A CuI / Bi5O7I composite photocatalyst and its one-step hydrothermal synthesis method and application

Abstract

This invention discloses a CuI / Bi5O7I composite photocatalyst, its one-step hydrothermal synthesis method, and its application, belonging to the field of catalyst material technology. A template agent, a copper compound, and a bismuth compound are ultrasonically mixed in water to obtain an initial solution. Potassium iodide solution is then rapidly added. The pH of the solution is adjusted to 7-11, and after stirring, a hydrothermal reaction is carried out at 150-180℃ for 30-200 min. After the reaction, the product is separated by centrifugation. The separated product is then soaked in an organic solvent and freeze-dried to obtain the CuI / Bi5O7I composite photocatalyst. The CuI / Bi5O7I composite photocatalyst prepared by this invention can reduce CO2 to multi-carbon products under visible light irradiation. Furthermore, the catalyst has a narrow band gap, a wider light absorption range, and the formation of a heterojunction reduces electron-hole recombination, showing great application potential in the field of photocatalytic CO2 reduction.

Description

Technical Field

[0001] This invention belongs to the field of catalyst synthesis and application technology, specifically relating to a CuI / Bi5O7I composite photocatalyst and its one-step hydrothermal synthesis method and application. Background Technology

[0002] Given the urgency of achieving the "dual carbon" goal, exploring effective carbon reduction and decarbonization strategies is urgently needed. Photocatalysis, as a green and pollution-free clean carbon fixation technology, has been widely studied and reported. However, currently, the products of photocatalytic CO2 reduction are mainly C1 species, and due to the limitations of multi-electron and multi-proton reaction processes, the selectivity for higher-value multi-carbon products is poor.

[0003] Research has found that Cu + Species can enhance the adsorption capacity of CO species, enabling them to further hydrogenate and couple, thus possessing the potential to promote coupling. Therefore, developing C... 2+ The key to photocatalysts is designing catalysts that sustainably produce and stabilize *CO for subsequent hydrogenation and coupling. However, Cu... + It is usually easily oxidized to Cu. 2+ This leads to catalyst deactivation. Therefore, a stable Cu... + Catalysts are of great significance. Based on previous findings that iodide ions can react with Cu... 2+ The reaction produces stable CuI, which provides a basis for constructing stable Cu. + Catalysts made this possible. Among numerous bismuth-based halides, Bi5O7I has been widely studied and reported due to its unique lamellar structure, suitable band gap, strong reducing power, and stability. However, in the process of CuI and Bi5O7I composite, it was found that CuI excessively covered Bi sites on the Bi5O7I surface, failing to fully expose Cu. + The presence of Bi bimetallic sites limits its composite catalytic activity. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a CuI / Bi5O7I composite photocatalyst, its one-step hydrothermal synthesis method, and its application. The one-step hydrothermal method is simple to prepare and has a low cost. By forming a heterojunction through the misaligned band structure between CuI and Bi5O7I, the light absorption capacity of the single catalyst and the separation efficiency of photogenerated electrons and holes can be improved, thereby enhancing the photocatalytic activity.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, this invention discloses a one-step hydrothermal synthesis method for a CuI / Bi5O7I composite photocatalyst, comprising the following steps:

[0007] (1) Place the template agent, copper compound and bismuth compound in water and sonicate to mix, then quickly add potassium iodide solution;

[0008] (2) Adjust the pH of the solution in step (1) to 7-11, stir, and then perform a hydrothermal reaction at 150-180℃ for 30-200 min. After the reaction is completed, centrifuge to separate the product.

[0009] (3) The product separated in step (2) is soaked in an organic solvent and then freeze-dried to obtain CuI / Bi5O7I composite photocatalyst.

[0010] Further, the template agent mentioned in step (1) is mannitol and / or polyvinylpyrrolidone, the copper compound is one or more of copper chloride, copper nitrate, and copper sulfate, and the bismuth compound is one or more of basic bismuth carbonate, bismuth nitrate, and bismuth oxide.

[0011] Further, in step (1), the molar ratio of the copper compound to the bismuth compound is 1:10-30, and the molar ratio of the bismuth compound to potassium iodide is 1:20-50.

[0012] Further, the amount of template agent added in step (1) is 1-2 times the total mass of the copper compound and bismuth compound, and the concentration of the potassium iodide solution is 5-10M.

[0013] Furthermore, in step (2), a 1-3M alkaline solution is used to adjust the pH of the solution in step (1) to 7-11. The alkaline solution is one or more of sodium hydroxide, ammonia, and potassium hydroxide solution.

[0014] Further, the organic solvent mentioned in step (3) is one or more of ethanol, N,N-dimethylformamide, acetonitrile, and acetone.

[0015] In a second aspect, the present invention discloses a CuI / Bi5O7I composite photocatalyst synthesized by the method described above, wherein the CuI / Bi5O7I composite photocatalyst has a two-dimensional sheet-like structure.

[0016] In a third aspect, the present invention discloses the application of the CuI / Bi5O7I composite photocatalyst in the photocatalytic reduction of CO2 to multi-carbon products, wherein the multi-carbon products include carbon monoxide and ethylene.

[0017] This invention prepares a CuI / Bi5O7I composite photocatalyst via a one-step hydrothermal synthesis method, utilizing I... - Stable Cu + Species, further combined with Cu +The strong adsorption capacity of *CO intermediates and the advantage of heteronuclear bimetallic atomic sites formed by Bi and Cu improve the CC coupling efficiency, thereby enhancing the selectivity of ethylene products from a kinetic perspective. Addressing the issue that the photocatalytic reduction of CO2 to prepare multi-carbon products requires the participation of multiple electrons, a CuI / Bi5O7I heterojunction is constructed. This expands the light absorption capacity of the composite heterojunction material, effectively improving the photogenerated electron-hole separation efficiency and providing a large amount of effective charge for the photocatalytic CC coupling reaction, thus promoting ethylene production from a thermodynamic perspective. Simultaneously, to address the issue that the solubility of CuI in solution during the preparation process leads to the preferential precipitation of Bi5O7I upon pH adjustment, followed by CuI deposition on the Bi5O7I surface which would cover the Cu / Bi dual active sites, hindering the CC coupling reaction, this invention employs an organic solvent to wash and soak the catalyst, overcoming the problem of CuI covering the bimetallic active sites and promoting the formation of multi-carbon products.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0019] This invention provides a CuI / Bi5O7I heterojunction composite photocatalyst prepared via a one-step hydrothermal synthesis method, utilizing I... - Stable Cu + Species, further combined with Cu + The strong adsorption capacity of the CO intermediate and the advantages of the heteronuclear bimetallic atomic sites formed by Bi and Cu improve the coupling efficiency of CC and enhance the selectivity of ethylene products from a kinetic perspective. At the same time, washing the catalyst with organic solvents can expose more bimetallic active sites, which is beneficial to improving the photocatalytic reduction performance of CO2 and the selectivity of double carbon products. Attached Figure Description

[0020] Figure 1 XRD patterns of the catalysts prepared in Examples 1-3 and Comparative Examples 1-3;

[0021] Figure 2 Electron microscopy images of the CuI / Bi5O7I composite photocatalyst prepared in Example 1: (a) TEM image, (b) HRTEM image;

[0022] Figure 3 SEM image and elemental distribution diagram of the CuI / Bi5O7I composite photocatalyst prepared in Example 1;

[0023] Figure 4 The transient photocurrent response diagram of the CuI / Bi5O7I composite photocatalyst prepared in Example 1 is shown.

[0024] Figure 5 The figures show the experimental results of photocatalytic reduction of CO2 using the catalysts prepared in Examples 1-3 and Comparative Examples 1-3. Detailed Implementation

[0025] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and the raw materials used are commercially available products.

[0026] Example 1

[0027] (1) Dissolve 0.27 g mannitol, 0.4 g polyvinylpyrrolidone (PVP) and 0.48 g bismuth nitrate pentahydrate in 15 mL of distilled water in sequence, sonicate and stir continuously until completely dissolved, then add 12 mg copper sulfate pentahydrate to the solution, stir for 20 min, and then quickly add potassium iodide solution (6.63 g potassium iodide dissolved in 5 mL of distilled water);

[0028] (2) Adjust the pH of the solution to 10.5 with 2M sodium hydroxide, continue stirring for 10 min, transfer the solution to a polytetrafluoroethylene reactor, react for 180 min, react at 160℃, wash the product after reaction with ethanol and water, and separate by centrifugation.

[0029] (3) The product separated in step (2) was dispersed in N,N-dimethylformamide and soaked for 30 min, centrifuged, freeze-dried and ground to obtain CuI / Bi5O7I composite photocatalyst.

[0030] Example 2

[0031] (1) Dissolve 0.27 g mannitol, 0.4 g polyvinylpyrrolidone (PVP) and 0.48 g bismuth nitrate pentahydrate in 15 mL of distilled water in sequence, sonicate and stir continuously until completely dissolved, then add 4 mg copper sulfate pentahydrate to the solution, stir for 20 min, and then quickly add potassium iodide solution (6.63 g potassium iodide dissolved in 5 mL of distilled water);

[0032] (2) Adjust the pH of the solution to 10.5 with 2M sodium hydroxide, continue stirring for 10 min, transfer the solution to a polytetrafluoroethylene reactor, react for 180 min, react at 160℃, wash the product after reaction with ethanol and water, and separate by centrifugation.

[0033] (3) The product separated in step (2) was dispersed in N,N-dimethylformamide and soaked for 30 min, centrifuged, freeze-dried and ground to obtain CuI / Bi5O7I composite photocatalyst.

[0034] Example 3

[0035] (1) Dissolve 0.27 g mannitol, 0.4 g polyvinylpyrrolidone (PVP) and 0.48 g bismuth nitrate pentahydrate in 15 mL of distilled water in sequence, sonicate and stir continuously until completely dissolved, then add 16 mg copper sulfate pentahydrate to the solution, stir for 20 min, and then quickly add potassium iodide solution (6.63 g potassium iodide dissolved in 5 mL of distilled water);

[0036] (2) Adjust the pH of the solution to 10.5 with 2M sodium hydroxide, continue stirring for 10 min, transfer the solution to a polytetrafluoroethylene reactor, react for 180 min, react at 160℃, wash the product after reaction with ethanol and water, and separate by centrifugation.

[0037] (3) The product separated in step (2) was dispersed in N,N-dimethylformamide and soaked for 30 min, centrifuged, freeze-dried and ground to obtain CuI / Bi5O7I composite photocatalyst.

[0038] Comparative Example 1

[0039] Compared with Example 1, Comparative Example 1 did not add copper sulfate pentahydrate in step (1), and the remaining steps were the same as in Example 1 to prepare Bi5O7I catalyst.

[0040] Comparative Example 2

[0041] 1.25 g of copper sulfate pentahydrate was dissolved in 100 mL of distilled water to form solution A, and 1.66 g of potassium iodide was dissolved in 100 mL of distilled water to form solution B. Solution B was poured into solution A and stirred continuously for 30 min. The solution was collected by centrifugation, washed three times alternately with distilled water and ethanol, and dried under vacuum at 60 °C overnight to obtain the CuI catalyst.

[0042] Comparative Example 3

[0043] Compared with Example 1, Comparative Example 3 did not perform step (3), but the remaining steps were the same as in Example 1, and CuI / Bi5O7I composite photocatalyst was prepared.

[0044] Performance testing

[0045] The XRD patterns of the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 1 As shown in the figure, the CuI / Bi5O7I composite photocatalysts prepared in Examples 1-3 have Bi5O7I as the main component. The peaks at 2θ=28.2°, 29.3°, and 31.6° represent the Bi5O7I phase, and the peak at 2θ=25.5° represents the CuI phase, indicating that the CuI / Bi5O7I composite photocatalyst was successfully synthesized.

[0046] The CuI / Bi5O7I composite photocatalyst prepared in Example 1 was observed using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), and the results are as follows: Figure 2 The images shown are (a) TEM images and (b) HRTEM images. Figure 2 As shown in (a), the CuI / Bi5O7I composite photocatalyst prepared in Example 1 has a two-dimensional sheet-like structure with a sheet thickness of approximately 15-20 nm and a relatively uniform sheet distribution; Figure 2 As shown in (b) of the diagram, lattice spacing can be observed in the lattice fringe pattern. d =0.32 nm lattice fringes belonging to the (311) crystal plane of Bi5O7I crystal and d =0.21 nm lattice fringes belonging to the (220) crystal plane of CuI crystal. Therefore, the CuI / Bi5O7I composite photocatalyst prepared in Example 1 is a CuI / Bi5O7I heterojunction with a sheet-like structure.

[0047] The microstructure and elemental distribution of the CuI / Bi5O7I composite photocatalyst prepared in Example 1 were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results are as follows: Figure 3 As shown, the results indicate that Cu, I, Bi, and O elements are uniformly distributed on the composite photocatalyst.

[0048] Electrochemical tests were performed using a CHI660A electrochemical workstation equipped with a standard three-electrode system. The photoelectrode was prepared using a drop-coating method. Specifically, 5 mg of catalyst powder was dispersed in a mixture of 0.2 mL ethanol and 20 μL Nafion, ultrasonicated to form a homogeneous suspension, and then drop-coated onto a clean FTO glass (1 cm × 1 cm) surface using a pipette. The suspension was then dried overnight under vacuum. During the measurement, the FTO glass coated with the catalyst sample served as the working electrode, a platinum sheet as the counter electrode, Ag / AgCl as the reference electrode, and a 0.5 mol / L Na₂SO₄ aqueous solution as the electrolyte. An LED lamp was used as the excitation source. The transient photocurrent response diagrams of the CuI / Bi₅O₇I composite photocatalyst prepared in Example 1, the Bi₅O₇I catalyst prepared in Comparative Example 1, and the CuI catalyst prepared in Comparative Example 2 are shown below. Figure 4 As shown, by Figure 4 It can be seen that the construction of heterojunction in Example 1 effectively improved the photogenerated electron-hole separation efficiency, generated a large number of freely moving electrons, and effectively improved the photocatalytic activity of the sample.

[0049] Photocatalytic CO2 Reduction Experiment: The photocatalytic CO2 reduction experiment was conducted using a double-layer quartz reactor. A 300W xenon lamp (MC-PF300C, Beijing MerryChange) with an AM1.5 filter was used to simulate sunlight. In the photocatalytic CO2 reduction reaction, 30 mg of photocatalyst (catalysts prepared in Examples 1-3 and Comparative Examples 1-3) was ultrasonically dispersed in ethanol, uniformly coated on a 4 cm diameter filter membrane, dried, and then placed in the quartz reactor. A mixed solution of 0.3 mL water and 0.3 mL triethanolamine was added as a proton source and sacrificial agent. The reactor was then evacuated and high-purity CO2 (after passing through water) was introduced, repeated three times to remove air from the reaction system. The xenon lamp was used for 5 h of irradiation to calculate the average product formation rate. The reaction products were detected by gas chromatography. CO and C2H4 gases were detected by a gas chromatography-inductively coupled plasma (FID) detector, and CO2 gas was detected by a gas chromatography-transfer chromatography (TCD) detector. The experimental results of CO2 reduction by the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 are as follows: Figure 5 As shown; by Figure 5 It can be seen that the yield of ethylene in the catalytic products of the CuI / Bi5O7I composite photocatalyst is significantly increased, and the yield exhibits a volcano-shaped curve distribution with increasing CuI content. The CO production rate of the CuI / Bi5O7I composite photocatalyst prepared in Example 1 reached 129.75 μmol·g. -1 ·h -1 The yield of ethylene was 14.71 μmol·g. -1 ·h -1 This is because the formation of a heterojunction promotes charge separation, allowing electrons that were originally annihilated with holes to re-enter the reaction, thus promoting ethylene production. In Comparative Example 1, the Bi5O7I catalyst produced relatively small amounts of both CO and ethylene in the photocatalytic reduction of CO2. The CuI catalyst prepared in Comparative Example 2 also produced only small amounts of CO and ethylene in the photocatalytic reduction of CO2. However, in Comparative Example 3, without soaking and washing with organic solution, the photocatalytic reduction performance of CO2 decreased, and the ethylene selectivity decreased significantly.

Claims

1. A one-step hydrothermal synthesis method for a CuI / Bi5O7I composite photocatalyst, characterized in that, Includes the following steps: (1) Place the template agent, copper compound and bismuth compound in water and sonicate to mix, then quickly add potassium iodide solution; (2) Adjust the pH of the solution in step (1) to 7-11, stir, and then perform a hydrothermal reaction at 150-180℃ for 30-200 min. After the reaction is completed, centrifuge to separate the product. (3) The product separated in step (2) was soaked in an organic solvent and then freeze-dried to obtain CuI / Bi5O7I composite photocatalyst; The template agent mentioned in step (1) is mannitol and / or polyvinylpyrrolidone; The molar ratio of the copper compound to the bismuth compound in step (1) is 1:10-30, and the molar ratio of the bismuth compound to potassium iodide is 1:20-50. The organic solvent mentioned in step (3) is one or more of ethanol, N,N-dimethylformamide, acetonitrile, and acetone.

2. The one-step hydrothermal synthesis method of the CuI / Bi5O7I composite photocatalyst according to claim 1, characterized in that, The copper compound mentioned in step (1) is one or more of copper chloride, copper nitrate, and copper sulfate, and the bismuth compound is one or more of basic bismuth carbonate, bismuth nitrate, and bismuth oxide.

3. The one-step hydrothermal synthesis method of the CuI / Bi5O7I composite photocatalyst according to claim 1, characterized in that, The amount of template agent added in step (1) is 1-2 times the total mass of the copper compound and bismuth compound, and the concentration of the potassium iodide solution is 5-10M.

4. The one-step hydrothermal synthesis method of the CuI / Bi5O7I composite photocatalyst according to claim 1, characterized in that, In step (2), the pH of the solution in step (1) is adjusted to 7-11 using a 1-3M alkaline solution. The alkaline solution is one or more of sodium hydroxide, ammonia, and potassium hydroxide solutions.

5. A CuI / Bi5O7I composite photocatalyst synthesized by the method according to any one of claims 1-4, characterized in that, The CuI / Bi5O7I composite photocatalyst has a two-dimensional sheet-like structure.

6. The application of the CuI / Bi5O7I composite photocatalyst according to claim 5 in the photocatalytic reduction of CO2 to multi-carbon products, characterized in that, The multi-carbon products mentioned include ethylene.

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