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

Abstract

The application discloses a preparation method of hollow square block Cu / CuI catalyst and application of the catalyst in photocatalytic reduction of CO2 into multi-carbon products, 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 Cu single-element square blocks through one-step precipitation; then, adding acid into a mixed solution of the Cu single-element square blocks and iodine ions, etching the Cu single-element square blocks through the acid, and growing CuI on the surface of the Cu single-element square blocks in situ through reaction between copper ions and I ‑ ions under oxidation / reduction conditions, so as to prepare the Cu / CuI catalyst. The preparation method of the Cu / CuI catalyst has the advantages of simple process and adjustable proportion, and the prepared catalyst has the advantages of small crystal grain size and large specific surface area; CO2 can be reduced into CO, CH4, C2H4 and C2H6 under light irradiation, and the electron selectivity for C2 can reach 57%, so that the Cu / CuI catalyst has the advantage of excellent photocatalytic reduction of CO2 into double-carbon products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysts, and relates to catalyst material preparation and application of converting greenhouse gases into multi-carbon products, in particular to a preparation method of a hollow square-shaped Cu / CuI catalyst and application of the hollow square-shaped Cu / CuI catalyst in photocatalytic reduction of CO2 into multi-carbon products. BACKGROUND

[0002] Carbon dioxide (CO2) is one of the main greenhouse gases, and its excessive emission has led to serious environmental problems such as global warming. Photocatalytic technology uses solar energy to drive CO2 reduction, has the advantages of mild reaction conditions and green sustainability, and has attracted much attention. However, it is difficult to generate high-value multi-carbon products (such as ethylene C2H4) by photocatalytic reduction of CO2, which is mainly limited by factors such as CO2 molecular stability, multi-electron transfer requirement, and slow C-C coupling kinetics. Currently, the products are still mainly C1 (CO, CH4).

[0003] Copper (Cu) -based catalysts have become a research hotspot due to their potential in promoting C-C coupling and cost advantage. Cu + (electron configuration 3d 10 4s 0 ) can effectively adsorb the key intermediate *CO, creating conditions for coupling; Cu 0 produces surface plasmon resonance (LSPR) under visible light, providing abundant electrons. However, Cu-based catalysts have significant bottlenecks: (1) Cu + is prone to disproportionation (2Cu + → Cu 0 + Cu 2+ ) or redox in the reaction environment, resulting in poor stability; (2) the hot electrons produced by Cu 0 have a short lifetime, and the photo-generated carriers are severely recombined, resulting in low electron utilization efficiency. These problems seriously restrict the ability of Cu-based catalysts to generate multi-carbon products efficiently and stably.

[0004] Constructing a heterojunction is one of the strategies to improve performance. I - ions in cuprous iodide (CuI) can effectively stabilize Cu + and inhibit deactivation; at the same time, the heterostructure formed by Cu and CuI helps to promote photo-induced charge separation. However, how to improve charge separation efficiency and optimize the C-C coupling process while stabilizing the active site through precise catalyst design remains a difficult problem to be solved.

[0005] Therefore, it is necessary to develop a preparation method of a Cu / CuI composite catalyst with a specific morphology (such as hollow square shape) and apply it to the efficient and high-selectivity photocatalytic reduction of CO2 to multi-carbon products. This structure is expected to combine the advantages of Cu 0LSPR effect, CuI stabilizes Cu + The advantages of promoting C-C coupling and the characteristics of heterojunction accelerating charge separation, and the square shape may provide a high activity exposure surface, providing a new way to break through the bottleneck of the prior art. SUMMARY

[0006] In view of the Cu + species prone to disproportionation inactivation, poor stability, serious photogenerated carrier recombination limits electron utilization efficiency, and the difficulty of high efficiency and high selectivity to generate multi-carbon products (C 2+ ), the present application provides a preparation method of Cu / CuI composite catalyst with specific morphology (such as square shape), and applies it to high-efficiency and high-selectivity photocatalytic reduction of CO2 to generate multi-carbon products, which can effectively stabilize the active Cu + species, significantly improve the photogenerated charge separation and utilization efficiency, reduce the C-C coupling energy barrier, thereby significantly improve the activity, selectivity and stability of photocatalytic reduction of CO2 to generate multi-carbon products (such as C2H4, C2H6), and the square structure can provide a regular active surface.

[0007] To achieve the above object, the present application provides the following technical scheme: a preparation method of hollow square Cu / CuI catalyst, comprising the following steps:

[0008] S1: stirring and mixing water, alkali source, copper source and reducing agent under heating condition to obtain square Cu element by one-step precipitation method to control the reduction time;

[0009] S2: dispersing the Cu element obtained in S1 in a solvent, then adding an I - ion-containing solution to form a mixed solution, then adding acid dropwise according to the ratio V1: V2= (100~500):1 of the volume V1 of the mixed solution to the volume V2 of the acid solution, and then centrifuging, washing and drying after stirring to obtain the hollow square Cu / CuI catalyst.

[0010] Preferably, the alkali source in step S1 is sodium hydroxide, and the concentration is 0.1~1mol / L.

[0011] Preferably, the copper source in step S1 is at least one of copper sulfate, copper chloride, copper acetate and copper nitrate, and the concentration of copper ions is 0.01~0.1mol / L.

[0012] 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 0.01~0.1mol / L.

[0013] Preferably, the heating condition in step S1 is 60℃.

[0014] Preferably, the compound containing I in step S2 - The ion solution is any one of water, ethanol, ethylene glycol or a mixed solution.

[0015] Preferably, the compound containing I in step S2 - 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.

[0016] 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.

[0017] 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.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 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.

[0020] 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 + .

[0021] 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.

[0022] 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.

[0023] 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

[0024] Figure 1 This is the X-ray diffraction spectrum of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention;

[0025] Figure 2 This is a scanning electron microscope image of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention;

[0026] Figure 3 This is a transmission electron micrograph of the hollow block Cu / CuI catalyst prepared in Example 1 of the present invention;

[0027] Figure 4 This is a transmission electron microscope image of the solid square Cu / CuI catalyst prepared in Comparative Example 1 of the present invention;

[0028] Figure 5 This is the Auger electron spectrum of the hollow square Cu / CuI catalyst prepared in Example 1 of the present invention;

[0029] 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;

[0030] Figure 7 This is the cycle performance diagram of the Cu / CuI catalyst prepared in Example 1. DETAILED DESCRIPTION

[0031] 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

[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:

[0033] 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.

[0034] 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.

[0035] The hollow block Cu / CuI catalyst prepared in Example 1 was characterized and analyzed. Figures 1-7 As shown:

[0036] 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.

[0037] 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.

[0038] Attachment Figure 3 This is a transmission electron micrograph of the Cu / CuI catalyst prepared in Example 1. It can be clearly seen from the transmission electron micrograph that the prepared Cu / CuI catalyst has a hollow block structure and a shell thickness of about 50 nm.

[0039] 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.

[0040] 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 + .

[0041] AttachmentFigure 6 The performance comparison chart of the photocatalytic reduction of CO2 of the Cu / CuI catalyst prepared for 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 -1 )and C2 product electronic selectivity (57.5%); while the C2 product yield and selectivity of Comparative Example 1 (high acid amount, V1:V2=100:1) and Comparative Example 2 (low acid amount, V1:V2=500:1) are significantly reduced, which directly proves that the acid addition amount plays a key role in maintaining the Cu + valence state and further regulating the selectivity of C2 products (see Figure 6 ).

[0042] The cycle performance chart of the Cu / CuI catalyst prepared for Example 1 shows that after five cycles, the catalyst still maintains good catalytic activity. Figure 7 The cycle performance chart of the Cu / CuI catalyst prepared for Example 1 shows that after five cycles, the catalyst still maintains good catalytic activity. Example 2

[0043] A method for preparing a hollow cube Cu / CuI catalyst and its application in photocatalytic reduction of CO2 to multi-carbon products, comprising the following steps:

[0044] S1: Dissolve 2.4mmol of copper nitrate trihydrate and 0.024mol of sodium hydroxide in 240mL of deionized water at a temperature of 60℃ and stir for 2h, then add 2.4mmol of hydrazine hydrate and stir for 30min, centrifuge, wash and dry to obtain Cu single element.

[0045] S2: Dissolve 80mg of Cu in 50mL of ethanol, dissolve 3mmol of NaI in 30mL of water, then pour the prepared NaI solution into the above solution, add dilute sulfuric acid with a concentration of 0.005mol / L at a ratio of V1:V2=500:1, stir for 1h, centrifuge, wash and dry to obtain Cu / CuI. Example 3

[0046] A method for preparing a hollow cube Cu / CuI catalyst and its application in photocatalytic reduction of CO2 to multi-carbon products, comprising the following steps:

[0047] S1: Dissolve 24mmol of copper acetate and 0.24mol of sodium hydroxide in 240mL of deionized water at a temperature of 60℃ and stir for 2h, then add 24mmol of ascorbic acid and stir for 30min, centrifuge, wash and dry to obtain Cu single element.

[0048] ​S2: 80 mg of Cu was dissolved in 50 mL of ethanol, 3 mmol of KI was dissolved in 3 mL of water, and then the prepared NH4I solution was poured into the above solution, 0.005 mol / L of dilute sulfuric acid was added at a concentration of V1:V2=100:1, stirred for 1 h, centrifuged, washed, and dried to obtain Cu / CuI.

[0049] Comparative Example 1

[0050] 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 a temperature of 60°C, stirred for 2 h, and finally 8 mmol of hydrazine hydrate was added, stirred for 30 min, centrifuged, washed, and dried to obtain Cu single element.

[0051] S2: 80 mg of Cu was dissolved in 50 mL of ethanol, 3 mmol of I2 solution was added, stirred for 1 h, centrifuged, washed, and dried to obtain Cu / CuI.

[0052] Comparative Example 2

[0053] 1M NaI was dissolved in 100 mL of deionized water, 100 mL of 0.1M copper sulfate pentahydrate was added, stirred for 1 h, centrifuged, washed, and dried to obtain CuI.

[0054] Comparative Example 3

[0055] 8 mmol of copper sulfate pentahydrate and 0.12 mol of sodium hydroxide were mixed and dissolved in 240 mL of deionized water at a temperature of 60°C, stirred for 2 h, and finally 8 mmol of ascorbic acid was added, stirred for 30 min, centrifuged, washed, and dried to obtain Cu single element.

[0056] Application Test:

[0057] The activity of the catalysts prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 was verified, and the specific process was as follows:

[0058] 30 mg of the above five catalysts were dispersed in an ethanol solution, and were uniformly added to a quartz membrane and naturally air-dried; 0.8 mL of deionized water and 0.2 mL of a sacrificial agent (TEOA) were injected into the bottom of the reactor, and then the quartz membrane was transferred to a quartz container, and the quartz reaction container was sealed with a quartz cover; the quartz reaction container was vacuumed, and then filled with CO2, and the circulation operation was performed twice; circulating cooling water was introduced to maintain room temperature, and the CO2 was photocatalytically reduced under the irradiation of a 300W xenon lamp equipped with a 420nm filter. A xenon lamp was used as a light source to irradiate the catalyst, and every hour 1 mL of gas was extracted from the reactor with a syringe, and the concentrations of CO, CH4, C2H4 and C2H6 were detected by gas chromatography.

[0059] The catalysts prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested for performance using gas chromatography, as shown in Figure 6 It can be seen that the catalytic activity of Example 1 is the best, with a C2H4 yield of 2 μmol·g -1 ·h -1 , a C2H6 yield of 5.64 μmol·g -1 ·h -1 , and a C2 (C2H4+C2H6) yield of 7.64 μmol·g -1 ·h -1 , a double carbon product selectivity of 57.5%, and the performance of the catalyst obtained is shown in Table 1 below and the accompanying Figure 6 .

[0060] Table 1 - Photocatalytic performance test and C2 electron selectivity of examples and comparative examples

[0061]

[0062] In summary, the present application constructs a Cu 0 / Cu + gradient interface by precisely regulating the acid etching ratio, and successfully breaks through the technical bottlenecks of existing copper-based catalysts in photocatalytic CO2 reduction, such as easy deactivation of active sites, serious carrier recombination and high C-C coupling energy barrier, through a triple synergistic mechanism of in-situ iodine ion stabilizing Cu + active sites and hollow square structure strengthening charge separation. Experimental data fully demonstrate that the catalyst prepared under the optimal process not only realizes the significant outperformance of C2 product electron selectivity over C1 product, but also exhibits catalytic activity and stability far exceeding single component and non-controlled acid process, fundamentally solving the core problem of low multi-carbon product generation efficiency, and verifying the creative breakthrough of the present application in promoting the development of CO2 photocatalytic conversion to high value-added multi-carbon products.

[0063] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent substitutions or changes to the technical solutions and inventive concepts of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a hollow block Cu / CuI catalyst, characterized in that , including 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. S2: Disperse the Cu element obtained in S1 in a solvent, and then add I - The ion solution forms a mixed solution, and then the acid is added dropwise at a ratio of the mixed solution volume V1 to the acid solution volume V2 (V1:V2=(100~500):1). After stirring, centrifugation, washing, and drying, a hollow block-shaped Cu / CuI catalyst is obtained. 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.

2. 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.

3. The method for preparing a hollow block-shaped Cu / CuI catalyst according to claim 2, wherein: 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.

4. 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 3, characterized in that: Applied to photocatalytic reduction of CO2 to C2 and above hydrocarbons.

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