Preparation of Cu monatomic modified carbon nitride loaded SnO2 quantum dot composite material and application of Cu monatomic modified carbon nitride loaded SnO2 quantum dot composite material in reaction for preparing ethanol through photocatalytic CO2 reduction

Abstract

The invention discloses a Cu monatomic modified carbon nitride loaded SnO2 quantum dot composite material, a preparation method thereof and application of the Cu monatomic modified carbon nitride loaded SnO2 quantum dot composite material in photocatalytic CO2 reduction to generate ethanol. The material takes a carbon nitride material as a carrier, Cu single atoms are introduced through a thermal polymerization method, SnO2 quantum dots are further introduced through a light induction method, and the Cu single atoms and the SnO2 quantum dots respectively provide sufficient C-C coupling catalytic sites and a large amount of activated protons, so that the material shows excellent catalytic performance in a system for reducing CO2 into ethanol through photocatalysis; and good stability is shown in multiple cycles.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic CO2 reduction reaction technology. More specifically, it relates to a method for preparing a Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material and its application in the photocatalytic reduction of CO2 to ethanol. Background Technology

[0002] Photocatalysis is an important pathway for the resource utilization of CO2, reducing it to high-value-added fuels or chemicals. Ethanol, as an important liquid fuel and chemical feedstock, possesses advantages such as high energy density and convenient storage and transportation, making it considered an ideal target product for CO2 photocatalytic conversion. However, in practical applications, the photocatalytic reduction of CO2 to ethanol still faces challenges such as complex reaction pathways, low product selectivity, and limited catalytic efficiency. Carbon nitride-based photocatalysts are a class of organic semiconductor photocatalysts with stable conjugated structures and visible light responsiveness. They have attracted widespread attention due to their wide availability of raw materials, simple preparation methods, and good chemical stability. Furthermore, their suitable band structure allows them to generate photogenerated carriers under visible light irradiation, demonstrating potential for application in the photocatalytic CO2 conversion field. However, carbon nitride materials also suffer from insufficient C / C coupled active sites and insufficient proton attack during the reaction. Introducing Cu single-atom sites into the carbon nitride support helps provide sufficient reaction sites. Furthermore, introducing SnO2 quantum dots as water oxidation reaction sites provides a large number of protons, effectively promoting the photocatalytic reduction of CO2 to ethanol. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing CO2 photocatalytic reduction process, such as low reaction efficiency, insufficient selectivity of target products and limited active sites of catalytic materials, and to provide a Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material with mild reaction conditions, high catalytic efficiency and stable structure.

[0004] The purpose of this invention is to provide a method for preparing the Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material for the photocatalytic reduction of CO2 to ethanol.

[0005] Another objective of this invention is to provide the application of the Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material in the photocatalytic reduction of CO2 to ethanol.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: A composite photocatalytic material for the photocatalytic reduction of CO2 to ethanol is obtained by introducing Cu single-atom active sites and loading SnO2 quantum dots on the basis of carbon nitride semiconductor material to construct a multi-scale synergistic composite structure, thereby obtaining a photocatalytic material with both high active site utilization and good photogenerated carrier separation capability.

[0007] The carbon nitride material in this invention is an organic semiconductor photocatalyst with a conjugated structure. Its crystal structure is formed by triazine units linked by covalent bonds, exhibiting a stable framework structure and excellent visible light response. This structure enables carbon nitride to effectively generate photogenerated electrons and holes under visible light irradiation. Furthermore, Cu single atoms are anchored on the surface of the carbon nitride support in a highly dispersed manner, which is beneficial for providing uniform and sufficient metal active sites; SnO2 quantum dots are loaded on the Cu single-atom-modified carbon nitride surface, forming a tight contact interface with the support. Through the above structural design, multiple reactive sites can be introduced into the material, improving the separation and migration behavior of photogenerated carriers, enhancing the adsorption and conversion capacity of CO2, thereby significantly improving the overall catalytic performance of photocatalytic CO2 reduction to ethanol.

[0008] In addition, the present invention also provides a method for preparing the Cu single-atom and SnO2 quantum dot synergistic carbon nitride photocatalytic material for photocatalytic CO2 reduction to ethanol, specifically including the following steps: S1. Cu metal salt and nitrogen-containing organic precursor are added to deionized water, fully dissolved and mixed, and then dried by rotary evaporation to obtain Cu-containing precursor; S2. Using the thermal polymerization method, the Cu-containing precursor obtained in step S1 is subjected to high-temperature calcination at 500 °C until the reaction is complete, followed by post-treatment to obtain Cu single-atom modified carbon nitride material. S3. Using a photo-induced method, the Cu single-atom modified carbon nitride material obtained in step S2 is mixed with Sn metal salt in water, and isopropanol is added. The reaction is completed under light and stirring conditions. After post-treatment, Sn metal salt is converted in situ on the surface of carbon nitride and loaded to form SnO2 quantum dots, thus obtaining carbon nitride photocatalytic material synergistically loaded with Cu single atoms and SnO2 quantum dots.

[0009] Carbon nitride materials are typically prepared via thermal polymerization of nitrogen-containing organic precursors. This method is simple, reproducible, and suitable for constructing stable carbon nitride framework structures. This invention also employs thermal polymerization to prepare carbon nitride materials, introducing Cu metal salts during the polymerization process. This allows Cu atoms to exist stably in a highly dispersed form within the carbon nitride support, forming Cu single-atom active sites. Furthermore, this invention uses a photo-induced method to introduce Sn metal salts under mild conditions, enabling in-situ transformation and loading of SnO2 quantum dots on the carbon nitride surface. This avoids Sn species aggregation or structural damage during high-temperature processing, promoting the uniform distribution of SnO2 quantum dots on the support surface and their close contact with the carbon nitride. Constructing a composite structure on the same carbon nitride support, where Cu single-atom active sites and SnO2 quantum dots coexist, improves the separation and migration behavior of photogenerated carriers, enhances CO2 adsorption and conversion capabilities, and thus improves the overall performance of photocatalytic CO2 reduction to ethanol.

[0010] Further, the Cu metal salt mentioned in step S1 is one or more of copper nitrate, copper chloride, or copper bromide.

[0011] Furthermore, the nitrogen-containing organic precursor mentioned in step S1 is at least one of urea, melamine, and dicyandiamide.

[0012] Furthermore, the concentration of Cu metal salt in the mixed solution in step S1 is 0.1~0.3 g / L.

[0013] Furthermore, the concentration of the nitrogen-containing organic precursor in the mixed solution in step S1 is 100~300 g / L.

[0014] Furthermore, in step S1, before rotary evaporation drying, the mixed solution may be subjected to ultrasonic and / or stirring treatment for 1 to 5 hours.

[0015] Furthermore, the rotary evaporation drying temperature in step S1 is 75~85 ℃.

[0016] Furthermore, the high-temperature calcination time in step S2 is 1~3 h.

[0017] Further, the post-treatment in step S2 is as follows: the solid obtained after the reaction is washed by centrifugation with deionized water 5 to 8 times, and then dried at 60 to 80 °C for 10 h to obtain the final product.

[0018] Furthermore, the Sn metal salt mentioned in step S3 is one or more of tin nitrate, tin chloride, or tin bromide.

[0019] Furthermore, the mixing described in step S3 refers to dispersing the Cu single-atom modified carbon nitride material and Sn metal salt in water and mixing them thoroughly by ultrasound and / or stirring.

[0020] Further, the volume fraction of isopropanol in step S3 is 0.1~0.2 L / L.

[0021] Furthermore, the illumination conditions described in step S3 are as follows: a xenon lamp is used as the light source, the power is 300 W, and the illumination wavelength range is the full spectrum.

[0022] Preferably, the light irradiation and stirring reaction time in step S3 is 3 h.

[0023] Further, the post-treatment in step S3 is as follows: the solid obtained after the reaction is washed by centrifugation with deionized water 5 to 8 times, and then dried at 60 to 80 °C for 10 h to obtain the final product.

[0024] Furthermore, the centrifugal cleaning conditions are: centrifugal speed of 5000~10000 r / min, and centrifugation time of not less than 10 min.

[0025] Therefore, the present invention also provides the application of the above-mentioned Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material in photocatalysis, preferably for the photocatalytic reduction of CO2 to produce ethanol.

[0026] Furthermore, the catalyst is used for the photocatalytic reduction of CO2 to ethanol.

[0027] Furthermore, the photocatalytic CO2 reduction to ethanol reaction specifically includes the following steps: dispersing the catalyst for the photocatalytic CO2 reduction reaction, namely the Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material, in an aqueous organic phase mixed system, introducing CO2 gas under light conditions to carry out the photocatalytic reduction reaction, and obtaining ethanol after the reaction is completed.

[0028] Preferably, the reaction system is an aqueous-organic mixed system.

[0029] More preferably, the organic phase is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile.

[0030] Preferably, the illumination conditions use a xenon lamp as the light source, with a power of 300 W and a wavelength range of the full spectrum.

[0031] More preferably, the photocatalytic reaction is carried out under normal pressure conditions for a reaction time of 2 to 12 h.

[0032] This invention has the following significant advantages: This invention, based on carbon nitride semiconductor materials, constructs Cu single-atom active sites by introducing Cu metal salts during thermal polymerization, and further employs photo-induced loading of SnO2 quantum dots under mild conditions. The Cu single atoms and SnO2 quantum dots provide ample CC coupling catalytic sites and a large number of activated protons, respectively. This structural design improves the utilization rate of the metal active sites, enhances the separation and migration behavior of photogenerated carriers, and strengthens the proton supply capacity, thereby effectively improving the photocatalytic CO2 reduction to ethanol reaction performance. Attached Figure Description

[0033] Figure 1 The XRD patterns are those of Example 1 SnO2 / Cu-CN, Comparative Example 1 CN, Comparative Example 2 Cu-CN, and Comparative Example 3 SnO2-CN.

[0034] Figure 2 The images show the SEM morphology of CN, Cu-CN, and SnO2 / Cu-CN obtained in Comparative Examples 1, 2, and Example 1 of this invention.

[0035] Figure 3 This is a TEM image of the SnO2 / Cu-CN obtained in Example 1 of the present invention.

[0036] Figure 4 The image shows the Cu edge XANES spectrum of SnO2 / Cu-CN obtained in Example 1 of this invention.

[0037] Figure 5 This is a comparison chart of the photocatalytic performance of different catalysts in Example 5 for reducing CO2 to ethanol.

[0038] Figure 6 The graph shows the performance test results of the control variables in Experiment Example 4.

[0039] Figure 7 The graph shows the cyclic stability test results in Experiment Example 5.

[0040] Figure 8 The figures are the photoelectric characterization experiments in Experiment Example 6, where a) is the photoluminescence spectrum of Experiment Example 6; b) is the transient photocurrent response diagram; and c) is the electrochemical impedance diagram. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0042] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0043] Example 1. A SnO2 quantum dot / Cu single-atom supported carbon nitride material for photocatalytic CO2 reduction reaction The preparation method of the SnO2 quantum dot / Cu single atom supported carbon nitride material specifically includes the following steps: S1. Weigh 12 g of urea and 6 mg of copper nitrate and disperse them in 60 mL of water. Stir for 3 h to ensure uniform dispersion. Transfer the resulting mixed solution to a rotary evaporator and evaporate to dryness at 80 °C to obtain a mixed powder of copper nitrate and urea. Place the mixed powder in a muffle furnace and calcine at 500 °C for 2 h at a heating rate of 5 °C / min. After cooling at room temperature, thoroughly wash the product with deionized water at least 5 times and dry at 60 °C for 10 h. The obtained product is a Cu-doped carbon nitride material, labeled Cu-CN.

[0044] S2. 150 mg Cu-CN was dispersed in 30 mL of water and sonicated for 10 min to ensure uniform dispersion. Then, the mixture was stirred at 400 r / min, and 6 mg tin chloride and 4 mL isopropanol were added during stirring. After stirring for 30 min, the suspension was irradiated under a 300 W xenon lamp for 3 h. Finally, the sample was washed five times with deionized water and dried in an oven at 60 ℃ for 10 h to obtain a Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material, labeled SnO2 / Cu-CN.

[0045] Comparative Example 1. Preparation of Carbon Nitride 12 g of urea was weighed and thoroughly ground, then placed in a muffle furnace and calcined at 500 °C for 2 h at a heating rate of 5 °C / min. After cooling at room temperature, the product was thoroughly washed with deionized water at least 5 times and dried at 60 °C for 10 h. The resulting product was carbon nitride material, labeled CN.

[0046] Comparative Example 2. Preparation of Cu-supported carbon nitride The preparation method of Cu-CN is the same as step (1) in Example 1.

[0047] Comparative Example 3. Preparation of SnO2 quantum dots supporting carbon nitride 150 mg CN was dispersed in 30 mL of water and sonicated for 10 min to ensure uniform dispersion. Then, the mixture was stirred at 400 rpm, and 6 mg tin chloride and 4 mL isopropanol were added during stirring. After stirring for 30 min, the suspension was irradiated under a 300 W xenon lamp for 3 h. Finally, the sample was washed five times with deionized water and dried in an oven at 60 °C for 10 h to obtain SnO2 quantum dot-supported carbon nitride material, labeled SnO2-CN.

[0048] Experimental Example 1. X-ray Powder Diffraction Analysis The crystal structures of the materials obtained in Example 1 and Comparative Examples 1-3 of this invention were characterized using a Bruker Smart Lab powder diffractometer (Germany). The operating conditions were: voltage and current of 40 kV and 30 mA, respectively; scanning was performed using Cu-Kα rays within a range of 5–80° at twice the diffraction angle; and the scanning speed was 5. o / min, see results Figure 1 .

[0049] As shown in the figure, the two typical diffraction peaks at 13.1° and 27.2° of the synthesized CN, Cu-CN, Sn-CN, and SnO2 / Cu-CN correspond to the (100) and (002) crystal planes in carbon nitride, respectively, reflecting the in-plane ordered packing and interlayer packing of the conjugated triazine structure. For Cu-CN, SnO2-CN, and SnO2 / Cu-CN, the structure did not change significantly compared to pure CN, indicating that the CN structure remained stable after the introduction of SnO2 quantum dots and Cu single atoms, and no cluster structure formed within it.

[0050] Experimental Example 2. Scanning Electron Microscopy Characterization The morphologies of Examples 1, Comparative Examples 1 and 2 of this invention were characterized using a Hitachi SU8010 ultra-high resolution field emission scanning electron microscope (USA). The accelerating voltage was 10 kV and the current was 10 mA. Gold sputtering pretreatment was required before testing. The results are shown in [reference needed]. Figure 2 .

[0051] As shown in the figure, CN exhibits a typical layered stacking morphology. After the introduction of Cu atoms or Cu atoms and SnO2 quantum dots, Cu–CN and SnO2 / Cu–CN maintain an overall layered structure similar to CN, with only slight layered wrinkles or stacking densification in local areas. This indicates that the introduction of Cu atoms or SnO2 quantum dots has little impact on the microstructure of CN and does not destroy its layered structural framework.

[0052] Experimental Example 3. Transmission Electron Microscopy Characterization The morphology of the composite material of Example 1 of this invention was characterized using a high-resolution transmission electron microscope (HR-TEM, JEM-2100F, JEOL) with an accelerating voltage of 200 kV. The results are shown in [reference needed]. Figure 3 .

[0053] Quantum dots were observed in SnO2 / Cu–CN, and the interplanar spacing was measured to be 0.33 nm, corresponding to the interplanar spacing of SnO2(110), indicating that SnO2 is exposed on the surface of CN material.

[0054] Experimental Example 4. Synchrotron Radiation Characterization The atomic coordination environment of the composite material in Example 1 of this invention was characterized using fluorescence mode measurements at the Beijing Synchrotron Radiation Facility (BSRF) 4B9A beamline. The results are shown in [reference needed]. Figure 4 .

[0055] The observation that Cu in SnO2 / Cu–CN has a valence between 0 and +2 and that no Cu-Cu bonds were formed indicates that Cu exists in an atomically dispersed form.

[0056] Experimental Example 5. Photocatalytic Carbon Dioxide Reduction Performance Test Take 4 mg of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 and add them to 21 mL of N. N Dimethylacetamide and 7 mL of water were ultrasonically stirred for 10 min to ensure uniform dispersion. The solution was then transferred to a 50 mL reactor, evacuated to a vacuum state, and pure CO2 gas was introduced. This process was repeated three times, maintaining a pressure of 1 atm. The reaction was maintained at 25 °C using a constant temperature circulator (model CC-1008E). The quartz reactor was then irradiated with a 300 W xenon lamp for 2 h. After the reaction was complete, the quartz reactor was removed, and the insoluble matter was filtered out using a 0.22 μm organic filter membrane. The reaction solution was then transferred to a chromatographic vial and analyzed using a Shimadzu GC-2014 gas chromatograph.

[0057] Figure 5 The graphs show the performance of photocatalytic carbon dioxide reduction using different photocatalysts. Comparative Examples 1, 2, and 3 produced relatively few CO2 reduction products. In contrast, the SnO2 / Cu–CN photocatalyst prepared in Example 1 exhibited excellent ethanol production performance, with an ethanol production rate of 87 μmol·g⁻¹. 1 ·h 1 The selectivity rate is as high as 98.97%.

[0058] Figure 6To conduct blank control experiments under the conditions of argon gas introduction, no light exposure, and no catalyst addition, as shown in the figure, no ethanol was generated under these conditions.

[0059] Figure 7 The image shows the cyclic stability test of the SnO2 / Cu–CN photocatalyst prepared in Example 1 for the photoreduction of CO2. After 10 cycles, it still exhibits good photocatalytic activity, indicating that the prepared Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material has good stability.

[0060] Experiment Example 6. Photoelectric Characterization Experiment Photoluminescence spectra were measured using a fluorescence spectrophotometer (HITACHI F-7100), and the test results are shown below. Figure 8 a.

[0061] As can be seen from the figure, the comparative example has a higher luminescence intensity, while the SnO2 / Cu–CN prepared in Example 1 exhibits the weakest luminescence intensity. This indicates that the synergistic effect of Cu single metal atomic sites and SnO2 quantum dots suppresses the carrier recombination efficiency, thereby promoting the photocatalytic reduction of CO2 to ethanol.

[0062] Electrochemical tests of the samples were performed using an electrochemical workstation (CHI 760E, Shanghai) in a standard three-electrode system. An Ag / AgCl (saturated KCl) electrode was used as the reference electrode, a platinum wire as the counter electrode, and 0.5M Na₂SO₄ as the electrolyte. The working electrode was prepared by dispersing 5 mg of sample in 0.5 mL of a 5% Nafion-ethanol mixture, ultrasonically dispersing to form a homogeneous suspension, then drop-coating it onto ITO glass (20 mm × 40 mm) and air-drying for 8 hours. Test results are shown in [link to relevant documentation]. Figure 8 bc.

[0063] As can be seen from the figure, the comparative example has a lower photocurrent response and a higher electrochemical impedance, while the SnO2 / Cu–CN prepared in Example 1 exhibits an excellent photocurrent response and a lower electrochemical impedance, demonstrating the excellent light energy utilization and photogenerated charge transfer efficiency of SnO2 / Cu–CN.

[0064] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material in the photocatalytic reduction of CO2 to ethanol, characterized in that, Cu single atoms are introduced into carbon nitride materials using thermal polymerization, and SnO2 quantum dots are further introduced using photoinduction, thereby providing sufficient CC coupling catalytic reaction sites and activated protons, thus efficiently photoreducing CO2 to ethanol. The preparation method of the Cu single atom modified carbon nitride supported SnO2 quantum dot composite material specifically includes the following steps: (1) Dissolve Cu metal salt and nitrogen-containing organic ligand in water, mix thoroughly, and dry by rotary evaporator to obtain Cu-containing precursor; the Cu metal salt is one or more of copper nitrate, copper chloride or copper bromide; the nitrogen-containing organic ligand is at least one of urea, melamine or dicyandiamide; (2) The Cu-containing precursor obtained in step (1) was calcined at 500°C using a thermal polymerization method and then post-treated to obtain Cu single-atom modified carbon nitride material. (3) Using a photo-induced method, Sn metal salt and Cu single-atom modified carbon nitride are mixed and dissolved in water, isopropanol is added, and the reaction is carried out under light and stirring. After post-processing, the SnO2 quantum dot / Cu single-atom supported carbon nitride material is obtained; the Sn metal salt is one or more of tin nitrate, tin chloride or tin bromide.

2. The application of the Cu single-atom modified carbon nitride supported SnO2 quantum dot composite material according to claim 1 in the photocatalytic CO2 reduction to ethanol reaction.

3. The reaction system for reducing CO2 to ethanol according to claim 1 is an aqueous-organic phase mixed system; the organic phase in the system is at least one of N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile.

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