A W 18 O 49 / rGO composite photothermal catalyst and preparation method and application thereof

Abstract

The application discloses a kind of W 18 O 49 / rGO composite photo-thermal catalyst and its preparation method and application, the catalyst includes the W 18 O 49 Nanorod and the reduced graphene oxide rGO carrier of loading the W 18 O 49 Nanorod.Its preparation method is: dispersing tungsten source and graphene oxide in solvent, by solvothermal reaction, W 18 O 49 In situ growth on rGO.The catalyst of the application exhibits excellent photo-thermal conversion performance and photo-generated charge separation efficiency under light, can efficiently and selectively catalyze CO2 and epoxide to generate cyclic carbonate under the condition of no additional heat source, normal pressure and mildness, the yield can be up to 95% (173mmol·g ‑1 ·h ‑1 ), and excellent cycle stability.The preparation method of the application is simple, low in cost, provides a new type of efficient photo-thermal catalyst for realizing CO2 resource utilization under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a defective tungsten oxide (W 18 O 49 ) / reduced graphene oxide (rGO) composite photothermal catalyst, its preparation method and its application in photothermal catalytic carbon dioxide cycloaddition reaction. Background Technology

[0002] Excessive emissions of carbon dioxide (CO2) have led to environmental problems such as global warming. Converting CO2 into high-value-added cyclic carbonates is an efficient carbon utilization pathway with 100% atom economy. However, traditional thermocatalytic CO2 cycloaddition reactions typically require harsh conditions of high temperature (>100℃) and high pressure (>1MPa), resulting in high energy consumption. In recent years, research on using solar energy to drive CO2 cycloaddition reactions under milder conditions has attracted widespread attention.

[0003] While existing technologies, such as metal-organic frameworks (MOFs), can achieve CO2 cycloaddition under light illumination, they suffer from problems such as low light utilization, high recombination rate of photogenerated carriers, and high and complex synthesis costs, limiting their practical applications. Defective tungsten oxide (W... 18 O 49 Due to its abundant oxygen vacancies and Lewis acidic sites, it exhibits good light absorption capacity and catalytic potential, but a single W... 18 O 49 The photogenerated charge separation efficiency of W still needs improvement, resulting in insufficient catalytic activity. Previous studies have attempted to... 18 O 49 Combining catalysts with carbon-based materials (such as g-C3N4 and biochar) can improve performance, but these composite systems mainly rely on type II heterojunctions to promote charge separation, failing to fully utilize the photothermal effect, and there is still considerable room for improvement in catalytic activity. Therefore, developing a novel catalyst that is low-cost, highly efficient, and capable of efficiently catalyzing the CO2 cycloaddition reaction under mild conditions (room temperature and pressure) is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a W 18 O 49 The / rGO composite photothermal catalyst, its preparation method and application aim to solve the defects of the existing technology, such as harsh conditions for CO2 cycloaddition reaction, insufficient catalyst activity and high recombination rate of photogenerated carriers. The catalyst can efficiently and selectively catalyze the synthesis of cyclic carbonates from CO2 and epoxides under mild conditions of normal pressure without external light source or heat source.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is: a W 18 O 49 / rGO composite photothermal catalyst, including oxygen-vacancy-rich W 18 O 49 Nanorods and the W supported 18 O 49 Nanorod-based reduced graphene oxide (rGO) carrier; the W 18 O 49 Nanorods are grown in situ on the surface of rGO to form nanoflower-like structures.

[0006] Preferably, the specific surface area of ​​the composite photothermal catalyst is 110-130 m². 2 / g, preferably 123m 2 / g; The oxygen vacancy concentration of the composite photothermal catalyst is higher than that of the pure phase W. 18 O 49 .

[0007] To achieve the above-mentioned objectives, the present invention also provides the aforementioned W. 18 O 49 The preparation method of / rGO composite photothermal catalyst includes the following steps: S1. Disperse tungsten source and graphene oxide (GO) in a solvent and stir to obtain a precursor suspension; S2. The precursor suspension obtained in step S1 is subjected to a solvothermal reaction at a temperature of 160-200℃ for 10-14 hours. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the reaction product. S3. Wash and dry the reaction product obtained in step S2 to obtain the W. 18 O 49 / rGO composite photothermal catalyst.

[0008] Preferably, in step S1, the tungsten source is tungsten hexachloride (WCl6); the mass ratio of graphene oxide (GO) to tungsten hexachloride (WCl6) is 1:(2-4); the solvent is anhydrous ethanol; and the stirring time is 4-8 hours.

[0009] Preferably, in step S2, the reaction temperature is 180°C and the reaction time is 12 hours.

[0010] To achieve the above-mentioned objectives, the present invention also provides the aforementioned W. 18 O 49 Application of / rGO composite photothermal catalyst in catalytic carbon dioxide cycloaddition reaction.

[0011] Furthermore, the application involves catalyzing the reaction of carbon dioxide with epoxides to generate cyclic carbonates under photothermal synergistic catalytic conditions.

[0012] Preferably, the epoxide is styrene oxide; the reaction conditions are: under simulated sunlight irradiation, at normal pressure, without any other external heat source.

[0013] Furthermore, tetrabutylammonium bromide (TBAB) is added as a co-catalyst.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The W provided by the present invention 18 O 49 The rGO composite photothermal catalyst, through the introduction of rGO, significantly increases the specific surface area of ​​the catalyst, provides more reactive active sites, and enhances the adsorption capacity for CO2; under the same reaction conditions, the catalytic activity of this invention is significantly superior to that of W. 18 O 49 / g-C3N4 composite system (see Comparative Example 3).

[0015] (2) The excellent conductivity of rGO in this invention effectively promotes W 18 O 49 The migration and separation of photogenerated electrons suppress the recombination of electron-hole pairs, prolong the lifetime of photogenerated carriers, and thus significantly improve quantum efficiency. Unlike the type II heterojunction formed by g-C3N4, rGO provides a more direct electron transport channel as a conductor.

[0016] (3) The W prepared by this invention 18 O 49 The rGO composite catalyst exhibits excellent photothermal effect under light irradiation, which can rapidly increase the temperature of the reaction system. Through the coupling effect of photocatalysis and thermal catalysis, it further accelerates the kinetic process of epoxide ring opening and CO2 activation. This photothermal effect is a unique property of rGO that is not observed in the comparative system with g-C3N4 as support.

[0017] (4) The catalyst of this invention can efficiently catalyze the CO2 cycloaddition reaction under mild conditions of normal pressure and simulated sunlight without the addition of other heat sources, and the yield of styrene carbonate can reach up to 95% (173 mmol·g). -1 ·h -1 It also has excellent cycle stability, which greatly reduces energy consumption and production costs.

[0018] (5) The preparation method of the present invention is simple and low in cost: it adopts a one-step in-situ solvothermal method, which is simple, mild and easy to scale up. Attached Figure Description

[0019] Figure 1 The XRD and Raman spectra of the comparative sample prepared in the embodiments of the present invention and the catalyst of the present invention are shown, wherein (a) represents WO3 and W18 O 49 PXRD patterns, (b) are the W prepared by GO and Examples 1-3 respectively. 18 O 49 PXRD pattern of / rGO complex, (c) is Raman spectrum of GO and 600W-G prepared in Example 1. Figure 2 The images shown are electron microscope (EM) images of the comparative sample prepared in the embodiments of the present invention and the catalyst of the present invention, wherein (a) is W 18 O 49 (a) is a SEM image of GO, (b) is a SEM image of GO, (c) is a SEM image of catalyst 600W-G prepared in Example 1 of the present invention, and (d) is a TEM image of catalyst 600W-G prepared in Example 1 of the present invention. Figure 3 The XPS and EPR spectra of the comparative sample prepared in the embodiments of the present invention and the catalyst of the present invention are shown, wherein (a) is the full spectrum, (b) is the C1s spectrum, (c) is the W4f spectrum, and (d) is the W4f spectrum. 18 O 49 EPR spectrum of oxygen vacancy at 600 W-G. Figure 4 The figures shown are physicochemical characterization diagrams of the catalysts in the embodiments of the present invention, wherein (a) is the N2 adsorption-desorption isotherm, (b) is the pore size distribution diagram, and (c) is the CO2 adsorption isotherm. Figure 5 The figures shown are optical property characterization diagrams of the catalyst in the embodiments of the present invention, wherein (a) is the UV-Vis diffuse reflectance absorption spectrum, and (b) is the W... 18 O 49 The Tauc curve. Figure 6 The figure shows the evaluation results of the photocatalytic CO2 cycloaddition reaction performance of the catalyst in the embodiments of the present invention. Among them, (a) is a comparison of the catalytic performance of different samples, (b) is the cycle stability test of 600W-G prepared in Example 1, (c) is the PxRD diagram of 600W-G before and after the cycle test, and (d) is the temperature change curve of different reaction systems. Figure 7 The following are characterization diagrams of the acid-base properties and photoelectric properties of the catalyst in the embodiments of the present invention, wherein (a) is the NH3-TPD diagram, (b) is the CO2-TPD diagram, (c) is the EIS spectrum, and (d) is the transient photocurrent density diagram. Detailed Implementation

[0020] To better understand the present invention, the present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the scope shown in the embodiments. Example 1

[0021] A W 18 O 49 The preparation method of / rGO composite photothermal catalyst (600W-G) includes the following steps: S1. Weigh 0.2g of graphene oxide (GO), disperse it in 50mL of anhydrous ethanol, and ultrasonically disperse it evenly; then add 0.6g of tungsten hexachloride (WCl6), and continue stirring for 6 hours to obtain a precursor suspension; S2. Transfer the above suspension to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and solvothermal react at 180°C for 12 hours. After the reaction, allow it to cool naturally to room temperature. During the reaction, GO is reduced to rGO, while W... 18 O 49 In-situ growth on rGO yielded the reaction products; S3. The reaction product obtained in step S2 is washed several times by centrifugation with anhydrous ethanol and deionized water, and finally dried overnight in a vacuum drying oven at 80°C to obtain W. 18 O 49 / rGO composite photothermal catalyst, denoted as 600W-G. Example 2

[0022] In this embodiment, the only difference is that 0.4g of tungsten hexachloride (WCl6) is added in step S1. All other steps and conditions remain the same as in Example 1. The resulting W... 18 O 49 / rGO composite photothermal catalyst, denoted as 400W-G. Example 3

[0023] In this embodiment, the only difference is that 0.8g of tungsten hexachloride (WCl6) is added in step S1. All other steps and conditions remain the same as in Example 1. The resulting W... 18 O 49 / rGO composite photothermal catalyst, denoted as 800W-G.

[0024] Comparative Example 1 Pure phase W 18 O 49 Preparation: Dissolve 0.8 g WCl6 in 50 mL of anhydrous ethanol and stir for 4 hours; transfer the solution to the reaction mixture. The reaction was carried out in a reactor at 180°C for 12 hours; after centrifugation and washing, the product was dried overnight in a vacuum drying oven at 80°C to obtain pure phase W. 18 O 49 .

[0025] Comparative Example 2 Preparation of pure phase WO3: Monoclinic phase WO3 was prepared as a control sample according to the literature (K. Wenderich, J. Noack, A. Kärgel, A. Trunschke, G. Mul, Effect of Temperature and pH on Phase Transformations in Citric Acid Mediated Hydrothermal Growth of Tungsten Oxide, European Journal of Inorganic Chemistry, 2018 (2018) 917-923).

[0026] Comparative Example 3 A W 18 O 49 The preparation method of / g-C3N4 composite photocatalyst (600W-CN) includes the following steps: S1. g-C3N4 was prepared by calcining urea at 550℃ for 2 hours. 0.2g of g-C3N4 was weighed and dispersed in 50mL of anhydrous ethanol and ultrasonically dispersed evenly. Then 0.6g of tungsten hexachloride (WCl6) was added and stirred for 6 hours to obtain a precursor suspension. S2. Transfer the above suspension to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, seal it, and solvothermal react at 180 °C for 12 hours; after the reaction is completed, allow it to cool naturally to room temperature to obtain the reaction product. S2. The reaction product obtained in step S2 is washed several times by centrifugation with anhydrous ethanol and deionized water, and finally dried overnight in a vacuum drying oven at 80°C to obtain W. 18 O 49 / g-C3N4 composite photocatalyst, denoted as 600W-CN.

[0027] The catalysts prepared above were characterized structurally as follows: 1. The 600W-G prepared in Example 1 and the pure phase W of Comparative Example 1 18 O 49 The structure was characterized by XRD, Raman, SEM, TEM, XPS, and EPR, and the results are as follows: Figure 1-3 As shown.

[0028] Figure 1 a represents WO3 and W 18 O 49 PXRD plot. W 18 O 49 Diffraction peaks appear at 23.3°, 24.4°, 33.4°, and 47.2°, corresponding to the monoclinic phase W.18 O 49 (PDF#71-2450), while the diffraction peaks of WO3 are significantly different, indicating that the pure phase W 18 O 49 Successfully synthesized. Figure 1 b represents GO and different W. 18 O 49 PXRD pattern of the / rGO complex. GO shows a characteristic peak at approximately 10.5°, which disappears in the complex, while a broad peak appears at approximately 24°, indicating that GO is reduced to rGO. With increasing WCl6 content, W... 18 O 49 The diffraction peaks gradually increase, proving that W 18 O 49 Successfully loaded onto rGO. Figure 1 In the Raman spectrum of c, 600W-G exhibits a D band (1350 cm⁻¹). -1 ) and G-band (1590 cm) -1 This further confirms the existence of rGO.

[0029] Figure 2 SEM images of a show pure W 18 O 49 It has a nanorod-like structure with a length of approximately 200-400 nm. Figure 2 b's GO exhibits a typical lamellar morphology. Figure 2 The SEM image of c at 600W-G shows that W 18 O 49 Nanorods are tightly coated on the surface of rGO sheets, forming a unique "nanoflower-like" three-dimensional structure. Figure 2 TEM further confirmed that this closely contacted heterogeneous interface is conducive to the interfacial migration of photogenerated charges.

[0030] Figure 3 The XPS spectrum of ac shows the presence of W, C, and O elements. W4f spectrum ( Figure 3 c) In this context, the W of 600W-G 6+ and W 5+ Peak position compared to pure phase W 18 O 49 A slight displacement occurred, indicating that W 18 O 49 There is an electronic interaction between it and rGO. Figure 3 In the EPR spectrum of phase d, the oxygen vacancy signal intensity of 600W-G is significantly higher than that of pure phase W. 18 O 49 This indicates that the introduction of rGO promotes the generation of more oxygen vacancies, providing more active sites for CO2 activation.

[0031] 2. Specific surface area and CO2 adsorption performance Figure 4 The N2 adsorption-desorption isotherm of α shows that 600W-G exhibits a typical Type IV isotherm, with a specific surface area as high as 123 m². 2 / g, far higher than pure phase W 18 O 49 (approximately 48 m) 2 / g). Pore size distribution diagram ( Figure 4 b) indicates that the catalyst has a mesoporous structure. The CO2 adsorption isotherm ( Figure 4 c) shows that the adsorption capacity of 600W-G for CO2 is significantly better than that of pure phase W. 18 O 49 And WO3, which is attributed to its higher specific surface area and abundant oxygen vacancies.

[0032] 3. Optical properties Figure 5 The UV-Vis diffuse reflectance absorption spectrum of phase a shows that the absorption intensity of 600W-G is higher than that of pure phase W across the entire spectral range. 18 O 49 Both WO3 and rGO exhibit significant absorption tails, especially in the visible light region (>450 nm), indicating that the introduction of rGO enhances light absorption. This is confirmed by Tauc curves (…). Figure 5 b) Calculate W 18 O 49 The band gap is approximately 2.8 eV.

[0033] In summary, the performance characterization results above confirm that the W prepared in this invention... 18 O 49 / rGO composite photothermal catalyst successfully constructed a heterojunction with a larger specific surface area (123 m²). 2 It exhibits enhanced CO2 adsorption capacity, a wider light absorption range, higher oxygen vacancy concentration, and superior photogenerated charge separation and transport efficiency. These excellent physicochemical properties form the basis of its outstanding catalytic performance.

[0034] The catalysts prepared above were subjected to the following tests: 1. Performance Testing: Photocatalytic CO2 Cycloaddition Reaction 30 mg of the catalyst to be tested (Examples 1-3 and Comparative Examples 1-3) and 36 mg of tetrabutylammonium bromide (TBAB) were weighed and placed into a closed quartz reactor containing 5 mL of styrene oxide. Pure CO2 was introduced as a replacement gas to bring the pressure inside the reactor to 100 kPa. The reactor was irradiated with a 300 W xenon lamp (equipped with an AM1.5 filter) to simulate sunlight for 8 hours. The temperature change of the reaction system was recorded using an infrared thermal imager during the reaction. After the reaction was completed, the reaction solution was centrifuged and extracted. The yield of the product styrene carbonate was analyzed by gas chromatography using dodecane as an internal standard. The test results are as follows: Figure 6 As shown in Figure a. The results show that W in Comparative Example 1 18 O 49 The conversion rate of styrene oxide was 29%, significantly higher than that of WO3 in Comparative Example 2 (8%). The W3 prepared in this invention… 18 O 49 / rGO composite photothermal catalyst has significantly higher activity than pure phase W 18 O 49 In Example 1, the 600W-G achieved a styrene oxide conversion rate of up to 95% after 8 hours of reaction, with a yield of up to 173 mmol·g. -1 ·h -1 The conversion rate of 600W-CN in Comparative Example 3 was approximately 74% under the same reaction conditions (8 hours) (it reached 74% at 4 hours, and the yield did not increase significantly with extended reaction time), which was much lower than the 95% of 600W-G. Under visible light irradiation greater than 420 nm, the conversion rate of 600W-G could still be maintained at 36%, demonstrating excellent visible light photocatalytic performance.

[0035] 2. Cyclic stability test Following the performance testing method, a cyclic experiment was conducted on the 600W-G catalyst from Example 1. After each reaction, the catalyst was recovered, washed, dried, and used for the next reaction. The results are as follows: Figure 6 As shown in b, after four cycles (32 hours in total), the catalyst activity did not decrease significantly, as indicated by the PXRD pattern ( Figure 6 c) also shows that the catalyst structure did not change before and after the reaction, proving that it has excellent cycle stability and structural stability.

[0036] 3. Experiment to investigate the photothermal effect (1) Track the temperature change of the reaction system under light, such as Figure 6As shown in Figure d, the temperature of the 600W-G system in Example 1 rose sharply from 16°C to 52.9°C after 20 minutes of illumination, and remained at approximately 68°C for 8 hours. In contrast, the 600W-CN system in Comparative Example 3, under the same illumination conditions, only reached a maximum temperature of approximately 45°C, and no significant photothermal temperature rise was observed. The photothermal conversion performance of the 600W-G prepared in Example 1 is far superior to that of Comparative Examples 1-3.

[0037] (2) Setting up an external water bath for temperature control: When the reaction temperature is controlled at 70℃, the W of Comparative Example 1 18 O 49 The conversion rate increased to 57%, indicating that the thermal effect promoted the reaction. When the temperature of the 600W-G reaction system was controlled at 20℃ using circulating water, the conversion rate dropped sharply from 95% to 33%, indicating that the photothermal effect played a key role in the reaction.

[0038] (3) Dark reaction control experiment: At 70℃ and without light, the conversion rate on 600W-G was only 19%, indicating that photogenerated charge plays a dominant role in the reaction.

[0039] Since Lewis acid-base sites play a crucial role in the thermocatalytic CO2 cycloaddition reaction, NH3-TPD and CO2-TPD were used to target W... 18 O 49 The acid-base properties of WO3 were characterized. For example... Figure 7 As shown in a, W 18 O 49 The TPD curve shows a desorption peak at around 100°C from the physical adsorption of NH3, and a main peak at around 350°C, indicating that it is a moderately strong acid, much stronger than WO3. CO2-TPD also indicates that WO3... 18 O 49 There are moderately strong alkaline sites in it. Figure 7 b) WO3 has almost no basic sites, W 18 O 49 The abundant Lewis acid-base sites in the rGO matrix are conducive to the CO2 cycloaddition reaction. To further demonstrate the unique advantages of the rGO support selected in this invention, based on the above performance comparison results and combined with physicochemical characterization, W... 18 O 49 / rGO and W 18 O 49 The mechanism of action of the two composite systems / g-C3N4 was analyzed in depth: (1) rGO provides a more efficient electron transport channel Electrochemical impedance spectroscopy (EIS) shows ( Figure 7 c), the present invention W 18 O49 The charge transfer resistance of the / rGO catalyst is much smaller than that of W. 18 O 49 / g-C3N4. Transient photocurrent response ( Figure 7 d) also indicates that W 18 O 49 / rGO exhibits a higher photocurrent density. This confirms that the metalloid high conductivity of rGO endows it with superior electron mobility compared to g-C3N4, enabling more efficient extraction of W. 18 O 49 The photogenerated electrons greatly suppress the recombination of electron-hole pairs.

[0040] (2) rGO brings superior photothermal conversion performance Experiments investigating the photothermal effect show that under illumination, W 18 O 49 The temperature of the / rGO (600W-G) reaction system can rapidly rise to approximately 52.9℃ within 20 minutes and stabilize at around 68℃ within 8 hours; while under the same conditions, W 18 O 49 The heating effect of the / g-C3N4 (600W-CN) system is significantly inferior (the highest temperature is only about 45℃ after 8 hours of illumination). This significant photothermal effect stems from the excellent photothermal conversion capability of rGO itself, which, together with W 18 O 49 The synergistic effect creates a photothermal synergistic catalytic microenvironment for the reaction, which is not present in composite systems supported by g-C3N4.

[0041] (3) rGO formed a denser "nanoflower-like" three-dimensional structure. Scanning electron microscope (SEM) image ( Figure 2 c) shows that the catalyst of the present invention forms a unique "nanoflower-like" three-dimensional structure, which is composed of W 18 O 49 The nanorods are tightly coated and anchored on rGO sheets. This significantly increases the specific surface area (up to 123 m²). 2 / g) provides more reactive sites and also promotes the adsorption of CO2 by the catalyst ( Figure 4 c). In contrast, W 18 O 49 The / g-C3N4 system typically exhibits a two-dimensional structure with "surface-to-line" contact, which is disadvantageous in terms of interfacial charge transfer and the construction of a three-dimensional porous structure, resulting in its catalytic activity being far lower than that of W. 18 O 49 / rGO.

[0042] Based on the above comparative analysis, it can be seen that the present invention, by using rGO as a carrier, is significantly superior to the existing technical solutions using g-C3N4 as a carrier in terms of electron transport efficiency, photothermal conversion capability, and three-dimensional structure construction, achieving unexpected technical effects.

Claims

1. A type of W 18 O 49 / rGO composite photothermal catalyst, characterized in that... Including oxygen-rich vacancy W 18 O 49 Nanorods and the W supported 18 O 49 Nanorod-based reduced graphene oxide (rGO) carrier; the W 18 O 49 Nanorods are grown in situ on the surface of rGO to form nanoflower-like structures.

2. A W according to claim 1 18 O 49 / rGO composite photothermal catalyst, characterized in that... The specific surface area of ​​the composite photothermal catalyst is 110-130 m². 2 / g; The oxygen vacancy concentration of the composite photothermal catalyst is higher than that of the pure phase W. 18 O 49 .

3. A W according to claim 2 18 O 49 / rGO composite photothermal catalyst, characterized in that... The specific surface area of ​​the composite photothermal catalyst is 123 m². 2 / g.

4. A W as described in any one of claims 1-3 18 O 49 The method for preparing / rGO composite photothermal catalyst is characterized by, Includes the following steps: S1. Disperse tungsten source and graphene oxide (GO) in a solvent and stir to obtain a precursor suspension; S2. The precursor suspension obtained in step S1 is subjected to a solvothermal reaction at a temperature of 160-200℃ for 10-14 hours. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the reaction product. S3. Wash and dry the reaction product obtained in step S2 to obtain the W. 18 O 49 / rGO composite photothermal catalyst.

5. A W according to claim 1 18 O 49 The method for preparing / rGO composite photothermal catalyst is characterized by, In step S1, the tungsten source is tungsten hexachloride (WCl6); the mass ratio of graphene oxide (GO) to tungsten hexachloride (WCl6) is 1:(2-4); the solvent is anhydrous ethanol; and the stirring time is 4-8 hours.

6. A W according to claim 1 or 2 18 O 49 The method for preparing / rGO composite photothermal catalyst is characterized by, In step S2, the reaction temperature is 180℃ and the reaction time is 12 hours.

7. The W as described in any one of claims 1-3 18 O 49 / rGO composite photothermal catalyst or W prepared by the method according to any one of claims 4-6 18 O 49 Application of / rGO composite photothermal catalyst in catalytic carbon dioxide cycloaddition reaction.

8. The application according to claim 7, characterized in that, The application involves catalyzing the reaction of carbon dioxide with epoxides to generate cyclic carbonates under photothermal synergistic catalysis.

9. The application according to claim 8, characterized in that, The epoxide is styrene oxide; the reaction conditions are: under simulated sunlight irradiation, at normal pressure, without any other external heat source.

10. The application according to claim 9, characterized in that, In the reaction, tetrabutylammonium bromide (TBAB) was also added as a co-catalyst.

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