A porous ultrathin Cs 0.33 WO3 nanosheets, methods of making and using the same

Abstract

This invention relates to a porous ultrathin Cs 0.33 A method for preparing WO3 nanosheets includes: dispersing Na2WO4·4H2O in dilute nitric acid solution, mixing and stirring, centrifuging, washing, and drying to obtain a layered WO3·2H2O nanosheet precursor; dispersing the layered WO3·2H2O nanosheet precursor in deionized water; ultrasonically vibrating, centrifuging, filtering, and drying to obtain porous ultrathin WO3·2H2O nanosheets; adding the porous ultrathin WO3·2H2O nanosheets to anhydrous ethanol and ultrasonically treating; then adding Cs2CO3 and stirring until Cs2CO3 is completely dissolved; then adding CH3COOH and stirring to obtain a mixed solution; reacting the mixed solution in a reaction vessel; and finally washing and drying to obtain porous ultrathin Cs2CO3 nanosheets. 0.33 WO3 nanosheets. Preparation of porous ultrathin Cs 0.33 WO3 nanosheet photocatalysts not only provide a large number of active sites, but also optimize the electronic structure and improve the intrinsic activity of the active sites; at the same time, they are beneficial to the separation and transfer of photogenerated carriers; and they exhibit excellent photocatalytic CO2 conversion performance under full-spectrum light, visible light and near-infrared light irradiation.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of photocatalyst materials, in particular to a porous ultrathin Cs 0.33 WO3 nanosheet and a preparation method and application thereof. BACKGROUND

[0002] Sustainable technologies that capture carbon dioxide and convert it into renewable fuels and high-value chemicals have attracted considerable attention, aiming to mitigate the rising concentration of carbon dioxide in the atmosphere. Among numerous countermeasures, photocatalytic technology is an extremely attractive way to produce value-added chemicals and fuels using CO2 as a carbon source. However, conventional semiconductor photocatalysts generally have a wide band gap, and their spectral response is limited to the ultraviolet and visible light regions, which cannot effectively utilize about 50% of the near-infrared light in the solar spectrum. In addition, the poor CO2 molecule adsorption and activation ability and the rapid recombination of photo-generated carriers still limit the photocatalytic CO2 conversion activity. SUMMARY

[0003] The technical problem to be solved by the application is to research a porous ultrathin Cs 0.33 WO3 nanosheet and a preparation method and application thereof, which have near-infrared light absorption, high efficiency and high selectivity of CO2 conversion ability.

[0004] The technical solution of the application to solve the above technical problem is as follows:

[0005] A porous ultrathin Cs 0.33 WO3 nanosheet and a preparation method thereof, comprising the following steps:

[0006] Step 1, preparing a layered WO3.2H2O nanosheet precursor: dispersing Na2WO4.4H2O in a dilute nitric acid solution, mixing, stirring, centrifuging, washing and drying to obtain a layered WO3.2H2O nanosheet precursor;

[0007] Step 2, liquid phase exfoliation of the layered WO3.2H2O nanosheet precursor: dispersing the layered WO3.2H2O nanosheet precursor in deionized water; ultrasonic oscillation, centrifugation, filtration and drying to obtain porous ultrathin WO3.2H2O nanosheets;

[0008] Step 3, preparing porous ultrathin Cs 0.33 WO3 nanosheets: adding the porous ultrathin WO3.2H2O nanosheets into anhydrous ethanol and ultrasonic treatment; then adding Cs2CO3 and stirring until the Cs2CO3 is completely dissolved; then adding CH3COOH and stirring to obtain a mixed solution; reacting the mixed solution in a reaction kettle for a period of time; and washing and drying to obtain the porous ultrathin Cs 0.33 WO3 nanosheets.

[0009] On the basis of the above technical solutions, the application can be further improved as follows.

[0010] Further, step 1 specifically comprises: weighing Na2WO4·4H2O and dispersing it in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by a centrifuge, and washing the yellow precipitate with deionized water several times until the pH value is neutral, and drying the yellow precipitate to obtain layered WO3·2H2O nanosheet precursors.

[0011] Further, step 2 specifically comprises: dispersing the layered WO3·2H2O nanosheet precursors in deionized water, ultrasonically oscillating in a cold water bath environment to obtain a light yellow suspension, separating the unpeeled yellow precipitate in the light yellow suspension by a centrifuge, collecting the precipitate in the upper solution by centrifugation, and drying to obtain porous ultra-thin WO3·2H2O nanosheets.

[0012] Further, step 3 specifically comprises: adding the porous ultra-thin WO3·2H2O nanosheets to anhydrous ethanol, ultrasonically treating to completely disperse the powder in the solution, adding Cs2CO3, stirring the solution until it is completely dissolved, then adding CH3COOH and stirring to obtain a mixed solution, pouring the mixed solution into a reaction kettle and reacting for a period of time, collecting the sample and washing it with water and ethanol several times, and then drying to obtain porous ultra-thin Cs 0.33 WO3 nanosheets.

[0013] Further, in step 1, the volume ratio of concentrated nitric acid to deionized water in the dilute nitric acid solution is 30-50%.

[0014] Further, the above drying is carried out in a vacuum environment.

[0015] Further, in step 2, the speed of the centrifuge for separating the yellow precipitate in the light yellow suspension is 4000-7000 rpm, and the time is 3-10 min; the speed of the centrifuge for separating the precipitate in the upper solution is 9000-10000 rpm, and the time is 5-10 min.

[0016] Further, in step 2, the temperature of the cold water bath environment is 0-3℃, and the ultrasonic oscillation time is 5-18 h.

[0017] Another technical solution of the application is as follows:

[0018] A porous ultra-thin Cs 0.33 WO3 nanosheet is prepared by the preparation method of the above porous ultra-thin Cs 0.33 WO3 nanosheet.

[0019] Another technical solution of the application is as follows:

[0020] A porous ultra-thin Cs0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs

[0021] The present application has the advantages that: the porous ultrathin WO3·2H2O nanosheets and Cs2CO3 are used as raw materials, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs

[0023] Figure 2 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs

[0024] Figure 3 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs 0.33 WO3nanosheets, the porous ultrathin Cs

[0025] Figure 4 Porous ultrathin Cs prepared by the present application 0.33 WO3 nanosheets, layered Cs 0.33 WO3 and non-porous ultrathin Cs 0.33 CO2 adsorption isotherm (a) and CO2-TPD graph (b) of WO3 nanosheets

[0026] Figure 5 Porous ultrathin Cs prepared by the present application 0.33 WO3 nanosheets, layered Cs 0.33 WO3 and non-porous ultrathin Cs 0.33 DMC production graph of WO3 nanosheets under full spectrum (a) and (b) near-infrared light irradiation. DETAILED DESCRIPTION

[0027] The principles and features of the present application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application.

[0028] As shown in the drawings, the porous ultrathin Cs prepared by the present application Figures 1 to 5 Figure, the porous ultrathin Cs prepared by the present application 0.33 The preparation method of the WO3 nanosheets comprises the following steps:

[0029] Step 1, preparation of layered WO3·2H2O nanosheet precursor: disperse Na2WO4·4H2O in dilute nitric acid solution, mix, stir, centrifuge, wash, and dry to obtain layered WO3·2H2O nanosheet precursor;

[0030] Step 2, liquid phase exfoliation of layered WO3·2H2O nanosheet precursor: disperse the layered WO3·2H2O nanosheet precursor in deionized water; ultrasonic oscillation, centrifugation, filtration, and drying to obtain porous ultrathin WO3·2H2O nanosheets;

[0031] Step 3, preparation of porous ultrathin Cs 0.33 WO3 nanosheets: add the porous ultrathin WO3·2H2O nanosheets to anhydrous ethanol, ultrasonic treatment; then add Cs2CO3, stir until the Cs2CO3 is completely dissolved; then add CH3COOH, stir to obtain a mixed solution; react the mixed solution in a reaction kettle for a period of time; wash and dry to obtain the porous ultrathin Cs 0.33 WO3 nanosheets.

[0032] The porous ultrathin Cs prepared by the present application 0.33The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

[0033] In specific implementation, the amount of Na2WO4·4H2O is 0.2 g, and the volume of the dilute nitric acid solution is 150 mL.

[0034] The application discloses a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

[0035] The application discloses a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor. 0.33 The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

[0036] The application discloses a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

[0037] The application discloses a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet comprises the following steps: dispersing Na2WO4·4H2O in a dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate in the yellow solution by using a centrifuge, and washing the yellow precipitate with deionized water until the pH value is neutral; and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

[0038] Embodiment 7 of the present application is a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet is based on embodiment 6, in step 2, when the centrifuge separates the yellow precipitate in the light yellow suspension, the rotation speed is 4000-7000 rpm, in specific implementation, the rotation speed is 5000-6000 rpm, and the time is 3-10 min; when the centrifuge separates the precipitate in the upper solution, the rotation speed is 9000-10000 rpm, and the time is 5-10 min.

[0039] Embodiment 8 of the present application is a porous ultrathin Cs 0.33 The preparation method of the WO3 nanosheet is based on embodiment 7, in step 2, the temperature of the cold water bath environment is 0-3℃, and the ultrasonic oscillation time is 5-18 h.

[0040] Embodiment 9 of the present application is a porous ultrathin Cs 0.33 The WO3 nanosheet adopts any one of the porous ultrathin Cs in embodiments 1-8 0.33 The preparation method of the WO3 nanosheet is prepared.

[0041] Embodiment 10 of the present application is a porous ultrathin Cs 0.33 The application of the WO3 nanosheet adopts any one of the porous ultrathin Cs in embodiments 1-8 0.33 The porous ultrathin Cs prepared by the preparation method of the WO3 nanosheet 0.33 The WO3 nanosheet is applied to photocatalytic CO2 conversion, and the porous ultrathin Cs 0.33 The WO3 nanosheet sample is placed in a reaction tank, CH3OH is filled into the reactor, the reactor is pumped to vacuum, high-purity CO2 gas is introduced, the pressure is at least equal to one atmosphere, and a xenon lamp is used as a full-spectrum light source for photocatalytic experiment; in addition, a filter is loaded on the xenon lamp to serve as a visible light and near-infrared light source for photocatalytic experiment. In specific implementation, the power of the xenon lamp is 300W.

[0042] The present application uses porous ultrathin WO3·2H2O nanosheets and Cs2CO3 as raw materials, and prepares porous ultrathin Cs 0.33 The WO3 nanosheet photocatalyst; the preparation method of the present application has the characteristics of simple production process, low cost and high yield; the porous ultrathin Cs 0.33 The WO3 nanosheet photocatalyst not only provides a large number of active sites, but also optimizes the electronic structure, thereby improving the intrinsic activity of the active sites; in addition, the porous ultrathin Cs 0.33 The WO3 nanosheet is conducive to the separation and transfer of photo-generated carriers; the porous ultrathin Cs 0.33 The WO3 nanosheet exhibits excellent photocatalytic CO2 conversion performance under full-spectrum light, visible light and near-infrared light irradiation. Specific embodiment 1

[0044] Step 1, 0.2 g of Na2WO4·4H2O was dispersed in 150 mL of dilute nitric acid solution (48 mL of concentrated nitric acid was added to 102 mL of deionized water), a yellow solution was obtained after stirring at room temperature for 72 h, then the yellow precipitate was separated by centrifuge and the yellow precipitate was washed with deionized water several times until the pH value was neutral, and the yellow precipitate was dried in a vacuum drying oven at 70 ℃ for 12 h to obtain layered WO3·2H2O nanosheet precursor;

[0045] Step 2, 0.2 g of layered WO3·2H2O was dispersed in 200 mL of deionized water, and a light yellow suspension was obtained by ultrasonic oscillation in a cold water bath environment at 3 ℃ for 12 h; the unpeeled yellow precipitate in the light yellow suspension was separated by centrifuge at a speed of 5000 rpm, and the upper layer solution was centrifuged at a speed of 10000 rpm for 10 min, and the precipitate was collected and vacuum dried in a vacuum drying oven for 12 h to obtain porous ultrathin WO3·2H2O nanosheets;

[0046] Step 3, 0.18 g of porous ultrathin WO3·2H2O nanosheets was added to 50 mL of anhydrous ethanol, and the powder was completely dispersed in the solution after ultrasonic treatment for 15 min, 0.036 g of Cs2CO 3， was added, the solution was stirred until the Cs2CO3 was completely dissolved, then 10 mL of CH3COOH was added and stirred to obtain a mixed solution, which was poured into a 90 mL polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle and reacted at 240 ℃ for 30 h, the sample was collected and washed with water and ethanol several times, then vacuum dried in a vacuum drying oven at 70 ℃ for 12 h to obtain porous ultrathin Cs 0.33 WO3 nanosheets. Specific embodiment 2

[0048] Step 1, 0.2 g of Na2WO4·4H2O was dispersed in 150 mL of dilute nitric acid solution (48 mL of concentrated nitric acid was added to 102 mL of deionized water), a yellow solution was obtained after stirring at room temperature for 72 h, then the yellow precipitate was separated by centrifuge and the yellow precipitate was washed with deionized water several times until the pH value was neutral, and the yellow precipitate was dried in a vacuum drying oven at 70 ℃ for 12 h to obtain layered WO3·2H2O nanosheet precursor;

[0049] Step 2, 0.2 g layered WO3·2H2O was dispersed in 200 mL deionized water, and ultrasonic oscillation was performed in a cold water bath environment at 0°C for 18 h to obtain a light yellow suspension. The unexfoliated yellow precipitate in the light yellow suspension was separated by centrifuge at a speed of 5000 rpm, and the upper solution was centrifuged at a speed of 90000 rpm for 5 min. The precipitate was collected and vacuum dried in a vacuum drying oven for 12 h to obtain porous ultrathin WO3·2H2O nanosheets;

[0050] Step 3, 0.18 g of porous ultrathin WO3·2H2O nanosheets was added to 30 mL of anhydrous ethanol, and the powder was completely dispersed in the solution after ultrasonic treatment for 15 min. 0.038 g of Cs2CO3 was added, and the solution was stirred until the Cs2CO3 was completely dissolved. Then 15 mL of CH3COOH was added and stirred to obtain a mixed solution. The mixed solution was poured into a 90 mL polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, and the reaction was carried out at 240°C for 30 h. After the sample was collected, it was washed with water and ethanol several times, and then vacuum dried at 80°C in a vacuum drying oven for 12 h to obtain porous ultrathin Cs 0.33 WO3 nanosheets. Specific embodiment 3

[0052] 0.2 g of Na2WO4·4H2O was weighed and dispersed in 150 mL of dilute nitric acid solution (43 mL of concentrated nitric acid was added to 107 mL of deionized water), and the remaining steps were the same as in specific embodiment 1. Porous ultrathin Cs 0.33 WO3 nanosheets were also prepared.

[0053] Layered Cs 0.33 WO3 and porous ultrathin Cs 0.33 WO3 nanosheets control group

[0054] 0.5 g of Na2WO4·4H2O was weighed and dispersed in 150 mL of hot water (70°C). After it was completely dissolved, 150 mL of concentrated nitric acid was added to the original solution. After stirring vigorously for 72 h, a yellow solution was obtained. Then the yellow precipitate was separated by centrifuge and washed several times. Finally, the collected yellow precipitate was dried in a vacuum oven at 70°C for 12 h to obtain precursor WO3·0.33H2O nanosheets.

[0055] 0.166 g of WO3·0.33H2O was added to 50 mL of anhydrous ethanol, and the mixture was sonicated for 15 min to completely disperse the powder in the solution. 0.0375 g of Cs2CO3 was added and stirred for 20 min until completely dissolved. Then, 10 mL of glacial acetic acid was added and stirred for 2 h. The resulting yellow turbid liquid was sealed in a 90 mL polytetrafluoroethylene-lined autoclave and reacted at 70 °C for 30 h. After collecting the sample, it was washed several times with water and ethanol, and then vacuum dried at 70 °C for 12 h to obtain layered Cs. 0.33 WO3, denoted as bulk.

[0056] Layered Cs 0.33 Liquid phase exfoliation with WO3 yielded non-porous ultrathin Cs. 0.33 WO3 nanosheets are referred to as porous-free nanosheets.

[0057] The porous ultrathin Cs material prepared by this invention 0.33 WO3 nanosheets are abbreviated as porous nanosheets.

[0058] test:

[0059] Application tests were conducted on bulk, porous-free nanosheets, and porous nanosheets. The specific method was as follows: First, 30 mg of the sample to be tested was placed in the reaction vessel. Then, 10 mL of CH3OH was introduced into the reactor. The reactor was evacuated to a vacuum, and high-purity CO2 gas was introduced. The pressure was at least one atmosphere. A 300 W xenon lamp was used as a full-spectrum light source for photocatalysis experiments. In addition, filters were loaded onto the xenon lamp as visible light and near-infrared light sources for photocatalysis experiments.

[0060] like Figure 1 As shown, all the characteristic diffraction peaks of the three samples are completely consistent with those of pure hexagonal tungsten bronze phase (JCPDS: 83-1334), indicating that the samples have high purity.

[0061] like Figure 2 As shown, layered Cs 0.33 WO3 has an accordion-like morphology formed by the stacking of many two-dimensional nanosheets, and the numerous stacked layers facilitate the exfoliation of ultrathin Cs. 0.33 WO3 nanosheets offer this possibility. In porous ultrathin Cs... 0.33 High-density pores with a size of approximately 20 nm can be clearly observed on the surface of WO3 nanosheets, creating porous ultrathin Cs 0.33 The WO3 nanosheets have an average length of 150 nm and a width of 50 nm. Non-porous ultrathin Cs 0.33The WO3 nanosheets have an average length of 300 nm and a width of 120 nm.

[0062] like Figure 3 As shown, at an excitation wavelength of 290 nm, the layered Cs in the sample... 0.33 WO3 and non-porous ultra-thin Cs 0.33 WO3 nanosheets all exhibited strong fluorescence peaks, indicating a high recombination rate of photogenerated carriers within them. Porous ultrathin Cs 0.33 The significantly reduced fluorescence peak intensity of WO3 nanosheets confirms that the introduction of the porous structure promotes the separation of photogenerated carriers. This result is consistent with its excellent photocatalytic CO2 conversion performance. Electrochemical impedance spectroscopy indicates that the porous ultrathin Cs... 0.33 WO3 nanosheets have the smallest EIS arc diameter, which means they exhibit higher separation and transfer efficiency of photogenerated carriers. Furthermore, porous ultrathin Cs under full-spectrum illumination... 0.33 The photocurrent intensity of WO3 nanosheets was higher than that of all other samples. Porous ultrathin Cs 0.33 WO3 nanosheets also exhibited the highest photocurrent intensity under near-infrared light irradiation. These results verify that the introduction of porous structures and their combination with ultrathin structures can reduce charge transfer resistance and promote enhanced photocatalytic activity.

[0063] like Figure 4 As shown, the layered Cs were studied using CO2 adsorption isotherms and CO2 temperature-programmed desorption tests. 0.33 WO3, non-porous and porous ultra-thin Cs 0.33 The adsorption capacity of WO3 nanosheets for CO2. The ultrathin structure provides a larger contact area, effectively enhancing the adsorption capacity of active sites for CO2. Introducing pores into the ultrathin nanosheets may expose more active sites on the material surface, further improving the photocatalyst's CO2 adsorption capacity and facilitating CO2 reduction. Porous ultrathin Cs 0.33 The desorption peak area of ​​WO3 nanosheets is the most prominent, indicating that a stronger interaction occurred between the adsorption sites and CO2 molecules, which further promoted the adsorption and activation of CO2.

[0064] like Figure 5 As shown, during the photocatalytic CO2 conversion process under continuous full-spectrum light irradiation for 4 h, the main carbon-containing product was dimethyl carbonate (DMC). Layered Cs 0.33 The DMC yield of WO3 was poor, at 0.0356 mmol g. -1 (Due to the low temperature, Figure 5 (Not shown in the image), while the non-porous ultra-thin Cs 0.33 WO3 nanosheets slightly improved the yield of DMC by 1.053 mmol g. -1. Notably, when the hole structure was introduced to the porous ultrathin Cs 0.33 WO3nanosheets, the DMC production was greatly improved, reaching 9.562 mmol g -1 , which was almost 268 and 9 times that of layered Cs 0.33 WO3and non-porous Cs 0.33 WO3ultrathin nanosheets, respectively. Under near-infrared light irradiation, all the porous ultrathin Cs 0.33 WO3nanosheets exhibited excellent DMC generation activity, with a conversion amount of 4.462 mmol g -1 .

[0065] The above description is merely preferred embodiments of the present application, and not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A porous ultrathin Cs 0.33 The method for preparing WO3 nanosheets is characterized by, Includes the following steps: Step 1: Preparation of layered WO3·2H2O nanosheet precursor: Disperse Na2WO4·4H2O in dilute nitric acid solution, mix and stir, centrifuge, wash and dry to obtain layered WO3·2H2O nanosheet precursor; Step 2: Liquid phase exfoliation of the layered WO3·2H2O nanosheet precursor: The layered WO3·2H2O nanosheet precursor was dispersed in deionized water; after ultrasonic vibration, centrifugation, filtration and drying, porous ultrathin WO3·2H2O nanosheets were obtained. Step 3: Preparation of porous ultrathin Cs 0.33 WO3 nanosheets: Porous ultrathin WO3·2H2O nanosheets were added to anhydrous ethanol and sonicated; then Cs2CO3 was added and stirred until Cs2CO3 was completely dissolved; then CH3COOH was added and stirred to obtain a mixed solution; the mixed solution was reacted in a reaction vessel for a period of time. Washing and drying yield porous ultrathin Cs 0.33 WO3 nanosheets.

2. The porous ultrathin Cs as described in claim 1 0.33 The method for preparing WO3 nanosheets is characterized by, Step 1 specifically includes: weighing Na2WO4·4H2O and dispersing it in dilute nitric acid solution, stirring at room temperature to obtain a yellow solution, separating the yellow precipitate from the yellow solution using a centrifuge, washing the yellow precipitate several times with deionized water until the pH value is neutral, and drying the yellow precipitate to obtain a layered WO3·2H2O nanosheet precursor.

3. The porous ultrathin Cs according to claim 2 0.33 The method for preparing WO3 nanosheets is characterized by, Step 2 specifically includes: dispersing the layered WO3·2H2O nanosheet precursor in deionized water, ultrasonically oscillating it in a cold water bath to obtain a light yellow suspension, separating the unpeeled yellow precipitate in the light yellow suspension by centrifugation, collecting the precipitate by centrifugation of the upper solution, and drying it to obtain porous ultrathin WO3·2H2O nanosheets.

4. A porous ultrathin Cs as described in claim 3 0.33 The method for preparing WO3 nanosheets is characterized by, Step 3 specifically includes: adding porous ultrathin WO3·2H2O nanosheets to anhydrous ethanol, ultrasonicating to completely disperse the powder in the solution, adding Cs2CO3, stirring the solution until completely dissolved, adding CH3COOH, stirring, pouring the resulting mixed solution into a reaction vessel and reacting for a period of time, collecting the sample and washing it several times with water and ethanol respectively, and then drying it to obtain porous ultrathin Cs2CO3 nanosheets. 0.33 WO3 nanosheets.

5. A porous ultrathin Cs according to claim 4 0.33 The method for preparing WO3 nanosheets is characterized by, In step 1, the volume ratio of concentrated nitric acid to deionized water in the dilute nitric acid solution is 30-50%.

6. A porous ultrathin Cs according to claim 5 0.33 The method for preparing WO3 nanosheets is characterized by, The drying in steps 1, 2, and 3 is carried out in a vacuum environment.

7. A porous ultrathin Cs according to claim 6 0.33 The method for preparing WO3 nanosheets is characterized by, In step 2, the centrifuge speed for separating the yellow precipitate from the light yellow suspension is 4000-7000 rpm, and the time is 3-10 min; the centrifuge speed for separating the precipitate from the upper layer solution is 9000-10000 rpm, and the time is 5-10 min.

8. A porous ultrathin Cs according to claim 7 0.33 The method for preparing WO3 nanosheets is characterized by, In step 2, the ambient temperature of the cold water bath is 0–3°C, and the ultrasonic oscillation time is 5–18 h.

9. A porous ultrathin Cs 0.33 WO3 nanosheets, characterized in that, Using a porous ultrathin Cs as described in any one of claims 1-8 0.33 WO3 nanosheets were prepared by a specific method.

10. A porous ultrathin Cs 0.33 The application of WO3 nanosheets is characterized by, The porous ultrathin Cs as described in any one of claims 1 to 8 0.33 Porous ultrathin Cs nanosheets prepared by a method for preparing WO3 nanosheets 0.33 WO3 nanosheets are used in photocatalytic CO2 conversion, integrating porous ultrathin Cs 0.33 WO3 nanosheet samples were placed in a reaction vessel, CH3OH was introduced into the reactor, the reactor was evacuated to a vacuum, and high-purity CO2 gas was introduced at a pressure of at least one atmosphere. A xenon lamp was used as a full-spectrum light source for photocatalysis experiments.

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