Catalyst for photocatalytic reduction of co2 to produce methane and preparation method thereof

Abstract

The application discloses a kind of nickel single atom modified molybdenum disulfide nanosheet and its preparation method and application, and specifically discloses using thioacetamide, sodium molybdate dihydrate to carry out simple hydrothermal reaction, prepare molybdenum disulfide nanosheet, then and by introducing nickel acetate preparation nickel single atom modified molybdenum disulfide nanosheet, and it is used in the reaction of photocatalytic reduction carbon dioxide. Relative to original molybdenum disulfide nanosheet, nickel single atom modified molybdenum disulfide nanosheet has more excellent photocatalytic reduction carbon dioxide (CO2) selectivity of CH4. The nickel single atom modified molybdenum disulfide nanosheet prepared can reduce CO2 into carbon monoxide (CO) and methane (CH4) under normal temperature and pressure by photocatalysis, and CH4 generation rate is about 27.2 μmol g ‑1 h ‑1 , CH4 Product selectivity and electron selectivity are about 80.4% and 94.2%.

Description

Technical Field

[0001] This invention relates to a catalyst for the photocatalytic reduction of CO2 to methane and its preparation method, belonging to the fields of nanomaterial preparation and photocatalysis. Background Technology

[0002] For decades, efforts have been made to address the problem of massive carbon dioxide (CO2) emissions into the atmosphere. These efforts include developing and promoting renewable energy sources, improving energy efficiency, reducing carbon emissions, and developing efficient carbon capture and storage technologies. Solar energy is considered an inexhaustible natural energy source, and converting CO2 into high-energy-density compounds using sunlight and efficient catalysts is seen as a very promising strategy. This is primarily because using CO2 as a feedstock can help close the carbon cycle and reduce fossil fuel consumption, while also contributing to the strategic goal of carbon neutrality. Furthermore, compared to other CO2 reduction methods, photocatalytic CO2 reduction typically occurs at room temperature and pressure, with mild reaction conditions. It directly utilizes solar energy without requiring other auxiliary energy sources, enabling true recycling of carbon materials. However, due to the chemical inertness and thermodynamic stability of CO2, photocatalytic CO2 reduction is very challenging. Additionally, the lack of effective active sites on the catalyst surface often results in unsatisfactory catalytic efficiency.

[0003] Two-dimensional transition metal dichalcogenides (2D TMDs) are a fascinating class of materials composed of transition metal atoms and sulfur atoms, forming a two-dimensional lattice structure in a plane. These materials possess unique physical and chemical properties, making them promising for applications in energy, optoelectronics, catalysts, and sensors. However, in most developed two-dimensional (2D) monolayer materials, only the edge regions exhibit catalytic activity, with basal plane atoms participating almost entirely outside the catalytic reaction. A typical example is monolayer MoS2, which is widely used as a catalyst in photocatalytic reactions due to its high specific surface area and unique electronic properties. However, in the structure of monolayer MoS2, a Mo atom plane is sandwiched between two other S atom planes by strong in-plane covalent bonds. While the active center is generally considered to be the unsaturated coordinating atoms at the surface edge, the high proportion of saturated coordinating atoms on the MoS2 surface do not participate in the construction of catalytic active sites. Therefore, this structure lacks active sites for activating and reducing CO2 molecules, which significantly limits its catalytic activity.

[0004] Constructing active sites on the MoS2 monolayer structure that can efficiently activate and reduce CO2 molecules is a feasible approach to maximize CO2 reduction efficiency. Recently, single-atom catalysts (SACs) have attracted increasing interest due to their high atom utilization and excellent catalytic performance in both electrocatalysis and photocatalysis. Anchoring transition metal single atoms (such as Ni, Cu, and Co) on semiconductor catalysts is an effective and economical strategy to improve photogenerated charge mobility and optimize the reaction energy barrier during CO2 photoreduction. For example, Liu et al. achieved Zn doping during the growth process via a hydrothermal method, obtaining Zn-doped MoS2 nanosheets with significantly enhanced catalytic activity (Electrochimica Acta, 2018, 260, 24-30); Lou et al. also used a hydrothermal method to obtain Co-doped MoS2 nanosheets, significantly improving the electrochemical reduction efficiency of dinitro to ammonia (J. Am. Chem. Soc. 2019, 49, 19269–19275). However, in previous works, metal atoms were mostly doped in the form of nanoclusters, resulting in relatively low atomic utilization, and there are few reports on their application in regulating the photocatalytic reduction pathway of carbon dioxide to produce methane. Therefore, developing and preparing a catalyst that can efficiently photocatalyze the reduction of CO2 and selectively produce methane has become a top priority in research. Summary of the Invention

[0005] The purpose of this invention is to provide a nickel-doped MoS2 nanosheet and its preparation method. By doping nickel into molybdenum disulfide nanosheets, nickel-doped molybdenum disulfide nanosheets are prepared, and the nickel-doped molybdenum disulfide nanosheets are used as a catalyst to improve 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.

[0006] To achieve the above objectives, the present invention provides a method for preparing a catalyst for the photocatalytic reduction of CO2 to methane, comprising the following steps:

[0007] (1) Preparation of molybdenum disulfide (MoS2) nanosheets:

[0008] Molybdate and thioacetamide were dissolved in water sequentially to obtain a mixed solution. After stirring for 30 min, the mixed solution was transferred to a high-pressure reactor and reacted under sealed conditions. After the reaction was completed, the mixture was naturally cooled to room temperature. The product was separated by centrifugation, washed, and dried in a vacuum drying oven to obtain MoS2 nanosheets.

[0009] (2) Preparation of nickel single-atom modified MoS2 nanosheets:

[0010] The MoS2 nanosheets prepared in step (1) were added to a nickel salt solution and ultrasonically mixed for 30 min. The solution was then heated to 80-90 °C and reacted for 4 h. After the reaction was completed, the solution was naturally cooled to room temperature. The product was separated by centrifugation, washed, and dried in a vacuum drying oven. The dried powder was then calcined in a tube furnace to obtain the nickel single-atom modified MoS2 nanosheets.

[0011] In one embodiment of the present invention, the molybdate is sodium molybdate dihydrate.

[0012] In one embodiment of the present invention, in step (1), the concentration of molybdate in the mixed solution is 11-13 g / L and the concentration of thioacetamide is 7-8 g / L.

[0013] In one embodiment of the present invention, in step (1), the stirring speed is 400-600 rpm and the time is 30 min.

[0014] In one embodiment of the present invention, in step (1), the reaction temperature is 180-220°C and the reaction time is 8-10 h.

[0015] In one embodiment of the present invention, in step (1), the drying temperature is 80°C and the drying time is 12h.

[0016] In one embodiment of the present invention, in step (2), the nickel salt is nickel acetate tetrahydrate.

[0017] In one embodiment of the present invention, in step (2), the concentration of nickel salt in the nickel salt solution is 3.5 to 4 g / L.

[0018] In one embodiment of the present invention, in step (2), the mass-to-volume ratio of the MoS2 nanosheets to the nickel salt solution is 1:2.1 to 2.4.

[0019] In one embodiment of the present invention, in step (2), the drying temperature is 80°C and the drying time is 12h.

[0020] In one embodiment of the present invention, in step (2), the atmosphere during calcination is a mixture of hydrogen and argon.

[0021] In one embodiment of the present invention, in step (2), the volume ratio of hydrogen in the mixed atmosphere is 3-5%.

[0022] In one embodiment of the present invention, in step (2), the calcination temperature is 300°C and the calcination time is 1 hour.

[0023] The present invention also provides a nickel single-atom modified MoS2 nanosheet prepared according to the above preparation method.

[0024] The present invention also provides an application of the above-mentioned nickel single-atom modified MoS2 nanosheets in the field of photocatalysis.

[0025] In one embodiment of the invention, the application includes using nickel single-atom modified MoS2 nanosheets as a catalyst for the photocatalytic reduction of carbon dioxide.

[0026] In one embodiment of the present invention, the photocatalytic reduction of CO2 reaction process includes: placing nickel single-atom modified MoS2 nanosheet powder in a sealed container, injecting water into the container, evacuating the vacuum before filling with CO2, using a 300W xenon lamp to simulate sunlight as the light energy source for the reaction, and reacting for 6 hours to obtain methane.

[0027] Beneficial effects of the present invention

[0028] (1) In this invention, MoS2 nanosheets were first synthesized using molybdate and thioacetamide as raw materials. Then, the MoS2 nanosheets were added to a nickel salt solution for hydrothermal reaction. The product obtained after the reaction was calcined in a tube furnace, and nickel single-atom modified MoS2 nanosheets were successfully prepared.

[0029] (2) Using the nickel-modified MoS2 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 27.2 μmol g. -1 h -1 This is far higher than the yield of CO produced (less than 10 μmol g). -1 h -1 This demonstrates that the nickel-modified MoS2 nanosheets of the present invention exhibit high selectivity for the products during the photocatalytic reduction of CO2.

[0030] (3) In the photocatalytic reduction of CO2 by the nickel single-atom modified MoS2 nanosheets of the present invention, the selectivity for CH4 products and the electron selectivity can reach 80.4% and 94.2%, respectively. Among them, electron selectivity refers to the ratio of electrons used to generate the target product to the total transferred electrons. The high electron selectivity indicates that most electrons are transferred from CO2 to CH4 during the CO2 reduction process.

[0031] (4) The preparation method is simple to operate, and the prepared nickel single-atom modified MoS2 nanosheets have strong catalytic ability; the established practical method for photocatalytic reduction of CO2 is highly efficient, stable, environmentally friendly and sustainable. Attached Figure Description

[0032] Figure 1These are the nickel single-atom modified MoS2 nanosheets and the XRD diffraction patterns of the MoS2 nanosheets prepared in Example 1 and Comparative Example 1, where (1) is the XRD pattern of the nanosheets prepared in Example 1 and (2) is the XRD pattern of the nanosheets prepared in Comparative Example 1.

[0033] Figure 2 These are transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of nickel single-atom modified MoS2 nanosheets and MoS2 nanosheets prepared in Example 1 and Comparative Example 1, where (a) and (b) are TEM and HRTEM images of nanosheets prepared in Comparative Example 1, and (c) and (d) are TEM and HRTEM images of nanosheets prepared in Example 1.

[0034] Figure 3 These are aberration-corrected high-angle annular dark-field scanning transmission microscopy (ac-HAADF-STEM) images and corresponding elemental mapping diagrams of the nickel-monomer-modified MoS2 nanosheets prepared in Example 1, where (a) is the HAADF-STEM image and (b) is the corresponding elemental mapping diagram.

[0035] Figure 4 The graph shows the yields of carbon monoxide (gray) and methane (white) obtained from the photocatalytic reduction of CO2 by nickel single-atom modified MoS2 nanosheets prepared in Example 2 and Comparative Example 2.

[0036] Figure 5 The graph shows the product selectivity (solid spheres) and electron selectivity (solid squares) of the photocatalytic reduction of carbon dioxide to methane by nickel single-atom modified MoS2 nanosheets prepared in Example 2, as well as the product selectivity (hollow spheres) and electron selectivity (hollow squares) of carbon monoxide production.

[0037] Figure 6 The Ni 2p X-ray photoelectron spectroscopy (XPS) pattern of the nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 3;

[0038] Figure 7 Aberration-corrected high-angle annular dark-field scanning transmission microscope image of nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 4.

[0039] Figure 8 Aberration-corrected high-angle annular dark-field scanning transmission microscope image of the nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 5. Detailed Implementation

[0040] Example 1

[0041] A method for preparing a catalyst for the photocatalytic reduction of CO2 to methane includes the following steps:

[0042] (1) Preparation of molybdenum disulfide (MoS2) nanosheets:

[0043] 300 mg of thioacetamide and 484 mg of sodium molybdate dihydrate were dissolved sequentially in 40 mL of water. After stirring at 500 rpm for 30 min, the resulting mixture was transferred to a 50 mL high-pressure reactor, sealed, and reacted at 200 °C for 10 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature and centrifuged at 8000 rpm for 2 min to separate the product. The product was then washed five times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was the MoS2 nanosheets.

[0044] (2) Preparation of nickel single-atom modified MoS2 nanosheets:

[0045] 50 mg of the MoS2 nanosheets prepared in step (1) was added to 30 mL of nickel acetate tetrahydrate (0.015 M) solution. After ultrasonic mixing for 30 min, the mixture was heated to 90 °C and reacted for 4 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature and centrifuged at 8000 rpm for 2 min to separate the product. The product was then washed three 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 tube furnace at 300 °C for 1 h under a 5% H2 / Ar atmosphere to obtain the nickel single-atom modified MoS2 nanosheets.

[0046] Comparative Example 1

[0047] 300 mg of thioacetamide and 484 mg of sodium molybdate dihydrate were dissolved sequentially in 40 mL of water. After stirring at 500 rpm for 30 min, the resulting mixture was transferred to a 50 mL high-pressure reactor, sealed, and reacted at 200 °C for 10 h. After the reaction was complete, the mixture was allowed to cool naturally to room temperature and centrifuged at 8000 rpm for 2 min to separate the product. The product was then washed five times with water. After washing, the product was dried in a vacuum drying oven at 80 °C for 12 h. The dried powder was the MoS2 nanosheets.

[0048] The structures of the compounds prepared in Example 1 and Comparative Example 1 were identified, and the results are shown in the figure. Figures 1-2 , Figure 1 The nickel single-atom modified MoS2 nanosheets and the XRD diffraction pattern of the MoS2 nanosheets prepared in Example 1 and Comparative Example 1; Figure 2 The images show transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of nickel single-atom modified MoS2 nanosheets prepared in Example 1 and Comparative Example 1; from Figure 1 As can be seen from Figure 2, both have the morphology of nanosheets, and the XRD results show that there are no additional diffraction peaks compared with the standard diffraction pattern of 2H-MoS2, indicating that MoS2 nanosheets were successfully synthesized.

[0049] Figure 3 The image shows an aberration-corrected high-angle annular dark-field scanning transmission microscopy (ac-HAADF-STEM) image and corresponding elemental mapping of the nickel single-atom modified MoS2 nanosheets prepared in Example 1. The bright spots in the Ac-HAADF-STEM image represent the loaded Ni atoms, indicating that Ni exists in a single-atom form. The corresponding elemental mapping also confirms that Ni atoms are uniformly distributed on the MoS2 nanosheets, proving that Ni single-atom modified MoS2 nanosheets were successfully synthesized in Example 1.

[0050] Example 2: Photocatalytic reduction of CO2 by nickel-modified MoS2

[0051] 10 mg of nickel-modified MoS2 powder was uniformly dispersed on a glass slide and placed in a sealed glass instrument. 2 mL of water was added to the container, and a vacuum was drawn before introducing high-purity CO2 (concentration >99.999%). This process was repeated three times. The instrument was sealed once atmospheric pressure was reached. A 300 W xenon lamp was used to simulate sunlight as the light source for the reaction, providing continuous visible light irradiation. The reaction proceeded for 6 hours to yield CO and CH4. The preparation method of the nickel-modified MoS2 powder was the same as in Example 1.

[0052] Comparative Example 2

[0053] The difference between Comparative Example 2 and Example 2 is that the nickel single-atom modified MoS2 nanosheets are replaced with MoS2 nanosheets, wherein the preparation method of MoS2 nanosheets is the same as that of Comparative Example 1.

[0054] Figure 4 The graph shows the yields of carbon monoxide (gray) and methane (white) obtained from the photocatalytic reduction of CO2 by nickel single-atom modified MoS2 nanosheets prepared in Example 2 and Comparative Example 2. Figure 5 The graphs show the product selectivity (solid spheres) and electron selectivity (solid squares) of the photocatalytic reduction of carbon dioxide to methane by nickel single-atom modified MoS2 nanosheets prepared in Example 2, as well as the product selectivity (hollow spheres) and electron selectivity (hollow squares) of the generation of carbon monoxide. The electron selectivity refers to the ratio of electrons used to generate the target product to the total transferred electrons.

[0055] The calculation method is as follows: Methane 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).

[0056] Carbon monoxide electron selectivity = number of electrons generated to produce carbon monoxide * amount of carbon monoxide / (number of electrons generated to produce methane * amount of methane + number of electrons generated to produce carbon monoxide * amount of carbon monoxide).

[0057] from Figure 4 The results show that both MoS2 nanosheets and nickel-modified MoS2 nanosheets can reduce carbon dioxide under both ambient temperature and pressure, and under light irradiation. The product of MoS2 nanosheets is entirely CO, with a CO formation rate of 6.5 μmol g⁻¹ h⁻¹. In contrast, nickel-modified MoS2 nanosheets can reduce CO₂ to CH₄ at a rate of 27.2 μmol g⁻¹ h⁻¹. Figure 5 It can be seen that the photocatalytic reduction of CO2 product CH4 by nickel single-atom modified MoS2 nanosheets has high selectivity, with a CH4 product selectivity of 80.4% and an electron selectivity of up to 94.2%.

[0058] Comparative Example 3

[0059] The difference between Comparative Example 3 and Example 1 is that, in step (2), the heating temperature during the reaction is adjusted to 40°C.

[0060] Figure 6 The X-ray photoelectron spectroscopy (XPS) pattern of the nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 3 is shown in the Ni 2p spectrum. No Ni peak was observed, indicating that the product obtained is not a nickel single-atom modified MoS2 nanosheet.

[0061] Comparative Example 4

[0062] The difference between Comparative Example 4 and Example 1 is that in step (2), the concentration of nickel acetate tetrahydrate was adjusted to 0.03M.

[0063] Figure 7 The image shows a spherical aberration-corrected high-angle annular dark-field scanning transmission microscope image of the nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 4. It can be observed that nickel atoms mainly exist in the form of nanoclusters, thus indicating that the product obtained is not a nickel single-atom modified MoS2 nanosheet.

[0064] Comparative Example 5

[0065] The difference between Comparative Example 5 and Example 1 is that, in step (2), the calcination temperature is adjusted to 500°C.

[0066] Figure 8 The image shows a spherical aberration-corrected high-angle annular dark-field scanning transmission microscope image of the nickel single-atom modified MoS2 nanosheets prepared in Comparative Example 5. It can be observed that nickel atoms mainly exist in the form of nanoclusters, thus indicating that the product obtained is not a nickel single-atom modified MoS2 nanosheet.

[0067] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined in the claims of this invention.

Claims

1. Use of a nickel monatomic modified MoS2 nanosheet in photocatalytic reduction of CO2 to produce methane, characterized in that, The process of the photocatalytic reduction of CO2 to produce methane comprises the following steps: (1) Preparation of MoS2 nanosheets: Dissolve molybdate and thioacetamide in water in sequence to obtain a mixed solution, stir for 30 min, then move the stirred mixed solution into a high-pressure reaction kettle for reaction under sealed conditions, naturally cool to room temperature after the reaction is completed, centrifugally separate the obtained product, wash and dry in a vacuum drying box to obtain MoS2 nanosheets; (2) Preparation of MoS2 nanosheets modified by nickel monatomic: Add the MoS2 nanosheets prepared in step (1) into a nickel salt solution, ultrasonically mix for 30 min, then heat to 80-90℃ for reaction for 4 h, naturally cool to room temperature after the reaction is completed, centrifugally separate the obtained product, wash and dry in a vacuum drying box, and calcine the dried powder in a tube furnace to obtain the MoS2 nanosheets modified by nickel monatomic; the atmosphere during calcination is a mixed atmosphere of hydrogen and argon, and the volume ratio of hydrogen in the mixed atmosphere is 3-5%.

2. Use according to claim 1, characterized in that, In step (1), the molybdate is sodium molybdate dihydrate, the concentration of molybdate in the mixed solution is 11-13 g / L, and the concentration of thioacetamide is 7-8 g / L.

3. Use according to claim 1, characterized in that, In step (1), the reaction temperature is 180-220℃, the reaction time is 8-10 h, the drying temperature is 80℃, and the drying time is 12 h.

4. Use according to claim 1, characterized in that, In step (2), the nickel salt is nickel acetate tetrahydrate, and the concentration of nickel salt in the nickel salt solution is 3.5-4 g / L.

5. Use according to claim 1, characterized in that, In step (2), the mass-volume ratio of MoS2 nanosheets to nickel salt solution is 1:2.1-2.4, the drying temperature is 80℃, and the drying time is 12 h.

6. Use according to claim 1, characterized in that, In step (2), the calcination temperature is 300℃, and the calcination time is 1 h.

7. A method for preparing nickel single-atom decorated MoS2 nanosheets for photocatalytic reduction of CO2 to methane, characterized in that, The process of the photocatalytic reduction of CO2 to produce methane comprises the following steps: (1) Preparation of MoS2 nanosheets: Dissolve molybdate and thioacetamide in water in sequence to obtain a mixed solution, stir for 30 min, then move the stirred mixed solution into a high-pressure reaction kettle for reaction under sealed conditions, naturally cool to room temperature after the reaction is completed, centrifugally separate the obtained product, wash and dry in a vacuum drying box to obtain MoS2 nanosheets; (2) Preparation of MoS2 nanosheets modified by nickel monatomic: Add the MoS2 nanosheets prepared in step (1) into a nickel salt solution, ultrasonically mix for 30 min, then heat to 80-90℃ for reaction for 4 h, naturally cool to room temperature after the reaction is completed, centrifugally separate the obtained product, wash and dry in a vacuum drying box, and calcine the dried powder in a tube furnace to obtain the MoS2 nanosheets modified by nickel monatomic; the atmosphere during calcination is a mixed atmosphere of hydrogen and argon, and the volume ratio of hydrogen in the mixed atmosphere is 3-5%. The MoS2 nanosheet prepared in step (1) is added to a nickel acetate tetrahydrate solution, and after ultrasonic mixing for 30 min, it is heated to 80-90 DEG C and reacted for 4 h, and after the reaction is completed, it is naturally cooled to room temperature, the obtained product is centrifugally separated, washed and dried in a vacuum drying box, and the dried powder is calcined in a tube furnace, and the obtained powder is a nickel monatomic modified MoS2 nanosheet, the concentration of the nickel acetate tetrahydrate solution is 3.5-4 g / L, the atmosphere during calcination is a mixed atmosphere of hydrogen and argon, the volume ratio of hydrogen in the mixed atmosphere is 3-5%, the temperature during calcination is 300 DEG C, and the calcination time is 1 h.

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