and react at 200°C for 12 hours. Wash the product with deionized water and ethanol three times each, and dry it in a vacuum drying oven at 60°C for 12 hours to obtain Fe-doped SrTiO3 (Fe-SrTiO3) solid powder, recorded as FSTO.

[0023] Step 4: Disperse 100 mg FSTO, 392 mg cadmium acetate dihydrate and 110 mg thioacetamide prepared in step 3 in 50 ml deionized water, stir for 30 min to fully disperse, heat to 80 ° C and continue stirring for 3 h. Wash the product with deionized water and ethanol three times each, dry it in a vacuum drying oven at 60 ° C for 12 h, and obtain a type II heterojunction composite material CdS / Fe-SrTiO3, recorded as CFSTO-II.

[0024] Step 5: Disperse 100 mg FSTO, 39 mg cadmium acetate dihydrate, 243 mg zinc acetate and 110 mg thioacetamide prepared in step 3 in 50 ml deionized water, stir for 30 min to fully disperse, heat to 80 ° C and continue stirring for 3 h. Wash the product with deionized water and ethanol three times each, dry it in a vacuum drying oven at 60 ° C for 12 h, and obtain an S-type heterojunction composite material Zn-CdS / Fe-SrTiO3, recorded as ZCFSTO-S.

[0025] The photocatalytic reduction degradation of potassium dichromate solution uses a 300W xenon lamp to simulate sunlight. Place 10mg of the catalyst to be tested and 30mL of a 40mg / L potassium dichromate indicator solution in a 100mL beaker. Fix the beaker 5cm in front of the light source and maintain uniform magnetic stirring during the degradation reaction. Take the same time interval to detect the absorbance of the reaction solution, and calculate the concentration of the reaction solution to make a curve of the degradation rate changing with the illumination time, so as to analyze and evaluate the photocatalytic activity of the sample. Figure 6 shown.

[0026] from Figure 6 It can be seen that among the three heterojunction composite materials of CSTO-Ⅰ, CFSTO-Ⅱ and ZCFSTO-S, ZCFSTO-S has the best performance, degrading 92% of the potassium dichromate indicator solution in 6 minutes, and the degradation rate reaches 60.38μmol·min -1 ·g cat -1. CFSTO-Ⅱ is second, and CSTO-Ⅰ is the worst. The above performance shows that the modulation of heterojunction structure type is of great significance to the improvement of catalyst activity. The excellent S-type heterojunction catalyst significantly improves the separation efficiency of photogenerated carriers, which not only prolongs the lifetime of photogenerated electrons, but also effectively increases the reaction thermodynamic potential energy of photogenerated electrons, which is manifested in the significant improvement of the photocatalytic degradation performance of the material.

Claims

1. A method for preparing a heterojunction structured tunable composite material and its application, characterized in that The preparation method is completed by the following steps: Step 1, dispersing titanium dioxide, strontium nitrate, potassium hydroxide in deionized water, transferring to a reactor after sufficient stirring for hydrothermal reaction, washing and drying after cooling to room temperature to obtain SrTiO3 solid powder, recorded as STO. Step 2, dispersing the STO, cadmium acetate dihydrate, and thioacetamide obtained in step 1 in deionized water for water bath reaction, washing and drying after cooling to room temperature to obtain a type I heterojunction composite material CdS / SrTiO3, recorded as CSTO-I. Step 3, dispersing titanium dioxide, strontium nitrate, potassium hydroxide, and iron nitrate nonahydrate in deionized water, transferring to a reactor after sufficient stirring for hydrothermal reaction, washing and drying after cooling to room temperature to obtain Fe-doped SrTiO3 (Fe-SrTiO3) solid powder, recorded as FSTO. Step 4: Disperse the FSTO, cadmium acetate dihydrate and thioacetamide obtained in step 3 in deionized water for water bath reaction, cool to room temperature, wash and dry to obtain a type II heterojunction composite material CdS / Fe-SrTiO3, recorded as CFSTO-II. Step 5: Disperse the FSTO, cadmium acetate dihydrate, zinc acetate and thioacetamide obtained in step 3 in deionized water for water bath reaction, cool to room temperature, wash and dry to obtain an S-type heterojunction composite material Zn-CdS / Fe-SrTiO3, recorded as ZCFSTO-S.

2. The method according to claim 1, characterized in that In step 1, 750-850 mg of titanium dioxide, 2.5-3.0 g of strontium nitrate, and 1.5-2.0 g of potassium hydroxide are dissolved in 20-40 ml of deionized water.

3. The method according to claim 1, characterized in that In step 1, the hydrothermal reaction temperature is 180-220° C., and the hydrothermal reaction time is 10-14 h.

4. The method according to claim 1, characterized in that In step 1, the washing conditions are three times of deionized water and ethanol at room temperature, and the drying conditions are kept at 60° C. in a vacuum drying oven for 12 h.

5. The method according to claim 1, characterized in that In step 2, 80-120 mg of STO, 350-400 mg of cadmium acetate dihydrate, and 110-120 mg of thioacetamide are added to 40-60 ml of deionized water in sequence.

6. The method according to claim 1, characterized in that In step 2, the water bath reaction temperature is 60-90° C., the water bath reaction time is 2-4 hours, and the washing and drying conditions are the same as those in step 1.

7. The method according to claim 1, characterized in that In step three, 750-850 mg of titanium dioxide, 2.5-3.0 g of strontium nitrate, 1.5-2.0 g of potassium hydroxide, and 150-170 mg of ferric nitrate nonahydrate are dissolved in 20-40 ml of deionized water. The hydrothermal reaction, washing, and drying conditions are the same as those in step one.

8. The method according to claim 1, characterized in that In step 4, 80-120 mg of FSTO, 350-400 mg of cadmium acetate dihydrate, and 110-120 mg of thioacetamide are added to 40-60 ml of deionized water. The water bath reaction conditions are the same as those in step 2, and the washing and drying conditions are the same as those in step 1.

9. The method according to claim 1, characterized in that In step 5, 80-120 mg of FSTO, 35-40 mg of cadmium acetate dihydrate, 240-260 mg of zinc acetate, and 110-120 mg of thioacetamide are added to 50 ml of deionized water. The water bath reaction conditions are the same as those in step 2, and the washing and drying conditions are the same as those in step 1.

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