Preparation and application of photocatalytic material with metal oxide as protective layer
Patent Information
- Application Number
- CN202310332224.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-03-30
- Publication Date
- 2026-09-25
- Estimated Expiration
- 2043-03-30
AI Technical Summary
[0007](1)提供一种以金属氧化物作为保护层的光催化材料的制备方法，以解决无保护层的内核Cu2O易被光腐蚀，导致催化剂失活的问题；
[0016]本发明设计了一种以金属氧化物为保护层的核壳结构Cu2O@MgO、Cu2O@CaO和Cu2O@Al2O3光催化复合材料，金属氧化物保护层解决了Cu2O易被光腐蚀的问题，提高了光催化复合材料的循环稳定性。首先通过调节不同种类的金属氧化物保护层，筛选比表面积最大的光催化复合材料，从而选择最佳金属氧化物保护层的种类；其次调控金属氧化层的比例，从而控制光催化复合材料的带隙结构，提高光催化复合材料的循环稳定性，调控气体产物CO和CH4的生成速率与转化率。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of core-shell structure photocatalytic material preparation technology, and specifically relates to the preparation and application of a photocatalytic material with a metal oxide as a protective layer. Background Technology
[0002] The overuse of fossil fuels has exacerbated the energy crisis. The combustion of fossil fuels produces large amounts of carbon dioxide (CO2), which is a very stable small molecule (bonding energy as high as 750 kJ / mol). -1 How to utilize CO2 has become one of the most challenging scientific problems. Utilizing clean energy—solar energy—to drive the photocatalytic activation and conversion of CO2 is the most ideal way to convert and utilize CO2.
[0003] Highly efficient semiconductor photocatalysts possess excellent catalytic activity, generating photo-generated electrons and free radicals under illumination. The potentials for converting CO2 to CH4 and CO are -0.24V and -0.53V, respectively. In other words, the selection and design of photocatalysts must match the generation potentials of CH4 and CO. Cu2O, due to its variable band gap structure (-0.55 to -1.1 eV) and strong visible light activity, is widely used in CO2 reduction. However, Cu2O suffers from problems such as rapid recombination of photogenerated electron-hole pairs, susceptibility to photocorrosion, poor stability, and low quantum efficiency. Therefore, using Cu2O as the core to design core-shell structured catalysts can not only effectively avoid these problems but also adjust the catalyst's band structure, thereby improving photocatalytic performance.
[0004] Existing technology CuO / Cu2O (Efficient UV–visible photodetector based on singleCuO / Cu2O core-shell nanowire, Journal of Alloys and Compounds 895(2022), doi:10.1016 / j.jallcom.2021.162546); Cu2O@TiO2 / MOF (Double shell compositenanoarchitectonics of Cu2O core with TiO2 / metal-organic frameworks for efficient hydrogen generation,International Journal of Hydrogen Energy (48(2023), doi:10.1016 / j.ijhydene.2022.09.304) Core-shell photocatalysts with Cu2O cores were prepared using chemical deposition and nanoconfinement methods, respectively. However, problems such as uncontrolled outer layer thickness and poor dispersion exist. Uncontrolled outer layer thickness means that thick areas will cover the original reactive sites, while thin areas will expose Cu2O directly to light, leading to severe photocorrosion. This critical issue also leads to the easy loss of catalyst active sites and poor cycle stability during photocatalysis, limiting its further practical application. In addition, although the above technologies all use photocatalysts, which are also semiconductors, as the shell to construct heterostructures and improve photocatalytic activity, the shell does not have the ability to adsorb CO2. This means that there are no adsorption sites and active sites on the catalyst surface. Although the photocatalytic efficiency has been improved, how to solve the current problems and maximize the photocatalytic activity of the material remains the focus and difficulty of current research.
[0005] To address the shortcomings of existing technologies, this invention uses Cu2O as the core and selects different metal oxides as the outer protective layer. A core-shell structured photocatalytic composite material is prepared by combining a simple physical impregnation method with a high-temperature calcination method. The Cu2O@MgO photocatalytic composite material possesses a large specific surface area, high CO2 adsorption capacity, and abundant reactive sites. By adjusting the thickness of the MgO layer, not only can photocorrosion of Cu2O be prevented, but the band gap structure of the Cu2O@MgO photocatalytic composite material can also be further adjusted, thereby improving reusability and photocatalytic activity. This also results in adjustable generation rates and conversion rates of gaseous products (CO and CH4). Under optimal conditions, this photocatalytic composite material achieves a CO2 conversion rate of up to 97.5% and a CH4 selectivity of 86.8%. Summary of the Invention
[0006] The purpose of this invention:
[0007] (1) A method for preparing a photocatalytic material with a metal oxide as a protective layer is provided to solve the problem that the unprotected core Cu2O is easily photo-corroded, leading to catalyst deactivation;
[0008] (2) A photocatalytic material with a metal oxide protective layer for CO2 reduction is prepared by a simple method to realize the adsorption-reduction-desorption process, so as to solve the problem of small specific surface area and few CO2 adsorption active sites of Cu2O.
[0009] (3) Designing core-shell structured photocatalysts, screening different metal oxides as protective layers, and adjusting the thickness of the metal oxide protective layer can regulate the generation rate and conversion rate of gaseous products (CO and CH4), thus solving the problems of low conversion rate and poor selectivity of traditional CO2 reduction to CO and CH4.
[0010] The specific steps of this invention are as follows:
[0011] (1) Mix copper chloride (CuCl2·2H2O) and polyvinylpyrrolidone (PVP) in a mass ratio of 0.2:3:0.1.
[0012] Sodium citrate is dissolved in 100 mL of deionized water at a certain temperature.
[0013] (2) A certain molar mass of sodium hydroxide (NaOH) and ascorbic acid solution were added dropwise to (1), and the mixture was heated in a water bath at 50-80℃ for 2-4 hours to obtain crude Cu2O product. Then, the crude Cu2O product was washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60℃ for 2 hours to obtain Cu2O crystals with an octahedral structure.
[0014] (3) 5-20 mmol / L -1 Magnesium nitrate solution (Mg(NO3)2), calcium nitrate solution (Ca(NO3)2), and aluminum nitrate solution (Al(NO3)3) were respectively mixed with Cu2O crystals. The mixtures were then ultrasonicated at 60–90 W for 30 min in an ultrasonic cleaner to obtain homogeneous solutions. The resulting solutions were dried in an oven at 60 °C for 8–12 h to obtain crude Cu2O@Mg(NO3)2, Cu2O@Ca(NO3)2, and Cu2O@Al(NO3)3 products.
[0015] (4) The crude products of Cu2O@Mg(NO3)2, Cu2O@Ca(NO3)2, and Cu2O@Al(NO3)3 were transferred to a ceramic boat and placed in a tubular calcining furnace. The boat was then calcined at 300–500 °C for 4 hours. The calcined products were then allowed to cool naturally to room temperature to obtain photocatalytic composite materials of Cu2O@MgO, Cu2O@CaO, and Cu2O@Al2O3 with core-shell structures.
[0016] This invention designs core-shell structured Cu2O@MgO, Cu2O@CaO, and Cu2O@Al2O3 photocatalytic composites with metal oxide protective layers. The metal oxide protective layer solves the problem of Cu2O's susceptibility to photocorrosion and improves the cycling stability of the photocatalytic composite. First, by adjusting different types of metal oxide protective layers, the photocatalytic composite with the largest specific surface area is screened to select the optimal type of metal oxide protective layer. Second, the proportion of the metal oxide layer is controlled to regulate the band gap structure of the photocatalytic composite, thereby improving its cycling stability and controlling the generation and conversion rates of gaseous products CO and CH4. Attached Figure Description
[0017] Figure 1 This is a scanning electron microscope image of the Cu2O@MgO photocatalytic composite material;
[0018] Figure 2 The image shows the BET characterization of the Cu2O@MgO photocatalytic composite material and Cu2O. Detailed Implementation
[0019] These embodiments are merely illustrative of the invention, but the invention is not limited to these embodiments.
[0020] Example 1:
[0021] (1) Dissolve copper chloride (CuCl2·2H2O), polyvinylpyrrolidone (PVP), and sodium citrate in a mass ratio of 0.2:3:0.1 in 100 mL of deionized water at 55 °C. Add 2 mol / L... -1 Sodium hydroxide (NaOH) and 0.6 mol / L -1 Ascorbic acid solution was added dropwise to the above solution, and the mixture was heated in a water bath at 80°C to obtain crude Cu₂O. The crude Cu₂O was then washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60°C to obtain octahedral Cu₂O crystals.
[0022] (2) 10 mmol / L -1Magnesium nitrate solution (Mg(NO3)2) was mixed with Cu2O crystals. The mixture was then ultrasonically cleaned at 60–90 W for 30 min to obtain a homogeneous solution. The resulting solution was dried in an oven at 60 °C for 8–12 h to obtain the coated Cu2O@Mg(NO3)2 (10 mmol / L). -1 Crude product.
[0023] (3) The crude Cu2O@Mg(NO3)2 product was transferred to a porcelain boat and placed in a tubular calcining furnace. It was then calcined at 300–500 °C for 4 hours. The calcined product was allowed to cool naturally to room temperature, yielding 10 mmol / L of the product. -1 The Cu2O@MgO photocatalytic composite material is named CM10.
[0024] Comparative Example 1:
[0025] (1) Dissolve copper chloride (CuCl2·2H2O), polyvinylpyrrolidone (PVP), and sodium citrate in a mass ratio of 0.2:3:0.1 in 100 mL of deionized water at 55 °C. Add 2 mol / L... -1 Sodium hydroxide (NaOH) and 0.6 mol / L -1 Ascorbic acid solution was added dropwise to the above solution, and the mixture was heated in a water bath at 80°C to obtain crude Cu₂O. The crude Cu₂O was then washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60°C to obtain octahedral Cu₂O crystals.
[0026] (2) 10 mmol / L -1 Calcium nitrate solution (Ca(NO3)2) and aluminum nitrate solution (Al(NO3)3) were mixed with Cu2O crystals respectively. The mixtures were then ultrasonicated at 60–90 W for 30 min in an ultrasonic cleaner to obtain a homogeneous solution. The resulting solution was dried in an oven at 60 °C for 8–12 h to obtain crude Cu2O@Ca(NO3)2 and Cu2O@Al(NO3)3 products.
[0027] (3) The crude products of Cu2O@Ca(NO3)2 and Cu2O@Al(NO3)2 were transferred to a porcelain boat and placed in a tubular calcining furnace. The mixture was calcined at 300–500 °C for 4 hours. After calcination, the products were allowed to cool naturally to room temperature, and 10 mmol / L of each product was obtained. -1 The Cu2O@CaO and Cu2O@Al2O3 photocatalytic composite materials are named CC10 and CA10.
[0028] Comparative Example 2:
[0029] Copper chloride (CuCl2·2H2O), polyvinylpyrrolidone (PVP), and sodium citrate in a mass ratio of 0.2:3:0.1 were dissolved in 100 mL of deionized water at 55 °C. 2 mol / L -1 Sodium hydroxide (NaOH) and 0.6 mol / L -1 Ascorbic acid solution was added dropwise to the above solution, and the mixture was heated in a water bath at 80°C to obtain crude Cu₂O. The crude Cu₂O was then washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60°C to obtain octahedral Cu₂O crystals, which were named Cu₂O.
[0030] The CM10, CC10, CA10, and Cu2O obtained in Example 1, Comparative Example 1, and Comparative Example 2 were characterized by SEM and BET, and photocatalytic reduction of CO2 was performed. The specific process is as follows:
[0031] (1) Place 20 mg of CM10, CC10, CA10 and Cu2O into a stainless steel reactor with a quartz window at the top (100 mL), add 50 mL of H2O inside the reactor and stir to form a homogeneous mixed solution.
[0032] (2) Use a CO2 gas purging system for 1 hour to remove air from the reactor. Then, inject CO2 gas into the reactor until the pressure rises to 0.4 MPa;
[0033] (3) A 300W Xe lamp was used as the light source, with a light intensity of 150mWcm. -2 Gas products were analyzed using gas chromatography and flame ionization detector (FID).
[0034] Comparative SEM images of the samples obtained in Example 1, Comparative Example 1, and Comparative Example 2 revealed that Cu₂O exhibits an octahedral morphology. CM₁₀, CC₁₀, and CA₁₀ all showed encapsulated octahedral morphologies, with CM₁₀ exhibiting the most uniform surface and a unique spherical encapsulated octahedral morphology. BET characterization of the samples obtained in Example 1 and Comparative Example 2 showed that the specific surface area of Cu₂O was 0.12 m². 2 g -1 The specific surface area of CM10 is 8.8 m². 2 g -1 The surface area of the sample was much larger than that of the original Cu2O, indicating that coating with metal oxides can increase the surface area of the original sample, which is beneficial for CO2 adsorption and further enhances its photocatalytic reduction of CO2. The reaction rate of Cu2O to CO obtained in Comparative Example 2 was 5.1 μmol / g. -1 h -1No CH4 was generated, and the CO2 conversion rate was 56.4%. In Example 1, the reaction rate of CO formation from CM10 was 9.2 μmol / g. -1 h -1 The reaction rate for the formation of CH4 is 46.1 μmol / g. -1 h -1 The CO2 conversion rate was 97.0%, and the selectivity for CH4 was 86.8%.
[0035] Example 2:
[0036] (1) Dissolve copper chloride (CuCl2·2H2O), polyvinylpyrrolidone (PVP), and sodium citrate in a mass ratio of 0.2:3:0.1 in 100 mL of deionized water at 55 °C. Add 2 mol / L... -1 Sodium hydroxide (NaOH) and 0.6 mol / L -1 Ascorbic acid solution was added dropwise to the above solution, and the mixture was heated in a water bath at 80°C to obtain crude Cu₂O. The crude Cu₂O product was then washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60°C to obtain octahedral Cu₂O crystals.
[0037] (2) 10 mmol / L -1 Magnesium nitrate solution (Mg(NO3)2) was mixed with 0.1 g of Cu2O crystals. The mixture was then ultrasonicated at 60–90 W for 30 min to obtain a homogeneous solution. The resulting solution was dried in an oven at 60 °C to obtain a solution impregnated with 10 mmol / L of Cu2O crystals. -1 Cu2O crystals impregnated with Mg(NO3)2. The Cu2O crystals impregnated with Mg(NO3)2 were transferred to a ceramic boat and placed in a tube furnace for high-temperature calcination at 300℃ for 4 hours, with a heating rate of 5℃ / min. -1 The calcined product was naturally cooled to room temperature to obtain a Cu2O@MgO photocatalytic composite material with a core-shell structure. The photocatalytic composite material generated under these conditions is referred to as CM10.
[0038] Comparative Example 2:
[0039] (1) Dissolve copper chloride (CuCl2·2H2O), polyvinylpyrrolidone (PVP), and sodium citrate in a mass ratio of 0.2:3:0.1 in 100 mL of deionized water at 55 °C. Add 2 mol / L... -1 Sodium hydroxide (NaOH) and 0.6 mol / L -1Ascorbic acid solution was added dropwise to the above solution, and the mixture was heated in a water bath at 80°C to obtain crude Cu₂O. The crude Cu₂O product was then washed by centrifugation with water and ethanol. Finally, it was dried in an oven at 60°C to obtain octahedral Cu₂O crystals.
[0040] (2) Distribute 0, 5, 15 and 20 mmol / L -1 Magnesium nitrate solution (Mg(NO3)2) was mixed with 0.1 g of Cu2O crystals. The mixture was then ultrasonicated for 30 min at 60–90 W in an ultrasonic cleaner to obtain a homogeneous solution. The resulting solution was dried in an oven at 60 °C to obtain Cu2O crystals impregnated with Mg(NO3)2. The Mg(NO3)2-impregnated Cu2O crystals were transferred to a ceramic boat and placed in a tubular furnace for high-temperature calcination at 300 °C for 4 h, with a heating rate of 5 °C / min. -1 The calcined products were naturally cooled to room temperature to obtain Cu2O@MgO photocatalytic composite materials with core-shell structures, which were named Cu2O, CM5, CM15 and CM20, respectively.
[0041] The photocatalytic composite materials obtained in Example 2 and Comparative Example 2 were characterized by XRD, SEM, and TEM, and photocatalytic CO2 reduction experiments were conducted. The specific procedures are as follows:
[0042] (1) Place 20 mg of photocatalytic composite material into a stainless steel reactor (100 mL) with a quartz window on top, add 50 mL of H2O inside the reactor, and stir to form a homogeneous mixed solution.
[0043] (2) Use a CO2 gas purging system for 1 hour to remove air from the reactor. Then, inject CO2 gas into the reactor until the pressure rises to 0.4 MPa;
[0044] (3) A 300W Xe lamp was used as the light source, with a light intensity of 150mWcm. -2 Gas products were analyzed using gas chromatography and flame ionization detector (FID).
[0045] By comparing the XRD patterns of the photocatalytic composite materials obtained in Example 2 and Comparative Example 2, it was found that with the increase of the Mg(NO3)2 ratio, the peak value of the (400) crystal plane of MgO at θ = 38.4° gradually increased, indicating that Cu2O and MgO were successfully composited. By comparing the SEM and TEM images, it was found that the morphology of Cu2O was a relatively smooth octahedron. After being coated with metal oxide, the thickness also increased with the increase of the MgO ratio. Elemental mapping confirmed that MgO was deposited on Cu2O, corresponding to the (111) crystal plane of Cu2O and the (400) crystal plane of MgO, respectively.
[0046] The catalysts in Example 2 and Comparative Example 2 exhibited different reaction rates during the photocatalytic reduction of CO2: the reaction rate of Cu2O to CO was 5.1 μmol / g. -1 h -1 The reaction rate for CH4 formation is 0, the CO2 conversion rate is 56.4%, and the selectivity for CH4 is 0%; the reaction rate for CO formation in CM5 is 4.0 μmol / g. -1 h -1 The reaction rate for the formation of CH4 is 20.8 μmol / g. -1 h -1 The CO2 conversion rate was 95.1%, and the selectivity for CH4 was 84%; the reaction rate of CM10 to CO production was 9.2 μmol / g. -1 h -1 The reaction rate for the formation of CH4 is 46.1 μmol / g. -1 h -1 The CO2 conversion rate was 97.0%, and the selectivity for CH4 was 86.8%; the CO production rate of CM15 was 3.0 μmol / g. -1 h -1 The reaction rate for the formation of CH4 is 14.2 μmol / g. -1 h -1 The CO2 conversion rate was 67.0%, and the selectivity for CH4 was 86.1%; the reaction rate of CM20 to CO was 1.3 μmol / g. -1 h -1 The reaction rate for the formation of CH4 is 5.6 μmol / g. -1 h -1 The CO2 conversion rate was 27.7%, and the selectivity for CH4 was 84.8%. Furthermore, cyclic performance tests were conducted on CM10, which exhibited the best catalytic performance. After 5 cycles, its CO2 reduction capacity decreased by less than 10%, while Cu2O crystals showed a 98.4% decrease in CO2 reduction capacity after 5 cycles. These results indicate that the thickness of the metal oxide layer determines the metal ratio of the photocatalytic composite material, and the change in the metal ratio determines the number of photocatalytic active sites. Appropriate addition of MgO can promote the conversion of CO2 to CH4, and the MgO coating layer can effectively prevent Cu2O photocorrosion, significantly improving the cyclic stability of the Cu2O@MgO photocatalytic composite material, allowing for multiple cycles.
Claims
1. A method for preparing a photocatalytic material with a metal oxide protective layer, characterized in that, Follow these steps: (1) Dissolve copper chloride, polyvinylpyrrolidone and sodium citrate in a mass ratio of 0.2:3:0.1 in 100 mL of deionized water at a certain temperature; (2) Sodium hydroxide and ascorbic acid solution were added dropwise to (1) and heated in a water bath at 50-80°C for 2-4 hours to obtain crude Cu2O product; then, the crude Cu2O product was washed by centrifugation with water and ethanol; finally, it was dried in an oven at 60°C for 2 hours to obtain Cu2O crystals with an octahedral structure. (3) A certain concentration of magnesium nitrate solution, calcium nitrate solution, and aluminum nitrate solution were mixed with Cu2O crystals respectively; then, the mixture was ultrasonically cleaned in an ultrasonic cleaner at an ultrasonic power of 60-90W for 30 minutes to obtain a uniform mixed solution; the obtained mixed solution was dried in an oven at 60℃ for 8-12 hours to obtain crude Cu2O@Mg(NO3)2, Cu2O@Ca(NO3)2, and Cu2O@Al(NO3)3 impregnated products. (4) The crude products of Cu2O@Mg(NO3)2, Cu2O@Ca(NO3)2 and Cu2O@Al(NO3)3 were transferred to a ceramic boat and placed in a tubular calcining furnace. The boat was then calcined at a certain temperature for a period of time. The calcined products were naturally cooled to room temperature to obtain Cu2O@MgO, Cu2O@CaO and Cu2O@Al2O3 photocatalytic composite materials with core-shell structures. The reaction temperature in step (1) is 50–80 °C; The concentration of NaOH in step (2) is 1–3 mol·L⁻¹ -1 The concentration of ascorbic acid is 0.2–1 mol·L⁻¹. -1 ; The concentrations of the magnesium nitrate solution, calcium nitrate solution, and aluminum nitrate solution in step (3) are 5–20 mmol·L⁻¹. -1 ; The calcination temperature in step (4) is 300–500 °C, and the heating rate is 5 °C / min. -1 The calcination time is 4 hours.
2. A photocatalytic material with a metal oxide protective layer, characterized in that, It is obtained by the preparation method described in claim 1.
3. The application of a photocatalytic material with a metal oxide protective layer as described in claim 2 in the photocatalytic reduction of CO2, characterized in that, Using metal oxides as a protective layer increases the specific surface area of the photocatalytic material and enhances its CO2 adsorption capacity. It also enables the control of the protective layer thickness, reduces the occurrence of Cu2O photocorrosion in the core, and improves the cycle stability of the photocatalytic material.