A Bi / BiVO 4 Preparation method of composite heterojunction photocatalytic material

Abstract

The present invention provides a preparation method of a Bi / BiVO4 composite heterojunction photocatalytic material, comprising the following steps: mixing BiVO4 with an organic reducing agent, preheating and evacuating, and then heating to a reaction temperature under the protection of an inert gas for an in-situ reduction reaction. The preparation method of the present invention uses BiVO4 as a raw material, and in-situ reduces and synthesizes a Bi / BiVO4 composite heterojunction photocatalytic material by a solvothermal method in an organic reducing agent. The method has simple steps and convenient operation, and obtains a Bi / BiVO4 composite heterojunction photocatalytic material with good crystallization and uniform particles. The composite ratio of Bi and BiVO4 can be adjusted by the reaction time at the reaction temperature, and the controllability is high.

Description

Technical Field

[0001] The invention belongs to the field of composite material preparation, and in particular relates to a method for preparing a Bi / BiVO4 composite heterojunction photocatalytic material. Background Art

[0002] The sustainable development of the industrial economy of human society is constrained by environmental pollution, energy crisis and greenhouse effect. As a clean and renewable energy source, solar energy is of great significance in improving environmental quality and alleviating energy shortage. Semiconductor photocatalytic technology is one of the effective methods to utilize solar energy. It is based on the fact that when the photocatalyst is illuminated, the electrons in the valence band of the semiconductor are excited and transferred to the conduction band, forming photogenerated electrons and holes with strong oxidation and reduction capabilities, thereby generating a strong redox potential, leading to the cleavage of water molecules or the degradation of pollutants. It has the advantages of low energy consumption, high efficiency, and green friendliness, and is valued by energy and environmental workers.

[0003] Bismuth-based semiconductors are a new type of photocatalytic material. They have attracted widespread attention for their excellent visible light absorption capacity, high photocatalytic activity, non-toxicity and low price. As a promising new type of photocatalytic material, they have a very broad development space in the development of new energy and environmental purification. Among them, monoclinic BiVO4 is favored for its narrow bandgap and high photocatalytic activity under visible light, but its photocatalytic performance is limited by its high recombination rate of photogenerated electron pairs and holes and slow oxygen absorption kinetics on the surface. Therefore, morphology control, ion doping, heterojunction construction, auxiliary catalyst loading and other methods are common strategies to improve the photocatalytic efficiency of BiVO4 and broaden its application.

[0004] In addition, the composite of precious metals and semiconductors can also effectively improve the photocatalytic efficiency. A certain amount of precious metals loaded on the surface of the semiconductor as a photogenerated electron acceptor changes the distribution and transmission of electrons in the system, inhibits the recombination of electron-hole pairs, and thus improves the photocatalytic quantum yield. In addition, precious metals such as Au exhibit a plasma resonance effect (SPR), provide additional visible light absorption and promote charge separation. Therefore, coupling BiVO4 with metals or other matching semiconductors to make composite materials is also one of the commonly used methods for modifying the photocatalytic efficiency of BiVO4. Bismuth (Bi), as a typical semi-metallic material, has unique characteristics such as small band gap energy, low effective mass, large mean free path, and large carrier movement. At the same time, compared with precious metals, semi-metal Bi has an SPR effect, which can become a perfect SPR nanostructure candidate in the process of composite with BiVO4 and avoid the influence of foreign elements. In addition, Bi as a photocatalytic material can effectively degrade a variety of liquid and gas phase pollutants including potassium dichromate, rhodamine B, methyl blue, Congo red, and p-chlorophenol, and is widely studied. If Bi and BiVO4 can be compounded, it will be an effective way to replace precious metal composites economically and practically.

[0005] At present, research work at home and abroad is mainly focused on optimizing the synergistic effect of Bi / BiVO4 composite materials on visible light capture ability and the stability of photocatalytic activity. Li Shuwen et al. used a solvothermal method to synthesize Bi / BiVO4 using sodium orthovanadate as a vanadium source, bismuth chloride and hydrated bismuth nitrate as bismuth sources, respectively, and found that the electron-hole separation ability was enhanced after Bi self-doping; Hu Yin et al. used BiVO4 prepared by the sol-gel method to hydrothermally prepare Bi / BiVO4 heterostructure materials with commercial Bi powder, and the obtained materials had a high degradation effect on rhodamine B. However, the above preparations were all under aqueous conditions, the materials aggregated and did not disperse, and the obtained Bi / BiVO4 particles were uneven in size, which in turn affected the photocatalytic effect. Summary of the invention

[0006] In view of this, the present invention aims to propose a method for preparing a Bi / BiVO4 composite heterojunction photocatalytic material, so as to achieve in-situ reduction of Bi on the BiVO4 surface to obtain a Bi / BiVO4 heterojunction composite system.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for preparing a Bi / BiVO4 composite heterojunction photocatalytic material comprises the following steps:

[0009] BiVO4 is mixed with an organic reducing agent, preheated and evacuated, and then heated to a reaction temperature under the protection of an inert gas to perform an in-situ reduction reaction, wherein Bi is obtained by in-situ reduction on the surface of BiVO4, and the composite ratio of Bi to BiVO4 is controlled by the reaction time at the reaction temperature.

[0010] Preferably, the organic reducing agent is oleylamine.

[0011] Preferably, the preheating temperature is 150°C, the vacuuming time is more than 30 minutes, and the reaction temperature is 250-290°C.

[0012] Preferably, the inert gas is nitrogen.

[0013] Preferably, the usage ratio of BiVO4 to the organic reducing agent is 1 g:100 ml.

[0014] Preferably, the preparation method of BiVO4 comprises the following steps:

[0015] (1) mixing bismuth nitrate pentahydrate, polyvinyl pyrrolidone, and ethylene glycol to obtain a solution A;

[0016] (2) mixing sodium metavanadate and deionized water to obtain solution B;

[0017] (3) adding solution B dropwise to solution A and mixing well to obtain a mixed solution;

[0018] (4) The mixed solution was placed in a reactor and subjected to hydrothermal reaction at 180°C for 10 h.

[0019] Preferably, the method further comprises the following steps:

[0020] The reaction product is cleaned and dried to obtain the desired Bi / BiVO4 composite heterojunction photocatalytic material.

[0021] Preferably, the cleaning method is to use toluene and anhydrous ethanol to wash alternately three times.

[0022] Preferably, the drying temperature is 60° C. and the drying time is 12 h.

[0023] The application of the preparation method as described above in the field of photocatalytic degradation.

[0024] Compared with the prior art, the preparation method of the Bi / BiVO4 composite heterojunction photocatalytic material of the present invention has the following advantages:

[0025] (1) The preparation method of the present invention uses BiVO4 as a raw material, and prepares a Bi / BiVO4 composite heterojunction photocatalytic material by in-situ reduction synthesis in an organic reducing agent by a solvothermal method. The method has simple steps and is easy to operate. A Bi / BiVO4 composite heterojunction photocatalytic material with good crystallization and uniform particles is obtained. The composite ratio of Bi and BiVO4 can be adjusted by the reaction time at the reaction temperature, and the controllability is high.

[0026] (2) The preparation method of the present invention uses oleylamine as an organic reducing agent and a ligand to reduce the Bi on the surface of BiVO4 3+ In-situ reduction generates Bi nanoparticles, avoiding the introduction of other impurities;

[0027] (3) The BiVO4 raw material used in the preparation method of the present invention is synthesized by a hydrothermal method, and its morphology is a rugby-shaped structure with wrinkles on the surface and full of fine pores, which can provide a template for the growth of Bi nanoparticles, prepare a composite system with good crystallization and uniform particles, change the flow and distribution of electrons in the system, and also make the two have better contact when degrading pollutants, thereby improving the photocatalytic performance of the material;

[0028] (4) The raw materials used in the preparation method described in the present invention are all non-toxic, green and environmentally friendly, and are environmentally friendly reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 This is a scanning electron microscope photograph of BiVO4 described in an embodiment of the present invention;

[0031] Figure 2 X-ray diffraction patterns of Bi / BiVO4 composite heterojunction photocatalytic materials prepared in Examples 1, 2, and 3 of the present invention, wherein a is Example 1, b is Example 2, and c is Example 3;

[0032] Figure 3 X-ray diffraction patterns of Bi / BiVO4 composite heterojunction photocatalytic materials prepared in Examples 3, 4, 5, and 6 of the present invention, wherein a is Example 3, b is Example 4, c is Example 5, and d is Example 6;

[0033] Figure 4 This is a scanning electron micrograph of the Bi / BiVO4 composite heterojunction photocatalytic material prepared in Example 3;

[0034] Figure 5This is a scanning electron micrograph of the Bi / BiVO4 composite heterojunction photocatalytic material prepared in Example 4;

[0035] Figure 6 This is a scanning electron micrograph of the Bi / BiVO4 composite heterojunction photocatalytic material prepared in Example 5;

[0036] Figure 7 This is a scanning electron micrograph of the Bi / BiVO4 composite heterojunction photocatalytic material prepared in Example 6;

[0037] Figure 8 This is a graph showing the degradation rate of the BiVO4 described in the embodiment of the present invention and the Bi / BiVO4 composite heterojunction photocatalytic material prepared in Examples 3, 4, 5, and 6 for photodegradation of Rhodamine B solution. DETAILED DESCRIPTION

[0038] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0039] The present invention will be described in detail below with reference to the embodiments and the accompanying drawings.

[0040] Example 1

[0041] 1. Preparation of BiVO4 by hydrothermal method

[0042] 1.1 Wash the 50mL polytetrafluoroethylene reactor with tap water, distilled water, and anhydrous ethanol 1-3 times respectively, and dry it for later use;

[0043] 1.2 Use an electronic balance to weigh 0.1617g Bi(NO3)3·5H2O and 1g polyvinyl pyrrolidone in a clean beaker with a volume of 50mL, then add 25mL of ethylene glycol, stir and mix evenly, and mark it as solution A; weigh 0.06g NaVO3 in a clean beaker with a volume of 50mL, then add 15mL of deionized water, stir and mix evenly, and mark it as solution B. Then, while solution A is vigorously stirred, add solution B drop by drop into solution A. After stirring and mixing evenly, transfer the obtained mixture to a 50mL polytetrafluoroethylene reactor and place it at 180℃ for hydrothermal reaction for 10h. After the reaction is completed, cool it to room temperature, wash the reaction product alternately with anhydrous ethanol and deionized water 3 times, and dry it at 80℃ for 4h to obtain BiVO4. The product is bright yellow powder particles. The microstructure under a scanning electron microscope is a rugby-shaped structure with regular shape and uniform size, such as Figure 1 shown.

[0044] 2. Preparation of Bi / BiVO4 composite heterojunction photocatalytic materials

[0045] 2.1 Wash a 50 mL two-necked flask with tap water, distilled water, and anhydrous ethanol twice each, and dry it for later use;

[0046] 2.2 Add 0.1g BiVO4 prepared by hydrothermal method to a clean two-necked flask with a volume of 50mL, then add 10mL oleylamine and stir to mix evenly, heat to 150℃ under magnetic stirring and evacuate for 30min to remove internal oxygen and moisture, then heat to 250℃ under nitrogen protection and react at this temperature for 30min. After the reaction, the product is washed alternately with toluene and anhydrous ethanol three times, dried at 60℃ for 12h, and the Bi / BiVO4 composite heterojunction photocatalytic material is obtained after in-situ reduction for 30min. The product is dark green powder particles, and its crystal structure is characterized by X-ray powder diffractometer, such as Figure 2 As shown in the curve a in the middle.

[0047] Example 2

[0048] The difference from Example 1 is that in step 2.2, the temperature is raised to 270°C under nitrogen protection and the reaction is carried out at this temperature for 30 minutes. The other operation steps are the same as those in Example 1. The Bi / BiVO4 composite heterojunction photocatalytic material after in-situ reduction for 30 minutes is obtained. The product is dark green powder particles, and its crystal structure is characterized by an X-ray powder diffractometer, as shown in FIG. Figure 2 As shown in curve b.

[0049] Example 3

[0050] The difference from Example 1 is that in step 2.2, the temperature is raised to 290°C under nitrogen protection and the reaction is carried out at this temperature for 30 minutes. The other operation steps are the same as those in Example 1. The Bi / BiVO4 composite heterojunction photocatalytic material after in-situ reduction for 30 minutes is obtained. The product is dark green powder particles, and its crystal structure is characterized by an X-ray powder diffractometer, as shown in FIG. Figure 2 The c curve and Figure 3 As shown in the curve a in the figure, the microstructure under the scanning electron microscope is a loose structure with uniform distribution of large and small particles, such as Figure 4 shown.

[0051] Example 4

[0052] The difference from Example 3 is that in step 2.2, the temperature is raised to 290°C under nitrogen protection and the reaction is carried out at this temperature for 1 hour. The other operation steps are the same as those in Example 1. The Bi / BiVO4 composite heterojunction photocatalytic material is obtained after in-situ reduction for 1 hour. The product is black powder particles, and its crystal structure is characterized by an X-ray powder diffractometer, as shown in FIG. Figure 3As shown in the curve b, the microstructure under the scanning electron microscope is a loose structure with uniform distribution of large and small particles, such as Figure 5 shown.

[0053] Example 5

[0054] The difference from Example 3 is that in step 2.2, the temperature is raised to 290°C under nitrogen protection and the reaction is carried out at this temperature for 2 hours. The other operation steps are the same as those in Example 1. The Bi / BiVO4 composite heterojunction photocatalytic material is obtained after in-situ reduction for 2 hours. The product is black powder particles, and its crystal structure is characterized by an X-ray powder diffractometer, as shown in FIG. Figure 3 As shown in the curve c, the microstructure under a scanning electron microscope is a loose structure with uniform distribution of large and small particles, such as Figure 6 shown.

[0055] Example 6

[0056] The difference from Example 3 is that in step 2.2, the temperature is raised to 290°C under nitrogen protection and the reaction is carried out at this temperature for 3 hours. The other operation steps are the same as those in Example 1. The Bi / BiVO4 composite heterojunction photocatalytic material is obtained after in-situ reduction for 3 hours. The product is black powder particles, and its crystal structure is characterized by an X-ray powder diffractometer, as shown in FIG. Figure 3 As shown in the curve d in the figure, the microstructure under the scanning electron microscope is a loose structure with uniform distribution of large and small particles, such as Figure 7 shown.

[0057] like Figure 2 and Figure 3 As shown, except for the Bi diffraction peak marked with ◆, the other peaks all correspond to the standard diffraction peak of BiVO4 with the bottom vertical line, and no other impurity peaks appear.

[0058] Photocatalytic effect verification

[0059] 1. Prepare 10mg·L -1 Rhodamine B solution; wash a 50 mL glass test tube and a 4.5 mL quartz cuvette twice with distilled water and anhydrous ethanol respectively, and dry them for later use;

[0060] 2. Add 10 mg of the Bi / BiVO4 composite materials prepared in Examples 3, 4, 5, and 6 and the BiVO4 prepared in Example 1 to 5 clean glass test tubes with a volume of 50 mL, respectively, and then add 30 mL of rhodamine B solution (10 mg·L -1), after being evenly dispersed by ultrasonic, put it into a photocatalytic reactor and stir it for 1 hour under light-proof conditions to allow the sample and the solution to reach adsorption-desorption equilibrium. Then, a photocatalytic degradation experiment was carried out under 300W ultraviolet light. A certain amount of solution was centrifuged every 30 minutes, and the supernatant was taken to measure the change in its absorbance. The degradation rate was as follows: Figure 8 As shown, the degradation time is 2.5 h, and the degradation rates of the Bi / BiVO4 composite materials prepared in Examples 3, 4, 5, and 6 and the BiVO4 prepared in Example 1 are 53%, 78%, 45%, 27%, and 34%, respectively.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a Bi / BiVO4 composite heterojunction photocatalytic material, characterized in that: The following steps are involved: (1) Preparation of BiVO4 by hydrothermal method (1.1) Wash a 50 mL polytetrafluoroethylene reactor with tap water, distilled water, and anhydrous ethanol 1-3 times each, and dry it for later use; (1.2) Use an electronic balance to weigh 0.1617g Bi(NO3)3·5H2O and 1g polyvinylpyrrolidone into a clean beaker with a volume of 50mL, then add 25mL of ethylene glycol, stir and mix until evenly, and mark it as solution A; weigh 0.06g NaVO3 into a clean beaker with a volume of 50mL, then add 15mL of deionized water, stir and mix until evenly, and mark it as solution B; then, while solution A is vigorously stirred, solution B is added dropwise into solution A; after stirring and mixing until evenly, the obtained mixture is transferred to a 50mL polytetrafluoroethylene reactor and placed at 180℃ for hydrothermal reaction for 10h; after the reaction is completed, it is cooled to room temperature, and the reaction product is washed alternately with anhydrous ethanol and deionized water for 3 times, and dried at 80℃ for 4h to obtain BiVO4; the product is bright yellow powder particles; the microstructure under a scanning electron microscope is a rugby-shaped structure with regular shape and uniform size; (2) Preparation of Bi / BiVO4 composite heterojunction photocatalytic materials (2.1) Wash a 50 mL two-necked flask with tap water, distilled water, and anhydrous ethanol twice each, and dry it for later use; (2.2) 0.1 g of BiVO4 prepared by hydrothermal method was added to a clean two-necked flask with a volume of 50 mL, and then 10 mL of oleylamine was added and stirred to mix evenly. The temperature was raised to 150°C under magnetic stirring and vacuumed for 30 min to remove internal oxygen and moisture. Subsequently, the temperature was raised to 290°C under nitrogen protection and the reaction was carried out at this temperature for 1 h. After the reaction, the product was washed alternately with toluene and anhydrous ethanol three times and dried at 60°C for 12 h to obtain a Bi / BiVO4 composite heterojunction photocatalytic material after in-situ reduction for 1 h. The product was black powder particles, and its crystalline structure was characterized by an X-ray powder diffractometer. The microstructure under a scanning electron microscope was a loose structure with uniform distribution of large and small particles.

2. Application of the photocatalytic material prepared by the preparation method as claimed in claim 1 in the field of photocatalytic degradation.

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