Preparation method and application of BiOBr-Bi2O2SO4 heterojunction photocatalyst

Abstract

The application discloses a preparation method of a BiOBr-Bi2O2SO4 heterojunction photocatalyst for CO2 reduction and application thereof. The preparation method comprises the following steps: first, Bi2O2SO4 is prepared; second, the heterojunction is constructed. Thiocyanic acid and bismuth nitrate hydrate are used as raw materials to synthesize the photocatalyst Bi2O2SO4, and the substrate is modified in situ by using tetraethylammonium bromide as a material, so that the BiOBr-Bi2O2SO4 heterojunction is finally obtained. The materials used in the application are cheap and easy to purchase, and the economic cost is low. The photocatalyst prepared by the method has the advantages of high selectivity, high light absorption efficiency, large material surface area and high stability, and is a relatively ideal photocatalyst for CO2 photoreduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of preparation of photocatalysts, in particular to a preparation method of BiOBr-Bi2O2SO4 heterojunction photocatalyst and application thereof. BACKGROUND

[0002] Due to the increasing CO2 emissions from the combustion of fossil fuels, the concentration of CO2 in the air gradually increases, thereby causing global environmental and climate problems. Among numerous renewable technologies, it has broad appeal and prospects to utilize abundant solar energy through the development of photocatalytic technology to reduce CO2 into CO, methane, methanol, ethylene and other hydrocarbon fuels and chemicals. However, limited by the high chemical inertness of CO2 molecules and the complex path in the process of CO2 reduction, the activity of photocatalytic CO2 reduction is still a great challenge. Therefore, to improve the activity and product selectivity of CO2 reduction, it is necessary to rationally design the photocatalyst. The semiconductor heterojunction interface engineering plays a crucial role in the process of CO2 activation and conversion, and is one of the effective strategies for the high selectivity of carbon-hydrocarbon fuel and chemical production.

[0003] As a kind of wide band gap semiconductor material, bismuth oxysulfate (Bi2O2SO4) has a typical Sillén structure, and the alternately arranged (Bi2O2) 2+ and (SO4) 2- layers in the structure have potential application prospects in photocatalysis. However, the controllable synthesis of Bi2O2SO4 still faces certain difficulties. And single Bi2O2SO4 is limited by the wide band gap and the rapid recombination of carriers, and its wide application faces great challenges. The construction of heterojunction can promote the spatial separation of photo-generated carriers, and maximize the redox ability of photocatalyst, so it is widely used in photocatalytic CO2 reduction. As BiOBr with the same layered alternately arranged (Bi2O2) 2+ and Br - layers) structure, it can provide sufficient space for atomic and atomic orbital polarization, realize effective separation of electrons and holes, and is often used to construct heterojunction with other photocatalysts. In order to solve the problems of low CO2 reduction efficiency, high resource cost and large energy consumption, the controllable synthesis of Bi2O2SO4 through the preparation method and its application in the construction of heterojunction are the existing problems in the development technology of high-efficiency catalyst. SUMMARY

[0004] In view of the problems in the prior art, the application provides a preparation method and application of a BiOBr-Bi2O2SO4 heterojunction photocatalyst, which uses Bi2O2SO4 as a photocatalytic semiconductor material and tetraethylammonium bromide as a bromine source, and is prepared by an in-situ bromination method.

[0005] The application is achieved by the following technical scheme: a preparation method of a modified BiOBr-Bi2O2SO4 heterojunction photocatalytic material, which uses bismuth nitrate, thiourea and tetraethylammonium bromide as raw materials and forms a BiOBr / Bi2O2SO4 heterojunction through rapid ion exchange.

[0006] The preparation method comprises the following steps:

[0007] S1. Preparation of Bi2O2SO4:

[0008] S1.1 Thiourea is placed in a container, and an ethanol solution is added, and ultrasonic treatment is performed for 15-30 min until complete dissolution, then ground Bi(NO3)3.5H2O is added, and ultrasonic treatment is continued for 15-30 min, then the container is taken out, and is left to stand at 20-30 DEG C for 30-40 min, after complete precipitation, filtration is performed and the precipitate is washed with an ethanol solution for 3 times to obtain a bright yellow precipitate;

[0009] S1.2 The bright yellow precipitate obtained in S1.1 is laid flat in a porcelain cup, then the porcelain cup is placed in a muffle furnace, and is heated at 2 DEG C / min to 500 DEG C under an atmospheric atmosphere, and is kept at 500 DEG C for 3 h to obtain a pure-phase Bi2O2SO4 powder;

[0010] S2. Construction of a heterojunction:

[0011] S2.1 A certain amount of tetraethylammonium bromide is weighed and prepared into 100 mL of a tetraethylammonium bromide solution, the Bi2O2SO4 powder obtained in S1.2 is placed in a container, 100 mL of the tetraethylammonium bromide solution is added to the container, and stirring is performed for 2-10 min, after complete ion exchange, the mixture is washed with an ethanol solution for multiple times and is dried to obtain a BiOBr-Bi2O2SO4 heterojunction.

[0012] Preferably, the mass ratio of thiourea to Bi(NO3)3.5H2O in S1.1 is 1:2-5.

[0013] Preferably, the mass fraction of the ethanol solution used in the preparation method is 99%.

[0014] Preferably, the tetraethylammonium bromide in S2.1 is used as a bromine source and is added in a small amount during the reaction.

[0015] Preferably, the mass ratio of Bi2O2SO4 and tetraethylammonium bromide in S2.1 is 1:2-3.

[0016] Preferably, the BiOBr-Bi2O2SO4 heterojunction prepared is used as a photocatalyst for CO2 reduction.

[0017] Preferably, the BiOBr-Bi2O2SO4 heterojunction prepared is used as a photocatalyst for CO2 reduction.

[0018] The present application uses bismuth nitrate, thiourea and tetraethylammonium bromide as raw materials, and forms a heterojunction on the surface of the material through a rapid ion exchange reaction, thereby modifying the base material.

[0019] Compared with the prior art, the present application has the beneficial effects that the modified BiOBr-Bi2O2SO4 heterojunction photocatalyst prepared has a wide spectrum of reduction capacity, the micro-morphology gradually changes from granular to flaky during in-situ reduction, has a larger specific surface area, the construction of the heterojunction widens the light absorption range of the base material, can enhance the reduction capacity, and has a certain directionality for the reduction and degradation of CO2, and can be effectively applied to CO2 reduction. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is an XRD spectrum of Bi2O2SO4;

[0021] Figure 2 is an XRD spectrum of BiOBr-Bi2O2SO4 heterojunction;

[0022] Figure 3 is a SEM micrograph of Bi2O2SO4;

[0023] Figure 4 is a SEM micrograph of BiOBr-Bi2O2SO4 heterojunction;

[0024] Figure 5 is an EDS graph of BiOBr-Bi2O2SO4 heterojunction. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] Embodiment 1

[0027] Preparation of S1 Bi2O2SO4:

[0028] S1.1 First, take 2.0 g of thiourea, put it in a beaker, add 60 mL of 99% ethanol solution, ultrasonic for 20 min until completely dissolved, then add 4.0 g of ground Bi(NO3)3·5H2O to the above solution, continue to ultrasonic for 20 min, take out and stand at 25℃ for 30 min, after complete precipitation, filter and wash with 99% ethanol solution for 3 times, get light yellow precipitate;

[0029] S1.2 Take 2.0 g of the product prepared in step S1.1, lay it flat in a porcelain cup, put it in a muffle furnace, heat to 500℃ at a rate of 2℃ / min under atmospheric atmosphere, and keep for 3h, get Bi2O2SO4 product; S2 Construction of heterojunction:

[0030] S2.1 Take 1.5 g of tetraethylammonium bromide to prepare a 100 mL solution, take 0.5 g of Bi2O2SO4 powder prepared in step S1.2, add it to the solution, stir for 5 min, then wash with 99% ethanol for 3 times and dry in a 60℃ oven for 6h, get the mixed product.

[0031] The Figure 1 and Figure 2 Compared with the material crystal form before and after modification of Bi2O2SO4, it is found that the modification of Bi2O2SO4 by tetraethylammonium bromide does not destroy its physical structure.

[0032] Figure 3 The SEM image of bismuth sub-sulfate is shown in Figure 1, which is a nanoparticle. As shown in Figure 2, the morphology of the material before and after modification of Bi2O2SO4 appears difference, which indicates that the micromorphology gradually changes from granular to flaky during in-situ reduction, which can enhance its specific surface area and provide more active sites. Figure 4 As shown in Figure 3, (a) is the distribution of Br element in modified Bi2O2SO4 material, (b) is the distribution of Bi element in modified Bi2O2SO4 material, the content of Br element:Bi element is about 1:50, which indicates that tetraethylammonium bromide successfully modifies Bi2O2SO4 through rapid ion exchange, successfully constructs BiOBr-Bi2O2SO4 heterojunction, and the existence of heterojunction interface can make the light absorption range wider, thereby improving the utilization of light.

[0033] Figure 5 Example 2

[0034] S1 Preparation of Bi2O2SO4:

[0035] S1 Bi2O2SO4 preparation:

[0036] ​S1.1 First, take 2.0 g of thiourea, place it in a beaker, add 60 mL of 99% ethanol solution, and ultrasonic for 20 min until completely dissolved. Then, add 5.0 g of ground Bi(NO3)3·5H2O to the above solution, continue to ultrasonic for 20 min, and then take it out and stand still at 25℃ for 30 min. After the precipitation is complete, filter and wash with 99% ethanol solution for 3 times to obtain a bright yellow precipitate;

[0037] S1.2 Take 2.0 g of the product prepared in step S1.1, lay it flat in a porcelain cup, and place it in a muffle furnace. Heat it to 500℃ at a rate of 2℃ / min under atmospheric atmosphere, and keep it for 3 h to obtain a Bi2O2SO4 product;

[0038] S2 Construction of heterojunction:

[0039] S2.1 Take 1.2 g of tetraethylammonium bromide and prepare a 100 mL solution. Take 0.5 g of Bi2O2SO4 powder prepared in step S1.2 and add it to the solution. Stir for 3 min, then wash with 99% ethanol for 3 times, and then dry in a 60℃ oven for 6 h to obtain a mixed product.

[0040] Test Example 1

[0041] Take 10 mg of modified BiOBr-Bi2O2SO4 heterojunction, add an appropriate amount of deionized water, and ultrasonic for 30 min until completely dispersed and uniform. Then, disperse it uniformly on a filter membrane. Transfer it to a photocatalytic system, fill it with sufficient CO2, and irradiate it under a xenon lamp for 6 h. Record the gas catalytic reduction effect every 1 h. It is found that the modified catalyst shows high performance of CO2 reduction, mainly producing CO and methane. The rate of methane production is 478 μmolg -1 h -1 , and the selectivity of methane production is as high as 80%.

[0042] The above is only a preferred embodiment of the present application, and it should be noted that the above preferred embodiment should not be regarded as a limitation of the present application. The protection scope of the present application should be limited by the scope defined in the claims. For ordinary skilled persons in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing a BiOBr-Bi2O2SO4 heterojunction photocatalyst, characterized in that: Includes the following steps, Preparation of S1 Bi2O2SO4: S1.1 Place thiourea in a container, add ethanol solution, sonicate for 15-30 min until completely dissolved, then add ground Bi(NO3)3·5H2O, continue sonicating for 15-30 min, remove, and let stand at 20-30℃ for 30-40 min. After precipitation is complete, filter and wash 3 times with ethanol solution to obtain a bright yellow precipitate. S1.2 Spread the bright yellow precipitate obtained in S1.1 in a porcelain jar, then place the porcelain jar in a muffle furnace, and heat it to 500℃ at 2℃ / min under atmospheric conditions, and keep it at 500℃ for 3h to obtain pure phase Bi2O2SO4 powder. Construction of S2 heterojunction: S2.1 Weigh out tetraethylammonium bromide and prepare a 100 mL tetraethylammonium bromide solution. Place the Bi2O2SO4 powder obtained in S1.2 into a container, add 100 mL of tetraethylammonium bromide solution to the container, stir for 2-10 min, and after complete ion exchange, obtain a mixed product. Wash the product multiple times with ethanol solution and dry it to obtain a BiOBr-Bi2O2SO4 heterojunction. The mass ratio of Bi2O2SO4 to tetraethylammonium bromide is 1:2-3, and the Br content to Bi content in the heterojunction is 1:

50.

2. The preparation method of a BiOBr-Bi2O2SO4 heterojunction photocatalyst according to claim 1, characterized in that: The mass ratio of thiourea and Bi(NO3)3·5H2O in S1.1 is 1:2~5.

3. The method for preparing a BiOBr-Bi2O2SO4 heterojunction photocatalyst according to claim 1, characterized in that: The ethanol solution used in the preparation method has a mass fraction of 99%.

4. The preparation method of a BiOBr-Bi2O2SO4 heterojunction photocatalyst according to claim 1, characterized in that: After washing three times with the ethanol solution in S2.1, the solution is placed in a 60°C oven and dried for 6 hours.

5. The application of the BiOBr-Bi2O2SO4 heterojunction prepared by any one of the preparation methods according to claims 1-4, characterized in that: The BiOBr-Bi2O2SO4 heterojunction is used as a photocatalyst for CO2 reduction.

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