MOF-coated Co3O4 material, preparation method thereof and application of MOF-coated Co3O4 material in photocatalytic CO2 reduction
By growing Co3O4 in situ on UiO-66 or its functionalized derivatives, the core-shell structure of MOF@Co3O4 material was constructed, and the problem of insufficient catalytic activity at low concentrations of CO2 was solved, and efficient CO2 enrichment and conversion effects were achieved.
Patent Information
- Application Number
- CN202510555879.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-08-01
AI Technical Summary
Existing photocatalysts have insufficient catalytic activity at low concentrations of CO2, making it difficult to achieve efficient capture and conversion, especially in low concentrations of CO2 gases emitted by industrial emissions.
Using MOF@Co3O4 material, Co3O4 metal oxides are grown in situ on UiO-66 or its functionalized derivatives to form a core-shell structure. Using the porosity of MOF and the redox active sites of Co3O4, heterojunction is constructed to improve the adsorption and enrichment ability of CO2.
It shows efficient CO2 conversion ability in high-purity CO2 and low-concentration CO2 environments, realizes the enrichment and efficient conversion of low-concentration CO2, and improves catalytic activity and selectivity.
Smart Images
Figure CN120394092A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical fields of the preparation of MOF composite materials and photocatalysis, and particularly relates to a MOF@Co3O4 material, a preparation method thereof, and an application thereof in photocatalytic CO2 reduction. Background Art
[0002] At present, as the main greenhouse gas, the excessive emission of CO2 has led to a series of severe environmental problems such as global warming, frequent extreme weather, and rising sea levels. Under the "dual carbon" goal, the utilization of clean and renewable solar energy to drive the resource utilization of CO2 has become an important research topic. In the actual application scenario of photocatalytic CO2 reduction technology, due to the too low concentration of CO2 in the environment, the catalytic activity is insufficient. Therefore, the research focus in this field has become to develop a photocatalyst that can simultaneously achieve the enrichment and conversion of CO2 gas to efficiently capture and quickly convert CO2 into fuels or other valuable chemicals.
[0003] At present, most photocatalysts show high photocatalytic conversion efficiency in a pure CO2 atmosphere. However, they often hardly show photocatalytic activity at a low CO2 concentration (<15%), and the conversion rate is extremely low. However, the CO2 concentration in actual industrial emissions (such as flue gas from coal-fired power plants) is usually only 3%-15%. Developing an efficient photocatalytic technology that can directly convert low-concentration CO2 without a pre-concentration link can not only significantly reduce energy consumption but also provide an innovative solution for the carbon resource utilization of industrial emissions, which has important research value for promoting green and low-carbon development. Thus, it is of great significance to design a photocatalyst with high-efficiency capture ability under high-purity CO2 and low-concentration CO2, and it is particularly important to further improve the catalytic activity and selectivity of the photocatalyst.
[0004] Metal-organic framework (MOF) is a new type of porous functional material. Due to its characteristics such as a large specific surface area, high porosity, adjustable pore structure, and chemical environment in its structure, it shows significant advantages in the field of CO2 adsorption. Compared with traditional catalysts, MOF derivatives retain the porous structure, etc. In addition, the MOF derivative Co3O4 is a metal oxide with a strong activation effect on CO2 reduction due to its unique electronic structure and rich redox active sites. Therefore, by virtue of the MOF-on-MOF material characteristics, through regulating the pyrolysis temperature to construct semi-derivatives and constructing heterojunctions or cooperative active sites between MOF and Co3O4, it is expected to achieve the capture and enrichment as well as efficient conversion of low-concentration CO2, and further improve the integrated efficiency of CO2 adsorption-activation-reduction. Summary of the Invention
[0005] Aiming at the problems existing in the prior art, the present invention provides a MOF@Co3O4 material, its preparation method and application in photocatalytic CO2 reduction. The porous MOF substrate and the hollow Co3O4 layer both contribute to the adsorption and enrichment of CO2 by the catalyst, realizing efficient CO2 conversion.
[0006] To achieve the above object, the present invention provides the following technical solutions: A MOF@Co3O4 material, the MOF@Co3O4 material is a "core-shell" structure, the "core" is UiO-66 or a functionalized derivative UiO-66-X, and Co3O4 metal oxide is in-situ grown on the core formed by UiO-66 and its functionalized derivative UiO-66-X.
[0007] A preparation method of a MOF@Co3O4 material, comprising the following steps: (1) Prepare the substrate MOF material: the substrate MOF material is UiO-66 or a UiO-66-X functionalized derivative; disperse the substrate MOF material and a surfactant in water to obtain solution A; (2) Weigh 2-methylimidazole, a surfactant and a regulator, dissolve them in water to obtain solution B; pour solution B into solution A to obtain a mixed solution C; (3) Weigh a cobalt salt, dissolve it in water to obtain solution D, pour solution D into the mixed solution C, react, collect the product, centrifuge, wash and dry to obtain a MOF@ZIF-67 precursor; (4) Pyrolyze the MOF@ZIF-67 to obtain a UiO-66@Co3O4 material.
[0008] Further, the preparation method of the substrate MOF material UiO-66 or a UiO-66-X functionalized derivative comprises the following steps: add a zirconium salt and an organic ligand and its derivative to a solvent, carry out a solvothermal reaction, centrifuge, wash and dry to obtain a sample.
[0009] Further, the zirconium salt is selected from at least one of zirconium acetylacetonate, zirconium chloride octahydrate, and zirconium tetrachloride; the ligand is selected from at least one of terephthalic acid, 2-NH2-terephthalic acid, and 2-NO2-terephthalic acid; the solvent is a mixed solution of N,N-dimethylformamide and a regulator acetic acid with a volume ratio of 6:1; the molar ratio of the zirconium salt to the ligand is 1:1.3; the reaction temperature is 120°C; the reaction time is 12 hours.
[0010] Further, the surfactant is at least one of cetyltrimethylammonium bromide, sodium dodecylsulfonate, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.
[0011] Furthermore, the mass ratio of the UiO-66 material to the surfactant added is 2:1. The surfactant is used to disperse the substrate MOF particles in step (1) to prevent their agglomeration. The ratio of 2:1 can ensure that the UiO-66 particles are evenly dispersed in the solution, providing a stable substrate surface for the subsequent in-situ growth of ZIF-67. An excessive amount of surfactant may adsorb on the MOF surface, hindering the subsequent growth of ZIF-67; while a too low ratio cannot effectively disperse the MOF, resulting in an uneven core-shell structure. The balance point of 2:1 can ensure both dispersibility and not hinder the formation of the shell layer.
[0012] Furthermore, the mass ratio of 2-methylimidazole to the surfactant added is 7.9:1.
[0013] The ratios of the two steps together ensure that the surface of the MOF core is evenly covered by ZIF-67, forming a Co3O4 shell layer with a high specific surface area and abundant active sites after pyrolysis, enhancing the CO2 adsorption and photocatalytic activity. Deviating from the ratio may lead to an incomplete core-shell structure (such as shell layer fracture or excessive thickness), reducing the separation efficiency of photo-generated carriers or the CO2 diffusion ability, thus affecting the catalytic activity and selectivity.
[0014] Furthermore, the cobalt salt is selected from at least one of cobalt(II) chloride hexahydrate, cobalt(II) nitrate hexahydrate, and cobalt(II) acetate tetrahydrate; the molar ratio of the cobalt salt to the ligand is 1:25; the regulator is one of triethylamine, ethylenediamine, and tetrabutylammonium hydroxide.
[0015] Furthermore, the reaction temperature is 35 °C; the reaction time is 4 hours.
[0016] Furthermore, the atmosphere for low-temperature pyrolysis in step (3) is air; the temperature is 300 - 350 °C; the heating rate is 3 - 5 °C / min; the time is 2 - 4 hours.
[0017] When ZIF-67 (cobalt-based MOF) is pyrolyzed in an air atmosphere, cobalt ions will be oxidized to form Co3O4 (mixed-valence Co²⁺ / Co³⁺ oxide), and Co3O4 is an ideal active site for photocatalytic CO2 reduction due to its unique electronic structure and redox activity. If pyrolyzed in an inert atmosphere (such as N2, Ar), metallic cobalt (Co 0 ), or low-valence oxides (such as CoO) may be formed, and their catalytic activity is significantly lower than that of Co3O4. Oxygen in the air atmosphere can completely oxidize the organic ligand (2-methylimidazole) in ZIF-67, avoiding the residual carbon layer covering the active sites and ensuring the full exposure of the Co3O4 surface.
[0018] The thermal decomposition temperature of ZIF-67 is between 300 and 350 °C. When the temperature is lower than 300 °C, the organic ligands do not decompose completely, and the residual carbon or undecomposed MOF will hinder the formation of Co3O4. When the temperature is higher than 350 °C, the Co3O4 particles may agglomerate due to sintering, resulting in a decrease in specific surface area and a reduction in active sites. UiO-66 has high thermal stability (decomposition temperature > 500 °C), and its structure can remain intact at 300 - 350 °C, avoiding the collapse of the core layer and ensuring the stability of the core-shell structure. 300 - 350 °C is the optimal temperature for the formation of the Co3O4 spinel phase (Co²⁺Co³⁺2O4), and its unique electronic structure (Co²⁺ / Co³⁺ redox pair) can promote the separation of photo-generated carriers and enhance the CO2 activation ability.
[0019] The heating rate is 3 - 5 °C / min. At this rate, the core-shell structure can be prevented from cracking due to thermal stress, enabling the ZIF-67 shell to gradually decompose into Co3O4 while maintaining the morphological stability of the UiO-66 core. If the heating rate is too fast (such as > 5 °C / min), local overheating will occur, causing rapid aggregation of Co3O4 particles and pore collapse, reducing the specific surface area and CO2 adsorption capacity. Slow heating is beneficial for the formation of a porous Co3O6 shell and the retention of the pore structure of the MOF derivative.
[0020] The present invention also provides an application of MOF@Co3O4 as a photocatalyst in photocatalytic carbon dioxide reduction.
[0021] The beneficial technical effects of the present invention are as follows: In the present invention, UiO-66 and its derivatives are selected as the substrate MOF. UiO-66 and its derivatives have a large specific surface area, and the amorphous-UiO-66 after calcination exhibits an even larger specific surface area. At the same time, the hollow structure of the cobalt tetroxide coating layer is beneficial for the physical adsorption of carbon dioxide gas. In addition, the highly dispersed and exposed Co sites on the MOF substrate promote the improvement of photocatalytic activity. Therefore, the composite material can achieve the enrichment and efficient conversion of low-concentration carbon dioxide and can be applied to the efficient conversion of flue gas.
[0022] The catalyst provided by the present invention shows excellent performance in both photocatalytic high-purity CO2 (volume fraction > 99.999%) and flue gas, i.e., low-concentration carbon dioxide (CO2 / Ar < 10%). In an atmosphere of 0.01 Mpa and a triethylamine and water system, the MOF@Co3O4 catalyst can achieve an optimal CO production rate of 1.388 μmol / g / h in 10% CO2. Description of the Drawings
[0023] Figure 1 It is the X-ray powder diffraction pattern of the MOF@Co3O4 obtained in Example 2.
[0024] Figure 2 It is the transmission electron microscope image of MOF@ZIF-67 obtained in Example 2.
[0025] Figure 3 It is the scanning electron microscope image of MOF@Co3O4 obtained in Example 2.
[0026] Figure 4 It is the high-resolution transmission electron microscope image of MOF@Co3O4 obtained in Example 2.
[0027] Figure 5 It is the photocatalytic performance diagram of MOF@Co3O4 obtained in Example 4 under high and low concentrations of CO2.
[0028] Figure 6 It is the cyclic catalytic performance diagram of MOF@Co3O4 obtained in Example 4. Detailed implementation mode
[0029] Example 1 Preparation of UiO-66 or UiO-66-X substrate material Add 1.3 mmol zirconium tetrachloride and 1 mmol terephthalic acid or 2-NH2-terephthalic acid or 2-NO2-terephthalic acid to a mixed solution of 150 mL N,N-dimethylformamide and 25 mL acetic acid, and carry out hydrothermal reaction at 120 °C for 12 hours. Collect the product, wash, centrifuge and dry to obtain UiO-66, UiO-66-NH2 or UiO-66-NO2.
[0030] Example 2 Preparation of MOF@Co3O4 material A preparation method of a MOF@Co3O4 material includes the following steps: (1) Prepare UiO-66 or UiO-66-X substrate MOF material: Disperse 0.1 g of substrate MOF material and 0.05 g of cetyltrimethylammonium bromide in water to obtain solution A; (2) Weigh 0.393 g (4.79 mmol) of 2-methylimidazole, 0.050 g of cetyltrimethylammonium bromide, and 0.048 g of triethylamine, dissolve them in 20 mL of water to obtain solution B, and pour solution B into solution A to obtain mixed solution C; (3) Weigh 0.054 g (0.19 mmol) of cobalt nitrate hexahydrate, dissolve it in 10 mL of water to obtain solution D. Quickly pour solution D into mixed solution C, react at 35 °C for 4 hours, collect the product, centrifuge, wash and dry to obtain UiO-66-X@ZIF-67.
[0031] (4) Put UiO-66-X@ZIF-67 into a muffle furnace, under an air atmosphere, heat it to 300 °C at a heating rate of 3 °C / min; keep it at this temperature for 4 hours to obtain UiO-66-X@Co3O4.
[0032] Example 3 The difference between Example 3 and Example 2 is that the calcination conditions in step 4 are to put UiO-66-X@ZIF-67 into a muffle furnace, under an air atmosphere, heat it to 350 °C at a heating rate of 5 °C / min, and keep it at this temperature for 2 hours to obtain UiO-66@Co3O4; the other conditions are exactly the same.
[0033] The materials obtained in Example 2 and Example 3 are the same. The obtained materials were characterized, and the results are as follows: Figure 1 The X-ray powder diffraction pattern of UiO-66-X@Co3O4: The diffraction peaks at 31.3°, 36.8°, 44.8°, 55.6°, 59.4° and 65.2° are attributed to Co3O4. The diffraction peaks at 7.28° and 8.42° are attributed to UiO-66-X. Because the signal of the shell layer peak is strong and masks the UiO-66-X signal, the UiO-66-X signal is weak. UiO-66-X@Co3O4 has a broad peak at about 20.7°, which is attributed to partial derivatization and amorphous structure.
[0034] Figure 2 The transmission electron microscope image of UiO-66-X@ZIF-67: UiO-66-X is octahedral, and ZIF-67 is evenly dispersed on the surface of the UiO-66-X substrate, showing a clear "core-shell" structure, confirming the successful composite of UiO-66-X@ZIF-67.
[0035] Figure 3 The scanning electron microscope image of UiO-66-X@Co3O4: The substrate morphology is maintained after low-temperature pyrolysis, and the shell layer becomes rough, showing irregular aggregates.
[0036] Figure 4 The high-resolution transmission electron microscope image of UiO-66-X@Co3O4: The lattice fringe spacings of 0.466 nm, 0.232 nm, and 0.245 nm correspond to the (111), (002), and (311) crystal planes of Co3O4, respectively.
[0037] Example 4 Catalytic Performance Test Weigh 5 mg of the above-mentioned MOF@Co3O4 photocatalyst, 3 mL of acetonitrile, 2 mL of water, and 1 mL of triethylamine. Use a 300 W xenon lamp as the light source for the photocatalytic experiment. Charge low-concentration CO2 (10% CO2 + 90% Ar) or high-purity CO2 (99.999%). The reaction pressure is 0.1 MPa, and then perform light irradiation (the light irradiation intensity is 150 mW / cm 2 ), sample at 0.5, 1, 1.5, 2, and 2.5 hours respectively, and analyze the results by gas chromatography. Calculate the CO yield in 1 hour, and the results are shown in Figure 5 . The yield is 9153 μmol / g / h under high-concentration CO2 (99.999%), and 2979 μmol / g / h under low-concentration CO2 (10%).
[0038] Figure 6 This is the cyclic catalytic performance diagram of MOF@Co3O4. The photocatalyst still maintains good catalytic activity after 4 cycles.
Claims
1. A MOF@Co3O4 material, characterized in that: The MOF@Co3O4 material has a "core-shell" structure, where the "core" is UiO-66 or the functionalized derivative UiO-66-X, and Co3O4 metal oxide grows in-situ on the core formed by UiO-66 and its functionalized derivative UiO-66-X.
2. A method for preparing the MOF@Co3O4 material according to claim 1, characterized in that: It includes the following steps: (1) Prepare the substrate MOF material: The substrate MOF material is UiO-66 or the UiO-66-X functionalized derivative; Disperse the substrate MOF material and the surfactant in water to obtain solution A; (2) Weigh 2-methylimidazole, surfactant and regulator, dissolve them in water to obtain solution B; Pour solution B into solution A to obtain the mixed solution C; (3) Weigh cobalt salt, dissolve it in water to obtain solution D, pour solution D into the mixed solution C, react, collect the product, centrifuge, wash and dry to obtain the MOF@ZIF-67 precursor; (4) Pyrolyze MOF@ZIF-67 to obtain the UiO-66@Co3O4 material.
3. The preparation method of the MOF@Co3O4 material according to claim 2, characterized in that: The preparation method of the substrate MOF material UiO-66 or the UiO-66-X functionalized derivative includes the following steps: Add zirconium salt and the organic ligand and its derivative to the solvent, carry out solvothermal reaction, centrifuge, wash and dry to obtain the sample.
4. The preparation method of the MOF@Co3O4 material according to claim 2, characterized in that: The zirconium salt is selected from at least one of zirconium acetylacetonate, zirconium chloride octahydrate, and zirconium tetrachloride; The ligand is selected from at least one of terephthalic acid, 2-NH2-terephthalic acid, and 2-NO2-terephthalic acid; The solvent is a mixed solution of N,N-dimethylformamide and the regulator acetic acid with a volume ratio of 6:1; The molar ratio of zirconium salt to ligand is 1:1.3; The reaction temperature is 120 °C; The reaction time is 12 hours.
5. The preparation method of the MOF@Co3O4 material according to claim 2, characterized in that: The surfactant is one of cetyltrimethylammonium bromide, sodium dodecyl sulfonate, and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer.
6. The preparation method of the MOF@Co3O4 material according to claim 2, wherein: In step (1), the mass ratio of the UiO-66 material to the surfactant added is 2:1; In step (2), the mass ratio of 2-methylimidazole to the surfactant added is 7.9:
1.
7. The preparation method of the MOF@Co3O4 material according to claim 2, characterized in that: The cobalt salt is selected from at least one of cobalt chloride hexahydrate, cobalt nitrate hexahydrate, and cobalt acetate tetrahydrate; The molar ratio of cobalt salt to ligand is 1:25; The regulator is one of triethylamine, ethylenediamine, and tetrabutylammonium hydroxide.
8. The preparation method of the MOF@Co3O4 material according to claim 2, wherein: The reaction temperature in step (3) is 35 °C; The reaction time is 4 hours.
9. The preparation method of the MOF@Co3O4 material according to claim 2, characterized in that: In step (3), the atmosphere for low-temperature pyrolysis is air; The temperature is 300 - 350 °C; The heating rate is 3 - 5 °C / min; The time is 2 - 4 hours.
10. Application of the MOF@Co3O4 material as described in claim 1 in photocatalytic CO2 reduction.