A novel nanocomposite photocatalyst, a preparation method thereof and application thereof in photocatalytic reduction of carbon dioxide

Abstract

The application discloses a novel nanocomposite photocatalyst, a preparation method thereof and application of the nanocomposite photocatalyst in photocatalytic reduction of carbon dioxide. The photocatalyst is prepared by using cerium nitrate and trimanganese tetraoxide as raw materials, using a mixed solution of ethanol and water as a solvent and using a muffle furnace for high-temperature calcination. The microstructure of the prepared CeO2 / Mn3O4 nanocomposite photocatalyst is a flower-like structure and contains high-concentration oxygen vacancies. The method solves the problem that pure trimanganese tetraoxide is not suitable for reduction of carbon dioxide by constructing a heterojunction. The CeO2 / Mn3O4 nanocomposite photocatalyst prepared by the method has good photocatalytic reduction activity of carbon dioxide under visible light.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photocatalysis, specifically relating to a novel cerium dioxide / manganese tetroxide nanocomposite photocatalyst, its preparation method, and its application in the photocatalytic reduction of carbon dioxide. Technical Background

[0002] With the acceleration of global industrialization and urbanization, carbon dioxide emissions have continued to increase, triggering global climate change and environmental problems. While mitigating the greenhouse effect, converting carbon dioxide into valuable compounds such as methane and carbon monoxide has become a key research topic. Among many potential conversion methods, the use of photocatalysts for carbon dioxide reduction is a cutting-edge and promising technology. However, many current photocatalytic technologies still face challenges in terms of efficiency, cost, and stability. Developing efficient, selective, and low-cost carbon dioxide conversion technologies, especially methods using photocatalysts to reduce carbon dioxide to methane and carbon monoxide, has significant scientific and social value for promoting sustainable energy development and long-term environmental health, providing new perspectives and possible solutions to the current global energy crisis and environmental problems.

[0003] Cerium dioxide is a widely studied semiconductor material, highly valued in environmental protection and energy applications for its superior oxygen storage capacity and high thermal stability. Its tunable bandgap makes it sought after in photocatalysis, fuel cells, and sensors. Manganese tetroxide, with its flower-like structure and suitable valence band position, can photocatalyze the release of oxygen from water and the degradation of water pollutants. However, the conduction band position of manganese tetroxide makes it unsuitable for carbon dioxide reduction. By constructing a type II heterojunction, the conduction band position can be adjusted, allowing photogenerated electrons to move from higher to lower conduction bands, leaving high-energy electrons / holes for their respective redox reactions. Oxygen vacancies in the material can act as active sites to collect carbon dioxide molecules and lower their adsorption energy on the photocatalyst surface, thus activating them more effectively. Oxygen vacancies can also promote carrier movement and extend carrier lifetime. Heterojunctions with high concentrations of oxygen vacancies can combine these two advantages, improving the ability of photocatalysts to reduce carbon dioxide and produce carbon monoxide and methane. Summary of the Invention

[0004] To address the problems existing in the background technology, the present invention provides a cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst and its preparation method.

[0005] The present invention specifically adopts the following technical solution:

[0006] A novel method for preparing a nanocomposite photocatalyst involves using cerium nitrate and manganese tetroxide as raw materials, a mixture of ethanol and water as a solvent, and high-temperature calcination in a muffle furnace.

[0007] Furthermore, the preparation method of the novel nanocomposite photocatalyst includes the following steps:

[0008] (1) Ethanol and water are mixed evenly in a certain proportion. A certain amount of manganese tetroxide solid is added to the mixed solvent. The resulting solution is stirred for a certain time to make it evenly mixed, and a manganese tetroxide suspension is obtained.

[0009] (2) Then a certain amount of cerium nitrate solution was added to the manganese tetroxide suspension obtained above, and the mixture was stirred continuously at room temperature;

[0010] (3) After the above stirring process is completed, the solvent is evaporated at a higher temperature, and the obtained solid is dried in an oven after evaporation;

[0011] (4) After drying, the solid is placed in a muffle furnace and heated at a certain rate, and the solid is kept at a constant temperature in the muffle furnace for a period of time to obtain a new type of cerium dioxide / manganese tetroxide nanocomposite photocatalyst.

[0012] Further, the volume ratio of ethanol to water in step (1) is 1:0.8 to 1.2, and the total volume is 80 to 120 mL.

[0013] Further, the amount of manganese tetroxide solid mentioned in step (1) is 0.8 to 1.2 g, and the stirring time is 25 to 35 min.

[0014] Furthermore, the molar concentration of the cerium nitrate solution mentioned in step (2) is 0.08–0.12 mol / L, and the volume of the added solution is 3–8 mL.

[0015] Furthermore, the stirring time in step (2) is 20 to 28 hours.

[0016] Furthermore, the temperature for evaporating the solvent in step (3) is 60–100°C.

[0017] Furthermore, in step (4), the heating rate of the muffle furnace is 4-6℃ / min, the constant temperature is 300-400℃, and the constant temperature time is 40-80min.

[0018] This invention also provides the application of a novel nanocomposite photocatalyst in the photocatalytic reduction of carbon dioxide.

[0019] The present invention has the following beneficial effects:

[0020] In this invention, cerium nitrate and manganese tetroxide are used as raw materials, and a mixture of ethanol and water is used as a solvent. The mixture is prepared by high-temperature calcination in a muffle furnace. The ethanol and water mixture ensures both solubility and regulates the overall reaction stability. Cerium nitrate and manganese tetroxide provide the necessary cerium and manganese elements for the nanocomposite material, forming a specific flower-like microstructure. Furthermore, the flower-like structure provides a large surface area, thereby enhancing catalytic activity. The high-temperature calcination process in a muffle furnace helps form a stable cerium dioxide / manganese tetroxide nanocomposite material and generates a high concentration of oxygen vacancies, which contribute to improved photocatalytic activity. This invention solves the problem that pure manganese tetroxide is unsuitable for photocatalytic reduction of carbon dioxide. The resulting nanocomposite material exhibits excellent photocatalytic activity under visible light, providing a new and effective material option for the photocatalytic reduction of carbon dioxide. Attached Figure Description

[0021] Figure 1 The X-ray diffraction pattern of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in Example 1 of this invention;

[0022] Figure 2 Scanning electron microscope (SEM) image, transmission electron microscope (TEM) image, selected area electron diffraction (SED) pattern, and elemental distribution map of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in Example 1 of this invention.

[0023] Figure 3 The image shows the photocatalytic reduction performance of carbon dioxide by the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in Example 1 of this invention.

[0024] Figure 4 The photoluminescence spectrum of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in Example 1 of this invention is shown below.

[0025] Figure 5 The transient photocurrent curve of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in Example 1 of this invention is shown.

[0026] Specific Implementation Cases

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] Example 1

[0029] A method for preparing a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst includes the following steps:

[0030] (1) Ethanol and water are mixed uniformly at a volume ratio of 1:1, with a total volume of 100 mL. 1 g of manganese tetroxide solid is added to the mixed solvent, and the resulting solution is stirred for 30 min to make it uniformly mixed, thus obtaining a manganese tetroxide suspension.

[0031] (2) Then 5.74 mL of 0.1 mol / L cerium nitrate solution was added to the manganese tetroxide suspension obtained above, and the mixture was stirred continuously at room temperature for 24 h.

[0032] (3) After the above stirring process is completed, the solvent is evaporated at 80°C, and the obtained solid is dried in an oven after evaporation.

[0033] (4) After drying, the solid was placed in a muffle furnace and heated at 5℃ / min. The solid was then kept at 350℃ for 60 min in the muffle furnace to obtain a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst.

[0034] Photocatalytic experiment: 100 mg of the prepared cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst was placed in a 100 mL reaction vessel, and then 5 mL of deionized water was added to the above reaction vessel. The catalyst was fully dispersed in the solution by ultrasound. The material was then stabilized in a carbon dioxide / water vapor system for 20 min, and finally irradiated under visible light for 4 h. Samples were taken after fixed intervals.

[0035] Figure 1 The X-ray diffraction pattern of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in this embodiment is shown. Almost all diffraction peaks are attributed to manganese tetroxide, whose standard PDF card number is 24-0734. In the spectrum, there is a peak at 47.75°, which corresponds to the (220) crystal plane of cerium dioxide, and the corresponding standard PDF card number of cerium dioxide is 34-0394.

[0036] Figure 2 The images show scanning electron microscope (SEM) images, transmission electron microscope (TEM) images, selected area electron diffraction (SED) patterns, and elemental distribution diagrams of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in this embodiment. As can be seen from the figures, after the introduction of cerium dioxide, the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite still maintains a flower-like morphology similar to that of manganese tetroxide.

[0037] Figure 3The figure shows the photocatalytic reduction performance of carbon dioxide by the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in this embodiment. As can be seen from the figure, the amount of methane produced by the reduction of carbon dioxide by cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) is 12 μmol / h / g, and the amount of carbon monoxide produced by the reduction of carbon dioxide is 2 μmol / h / g.

[0038] Figure 4 The photoluminescence spectrum of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in this embodiment is shown in the figure. As can be seen from the figure, the luminescence of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite is very weak, which indicates that the oxygen vacancies in the heterojunction greatly suppress charge recombination.

[0039] Figure 5 The transient photocurrent curve of the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst prepared in this embodiment is shown in the figure. As can be seen from the figure, the photocurrent density increases sharply under illumination, while it decreases sharply when the light source is turned off, indicating that there is effective charge separation in the cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite.

[0040] Example 2

[0041] A method for preparing a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst includes the following steps:

[0042] (1) Ethanol and water are mixed uniformly at a volume ratio of 1:1, with a total volume of 100 mL. 1 g of manganese tetroxide solid is added to the mixed solvent, and the resulting solution is stirred for 30 min to make it uniformly mixed, thus obtaining a manganese tetroxide suspension.

[0043] (2) Then add 3.70 mL of 0.1 mol / L cerium nitrate solution to the above-obtained manganese tetroxide suspension and stir continuously at room temperature for 24 h;

[0044] (3) After the above stirring process is completed, the solvent is evaporated at 80°C, and the obtained solid is dried in an oven after evaporation.

[0045] (4) After drying, the solid was placed in a muffle furnace and heated at 5℃ / min. The solid was then kept at 350℃ for 60 min in the muffle furnace to obtain a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst.

[0046] Example 3

[0047] A method for preparing a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst includes the following steps:

[0048] (1) Ethanol and water are mixed uniformly at a volume ratio of 1:1, with a total volume of 100 mL. 1 g of manganese tetroxide solid is added to the mixed solvent, and the resulting solution is stirred for 30 min to make it uniformly mixed, thus obtaining a manganese tetroxide suspension.

[0049] (2) Then 7.92 mL of 0.1 mol / L cerium nitrate solution was added to the manganese tetroxide suspension obtained above, and the mixture was stirred continuously at room temperature for 24 h.

[0050] (3) After the above stirring process is completed, the solvent is evaporated at 80°C, and the obtained solid is dried in an oven after evaporation.

[0051] (4) After drying, the solid was placed in a muffle furnace and heated at 5℃ / min. The solid was then kept at 350℃ for 60 min in the muffle furnace to obtain a novel cerium dioxide / manganese tetroxide (CeO2 / Mn3O4) nanocomposite photocatalyst.

[0052] The above description is only for understanding the method and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A method for preparing a novel nanocomposite photocatalyst, characterized in that: Includes the following steps: (1) Ethanol and water are mixed evenly in a certain proportion. A certain amount of manganese tetroxide solid is added to the mixed solvent. The resulting solution is stirred for a certain time to make it evenly mixed, and a manganese tetroxide suspension is obtained. (2) Then a certain amount of cerium nitrate solution was added to the manganese tetroxide suspension obtained above, and the mixture was stirred continuously at room temperature; (3) After the above stirring process is completed, the solvent is evaporated at a higher temperature, and the obtained solid is dried in an oven after evaporation; (4) After drying, the solid is placed in a muffle furnace and heated at a certain rate, and the solid is kept at a constant temperature in the muffle furnace for a period of time to obtain a new type of cerium dioxide / manganese tetroxide nanocomposite photocatalyst. The amount of manganese tetroxide solid mentioned in step (1) is 0.8-1.2g, and the stirring time is 25-35min; The molar concentration of the cerium nitrate solution mentioned in step (2) is 0.08 to 0.12 mol / L, and the volume of the added solution is 3 to 8 mL; The stirring time in step (2) is 20–28 hours; In step (3), the temperature for evaporating the solvent is 60–100°C; In step (4), the heating rate of the muffle furnace is 4-6℃ / min, the constant temperature is 300-400℃, and the constant temperature time is 40-80min.

2. The method for preparing the novel nanocomposite photocatalyst according to claim 1, characterized in that, The volume ratio of ethanol to water in step (1) is 1:0.8 to 1.2, and the total volume is 80 to 120 mL.

3. A novel nanocomposite photocatalyst prepared according to the method described in claim 1 or 2.

4. The application of a novel nanocomposite photocatalyst according to claim 3 in the photocatalytic reduction of carbon dioxide.

Images