NiAlEu-LDHs photocatalyst, preparation method thereof and application of NiAlEu-LDHs photocatalyst in preparation of synthesis gas by catalyzing CO2

Abstract

The invention discloses a NiAlEu-LDHs photocatalyst, a preparation method of the NiAlEu-LDHs photocatalyst and application of the NiAlEu-LDHs photocatalyst to preparation of synthesis gas by catalyzing CO2, and belongs to the technical field of catalyst preparation. The NiAlEu-LDHs photocatalyst is europium-doped layered double hydroxide prepared from a nickel source, an aluminum source and a europium source through a hydrothermal reaction, and has a multi-stage nano flower-shaped structure formed by assembling nanosheets. The preparation method comprises the following steps: dissolving a nickel source, an aluminum source, a europium source, urea and ammonium fluoride in deionized water through a one-step hydrothermal method, and transferring the solution into an autoclave with a polytetrafluoroethylene lining for hydrothermal reaction; according to the preparation method, europium is introduced through a one-step hydrothermal method, the europium-doped nano flower-shaped NiAlEu-LDHs photocatalyst is constructed, and in production and application, the preparation method is simple and novel, low in synthesis cost and easy for batch production, and has very good application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and particularly relates to a NiAlEu-LDHs photocatalyst, a preparation method thereof and application of the photocatalyst in catalyzing CO2 to prepare synthesis gas. BACKGROUND

[0002] Since the industrial revolution, the overexploitation and utilization of traditional non-renewable fuels such as coal, oil and natural gas have provided sustained impetus for industrial development. However, the greenhouse effect and energy crisis caused by the overexploitation of such resources have become major problems that need to be solved by mankind. Global observation data clearly shows that a substantial increase in the concentration of greenhouse gases is the main cause of climate warming, and the combustion of fossil energy produces a large amount of greenhouse exhaust gas mainly in the form of carbon dioxide (CO2).

[0003] Among the many solutions to alleviate the energy crisis and the greenhouse effect, the development and utilization of clean solar energy are favored. Among them, the photocatalytic technology takes a semiconductor material with light excitation ability as the core and uses light as the driving force, and shows potential application value due to the mild reaction conditions. Through this technology, CO2 is converted into hydrocarbons or chemicals (i.e., artificial photosynthesis) using solar energy in the presence of water (H2O), which is considered a viable way to solve global warming and alleviate the energy crisis.

[0004] Converting captured CO2 into synthesis gas as a carbon source can not only achieve carbon recycling, but also solve environmental problems while breaking through the carbon neutralization bottleneck in the fields of resources and energy. As an important raw material in the chemical industry, synthesis gas with different hydrogen-carbon ratios (H2 / CO) has different applications in chemical synthesis. At present, the production of synthesis gas mainly relies on natural gas catalytic reforming and coal gasification processes, which are highly dependent on fossil fuels, thereby bringing double pressure on the environment and energy. Therefore, it is urgent to find a green alternative method for producing synthesis gas.

[0005] Light-driven CO2 reduction (CO2RR) into CO / H2 with adjustable proportions is a highly potential strategy to replace traditional synthesis gas production. However, due to the high thermodynamic stability of the CO2 molecule, a large amount of energy is required to break the C=O bond, and in addition, the photo-generated electrons and holes are prone to recombination, making it still a great challenge to construct an efficient and stable photocatalyst for CO2 reduction.

[0006] Among a large number of photocatalysts, two-dimensional (2D) nanostructured photocatalysts have a wide application prospect due to sufficient exposure of active sites, short electron-hole transport distance, large specific surface area and other advantages. Among them, layered double hydroxides (hydrotalcite, LDHs) as a kind of 2D anionic clay material have attracted extensive attention as a new type of inorganic functional material. LDHs have unique advantages such as adjustable layer element composition, controllable morphology and structure, and wide range of controllable band structure, so they have been deeply studied in the field of CO2 reduction. It is of great research significance to finely regulate the microstructure of LDHs in order to further enhance the catalytic performance of LDHs and expand its application range. SUMMARY

[0007] In view of the above technical problems, the present application provides a NiAlEu-LDHs photocatalyst, a preparation method thereof and an application thereof in catalyzing CO2 to prepare synthesis gas, so as to ensure that CO2 is reduced to synthesis gas with high activity and high selectivity.

[0008] To achieve the above object, the present application provides the following technical scheme:

[0009] One of the objects of the present application is to provide a NiAlEu-LDHs photocatalyst, which is a europium-doped layered double hydroxide prepared by hydrothermal reaction of a nickel source, an aluminum source and a europium source, and has a multi-level nanoflower structure formed by assembly of nanosheets.

[0010] The present application adopts a gradient orbital coupling engineering strategy, dopes Eu in NiAl-LDHs (NiAlEu-LDHs) to construct an asymmetric 3d-2p-4f electronic configuration, and the introduction of Eu effectively improves the small energy difference of 3d-2p orbital hybridization in NiAl-LDHs, so as to provide more sufficient electrons for the d orbital of active site Ni. This regulation is expected to enhance the electron transfer ability between metal atoms and improve the photoelectron-hole separation efficiency to realize efficient preparation of synthesis gas from CO2. In addition, the introduction of Eu causes the band gap to decrease from 2.3eV to 2.1eV, which narrows the band gap to reduce the energy required for photoexcitation, thereby improving the visible light response, while the multi-level structure of nanosheet assembly exposes more active sites, improves the CO2 adsorption capacity, and the two-dimensional nanosheet shortens the diffusion distance of photoelectron-hole pairs and inhibits the recombination.

[0011] The second object of the present application is to provide a preparation method of the NiAlEu-LDHs photocatalyst, comprising the following steps:

[0012] Dissolve the nickel source, the aluminum source and the europium source in deionized water to form solution A;

[0013] Dissolve urea and ammonium fluoride in deionized water to form solution B;

[0014] Solution A is added to solution B to obtain a mixed solution;

[0015] The mixed solution is subjected to hydrothermal reaction at 110-140℃ for 8-24h, and the NiAlEu-LDHs photocatalyst is obtained after centrifugation, washing and drying.

[0016] The present application takes nickel nitrate, aluminum nitrate and europium nitrate as raw materials to provide Ni 2+ , Al 3+ , Eu 3+ as the source of LDHs layer metal cation. Ni 2+ is the active center (photocatalytic reduction of CO2), Al 3+ stabilizes the layer structure, and Eu 3+ controls the electronic structure; urea (CO(NH2)2) is used as a homogeneous precipitant, slowly releases OH - and CO3 2- during hydrothermal decomposition, controls the growth rate of LDHs crystal nucleus, avoids agglomeration, CO3 2- balances the charge inserted into the LDHs interlayer, and maintains the layered structure; ammonium fluoride (NH4F) is used as a morphology directing agent: F - selectively adsorbs on the LDHs crystal surface, induces the growth of nanosheets in a specific direction, forms a nanoflower structure, and F - may replace part of OH - , introduces lattice defects, and promotes the separation of photo-generated carriers. Ni 2+ , Al 3+ , Eu 3+ co-precipitate with OH - and CO3 2- to form an LDHs precursor, Eu 3+ enters the layer by isomorphism substitution of Al 3+ , and then after hydrothermal reaction, high temperature and high pressure promote the ordered stacking of LDHs layers, improve the crystallinity, and ensure that Eu 3+ is uniformly dispersed in the layer to avoid local aggregation.

[0017] Further, the nickel source is nickel nitrate; the aluminum source is aluminum nitrate; the europium source is europium nitrate; and the molar ratio of the aluminum nitrate to the europium nitrate is (1-19)∶1, preferably 9∶1.

[0018] In the present application, Eu 3+ substitutes Al 3+ , and the positive charge density of the layer should be moderate. If it is too high (such as 1∶1), the layer charge will be excessive and the structure will collapse; if it is too low (such as 19∶1), the Eu 3+ doping amount is insufficient and cannot significantly regulate the energy band; under the ratio of 9∶1, the Eu 3+ introduction amount is sufficient to reduce the band gap without destroying the layer structure.

[0019] Further, the molar ratio of the nickel source (divalent nitrate salt) to the total amount of substance of the aluminum source and the europium source (trivalent nitrate salt) is (2-4) : 1, preferably the molar ratio is 3:1.

[0020] The present application preferably sets the molar ratio of the divalent nitrate salt and the trivalent nitrate salt, aiming to avoid the generation of hydroxide impurity phases (such as Ni(OH)2).

[0021] Further, in the solution B, the concentration of urea is 100-400 mmol / L, preferably the concentration is 186.7 mmol / L; the concentration of ammonium fluoride is 100-400 mmol / L, preferably the concentration is 166.7 mmol / L.

[0022] The concentration of urea in the present application determines the OH - The release rate cooperates with the metal ion concentration to avoid agglomeration caused by rapid precipitation; the concentration of ammonium fluoride affects the adsorption equilibrium of F - The concentration of 166.7 mmol / L can fully cover the crystal surface to induce the growth of nanosheets, and an excess amount may cause excessive etching.

[0023] Further, the temperature of the hydrothermal reaction is 130℃, and the time is 24h.

[0024] The purpose of setting the temperature of the hydrothermal reaction to 130℃ in the present application is to provide sufficient energy to overcome the nucleation energy barrier of LDHs, and 24h ensures complete crystal growth. A temperature that is too low (<110℃) causes incomplete crystallization, and a temperature that is too high (>140℃) may generate impurity phases (such as NiO).

[0025] The third purpose of the present application is to provide an application of the NiAlEu-LDHs photocatalyst in the preparation of synthesis gas from carbon dioxide. The catalysis is carried out in a photocatalytic reactor with a volume of 50cm 3 The light source is a 300W xenon lamp with a full reflection sheet.

[0026] The working principle of the present application: the present application provides a nano-flower-like NiAlEu-LDHs photocatalyst and a preparation method thereof. The morphology of the material is a multi-level nano-flower-like structure composed of nanosheets. By doping Eu to construct an asymmetric 3d-2p-4f configuration, efficient CO2 synthesis gas is realized. The coupling of rare earth sites (RE) with 4f empty orbitals and transition metal sites (TM) changes the local coordination environment and the electronic structure, which is beneficial to adjusting the photocatalytic activity, thereby enhancing the adsorption and activation of CO2 and improving the photocatalytic rate. Therefore, the catalytic material has high yield and high selectivity for photocatalytic reduction of CO2 to generate synthesis gas.

[0027] Compared with the prior art, the present application has the following advantages and technical effects:

[0028] The present application realizes the triple goals of band engineering (2.1 eV band gap), active site exposure and carrier separation efficiency improvement through the synergistic design of element doping (Eu 3+ The triple goals of band engineering (2.1 eV band gap), active site exposure and carrier separation efficiency improvement are realized through the synergistic design of structure regulation (nanoflower), process optimization (proportion, temperature, time), so as to finally drive the efficient conversion of CO2 and H2O into syngas (CO / H2) with adjustable proportions.

[0029] In order to design and develop a photocatalyst with high performance, stable structure and low cost for the preparation of syngas by CO2 reduction, the present application prepares a nanoflower-shaped NiAlEu-LDHs photocatalyst by a one-step hydrothermal method. In terms of photocatalytic performance, compared with a single NiAl-LDHs photocatalyst, the introduction of an appropriate amount of Eu adjusts the electronic structure of the active metal of the catalyst, reduces the band gap width, thereby accelerating the separation efficiency of photo-generated charges and holes, improving the utilization rate of photo-generated carriers, and significantly improving the activity and selectivity of photocatalytic CO2 conversion into syngas with different proportions; in terms of production and application, the preparation method of the present application is simple and novel, the synthesis cost is low, and it is easy to mass-produce, and has good application value. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which form a part of this application, are used to provide a further understanding of the application. The illustrative embodiments of the present application and their description serve to explain the application. The drawings should not be considered limiting the scope of the present application. In the drawings:

[0031] Figure 1 FIG. 1 is an X-ray powder diffraction pattern of the NiAlEu-LDHs photocatalyst in Example 1 of the present application;

[0032] Figure 2 FIG. 2 is an X-ray powder diffraction pattern of the NiAl-LDHs photocatalyst in Comparative Example 1 of the present application;

[0033] Figure 3 FIG. 3 is a scanning electron microscope image of the NiAlEu-LDHs photocatalyst in Example 1 of the present application;

[0034] Figure 4 FIG. 4 is a scanning electron microscope image of the NiAl-LDHs photocatalyst in Comparative Example 1 of the present application;

[0035] Figure 5 FIG. 5 is a high-resolution transmission electron microscope image of the NiAlEu-LDHs photocatalyst in Example 1 of the present application;

[0036] Figure 6 FIG. 6 is a surface element distribution map of the NiAlEu-LDHs photocatalyst in Example 1 of the present application;

[0037] Figure 7The solid UV diffuse reflectance spectra of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0038] Figure 8 The Tauc plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0039] Figure 9 The Mott-Schottky plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0040] Figure 10 The valence band X-ray photoelectron spectroscopy (VB-XPS) plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0041] Figure 11 The energy band structure diagrams of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0042] Figure 12 The Ni 2p X-ray photoelectron spectroscopy plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0043] Figure 13 The Al 2p X-ray photoelectron spectroscopy plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0044] Figure 14 The O 1s X-ray photoelectron spectroscopy plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application and the NiAl-LDHs photocatalyst in Comparative Example 1;

[0045] Figure 15 The Eu 3d X-ray photoelectron spectroscopy plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application;

[0046] Figure 16 The catalytic performance plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application for catalyzing the reduction of carbon dioxide and water into carbon monoxide;

[0047] Figure 17 The catalytic performance plots of the NiAlEu-LDHs photocatalyst in Example 1 of the present application for catalyzing the reduction of carbon dioxide and water into hydrogen;

[0048] Figure 18 Catalytic performance graph for the catalytic reduction of carbon dioxide and water to carbon monoxide by the NiAl-LDHs photocatalyst in Inventive Example 1;

[0049] Figure 19 Catalytic performance graph for the catalytic reduction of carbon dioxide and water to hydrogen by the NiAl-LDHs photocatalyst in Inventive Example 1;

[0050] Figure 20 Catalytic performance bar graph for the catalytic reduction of carbon dioxide and water to carbon monoxide and hydrogen by the NiAlEu-LDHs photocatalyst in Inventive Example 1 and the NiAl-LDHs photocatalyst in Inventive Example 1. DETAILED DESCRIPTION

[0051] Various illustrative embodiments of the present application are described in detail below. This detailed description is not intended to be a limitation on the application, but rather an exemplification of the present application. It is thus contemplated that there can be other embodiments of the application that fall within the scope of the present application.

[0052] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments of the application only and is not intended to be limiting of the application. Additionally, the use of "including," "comprising," "having," "containing," and variations thereof in the present description are not meant to be limiting to the extent that the products, compositions, processes, methods, and / or fields described herein are open to encom passing additional products, compositions, processes, methods, and / or fields not expressly named or otherwise described. These

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference is not construed as an admission that it is prior art with respect to the present application.

[0054] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent laws. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples given are exemplary only and are not intended to be limiting.

[0055] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0056] The embodiment of the present application provides a preparation method of a NiAlEu-LDHs photocatalyst, which comprises the following steps:

[0057] Dissolving nickel nitrate, aluminum nitrate and europium nitrate in deionized water to form solution A;

[0058] Dissolving urea and ammonium fluoride in deionized water to form solution B;

[0059] Adding solution A into solution B to obtain a mixed solution;

[0060] Carrying out hydrothermal reaction on the mixed solution at 110-140 DEG C for 8-24h, and then carrying out centrifugation, washing and drying to obtain the NiAlEu-LDHs photocatalyst.

[0061] In the following preferred embodiments of the present application, the molar ratio of the aluminum nitrate and the europium nitrate is (1-19) : 1, and more preferably 9:1.

[0062] In the following preferred embodiments of the present application, the molar ratio of the nickel nitrate (divalent nitrate salt) to the total molar amount of the aluminum nitrate and the europium nitrate (trivalent nitrate salt) is (2-4) : 1, and more preferably 3:1.

[0063] In the following preferred embodiments of the present application, in the solution B, the concentration of the urea is 100-400mmol / L, and more preferably 186.7mmol / L; and the concentration of the ammonium fluoride is 100-400mmol / L, and more preferably 166.7mmol / L.

[0064] In the following preferred embodiments of the present application, the temperature of the hydrothermal reaction is more preferably 130 DEG C, and the time is more preferably 24h.

[0065] The NiAlEu-LDHs photocatalyst can be prepared by using the above preparation method.

[0066] The NiAlEu-LDHs photocatalyst can be applied to catalyze the preparation of synthesis gas from carbon dioxide and water. The catalysis is carried out in a photocatalytic reactor with a volume of 50cm 3 The light source is a 300W xenon lamp with a full reflection sheet.

[0067] In the present application, the "room temperature" refers to 25±2 DEG C, unless otherwise specified.

[0068] The raw materials used in the present application are all purchased from the market.

[0069] The technical solutions of the present application are further described through the following examples.

[0070] Example 1

[0071] A method for preparing a NiAlEu-LDHs photocatalyst, comprising the following steps:

[0072] Weigh out 832 mg of nickel nitrate hexahydrate, 338 mg of aluminum nitrate nonahydrate, and 44.6 mg of europium nitrate hexahydrate (Ni in the solution). 2+ ∶Al 3+ Eu 3+ The molar ratio of ammonium fluoride to urea (3:0.9:0.1) was dissolved in 30 mL of deionized water to obtain solution A; 370 mg of ammonium fluoride and 673 mg of urea were weighed and dissolved in 30 mL of deionized water to obtain solution B; solutions A and B were mixed by ultrasonic stirring, and the concentration of urea in the resulting mixed solution was 186.7 mmol / L and the concentration of ammonium fluoride was 166.7 mmol / L; the mixed solution was transferred to a 100 mL Teflon-lined autoclave, and NiAlEu-LDHs were prepared by hydrothermal synthesis, wherein the hydrothermal reaction conditions were controlled at 130 °C and constant temperature for 24 h; finally, the obtained precipitate (NiAlEu-LDHs) was washed three times with deionized water and once with ethanol, and dried at 60 °C for 12 h.

[0073] Comparative Example 1

[0074] A method for preparing NiAl-LDHs photocatalyst, comprising the following steps:

[0075] Weigh out 832 mg of nickel nitrate hexahydrate and 375 mg of aluminum nitrate nonahydrate (Ni in the solution). 2+ ∶Al 3+ The molar ratio of ammonium fluoride to urea was 3:1. The solutions were dissolved in 30 mL of deionized water to obtain solution A. 370 mg of ammonium fluoride and 673 mg of urea were weighed and dissolved in 30 mL of deionized water to obtain solution B. Solutions A and B were mixed by ultrasonic stirring. The resulting mixed solution had a urea concentration of 186.7 mmol / L and an ammonium fluoride concentration of 166.7 mmol / L. The mixed solution was transferred to a 100 mL Teflon-lined autoclave, and NiAl-LDHs were prepared by hydrothermal synthesis. The hydrothermal reaction was controlled at 130 °C for 24 h. Finally, the obtained precipitate (NiAl-LDHs) was washed three times with deionized water and once with ethanol, and dried at 60 °C for 12 h.

[0076] Performance testing

[0077] 1. Structural morphology characterization of photocatalytic materials

[0078] Figure 1 The image shows the X-ray powder diffraction pattern of the NiAlEu-LDHs photocatalyst in Example 1. Figure 3 This is a scanning electron microscope image of the NiAlEu-LDHs photocatalyst in Example 1.Figure 5 High-resolution transmission electron microscopy image of the NiAlEu-LDHs photocatalyst in Example 1; Figure 6 Surface element distribution map of the NiAlEu-LDHs photocatalyst in Example 1. The intensity reduction of NiAlEu-LDHs indicates that the doping of Eu with a large ionic radius induces the deformation of MO6 octahedron, resulting in the reduction of crystallinity Figure 1 ), but still retains a good nanoflower morphology Figure 3 and Figure 5 ) with large surface area and high CO2 adsorption capacity. The elements of Ni, Al, Eu and O are uniformly distributed on the surface of the catalyst Figure 6 .

[0079] Figure 2 X-ray powder diffraction pattern of the NiAl-LDHs photocatalyst in Comparative Example 1; Figure 4 Scanning electron microscopy image of the NiAl-LDHs photocatalyst in Comparative Example 1. It can be seen from Figure 3 , Figure 4 that the products of Example 1 and Comparative Example 1 have little difference in micro-morphology, which is mainly caused by the low amount of Eu introduced in Example 1; when the molar ratio of Al:Eu is 9:1, it is still not enough to have a great impact on the micro-morphology of the product.

[0080] 2. Band structure characterization of the photocatalytic material

[0081] Figure 7 Solid-state ultraviolet diffuse reflectance spectrogram of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1. It can be seen from Figure 7 that there is no obvious difference in light absorption intensity between the NiAlEu-LDHs photocatalyst and the NiAl-LDHs photocatalyst.

[0082] Figure 8 Tauc diagram of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1. Figure 8 It is shown that after the introduction of Eu, the band gap width decreases from 2.3 eV to 2.1 eV, indicating that the introduction of Eu changes the band structure of LDHs.

[0083] Figure 9 Mott-Schottky (Mott-Schottky) diagram of the NiAlEu-LDHs photocatalyst in Example 1 (right) and the NiAl-LDHs photocatalyst in Comparative Example 1 (left). Figure 9The flat band potential of the NiAlEu-LDHs photocatalyst and the NiAl-LDHs photocatalyst is measured to be -0.70 eV and -0.50 eV (relative to a saturated Ag / AgCl electrode) respectively.

[0084] Figure 10 The valence band X-ray photoelectron spectroscopy (VB-XPS) diagrams of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1 are shown in FIG. 2. Figure 10 As shown in FIG. 2, the valence bands of the NiAlEu-LDHs photocatalyst and the NiAl-LDHs photocatalyst are located at 1.00 eV and 1.73 eV respectively relative to the Fermi level.

[0085] Figure 11 The energy band structure diagrams of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1 are shown in FIG. 3. Figure 11 As shown in FIG. 3, after the introduction of Eu, the energy band structure of the catalyst is adjusted, and the band gap width is reduced (obtained by E g = E CB -E VB ). Therefore, the photo-induced electron-hole separation and migration of the NiAlEu-LDHs photocatalyst after the introduction of Eu is obviously changed compared with the NiAl-LDHs photocatalyst, which is more conducive to the electron transition to the conduction band, thereby promoting the progress of the photocatalytic CO2 reduction reaction.

[0086] 3. Electron structure characterization of the photocatalytic material

[0087] In order to explore the influence of Eu doping on the electronic structure and chemical valence state of the catalyst, the present application carries out X-ray photoelectron spectroscopy characterization. Figure 12 The Ni 2p X-ray photoelectron spectrograms of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1 are shown in FIG. 4. The Ni 2p spectrum shows main peaks at ~873.3 and ~855.7 eV corresponding to Ni 2p 1 / 2 and Ni 2p 3 / 2 respectively, and the nearby satellite peaks confirm the existence of Ni 2+ .

[0088] Figure 13 The Al 2p X-ray photoelectron spectrograms of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1 are shown in FIG. 5. The Al 2p spectrum shows main peaks at 73.0 eV and 67.1 eV corresponding to Al 2p 1 / 2 and Al 2p 3 / 2 respectively.

[0089] Figure 14O 1s X-ray photoelectron spectroscopy of the NiAlEu-LDHs photocatalyst in Example 1 and the NiAl-LDHs photocatalyst in Comparative Example 1. The main peak located at ~ 531.1 eV is the signal peak of hydroxyl, and the peaks located at ~ 529.3 eV and ~ 532.6 eV are attributed to Ni / Al-O and adsorbed H2O, respectively.

[0090] Figure 15 Eu 3d X-ray photoelectron spectroscopy of the NiAlEu-LDHs photocatalyst in Example 1. The main peaks located at ~ 1135.2 eV and 1166.0 eV correspond to Eu 3+ 3d 5 / 2 orbitals of Eu3+, while the satellite peaks at ~ 1124.8 eV and 1156.2 eV are characteristic of Eu2+species. 3 / 2 2+

[0091] As shown in FIGS. 1, 2, 3 and 4, compared with NiAl-LDHs, there is a similar binding energy negative shift in Ni 2p, Al 2p and O 1s spectra in NiAlEu-LDHs, the introduction of electron-rich Eu adjusts the electronic state of Ni, Al and O, and the exchange of valence electrons of internal atoms increases the degree of electron delocalization, thereby adjusting the CO2 photoreduction activity. Figure 12 Figure 13 Figure 14 Figure 15 The photocatalyst prepared in Example 1 and Comparative Example 1 was tested for CO2 reduction performance, and the test method was as follows: 10 mg of the photocatalyst was weighed into 50 μL of deionized water, and then spread in an offline photocatalytic reactor with a volume of 50 cm3. CO2 was used as the reaction gas, and a 300 W xenon lamp with a full reflection sheet spectrum was used for light irradiation under normal pressure. The gas was sampled every 1 h with a gas-tight needle, and the gas product composition was analyzed by gas chromatography; after 5 h of reaction, the CO2 and water reduction to CO and H2 was stopped, and the yield was tested. 3

[0092] Application Example 1

[0093] The photocatalyst prepared in Example 1 and Comparative Example 1 was tested for CO2 reduction performance, and the test method was as follows: 10 mg of the photocatalyst was weighed into 50 μL of deionized water, and then spread in an offline photocatalytic reactor with a volume of 50 cm3. CO2 was used as the reaction gas, and a 300 W xenon lamp with a full reflection sheet spectrum was used for light irradiation under normal pressure. The gas was sampled every 1 h with a gas-tight needle, and the gas product composition was analyzed by gas chromatography; after 5 h of reaction, the CO2 and water reduction to CO and H2 was stopped, and the yield was tested.

[0094] Figure 16 , Figure 17 are the catalytic performance diagrams of the NiAlEu-LDHs photocatalyst in Example 1 for catalytic reduction of carbon dioxide to CO and H2, respectively.

[0095] Figure 18 , Figure 19 are the catalytic performance diagrams of the NiAl-LDHs photocatalyst in Comparative Example 1 for catalytic reduction of carbon dioxide to CO and H2, respectively.

[0096] Figure 20 ​​​​​​Columnar chart of catalytic performance of NiAlEu-LDHs photocatalyst in Example 1 and NiAl-LDHs photocatalyst in Comparative Example 1 for catalytic reduction of carbon dioxide and water into carbon monoxide and hydrogen.

[0097] As shown in FIG. 1, the CO and H2 production rates of NiAlEu-LDHs photocatalyst were 3.1 times and 14.2 times higher than those of NiAl-LDHs photocatalyst, respectively, due to the appropriate doping of Eu, which regulated the electronic structure of Ni. Figures 16-20 In addition, the introduction of Eu sites greatly promoted the production of H2. This was mainly due to the unique advantages conferred by the asymmetric 3d-2p-4f electronic configuration of Eu doping, which effectively optimized the electron-hole separation and surface reaction kinetics of photocatalytic CO2 reduction.

[0098] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A NiAlEu-LDHs photocatalyst, characterized in that, It is a europium-doped layered double hydroxide prepared by hydrothermal reaction of nickel, aluminum and europium sources, and has a multi-level nanoflower-like structure formed by the assembly of nanosheets.

2. A method for preparing the NiAlEu-LDHs photocatalyst as described in claim 1, characterized in that, Includes the following steps: The nickel source, aluminum source, and europium source are dissolved in deionized water to form solution A; Dissolve urea and ammonium fluoride in deionized water to form solution B; Solution A is added to solution B to obtain a mixture; The mixture was subjected to hydrothermal reaction at 110-140℃ for 8-24 hours, and the NiAlEu-LDHs photocatalyst was obtained after centrifugation, washing and drying.

3. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 2, characterized in that, The nickel source is nickel nitrate; the aluminum source is aluminum nitrate; the europium source is europium nitrate; and the molar ratio of the aluminum source to the europium source is (1-19):

1.

4. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 2, characterized in that, The molar ratio of the aluminum source to the europium source is 9:

1.

5. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 2, characterized in that, The total molar ratio of the nickel source to the aluminum source and europium source is (2-4):

1.

6. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 5, characterized in that, The total molar ratio of the nickel source to the aluminum and europium sources is 3:

1.

7. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 2, characterized in that, In solution B, the concentration of urea is 100-400 mmol / L, and the concentration of ammonium fluoride is 100-400 mmol / L.

8. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 7, characterized in that, The concentration of urea was 186.7 mmol / L, and the concentration of ammonium fluoride was 166.7 mmol / L.

9. The method for preparing the NiAlEu-LDHs photocatalyst according to claim 2, characterized in that, The hydrothermal reaction was carried out at a temperature of 130°C for 24 hours.

10. The application of the NiAlEu-LDHs photocatalyst as described in claim 1 in the catalytic production of syngas from carbon dioxide.

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