Nitrogen-doped lanthanum titanate nanosheet and preparation method and application thereof

Abstract

The application discloses nitrogen-doped lanthanum titanate nanosheets and a preparation method and application thereof, and particularly discloses that a simple hydrothermal reaction is carried out by using lanthanum nitrate hexahydrate, titanium sulfate and sodium hydroxide to prepare nitrogen-doped lanthanum titanate nanosheets, and the nitrogen-doped lanthanum titanate nanosheets are used as a catalyst and are used in a photocatalytic reduction of carbon dioxide reaction. Compared with undoped lanthanum titanate nanosheets, the nitrogen-doped lanthanum titanate nanosheets have more excellent selectivity of photocatalytic reduction of carbon dioxide (CO2) to CH4. The prepared nitrogen-doped lanthanum titanate (La2Ti2O7) nanosheets can reduce the photocatalytic CO2 to carbon monoxide (CO) and methane (CH4) under normal temperature and pressure, and the CH4 generation rate is about 35.6 μmol g ‑1 h ‑1 , and the product selectivity and electron selectivity of CH4 are about 87.65% and 97.70%.

Description

Technical Field

[0001] This invention relates to a nitrogen-doped lanthanum titanate nanosheet, its preparation method, and its application, belonging to the field of photocatalysis. Background Technology

[0002] In recent decades, along with the rapid development of science and technology, industry has also entered a phase of rapid growth. The resulting environmental pollution and energy shortages have become a major global concern. Excessive use of fossil fuels has led to a continuous increase in greenhouse gas emissions, primarily CO2, causing numerous environmental changes detrimental to humankind and significantly hindering sustainable development. While CO2 and other greenhouse gas emissions pose a threat to the environment, CO2 molecules are also a potential carbon resource. Converting CO2 into clean energy could not only mitigate the greenhouse effect but also replenish the depletion of fossil fuels. Among various methods, photocatalytic reduction of CO2 is considered a highly promising solution because light energy is an inexhaustible and clean energy source that can meet global demand. Furthermore, compared to other methods, photocatalytic reduction of CO2 typically occurs at room temperature and pressure, with mild reaction conditions. It directly utilizes solar energy without requiring other auxiliary energy sources, truly enabling the recycling of carbon materials. To date, many photocatalytic materials, such as TiO2 and Co3O4, have been applied to the photocatalytic reduction of CO2, but their extremely low conversion efficiency severely hinders practical application. Therefore, the search for efficient, stable, and inexpensive photocatalysts has attracted widespread attention.

[0003] Perovskite materials, as compounds with excellent structure and chemical stability, play an irreplaceable role in fields such as solid oxide fuel cells, metal-air batteries, and solar cells. Perovskite semiconductor materials exhibit superior electronic and optical properties. In perovskite materials, two different metals have the potential to provide synergistic sites, thereby lowering the activation energy of charge transfer and accelerating intrinsic electron transfer, which is beneficial for the reduction of water or carbon dioxide. To date, perovskite catalysts such as cesium tribromide lead oxide (CsPbBr3) have been proven to achieve photocatalytic reduction of CO2. However, these perovskite materials suffer from drawbacks such as a lack of active sites for CO2 catalytic reduction and the inability of both metals to simultaneously serve as active sites, which severely affect their photocatalytic CO2 reduction activity. Furthermore, because perovskite catalysts have a single active site in the photocatalytic process, they only possess the ability to generate CO. Therefore, developing a perovskite catalyst that can improve the photocatalytic CO2 reduction activity while achieving high product selectivity has become a current research focus. Summary of the Invention

[0004] The purpose of this invention is to provide nitrogen-doped lanthanum titanate nanosheets, their preparation method, and applications. Nitrogen-doped lanthanum titanate nanosheets are prepared by doping nitrogen into the perovskite-type material lanthanum titanate, and the nitrogen-doped lanthanum titanate nanosheets are used as catalysts to enhance the photocatalytic reduction of carbon dioxide, while increasing the proportion and yield of CH4 in the product, thereby improving the selectivity of photocatalytic reduction of carbon dioxide to methane.

[0005] To achieve the above objectives, the present invention provides a method for preparing nitrogen-doped lanthanum titanate nanosheets, comprising the following steps:

[0006] (1) Preparation of La2Ti2O7 nanosheets: Lanthanum nitrate hexahydrate, titanium sulfate and sodium hydroxide were dissolved in water in sequence and stirred to obtain a mixed solution. The mixed solution was transferred to a high-pressure reactor and reacted under sealed conditions. After cooling to room temperature, the mixture was centrifuged at 14000 rpm for 3 min to separate the solid. After washing, the solid was placed in a vacuum drying oven at 80℃ and dried for 12 h to obtain La2Ti2O7 nanosheets.

[0007] (2) Preparation of nitrogen-doped La2Ti2O7 nanosheets: The La2Ti2O7 nanosheets obtained in step (1) were placed in a muffle furnace and calcined for 2 hours in an ammonia atmosphere to obtain nitrogen-doped La2Ti2O7 nanosheets.

[0008] In one embodiment of the present invention, in step (1), the concentration of lanthanum nitrate hexahydrate in the mixed solution is 13-17 g / L.

[0009] In one embodiment of the present invention, in step (1), the concentration of titanium sulfate in the mixed solution is 6 to 10 g / L.

[0010] In one embodiment of the present invention, in step (1), the concentration of sodium hydroxide in the mixed solution is 10-17 g / L.

[0011] In one embodiment of the present invention, in step (1), the stirring speed is 500-1000 rpm and the stirring time is 30 min.

[0012] In one embodiment of the present invention, in step (1), the reaction temperature of the mixed solution in the high-pressure reactor is 180-220°C and the reaction time is 18-22h.

[0013] In one embodiment of the present invention, in step (1), the washing process involves first washing with hydrochloric acid 2 to 5 times, and then washing with water 2 to 5 times.

[0014] In one embodiment of the present invention, in step (2), the heating rate of the muffle furnace is 10°C / min, the temperature is raised to 600°C, and calcined at 600°C for 2 hours.

[0015] The present invention also provides nitrogen-doped La2Ti2O7 nanosheets prepared by the above method.

[0016] The present invention also provides an application of the above-mentioned nitrogen-doped La2Ti2O7 nanosheets in the field of photocatalysis.

[0017] In one embodiment of the invention, the use includes serving as a catalyst for the photocatalytic reduction of carbon dioxide.

[0018] The beneficial effects of this invention are:

[0019] (1) In this invention, lanthanum titanate was synthesized by reacting lanthanum nitrate, titanium sulfate and sodium hydroxide at 200°C for 20 h and then calcined at 600°C for 2 h in an ammonia atmosphere to successfully prepare nitrogen-doped lanthanum titanate nanosheets.

[0020] (2) Using the nitrogen-doped lanthanum titanate nanosheets prepared by the method of this invention as a catalyst, the photocatalytic reduction of CO2 can produce a large amount of methane, with a methane yield as high as 35.6 μmol g. -1 h -1 The yield is much higher than that of CO produced (less than 5 μmol g). -1 h -1 This demonstrates that the nitrogen-doped lanthanum titanate nanosheets of the present invention exhibit high selectivity for the products during the photocatalytic reduction of CO2.

[0021] (3) In the photocatalytic reduction of CO2 by the nitrogen-doped lanthanum titanate nanosheets of the present invention, the selectivity for CH4 products and the electron selectivity can reach 87.65% and 97.70%, respectively. Among them, electron selectivity refers to the ratio of electrons used to generate the target product to the total transferred electrons. High electron selectivity indicates that most electrons are transferred from CO2 to CH4 during the CO2 reduction process.

[0022] (4) The preparation method is simple to operate, the nitrogen-doped La2Ti2O7 nanosheets prepared have strong catalytic ability, and the established practical method for photocatalytic reduction of CO2 is efficient, stable, environmentally friendly and sustainable. Attached Figure Description

[0023] Figure 1 The XRD diffraction patterns of undoped and nitrogen-doped La2Ti2O7 nanosheets prepared in Comparative Example 1 and Example 1 are shown, where (a) is the XRD pattern of undoped La2Ti2O7 nanosheets and (b) is the XRD pattern of nitrogen-doped La2Ti2O7 nanosheets.

[0024] Figure 2 Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of undoped and nitrogen-doped La2Ti2O7 nanosheets prepared in Comparative Example 1 and Example 1, respectively. (A) and (B) are the TEM and HRTEM images of undoped La2Ti2O7 nanosheets, respectively, and (C) and (D) are the TEM and HRTEM images of nitrogen-doped La2Ti2O7 nanosheets, respectively.

[0025] Figure 3 The X-ray photoelectron spectroscopy (XPS) spectra of undoped and nitrogen-doped La2Ti2O7 nanosheets prepared in Comparative Example 1 and Example 1 are shown, where (A) to (D) are N spectrum, O spectrum, Ti spectrum and La spectrum, respectively.

[0026] Figure 4 The graph shows the yields of CO (gray) and CH4 (white) obtained by photocatalytic reduction of carbon dioxide from undoped and nitrogen-doped La2Ti2O7 nanosheets prepared in Comparative Example 7 and Example 2.

[0027] Figure 5 The graphs show the selectivity (solid) and electron selectivity (hollow) of the photocatalytic reduction of carbon dioxide to methane by nitrogen-doped La2Ti2O7 nanosheets prepared in Example 2.

[0028] Figure 6 Transmission electron microscope (TEM) image and XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared for Comparative Example 2, wherein (a) is a TEM image and (b) is an XRD diffraction pattern.

[0029] Figure 7 Transmission electron microscope (TEM) image and XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 3, wherein (a) is the TEM image and (b) is the XRD diffraction pattern.

[0030] Figure 8 Transmission electron microscope (TEM) image and XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 4, wherein (a) is the TEM image and (b) is the XRD diffraction pattern.

[0031] Figure 9 Transmission electron microscope (TEM) image and XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 5, wherein (a) is the TEM image and (b) is the XRD diffraction pattern.

[0032] Figure 10Transmission electron microscope (TEM) image and XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 6, where (a) is the TEM image and (b) is the XRD diffraction pattern. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1: Preparation of nitrogen-doped La2Ti2O7 nanosheets

[0035] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 200 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was separated by centrifugation at 14000 rpm for 3 min, washed four times with hydrochloric acid, and then washed four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then placed in a muffle furnace and heated to 600 °C at a rate of 10 °C / min, and calcined at 600 °C under an ammonia atmosphere for 2 h to obtain nitrogen-doped La₂Ti₂O₇ nanosheets, which were stored in a desiccator for later use.

[0036] The structure of the compound prepared in Example 1 was identified, and the results are shown in the figure. Figures 1-3 , Figure 1 (b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Example 1; Figure 2 (CD) are transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Example 1, respectively. Figure 3 The image shows the X-ray photoelectron spectrum (XPS) of the nitrogen-doped La2Ti2O7 ultrathin nanosheets (b) prepared in Example 1. As can be seen from the transmission electron microscope image, the obtained product is a nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are no additional diffraction peaks. The X-ray photoelectron spectrum (A) of N 1s indicates that nitrogen was successfully doped into the La2Ti2O7 ultrathin nanosheets.

[0037] Example 2: Photocatalytic reduction of CO2 by nitrogen-doped La2Ti2O7 nanosheets

[0038] 10 mg of nitrogen-doped La₂Ti₂O₇ powder was uniformly dispersed on a glass slide and placed in a sealed glass apparatus. 2 mL of water was added to the container, followed by the introduction of high-purity CO₂ (concentration >99.999%), and then a vacuum was applied. This process was repeated three times. Once the pressure inside the apparatus reached atmospheric pressure, the apparatus was sealed, and the reaction temperature was controlled at 25°C using circulating water. A 300 W xenon lamp was used to simulate sunlight as the light source for the reaction. The preparation method of the nitrogen-doped La₂Ti₂O₇ powder was the same as in Example 1. After a period of reaction, a certain amount of CO and CH₄ were detected.

[0039] Figure 4 The yields of CO (gray) and methane (white) obtained from the photocatalytic reduction of CO2 by nitrogen-doped La2Ti2O7 nanosheets prepared in Example 2 are shown. As can be seen from the figure, the nitrogen-doped La2Ti2O7 nanosheets prepared by the method of this invention can reduce CO2 to carbon monoxide (CO) and methane (CH4) under ambient temperature, ambient pressure, and light irradiation, while exhibiting high selectivity for the CH4 product, and the CH4 formation rate can reach 35.6 μmol g. -1 h -1 . Figure 5 The graphs show the selectivity (solid) and electron selectivity (hollow) of the photocatalytic reduction of carbon dioxide to methane using nitrogen-doped La₂Ti₂O₇ nanosheets prepared in Example 2. Electron selectivity refers to the ratio of electrons used to generate the target product to the total transferred electrons. The calculation methods are: methane selectivity = amount of methane / (amount of methane + amount of carbon monoxide); electron selectivity = number of electrons generated to produce methane * amount of methane / (number of electrons generated to produce methane * amount of methane + number of electrons generated to produce carbon monoxide * amount of carbon monoxide). As can be seen from the graphs, the product selectivity and electron selectivity for CH₄ can reach 87.65% and 97.70%, respectively.

[0040] Comparative Example 1: Preparation of Undoped La2Ti2O7 Nanosheets

[0041] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 200 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was separated by centrifugation at 14000 rpm for 3 min, washed four times with hydrochloric acid, and then four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 600 °C in air for 2 h to obtain undoped La₂Ti₂O₇ ultrathin nanosheets, which were stored in a desiccator for later use.

[0042] The structure of the compound prepared in Comparative Example 1 was identified, and the results are shown in the figure. Figures 1-3 , Figure 1 (a) is the XRD diffraction pattern of the undoped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 1; Figure 2 (AB) are transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the undoped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 1. Figure 3 In Figure (a), the X-ray photoelectron spectrum (XPS) of the undoped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 1 is shown. The X-ray photoelectron spectrum (A) of N 1s indicates that the undoped La2Ti2O7 ultrathin nanosheets doped with nitrogen are not nitrogen-containing.

[0043] Comparative Example 2: Changing the reaction temperature

[0044] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 160 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then separated by centrifugation, washed four times with hydrochloric acid, and then four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 600 °C under an ammonia atmosphere for 2 h.

[0045] The structure of the compound prepared in Comparative Example 2 was identified, and the results are shown in the figure. Figure 6 , Figure 6 (a) Transmission electron microscope (TEM) image of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared for Comparative Example 2; Figure 6 (b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 2. As can be seen from the transmission electron microscope image, the obtained product is not a nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are additional diffraction peaks, indicating that the obtained product is not a nitrogen-doped La2Ti2O7 nanosheet.

[0046] Comparative Example 3 without added sodium hydroxide

[0047] 433 mg of lanthanum nitrate hexahydrate and 240 mg of titanium sulfate were dissolved sequentially in 30 mL of water. After stirring at 700 rpm for 30 min, the resulting mixture was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 160 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, centrifuged to separate the product, washed four times with hydrochloric acid and then four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 600 °C under an ammonia atmosphere for 2 h. The resulting product, after detailed characterization, was a non-nitrogen-doped La₂Ti₂O₇ ultrathin nanosheet.

[0048] The structure of the compound prepared in Comparative Example 3 was identified, and the results are shown in the figure. Figure 7 , Figure 7 (a) Transmission electron microscope (TEM) image of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 3; Figure 7 (b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 3. As can be seen from the transmission electron microscope image, the obtained product is not a nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are additional diffraction peaks, indicating that the obtained product is not a nitrogen-doped La2Ti2O7 nanosheet.

[0049] Comparative Example 4: Changing the reaction time

[0050] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 200 °C for 8 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, centrifuged to separate the product, washed four times with hydrochloric acid, and then washed four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 600 °C under an ammonia atmosphere for 2 h. The resulting product, after detailed characterization, was a non-nitrogen-doped La₂Ti₂O₇ ultrathin nanosheet.

[0051] The structure of the compound prepared in Comparative Example 4 was identified, and the results are shown in the figure. Figure 8 , Figure 8 (a) Transmission electron microscope (TEM) image of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 4; Figure 8 (b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 4. As can be seen from the transmission electron microscope image, the obtained product is not a nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are additional diffraction peaks, indicating that the obtained product is not nitrogen-doped La2Ti2O7 ultrathin nanosheets.

[0052] Comparative Example 5: Changing the calcination atmosphere

[0053] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 200 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then centrifuged, washed four times with hydrochloric acid, and then four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 600 °C under a nitrogen atmosphere for 2 h. The resulting product, after detailed characterization, was a non-nitrogen-doped La₂Ti₂O₇ ultrathin nanosheet.

[0054] The structure of the compound prepared in Comparative Example 5 was identified, and the results are shown in the figure. Figure 9 , Figure 9 (a) Transmission electron microscope (TEM) image of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 5; Figure 9 (b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 5. As can be seen from the transmission electron microscope image, the obtained product is not an ultrathin nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are additional diffraction peaks, indicating that the obtained product is not a nitrogen-doped La2Ti2O7 ultrathin nanosheet.

[0055] Comparative Example 6: Changing the calcination temperature

[0056] 433 mg of lanthanum nitrate hexahydrate, 240 mg of titanium sulfate, and 400 mg of sodium hydroxide were dissolved sequentially in 30 mL of water. The mixture was stirred at 700 rpm for 30 min, and the resulting solution was transferred to a 40 mL high-pressure reactor, sealed, and reacted at 200 °C for 20 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then centrifuged, washed four times with hydrochloric acid, and then four times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was then calcined in a muffle furnace at 200 °C under an ammonia atmosphere for 2 h. The resulting product, after detailed characterization, was a non-nitrogen-doped La₂Ti₂O₇ ultrathin nanosheet.

[0057] The structure of the compound prepared in Comparative Example 6 was identified, and the results are shown in the figure. Figure 10 , Figure 10 (a) Transmission electron microscope (TEM) image of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 6; Figure 10(b) is the XRD diffraction pattern of nitrogen-doped La2Ti2O7 ultrathin nanosheets prepared in Comparative Example 6. As can be seen from the transmission electron microscope image, the obtained product is not an ultrathin nanosheet. Compared with the standard diffraction pattern of La2Ti2O7, there are additional diffraction peaks, indicating that the obtained product is not a nitrogen-doped La2Ti2O7 ultrathin nanosheet.

[0058] Comparative Example 7

[0059] 10 mg of undoped La₂Ti₂O₇ powder was uniformly dispersed on a glass slide and placed in a sealed glass apparatus. 2 mL of water was added to the container, followed by the introduction of high-purity CO₂ (concentration >99.999%), and then a vacuum was created. This process was repeated three times. Once the pressure inside the apparatus reached atmospheric pressure, the apparatus was sealed, and the reaction temperature was controlled at 25°C using circulating water. A 300 W xenon lamp was used to simulate sunlight as the light source for the reaction. The preparation method of the undoped La₂Ti₂O₇ powder was the same as in Comparative Example 1.

[0060] Figure 4 The yields of CO (gray) and methane (white) obtained by photocatalytic reduction of CO2 using undoped La2Ti2O7 nanosheets prepared in Comparative Example 1 are shown. As can be seen from the figure, using undoped La2Ti2O7 nanosheets at room temperature and pressure and under light irradiation, only CO2 can be reduced to carbon monoxide (CO), and methane cannot be obtained.

[0061] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. Use of nitrogen-doped lanthanum titanate nanoplatelets for improving the selectivity of photocatalytic reduction of carbon dioxide to generate methane, characterized in that, The preparation method of the nitrogen-doped lanthanum titanate nanosheet comprises the following steps: (1) Preparation of La2Ti2O7 nanosheet: dissolve lanthanum nitrate hexahydrate, titanium sulfate and sodium hydroxide in water in sequence, stir to obtain a mixed solution, transfer the mixed solution to a high-pressure reaction kettle, react under the condition of sealing at 180-220 ℃ for 18-22 h, cool to room temperature, centrifuge at a rotation speed of 14000 rpm for 3 min, separate the obtained solid, wash and then place in a 80 ℃ vacuum drying box for drying for 12 h to obtain La2Ti2O7 nanosheet; (2) Preparation of nitrogen-doped La2Ti2O7 nanosheet: place the La2Ti2O7 nanosheet obtained in step (1) in a muffle furnace, heat the muffle furnace at a heating rate of 10 ℃ / min to 600 ℃, and calcine at 600 ℃ under an ammonia atmosphere for 2 h to obtain nitrogen-doped La2Ti2O7 nanosheet.

2. Use according to claim 1, characterized in that, In step (1), the concentration of lanthanum nitrate hexahydrate in the mixed solution is 13-17 g / L.

3. Use according to claim 1, characterized in that, In step (1), the concentration of titanium sulfate in the mixed solution is 6-10 g / L.

4. Use according to claim 1, characterized in that, In step (1), the concentration of sodium hydroxide in the mixed solution is 10-17 g / L.

5. Use according to claim 1, characterized in that, In step (1), the rotation speed during stirring is 500-1000 rpm, and the stirring time is 30 min.

Images