Preparation method, product and application of heterojunction composite photocatalyst Bi2MoO6 / ZnO

Abstract

The invention discloses a preparation method, a product and application of a heterojunction composite photocatalyst Bi2MoO6 / ZnO, and belongs to the technical field of capacity storage and conversion. And preparing the three-dimensional ordered ball-flower-shaped Bi2MoO6 / ZnO heterojunction composite photocatalyst by adopting a solvent hydrothermal method. The preparation method is simple in process and convenient to operate, and the obtained catalyst is small in particle size and large in specific surface area, so that the catalyst has higher photocatalytic activity in an ultraviolet visible region compared with pure Bi2MoO6 and ZnO. Meanwhile, a capture experiment shows that the hole, the hydroxyl free radical and the superoxide free radical play an important role in photocatalytic degradation of tetracycline hydrochloride under simulated sun irradiation in the Bi2MoO6 / ZnO heterojunction composite photocatalyst, which is also one of important reasons for obvious improvement of the degradation rate of the Bi2MoO6 / ZnO heterojunction composite photocatalyst in degradation of tetracycline hydrochloride. The Bi2MoO6 / ZnO heterojunction composite photocatalyst has strong light absorption capability and green high degradation performance in an ultraviolet visible region, so that the Bi2MoO6 / ZnO heterojunction composite photocatalyst has a certain application prospect in the field of degradation of tetracycline hydrochloride in wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor optoelectronic materials, and particularly relates to a preparation method of a heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO and its application in photocatalytic degradation of tetracycline hydrochloride. Background Art

[0002] Antibiotics are the most commonly used drugs and play an important role in preventing human diseases, animals and aquaculture products. Although large amounts of antibiotics are needed for humans, animals and aquatic products, only a small part can be absorbed by the human body, animals and aquatic products, and most of them will be discharged into the environment in the form of feces. If not properly treated, it will cause great environmental pollution. Therefore, in order to reduce the environmental pollution caused by antibiotics, humans must reduce the environmental pollution caused by antibiotics from the source. ZnO is a wide-bandgap semiconductor ( ～ 3.37 eV), with a relatively large exciton binding energy (60 meV), so it has received extensive attention from researchers in the fields of optoelectronics, sensors, pharmaceuticals, etc. However, the ZnO photocatalyst can only absorb ultraviolet light, and the utilization rate of sunlight is very low. Therefore, there is an urgent need to develop a photocatalytic material with high utilization rate of sunlight.

[0003] Due to the above reasons, researchers are committed to studying visible light catalysts. Among them, Bi 2 MoO 6 is an important bismuth-based semiconductor, with a [MoO 4 2- and (Bi 2 O 2 ) 2+ formed layered structure, showing the advantages of stability, non-toxicity, low cost and corrosion resistance. And Bi 2 MoO 6 is a narrow-bandgap semiconductor (2.5 - 2.8 eV), with visible light photocatalytic activity. However, the rapid recombination of its electron-hole pairs limits its quantum conversion efficiency. Therefore, how to improve its quantum efficiency has become a key issue for bismuth-based catalysts.

[0004] Selecting a semiconductor with a band gap matching that of Bi 2 MoO 6 to construct a heterojunction is an ideal method to solve the above problems. Coupling the wide-bandgap ZnO with the narrow-bandgap Bi 2 MoO 6 to form a heterojunction composite material can effectively reduce the recombination rate to increase the absorption rate of visible light. In addition, the surface oxygen defects with a large number of localized electrons can enhance the adsorption and activation of oxygen to generate active free radicals, improving the separation efficiency of photogenerated carriers. Therefore, it is expected to prepare Bi with high visible light catalytic activity​2 MoO 6 / ZnO heterojunction composite catalyst and applied to the degradation of tetracycline hydrochloride in wastewater. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to improve the utilization rate of sunlight and provide a heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO preparation method and product.

[0006] To achieve the above object, the technical solution adopted by the present invention: A preparation method of a heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO, comprising the following steps:

[0007] (a) Preparation of ZnO nanosheets

[0008] First, an appropriate amount of ZnCl solution with a certain molar concentration is prepared, then an equimolar amount of NaOH solution is added under the condition of a magnetic stirrer and stirred strongly. The product is separated by a centrifuge, washed with deionized water and absolute ethanol, and then dried at 60 °C to obtain a precursor. The prepared precursor is heated at 400 °C to obtain ZnO nanosheets; 2 solution, then an equimolar amount of NaOH solution is added under the condition of a magnetic stirrer and stirred strongly. The product is separated by a centrifuge, washed with deionized water and absolute ethanol, and then dried at 60 °C to obtain a precursor. The prepared precursor is heated at 400 °C to obtain ZnO nanosheets;

[0009] (b) Preparation of three-dimensional ordered nanorod flower spheres Bi 2 MoO 6

[0010] Dissolve Bi(NO 3 ) 3 ·5H 2 O and NaMoO 4 ·2H 2 O in ethylene glycol respectively, then mix them and add absolute ethanol. After magnetic stirring, transfer the above mixture to a polytetrafluoroethylene reaction kettle, and then heat at 160 °C. After cooling, filter the obtained precipitate, wash it alternately with deionized water and ethanol, and then dry at 80 °C to obtain three-dimensional ordered nanorod flower spheres Bi 2 MoO 6 .

[0011] (c) Preparation of Bi 2 MoO 6 / ZnO heterojunction composite photocatalyst

[0012] Dissolve Bi(NO 3 ) 3 ·5H 2 O and Na 2 MoO 4 ·2H2 O is dissolved in ethylene glycol solution respectively. The two solutions are mixed, and anhydrous ethanol is added dropwise under magnetic stirring. Then, nano-ZnO is dispersed into the solution and stirred magnetically. Subsequently, the above mixture is transferred to a high-pressure polytetrafluoroethylene reaction kettle, heated at 160 °C, cooled, washed with deionized water and ethanol, and dried at 80 °C to obtain the heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO.

[0013] Preferably, when preparing ZnO nanosheets in step (a), the molar concentration of ZnCl 2 is 0.1 mol / L - 1.5 mol / L, and ZnCl 2 and NaOH are in equimolar amounts.

[0014] Preferably, when preparing the three-dimensional ordered nanorod flower ball Bi 2 MoO 6 in step (b), the molar reaction ratio of Bi(NO 3 ) 3 ·5H 2 O and NaMoO 4 ·2H 2 O is 2:1, the volume of anhydrous ethanol added is 30 - 60 ml, the heating temperature of the polytetrafluoroethylene high-pressure reaction kettle is 160 - 240 °C, and the heating time is 16 - 24 h.

[0015] The heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO product prepared according to the described preparation method.

[0016] The application of the heterojunction composite photocatalyst Bi 2 MoO 6 / ZnO product prepared according to the described preparation method in the visible-light photocatalytic degradation of tetracycline hydrochloride.

[0017] Advantages of the present invention: The mechanism of the Bi 2 MoO 6 / ZnO heterojunction composite material prepared by the present invention for photocatalytic degradation of tetracycline hydrochloride in wastewater is as follows: The enhanced photocatalytic activity of the heterojunction may be attributed to its effectiveness in the separation of electron-hole pairs. In this photocatalytic degradation reaction system, when light energy drops on the non-connected photocatalyst (Bi 2 MoO 6 / ZnO), electrons are excited from the valence band to the conduction band in the two conductors. Then, the excited electrons in the conduction band of Bi 2 MoO 6 (-4.28 eV) move to zinc oxide (-2.62 eV) and combine with O in the donor solution 2The molecule (photoreduction) reacts to generate ·O -2 radical. When the holes (-0.59 eV) formed in the valence band of ZnO move to the valence band of Bi 2 MoO 6 (-1.59 eV), and then react with water molecules in the donor solution (photooxidation), thereby generating ·OH radicals from OH - . Then the generated ·O -2 and ·OH transfer from the photocatalyst to the interface of the donor solution (wastewater solution), and degrade tetracycline hydrochloride into harmless products such as carbon dioxide and water and some non-toxic products such as formate, acetate, etc. The degradation mechanism of pure Bi 2 MoO 6 is consistent with the above results, but in pure Bi 2 MoO 6 , the h + and e - in the conduction band and valence band are easily recombined, so that there are not enough h + and e - to oxidize O 2 and H 2 O into active substances such as ·O -2 and ·OH, which will reduce the degradation ability of tetracycline hydrochloride. Different from pure Bi 2 MoO 6 , the Bi 2 MoO 6 / ZnO heterojunction composite material prepared in the present invention can avoid this situation and greatly improve the photocatalytic degradation performance. Description of the Drawings

[0018] Figure 1 are SEM diagrams of ZnO nanosheets, Bi 2 MoO 6 nanomaterials and Bi 2 MoO 6 / ZnO heterojunction composite materials;

[0019] Figure 2 are EDS diagrams of Bi 2 MoO 6 / ZnO heterojunction composite materials;

[0020] Figure 3 are the degradation rate curve diagrams of pure ZnO, pure Bi 2 MoO 6 and Bi 2 MoO 6 / ZnO heterojunction composite materials with different ratios for tetracycline hydrochloride in wastewater. Detailed Embodiments

[0021] To make the present invention more understandable, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0022] (1) Preparation of Bi2MoO6 nanomaterials

[0023] Dissolve 1.2615 g of Bi(NO 3 )3·5H 2 O (2.6 mmol) and 0.08170 g of NaMoO 4 ·.2H 2 O (1.3 mmol) (the molar ratio of the two is 2:1) in 10 mL of ethylene glycol solution respectively, then mix the two solutions, stir with a magnetic stirrer for 30 min, pour the mixed solution into a polytetrafluoroethylene high-pressure reaction kettle, place it in a forced-air oven, set the temperature to 160 °C, keep it at a constant temperature for 24 h, then take it out and cool it to room temperature. Then rinse it three times with deionized water and ethanol solution respectively, and then put it into a vacuum oven, set the temperature to 80 °C, and dry it at a constant temperature for 12 h.

[0024] (2) Preparation of ZnO nanosheets

[0025] Weigh ZnCl with a molar ratio of 2:1 2 and NaOH. Add ZnCl 2 to 100 mL of distilled water and stir with a magnetic stirrer. Then slowly add the weighed NaOH while stirring. After stirring for 30 min, let it stand for stratification, pour out part of the upper clear water, and then wash it 2 - 3 times with 50 mL of distilled water and 50 mL of absolute ethanol respectively. Separate it with a centrifuge (8000 r / min, 5 min), then place it in an oven to heat, set the temperature to 60 °C, heat for 30 min until it is basically dried, then crush it, put it into a ceramic crucible, and set the temperature to 400 °C in a muffle furnace, and keep it at a constant temperature for 1 h. That is, the ZnO finished product is obtained.

[0026] (3) Preparation of Bi 2 MoO 6 / ZnO heterojunction composite materials

[0027] Dissolve 0.6306 g of Bi(NO 3 ) 3 ·5H 2 O and 0.1573 g of NaMoO 4 ·2H 2O (the molar ratio of the two is: 0.65:1) were respectively dissolved in 10 ml of ethylene glycol, and after mixing evenly, 30 mL of absolute ethanol was added. After stirring for 30 min with a magnetic stirrer, 0.081 g of ZnO prepared in

[0008] step was weighed and dispersed into the mixed solution, and then stirred for another 60 min. Then it was poured into a polytetrafluoroethylene high-pressure reaction kettle and placed in a forced-air oven at a set temperature of 160 °C for drying for 24 h. Then it was taken out and cooled to room temperature. After rinsing three times with deionized water and ethanol solution respectively, it was placed in a vacuum oven at a set temperature of 80 °C for constant-temperature drying for 12 h. Bi 2 MoO 6 / ZnO heterojunction composite material was obtained.

[0028] Figure 1 (a and b) are SEM scanning electron microscope images of pure ZnO nanosheets magnified at different multiples, the SEM scanning electron microscope image of pure ZnO. As Figure 1 (a and b) show, the synthesized ZnO is in the form of nanosheets, the size of the nanosheets is about 50 - 150 nm, and the thickness is about 10 nm. Figure 1 (c) is the SEM scanning electron microscope image of pure Bi 2 MoO 6 nanomaterials. As Figure 1 (c) shows, the prepared pure Bi 2 MoO 6 nanomaterials mainly exist in the form of nanorods, the diameter of the nanorods is about 5 nm, forming a three-dimensional cross-interleaved three-dimensional spatial configuration and arranged neatly and orderly. Figure 1 (d) is the Bi 2 MoO 6 / ZnO heterojunction composite material. As shown in the figure, in Example 2, when the molar ratio of Bi(NO 3 ) 3 ·5H 2 O and 0.1573 g of NaMoO 4 ·2H 2 O is 0.65:1, and the reaction molar ratio of Bi 2 MoO 6 and ZnO is 0.65:1, a large number of ZnO flakes are deposited on the three-dimensional cross-ordered and interleaved Bi 2 MoO 6 nanorods, and finally a unique structure of Bi 2 MoO 6 / ZnO three-dimensional ordered nanoflower ball clusters is formed, which indicates that in the solvent preparation method using Bi 2 MoO 6 as the precursor, Bi 2 MoO 6can serve as a substrate and greatly inhibit the aggregation of ZnO nanosheets during their growth. In addition, this hybrid structure can increase the surface area and expose more surface active sites to participate in the photocatalytic reaction.

[0029] Figure 2 is Bi 2 MoO 6 / ZnO heterojunction composite material. As Figure 2 shown, it confirms the presence of Bi, Mo, O, and Zn elements in the composite material, indicating that this method can successfully synthesize Bi 2 MoO 6 / ZnO heterojunction composite material.

[0030] Figure 3 are the EDS diagrams of pure ZnO, pure Bi 2 MoO 6 and Bi 2 MoO 6 / ZnO heterojunction composite materials with different ratios for the degradation rate of tetracycline hydrochloride in wastewater. It can be seen that after 3 h of degradation reaction, the degradation rates of pure ZnO, pure Bi 2 MoO 6 and Bi 2 MoO 6 / ZnO molar ratios of 0.33:1, 0.65:1, and 0.99:1 (hereinafter abbreviated as B / Z-0.33, B / Z-0.65, and B / Z-0.99 respectively) for tetracycline hydrochloride in wastewater are: 0.65, 0.70, 0.80, 93, 0.89. Thus, when the molar reaction ratio of Bi 2 MoO 6 to ZnO is 0.65, the prepared Bi 2 MoO 6 / ZnO heterojunction composite material has the best degradation performance for tetracycline hydrochloride in wastewater.

[0031] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing a heterojunction composite photocatalyst Bi2MoO6 / ZnO, characterized in that: The steps include: (a) Preparation of ZnO nanosheets First, an appropriate amount of ZnCl2 solution with a certain molar concentration is prepared, and then an equimolar NaOH solution is added under the condition of a magnetic stirrer and stirred vigorously. The product is separated by a centrifuge, washed with deionized water and anhydrous ethanol, and then dried at 60°C to obtain a precursor. The obtained precursor is heated at 400°C to obtain ZnO nanosheets. (b) Preparation of three-dimensional ordered nanorod flower balls Bi2MoO6 Bi(NO3)3·5H2O and NaMoO4·2H2O were dissolved in ethylene glycol respectively, then mixed and added with anhydrous ethanol, and the mixture was transferred to a polytetrafluoroethylene reactor after magnetic stirring, and then heated at 160°C. After cooling, the obtained precipitate was filtered, washed alternately with deionized water and ethanol, and then dried at 80°C to obtain three-dimensional ordered nanorod flower balls Bi2MoO6; (c) Preparation of Bi2MoO6 / ZnO heterojunction composite photocatalyst Bi(NO3)3·5H2O and Na2MoO4·2H2O were dissolved in ethylene glycol solution respectively, the two solutions were mixed, anhydrous ethanol was added dropwise under magnetic stirring, nano ZnO was dispersed into the solution and magnetically stirred, and then the mixture was transferred to a high-pressure polytetrafluoroethylene reactor, heated at 160°C, washed with deionized water and ethanol after cooling, and dried at 80°C to obtain the heterojunction composite photocatalyst Bi2MoO6 / ZnO.

2. The method for preparing a heterojunction composite photocatalyst Bi2MoO6 / ZnO according to claim 1, characterized in that: When preparing ZnO nanosheets in step (a), the molar concentration of ZnCl2 is 0.1 mol / L-1.5 mol / L, and the molar ratio of ZnCl2 and NaOH is equimolar.

3. The method for preparing a heterojunction composite photocatalyst Bi2MoO6 / ZnO according to claim 1, characterized in that: In step (b), when preparing three-dimensional ordered nanorod flower balls Bi2MoO6, the molar reaction ratio of Bi(NO3)3·5H2O and NaMoO4·2H2O is 2:1, the volume of anhydrous ethanol added is 30-60 ml, the heating temperature of the polytetrafluoroethylene high-pressure reactor is 160-240°C, and the heating time is 16-24 hours.

4. The heterojunction composite photocatalyst Bi2MoO6 / ZnO product prepared by the preparation method according to claim 1.

5. Application of the heterojunction composite photocatalyst Bi2MoO6 / ZnO product prepared by the preparation method according to claim 1 in visible light photocatalytic degradation of tetracycline hydrochloride.

Images