Preparation method of hollow square Cu / CuI catalyst and application of hollow square Cu / CuI catalyst in photocatalytic reduction of CO2 into multi-carbon product

Abstract

The invention discloses a preparation method of a hollow square Cu / CuI catalyst and application of the hollow square Cu / CuI catalyst to photocatalytic reduction of CO2 into a multi-carbon product, and belongs to the technical field of photocatalysts. The preparation method comprises the following steps: firstly, taking water, an alkali source, a copper source and a reducing agent as precursors to obtain a square Cu elementary substance through a one-step precipitation method; the method comprises the following steps: firstly, preparing a Cu elementary substance, then dropwise adding acid into a mixed solution of the Cu elementary substance and iodide ions, carrying out peracid etching, and under oxidation / reduction conditions, enabling copper ions formed on the surface of the Cu elementary substance to react with I-ions to grow into CuI in situ, thereby preparing the Cu / CuI catalyst. The preparation method of the Cu / CuI catalyst has the advantages of simple process, adjustable proportion and the like, and the prepared catalyst has the advantages of small grain size, large specific surface area and the like; according to the present invention, CO2 is reduced into CO, CH4, C2H4 and C2H6 under the illumination condition, the electron selectivity on C2 can achieve 57%, and the excellent advantage of CO2 photocatalytic reduction into the double-carbon product is provided.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts, and relates to the preparation of catalyst materials and their application in converting greenhouse gases into multi-carbon products. Specifically, it relates to a method for preparing a hollow block-shaped Cu / CuI catalyst and its application in photocatalytic reduction of CO2 into multi-carbon products. Background Art

[0002] Carbon dioxide (CO2) is a major greenhouse gas, and its excessive emissions contribute to severe environmental problems such as global warming. Photocatalytic technology, which utilizes solar energy to drive the reduction of CO2, has attracted considerable attention due to its mild reaction conditions and sustainable, environmentally friendly nature. However, the photocatalytic reduction of CO2 to high-value-added multi-carbon products (such as ethylene, C2H4) is difficult, primarily due to limitations such as the stability of the CO2 molecule, the need for multiple electron transfer, and the sluggish kinetics of C-C coupling. Currently, the products are primarily C1 (CO, CH4).

[0003] Copper (Cu)-based catalysts have become a research hotspot due to their potential and cost advantages in promoting CC coupling. + (Electron configuration 3d 10 4s 0 ) can effectively adsorb the key intermediate *CO, creating conditions for coupling; Cu 0 Surface plasmon resonance (LSPR) is generated under visible light, providing abundant electrons. However, there are significant bottlenecks in Cu-based catalysts: (1) Cu + Disproportionation (2Cu + →Cu 0 +Cu 2+ ) or deactivated by oxidation and reduction, with poor stability; (2) Cu 0 The short lifetime of the generated hot electrons and the serious recombination of photogenerated carriers lead to low electron utilization efficiency. These problems seriously restrict its ability to efficiently and stably generate multi-carbon products.

[0004] Constructing a heterojunction is one of the strategies to improve performance. - Ions can effectively stabilize Cu + , inhibiting deactivation; at the same time, the heterostructure formed by Cu and CuI helps promote the separation of photogenerated charges. However, how to achieve significant improvement in charge separation efficiency and optimization of CC coupling process while stabilizing active sites through precise catalyst design remains a challenge that needs to be solved.

[0005] Therefore, it is urgent to develop a method for preparing a Cu / CuI composite catalyst with a specific morphology (such as a hollow block) and apply it to the efficient and highly selective photocatalytic reduction of CO2 to produce multi-carbon products. 0LSPR effect, CuI stabilizes Cu + , the advantages of promoting CC coupling and the characteristics of heterojunction accelerating charge separation. At the same time, the square shape may provide highly active exposed surfaces, providing a new way to break through the bottleneck of existing technologies. Summary of the Invention

[0006] In view of the Cu + The species are easily deactivated by disproportionation, resulting in poor stability, severe restriction of electron utilization efficiency by photogenerated carrier recombination, and efficient and highly selective generation of multi-carbon products (C 2+ ) difficulties and other key issues, the present invention provides a method for preparing a Cu / CuI composite catalyst with a specific morphology (such as a block shape), and applies it to the efficient and highly selective photocatalytic reduction of CO2 to produce multi-carbon products, which can effectively stabilize the active Cu + species, significantly improving the separation and utilization efficiency of photogenerated charges and reducing the CC coupling energy barrier, thereby significantly improving the activity, selectivity and stability of the photocatalytic reduction of CO2 to generate multi-carbon products (such as C2H4, C2H6), and the block structure can provide a regular active surface.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing a hollow block-shaped Cu / CuI catalyst, comprising the following steps: S1: water, alkali source, copper source and reducing agent are stirred and mixed under heating conditions, and the reduction time is controlled by a one-step precipitation method to obtain a cube-shaped Cu element; S2: Disperse the Cu element obtained in S1 in a solvent, and then add I - The ion solution forms a mixed solution, and then acid is added dropwise according to the ratio of the mixed solution volume V1 to the acid solution volume V2 (V1: V2= (100~500):1). After stirring, centrifugation, washing and drying are carried out to obtain a hollow block-shaped Cu / CuI catalyst.

[0008] Preferably, the alkali source in step S1 is sodium hydroxide with a concentration of 0.1-1 mol / L.

[0009] Preferably, the copper source in step S1 is at least one of copper sulfate, copper chloride, copper acetate, and copper nitrate, and the copper ion concentration is 0.01-0.1 mol / L.

[0010] Preferably, the reducing agent in step S1 is at least one of ascorbic acid, glucose, sodium ascorbate, ammonia borane, hydrazine hydrate, and potassium borohydride, and the concentration of the reducing agent is 0.01-0.1 mol / L.

[0011] Preferably, the heating condition in step S1 is 60°C.

[0012] Preferably, the step S2 containing I- The ion solution is any one of water, ethanol, ethylene glycol or a mixed solution.

[0013] Preferably, the step S2 containing I - The iodine source of the ion solution is at least one of sodium iodide, potassium iodide, and ammonium iodide, and the iodine ion concentration is 0.1-1.0 mol / L.

[0014] Preferably, the acid in step S2 is at least one of acetic acid, dilute sulfuric acid, and hydrochloric acid, with a concentration of 0.005 mol / L.

[0015] Another technical purpose of the present invention is to provide an application of the Cu / CuI catalyst in the photocatalytic reduction of CO2 to multi-carbon products.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention constructs Cu by in-situ growing cuprous ions in a copper solution. 0 / Cu + The valence gradient interface is beneficial to reducing the CC coupling energy barrier.

[0017] 2. The present invention controls the CuI ratio by controlling the amount of added acid, and the preparation process is controllable. - The introduction of Cu stabilizes + .

[0018] 3. The Cu / CuI catalyst constructed by the present invention has both the surface localized plasmon resonance effect (LSPR) of Cu element and the stable Cu / Cu + The LSPR effect can provide a large number of electrons for the reaction, and I can stabilize Cu + , enhance the adsorption capacity of C1 intermediate species, and construct Cu 0 / Cu + The valence gradient interface can reduce the CC coupling energy barrier, thereby achieving the dimerization of C1 species to generate C2 products during the photocatalytic process.

[0019] 4. The in-situ grown Cu / CuI catalyst of the present invention has a hollow cubic structure and can form a small-sized nanostructure (eg, about 250 nm), which can increase the specific surface area, improve the carrier separation efficiency, and enhance the photocatalytic activity.

[0020] 5. The Cu / CuI catalyst prepared by the present invention has good photocatalytic reduction of CO2 performance, and the preparation process is simple, environmentally friendly and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the X-ray diffraction spectrum of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention; Figure 3 This is a transmission electron micrograph of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention; Figure 4 This is a transmission electron micrograph of the solid square Cu / CuI catalyst prepared in Comparative Example 1 of the present invention; Figure 5 This is the Auger electron spectrum of the hollow square Cu / CuI catalyst prepared in Example 1 of the present invention; Figure 6 These are product performance diagrams of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention; Figure 7 This is the cycle performance diagram of the Cu / CuI catalyst prepared in Example 1. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0023] A method for preparing a hollow square Cu / CuI catalyst and its application in photocatalytic reduction of CO2 to multi-carbon products, comprising the following steps: S1: 10 mmol of copper sulfate pentahydrate and 0.12 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at 60°C and stirred for 2 h. Finally, 12 mmol of ammonia borane was added and stirred for 30 min. The mixture was centrifuged, washed, and dried to obtain Cu elemental substance.

[0024] S2: Dissolve 80 mg of Cu in 50 mL of ethanol and 3 mmol of KI in 6 mL of water. Then pour the prepared KI solution into the above solution and add 0.005 mol / L dilute sulfuric acid at a ratio of V1:V2=250:1, where V1 is the mixed solution containing Cu element and I ions (mL), and V2 is the volume of the added acid solution (mL). Stir for 1 h, centrifuge, wash, and dry to obtain Cu / CuI.

[0025] The hollow block Cu / CuI catalyst prepared in Example 1 was characterized and analyzed. Figures 1 to 7 As shown: Attachment Figure 1 The Cu / CuI catalyst prepared in Example 1 has characteristic diffraction peaks at 2θ=25.479°, 29.504°, 42.214°, 49.960°, and 52.325°, corresponding to the (111), (200), (220), (311), and (222) crystal planes, which is consistent with the PDF standard card (PDF#06-0246) of CuI. The characteristic diffraction peaks at 2θ=43.316°, 50.448°, and 74.124° in the figure correspond to the (111), (200), and (220) crystal planes, which is consistent with the PDF standard card (PDF#99-0034) of Cu. The peaks of both substances appear on the Cu / CuI catalyst, indicating that CuI was successfully grown in situ on Cu without the formation of impurities.

[0026] Attachment Figure 2 The Cu / CuI catalyst was prepared in Example 1. The Cu / CuI catalyst was in the form of regular cubic blocks with clear particles, complete morphology, and small size. CuI was in situ grown on elemental Cu.

[0027] Attachment Figure 3 This is a transmission electron micrograph of the Cu / CuI catalyst prepared in Example 1, from which it can be clearly seen that the prepared Cu / CuI catalyst has a hollow block structure with a shell thickness of about 50 nm.

[0028] Attachment Figure 4 This is a transmission electron microscope image of the Cu / CuI catalyst prepared in Comparative Example 1. It can be seen from the image that the prepared Cu / CuI catalyst has a solid block structure.

[0029] Attachment Figure 5 This is the Auger electron spectrum of the Cu / CuI catalyst prepared in Example 1. It can be seen from the figure that the valence state of Cu element is Cu 0 and Cu + , and mainly Cu + .

[0030] Attachment Figure 6 The comparison chart of the photocatalytic reduction of CO2 performance of Cu / CuI catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 shows that when the acid addition amount is controlled according to the optimal ratio (V1:V2=250:1), the catalyst exhibits the highest total yield of C2 products (7.64μmol·g -1 ·h -1) and C2 product electron selectivity (57.5%); while the C2 product yield and selectivity of Comparative Example 1 (high acid content, V1:V2=100:1) and Comparative Example 2 (low acid content, V1:V2=500:1) decreased significantly, which directly confirmed the effect of acid addition on maintaining Cu + The valence state can further regulate the selectivity of C2 products (attached Figure 6 ) plays a key role.

[0031] Attachment Figure 7 This is a cycle performance diagram of the Cu / CuI catalyst prepared in Example 1. It can be seen from the figure that after five cycles, the catalyst still maintains good catalytic activity. Example 2

[0032] A method for preparing a hollow square Cu / CuI catalyst and its application in photocatalytic reduction of CO2 to multi-carbon products, comprising the following steps: S1: 2.4 mmol of copper nitrate trihydrate and 0.024 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at 60°C and stirred for 2 h. Finally, 2.4 mmol of hydrazine hydrate was added and stirred for 30 min. The mixture was centrifuged, washed, and dried to obtain Cu elemental substance.

[0033] S2: Dissolve 80 mg of Cu in 50 mL of ethanol and 3 mmol of NaI in 30 mL of water. Pour the prepared NaI solution into the above solution, add 0.005 mol / L dilute sulfuric acid at a ratio of V1:V2=500:1, stir for 1 h, centrifuge, wash, and dry to obtain Cu / CuI. Example 3

[0034] A method for preparing a hollow square Cu / CuI catalyst and its application in photocatalytic reduction of CO2 to multi-carbon products, comprising the following steps: S1: 24 mmol of copper acetate and 0.24 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at 60°C and stirred for 2 h. Finally, 24 mmol of ascorbic acid was added and stirred for 30 min. The mixture was centrifuged, washed, and dried to obtain Cu elemental substance.

[0035] S2: Dissolve 80 mg of Cu in 50 mL of ethanol and 3 mmol of KI in 3 mL of water. Then pour the prepared NH4I solution into the above solution. Add 0.005 mol / L dilute sulfuric acid at a ratio of V1:V2=100:1. Stir for 1 h, centrifuge, wash, and dry to obtain Cu / CuI.

[0036] Comparative Example 1 S1: 8 mmol of copper sulfate pentahydrate and 0.12 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at 60°C and stirred for 2 h. Finally, 8 mmol of hydrazine hydrate was added and stirred for 30 min. The mixture was centrifuged, washed, and dried to obtain Cu elemental substance.

[0037] S2: Dissolve 80 mg of Cu in 50 mL of ethanol, add 3 mmol of I2 solution, stir for 1 h, centrifuge, wash, and dry to obtain Cu / CuI.

[0038] Comparative Example 2 Dissolve 1 M NaI in 100 mL of deionized water, add 100 mL of 0.1 M copper sulfate pentahydrate, stir for 1 h, centrifuge, wash, and dry to obtain CuI.

[0039] Comparative Example 3 8 mmol of copper sulfate pentahydrate and 0.12 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at 60° C. and stirred for 2 h. Finally, 8 mmol of ascorbic acid was added and stirred for 30 min. The mixture was centrifuged, washed, and dried to obtain Cu elemental substance.

[0040] Application testing: The activities of the catalysts prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention were verified, and the specific process is as follows: 30mg of the five catalysts were dispersed in an ethanol solution, evenly added dropwise to a quartz membrane, and allowed to air dry. 0.8mL of deionized water and 0.2mL of a sacrificial agent (TEOA) were injected into the bottom of the reactor. The quartz membrane was then transferred to a quartz container, which was then sealed with a quartz lid. The quartz container was evacuated and then filled with CO2, repeating the process twice. Circulating condensed water was introduced to maintain room temperature, and CO2 was photocatalytically reduced under the illumination of a 300W xenon lamp equipped with a 420nm filter. The xenon lamp was used as the light source to illuminate the catalyst, and 1mL of gas was extracted from the reactor every hour using a syringe. The concentrations of CO, CH4, C2H4, and C2H6 were measured by gas chromatography.

[0041] The performance of the catalysts prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 was tested by gas chromatography. Figure 6 As shown in the figure, it can be seen that the catalytic activity of Example 1 is the best, and the yield of C2H4 is 2 μmol·g -1 ·h -1 The yield of C2H6 was 5.64 μmol·g -1 ·h -1 The yield of C2(C2H4+C2H6) was 7.64 μmol·g -1 ·h-1 The selectivity of the double carbon product was 57.5%. The performance of the obtained catalyst is shown in Table 1 and the attached Figure 6 .

[0042] Table 1 - Photocatalytic performance test and C2 electron selectivity of examples and comparative examples

[0043] In summary, the present invention constructs Cu by precisely controlling the acid etching ratio. 0 / Cu + Gradient interface, combined with in situ iodide ion stabilization of Cu + The triple synergistic mechanism of active sites and hollow square structure-enhanced charge separation successfully overcomes the technical bottlenecks faced by existing copper-based catalysts in photocatalytic CO2 reduction, namely, easy deactivation of active sites, severe carrier recombination, and high CC coupling energy barriers. Experimental data fully confirms that the catalyst prepared under the optimized process not only achieves significant electronic selectivity for C2 products over C1 products, but also exhibits catalytic activity and stability far exceeding that of single-component and non-controlled acid processes. This fundamentally solves the core problem of low efficiency in generating multi-carbon products and verifies the innovative breakthrough of this invention in promoting the photocatalytic conversion of CO2 towards high-value-added multi-carbon products.

[0044] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a hollow block Cu / CuI catalyst, characterized in that , including the following steps: S1: water, alkali source, copper source and reducing agent are stirred and mixed under heating conditions, and the reduction time is controlled by a one-step precipitation method to obtain a cube-shaped Cu element; S2: Disperse the Cu element obtained in S1 in a solvent, and then add I - The ion solution forms a mixed solution, and then acid is added dropwise according to the ratio of the mixed solution volume V1 to the acid solution volume V2 (V1:V2=(100~500):1). After stirring, centrifugation, washing and drying are carried out to obtain a hollow block-shaped Cu / CuI catalyst.

2. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 1, wherein: The alkali source described in step S1 is sodium hydroxide with a concentration of 0.1~1 mol / L.

3. The method for preparing a hollow block Cu / CuI catalyst according to claim 1, wherein: The copper source described in step S1 is at least one of copper sulfate, copper chloride, copper acetate, and copper nitrate, and the copper ion concentration is 0.01-0.1 mol / L.

4. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 1, wherein: The reducing agent in step S1 is at least one of ascorbic acid, glucose, sodium ascorbate, ammonia borane, hydrazine hydrate, and potassium borohydride, and the concentration of the reducing agent is 0.01-0.1 mol / L.

5. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 1, wherein: The heating condition in step S1 is 60°C.

6. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 1, wherein: The I-containing - The ion solution is any one of water, ethanol, ethylene glycol or a mixed solution.

7. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 6, characterized in that: The I-containing - The iodine source of the ion solution is at least one of sodium iodide, potassium iodide, and ammonium iodide, and the iodine ion concentration is 0.1-1.0 mol / L.

8. The method for preparing a hollow block Cu / CuI catalyst according to claim 1, wherein: The acid in step S2 is at least one of acetic acid, dilute sulfuric acid, and hydrochloric acid, and the concentration is 0.005 mol / L.

9. Use of the Cu / CuI catalyst prepared by the method for preparing the hollow block-shaped Cu / CuI catalyst according to any one of claims 1 to 8, characterized in that: Applied to photocatalytic reduction of CO2 to C2 and above hydrocarbons.

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