Z-type heterojunction ReS2 / Bi2WO6 composite catalyst for photocatalytic reduction of carbon dioxide and preparation method thereof

Abstract

The present invention belongs to the field of photocatalysts, and specifically relates to a Z-type heterojunction ReS2 / Bi2WO6 composite catalyst for the photocatalytic reduction of carbon dioxide and a preparation method thereof. Bi2WO6 is first prepared, followed by ReS2. ReS2 and Bi2WO6 are then dissolved in deionized water. The ReS2 / Bi2WO6 composite catalyst is synthesized using a simple impregnation method. The catalytic reduction of CO2 is performed through the synergistic effects of light irradiation and ultrasound. The ReS2 / Bi2WO6 composite catalyst has a much higher CO2 reduction rate than Bi2WO6 and ReS2. The catalyst of the present invention is simple to synthesize, is green and pollution-free, and has strong operability. The prepared catalyst has abundant active sites, excellent stability, and does not produce secondary pollution.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysts, and in particular relates to a Z-type heterojunction ReS2 / Bi2WO6 composite catalyst for photocatalytic reduction of carbon dioxide and a preparation method thereof. Background Art

[0002] Among semiconductor photocatalysts, perovskite catalysts have attracted attention due to their high stability, suitable band gap, safety and non-toxicity. Currently, some perovskite materials have piezoelectric properties, which can combine light energy and mechanical energy to achieve better catalytic effects. Bi2WO6 is a typical piezoelectric photocatalytic material. Bi2WO6 nanomaterials have significant advantages such as safety, non-toxicity, simple preparation, and good photostability. However, pure Bi2WO6 has a band gap of 2.7-3.2eV. The wide band gap means that the energy of the excitation light must be very large (such as ultraviolet light), but long-wavelength light accounts for the majority of sunlight, that is, the utilization rate of sunlight by pure Bi2WO6 is very low; secondly, Bi2WO6 has fewer active sites on the surface, resulting in insufficient adsorption capacity for CO2; finally, Bi2WO6 has a serious problem of photogenerated charge recombination.

[0003] Currently, the design of composite materials to harvest mechanical energy to generate a built-in polarization electric field and the construction of heterostructures to reduce the recombination probability of surface electron-hole pairs are hot topics in recent research. Properly designed composite materials that create a strong built-in electric field as a driving force can enhance photocatalytic performance. The construction of heterostructures is also an effective method for improving photocatalytic activity by reducing the recombination probability of surface electron-hole pairs and modifying surface defects in Bi2WO6 crystals.

[0004] Many Bi2WO6-based heterojunctions with different designs show better photoreduction activity, such as Bi2O3 / Bi2WO6, Bi2S3 / Bi2WO6, PbBr3 / Bi2WO6, etc. The photocatalytic performance of two-dimensional Bi2WO6 is improved by the design of heterojunction, but there is still a serious problem of photogenerated charge recombination. Summary of the Invention

[0005] The present invention aims to provide a Z-type heterojunction ReS2 / Bi2WO6 composite catalyst and its preparation method, which is then applied to the photocatalytic reduction of CO2, demonstrating high catalytic activity and good stability. Under the combined action of light and ultrasound, the ReS2 / Bi2WO6 composite catalyst achieves higher CO2 reduction efficiency than independent photocatalysis and ultrasound catalysis, or compared to either ReS2 or Bi2WO6 catalysts alone.

[0006] The preparation method of the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst provided by the present invention is:

[0007] (1) Preparation of Bi2WO6:

[0008] Disperse Bi(NO₃)₃·5H₂O and Na₂WO₄·4H₂O in deionized water at a molar ratio of 2:1 and vigorously stir to dissolve, yielding a white solution. This solution is then placed in a polytetrafluoroethylene-lined hydrothermal autoclave and maintained at 190°C for 2 hours. After cooling to room temperature, the solution is thoroughly rinsed with deionized water and anhydrous ethanol and dried under vacuum at 60°C for 24 hours to yield a white powder, Bi₂WO₆.

[0009] (2) Preparation of ReS2:

[0010] NH4ReO4 and CH4N2S were mixed in a molar ratio of 2:9, dissolved in deionized water, and fully dispersed before a hydrothermal reaction at 240°C for 24 hours. After cooling to room temperature, the mixture was thoroughly rinsed with deionized water and anhydrous ethanol, and dried under vacuum at 60°C for 24 hours to obtain a black powder, ReS2.

[0011] (3) Preparation of ReS2 / Bi2WO6 composite catalyst:

[0012] The ReS2 catalyst and Bi2WO6 catalyst were dissolved in deionized water, ultrasonicated, and stirred. The mixture was filtered, washed, and dried at room temperature to obtain a gray powder, which was the ReS2 / Bi2WO6 composite catalyst.

[0013] Among them, the added amount of ReS2 is 5% to 15% of the mass of Bi2WO6, and preferably the added amount of ReS2 is 10% of the mass of Bi2WO6.

[0014] The ultrasonic time is 30-60 min, the ultrasonic power is 240 w, the stirring speed is 300-600 r / min, and the stirring is 22 h.

[0015] The ReS2 / Bi2WO6 composite catalyst prepared by the above method is used as a photocatalyst in the catalytic reduction of CO2: the ReS2 / Bi2WO6 composite catalyst is weighed, added to water, ultrasonically dispersed uniformly, and CO2 reduction is carried out under the combined conditions of ultrasound and light.

[0016] The dosage of ReS2 / Bi2WO6 composite catalyst in water is 0.001-0.005g / 20ml.

[0017] The ultrasonic power was 240W, and the illumination condition was sunlight simulated by a 55W xenon lamp.

[0018] The Z-type heterojunction structure of the present invention is shown in FIG. Figure 9When light irradiates the surface of the Z-type heterojunction photocatalyst, the electrons of B jump from the valence band (VB) to the conduction band (CB) of B, and then the electrons of B transfer to the valence band of A, exciting the transfer of electrons in the valence band of A to the conduction band of A. The photogenerated electron-hole pairs can separate and migrate to the active reaction sites more quickly, effectively improving the photocatalytic efficiency.

[0019] The present invention has the advantages that:

[0020] (1) The catalyst provided by the present invention is a ReS2 / Bi2WO6 composite catalyst, which has simple synthesis conditions, is easy to operate, and has the characteristics of being fast and efficient, energy-saving and environmentally friendly, and does not require the use of sacrificial agents.

[0021] (2) The ReS2 / Bi2WO6 composite catalyst catalyzes the reduction of CO2 to produce methane (CH4) and carbon monoxide (CO) under the synergistic effect of ultrasound and light. Its catalytic performance is 13.5 times that of pure Bi2WO6 catalyst and 10.7 times that of pure ReS2. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These are the XRD patterns of ReS2 / Bi2WO6 composite materials of different proportions synthesized in Examples 1-3 and Comparative Examples 1-2, as well as Bi2WO6 and ReS2.

[0023] Figure 2 These are the solid UV-visible absorption spectra of the ReS2 / Bi2WO6 composite materials synthesized in Example 1 and Comparative Examples 1-2, and of Bi2WO6 and ReS2.

[0024] Figure 3 It is the band gap diagram of the ReS2 / Bi2WO6 composite material synthesized in Example 1 and Comparative Examples 1-2 and Bi2WO6 and ReS2.

[0025] Figure 4 The following are X-ray electron spectra of the ReS2 / Bi2WO6 composite materials synthesized in Example 1 and Comparative Examples 1-2, as well as Bi2WO6 and ReS2. (The upper half of the left figure shows the 4f electron orbitals of the Bi element in Bi2WO6, and the lower half shows the 4f electron orbitals of the Bi element in the ReS2 / Bi2WO6 composite. The upper half of the right figure shows the 4f electron orbitals of the W element in Bi2WO6, and the lower half shows the 4f electron orbitals of the W element in the ReS2 / Bi2WO6 composite. The upper half of the lower figure shows the 4f electron orbitals of the Re element in ReS2, and the lower half shows the 4f electron orbitals of the Re element in the ReS2 / Bi2WO6 composite.)

[0026] Figure 5These are the steady-state fluorescence spectra of the ReS2 / Bi2WO6 composite materials synthesized in Example 1 and Comparative Examples 1-2, and of Bi2WO6 and ReS2.

[0027] Figure 6 It is a performance diagram of reducing CO2 to produce CH4 and CO by Bi2WO6 and ReS2 under the action of ultrasound and light at the same time, using different proportions of ReS2 / Bi2WO6 composite materials synthesized in Examples 1-3 and Comparative Examples 1-2.

[0028] Figure 7 This is a performance diagram of reducing CO2 to produce CH4 and CO using different ratios of ReS2 / Bi2WO6, Bi2WO6 and ReS2 under light only.

[0029] Figure 8 This is a performance diagram of reducing CO2 to produce CH4 and CO using different ratios of ReS2 / Bi2WO6, Bi2WO6 and ReS2 under ultrasound alone.

[0030] Figure 9 This is a diagram of the Z-type heterojunction piezoelectric photocatalytic mechanism. DETAILED DESCRIPTION

[0031] The present invention is not limited to the following specific embodiments. Based on the disclosure of the present invention, a person skilled in the art may adopt a variety of other specific embodiments to implement the present invention. Any simple changes or modifications made to the design structure and concept of the present invention fall within the scope of protection of the present invention. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other unless they conflict.

[0032] The CH4 or CO production efficiency is calculated according to the following formula:

[0033]

[0034] R: CH4 or CO yield, unit: μmol g -1 h -1

[0035] S: Peak area of ​​CH4 or CO in gas chromatograph

[0036] m: catalyst mass, unit: g

[0037] t: time, unit: h.

[0038] Example 1

[0039] Mix NH4ReO4 and CH4N2S in a molar ratio of 2:9, dissolve them in deionized water, and after thorough dispersion, conduct a hydrothermal reaction at 240°C for 24 hours. After cooling to room temperature, rinse thoroughly with deionized water and anhydrous ethanol, and dry them in a vacuum at 60°C for 24 hours to obtain a black powder, ReS2.

[0040] Dissolve Bi(NO₃)₃·5H₂O and Na₂WO₄·4H₂O in a 2:1 molar ratio in 50 mL of deionized water with vigorous stirring to obtain a white solution. Transfer the solution to a polytetrafluoroethylene-lined hydrothermal autoclave and maintain the temperature at 190°C for 2 hours. After cooling to room temperature, rinse thoroughly with deionized water and anhydrous ethanol, and dry under vacuum at 60°C for 24 hours to obtain a white powder, the Bi₂WO₆ catalyst.

[0041] The ReS2 and Bi2WO6 catalysts were dissolved in deionized water and ultrasonicated for 1 hour at 240W. The mixture was stirred at 400 rpm for 22 hours. The mixture was filtered, washed, and dried at room temperature to obtain a gray powder, the ReS2 / Bi2WO6 composite catalyst. The mass of ReS2 was 10% of the mass of Bi2WO6.

[0042] from Figure 4 It can be seen that compared with Bi2WO6 and ReS2, the electron energy of Bi and W elements in ReS2 / Bi2WO6 moves in the positive direction, indicating that Bi2WO6 loses electrons (electrons are negatively charged) in the ReS2 / Bi2WO6 composite material. Similarly, the electron energy of Re element in ReS2 / Bi2WO6 moves in the negative direction, indicating that ReS2 gains electrons in the ReS2 / Bi2WO6 composite material. Then, based on the solid UV and XPS valence band spectra, the heterojunction type of the composite material can be obtained.

[0043] Application method of 10% ReS2 / Bi2WO6 composite catalyst:

[0044] Weigh 0.002g of a 10% ReS2 / Bi2WO6 composite catalyst, add 20mL of deionized water, and ultrasonically disperse for half an hour to evenly disperse the catalyst in the water. Then, pass CO2 through the mixture for 30 minutes. The reaction was then allowed to proceed for 2 hours under ultrasound (240W) and illumination (55W xenon lamp simulated sunlight). After the experiment, 0.5mL of gas was extracted from the tube, and the peak area was measured using a gas chromatograph to calculate the CH4 or CO production rate. The calculated CH4 and CO production rates were 2.63μmol g, respectively. -1 h -1 and 5.69 μmol g -1 h -1 .

[0045] Example 2

[0046] Compared with Example 1, the difference is that the mass of ReS2 added during the preparation process is 5% of the mass of Bi2WO6, and the other preparation methods are the same as Example 1.

[0047] The application method is the same as that of Example 1. The CH4 and CO production rates of the 5% ReS2 / Bi2WO6 composite catalyst prepared in Example 2 are 0.67 μmol g -1 h -1 and 1.17 μmol g -1 h -1 .

[0048] Example 3

[0049] Compared with Example 1, the difference is that the mass of ReS2 added during the preparation process is 15% of the mass of Bi2WO6, and the other preparation methods are the same as Example 1.

[0050] The application method is the same as that of Example 1. The 15% ReS2 / Bi2WO6 composite catalyst prepared in Example 3 produces CH4 and CO at rates of 0.98 μmol g -1 h -1 and 3.58 μmol g -1 h -1 .

[0051] Example 4

[0052] Compared with Example 1, the difference is that the amount of 10% ReS2 / Bi2WO6 composite catalyst used in water is 0.005g / 20ml, and the other preparation methods are the same as Example 1.

[0053] The preparation method is the same as that of Example 1. The CH4 and CO production rates of the 10% ReS2 / Bi2WO6 composite catalyst under the application amount of Example 4 are 1.67 μmol g -1 h -1 and 3.83 μmol g -1 h -1 .

[0054] Example 5

[0055] Compared with Example 1, the difference is that the amount of 10% ReS2 / Bi2WO6 composite catalyst used in water is 0.001 g / 20 ml, and the other preparation methods are the same as Example 1.

[0056] The preparation method is the same as that of Example 1. The CH4 and CO production rates of the 10% ReS2 / Bi2WO6 composite catalyst under the application amount of Example 5 are 2.15 μmol g -1 h -1and 4.82 μmol g -1 h -1 .

[0057] Comparative Example 1

[0058] The preparation method of pure Bi2WO6 catalyst is the same as the preparation of Bi2WO6 catalyst in Example 1.

[0059] The application method is the same as that in Example 1. The production rates of CH4 and CO by pure Bi2WO6 catalyst are 0.25 μmol g -1 h -1 and 0.42 μmol g -1 h -1 .

[0060] Comparative Example 2

[0061] The preparation of pure ReS2 catalyst is the same as the preparation of ReS2 catalyst in Example 1.

[0062] The application method is the same as that in Example 1. The production rates of CH4 and CO by pure ReS2 catalyst are 0.14 μmol g -1 h -1 and 0.53 μmol g -1 h -1 .

[0063] Comparative Example 3

[0064] Compared with Example 1, the difference is that the application method is changed from ultrasound (240W) and light (55W xenon lamp simulated sunlight) to ultrasound (240W), and the rest is the same as Example 1. The CH4 and CO production rates of ReS2 / Bi2WO6 catalyst are 0.43μmol g -1 h -1 and 2.18 μmol g -1 h -1 .

[0065] Comparative Example 4

[0066] Compared with Example 1, the difference is that the application method is changed from ultrasound (240W) and light (55W xenon lamp simulated sunlight) to light only (55W xenon lamp simulated sunlight), and the rest is the same as Example 1. The CH4 and CO production rates of ReS2 / Bi2WO6 catalyst are 0.48μmol g -1 h -1 and 3.75 μmol g -1 h -1 .

Claims

1. A method for preparing a Z-type heterojunction ReS2 / Bi2WO6 composite catalyst, characterized in that: The preparation method comprises the following steps: (1) Preparation of Bi2WO6: Bi(NO3)3·5H2O and Na2WO4·4H2O were dispersed in deionized water at a molar ratio of 2:1 and vigorously stirred to dissolve to obtain a white solution. The solution was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene and maintained at 190°C for 2 hours. After cooling to room temperature, the solution was thoroughly rinsed with deionized water and anhydrous ethanol and dried in a vacuum at 60°C for 24 hours to obtain a white powder, namely Bi2WO6. (2) Preparation of ReS2: Dissolve NH4ReO4 and CH4N2S in deionized water at a molar ratio of 2:9, fully disperse, and then perform a hydrothermal reaction at 240°C for 24 hours. After cooling to room temperature, rinse thoroughly with deionized water and anhydrous ethanol, and dry in a vacuum at 60°C for 24 hours to obtain a black powder, which is ReS2. (3) Preparation of ReS2 / Bi2WO6 composite catalyst: ReS2 and Bi2WO6 are dissolved in deionized water, ultrasonicated and stirred; filtered, washed and dried at room temperature to finally obtain a gray powder, which is the ReS2 / Bi2WO6 composite catalyst.

2. The method for preparing the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst according to claim 1, wherein: In step (3), the amount of ReS2 added is 5% to 15% of the mass of Bi2WO6.

3. The method for preparing the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst according to claim 1, wherein: Step (3) ultrasonication for 30-60 min, ultrasonic power of 240 W, stirring speed of 300-600 r / min, stirring for 22 h.

4. A Z-type heterojunction ReS2 / Bi2WO6 composite catalyst prepared by the method according to any one of claims 1 to 3.

5. An application of a Z-type heterojunction ReS2 / Bi2WO6 composite catalyst prepared by the method according to any one of claims 1 to 3, characterized in that: The composite catalyst is used for photocatalytic reduction of CO2.

6. The use of the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst according to claim 5, characterized in that: The method for using the composite catalyst for photocatalytic reduction of CO2 is as follows: weighing the ReS2 / Bi2WO6 composite catalyst, adding it to water, and irradiating it with light while performing ultrasound to catalytically reduce CO2 to produce methane and carbon monoxide.

7. The use of the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst according to claim 6, characterized in that: The amount of the ReS2 / Bi2WO6 composite catalyst added to water is 0.001-0.005 g / 20 ml.

8. The use of the Z-type heterojunction ReS2 / Bi2WO6 composite catalyst according to claim 6, characterized in that: The ultrasonic power is 240W, and the illumination condition is sunlight simulated by a 55W xenon lamp.

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