Organic small molecule modified composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a small organic molecule modified composite photocatalyst as well as a preparation method and application thereof. The composite photocatalyst comprises small organic molecules and a photocatalyst containing active vacancies, wherein the small organic molecules can interact with the active vacancies and are embedded into the active vacancies; the active vacancies are generated by carrying out chemical etching treatment on the surface of the photocatalyst; the photocatalyst is an oxide, a sulfide or a nitride, and the composite photocatalyst enhances CO2 adsorption and electron transfer efficiency and improves separation efficiency, so that the catalyst can perform photocatalytic CO2 reduction under sunlight, and shows good catalytic stability under long-term continuous illumination.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic CO2 reduction technology, specifically relating to a composite photocatalyst modified with organic small molecules, its preparation method, and its application. Background Technology

[0002] Carbon dioxide (CO2), a major greenhouse gas, can be efficiently converted into carbon-based energy chemicals, which can not only alleviate climate change caused by excessive CO2 concentrations but also effectively realize the recycling of carbon resources. Against this backdrop, photocatalytic carbon dioxide reduction technology, as a clean and efficient energy conversion pathway, has attracted widespread attention.

[0003] Carbon dioxide can be converted into various C1 / C2+ chemicals, such as formic acid (HCOOH), carbon monoxide (CO), methanol (CH3OH), methane (CH4), and ethanol (C2H5OH), during photocatalytic reduction, showing broad application prospects. However, due to its chemical inertness, the direct conversion of CO2 molecules in photocatalytic reduction reactions faces significant challenges. In photocatalytic reactions, the reduction of CO2 typically requires effective photogenerated carrier separation, efficient electron transfer, and support from active sites on the catalyst surface; the combined effect of these factors determines the catalyst's performance.

[0004] Currently, the concentration of CO2 in the air is extremely low (approximately 0.04 vol%), which places higher demands on the effective adsorption capacity of catalysts. Therefore, how to efficiently achieve carbon dioxide conversion under low-concentration CO2 conditions has become one of the key challenges in the field of photocatalysis. Nevertheless, researchers have made some breakthroughs by optimizing the surface structure of catalysts and enhancing their adsorption capacity in low-concentration CO2 environments.

[0005] In photocatalytic reactions, vacancies, as key active sites, play a crucial role in enhancing catalytic activity. For example, patent application CN116493000A discloses a titanium dioxide photocatalyst with atomically adjacent dual-defect sites, its preparation method, and its applications. This technology constructs atomically adjacent dual-defect sites by introducing titanium vacancies (VTi) and inducing the formation of adjacent oxygen vacancies (VO) in situ during the photocatalytic reaction, thereby improving the selectivity and activity of CO2 photoreduction to CH4. Although this application utilizes the synergistic effect of dual sites to promote further protonation of intermediates during CO2 conversion, ultimately achieving high selectivity for CH4, it mainly targets the titanium dioxide system. The defect construction depends on specific precursor ratios, calcination conditions, and photoinduced processes, resulting in a narrow application scope that is difficult to directly extend to other types of semiconductor materials. Furthermore, its ability to regulate other valuable C2+ products in CO2 reduction (such as ethanol and ethylene) is not yet clear, leading to a relatively limited product spectrum.

[0006] Patent application CN118807785B discloses a WO3 / V5-Zn3In2S6 composite photocatalyst based on the synergistic effect of an S-type heterojunction and sulfur vacancies. This application significantly improves the activity and selectivity of photocatalytic CO2 reduction to CH4 by constructing a heterojunction to promote charge separation and utilizing sulfur vacancies to enhance CO2 adsorption and activation. However, the WO3 loading needs to be strictly controlled at around 20% to achieve optimal performance. When the loading is below 20%, there are insufficient adsorption and activation sites; when it is above 20%, the activity decreases due to aggregation and shielding effects, resulting in a narrow process control window.

[0007] Furthermore, vacancies themselves, as crystal defects, become recombination centers for photogenerated electron-hole pairs, thus significantly reducing photon utilization efficiency. Currently, defective photocatalysts generally have lower photon utilization rates than ideal crystalline materials.

[0008] Therefore, the core challenge facing current photocatalytic CO2 reduction technology is how to develop efficient, stable photocatalysts that can operate continuously in the air environment to achieve large-scale, low-cost CO2 resource utilization. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the first aspect of this invention provides a composite photocatalyst modified with small organic molecules, which can achieve efficient CO2 reduction in an air environment.

[0010] The present invention provides a composite photocatalyst modified with organic small molecules, comprising organic small molecules and a photocatalyst containing active vacancies; The organic small molecule is an organic small molecule that interacts with and is embedded in the active vacancy; The active vacancies are generated by chemical etching of the photocatalyst surface. The photocatalyst is an oxide, sulfide, or nitride.

[0011] The composite photocatalyst provided by this invention has electron donor or acceptor functional groups embedded in small organic molecules, which can then regulate the electronic structure and surface charge distribution of the photocatalyst through electron transfer and coordination effects, thereby enhancing the adsorption and activation capacity of CO2, improving the selectivity and efficiency of the catalytic reaction, and achieving the goal of efficient CO2 reduction in the air environment.

[0012] Furthermore, the organic small molecules described in this invention selectively bind to the active vacancies fully exposed on the surface of the photocatalyst after etching treatment, which can significantly enhance the stability and strong adhesion of the organic small molecules on the surface of the composite photocatalyst, optimize the surface active sites of the catalyst, and improve the performance and durability of the composite photocatalyst in the catalytic process.

[0013] Preferably, the organic small molecules are oxygen-containing organic small molecules, sulfur-containing organic small molecules, or nitrogen-containing organic small molecules.

[0014] The oxygen, sulfur, and nitrogen atoms in the organic small molecules provided by this invention have lone pairs of electrons or specific electron cloud distributions, enabling them to act as effective electron donors or acceptors. Moreover, they can undergo highly selective and strong coordination or chemical bonding with active vacancies of the same type of element generated by chemical etching on the surface of the photocatalyst, such as oxygen vacancies, sulfur vacancies, or nitrogen vacancies, anchoring them on the surface of the photocatalyst, optimizing CO2 adsorption and electron transfer, and improving the selectivity and efficiency of the photocatalytic reaction.

[0015] More preferably, the oxygen-containing small organic molecule is an organic compound containing a hydroxyl group, an aldehyde group, a carbonyl group, or a carboxyl group; the sulfur-containing small organic molecule is an organic compound containing a mercapto group or a thioether; and the nitrogen-containing small organic molecule is an organic compound containing an amino group or a nitrile group.

[0016] More preferably, the organic compound containing a carboxyl group is betaine phosphate, the organic compound containing a hydroxyl group is phenol, the organic compound containing an aldehyde group is benzaldehyde, the organic compound containing a thiol group is mercaptopropionic acid, and the organic compound containing an amino group is glycine.

[0017] Preferably, the oxide is Bi2MoO6, TiO2, SrTiO3, Bi2WO6 or BiVO4; the sulfide is MoS2, CdS or ZnIn2S4; and the nitride is SrTaON or Ta3N5.

[0018] Preferably, the molar ratio of the photocatalyst containing active vacancies to the organic small molecules is 1:1 to 100.

[0019] By controlling the molar ratio of the photocatalyst containing active vacancies to the organic small molecules, this invention can ensure that an excess of organic small molecules covers the active vacancies on the surface of the photocatalyst, further optimizing CO2 adsorption and electron transfer, and improving the light absorption efficiency, reaction rate, and stability of the composite photocatalyst.

[0020] On the other hand, the present invention also provides a method for preparing the aforementioned organic small molecule modified composite photocatalyst, comprising: (1) The photocatalyst is placed in a chemical etching solution for chemical etching to obtain a photocatalyst containing active vacancies; (2) The composite photocatalyst is obtained by surface modification of a photocatalyst containing active vacancies and an organic small molecule.

[0021] This invention involves chemically etching the photocatalyst to create active vacancies for specific elements such as nitrogen, oxygen, or sulfur on its surface. These vacancies provide specific and stable anchoring sites for subsequent organic small molecules, which then firmly intercalate through coordination bonds or chemical bonds, resulting in a composite photocatalyst containing organic small molecules embedded in the active vacancies. The intercalation of these organic small molecules provides electron donors or acceptors to the photocatalyst, modulating its electronic structure and optimizing the charge distribution on its surface, thereby enhancing its CO2 adsorption and activation capabilities.

[0022] Preferably, the chemical etching step is as follows: the photocatalyst is dispersed in a chemical etching solution, stirred at 20~85 °C for 0.5~12 h, the precipitate is collected by centrifugation, washed, dried and ground to obtain a photocatalyst containing active vacancies.

[0023] Preferably, the chemical etching is acid etching or alkaline etching, wherein the chemical etching solution for acid etching is an aqueous solution of an inorganic acid or an organic acid, wherein the inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and sulfuric acid, and the organic acid is selected from one or more of lactic acid, citric acid, acetic acid, and oxalic acid; the chemical etching solution for alkaline etching is an aqueous solution of an alkaline compound, wherein the alkaline compound is selected from one or more of sodium hydroxide, potassium hydroxide, and ammonia.

[0024] Preferably, the concentration of the chemical etching solution is 0.001~1 mol / L.

[0025] This invention, by providing a suitable molar concentration of the chemical etching solution, can promote the efficient construction of active vacancies and suppress photocatalyst aggregation or the formation of impurity phases while preserving the photocatalyst's activity. This facilitates the efficient generation and migration of photogenerated carriers, thereby improving the photocatalyst's catalytic performance and stability.

[0026] Preferably, the chemical etching temperature is 20~200 ℃ and the chemical etching time is 0.5~10 h.

[0027] Preferably, the surface modification is performed by impregnation or in-situ adsorption.

[0028] More preferably, the impregnation method is as follows: dispersing small organic molecules in a solvent, adding a photocatalyst containing active vacancies, and ultrasonically stirring, followed by washing and drying to obtain the composite photocatalyst.

[0029] More preferably, the in-situ adsorption method is as follows: a photocatalyst containing active vacancies is dispersed in a solvent, organic small molecules are added and ultrasonic treatment is performed, and the resulting mixture does not need to be separated and can be directly used for the photocatalytic reduction of carbon dioxide.

[0030] On the other hand, the present invention also provides the application of the organic small molecule modified composite photocatalyst in the photocatalytic CO2 reduction reaction.

[0031] Preferably, during the CO2 reduction process, the feed atmosphere is a gas mixture containing CO2 and at least one of O2, N2, and Ar, with a CO2 volume fraction of 0.04–99.99%, a reaction temperature of 15–120 °C, a radiation wavelength of 250–1200 nm, and a light intensity of 10–1000 mW / cm². 2 .

[0032] More preferably, the raw material atmosphere is air, the wavelength of the radiated light is the wavelength of sunlight, and the light intensity is the light intensity of sunlight.

[0033] Using the composite photocatalyst of this invention, the yield of CO2 reduction reaction is 5~50 μmol·g. -1 ·h -1 .

[0034] Compared with the prior art, the present invention has the following beneficial effects: Compared to traditional photocatalysts, the composite photocatalyst provided by this invention, due to the embedded small organic molecules having electron donor or acceptor functional groups, can adjust the electronic structure and surface charge distribution of the photocatalyst through electron transfer and coordination effects, thereby enhancing CO2 adsorption and electron transfer efficiency and improving separation efficiency. This allows the composite photocatalyst to perform photocatalytic CO2 reduction even under sunlight.

[0035] Furthermore, this invention selectively binds to small organic molecules through active vacancies generated by etching, significantly enhancing the adhesion stability of molecules on the catalyst surface. This optimizes surface active sites, improves catalytic performance and durability, and exhibits excellent catalytic stability under long-term continuous light irradiation. The raw materials used in this catalyst are green, environmentally friendly, and inexpensive. The preparation process is mild and safe, requiring no precursors or complex post-processing, making it suitable for large-scale production. Attached Figure Description

[0036] Figure 1 The image shows a comparison of the XRD patterns of the oxygen-vacant Bi2MoO6 prepared in Example 1 of this invention and the original Bi2MoO6.

[0037] Figure 2 The image shows the energy dispersive spectrum (EDS) of the organic small molecule modified composite photocatalyst prepared in Example 1 of this invention.

[0038] Figure 3 The image shows the XRD pattern of the sulfur-vacancy-containing MoS2 prepared in Example 4 of this invention.

[0039] Figure 4 The XRD pattern of oxygen-vacancy-containing SrTaON prepared in Example 6 of this invention.

[0040] Figure 5 The graph shows the ethanol yield-time relationship of the composite photocatalyst prepared in Example 1 of this invention under sunlight / air conditions for catalytic CO2 reduction.

[0041] Figure 6 The diagram shows the photocurrent response of the composite photocatalyst prepared in Example 1 of this invention, the oxygen-vacancy-containing Bi2MoO6 prepared in Comparative Example 1, and the original photocatalyst Bi2MoO6.

[0042] Figure 7 Electrochemical impedance spectroscopy diagrams of the composite photocatalyst prepared in Example 1 of this invention, the oxygen-vacancy-containing Bi2MoO6 prepared in Comparative Example 1, and the original photocatalyst Bi2MoO6.

[0043] Figure 8 This is a schematic diagram showing the long-term stability test results (reaction time vs. C2H5OH yield) of the composite photocatalyst prepared in Example 1 of this invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1 (1) Bi2MoO6 was placed in a 0.01 mol / L NaOH solution and stirred at 80 °C for 2 h. Then, it was centrifuged, the precipitate was collected, washed three times with deionized water and ethanol respectively, and then dried under vacuum at 40 °C for 3.5 h. Finally, it was ground to obtain Bi2MoO6 containing oxygen vacancies.

[0046] (2) 50 mg of Bi2MoO6 containing oxygen vacancies and phosphate betaine were dissolved in deionized water at a molar ratio of 1:15. The mixture was then sonicated for 15 s at room temperature and stirred for 2-3 h. The reaction solution was centrifuged, washed, and the precipitate was collected. The resulting sample was vacuum dried at 30°C for 12 h to obtain the organic small molecule modified composite photocatalyst.

[0047] Test results: XRD comparison images of the oxygen-vacant Bi2MoO6 prepared in Example 1 of this invention and the original Bi2MoO6 are shown below. Figure 1 As shown, the characteristic peaks of Bi₂MoO₆ correspond to those on the standard card, confirming the successful preparation of Bi₂MoO₆. It can also be seen that the diffraction patterns of the oxygen-vacant Bi₂MoO₆ exhibit similar characteristics to the original Bi₂MoO₆, but the peak intensities at the characteristic peaks (020), (060), (151), (062), and (191) are significantly enhanced. The introduction of oxygen vacancies leads to a slight change in the crystal structure of Bi₂MoO₆. The XRD pattern shows changes in diffraction peak intensity, indicating that oxygen vacancies affect the lattice and electronic structure, thereby causing changes in the material's lattice structure, charge distribution, and photocatalytic performance.

[0048] The energy dispersive spectrum (EDS) of the organic small molecule-modified composite photocatalyst prepared in Example 1 of this invention is shown below. Figure 2 As shown, signals of C and P were detected, indicating that oxygen-containing organic small molecules were successfully inserted into the oxygen-containing vacancy Bi2MoO6.

[0049] Example 2 The only difference from Example 1 is that the oxygen-containing organic small molecule in Example 2 of this invention is phenol, and an organic small molecule modified composite photocatalyst is obtained.

[0050] Example 3 The only difference from Example 1 is that the oxygen-containing organic small molecule in Example 3 of this invention is benzaldehyde, and an organic small molecule modified composite photocatalyst is obtained.

[0051] Example 4 (1) MoS2 was placed in a 1 mol / L HCl solution and stirred at 20 °C for 10 h. Then, the precipitate was centrifuged, collected, washed three times with deionized water and ethanol respectively, dried under vacuum at 40 °C for 3.5 h, and then ground to obtain MoS2 containing sulfur vacancies.

[0052] (2) 50 mg of sulfur-containing MoS2 and mercaptopropionic acid were dissolved in deionized water at a molar ratio of 1:1. The mixture was then sonicated for 15 s at room temperature and stirred for 2-3 h. The reaction solution was centrifuged, washed, and the precipitate was collected. The resulting sample was vacuum dried at 30 °C for 12 h to obtain the organic small molecule modified composite photocatalyst.

[0053] The XRD comparison diagram of sulfur-vacancy-containing MoS2 and original MoS2 obtained in Example 4 of this invention is shown below. Figure 3As shown, the characteristic peaks of MoS2 correspond to those of the standard card, confirming the successful preparation of MoS2. At the same time, it can be seen that the diffraction peaks of MoS2 containing sulfur vacancies are stronger than those of the original MoS2, proving the formation of sulfur vacancies.

[0054] Example 5 The only difference from Example 1 is that the surface modification in Example 5 of this invention involves embedding mercaptopropionic acid into MoS2 containing sulfur vacancies through in-situ adsorption. Specifically, the MoS2 containing sulfur vacancies is uniformly dispersed in deionized water and ultrasonically treated at room temperature for 2 h to obtain an aqueous solution of the organic small molecule modified composite photocatalyst, which can be directly used for photocatalytic CO2 reduction reaction.

[0055] Example 6 (1) SrTaON was placed in 0.001 mol / L HCl solution and stirred at 200 °C for 0.5 h. Then, it was centrifuged, the precipitate was collected, washed three times with deionized water and ethanol respectively, dried under vacuum at 40 °C for 3.5 h, and then ground to obtain SrTaON containing nitrogen vacancies.

[0056] (2) 50 mg of nitrogen-vacant SrTaON and glycine were dissolved in deionized water at a molar ratio of 1:100. The mixture was then sonicated for 15 s at room temperature and stirred for 2 h. The reaction solution was centrifuged, washed, and the precipitate was collected. The resulting sample was vacuum dried at 30 °C for 12 h to obtain the organic small molecule modified composite photocatalyst.

[0057] The XRD comparison images of nitrogen-vacant SrTaON obtained in Example 6 of this invention and the original SrTaON are shown below. Figure 4 As shown, the characteristic peaks of SrTaON correspond to those on the standard card, confirming the successful preparation of SrTaON.

[0058] Comparative Example 1 The only difference from Example 1 is that, after obtaining Bi2MoO6 containing oxygen vacancies, Comparative Example 1 of the present invention does not perform the subsequent oxygen-containing organic small molecule intercalation step.

[0059] Sample testing and analysis The composite photocatalyst prepared in Example 1 of this invention, the oxygen-vacancy-containing Bi2MoO6 prepared in Comparative Example 1, and the original photocatalyst Bi2MoO6 were subjected to photocatalytic photocurrent response. Figure 6 ) and electrochemical impedance spectroscopy ( Figure 7 ).

[0060] Figure 6This indicates that the photocurrent response intensity of the composite photocatalyst prepared in Example 1 of the present invention is significantly stronger than that of the oxygen-vacant Bi2MoO6 prepared in Comparative Example 1 and the original photocatalyst Bi2MoO6. The enhanced current response intensity confirms the enhanced adsorption and electron transfer efficiency of CO2 molecules, thereby improving the separation efficiency.

[0061] Figure 7 This indicates that the impedance of the composite photocatalyst prepared in Example 1 of the present invention is lower than that of the oxygen-vacant Bi2MoO6 prepared in Comparative Example 1 and the original photocatalyst Bi2MoO6. The reduction in impedance indicates that the interfacial charge transfer resistance is reduced, which is beneficial to the separation and migration of photogenerated carriers, thereby improving the photocatalytic performance.

[0062] Application Examples 1-8 In a 100 mL sealed quartz photoreactor, 50 mg of the organic small molecule modified composite photocatalyst prepared in Examples 1-6 of the present invention (Application Examples 1-6), the original photocatalyst Bi2MoO6 (Application Example 8) prepared in Comparative Example 1 were dispersed in 50 mL of deionized water. After CO2 gas was introduced for 30 min, the quartz photoreactor was sealed and placed under a xenon lamp for photoreaction for 4 h.

[0063] Results Analysis Figure 8 shows that the composite photocatalyst prepared in Example 1 of this invention maintained a stable ethanol yield for five consecutive cycles (4 hours of illumination each time), indicating that the catalyst has good cycle stability. Simultaneously, this composite photocatalyst also exhibited high reaction performance under both sunlight and air irradiation, significantly outperforming the comparative catalyst and the original photocatalyst, demonstrating excellent photocatalytic activity.

[0064] The yields of the reduction products from the photocatalytic CO2 reduction reactions in Examples 1-8 of this invention are shown in Table 1. The yields were quantitatively analyzed for both gaseous and liquid products using gas chromatography, ion chromatography, and high-performance liquid chromatography.

[0065] As can be seen, compared with the non-intercalated oxygen-containing small organic molecules (Application Example 7), the yields of C2 reduction products (ethanol, acetic acid, ethylene, ethane or acetylene) and C1 reduction products (CO, methane, methanol or formic acid) are significantly increased after intercalation of oxygen-containing small organic molecules (Application Examples 1-6).

[0066] When phosphate betaine was used as an oxygen-containing organic small molecule (Application Example 1), the ethanol yield increased by more than 7 times, which proved that the insertion of oxygen-containing organic small molecules enhanced the adsorption and electron transfer efficiency of CO2 molecules and improved the separation efficiency.

[0067] Table 1. Yields of reduction products in the photocatalytic CO2 reduction reactions of Examples 1-8 of this invention. Application Examples 9-14 In a 100 mL sealed quartz photoreactor, 50 mg of the organic small molecule modified composite photocatalyst prepared in Example 1 was dispersed in 50 mL of deionized water. Argon (Application Example 9), air (Application Example 10), a mixture of 15% CO2 (the remaining gas components were nitrogen, and the remaining gas components in the mixtures listed later are the same) (Application Example 11), a mixture of 2% CO2 (Application Example 12), a mixture of 1.1% CO2 (Application Example 13), and a mixture of 0.2% CO2 (Application Example 14) were introduced respectively. After 30 min of introduction, the quartz photoreactor was sealed and placed under a xenon lamp for photoreaction for 4 h.

[0068] Results Analysis The ethanol yields of the photocatalytic CO2 reduction reactions in Examples 9-14 of this invention are shown in Table 2. It can be seen that under different atmospheres, the ethanol yield is positively correlated with the atmospheric gas pressure (volume concentration of CO2). Higher CO2 concentrations can significantly promote its adsorption on the catalyst surface, thereby greatly enhancing the reaction activity.

[0069] When the CO2 concentration is below 2%, the ethanol production does not show a significant downward trend. This indicates that the composite photocatalyst provided by this invention can still maintain relatively high catalytic activity at low CO2 concentrations (close to the air environment). In other words, the catalytic system provided by this invention has excellent adaptability and conversion ability for low-concentration CO2 environments (such as air), providing a basis for its application in actual atmospheric environments or low-concentration CO2 sources.

[0070] Under low CO2 concentration conditions, due to the abundant active vacancies on the surface of the composite photocatalyst of this invention and the electron-rich environment formed by the regulation of small organic molecules, CO2 molecules can be effectively adsorbed and activated, thus exhibiting high reactivity and ethanol production capacity. As the CO2 concentration further decreases, the number of CO2 molecules that can participate in the reaction in the system decreases, and the ethanol yield decreases accordingly; however, when the CO2 volume fraction is below 2%, the reaction rate tends to stabilize, and the decrease in ethanol yield slows down significantly, indicating that the catalytic system still has good reaction stability and applicability under ultra-low CO2 concentration conditions.

[0071] Table 2: Summary of Ethanol Yield Data under Different Atmospheres in Example 1 Application Example 15 In a 250 mL beaker, 50 mg of the composite photocatalyst prepared in Example 1 of this invention was dispersed in deionized water. The reaction vessel was placed under sunlight and exposed to air (CO2 volume fraction of 0.04%). The reaction was stopped after 8 h.

[0072] Results Analysis Quantitative analysis of the liquid products yielded the following graph: the ethanol yield-time relationship of the composite photocatalyst prepared in Example 1 of this invention under sunlight / air conditions for CO2 reduction, as shown in the graph. Figure 5 As shown, the composite photocatalyst provided by this invention can continuously catalyze the reduction reaction to produce ethanol under natural sunlight by using only extremely low concentrations of CO2 in the air as a carbon source, exhibiting both excellent catalytic activity and good operational stability.

Claims

1. A composite photocatalyst modified with organic small molecules, characterized in that, Including small organic molecules and photocatalysts containing active vacancies; The organic small molecule is an organic small molecule that interacts with and is embedded in the active vacancy; The active vacancies are generated by chemical etching of the photocatalyst surface. The photocatalyst is an oxide, sulfide, or nitride.

2. The organic small molecule modified composite photocatalyst according to claim 1, characterized in that, The organic small molecules mentioned are oxygen-containing organic small molecules, sulfur-containing organic small molecules, or nitrogen-containing organic small molecules.

3. The organic small molecule modified composite photocatalyst according to claim 1, characterized in that, The oxygen-containing organic small molecules are organic compounds containing hydroxyl, aldehyde, carbonyl, or carboxyl groups; The sulfur-containing small organic molecules are organic compounds containing thiol groups or thioethers; the nitrogen-containing small organic molecules are organic compounds containing amino or nitrile groups.

4. The organic small molecule modified composite photocatalyst according to claim 1, characterized in that, The oxide is Bi2MoO6, TiO2, SrTiO3, Bi2WO6 or BiVO4; the sulfide is MoS2, CdS or ZnIn2S4; and the nitride is SrTaON or Ta3N5.

5. The organic small molecule modified composite photocatalyst according to claim 1, characterized in that, The molar ratio of the photocatalyst containing active vacancies to the organic small molecules is 1:1 to 100.

6. The method for preparing the organic small molecule modified composite photocatalyst according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) The photocatalyst is placed in a chemical etching solution for chemical etching to obtain a photocatalyst containing active vacancies; (2) The composite photocatalyst is obtained by surface modification of a photocatalyst containing active vacancies and an organic small molecule.

7. The method for preparing the organic small molecule modified composite photocatalyst according to claim 6, characterized in that, The chemical etching is either acid etching or alkaline etching.

8. The method for preparing the organic small molecule modified composite photocatalyst according to claim 6 or 7, characterized in that, The concentration of the chemical etching solution is 0.001~1 mol / L.

9. The application of the organic small molecule modified composite photocatalyst according to any one of claims 1 to 5 in the photocatalytic CO2 reduction reaction.

10. The application according to claim 9, characterized in that, During CO2 reduction, the feed atmosphere is a gaseous mixture containing CO2 and at least one of O2, N2, and Ar, with a CO2 volume fraction of 0.04–99.99%, a reaction temperature of 15–120°C, a radiation wavelength of 250–1200 nm, and a light intensity of 10–1000 mW / cm². 2 .

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