A novel composite heterojunction photocatalyst, a preparation method thereof, and applications thereof in carbon dioxide reduction

Abstract

The present invention discloses a novel composite heterojunction photocatalyst, a preparation method thereof, and its application in carbon dioxide reduction. The photocatalyst is prepared by a hydrothermal method using WCl6 as the tungsten source, thioacetamide (TAA) as the sulfur source, cobalt phthalocyanine as the CoPc source, phosphoric acid (H3PO4) as the phosphoric acid source, and deionized water (H2O) as the solvent. The prepared (CoPc-P / WS2) photocatalyst has a spherical structure with a diameter of about 500 nm, and the surface contains rich functional groups, and it exhibits excellent photocatalytic CO2 reduction activity under visible light.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor photocatalysis, and particularly relates to a novel composite heterojunction photocatalyst, a preparation method thereof, and an application thereof in carbon dioxide reduction. Background Art

[0002] The world today is facing the severe challenges of continuous depletion of fossil energy and increasingly serious environmental pollution. Developing renewable clean energy has become a major issue related to human survival and sustainable development. Photocatalytic reduction of carbon dioxide is a process that converts carbon dioxide (CO2) into useful chemicals (such as fuels and chemicals) with the aid of a photocatalyst. This process provides a possible solution for reducing the concentration of carbon dioxide in the atmosphere and mitigating the impact of climate change.

[0003] The photocatalytic reduction of CO2 involves the use of a photocatalyst, usually a metal oxide semiconductor, which absorbs light and generates electron-hole pairs. These electron-hole pairs drive the reduction of CO2 to form a series of products such as formic acid, methanol, and other organic compounds. This reaction is usually carried out in an aqueous solution in the presence of a sacrificial electron donor (such as hydrogen).

[0004] The choice of photocatalyst and reaction conditions (such as pH, temperature, and light source) significantly affects the efficiency and selectivity of the photocatalytic CO2 reduction process. The latest progress in the development of new photocatalysts and reaction conditions has improved the efficiency and selectivity, making photocatalytic reduction of carbon dioxide a promising technology for the sustainable production of chemicals and fuels. In short, photocatalytic CO2 reduction provides a promising solution for reducing atmospheric CO2 concentration and mitigating the impact of climate change by converting CO2 into useful chemicals. The ongoing research work focuses on improving the efficiency and selectivity of this process to make it more sustainable economically and environmentally.

[0005] In semiconductor materials, WS2 has a narrow bandgap of 1.8 eV, making it one of the most promising materials for detecting visible light radiation. It is considered an important material in the field of optoelectronics, such as optical displays, solar cells, light-emitting diodes, and transistors. In addition to these applications, it has also created new research hotspots in the field of visible light-driven photocatalysis. As is well known, photocatalytic reactions are surface catalytic reactions strongly affected by changes in the shape, size, and morphology of the catalyst. Therefore, various attempts have been made to prepare 1D to 3D WS2 nanostructure photocatalysts using different methods, such as the colloidal method, hydrothermal / solvothermal method, laser growth method, template method, electrochemical induced deposition method, and thermal evaporation method. However, there is less research on morphology control and its impact on the photocatalytic performance of the same system. Especially under mild conditions, there are still many challenges in preparing a large number of uniform WS2 nanospherical photocatalysts. Summary of the Invention

[0006] To solve the technical problems existing in the background art, the present invention provides a novel composite heterojunction photocatalyst, a preparation method thereof, and an application thereof in carbon dioxide reduction. The catalyst prepared by the present invention has rich functional groups on its surface and has relatively high catalytic activity for CO2 reduction.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A preparation method of a novel composite heterojunction photocatalyst uses WCl6 as the W source, thioacetamide as the S source, cobalt phthalocyanine as the CoPc source, phosphoric acid as the phosphoric acid source, and deionized water as the solvent, and prepares the novel composite heterojunction photocatalyst by a hydrothermal method.

[0009] Furthermore, the preparation method of the novel composite heterojunction photocatalyst includes the following steps:

[0010] a) WS2 nanoparticles were synthesized by a one-step method using WCl6 as the W source and thioacetamide as the S source; First, thioacetamide powder was ultrasonically dissolved in deionized water;

[0011] b) WCl6 was quickly added to the solution, and then magnetic stirring was carried out to obtain a uniform dark blue solution;

[0012] c) Then the reaction mixture was transferred to a high-pressure autoclave lined with parylene and kept at a certain temperature;

[0013] d) After the reaction, the black precipitate was collected by centrifugation, then washed several times with absolute ethanol and deionized water, and then the product was freeze-dried and vacuum-sealed;

[0014] e) The WS2 nanoparticles were added to the H3PO4 solution to prepare a mixed suspension; The mixed suspension was ultrasonically treated and continuously stirred, and then dried and annealed;

[0015] f) The WS2 modulated by phosphoric acid was ultrasonically dispersed in ethanol. To obtain a uniform suspension, the CoPc ethanol solution was added to the WS2 suspension modulated by phosphoric acid according to the calculated volume, and then ultrasonically treated and stirred;

[0016] g) Stir at room temperature, then evaporate the solvent under stirring, and finally dry to prepare the novel composite heterojunction photocatalyst.

[0017] Furthermore, in step a), the mass ratio of WCl6 to thioacetamide is 1.19:2.276.

[0018] Furthermore, in step a), the thioacetamide powder was ultrasonically dissolved in 40 mL of deionized water for 30 min.

[0019] Further, in step b), magnetic stirring is carried out for 30 min.

[0020] Further, in step c), the reaction mixture is kept at 250 °C for 24 h.

[0021] Further, in step d), then the product is freeze-dried at -50 °C for 10 h and vacuum-sealed at 60 °C for 6 h.

[0022] Further, in step e), the mixed suspension is ultrasonicated at an ultrasonic power of 100 - 150 W for 20 min and continuously stirred for 12 h, and then dried at 80 °C and annealed at 450 °C for 1 h.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The (CoPc-P / WS2) photocatalyst prepared by the process of the present invention has a spherical structure with a diameter of about 500 nm, and the surface contains rich functional groups, and it exhibits excellent photocatalytic CO2 reduction activity under visible light. Description of the Drawings

[0025] Figure 1 is the scanning electron microscope image of the photocatalyst prepared in Example 1 of the present invention;

[0026] Figure 2 is the elemental surface distribution diagram of the photocatalyst prepared in Example 1 of the present invention;

[0027] Figure 3 is the XRD pattern of the photocatalyst prepared in Example 1 of the present invention;

[0028] Figure 4 is the schematic diagram of tungsten disulfide (WS2) and CoPc-P / WS2 photocatalyst for catalyzing CO2 in Example 1 of the present invention. Detailed Embodiments

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the drawings.

[0030] Example 1

[0031] A preparation method of a novel CoPc / phosphate / WS2 composite heterojunction photocatalyst, comprising the following steps:

[0032] (1) Using WCl6 as the W source and thioacetamide (TAA) as the S source, WS2 nanoparticles were synthesized. First, 2.276 g of TAA powder was ultrasonically dissolved in 40 mL of deionized water (DI) for 30 min. Then, 1.19 g of WCl6 was quickly added to the solution, and magnetic stirring was carried out for 30 min to obtain a uniform dark blue solution. Subsequently, the reaction mixture was transferred to a 50 mL polystyrene-lined autoclave and maintained at 250 °C for 24 h.

[0033] (2) After the reaction, the precipitate was collected by centrifugation and then washed several times with absolute ethanol and deionized water.

[0034] (3) The product was freeze-dried at -50 °C for 10 h and vacuum-sealed at 60 °C for 6 h.

[0035] (4) Subsequently, 1 g of the prepared WS2 nanoparticles was ultrasonically dispersed in 50 mL of deionized water. 0.025 g of cobalt phthalocyanine was added to the solution, and ultrasonic stirring was carried out for 6 h to make it uniformly dispersed. Then it was dried at 60 °C for 12 h to obtain a novel CoPc / phosphate / WS2 composite heterojunction photocatalyst.

[0036] Photocatalytic reaction conditions: The photocatalytic reaction was carried out in a batch mode with a total volume of 50 ml. CO2 was introduced into the reactor at a flow rate of 50 mL / min, and the reaction was carried out at room temperature (25 °C) and ambient pressure (1 atmosphere).

[0037] Photocatalytic reaction: 50 mg of the prepared photocatalyst with a total volume of 50 ml was exposed to a xenon lamp for a certain reaction time (such as 1 h) to initiate the photocatalytic reaction. Gas chromatography (GC) was used to analyze the photocatalytic products to determine the conversion rate of CO2 to products such as CO, formic acid, or methanol.

[0038] Data analysis: The conversion rate of CO2 was calculated based on the product concentration obtained from GC analysis. Then the results were compared with other photocatalysts or reaction conditions to evaluate the efficiency of the photocatalytic reaction.

[0039] Characterization of the photocatalyst: The photocatalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometry.

[0040] Figure 1 This is a scanning electron microscope schematic diagram of the tungsten disulfide (WS2) nanoparticle photocatalyst prepared by the hydrothermal method in this example. It can be seen from Figure 1 that the morphology of the tungsten disulfide (WS2) nanoparticles is uniform, the quantity is large, and the structure is intact without other impurity morphological structures.

[0041] Figure 2It is the elemental surface distribution map of the tungsten disulfide (WS2) nanoparticle photocatalyst prepared in this embodiment. From Figure 2 it can be seen that the tungsten disulfide wafer is composed of tungsten ions and sulfur ions, and there are no other elements, which is relatively pure.

[0042] Figure 3 It is the X-ray diffraction pattern of the tungsten disulfide (WS2) particle photocatalyst prepared in this embodiment. From Figure 3 it can be seen that the diffraction peaks of the tungsten disulfide (WS2) particles are significantly broadened, which means it has a nanostructure, which is consistent with the scanning electron microscope results. In addition, the standard PDF card number corresponding to the tungsten disulfide (WS2) particles prepared this time is 08-0237.

[0043] Figure 4 This figure is a schematic diagram of the photocatalysis of tungsten disulfide (WS2) and CoPc-P / WS2 photocatalysts for CO2 in this embodiment. From Figure 4 it can be seen that the visible light catalytic reduction of CO2 by tungsten disulfide (WS2) and CoPc-P / WS2 is 24 micromoles per hour, showing excellent photocatalytic activity. In addition, during the 5h collection process, its photocatalytic performance did not show obvious attenuation, indicating that the structures of the tungsten disulfide (WS2) and CoPc-P / WS2 photocatalysts are relatively stable.

[0044] Example 2

[0045] Other conditions are the same as those in Example 1, except that the prepared WS2 nanoparticles are ultrasonically dispersed in 50 mL of deionized water, 0.0375 g of cobalt phthalocyanine is added to the solution, and ultrasonically stirred for 6 h to make it uniformly dispersed, and dried at 60 °C for 12 h.

[0046] Example 3

[0047] Other conditions are the same as those in Example 1, except that the prepared WS2 nanoparticles are ultrasonically dispersed in 50 mL of deionized water, 0.05 g of cobalt phthalocyanine is added to the solution, and ultrasonically stirred for 6 h to make it uniformly dispersed, and dried at 60 °C for 12 h.

[0048] Example 4

[0049] Other conditions are the same as those in Example 1, except that 1 g of WS2 nanoparticles are added to the H3PO4 solution (100 mL) with the required concentration. The mixed suspension is ultrasonically treated for 20 min and continuously stirred for 12 h, then dried at 80 °C and annealed at 450 °C for 1 h. The obtained powder is classified as XP-WS2, where X represents the mass ratio of NaH2PO4 to WS2 (0.2%, 0.4, 0.6 and 0.8%).

[0050] Then, 1 g of WS2 modulated by phosphoric acid was ultrasonically dispersed in 30 mL of ethanol for 30 min. To obtain a homogeneous suspension, a calculated volume of ethanol CoPc solution was added to the phosphoric acid-modulated WS2 suspension, followed by ultrasonic treatment and stirring for 30 min, then stirring at room temperature for 6 h, and then evaporating the solvent under stirring at 80 °C, and finally drying overnight at 60 °C.

[0051] Example 5

[0052] Under the same other conditions as in Example 1, the difference is that 1 g of the prepared 0.2P-WS2 nanoparticles were ultrasonically dispersed in 50 mL of deionized water, 0.05 g of cobalt phthalocyanine was added to the solution, and ultrasonic stirring was carried out for 6 h to make it uniformly dispersed, and then dried at 60 °C for 12 h.

[0053] Example 6

[0054] Under the same other conditions as in Example 1, the difference is that 1 g of the prepared 0.4P-WS2 nanoparticles were ultrasonically dispersed in 50 mL of deionized water, 0.05 g of cobalt phthalocyanine was added to the solution, and ultrasonic stirring was carried out for 6 h to make it uniformly dispersed, and then dried at 60 °C for 12 h.

[0055] Example 7

[0056] Under the same other conditions as in Example 1, the difference is that 1 g of the prepared 0.6P-WS2 nanoparticles were ultrasonically dispersed in 50 mL of deionized water, 0.5 g of cobalt phthalocyanine was added to the solution, and ultrasonic stirring was carried out for 6 h to make it uniformly dispersed, and then dried at 60 °C for 12 h.

[0057] Example 8

[0058] Under the same other conditions as in Example 1, the difference is that 1 g of the prepared 0.8P-WS2 nanoparticles were ultrasonically dispersed in 50 mL of deionized water, 0.5 g of cobalt phthalocyanine was added to the solution, and ultrasonic stirring was carried out for 6 h to make it uniformly dispersed, and then dried at 60 °C for 12 h.

Claims

1. A method for preparing a composite heterojunction photocatalyst, characterized in that: The steps include: a) WS2 nanoparticles were synthesized in one step using WCl6 as the W source and thioacetamide as the S source. First, thioacetamide powder was ultrasonically dissolved in deionized water. b) WCl6 was quickly added to the solution and then magnetically stirred to obtain a uniform dark blue solution; c) the reaction mixture is then transferred to a para-polyphenylene-lined autoclave and maintained at a certain temperature; d) After the reaction, the black precipitate was collected by centrifugation, washed several times with anhydrous ethanol and deionized water, and then freeze-dried and vacuum-sealed; e) adding WS2 nanoparticles to a H3PO4 solution to prepare a mixed suspension; ultrasonically treating the mixed suspension with continuous stirring, and then drying and annealing the mixed suspension; f) Ultrasonic dispersion of WS2 prepared with phosphoric acid in ethanol. To obtain a uniform suspension, the CoPc ethanol solution was added to the WS2 suspension prepared with phosphoric acid according to the calculated volume, followed by ultrasonic treatment and stirring. g) Stirring at room temperature, then evaporating the solvent under stirring, and finally drying to prepare the composite heterojunction photocatalyst CoPc-P / WS2.

2. The method for preparing a composite heterojunction photocatalyst according to claim 1, characterized in that: In step a), the mass ratio of WCl6 to thioacetamide is 1.19:2.

276.

3. The method for preparing a composite heterojunction photocatalyst according to claim 1, wherein: The thioacetamide powder in step a) was dissolved in 40 mL of deionized water by ultrasonication for 30 min.

4. The method for preparing a composite heterojunction photocatalyst according to claim 1, wherein: In step b), the mixture was stirred magnetically for 30 min.

5. The method for preparing a composite heterojunction photocatalyst according to claim 1, characterized in that: In step c), the reaction mixture is kept at 250°C for 24 hours.

6. The method for preparing a composite heterojunction photocatalyst according to claim 1, characterized in that: In step d), the product was then freeze-dried at -50°C for 10 h and vacuum-sealed at 60°C for 6 h.

7. The method for preparing a composite heterojunction photocatalyst according to claim 1, characterized in that: In step e), the mixed suspension is ultrasonically treated at an ultrasonic power of 100-150 W for 20 min and continuously stirred for 12 h, and then dried at 80° C. and annealed at 450° C. for 1 h.

8. A composite heterojunction photocatalyst prepared by the method according to any one of claims 1 to 7.

9. Use of the composite heterojunction photocatalyst according to claim 8 in reducing CO2.

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