A perovskite quantum dot composite photocatalyst loaded with multi-walled carbon nanotubes, a preparation method and applications thereof

Abstract

This invention discloses a perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, its preparation method, and its applications, belonging to the field of photocatalyst technology. The technical solution of this invention, while maintaining the main structure of CsPbBr3 perovskite quantum dots, effectively controls the separation and migration process of photogenerated carriers by introducing an interfacial electric field, overcoming the problems of severe carrier recombination and low electron utilization efficiency in single CsPbBr3 perovskite quantum dot systems. The composite photocatalyst preparation method adopted in this invention is simple, operates under mild conditions, is easy to repeat and scale up, and has good prospects for practical application.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, specifically relating to a perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, its preparation method, and its application. Background Technology

[0002] Utilizing solar energy to reduce carbon dioxide into high-value-added chemicals such as carbon monoxide and methane is considered an effective approach that combines environmental governance with energy conversion potential. Photocatalytic carbon dioxide reduction technology has attracted widespread attention in the field of carbon resource recycling due to its mild reaction conditions and ability to directly utilize renewable solar energy. Among the key factors determining the carbon dioxide reduction efficiency are the light absorption capacity, carrier separation efficiency, and interfacial reactivity of the photocatalytic material.

[0003] In recent years, halide perovskite quantum dot materials, especially CsPbBr3 quantum dots, have shown promising applications in photocatalytic carbon dioxide reduction due to their high light absorption coefficient, tunable band structure, long carrier diffusion length, and excellent photoelectric conversion performance. Compared with traditional bulk semiconductor materials, CsPbBr3 at the quantum dot scale exhibits significant quantum confinement and interface effects, enabling the generation of high-density photogenerated carriers under photoexcitation conditions, thus providing potential advantages for multi-electron-participating carbon dioxide reduction reactions.

[0004] However, in practical applications, CsPbBr3 quantum dot photocatalysts still face a series of key problems that urgently need to be solved. First, the strong Coulomb interaction between electrons and holes within CsPbBr3 quantum dots makes it easy for photogenerated carriers to recombine rapidly in the bulk phase, resulting in a low proportion of free carriers available for interfacial reactions and severely limiting the photocatalytic carbon dioxide reduction efficiency. Second, CsPbBr3 quantum dots are sensitive to polar molecules and environmental humidity, and are prone to structural degradation or performance decline under illumination and reaction conditions, exhibiting insufficient long-term stability. Furthermore, the lack of efficient carrier transport and extraction channels in a single CsPbBr3 quantum dot system makes it difficult for photogenerated electrons to migrate to the reaction interface in a timely manner, further exacerbating bulk recombination and energy loss. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, its preparation method and application, so as to solve the technical problems of low reduction efficiency and poor long-term stability of existing photocatalysts.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is to provide a perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, comprising a support and halogenated perovskite quantum dots supported on the support; the support is a carboxylated multi-walled carbon nanotube, and the halogenated perovskite quantum dots are supported on the carboxylated multi-walled carbon nanotubes through interfacial interaction with carboxyl groups.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Furthermore, the halide perovskite quantum dots are CsPbBr3.

[0009] Furthermore, the mass percentage of carboxylated multi-walled carbon nanotubes in the perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes is 0.9% to 2.5%.

[0010] This invention also discloses a method for preparing the above-mentioned perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, comprising the following steps: S1: Preparation of halide perovskite quantum dot solution; S2: Disperse carboxylated multi-walled carbon nanotubes in a halide perovskite quantum dot solution and stir for 0.5~2 h; S3: Centrifuge, collect the solid, wash and dry under vacuum conditions to obtain the final product.

[0011] Furthermore, the halide perovskite quantum dot solution is a CsPbBr3 perovskite quantum dot solution, which is prepared through the following steps: S11: Preparation of lead bromide precursor solution and cesium carbonate precursor solution; S12: Add the cesium carbonate precursor solution to the lead bromide precursor solution to carry out the reaction. After the reaction is completed, cool in an ice bath to terminate the reaction. S13: Centrifuge, collect the solid, and then disperse the collected solid in toluene to obtain a halide perovskite quantum dot solution.

[0012] Furthermore, the preparation method of lead bromide precursor solution includes the following steps: dissolving lead bromide in octadecene, heating to 110~130 ℃ under the protection of an inert gas, and holding at this temperature for 0.5~2 h; then adding oleylamine and oleic acid, heating the mixture to 140~160 ℃, and holding at this temperature until the solid is completely dissolved to obtain lead bromide precursor solution; the ratio of the amount of lead bromide, octadecene, oleylamine and oleic acid is 200~210 mg: 10~20 ml: 1~2 ml: 1~2 ml.

[0013] Furthermore, the preparation method of the cesium carbonate precursor solution includes the following steps: dissolving cesium carbonate in octadecene, adding oleic acid, and then heating to 110~130 ℃ under the protection of an inert gas, keeping warm until the solid is completely dissolved to obtain the cesium carbonate precursor solution; the ratio of the amount of cesium carbonate, octadecene and oleic acid is 220~230 mg: 5~15 ml: 1~0.5~2 ml.

[0014] Furthermore, the temperature of the cesium carbonate precursor solution in S12 is 120 °C, and the temperature of the lead bromide precursor solution is 150 °C; the reaction time is 5 s.

[0015] Furthermore, the drying temperature in S3 is 60~100 ℃.

[0016] The present invention also discloses the application of the above-mentioned perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes in carbon dioxide reduction.

[0017] The beneficial effects of this invention are: 1. This invention constructs a directional interfacial loading structure of CsPbBr3 perovskite quantum dots and carboxylated multi-walled carbon nanotubes: Instead of simply mixing the two materials physically, this invention utilizes the interfacial interaction between the functional groups on the surface of carboxylated multi-walled carbon nanotubes and CsPbBr3 perovskite quantum dots to uniformly and stably anchor the quantum dots to the carbon nanotube surface, constructing a heterogeneous interfacial composite structure of "zero-dimensional quantum dots / one-dimensional carbon nanotubes," while simultaneously preserving the [PbBr6] within the CsPbBr3 perovskite quantum dots. 4- The octahedral coordination structure remains intact, ensuring the integrity and stability of photoelectric properties at the material structure level. Furthermore, this invention constructs a composite system of CsPbBr3 perovskite quantum dots and carbon nanotubes, forming a stable energy level matching relationship and interfacial potential gradient at the interface between the two materials, thereby spontaneously building a built-in electric field in the composite interface region. This built-in electric field can directionally drive photogenerated carriers without external bias voltage, promoting the spatial separation of photogenerated electrons and holes on both sides of the interface, suppressing carrier recombination in the bulk phase of CsPbBr3 perovskite quantum dots, and improving the separation and utilization efficiency of photogenerated carriers. By regulating carrier migration behavior through the built-in electric field, more photogenerated electrons can effectively participate in the interfacial carbon dioxide reduction reaction, thereby improving the photocatalytic efficiency of the composite photocatalyst.

[0018] 2. This invention proposes a high-efficiency composite system design with ultra-low loading ratio: This invention limits the mass ratio of carboxylated multi-walled carbon nanotubes in the composite photocatalyst to only 0.9%~2.5%, and achieves a 4.26-fold improvement in photocatalytic carbon dioxide reduction performance under extremely low carbon content conditions. It breaks through the traditional design idea of ​​high carbon loading relying on electron sink effect and has significant engineering parameter innovation value.

[0019] 3. Design of Specialized Functional Materials for Photocatalytic Carbon Dioxide Reduction: This invention addresses the specific requirements of photocatalytic CO2 reduction reactions for carrier separation efficiency, interfacial electron concentration, and structural stability. It involves material structure and interface engineering design, fundamentally different from existing CsPbBr3 quantum dot preparation technologies primarily aimed at light-emitting devices, in terms of technical objectives and application areas. Specifically, this invention proposes for the first time a composite photocatalyst design based on the reconstruction of the interfacial energy levels of CsPbBr3 perovskite quantum dots and carbon nanotubes to construct a built-in electric field, and applies it to the photocatalytic carbon dioxide reduction reaction. This technical solution, while maintaining the main structure of the CsPbBr3 perovskite quantum dots, effectively controls the separation and migration process of photogenerated carriers by introducing an interfacial electric field, overcoming the problems of severe carrier recombination and low electron utilization efficiency in single CsPbBr3 perovskite quantum dot systems. The composite photocatalyst preparation method used in this invention is simple, operates under mild conditions, is easy to repeat and scale up, and has good practical application prospects. The photocatalyst preparation method proposed in this invention is simple, has mild reaction conditions, achieves high yield, and does not require high-temperature and high-pressure reactions.

[0020] 4. The structure-preserving process route of "first synthesizing quantum dots and then gently compositing": This invention first obtains highly crystalline CsPbBr3 perovskite quantum dots through hot injection, and then performs post-loading compositing with carboxylated multi-walled carbon nanotubes through low-speed stirring. This effectively avoids the lattice damage and size runaway problems that may be caused by in-situ growth or two-phase interface methods, and ensures the structural integrity of the photocatalytic active center. Attached Figure Description

[0021] Figure 1 A process flow diagram for the preparation of perovskite quantum dot composite photocatalysts supported on multi-walled carbon nanotubes; Figure 2 TEM image of CPB photocatalyst; Figure 3 TEM image of the CPB / CNT composite photocatalyst; Figure 4 XRD patterns of CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 5 XPS spectra of Cs elements in CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 6 XPS spectra of Pb in CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 7 XPS spectra of Br in CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 8PL diagrams of CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 9 UV-Vis DRS images of CPB photocatalyst and CPB / CNT composite photocatalyst; Figure 10 The diagram shows a comparison of the photocatalysts obtained in Examples 1-4 in terms of their activity in reducing carbon dioxide. Figure 11 A comparison of the long-term activity of CPB photocatalyst and CPB / CNT composite photocatalyst in reducing carbon dioxide. Detailed Implementation

[0022] This invention discloses a perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes and its preparation method. The composite photocatalyst includes a support and halide perovskite quantum dots supported on the support; the support is carboxylated multi-walled carbon nanotubes, and the halide perovskite quantum dots are loaded onto the carboxylated multi-walled carbon nanotubes through interfacial interactions with carboxyl groups; the mass percentage of carboxylated multi-walled carbon nanotubes in the perovskite quantum dot composite photocatalyst is 0.9%~2.5%. The preparation process of the composite photocatalyst is as follows: Figure 1 As shown, the specific steps include: S1: Preparation of halide perovskite quantum dot solution; S2: Disperse carboxylated multi-walled carbon nanotubes in a halide perovskite quantum dot solution and stir for 0.5~2 h; S3: Centrifuge, collect the solid, wash and dry under vacuum conditions to obtain the final product.

[0023] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0024] Example 1 A pure-phase CsPbBr3 perovskite quantum dot photocatalyst was prepared via the following steps: S1: Dissolve 207 mg lead bromide in 15 ml octadecene, heat to 120 °C under argon protection, and keep the temperature constant for 1 hour; then add 1.5 ml oleylamine and 1.5 ml oleic acid, raise the temperature to 150 °C, and keep the temperature until the solid is completely dissolved to obtain lead bromide precursor solution; S2: Dissolve 225 mg of cesium carbonate in 10 ml of octadecene, add 1 ml of oleic acid, heat to 120 °C under argon protection, keep the temperature constant for 1 hour to completely dissolve the cesium carbonate, and obtain the cesium carbonate precursor solution. S3: Take 1.2 ml of cesium carbonate precursor solution and quickly inject it into lead bromide precursor solution. React for 5 seconds, then quickly cool to room temperature in an ice bath to terminate the reaction. S4: After the reaction is terminated, the reaction solution is centrifuged at 10,000 rpm for 5 min and the lower solid layer is collected. The collected lower solid layer is added to 10 ml of toluene and dissolved completely. Then 15 ml of acetone is added to precipitate the solid. The solid layer is then centrifuged at 10,000 rpm for 5 min and the lower solid layer is collected. The mixture is washed and centrifuged 3 times. S5: Place the lower solid obtained in the last step into a vacuum oven and dry it at 80°C for 12 h (the vacuum oven is placed in a fume hood and kept under vacuum). This yields the pure-phase CsPbBr3 perovskite quantum dot photocatalyst, denoted as CPB.

[0025] Example 2 A perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes is prepared by the following steps: S1: Dissolve 207 mg lead bromide in 15 ml octadecene, heat to 120 °C under argon protection, and keep the temperature constant for 1 hour; then add 1.5 ml oleylamine and 1.5 ml oleic acid, raise the temperature to 150 °C, and keep the temperature until the solid is completely dissolved to obtain lead bromide precursor solution; S2: Dissolve 225 mg of cesium carbonate in 10 ml of octadecene, add 1 ml of oleic acid, heat to 120 °C under argon protection, keep the temperature constant for 1 hour to completely dissolve the cesium carbonate, and obtain the cesium carbonate precursor solution. S3: Take 1.2 ml of cesium carbonate precursor solution and quickly inject it into lead bromide precursor solution. React for 5 seconds, then quickly cool to room temperature in an ice bath to terminate the reaction. S4: After the reaction is terminated, the reaction solution is centrifuged at 10,000 rpm for 5 min and the lower solid is collected. The collected lower solid is added to 10 ml of toluene and dissolved completely. Then, 5 mg of carboxylated multi-walled carbon nanotubes (purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.) are added. The mixture is placed on a magnetic stirrer and stirred at 500 rpm for 1 h. Then, 30 ml of acetone is added to precipitate the solid. The solid is centrifuged at 10,000 rpm for 5 min and the lower solid is collected. The mixture is washed and centrifuged 3 times. S5: Place the last obtained lower solid into a vacuum oven and dry it at 80°C for 12 h (the vacuum oven is placed in a fume hood and kept under vacuum). This yields a perovskite quantum dot composite photocatalyst loaded with multi-walled carbon nanotubes, denoted as CPB / CNT. The loading of carboxylated carbon nanotubes in the obtained composite photocatalyst is 5 mg.

[0026] Example 3 A perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes is prepared in the same manner as in Example 2, except that the amount of carboxylated multi-walled carbon nanotubes added in S4 is adjusted to 3 mg, and the rest of the operation is the same as in Example 2.

[0027] Example 4 A perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes is prepared in the same manner as in Example 2, except that the amount of carboxylated multi-walled carbon nanotubes added in S4 is adjusted to 7 mg, and the rest of the operation is the same as in Example 2.

[0028] Experimental Example TEM image of pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) is shown below. Figure 2 As shown, Figure 2 The illustration in the image is an HRTEM diagram. From Figure 2 As can be seen, the average particle size of the CsPbBr3 perovskite quantum dot catalyst is 12 nm, and the lattice fringes of the CsPbBr3 perovskite quantum dot catalyst are 2.9 Å, which are consistent with the (2 0 0) crystal plane of the PDF standard card in the XRD of CsPbBr3, proving the successful synthesis of the CsPbBr3 perovskite quantum dot catalyst.

[0029] TEM image of perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes (CPB / CNT) is shown below. Figure 3 As shown, Figure 3 The illustration in the image is an HRTEM diagram. From Figure 3 As can be seen, the CPB / CNT composite catalyst and the pure-phase CsPbBr3 perovskite quantum dot catalyst have no obvious difference in morphology, indicating that the crystal structure of the CsPbBr3 perovskite quantum dot catalyst remains intact. At the same time, it can be observed that the CsPbBr3 perovskite quantum dots are attached to carboxylated multi-walled carbon nanotubes, indicating the successful preparation of the CPB / CNT composite catalyst.

[0030] XRD analysis was performed on the pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) prepared in Example 1 and the perovskite quantum dot composite photocatalyst (CPB / CNT) supported on multi-walled carbon nanotubes prepared in Example 2. The results are as follows: Figure 4 As shown. From Figure 4 As can be seen, the loading of carboxylated carbon nanotubes did not change the basic structure of CsPbBr3 perovskite quantum dots, and CPB / CNT has a complete and stable crystal structure of CsPbBr3 perovskite quantum dot catalyst; furthermore, no carbon element was found in XRD, which is inferred to be because the amount of carbon nanotubes loaded was too small to be detected.

[0031] XPS analysis was performed on the pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) prepared in Example 1 and the perovskite quantum dot composite photocatalyst (CPB / CNT) supported on multi-walled carbon nanotubes prepared in Example 2. The results are as follows: Figures 5-7 As shown. From Figures 5-7 As can be seen, after loading carboxylated multi-walled carbon nanotubes (CPB), the XPS characteristic peaks of relevant elements in CPB exhibit a consistent positive shift. Without observing the formation of new chemical components or changes in elemental valence states, this consistent positive shift can be attributed to the redistribution of the electronic environment at the interface. This indicates a decrease in electron density on the CPB side after recombination, suggesting electron transfer from CPB to CNTs, thereby creating an effective charge redistribution state at the two-phase interface.

[0032] The pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) prepared in Example 1 and the perovskite quantum dot composite photocatalyst (CPB / CNT) supported on multi-walled carbon nanotubes prepared in Example 2 were subjected to PL (fluorescence spectroscopy) tests, and the results are as follows: Figure 8 As shown. From Figure 8 As can be seen, the photoluminescence intensity (PL) of CPB / CNT is significantly weakened compared with that of pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB). This is due to the loading effect of carboxylated multi-walled carbon nanotubes, which significantly reduces the recombination rate of photogenerated electrons in the CPB / CNT composite photocatalyst.

[0033] The pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) prepared in Example 1 and the perovskite quantum dot composite photocatalyst (CPB / CNT) supported on multi-walled carbon nanotubes prepared in Example 2 were subjected to UV-Vis diffuse reflectance testing (UV-Vis DRS testing). The results are as follows: Figure 9 As shown, this is used to characterize its photogenerated carrier response properties. From... Figure 9 As can be seen, the photocurrent intensity of the CPB / CNT composite photocatalyst is significantly enhanced under illumination conditions, indicating that its ability to generate and transport photogenerated carriers is improved.

[0034] The photocatalytic reduction performance of carbon dioxide obtained in Examples 1-4 was tested using the following methods: 10 mg of the photocatalysts prepared in Examples 1-4 were uniformly dispersed in a small amount of toluene solution and sonicated for 5 minutes to ensure complete dissolution in the toluene. The resulting mixture was then uniformly coated onto a glass fiber membrane with a radius of 4.7 cm and a pore size of 0.25 μm. The coated glass fiber membrane was placed in a vacuum oven and continuously evacuated at 60°C for 24 hours to remove excess toluene. Photocatalytic reduction of carbon dioxide was carried out in a reactor of the Merry Change closed-loop system. A circulating cooling system was used to maintain the reactor temperature at 20°C. The reaction system was evacuated and purged with pure carbon dioxide using a gas cylinder. This evacuation and purging process was repeated three times, ultimately maintaining a carbon dioxide pressure of approximately 1 atmosphere in the reactor. The products of photocatalytic carbon dioxide reduction were quantitatively analyzed using a GC2002 gas chromatograph with a 300 W xenon lamp as the light source.

[0035] The photocatalytic reduction activity of the photocatalysts obtained in Examples 1-4 is as follows: Figure 10 As shown. From Figure 10 As can be seen, the CPB / CNT perovskite quantum dot photocatalyst with a carboxylated multi-walled carbon nanotube loading of 5 mg exhibits the highest activity, reducing carbon dioxide to 206.26 g after 3 hours of illumination. -1 The activity of carbon monoxide was increased by about 3 times compared with that of pure-phase CsPbBr3 perovskite quantum dot photocatalysts.

[0036] Long-term activity tests were conducted on the pure-phase CsPbBr3 perovskite quantum dot photocatalyst (CPB) prepared in Example 1 and the perovskite quantum dot composite photocatalyst (CPB / CNT) supported on multi-walled carbon nanotubes prepared in Example 2. The results are as follows: Figure 11 As shown. From Figure 11 As can be seen, after 10 hours of continuous reaction, the activity of the pure-phase CsPbBr3 perovskite quantum dot photocatalyst decreased by 45%, and the activity of the CPB / CNT composite photocatalyst with a carboxylated multi-walled carbon nanotube loading of 5 mg decreased by 20%, indicating that the loading of carboxylated multi-walled carbon nanotubes greatly improved the stability of the CsPbBr3 perovskite quantum dot photocatalyst.

[0037] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes, characterized in that: The invention includes a support and halide perovskite quantum dots loaded on the support; the support is a carboxylated multi-walled carbon nanotube, and the halide perovskite quantum dots are loaded on the carboxylated multi-walled carbon nanotube through interfacial interactions with carboxyl groups.

2. The perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes according to claim 1, characterized in that: The halide perovskite quantum dots are CsPbBr3.

3. The perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes according to claim 1, characterized in that: The perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes contains carboxylated multi-walled carbon nanotubes at a mass ratio of 0.9% to 2.5%.

4. The method for preparing the perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Preparation of halide perovskite quantum dot solution; S2: Disperse carboxylated multi-walled carbon nanotubes in a halide perovskite quantum dot solution and stir for 0.5~2 h; S3: Centrifuge, collect the solid, wash and dry under vacuum conditions to obtain the final product.

5. The preparation method according to claim 4, characterized in that, The halide perovskite quantum dot solution is a CsPbBr3 perovskite quantum dot solution, which is prepared through the following steps: S11: Preparation of lead bromide precursor solution and cesium carbonate precursor solution; S12: Add the cesium carbonate precursor solution to the lead bromide precursor solution to carry out the reaction. After the reaction is completed, cool in an ice bath to terminate the reaction. S13: Centrifuge, collect the solid, and then disperse the collected solid in toluene to obtain a halide perovskite quantum dot solution.

6. The preparation method according to claim 5, characterized in that, The preparation method of the lead bromide precursor solution includes the following steps: dissolving lead bromide in octadecene, heating to 110~130 ℃ under the protection of an inert gas, and holding at this temperature for 0.5~2 h; then adding oleylamine and oleic acid, heating the mixture to 140~160 ℃, and holding at this temperature until the solid is completely dissolved to obtain the lead bromide precursor solution; the ratio of the amounts of lead bromide, octadecene, oleylamine and oleic acid is 200~210 mg: 10~20 ml: 1~2 ml: 1~2 ml.

7. The preparation method according to claim 5, characterized in that, The preparation method of the cesium carbonate precursor solution includes the following steps: dissolving cesium carbonate in octadecene, adding oleic acid, and then heating to 110~130 ℃ under the protection of an inert gas, keeping warm until the solid is completely dissolved to obtain the cesium carbonate precursor solution; the ratio of the amount of cesium carbonate, octadecene and oleic acid is 220~230 mg: 5~15 ml: 1~0.5~2 ml.

8. The preparation method according to claim 5, characterized in that: The temperature of the cesium carbonate precursor solution in S12 is 120°C, and the temperature of the lead bromide precursor solution is 150°C; the reaction time is 5 s.

9. The preparation method according to claim 4, characterized in that: The drying temperature in S3 is 60~100 ℃.

10. The application of the perovskite quantum dot composite photocatalyst supported on multi-walled carbon nanotubes as described in any one of claims 1 to 3 in carbon dioxide reduction.

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