A cu2o / cu3vo4 heterojunction catalyst, a preparation method thereof and application thereof in photocatalytic reduction of co2 into multi-carbon products

Abstract

This invention discloses a Cu2O / Cu3VO4 heterojunction catalyst, its preparation method, and its application in the photocatalytic reduction of CO2 to multi-carbon products, belonging to the field of catalyst materials technology. The preparation method includes: dissolving a copper source and a vanadium source in water to obtain a solution; mixing the solutions and adjusting the pH to 5-8 to obtain an initial solution; dispersing the solid from the initial solution after centrifugation in a mixture of ethylene glycol and water; and performing a hydrothermal reaction at 150-200℃ for 8-12 hours; washing and drying the reactants, and then calcining them at 500-600℃ for 2-5 hours under an inert atmosphere to obtain the Cu2O / Cu3VO4 heterojunction catalyst. In this catalyst, Cu2O and Cu3VO4 form a closely contacted heterojunction structure, enabling efficient separation of photogenerated electrons and holes under a built-in electric field and enhancing the absorption of visible light. Under visible light irradiation, this catalyst can reduce CO2 to multi-carbon products such as CO, CH4, C2H4, and C2H6, with an electron selectivity of up to 79% for the C2 products. The preparation process of this invention is simple and low-cost, and the resulting catalyst has broad application prospects in the field of photocatalytic CO2 reduction.

Description

Technical Field

[0001] This invention belongs to the field of catalyst materials technology, and relates to a composite metal oxide catalyst for photocatalytic reduction of carbon dioxide, its preparation method and application, specifically a Cu2O / Cu3VO4 heterojunction catalyst, its preparation method and its application in the photocatalytic reduction of CO2 to multi-carbon products. Background Technology

[0002] Photocatalysis technology, due to its mild reaction conditions, environmental friendliness, and ease of operation, is considered a promising and effective method for reducing carbon dioxide (CO2) into high-value hydrocarbons. The core of this technology's development lies in creating highly efficient and stable photocatalysts to achieve the efficient conversion of solar energy into chemical energy.

[0003] Cuprous oxide (Cu₂O) has a narrow band gap (Eg=2.2eV) and can absorb visible light, but it is prone to auto-oxidation under light irradiation, leading to structural damage and decreased catalytic activity, and it also exhibits a high photogenerated electron-hole recombination rate. Cuprous vanadate (Cu₃VO₄) has high electron mobility and a more negative conduction band position, providing electrons with strong reducing power for CO₂ reduction. Combining Cu₂O and Cu₃VO₄ can form a Cu₂O / Cu₃VO₄ heterojunction.

[0004] Constructing heterojunctions is an effective strategy to improve the charge separation efficiency of photocatalysts. For the Cu₂O / Cu₃VO₄ composite system, a built-in electric field can be formed at the interface between the two phases, promoting the spatial separation of photogenerated electrons and holes, thereby extending carrier lifetime. More importantly, this heterojunction interface provides a heteronuclear bimetallic (Cu-V) active center, which can synergistically stabilize key intermediates in CO₂ reduction, effectively lowering the energy barrier of the CC coupling reaction and paving the way for highly selective C₂ generation. + Multi-carbon products provide a unique reaction microenvironment. However, reports on the controllable preparation of Cu2O and Cu3VO4 composite catalysts and their high-selectivity synthesis of C2 products in photocatalytic CO2 reduction remain lacking. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical problems of severe charge recombination, insufficient stability, and low selectivity of multi-carbon products in existing photocatalysts during CO2 reduction, and to provide a Cu2O / Cu3VO4 heterojunction catalyst with high charge separation efficiency, good stability, and strong selectivity for C2 products, as well as its preparation method and application.

[0006] This invention is achieved through the following technical solution:

[0007] The first technical objective of this invention is to provide a Cu2O / Cu3VO4 heterojunction catalyst, wherein the catalyst is composed of Cu2O and Cu3VO4, and a heterojunction structure is formed between the two phases of Cu2O and Cu3VO4, which can photocatalytically reduce CO2 to multi-carbon products.

[0008] The second technical objective of this invention is to provide a method for preparing the Cu2O / Cu3VO4 heterojunction catalyst, comprising the following steps:

[0009] S1: First, the vanadium source is dissolved in deionized water under heating conditions to obtain solution A;

[0010] S2: Dissolve the copper source in deionized water to obtain solution B;

[0011] S3: Add solution A dropwise to solution B while stirring, adjust the pH value, and stir for 0.5 h to obtain the initial solution;

[0012] S4: The solid obtained after centrifuging the initial solution is dispersed in a mixture of ethylene glycol and water in a reaction vessel for hydrothermal reaction. After the reaction is completed, the product is separated by centrifugation, washed, and then placed in a vacuum drying oven for drying.

[0013] S5: The product obtained in step S4 is calcined in a tube furnace under an inert atmosphere to obtain Cu2O / Cu3VO4 photocatalyst.

[0014] Preferably, the heating temperature in step S1 is 40-60°C.

[0015] Preferably, the vanadium source in step S1 is at least one of ammonium metavanadate, sodium vanadate, or sodium metavanadate.

[0016] Preferably, the concentration of vanadium ions in solution A in step S1 is 0.01~0.1 mol / L.

[0017] Preferably, the copper source in step S2 is at least one of copper sulfate pentahydrate, copper chloride, copper acetate, or copper nitrate.

[0018] Preferably, the concentration of copper ions in solution B in step S2 is 0.05~0.3 mol / L.

[0019] Preferably, in step S3, a sodium hydroxide solution, ammonia, or potassium hydroxide solution with a concentration of 1-3M is used to adjust the pH.

[0020] Preferably, the volume ratio of deionized water to ethylene glycol in the mixed solvent in step S4 is 1:1 to 3.

[0021] Another technical objective of this invention is to provide the application of the Cu2O / Cu3VO4 heterojunction catalyst in the photocatalytic reduction of CO2 to multi-carbon products.

[0022] Furthermore, this invention also proposes the application of the Cu2O / Cu3VO4 heterojunction catalyst in the photocatalytic reduction of CO2 to multi-carbon products, characterized in that: the catalyst promotes the separation of photogenerated carriers through the heterojunction interface formed by Cu2O and Cu3VO4, and reduces carbon dioxide to multi-carbon products including C2 hydrocarbons.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention first adjusts the molar ratio of Cu and V through precipitation, and then further increases the crystallinity of the catalyst through calcination, thus constructing a Cu2O / Cu3VO4 heterojunction photocatalyst with good crystallinity.

[0025] 2. This invention utilizes low-cost copper and vanadium sources, and achieves controllable growth of heterojunctions through gentle regulation of hydrothermal conditions. This increases the specific surface area and improves carrier separation efficiency.

[0026] 3. This invention promotes the separation of photogenerated electrons and holes and enhances the absorption and utilization rate of visible light by constructing a Cu2O / Cu3VO4 heterojunction photocatalyst.

[0027] 4. The Cu2O / Cu3VO4 heterojunction photocatalyst provided by this invention has a unique interface structure that may form asymmetric Cu-V active sites. This is experimentally demonstrated by a high selectivity of up to 79% for C2 products (such as C2H4 and C2H6), indicating that it can effectively promote the CC coupling step in the CO2 reduction process. Attached Figure Description

[0028] Figure 1 The images show the XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention.

[0029] Figure 2 Here is a high-resolution transmission electron microscope (HRTEM) morphology image of the catalyst in Example 1, wherein, Figure 2 (a) is a TEM image. Figure 2 (b) is an HRTEM image;

[0030] Figure 3 The fluorescence and photoluminescence spectra of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention are shown.

[0031] Figure 4 The it curves are for the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention.

[0032] Figure 5 The performance diagrams are of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 of this invention.

[0033] Figure 6 The image shows the X-ray diffraction pattern of the catalyst prepared in Example 4 of this invention. Detailed Implementation

[0034] To better understand the content of this invention, the invention will be further described below with reference to embodiments and accompanying drawings. However, the scope of protection of this invention is not limited to the following embodiments.

[0035] Example 1: Preparation of a Cu2O / Cu3VO4 heterojunction catalyst

[0036] Includes the following steps:

[0037] (1) Dissolve 1 mmol of ammonium metavanadate in 30 mL of deionized water at 50 °C.

[0038] (2) Dissolve 6 mmol of copper nitrate in 80 mL of deionized water.

[0039] (3) The ammonium metavanadate solution was slowly added dropwise to the copper nitrate solution, the pH was adjusted to 6 with 1M NaOH solution, and the initial solution was obtained after stirring for 0.5h.

[0040] (4) After centrifuging the initial solution, disperse it in 60 mL of 50% ethylene glycol solution (V / V), and hydrothermally react the initial solution at 150 °C for 10 h, then centrifuge, wash and dry.

[0041] (5) The obtained powder was calcined at 550°C for 3 hours in a tube furnace under an argon atmosphere to obtain Cu2O / Cu3VO4 catalyst.

[0042] Example 2: Preparation of a Cu2O / Cu3VO4 heterojunction catalyst

[0043] Includes the following steps:

[0044] (1) Dissolve 0.3 mmol of ammonium metavanadate in 30 mL of deionized water at 60 °C.

[0045] (2) Dissolve 2 mmol of copper nitrate in 40 mL of deionized water.

[0046] (3) The ammonium metavanadate solution was slowly added dropwise to the copper nitrate solution, the pH was adjusted to 7 with 1M NaOH solution, and the initial solution was obtained after stirring for 0.5h.

[0047] (4) After centrifuging the initial solution, disperse it in 60 mL of 50% ethylene glycol solution (V / V), and perform hydrothermal reaction of the initial solution at 200℃ for 10 h, then centrifuge, wash and dry.

[0048] (5) The obtained powder was calcined at 500°C for 3 hours in a tube furnace under an argon atmosphere to obtain Cu2O / Cu3VO4 catalyst.

[0049] Example 3: Preparation of a Cu2O / Cu3VO4 heterojunction catalyst

[0050] Includes the following steps:

[0051] (1) Dissolve 3 mmol of ammonium metavanadate in 30 mL of deionized water at 40 °C.

[0052] (2) Dissolve 12 mmol of copper nitrate in 40 mL of deionized water.

[0053] (3) The ammonium metavanadate solution was slowly added dropwise to the copper nitrate solution, the pH was adjusted to 7 with 3M NaOH solution, and the initial solution was obtained after stirring for 0.5 h.

[0054] (4) After centrifuging the initial solution, disperse it in 60 mL of 50% ethylene glycol solution (V / V), and perform hydrothermal reaction at 180℃ for 10 h, then centrifuge, wash and dry.

[0055] (5) The obtained powder was calcined at 600°C for 3 hours in a tube furnace under an argon atmosphere to obtain Cu2O / Cu3VO4 catalyst.

[0056] Example 4: Uncalcined Sample

[0057] Includes the following steps:

[0058] (1) Dissolve 1 mmol of ammonium metavanadate in 30 mL of deionized water at 40 °C.

[0059] (2) Dissolve 2 mmol of copper nitrate in 40 mL of deionized water.

[0060] (3) The ammonium metavanadate solution was slowly added dropwise to the copper nitrate solution, the pH was adjusted to 8 with 1M NaOH solution, and the initial solution was obtained after stirring for 0.5h.

[0061] (4) After centrifuging the initial solution, disperse it in 60 mL of 50% ethylene glycol solution (V / V), and hydrothermally react the initial solution at 150 °C for 10 h, then centrifuge, wash and dry.

[0062] Example 5: Preparation of a Cu2O / Cu3VO4 heterojunction catalyst

[0063] Includes the following steps:

[0064] (1) Dissolve 1 mmol of ammonium metavanadate in 30 mL of deionized water at 50 °C.

[0065] (2) Dissolve 9.6 mmol of copper sulfate pentahydrate in 40 mL of deionized water (copper ion concentration is 0.24 mol / L).

[0066] (3) The ammonium metavanadate solution was slowly added dropwise to the copper sulfate solution, the pH was adjusted to 6 with 2M NaOH solution, and the initial solution was obtained after stirring for 0.5h.

[0067] (4) After centrifuging the initial solution, disperse it in 60 mL of a 1:3 ethylene glycol-water mixed solution (15 mL of water and 45 mL of ethylene glycol) and hydrothermally react at 180 °C for 10 h. Then centrifuge, wash and dry.

[0068] (5) The obtained powder was calcined at 550°C for 3 hours in a tube furnace under an argon atmosphere to obtain Cu2O / Cu3VO4 catalyst.

[0069] Comparative Example 1: Preparation of pure phase Cu3VO4

[0070] 1.5 mol of cuprous oxide and 1 mol of ammonium metavanadate were mixed and ground for 0.5 h, then transferred to a crucible and calcined at 550 °C for 24 h to obtain Cu3VO4.

[0071] Comparative Example 2: Preparation of Pure Phase Cu2O

[0072] 0.0576 g of SDS was dissolved in 9.6 mL of deionized water and stirred until dissolved. Then, 0.5 mL of 0.1 mol / L CuSO4 solution was added, followed by the addition of 0.04 mmol (containing 0.04 mmol NaOH) NaOH solution with continued stirring. When the solution turned blue, 0.25 mL of 0.2 M sodium ascorbate solution was added. The mixture was centrifuged to obtain a yellow solid, which was washed three times with anhydrous ethanol, once with water, and twice with ethanol. The Cu2O photocatalyst material was obtained by vacuum drying.

[0073] Testing and Characterization

[0074] 1. Structural characterization

[0075] The Cu2O / Cu3VO4 catalysts prepared in Examples 1-3, the uncalcined comparative sample prepared in Example 4, and the pure phase Cu3VO4 and Cu2O catalysts prepared in Comparative Examples 1-2 were systematically characterized.

[0076] 1.1 X-ray diffraction analysis: Figure 1The XRD patterns of the catalyst in Example 1 and the catalysts in Comparative Examples 1 and 2 are shown. The characteristic peaks of the sample in Example 1 at 2θ = 34.2°, 39.5°, 40.2°, 57.2°, 57.9°, and 68.4° are consistent with the Cu3VO4 standard card (PDF#17-0584), while the characteristic peaks at 2θ = 36.4°, 42.3°, and 61.3° belong to Cu2O (PDF#99-0041). The simultaneous appearance of characteristic peaks from both phases without any impurities indicates the successful synthesis of the Cu2O / Cu3VO4 composite material. Figure 6 The XRD pattern of the sample from Example 4 (uncalcined) is shown, which reveals poor crystallinity and the presence of impurities, demonstrating the necessity of the calcination step for obtaining a pure phase and a highly crystalline heterostructure.

[0077] 1.2 Microscopic morphology analysis: Figure 2 (a) The TEM image shows that the catalyst of Example 1 has a plate-like morphology. Its high-resolution HRTEM image ( Figure 2 In (b), clear lattice stripes with interplanar spacing of 0.24 nm and 0.23 nm can be observed, corresponding to the (111) crystal plane of Cu2O and the (110) crystal plane of Cu3VO4, respectively. The two phases are in close contact, which directly confirms the formation of the heterojunction.

[0078] 1.3 Analysis of Photogenerated Charge Behavior: Figure 3 The fluorescence spectrum (PL) showed that the PL emission intensity of the catalyst in Example 1 was much lower than that of the pure phase Cu3VO4 and Cu2O, indicating that the heterojunction structure can effectively suppress the recombination of photogenerated electrons and holes. Figure 4 The transient photocurrent response (it) curves further confirmed that the photocurrent intensity of the catalyst in Example 1 was significantly higher than that of the two pure control samples, indicating that its charge separation and transport efficiency was higher.

[0079] 2. Photocatalytic performance test

[0080] 2.1 Test Method

[0081] The performance of the catalyst was evaluated using a gas-phase photocatalytic CO2 reduction system. The specific steps were as follows: 30 mg of catalyst was accurately weighed, dispersed in ethanol, and ultrasonically homogenized. The resulting solution was then coated onto a 4 cm² area... 2A catalyst layer was formed by drying the catalyst-loaded quartz sheet at room temperature. The quartz sheet was placed in a sealed reactor (approximately 100 mL in volume) with a quartz window. 0.5 mL of deionized water was injected into the bottom of the reactor as a proton source. After sealing, the reaction system was evacuated and repeatedly rinsed three times with high-purity CO2 (99.999%), and finally filled with CO2 at atmospheric pressure. A 300 W xenon lamp (equipped with a filter with λ>420 nm to remove ultraviolet light) was used as the visible light source. The reaction was carried out under illumination, and a quantitative amount of gas was extracted from the reactor every hour using a gas sampling needle and injected into a gas chromatograph equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD) for qualitative and quantitative analysis of the products (CO, CH4, C2H4, C2H6, etc.). All experiments were performed at room temperature and repeated at least twice to ensure data reproducibility.

[0082] 2.2 Performance Results and Analysis

[0083] Under visible light irradiation, the photocatalytic reduction performance of different catalysts for CO2 is as follows: Figure 5 As shown.

[0084] The Cu₂O / Cu₃VO₄ heterojunction catalyst prepared in Example 1 exhibited optimal activity and selectivity. After 5 hours of reaction, the average rate of C₂ product formation (the sum of C₂H₄ and C₂H₆) reached 81.7 μmol·g⁻¹. -1 ·h -1 Furthermore, the electron selectivity for the C2 product is as high as 79%. Even under conditions where the copper ion concentration (0.24 mol / L) and the water-ethylene glycol volume ratio (1:3) are close to the upper limit of the process (as in Example 5), the prepared catalyst still maintains excellent performance, with a C2 product formation rate and electron selectivity reaching 75.3 μmol·g⁻¹, respectively. -1 ·h -1 and 76%.

[0085] In contrast, the C2 product formation rate of the pure Cu3VO4 catalyst prepared in Comparative Example 1 was only about 4.3 μmol·g. -1 ·h -1 The C2 product electron selectivity of the Cu2O catalyst prepared in Comparative Example 1 was only 32.05%, far lower than the 79% in Example 1; and almost no C2 products were detected in the pure Cu2O catalyst prepared in Comparative Example 2. This fully demonstrates the key role of constructing Cu2O / Cu3VO4 heterojunction in promoting C-C coupling and improving the selectivity of multi-carbon products.

[0086] Furthermore, no significant hydrocarbon products were detected in the uncalcined sample prepared in Example 4 during testing (its XRD pattern is shown in [reference needed]). Figure 6(The structure is disordered), which highlights the importance of the "calcination" step in the claims for forming a crystalline phase with high catalytic activity.

[0087] Furthermore, the catalysts prepared in Examples 2 and 3 were subjected to the same photocatalytic performance tests. The results showed that the C2 product electron selectivity of the catalyst in Example 2 (vanadium concentration 0.01 mol / L, copper concentration 0.05 mol / L, calcination temperature 500℃) reached 73%; the C2 product electron selectivity of the catalyst in Example 3 (vanadium concentration 0.1 mol / L, copper concentration 0.3 mol / L, calcination temperature 600℃) reached 75%. This further demonstrates that the technical solution of the present invention can achieve the purpose of highly selectively reducing CO2 to multi-carbon products within the concentration range described in the claims.

[0088] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a Cu2O / Cu3VO4 heterojunction catalyst, characterized in that, Includes the following steps: S1: First, the vanadium source is dissolved in deionized water under heating conditions to obtain solution A; S2: Dissolve the copper source in deionized water to obtain solution B; S3: Add solution A dropwise to solution B while stirring, and adjust the pH value to 6, 7 or 8. Stir for 0.5 h to obtain the initial solution; S4: The solid obtained after centrifuging the initial solution is dispersed in a mixture of ethylene glycol and water and subjected to hydrothermal reaction in a reactor at 150℃, 180℃ or 200℃ for 10 hours. After the reaction is completed, the product is separated by centrifugation, washed and then placed in a vacuum drying oven for drying. S5: The product obtained in step S4 is calcined in a tube furnace under an inert atmosphere at 500℃, 550℃ or 600℃ to obtain Cu2O / Cu3VO4 photocatalyst.

2. A Cu2O / Cu3VO4 heterojunction catalyst prepared by the method described in claim 1, characterized in that, The catalyst is composed of Cu2O and Cu3VO4, and a heterojunction structure is formed between the two phases of Cu2O and Cu3VO4. It is used for photocatalytic reduction of CO2 into multi-carbon products, and the multi-carbon products include at least C2 hydrocarbons.

3. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1, characterized in that... In step S1, the heating temperature is 40~60℃.

4. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1 or 3, characterized in that... In step S1, the vanadium source is at least one of ammonium metavanadate, sodium vanadate, or sodium metavanadate.

5. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1, characterized in that... In step S1, the concentration of vanadium ions in solution A is 0.01~0.1 mol / L.

6. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1, characterized in that... In step S2, the copper source is at least one of copper sulfate pentahydrate, copper chloride, copper acetate, or copper nitrate.

7. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1 or 6, characterized in that... In step S2, the concentration of copper ions in solution B is 0.05~0.3 mol / L.

8. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1, characterized in that... In step S3, the pH is adjusted using a 1-3 M sodium hydroxide solution, ammonia, or potassium hydroxide solution.

9. The method for preparing the Cu2O / Cu3VO4 heterojunction catalyst according to claim 1, characterized in that, In step S4, the volume ratio of water to ethylene glycol in the mixture of water and ethylene glycol is 1:1 to 3.

10. The application of the Cu2O / Cu3VO4 heterojunction catalyst as described in claim 2 in the photocatalytic reduction of carbon dioxide to multi-carbon products, characterized in that: The catalyst promotes the separation of photogenerated carriers through the heterojunction interface formed by Cu2O and Cu3VO4, and reduces carbon dioxide to multi-carbon products including C2 hydrocarbons.

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