Preparation method and application of a sheet-shaped p-n heterojunction photo-thermal catalyst

Abstract

The application provides a preparation method and application of a sheet-shaped p-n heterojunction photo-thermal catalyst. First, a cubic block stacked Co3O4 microsphere precursor is synthesized through a simple solvothermal method, and then Co3O4 and Bi2WO6 are compounded to form a sheet-shaped p-n heterojunction material through a hydrothermal method. The construction of the heterojunction can promote the separation of carriers, enhance the photo-thermal conversion efficiency, and promote the photo-thermal catalytic degradation ability of toluene. The preparation method of the application constructs a p-n heterojunction between Bi2WO6 and Co3O4, so that the prepared Bi2WO6 / Co3O4 p-n heterojunction material is sheet-shaped, has a good morphology, uniform element distribution, rich active sites, improved interface charge transport capacity, effectively separated photo-generated electron-hole pairs at the heterojunction interface, improved visible light and near-infrared region light absorption capacity, and enhanced photo-thermal conversion efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and relates to a photo-thermal catalyst, in particular to a preparation method and application of a sheet-shaped p-n heterojunction photo-thermal catalyst. BACKGROUND

[0002] Toluene, as a common pollutant in life, has great harm to human body and environment. As one of the most effective and reliable technologies for degrading toluene at present, the catalytic oxidation method can completely degrade toluene into CO2 and H2O under the condition of heat or light. However, pure thermal catalysis needs to provide additional energy, which causes problems such as resource waste and environmental pollution. Pure photocatalysis shows problems such as incomplete degradation of toluene, low degradation efficiency and high selectivity to light. Therefore, using solar energy as a light source and a heat source to perform photo-thermal catalysis on toluene is an effective method for realizing efficient degradation of toluene, and has important application value.

[0003] At present, photo-thermal catalysts for degrading toluene mainly include noble metal-based catalysts and non-noble metal oxide catalysts. The former usually shows good catalytic performance, but is expensive and easy to be poisoned and deactivated. The non-noble metal oxide catalysts include oxides of copper, manganese, cobalt, iron and the like. Although the activity of the non-noble metal oxide catalysts may be lower than that of the noble metal catalysts, they are increasingly attracting people's attention due to their advantages such as low price and long-term thermal stability. In terms of activity and cost, Co3O4 is one of the most promising catalysts, and has good thermal catalytic capacity. However, when Co3O4 is applied to the field of photocatalysis, it faces problems such as fast recombination of photo-generated electrons and holes and low carrier separation efficiency, which makes the photocatalytic capacity low. Bi2WO6 has a unique energy band and an alternating layered structure. The alternating layered structure causes a large internal electric field and an asymmetric polarization effect, so that Bi2WO6 has excellent photocatalytic activity. However, the response range of Bi2WO6 to visible light is narrow and the carrier recombination rate is too fast, so the application of single-component Bi2WO6 is limited. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a preparation method and application of a sheet-shaped p-n heterojunction photo-thermal catalyst, so as to solve the technical problems of low photo-generated electron-hole separation efficiency and low photo-thermal conversion efficiency of the photo-thermal catalyst prepared by the preparation method in the prior art.

[0005] Another purpose of the present application is to provide the application of the sheet-shaped p-n heterojunction photo-thermal catalyst, so as to solve the technical problem that the degradation efficiency of the catalyst prepared by the prior art needs to be further improved in the photo-thermal catalytic degradation of toluene.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] A preparation method of a sheet-shaped p-n heterojunction photo-thermal catalyst, comprising the following steps:

[0008] Step 1, stirring and dissolving cobalt acetate tetrahydrate in ethylene glycol, adding urea, and stirring to make the mixture uniform; transferring the suspension into a stainless steel autoclave lined with tetrafluoroethylene, and carrying out a reaction at a first preset temperature and a first preset time; after the reaction, centrifuging after natural cooling, washing, and drying to obtain Co3O4 microsphere precursor.

[0009] Step 2, dissolving the Co3O4 microsphere precursor in step 1 in 40 mL of deionized water, and uniformly distributing by ultrasonicating and stirring; dissolving bismuth nitrate pentahydrate, sodium tungstate dihydrate, and cetyltrimethylammonium bromide in 40 mL of deionized water, adding the aqueous solution containing the Co3O4 microsphere precursor, and stirring to make the suspension uniformly mixed; transferring into a stainless steel autoclave lined with tetrafluoroethylene, and carrying out a hydrothermal reaction at a second preset temperature and a second preset time, and then centrifuging the obtained product after natural cooling, washing, and drying; calcining the dried product in a muffle furnace at a third preset temperature and a third preset time to obtain sheet-shaped Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst.

[0010] The present application also has the following technical features:

[0011] Preferably, in step 1, the amount of cobalt acetate tetrahydrate added is 10 mmol to 20 mmol, the amount of ethylene glycol added is 50 mL to 90 mL, and the amount of urea added is 20 mmol to 40 mmol.

[0012] Preferably, in step 1, the first preset temperature is 170°C to 190°C, and the first preset time is 10 h to 14 h.

[0013] Preferably, in step 2, the amount of Co3O4 microsphere precursor added is 0.20 g to 0.30 g, the amount of bismuth nitrate pentahydrate added is 0.5 mmol to 2 mmol, the amount of sodium tungstate dihydrate added is 0.5 mmol to 2 mmol, and the amount of cetyltrimethylammonium bromide added is 0.0125 g to 0.05 g.

[0014] Preferably, in step 2, the second preset temperature is 150°C to 170°C, and the second preset time is 22 h to 26 h.

[0015] Preferably, in step 2, the third preset temperature is 350°C, the third preset time is 3 h, and the heating rate is 5°C / min.

[0016] Preferably, in step 1 and step 2, the washing is performed by using deionized water and ethanol alternately for four times; and the drying is performed by placing in an oven with a set temperature of 80℃.

[0017] The application also protects the application of the flaky p-n heterojunction photocatalyst prepared by the preparation method of the flaky p-n heterojunction photocatalyst to the photocatalytic degradation of toluene.

[0018] Compared with the prior art, the application has the following technical effects:

[0019] (I) The preparation method of the application can make the prepared Bi2WO6 / Co3O4 p-n heterojunction material present a flaky shape, has good morphology, uniform element distribution, rich active sites, improved interface charge transport capacity, and the photo-generated electron-hole pairs at the heterojunction interface can be effectively separated.

[0020] (II) The heterojunction photocatalyst of the application not only can improve the light absorption capacity in the visible light region and the near-infrared region, enhance the photo-thermal conversion efficiency, but also can provide a channel for the migration of active components, so that the photo-thermal catalytic capacity is greatly enhanced.

[0021] (III) The catalyst of the application can greatly promote the degradation efficiency when applied in the field of photo-thermal catalytic degradation of toluene. The whole preparation method has the advantages of easy-to-obtain raw materials, low cost, environmental friendliness, high yield, etc., has important practical significance, and can provide a reference for the synthesis of p-n heterojunction and the application in photo-thermal catalysis.

[0022] (IV) The method has the advantages of easy-to-obtain raw materials, low production cost, high yield, environmental friendliness, and is suitable for industrialized mass production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the XRD pattern of the catalyst obtained in the embodiment of the application.

[0024] Figure 2 is the SEM pattern of each product obtained in the preparation process in the embodiment of the application.

[0025] Figure 3 is the HRTEM pattern of the Bi2WO6 / Co3O4 p-n heterojunction photocatalyst obtained in the embodiment of the application.

[0026] Figure 4 is the photo-thermal degradation efficiency of each p-n heterojunction catalyst on toluene in the embodiment of the application.

[0027] The specific content of the application will be further explained and described in detail in combination with the embodiments. DETAILED DESCRIPTION

[0028] It should be noted that all raw materials in the present application, such as no special instructions, all use known in the prior art raw materials.

[0029] It is increasingly concerned that the composite catalyst improves the charge separation efficiency by forming various heterojunctions and extends the light absorption of the catalyst to visible light or even near-infrared light. Among them, the p-n heterojunction can establish an internal electric field, thereby driving the faster transfer of interface charge carriers, improving the interface charge transport capacity, and greatly enhancing the catalytic ability. The effective separation of light-induced electron-hole pairs at the heterojunction interface can also enhance its light absorption range and expand the maximum utilization of solar energy. In addition, the heterojunction interface also provides a channel for the migration of active ingredients, improving the degradation efficiency of toluene under photo-thermal conditions. Therefore, it has a very high development prospect to synthesize Bi2WO6 / Co3O4 p-n heterojunction material and use it as a photo-thermal catalytic degradation toluene catalyst.

[0030] The present application first synthesizes a Co3O4 microsphere precursor by a solvothermal method, and then forms a sheet-shaped p-n heterojunction material by hydrothermal method by combining Co3O4 with Bi2WO6. Through this heterojunction material, the separation of charge carriers can be promoted, and the photo-thermal conversion efficiency can be enhanced, thereby promoting the photo-thermal catalytic degradation ability of toluene.

[0031] In the present application, the Bi2WO6 / Co3O4 sheet-shaped p-n heterojunction photo-thermal catalyst is used in the application of photo-thermal catalytic degradation of toluene. During the reaction, the temperature controller is used to measure the catalytic activity at different temperatures, and each temperature is maintained for one hour before detection. The tail gas is detected by a gas chromatograph, and the toluene conversion rate is obtained by the following formula:

[0032]

[0033] In the formula, X toluene represents the toluene conversion rate; [toluene] in and [toluene] out respectively represent the toluene inlet and outlet concentrations. T 50 The low-temperature activity of the catalyst is evaluated, T 90 The high-temperature activity of the catalyst is evaluated, which are the temperatures corresponding to the toluene conversion rates of 50% and 90%, respectively.

[0034] The following gives specific embodiments of the present application. It should be noted that the present application is not limited to the following specific embodiments, and any equivalent variations made on the basis of the technical solutions of the present application fall within the protection scope of the present application.

[0035] Example 1:

[0036] The embodiment provides a preparation method of a sheet-shaped p-n heterojunction photo-thermal catalyst, and the method comprises the following steps:

[0037] Step 1: 15 mmol of cobalt acetate tetrahydrate is stirred and dissolved in 70 mL of ethylene glycol, 30 mmol of urea is added, and the mixture is stirred for 30 min to make the mixture uniform. The suspension is transferred into a 100 mL stainless steel autoclave lined with a special tetrafluoroethylene liner, and a reaction is performed at 180 ℃ for 12 h. After the reaction is naturally cooled, centrifugation is performed, and the product is washed with deionized water and ethanol alternately for four times, and then dried in an oven at 80 ℃ for 12 h to obtain a Co3O4 microsphere precursor.

[0038] Step 2: 0.25 g of the Co3O4 microsphere precursor in step 1 is dissolved in 40 mL of deionized water, and the mixture is uniformly distributed through ultrasonic and stirring. 1 mmol of bismuth nitrate pentahydrate, 1 mmol of sodium tungstate dihydrate and 0.025 g of cetyltrimethylammonium bromide are dissolved in 40 mL of deionized water, and then the water solution containing the Co3O4 microsphere precursor is added, and the mixture is stirred for 1 h to make the suspension uniform. The mixture is transferred into a 100 mL stainless steel autoclave lined with a special tetrafluoroethylene liner, and a hydrothermal reaction is performed at 160 ℃ for 24 h, and then the obtained product is naturally cooled, centrifuged, washed with deionized water and ethanol alternately for four times, and dried in an oven at 80 ℃ for 12 h. The dried product is heated to 350 ℃ at a heating rate of 5 ℃ / min in a muffle furnace, and then calcined for 3 h to obtain a sheet-shaped Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst (Bi2WO6 / Co3O4-1).

[0039] Figure 1 is an XRD pattern of the catalyst obtained in the embodiment. Figure 2 is an SEM pattern of each product obtained in the preparation process in the embodiment. Figure 2 in which (a) is a Co3O4 microsphere precursor, (b) is a sheet-shaped Bi2WO6, and (c) and (d) are sheet-shaped Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalysts. Figure 3 is an HRTEM pattern of the Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst obtained in the embodiment. Figures 1 to 3 It can be known that the sheet-shaped Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst is prepared in the embodiment.

[0040] Embodiment 2:

[0041] The embodiment provides a preparation method of a sheet-shaped p-n heterojunction photo-thermal catalyst, and the method comprises the following steps:

[0042] Step 1, 15 mmol of cobalt acetate tetrahydrate was dissolved in 70 mL of ethylene glycol by stirring, 30 mmol of urea was added, and the mixture was stirred for 30 min to make it uniform. The suspension was transferred to a 100 mL stainless steel autoclave with a special tetrafluoroethylene liner, and a solvothermal reaction was carried out at 180℃ for 12 h. After the reaction was naturally cooled, centrifugation was performed, and the product was washed with deionized water and ethanol alternately four times, and then dried in an oven at 80℃ for 12 h to obtain a Co3O4 microsphere precursor.

[0043] Step 2, 0.25 g of the Co3O4 microsphere precursor in step 1 was dissolved in 40 mL of deionized water, and the mixture was uniformly distributed by ultrasonicating and stirring. 0.5 mmol of bismuth nitrate pentahydrate, 0.5 mmol of sodium tungstate dihydrate, and 0.0125 g of cetyltrimethylammonium bromide were dissolved in 40 mL of deionized water, and the solution was added to the aqueous solution containing the Co3O4 microsphere precursor. The suspension was stirred for 1 h to make it uniform, and then transferred to a 100 mL stainless steel autoclave with a special tetrafluoroethylene liner. A hydrothermal reaction was carried out at 160℃ for 24 h, and then the obtained product was naturally cooled, centrifuged, washed with deionized water and ethanol alternately four times, and dried in an oven at 80℃ for 12 h. The dried product was calcined in a muffle furnace at a heating rate of 5℃ / min to 350℃ for 3 h to obtain a flaky Bi2WO6 / Co3O4 p-n heterojunction catalyst (Bi2WO6 / Co3O4-2).

[0044] The Bi2WO6 / Co3O4 p-n heterojunction photocatalyst prepared in this example has a similar morphology to that of Example 1, which is also flaky.

[0045] Example 3:

[0046] The present example provides a method for preparing a flaky p-n heterojunction photocatalyst, which comprises the following steps:

[0047] Step 1, 15 mmol of cobalt acetate tetrahydrate was dissolved in 70 mL of ethylene glycol by stirring, 30 mmol of urea was added, and the mixture was stirred for 30 min to make it uniform. The suspension was transferred to a 100 mL stainless steel autoclave with a special tetrafluoroethylene liner, and a solvothermal reaction was carried out at 180℃ for 12 h. After the reaction was naturally cooled, centrifugation was performed, and the product was washed with deionized water and ethanol alternately four times, and then dried in an oven at 80℃ for 12 h to obtain a Co3O4 microsphere precursor.

[0048] Step 2, 0.25 g of Co3O4 microsphere precursor in step 1 was dissolved in 40 mL of deionized water, and was uniformly distributed by ultrasonic and stirring. 2 mmol of bismuth nitrate pentahydrate, 2 mmol of sodium tungstate dihydrate and 0.05 g of cetyltrimethylammonium bromide were dissolved in 40 mL of deionized water, and were added to the aqueous solution containing Co3O4 microsphere precursor, and the suspension was mixed uniformly by stirring for 1 h, and was transferred to a 100 mL stainless steel autoclave lined with a teflon inner liner, and was subjected to hydrothermal reaction at 160℃ for 24 h, and the obtained product was naturally cooled, and was centrifuged, and was washed with deionized water and ethanol alternately for four times, and was dried in an oven at 80℃ for 12 h. The dried product was calcined in a muffle furnace at a heating rate of 5℃ / min to 350℃ for 3 h to obtain a flaky Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst (Bi2WO6 / Co3O4-3).

[0049] The flaky Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst prepared in this example has a similar morphology as that of example 1.

[0050] As can be seen from examples 1 to 3, by adjusting the amount of bismuth nitrate pentahydrate, sodium tungstate dihydrate and cetyltrimethylammonium bromide to adjust the amount of Bi2WO6 loaded, flaky Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalysts with different proportions were obtained.

[0051] Example 4:

[0052] This example shows the application of the flaky p-n heterojunction photo-thermal catalyst in the photo-thermal catalytic degradation of toluene.

[0053] The flaky p-n heterojunction photo-thermal catalyst was prepared by the preparation method of examples 1 to 3.

[0054] Specifically, 0.1 g of the catalyst was dispersed into thermal insulation cotton, a 400 W metal halide lamp was used as a light source, and an electronic fan was used to maintain the temperature. Then, 60 mL / min (GHSV (gas hourly space velocity) was 36000 mL g -1 h -1 ) of standard gas of N2:O2=4:1 was used to generate 1000 ppm of gaseous toluene through a bubbler containing liquid toluene, and the performance of the catalyst in degrading toluene was evaluated in a quartz tube with an inner diameter of 10 mm. The toluene conversion rate was measured by a gas chromatograph equipped with a hydrogen flame ionization detector.

[0055] The results of gas chromatograph analysis are shown in Figure 4 .

[0056] From Figure 4It can be seen that the degradation efficiency of toluene by pure Bi2WO6 and Co3O4 catalysts under photo-thermal conditions is low, the degradation efficiency of toluene by the flaky p-n heterojunction catalyst prepared in Examples 1 to 3 is greatly enhanced, and the degradation efficiency of the flaky p-n heterojunction material prepared when 1 mmol of bismuth nitrate pentahydrate, 1 mmol of sodium tungstate dihydrate and 0.025 g of cetyltrimethylammonium bromide are added (i.e., the preparation method of Example 1) is the highest.

[0057] In summary, the p-n heterojunction photo-thermal catalyst prepared in the application has a flaky structure, has abundant active centers, constructs a p-n heterojunction between Bi2WO6 and Co3O4, forms an internal electric field, thereby improving the shortcoming of fast recombination rate of electron-hole pairs of pure Bi2WO6, and improving the light absorption capacity in the visible and near-infrared regions and the photo-thermal conversion efficiency. Therefore, the Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst prepared in the application exhibits strong toluene degradation capacity, and is suitable for photo-thermal catalytic degradation of toluene in the full spectrum range. In addition, the preparation in the examples has the advantages of low cost, easy availability of raw materials, high yield, green to the environment and the like, has important practical significance, and can provide a basis for the preparation and photo-thermal catalytic application field of other p-n heterojunctions.

Claims

1. Use of a sheet-shaped p-n heterojunction photo-thermal catalyst in photo-thermal catalytic degradation of toluene. The preparation method of the sheet-shaped p-n heterojunction photo-thermal catalyst comprises the following steps: Step 1: Dissolve cobalt acetate tetrahydrate in ethylene glycol by stirring, add urea, and stir to make the mixture uniform; transfer the suspension to a stainless steel autoclave lined with tetrafluoroethylene, and react at a first preset temperature of 170-190 DEG C and a first preset time of 10-14 h; after the reaction, centrifuge, wash, and dry after natural cooling to obtain Co3O4 microsphere precursor; Step 2: Dissolve the Co3O4 microsphere precursor in deionized water in step 1, and make it uniformly distributed by ultrasonic and stirring; dissolve bismuth nitrate pentahydrate, sodium tungstate dihydrate, and cetyltrimethylammonium bromide in deionized water, add the Co3O4 microsphere precursor-containing aqueous solution, and stir to make the suspension mixture uniform; transfer to a stainless steel autoclave lined with tetrafluoroethylene, and hydrothermally react at a second preset temperature of 150-170 DEG C and a second preset time of 22-26 h; centrifuge, wash, and dry after natural cooling of the obtained product; Dry the product in a muffle furnace at a third preset temperature of 350 DEG C and a third preset time of 3 h at a heating rate of 5 DEG C / min to obtain sheet-shaped Bi2WO6 / Co3O4 p-n heterojunction photo-thermal catalyst.

2. Use according to claim 1, wherein In step 1, the amount of cobalt acetate tetrahydrate added is 10-20 mmol, the amount of ethylene glycol added is 50-90 mL, and the amount of urea added is 20-40 mmol.

3. The use according to claim 1, wherein In step 2, the amount of Co3O4 microsphere precursor added is 0.20-0.30 g, the amount of bismuth nitrate pentahydrate added is 0.5-2 mmol, the amount of sodium tungstate dihydrate added is 0.5-2 mmol, and the amount of cetyltrimethylammonium bromide added is 0.0125-0.05 g.

4. The use according to claim 1, wherein In steps 1 and 2, the deionized water and ethanol are used alternately for washing four times; the drying is performed in an oven with a set temperature of 80 DEG C.

Images