Preparation method and application of BiOBr / TiO2 composite material

Abstract

The invention discloses a preparation method and application of a BiOBr / TiO2 composite material, and belongs to the technical field of photocatalytic materials. According to the composite material, tetrabutyl titanate, bismuth nitrate pentahydrate, hexadecyl trimethyl ammonium bromide and ammonium fluoride are used as raw materials, in-situ synthesis is carried out through a one-step hydrothermal method, and the mass fraction of BiOBr is controlled to be 20%, 30% and 40%, preferably 30%. The preparation process comprises the four steps of precursor solution preparation, hydrothermal reaction, suction filtration and washing, and drying and grinding, the process is mild, the operation is simple and convenient, and the product purity is high. According to the composite material, through construction of the II-type heterojunction, photon-generated carrier recombination is effectively inhibited, the visible light response range is widened, the performance of photocatalytic reduction of CO2 to generate CO is remarkably improved, the optimal sample yield is 6.5 times that of pure TiO2, and the cycling stability is excellent. The method can be widely applied to the field of photocatalytic CO2 reduction, is suitable for photocatalytic hydrogen production and organic pollutant degradation scenes, provides a new thought for development of efficient heterojunction photocatalysts, and has good industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to the preparation technology of a heterojunction type photocatalytic composite material, and more particularly to a preparation method of a BiOBr / TiO2 composite material and its application in the field of photocatalytic CO2 reduction. It can also be extended to the fields of photocatalytic hydrogen production and degradation of organic pollutants. Background Technology

[0002] With the acceleration of global industrialization, the excessive consumption of fossil fuels has led to a continuous rise in atmospheric CO2 concentration, causing environmental problems such as the greenhouse effect and climate anomalies. Achieving CO2 emission reduction and resource conversion has become a research hotspot in the fields of environmental governance and energy. Photocatalysis technology, with its advantages of being green and environmentally friendly, having low energy consumption, and being able to directly utilize solar energy, has become one of the core technologies for the targeted conversion of CO2 into high-value hydrocarbon fuels, combining both environmental and energy benefits.

[0003] TiO2 is currently the most widely studied semiconductor photocatalyst, possessing advantages such as low preparation cost, excellent chemical stability, non-toxicity, and good biocompatibility, and its application in the field of photocatalysis is mature. However, pure TiO2 has two major drawbacks: first, its wide band gap (approximately 3.2 eV) means it can only absorb ultraviolet light, resulting in extremely low utilization of visible light, which accounts for more than 45% of the energy of sunlight; second, its rapid recombination rate of photogenerated electron-hole pairs leads to low carrier separation efficiency, causing its actual photocatalytic activity to fall far short of the requirements for industrial applications. Therefore, modifying TiO2 and constructing heterojunction structures are key pathways to improve its visible light response and carrier separation efficiency.

[0004] BiOBr, a typical layered bismuth-based oxide halide semiconductor, possesses a unique layered structure, a moderate bandgap (approximately 2.7 eV), and can effectively respond to visible light. Furthermore, it exhibits strong chemical stability and a simple preparation process, making it an ideal semiconductor material for modifying TiO2. Constructing a type II heterojunction by combining BiOBr with TiO2 can create highly efficient carrier transfer channels, suppress photogenerated carrier recombination, broaden the photoresponse range, and simultaneously enhance the material's light absorption capacity and catalytic activity.

[0005] Existing methods for preparing BiOBr / TiO2 composite materials often suffer from cumbersome steps, harsh reaction conditions, uneven component distribution, and weak interfacial bonding, resulting in limited improvement in the photocatalytic performance of the composite materials. To address this, this invention utilizes a one-step hydrothermal method to precisely control the raw material ratio and reaction parameters, preparing a BiOBr / TiO2 composite material with tight interfacial bonding, high crystallinity, and stable performance. This overcomes the shortcomings of existing technologies and achieves highly efficient photocatalytic CO2 reduction. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing BiOBr / TiO2 composite materials and their applications. The method employs a one-step hydrothermal approach to achieve in-situ composite of BiOBr and TiO2, constructing a closely contacted type II heterojunction structure. This effectively improves the separation efficiency of photogenerated carriers and the utilization rate of visible light, significantly enhancing the photocatalytic CO2 reduction performance of the material. Furthermore, the preparation process is simple, the conditions are mild, and the reproducibility is strong, making it suitable for large-scale preparation.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A BiOBr / TiO2 composite material is prepared by a one-step hydrothermal method using tetrabutyl titanate, bismuth nitrate pentahydrate, hexadecyltrimethylammonium bromide, and ammonium fluoride as raw materials. The amounts of each raw material are as follows: 10-30 mL of tetrabutyl titanate, 0.3-1 g of bismuth nitrate pentahydrate, 0.3-1 g of hexadecyltrimethylammonium bromide, and 0.2-0.5 g of ammonium fluoride.

[0009] Further, the BiOBr / TiO2 composite material is expressed as x%BiOBr / TiO2, where x% is the mass fraction of BiOBr, and x takes values ​​of 20, 30, and 40, preferably 30%BiOBr / TiO2 composite material.

[0010] A method for preparing a BiOBr / TiO2 composite material includes the following steps:

[0011] (1) Preparation of precursor solution A: Weigh 0.2-0.5g of ammonium fluoride, dissolve it in 5-10mL of deionized water, stir until completely dissolved, add the obtained ammonium fluoride solution dropwise to 10-30mL of tetrabutyl titanate, stir continuously at room temperature for 1-2h to obtain a uniform suspension for later use;

[0012] (2) Preparation of precursor solution B: Weigh 0.3-1g of bismuth nitrate pentahydrate, dissolve it in 20-50mL of deionized water, stir at room temperature for 10-20min until completely dissolved, add hexadecyltrimethylammonium bromide of the same mass as bismuth nitrate pentahydrate, continue stirring for 3-4h to obtain a homogeneous solution for later use;

[0013] (3) Hydrothermal reaction: Mix precursor solution A and precursor solution B evenly, transfer to a 100-150mL polytetrafluoroethylene (Teflon) high-pressure reactor, seal and place in an oven, react at a constant temperature of 140-170℃ for 10-20h, and cool naturally to room temperature to obtain the reaction mixture.

[0014] (4) Post-processing: The reaction mixture obtained in step (3) is filtered, and the filter cake is washed repeatedly with deionized water and anhydrous ethanol until the pH of the filtrate is neutral. The washed solid is placed in an oven and dried at 120°C for 12-24 hours. After grinding, BiOBr / TiO2 composite material is obtained.

[0015] An application of a BiOBr / TiO2 composite material, wherein the BiOBr / TiO2 composite material is used in the field of photocatalytic CO2 reduction, and the specific application method is as follows:

[0016] 10 mg of BiOBr / TiO2 composite material and 10 mL of deionized water were added to a 60 mL quartz reaction tube and ultrasonically dispersed until the catalyst was evenly distributed. CO2 gas was continuously introduced into the reaction tube for 20 min while stirring to completely remove air from the system and ensure that the quartz tube was filled only with CO2 atmosphere. The reaction device was sealed and the light source was turned on to carry out the photocatalytic CO2 reduction reaction. After 2 h of illumination, an equal volume of reaction gas was extracted and the product type and concentration were detected by gas chromatography.

[0017] Furthermore, the BiOBr / TiO2 composite material can also be applied to photocatalytic hydrogen production and degradation of organic pollutants in water, showing broad prospects for industrial application.

[0018] The beneficial effects of this invention are:

[0019] 1. Significant advantages of the preparation process: The in-situ composite of BiOBr and TiO2 is achieved by a one-step hydrothermal method, which eliminates the need for complex subsequent modification steps. The process is mild, simple to operate, and the reaction conditions are easy to control. The raw materials are readily available and inexpensive, and the process is highly reproducible, making it suitable for industrial mass production. At the same time, by precisely controlling the raw material ratio, the product purity is ensured to be high, the component distribution is uniform, and the interface between BiOBr and TiO2 is tightly bonded, avoiding the defects of uneven component dispersion and weak interfacial bonding in traditional composite methods.

[0020] 2. Significantly improved photocatalytic performance: By constructing a type II heterojunction structure, the recombination of photogenerated electron-hole pairs is effectively suppressed, the carrier transfer rate is accelerated, and the photoresponse range of the material is broadened, extending the material from responding only to ultraviolet light to the visible light region, significantly improving the utilization rate of sunlight, and thus greatly enhancing the photocatalytic CO2 reduction activity. The CO yield of the 30% BiOBr / TiO2 composite material can reach 6.5 times that of pure TiO2, which is far superior to single BiOBr or TiO2 materials.

[0021] 3. Excellent stability and practicality: The BiOBr / TiO2 composite material prepared by this invention has strong chemical stability and can still maintain high catalytic activity after four photocatalytic cycles. It is highly reusable, reducing the cost of practical applications. At the same time, it is suitable for a variety of photocatalytic scenarios. It can not only be efficiently applied to the field of photocatalytic CO2 reduction, but also extended to the fields of photocatalytic hydrogen production and degradation of organic pollutants in water, with a wide range of applications.

[0022] 4. High Technological Innovation and Application Value: This invention provides a simple and efficient new pathway for TiO2 modification, solving the core defects of low visible light utilization and rapid carrier recombination in pure TiO2. It also provides a reference for developing high-efficiency heterojunction photocatalysts, contributing to CO2 emission reduction and resource conversion. It combines environmental, energy, and industrial benefits, possessing excellent potential for industrial application. Attached Figure Description

[0023] Figure 1 The XRD patterns of the catalysts in Examples 1-3 and Comparative Examples 1-2 of this invention are shown in comparison.

[0024] Figure 2 This is a comparison chart of the photocatalytic CO2 reduction performance of the catalysts in Examples 1-3 and Comparative Examples 1-2 of the present invention;

[0025] Figure 3 This is a graph showing the photocatalytic cycle stability of the catalyst in Example 1 of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can better understand the technical solution of the present invention. It should be noted that the following embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0027] Example 1: Preparation of 30% BiOBr / TiO2 composite material

[0028] (1) Preparation of precursor solution A: Weigh 0.3g of ammonium fluoride, dissolve it in 8mL of deionized water, stir to dissolve, and then add it dropwise to 9mL of tetrabutyl titanate. Stir at room temperature for 1h to obtain a uniform suspension for later use.

[0029] (2) Preparation of precursor solution B: Weigh 1g of bismuth nitrate pentahydrate, dissolve it in 50mL of deionized water, stir at room temperature for 20min until completely dissolved, add 1g of hexadecyltrimethylammonium bromide, continue stirring for 3h to obtain a homogeneous solution for later use.

[0030] (3) Hydrothermal reaction: Mix precursor solution A and precursor solution B evenly, transfer to a 100mL polytetrafluoroethylene autoclave, react at 170℃ for 14h, and then cool naturally to room temperature.

[0031] (4) Post-treatment: The reaction solution was filtered, and the filter cake was washed alternately with deionized water and anhydrous ethanol until the pH of the filtrate was 7. The solid was placed in an oven at 120℃ and dried for 24 hours. It was then ground for 30 minutes to obtain a 30% BiOBr / TiO2 composite material.

[0032] Example 2 Preparation of 20% BiOBr / TiO2 composite material

[0033] (1) Preparation of precursor solution A: Weigh 0.2g of ammonium fluoride, dissolve it in 8mL of deionized water, stir to dissolve, and then add it dropwise to 9mL of tetrabutyl titanate. Stir at room temperature for 1h to obtain a uniform suspension for later use.

[0034] (2) Preparation of precursor solution B: Weigh 0.67g of bismuth nitrate pentahydrate, dissolve it in 40mL of deionized water, stir at room temperature for 20min until completely dissolved, add 0.67g of hexadecyltrimethylammonium bromide, continue stirring for 3h to obtain a homogeneous solution for later use;

[0035] (3) Hydrothermal reaction: Mix precursor solution A and precursor solution B evenly, transfer to a 100mL polytetrafluoroethylene autoclave, react at 160℃ for 16h, and then cool naturally to room temperature.

[0036] (4) Post-treatment: The reaction solution was filtered, and the filter cake was washed alternately with deionized water and anhydrous ethanol until the pH of the filtrate was 7. The solid was placed in an oven at 110℃ and dried for 24 hours. It was then ground for 40 minutes to obtain a 20% BiOBr / TiO2 composite material.

[0037] Example 3 Preparation of 40% BiOBr / TiO2 composite material

[0038] (1) Preparation of precursor solution A: Weigh 0.2g of ammonium fluoride, dissolve it in 8mL of deionized water, stir to dissolve, and then add it dropwise to 6.7mL of tetrabutyl titanate. Stir at room temperature for 1h to obtain a uniform suspension for later use.

[0039] (2) Preparation of precursor solution B: Weigh 1g of bismuth nitrate pentahydrate, dissolve it in 50mL of deionized water, stir at room temperature for 20min until completely dissolved, add 1g of hexadecyltrimethylammonium bromide, continue stirring for 4h to obtain a homogeneous solution for later use.

[0040] (3) Hydrothermal reaction: Mix precursor solution A and precursor solution B evenly, transfer to a 100mL polytetrafluoroethylene autoclave, react at 170℃ for 14h, and then cool naturally to room temperature.

[0041] (4) Post-treatment: The reaction solution was filtered, and the filter cake was washed alternately with deionized water and anhydrous ethanol until the pH of the filtrate was 7. The solid was placed in an oven at 110℃ and dried for 24 hours. It was then ground for 40 minutes to obtain a 40% BiOBr / TiO2 composite material.

[0042] Comparative Example 1: Preparation of pure BiOBr material

[0043] (1) Weigh 0.8g of bismuth nitrate pentahydrate, dissolve it in 50mL of deionized water, stir at room temperature for 20min until completely dissolved, add 0.8g of hexadecyltrimethylammonium bromide, continue stirring for 4h to obtain a homogeneous solution for later use;

[0044] (2) Transfer the solution to a 100 mL polytetrafluoroethylene autoclave and react at a constant temperature of 170 °C for 14 h, then allow it to cool naturally to room temperature;

[0045] (3) Filter the reaction solution and wash the filter cake alternately with deionized water and anhydrous ethanol until the pH of the filtrate is 7. Place the solid in an oven at 120°C and dry for 20 hours. Grind for 40 minutes to obtain pure BiOBr material.

[0046] Comparative Example 2: Preparation of Pure TiO2 Material

[0047] (1) Weigh 3g of ammonium fluoride, dissolve it in 10mL of deionized water, stir to dissolve, and then add it dropwise to 20mL of tetrabutyl titanate. Stir at room temperature for 1h to obtain a uniform suspension for later use.

[0048] (2) Transfer the suspension to a 50 mL polytetrafluoroethylene autoclave and react at a constant temperature of 170 °C for 14 h, then allow it to cool naturally to room temperature;

[0049] (3) Filter the reaction solution and wash the filter cake alternately with deionized water and anhydrous ethanol until the pH of the filtrate is 7. Place the solid in an oven at 110°C and dry for 24 hours. Grind for 40 minutes to obtain pure TiO2 material.

[0050] Performance testing and characterization

[0051] 1. X-ray diffraction (XRD) test

[0052] The crystal structure of the materials prepared in Examples 1-3 and Comparative Examples 1-2 was characterized using X-ray diffraction, and the results are as follows: Figure 1As shown. Pure TiO2 exhibits characteristic diffraction peaks at 25.28°, 48.05°, and 55.06°, corresponding to the (101), (200), and (211) crystal planes of anatase TiO2 (PDF#21-1272); in the BiOBr / TiO2 composite material, characteristic diffraction peaks of both TiO2 and BiOBr are observed. The diffraction peaks of BiOBr at 10.9°, 21.93°, 31.69°, and 32.22° correspond to the (001), (002), (102), and (110) crystal planes (PDF#09-0393), and there are no impurity diffraction peaks, proving that the composite material has high crystallinity and excellent purity, and that BiOBr and TiO2 have been successfully combined.

[0053] 2. Photocatalytic CO2 reduction performance test

[0054] A photocatalytic CO2 reduction experiment was conducted according to the method of this invention. After 2 hours of illumination, the CO concentration of the product was detected by gas chromatography, and the yield was calculated. The results are as follows: Figure 2 As shown, the CO yields of pure TiO2 and pure BiOBr were 1.45 and 4.02 μmol·g⁻¹·h⁻¹, respectively; the CO yields of 20%, 30%, and 40% BiOBr / TiO2 were 7.59, 9.38, and 7.57 μmol·g⁻¹·h⁻¹, respectively. Among them, 30% BiOBr / TiO2 showed the best catalytic activity, with a CO yield 6.5 times that of pure TiO2.

[0055] The performance improvement is due to the fact that BiOBr forms a type II heterojunction with TiO2 in close contact, which effectively promotes the separation of photogenerated carriers and broadens the visible light response range. When the BiOBr loading exceeds 30%, the excess BiOBr accumulates on the TiO2 surface, which blocks the active sites and reduces the light absorption efficiency, resulting in a slight decrease in catalytic activity.

[0056] 3. Cyclic stability test

[0057] The 30% BiOBr / TiO2 composite material prepared in Example 1 was subjected to four photocatalytic cycle experiments, and the results are as follows: Figure 3 As shown, after four cycles of reaction, the composite material still maintains high photocatalytic CO2 reduction activity with extremely low activity decay rate, demonstrating excellent chemical stability and strong reusability.

[0058] Industrial practicality

[0059] The BiOBr / TiO2 composite material prepared by this invention has a simple preparation process, mild reaction conditions, readily available raw materials, and strong repeatability, making it suitable for industrial mass production. This composite material has excellent performance in photocatalytic CO2 reduction, photocatalytic hydrogen production, and organic pollutant degradation, and can be widely used in industries such as air pollution control and new energy development, possessing extremely high industrial utilization value and promotion prospects.

[0060] Although the technical solutions of the present invention have been described and enumerated in detail, it should be understood that modifications to the above embodiments or the adoption of equivalent alternatives are obvious to those skilled in the art. Such modifications or improvements made without departing from the spirit of the present invention are all within the scope of protection claimed by the present invention.

Claims

1. A BiOBr / TiO2 composite material, characterized in that, It is prepared by a one-step hydrothermal method using tetrabutyl titanate, bismuth nitrate pentahydrate, hexadecyltrimethylammonium bromide, and ammonium fluoride as raw materials. The amount of each raw material is as follows: 10-30 mL of tetrabutyl titanate, 0.3-1 g of bismuth nitrate pentahydrate, 0.3-1 g of hexadecyltrimethylammonium bromide, and 0.2-0.5 g of ammonium fluoride.

2. The BiOBr / TiO2 composite material according to claim 1, characterized in that, The composite material is expressed as x%BiOBr / TiO2, where x% is the mass fraction of BiOBr, and x takes values ​​of 20, 30, and 40.

3. A method for preparing the BiOBr / TiO2 composite material according to claim 1 or 2, characterized in that, Includes the following steps: (1) Preparation of precursor solution A: Weigh 0.2-0.5g of ammonium fluoride, dissolve it in 5-10mL of deionized water, add it dropwise to 10-30mL of tetrabutyl titanate, stir at room temperature for 1-2h, and obtain a suspension for later use; (2) Preparation of precursor solution B: Weigh 0.3-1g of bismuth nitrate pentahydrate, dissolve it in 20-50mL of deionized water, stir at room temperature for 10-20min, add an equal mass of hexadecyltrimethylammonium bromide, continue stirring for 3-4h, and obtain a solution for later use; (3) Hydrothermal reaction: Mix precursor solution A and precursor solution B, transfer to a 100-150 mL polytetrafluoroethylene autoclave, react at 140-170 °C for 10-20 h, and cool to room temperature; (4) Post-treatment: The reaction solution was filtered, washed until neutral, dried at 120℃ for 12-24h, and ground to obtain BiOBr / TiO2 composite material.

4. The preparation method according to claim 3, characterized in that, In step (4), the washing process involves alternating between deionized water and anhydrous ethanol until the pH of the filtrate reaches 7.

5. An application of the BiOBr / TiO2 composite material according to claim 1 or 2, characterized in that, It is applied in the field of photocatalytic CO2 reduction.

6. The application according to claim 5, characterized in that, The specific operating steps are as follows: Add 10mg of the composite material and 10mL of deionized water to a 60mL quartz tube and disperse them thoroughly; introduce CO2 gas into the device for 20min to remove air, seal it and carry out the photocatalytic reaction; after irradiation for 2h, detect the product by gas chromatography.

7. The application according to claim 5, characterized in that, The composite material can also be applied to photocatalytic hydrogen production and organic pollutant degradation.

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