Preparation method and application of monatomic Ni modified AuNi alloy catalyst

Abstract

The invention discloses a preparation method and application of a monatomic Ni modified AuNi alloy catalyst, a simple and efficient one-step photodeposition method is adopted, high-temperature annealing or reducing atmosphere treatment is not needed, formation of an AuNi alloy and accurate introduction of monatomic Ni can be synchronously achieved on the surfaces of Au nanoparticles, and the preparation method is simple and efficient. The synergistic effect of the two not only significantly enhances the adsorption and activation ability to reactant molecules, but also effectively promotes the separation and transmission of photon-generated carriers, thereby achieving the efficient conversion of the product in the CO2 reduction reaction from CO to high value-added fuel CH4. According to the prepared catalyst, the dosage of precious metal Au is reduced, meanwhile, the number of catalytic active sites is greatly increased, the catalyst shows higher activity, selectivity and stability in the catalysis process, and the wide application prospect of the material in the field of low-carbon conversion is fully proved.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite photocatalytic material preparation, and in particular relates to a preparation method and application of a single-atom Ni-modified AuNi alloy catalyst. Background Art

[0002] Since the Industrial Revolution, human society has consumed a large amount of fossil fuels to support economic development and population growth, resulting in a rapid increase in the concentration of carbon dioxide (CO2) in the atmosphere. It is predicted that by the end of this century, the concentration of atmospheric CO2 may reach three times that of the early days of the Industrial Revolution (about 270ppm), far exceeding the internationally recognized safety threshold of 350ppm. Therefore, under the background of the "dual carbon goals", there is an urgent need for advanced technologies that can convert CO2 into valuable chemicals / fuels to achieve a "closed loop" for the resource utilization of CO2. In recent years, artificial photosynthetic reactions that imitate the photosynthesis of plants in nature have received widespread attention at home and abroad. This is because the technology can convert greenhouse gas CO2 into CO, CH4, CH3OH and even C under the conditions of sunlight and water (H2O). 2+ This technology can not only realize the green cycle and sustainable utilization of carbon resources, but also significantly reduce the concentration of CO2 in the atmosphere, which is of great significance to alleviating the energy crisis and environmental protection.

[0003] Noble metals, such as gold (Au), with their unique geometric and electronic structures, can effectively modulate light absorption due to their characteristic plasma resonance (SPR) effect and semiconductor-like inter-d electron band transitions. By collecting photons to generate high-energy electrons, they increase the local electron density at surface adsorption sites, thereby achieving high CO2 conversion efficiency. However, the high cost of noble metals increases the cost of catalyst preparation, making it difficult to meet the economic requirements of practical applications. Furthermore, single pure noble metals, as photocatalysts, have weak chemical adsorption capacity for reactant molecules due to their filled or partially filled d orbitals and low d-band center, resulting in limited photocatalytic efficiency. In recent years, researchers have focused on constructing nano-alloy particles by incorporating non-noble metals, which can reduce the amount of noble metal while enhancing catalytic activity. The strong synergistic effect between the metals in such alloys can form excellent coordination structures and optimized electronic environments. Compared with single metal catalysts, bimetallic catalytic materials can help improve light absorption and regulate the separation and migration kinetics of interfacial photogenerated carriers, making them ideal metal catalysts for enhancing and controlling catalytic activity and selectivity.

[0004] However, most alloy catalysts currently still have problems such as a single catalytic active site and insufficient activity. In addition, the preparation process of existing alloy catalysts generally has many steps and harsh conditions (for example, the use of hydrogen reduction at high temperature is not only unsafe but also cumbersome), and the adsorption and activation ability of such metal-based catalytic materials for reactant molecules is poor, which limits the rational design and optimization of catalysts. Therefore, there is an urgent need to improve the activity and stability of alloy nanometal catalysts through modification strategies. Integrating and integrating multi-scale sites such as single atoms and nanoalloy particles to construct synergistic catalytic sites is an extremely effective approach. The combination of synergistic components can effectively regulate the electronic structure of the active site, thereby adjusting the adsorption strength of the reaction intermediates, improving the reaction kinetics, and maximizing the catalytic activity. However, at present, such single-atom modified nanoalloy materials still lack a simple, rapid and stable preparation method. Therefore, the development of a method for preparing single-atom modified nanoalloy metal catalytic materials that is efficient, economical, stable and easy to operate has become the focus of current research, aiming to promote the practical application of high-performance photocatalysts in fields such as CO2 reduction. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for preparing a single-atom Ni-modified AuNi alloy catalyst using a one-step photodeposition method and its application. This method uses AuNi nano-alloy particles with a plasma resonance (SPR) effect as a CO2 reduction activity enhancement center and a regulatory site for carrier separation. At the same time, a single Ni atom is introduced as an effective reactant molecule adsorption and activation site. The constructed catalyst structure effectively reduces the amount of precious metal Au while achieving efficient separation of electron-hole pairs through a synergistic effect, significantly improving CO2 reduction activity and regulating the conversion of the product CO to high-value-added fuel CH4.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention first discloses a method for preparing a single-atom Ni modified AuNi alloy catalyst, comprising the following steps:

[0008] Step 1: adding an AlOOH carrier to an Au nanoparticle solution, sequentially subjecting the Au nanoparticles to ultrasound and mechanical stirring to allow the AlOOH and Au nanoparticles to self-assemble under electrostatic interaction, and then collecting the precipitate by centrifugal washing; freeze-drying the precipitate and then annealing it to obtain an Au nanoparticle-loaded AlOOH composite material, denoted as Au / AlOOH;

[0009] Step 2: Add the Au / AlOOH composite material obtained in step 1 to deionized water and disperse it evenly by ultrasonication, then add Ni salt solution and methanol under vigorous stirring to obtain a suspension; irradiate the suspension with ultraviolet light under an inert gas atmosphere, and reduce Ni salt by electrons synergistically generated by photoexcitation of Au nanoparticles and AlOOH; after the irradiation, the obtained solution is centrifuged, washed with water, and the precipitate is collected and dried to obtain a single-atom Ni-modified AuNi alloy photocatalyst, which is recorded as AuNi-Ni SAC / AlOOH.

[0010] Preferably, in step 1, the annealing treatment is performed at a temperature of 200 to 600° C. and for a time of 1 to 2 hours.

[0011] Preferably, in step 1, the concentration of the Au nanoparticle solution is 0.1-1 mM, and the ratio of the AlOOH carrier to the Au nanoparticle solution is 0.1-2.5 g / 103 mL.

[0012] As preferably, in step 1, the particle diameter of the Au nanoparticles is 4-12nm. Studies have shown that the particle diameter of Au nanoparticles has a significant impact on the photodeposition reduction process. When the Au nanoparticle size is less than 4nm, due to the enhancement of the size effect, Au tends to cluster, resulting in an incomplete lattice structure and a reduction in the surface atomic coordination number, thereby reducing the stability of the overall structure; and when the particle size exceeds 12nm, the surface plasmon resonance (SPR) effect is significantly enhanced, resulting in an extremely short lifetime (only in femtoseconds) of the non-equilibrium hot carriers produced, which is not enough to effectively participate in the reduction reaction of Ni. It can be seen from this that selecting the particle size range of 4-12nm can both avoid the instability of clustering due to being too small, and suppress the phenomenon of the SPR effect being dominant due to being too large, thereby facilitating the interband transition effect of Au, generating photogenerated electrons (up to nanoseconds) with a longer lifespan. On this basis, light-excited electrons are then transferred to the Ni salt adsorbed on the Au nanoparticles and AlOOH surfaces, achieving the efficient preparation of single-atom Ni-modified AuNi alloy catalysts.

[0013] Preferably, in step 2, the Ni salt is selected from any one of Ni(NO3)2, NiCl2, NiSO4 and Ni(acac)2.

[0014] Preferably, in step 2, the concentration of the Ni salt solution is set to 10 g / L, and the usage ratio of the Au / AlOOH composite material, deionized water, Ni salt solution and methanol is 1.0 g: 50-150 mL: 10-100 mL: 30-100 mL. In the photodeposition process, methanol plays a vital role as a sacrificial agent in the consumption of holes and the overall photodeposition efficiency. Methanol can quickly react with photoexcited holes and effectively consume them, thereby inhibiting electron-hole recombination and prolonging the life of photogenerated electrons, which is beneficial to metal Ni. 2 The efficient reduction of metal ions is crucial. A moderate amount of methanol (30–100 mL) helps fully activate photogenerated electrons for the reduction reaction. However, excessive amounts of methanol (>100 mL) can introduce excessive concentrations of intermediate oxidation products (such as formaldehyde or formic acid). These intermediates may adsorb on the catalyst surface to a certain extent, thereby altering the catalyst's surface properties or interfering with the adsorption of reactants. Furthermore, excess organic components in the reaction system may disrupt the light absorption process, reducing the photoexcitation efficiency and indirectly affecting the reduction kinetics of metal ions.

[0015] Preferably, in step 2, the wavelength of the ultraviolet light is 250 to 350 nm, and the illumination time is 60 to 300 minutes. In contrast, visible light mainly induces the SPR effect, and the electron lifetime generated by it is too short and the energy is small. However, ultraviolet light can effectively stimulate the interband transition effect of Au nanoparticles, thereby generating photogenerated electrons with a longer lifetime, which can fully participate in and drive the Ni 2+ Therefore, using ultraviolet light as the main light source in the photodeposition process can significantly improve the Ni 2 + The reduction efficiency can be improved, thereby achieving better reaction performance during the catalyst construction process.

[0016] Preferably, the photodeposition reduction is performed under an inert atmosphere to maintain the stability of the AuNi alloy structure and the single-atom Ni.

[0017] The present invention further discloses a single-atom Ni-modified AuNi alloy catalyst prepared according to the above preparation method. The catalyst comprises an AlOOH support and a metal active component supported on the AlOOH support, wherein the metal active component comprises AuNi nanoalloy particles and single-atom Ni. The AuNi nanoalloy has a particle size of 5-15 nm.

[0018] The present invention also discloses the application of the single-atom Ni modified AuNi alloy catalyst in a photocatalytic CO2 reduction reaction, and the catalyst can efficiently convert CO2 into CH4.

[0019] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0020] 1) This invention utilizes a simple, mild, one-step photodeposition method to introduce Ni species. This method not only forms an AuNi alloy with the precious metal Au, but also precisely introduces Ni single atoms with unique properties. The simple operation process eliminates the need for high-temperature annealing or reducing atmosphere treatment, significantly simplifying the preparation process. Furthermore, the mild preparation conditions help maintain the stability of the alloy structure and single atoms, ensuring consistent catalyst performance.

[0021] 2) The introduction of single-atom Ni significantly enhances the catalyst's adsorption and activation of reactant molecules. This enhanced adsorption capacity promotes the effective reduction of CO2 and the efficient dissociation of H2O, generating more reaction intermediates. Furthermore, the high dispersion of single Ni atoms ensures the uniformity of active sites, further improving the catalyst's selectivity for reactants and reaction kinetics, thereby significantly enhancing the overall efficiency of the photocatalytic reaction.

[0022] 3) Single-atom Ni modification of relatively pure AuNi alloy catalysts can further optimize the electronic structure and geometric configuration of the active sites, thereby significantly improving the selectivity and efficiency of CO to CH4 conversion in the CO2 reduction reaction.

[0023] 4) The construction of AuNi alloy not only effectively reduces the amount of precious metal Au, but also greatly improves the separation and transmission efficiency of photogenerated electron-hole pairs. Only a Ni metal atom loading of 1 to 5 wt% is required to increase the reaction yield by more than 2 times. The amount of transition metal atoms added is at least 1 to 3 orders of magnitude lower than that of the existing technology, with low cost and high efficiency. Moreover, this feature enhances the selectivity of photocatalytic CO2 reduction to CH4 and the overall CO2 conversion activity. Stability tests show that the catalyst of the present invention exhibits excellent catalytic activity, selectivity and stability under visible light irradiation, and its catalytic performance does not show obvious attenuation after 8 hours of continuous reaction, showing broad application prospects in the field of sustainable energy.

[0024] 5) The preparation method of the present invention effectively overcomes the shortcomings of existing technologies, such as cumbersome preparation processes, low catalyst yields, and unstable structures. It specifically addresses the weak adsorption capacity of metal nanostructures for reactant molecules and the lack of active sites. This preparation method offers the advantages of cost-effectiveness, high efficiency, and ease of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 AlOOH, Au / AlOOH, AuNi-Ni prepared in the examples SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC / AlOOH-3's XRD pattern.

[0026] Figure 2 (a) to (d) are AuNi-Ni SAC / AlOOH-2 transmission electron microscopy, particle size distribution, high-resolution transmission electron microscopy and AC-HAADF-STEM images, (e) to (i) are AuNi-Ni at 50nm scale respectively. SAC Transmission electron microscope image of / AlOOH-2 and the corresponding EDS element distribution maps of O, Al, Au, and Ni.

[0027] Figure 3 (a) to (c) are the transmission electron microscopy images, high-resolution transmission electron microscopy images and particle size distribution diagrams of the Au / AlOOH sample respectively.

[0028] Figure 4 AlOOH, Au / AlOOH, Ni / AlOOH, AuNi-Ni prepared in the examples SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC XPS graph of UV-visible diffuse reflectance spectrum of / AlOOH-3;

[0029] Figure 5 (a) is Au / AlOOH and AuNi-Ni SAC / AlOOH-2 sample, (b) is the XPS full spectrum of AuNi-Ni SAC High-resolution XPS spectra of Ni 2p in Au / AlOOH-2, (c) and (d) are Au / AlOOH and AuNi-Ni, respectively. SAC High-resolution XPS spectra of Au 4f (c) and Al 2p (d) of / AlOOH-2 sample.

[0030] Figure 6 AlOOH, Au / AlOOH, Ni / AlOOH, AuNi / AlOOH, AuNi-Ni prepared in the examples SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC Comparison of the photocatalytic performance of AuNi-Ni / AlOOH-3, where: (a) is the yield of the reduction products CO, H2 and CH4; (b) is the selectivity of the products CO, H2 and CH4; (c) is the selectivity of the AuNi-Ni SAC / AlOOH-2 photocatalyst CO, H2 and CH4 yields as a function of reaction time; (d) AuNi-Ni under different light intensities SAC / CO yield of AlOOH-2.

[0031] Figure 7The Au / AlOOH, Ni / AlOOH, AuNi-Ni prepared in the examples SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC (a) Photoluminescence spectrum and (b) time-resolved fluorescence spectrum of / AlOOH-3. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the examples, so that those skilled in the art can understand the present invention. It is necessary to point out that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above-mentioned invention should still fall within the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or extraction methods that are not mentioned in detail are all process steps or extraction methods known to those skilled in the art; the instruments and equipment used in the following examples, unless otherwise specified, are all conventional laboratory instruments and equipment.

[0033] In the following examples, efforts have been made to ensure accuracy with respect to numbers used (including amounts, temperatures, reaction times, etc.) but some experimental errors and deviations should be accounted for.

[0034] Example 1

[0035] In this example, the single-atom Ni-modified AuNi alloy catalyst was prepared according to the following steps:

[0036] 1) Preparation of layered boehmite (AlOOH) carrier by microemulsion method

[0037] 100 mL of cyclohexane and 20 mg of polyethylene glycol were mixed and stirred at 50°C for 30 minutes. 20 mL of 0.3 mM aluminum nitrate and 3.5 mL of 27 wt% ammonia solution were added sequentially and stirred for another 30 minutes. The mixture was aged overnight at room temperature. 30 mL of isopropanol was then added and stirred for 5 minutes. The mixture was washed with deionized water and then centrifuged three times (10,000 rpm for 5 minutes) with ethanol. The precipitate was collected and dried in a vacuum oven at 60°C overnight to obtain a white powder. Finally, the powder was calcined in a muffle furnace at 450°C (heating rate of 5°C / min) for 2 hours to produce the AlOOH support.

[0038] 2) Preparation of Au nanoparticles

[0039] 3 mL of ice-bathed NaBH4 solution (0.1 M) was quickly added to 100 mL of 0.25 mM HAuCl4·xH2O solution. At this time, the color of the solution changed from light yellow to wine red. After stirring for 30 min, the obtained Au nanoparticle (Au NPs) solution was allowed to stand for aging for 24 h to completely hydrolyze the unreacted NaBH4 and then allowed to stand for use.

[0040] 3) Preparation of Au nanoparticles loaded with AlOOH

[0041] 1 g of AlOOH from step 1) was dispersed in 103 mL of the AuNPs solution (Au NPs concentration, 0.5 mM) from step 2). After sonication for 15 minutes, the mixture was stirred continuously at room temperature for 24 hours. The pink precipitate was collected by centrifugation (10,000 rpm, 5 minutes). The precipitate was placed in a freeze-drying oven overnight and then calcined in a muffle furnace at 400°C (heating rate, 1.25°C / min) for 2 hours to obtain an Au / AlOOH composite.

[0042] 4) Preparation of single-atom Ni-modified AuNi alloy catalysts

[0043] 1.0 g of the Au / AlOOH composite material powder prepared in step 3) was dispersed in 100 mL of deionized water and ultrasonically treated for 15 min. Ni(NO3)2·3H2O solution (10 g / L) was added under vigorous stirring, and after continuing to stir for 3 h, 50 mL of CH3OH was added to obtain a suspension; the suspension was irradiated with ultraviolet light under an argon atmosphere with a wavelength of 320 nm and an illumination time of 3 h. Finally, the obtained solution was washed with ultrapure water and centrifuged at 10,000 rpm for 10 min. After three cycles, the obtained precipitate was dried in a vacuum oven at 80 ° C for 12 h to obtain a single-atom Ni-modified AuNi alloy photocatalyst, which was recorded as AuNi-Ni SAC / AlOOH, and the amount of Ni(NO3)2·3H2O solution was adjusted to 5mL, 15mL, and 25mL respectively. The obtained samples were marked as AuNi-Ni SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2、AuNi-Ni SAC / AlOOH-3.

[0044] At the same time, the following samples were prepared for comparison:

[0045] Au / AlOOH: the Au / AlOOH composite material obtained in step 3) above.

[0046] Ni / AlOOH: The Au / AlOOH composite material in step 4) above was replaced with an equal amount of pure AlOOH support, and the amount of Ni(NO3)2·3H2O solution added was set to 15 mL. The resulting sample was Ni / AlOOH.

[0047] AuNi / AlOOH: 150 mg of Ni(NO₃)₂·6H₂O was dissolved in 100 mL of a 0.25 mM HAuCl₄·xH₂O solution. 1 g of AlOOH support was then added. The system was ultrasonically dispersed for 30 minutes, then magnetically stirred and heated at 80°C to gradually evaporate the solvent. The resulting solid powder was vacuum-dried at 80°C, ground into a fine powder, and then annealed at 400°C for 1 hour in a 5 vol% H₂ / Ar atmosphere to obtain the AuNi / AlOOH catalyst.

[0048] The samples prepared in this example were characterized as follows:

[0049] 1. Structural characterization:

[0050] First, the crystallinity and phase purity of the product were determined by XRD analysis. Figure 1 As shown in the figure, the diffraction peak of the prepared support AlOOH is clearly visible. SAC No diffraction peaks related to metallic Au and Ni were observed in the / AlOOH sample. Even when the Ni loading was increased to 5 wt%, no diffraction peaks related to Ni crystals were observed (JCPDS No. 21-1307). This may be because the loading of Au and Ni on the AlOOH surface is too low and they are highly dispersed on the support, resulting in their crystallinity being below the detection limit of XRD.

[0051] 2. Morphological characterization:

[0052] The prepared single-atom Ni modified AuNi alloy catalytic material (AuNi-Ni SAC / AlOOH-2) were characterized in terms of morphology, dispersion and element distribution. Figure 2 As shown in a, it is obvious that the spherical nanoparticles are dispersed relatively evenly, and the particle size distribution is shown in Figure 2 As shown in Figure 2b, the average particle size of the nanoparticles is about 5.5 nm, which is larger than the average particle size distribution of Au in Au / AlOOH (4.5 nm, as shown in Figure 2b). Figure 3 ), indicating that Ni may exist in the Au phase, resulting in the enlargement of the nanoparticle size. HRTEM image ( Figure 2c) shows clear lattice fringes. It can be seen from the figure that the lattice spacing is 0.22nm, 0.23nm and 0.235nm, which correspond to the (111) surface of AuNi nanoalloy, the (031) surface of the carrier AlOOH and the (111) surface of Au, respectively. SAC AuNi alloy exists in the / AlOOH-2 phase. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was used to observe the AuNi-Ni SAC / AlOOH-2 samples were observed. Figure 2 As shown in Figure d, many scattered bright spots (circled dots) with a size of about 0.3 nm were observed around the Au-Ni alloy nanoparticles, indicating that isolated Ni sites were dispersed on the AlOOH surface. Figure 2 ei), Au elements are mainly distributed on the carrier AlOOH in the form of nanoparticles. Figure 2 The uniform dispersion of Ni species observed in Figure 1, with a significant presence of Ni on the AuNPs, further indicates the formation of a Ni-Au alloy. Furthermore, relatively uniform dispersion of individual Ni elements was observed near the AuNi nanoparticles, demonstrating that the introduction of Ni species not only formed an AuNi alloy with Au but also existed as single atoms on the support surface. These morphological characterizations confirm the successful preparation of the single-atom Ni-modified AuNi alloy catalytic material.

[0053] 3. Light absorption characterization:

[0054] In order to study the effect of the introduction of Ni species on the light absorption properties of Au / AlOOH, the light absorption properties of the catalyst materials were tested by solid ultraviolet-visible diffuse reflectance spectroscopy (Uv-Vis DRS). Figure 4 As shown in Figure 2, the absorption band edge of Ni / AlOOH is around 450nm, and it only shows limited absorption below 450nm. Due to the localized plasmon resonance effect (LSPR, at 520nm) of Au NPs, Au / AlOOH and AuNi-Ni SAC / AlOOH samples have absorption in the range of 250-800nm, especially showing strong absorption in the visible light region. It is worth noting that the introduction of Ni species reduces the intensity of the LSPR peak, and as the Ni content increases from 1wt% to 5wt%, the LSPR absorption peak continues to decrease and a red shift occurs, which is consistent with the characteristics of metal alloying, indicating that the introduction of Ni species changes the structure of Au NPs and realizes Au-Ni alloying. Therefore, based on the above analysis results, it can be concluded that under light irradiation, Au with LSPR effect acts as an electron donor, while Ni species, as an electron acceptor, can effectively promote the generation and separation of photogenerated electrons and holes.

[0055] 4.Structure and valence characterization:

[0056] The AuNi-Ni SAC Surface chemical composition and element valence of / AlOOH-2. Figure 5 (a) shows the full XPS spectra of the sample before and after Ni addition. As can be seen from the figure, both samples contain C, Au, Al, and O. However, no obvious Ni characteristic peaks are found in the Ni-added sample, which is due to the relatively low Ni content and its high dispersion. Figure 5 b is AuNi-Ni SAC The high-resolution fine spectrum of Ni in / AlOOH-2 shows that the Ni 2p spectrum contains multiple sub-peaks due to multiple splitting and Ni satellite peaks. The binding energy peak is at 857.2eV, accompanied by a satellite binding energy peak at 862.1eV, which corresponds to the Ni 2p 3 / 2 orbital. The binding energy is at 874.9eV and the satellite peak is at 879.8eV, corresponding to Ni2p 1 / 2 orbital. Ni 2p 3 / 2 and Ni 2p 1 / 2 The main binding energy peak interval is 17.7eV, which is typical of Ni 2+ In addition, the peaks at 849.8eV and 868.4eV are attributed to metallic Ni 0 , indicating that AuNi-Ni SAC / AlOOH-2 also contains Ni 0 species, which is consistent with the above TEM analysis results. Figure 5 c is the high-resolution XPS spectrum of Au 4f of the Au / AlOOH sample before and after Ni addition. 7 / 2 and Au 4f 5 / 2 The two split orbitals are located at 83.6 and 87.2 eV, which correspond to the metallic state of Au. 0, and no other peaks appear. SAC In the Au 4f spectrum of / AlOOH-2, it is found that after the introduction of Ni species, the Au 4f 7 / 2 and Au 4f 5 / 2 The binding energies of Au and Ni shifted positively to 84.1 and 87.7 eV, respectively, indicating that electrons were transferred from Au to Ni. Figure 5 d shows the high-resolution XPS spectra of Al 2p before and after the introduction of Ni. It can be seen that the AuNi-Ni SAC The peak position of Al 2p in the Au / AlOOH-2 sample is consistent with that in the Au / AlOOH, both located at 74.3 eV, which indicates that the introduction of Ni has no effect on the electronic structure of the inert carrier AlOOH. The electron transfer only occurs between Au and Ni, which makes it difficult for Au and Ni to exert a strong interaction with AlOOH, and AlOOH only plays the role of carrier support.

[0057] 5. Evaluation of photocatalytic CO2 activity of catalytic materials:

[0058] The photocatalytic CO2 reduction reaction was carried out in a stainless steel reaction vessel (volume of about 450 mL) with a quartz window on the top for light irradiation. The temperature of the reaction system was controlled by an external heating element. A 300W xenon lamp (Perfil, Beijing) was used as the light source. The light source was 13.5 cm away from the catalyst surface. Before the photocatalytic reaction test, a certain amount of catalyst was weighed and placed in a glass container, and then the glass container was placed in the reaction vessel. After sealing, high-purity Ar gas (99.999%) was introduced for 30 minutes to ensure that the air in the reaction vessel was completely replaced, and the reactant CO2 was injected into the reaction vessel using a syringe. Subsequently, the light source was turned on for a photocatalytic activity test, and a certain amount of gas was extracted from the reaction vessel every hour, and the product was qualitatively and quantitatively analyzed by chromatography. The gas product was quantitatively calculated using the external standard method, and the yield was expressed in μmol g -1 h -1 Expression. CO2 reduction activity, selectivity and durability tests such as Figure 6 shown. Figure 6 a shows the average generation rates of CH4, H2, and CO during the photocatalytic CO2 reduction process of each photocatalyst. As can be seen from the figure, Au / AlOOH only exhibits the only CO product with a generation rate of 66.57 μmol g -1 h -1 . When Ni species were introduced into Au / AlOOH, the photocatalytic activity was significantly enhanced. This shows that Ni species as a co-catalyst may play an important role in improving charge separation and providing reaction active sites. It is worth noting that in addition to CO products, CH4 and H2 reduction products were also detected. Among them, the sample AuNi-Ni SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC The yields of the main product CO of / AlOOH-3 were 83.11, 130.61 and 56.78 μmol g -1 h -1 Correspondingly, the CH4 production was lower than the CO production, with yields of 7.60, 12.27, and 6.93 μmol g, respectively. -1 h -1 The yields of H2 were 45.95, 65.79, and 53.66 μmol g -1 h -1 Through the above analysis, it is found that with the AuNi-Ni SAC When the Ni content in AuNi-Ni / AlOOH increases from 0 to 3.0wt%, the CO generation rate increases gradually. SAC / AlOOH-2 had the highest CO yield, which was approximately twice that of Au / AlOOH, indicating the optimal Ni loading. Further increasing the Ni content to 5.0 wt% resulted in a decrease in CO yield. This resulted in a decrease in photocatalytic activity, which may be attributed to the formation of new sites for photoinduced carrier recombination due to the high Ni content. For Ni / AlOOH, only CO and H2 were detected, with yields of 16.34 and 13.98 μmol g, respectively. -1 h -1 This may be due to the lack of Au as an electron donor in the material, making it difficult for 8e - Therefore, the photocatalytic activity of Ni loaded on Au / AlOOH is significantly enhanced, which is attributed to the fact that the photogenerated electrons generated on the surface of AuNPs under light irradiation are transferred to the metal Ni, which effectively promotes the separation and transfer of charges and enhances the photocatalytic activity. In addition, the selectivity of the products CO, H2 and CH4 is compared. Figure 6 As shown in Figure b, the CO selectivity of Au / AlOOH is 100%. When the Ni content increases from 0wt% to 3.0wt%, the CO selectivity decreases from 100% to 47.0%, accompanied by the production of CH4 and H2. This indicates that the introduction of Ni reduces the CO selectivity. It is worth noting that in the AuNi-Ni SACIn the / AlOOH-2 sample, the selectivity for CH4 reached a maximum of 29.3%, while that for H2 reached 23.7%, indicating that the introduction of Ni facilitated further proton-electron coupling of *CO, promoting its conversion to CH4. Further increasing the Ni content to 5.0wt%, the CH4 selectivity dropped to 20.0%, while the CO selectivity further decreased to 41.1%, while the H2 selectivity increased to 38.8wt%, indicating that higher Ni content is detrimental to the conversion of *CO to CH4, with protons favoring the production of H2. Therefore, the above results demonstrate that the introduction of an appropriate amount of Ni promotes the conversion of *CO to CH4.

[0059] like Figure 6 As shown in c, the optimized catalyst AuNi-Ni SAC The yields of CO, H2, and CH4 on the surface of MgO / AlOOH-2 vary with illumination time. As can be seen from the figure, the production of each product increases with the increase of illumination time within 8 hours of reaction. The final production of CO, H2, and CH4 within 8 hours is 741.83, 487.60, and 129.23 μmol g, respectively. -1 Moreover, there is no obvious deactivation of the catalyst during the photocatalytic process, indicating that the catalyst has good stability. Figure 6 Figure d shows the photocatalytic activity of a 420nm LED light source with varying light intensities modulated by a light intensity modulator. As can be seen, the CO yield increases linearly with increasing light intensity. This linear dependence indicates that the photocatalytic CO reduction reaction is primarily an electron-driven process.

[0060] 6. Characterization of carrier separation efficiency:

[0061] Each photocatalytic material was characterized by steady-state (PL) / transient fluorescence (TRPL) and photoelectrochemical properties. Figure 7 As shown in a, the steady-state photoluminescence (PL) spectrum of the samples was first tested to further study the recombination rate of photogenerated carriers. As can be seen from the figure, all samples showed strong fluorescence intensity under 340nm light excitation. Compared with single metal Ni / AlOOH and Au / AlOOH, AuNi-Ni SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC / AlOOH-3 fluorescence peak weakened, and the photoluminescence lifetime prolonged, indicating that the separation ability of photogenerated electrons and holes was enhanced after the introduction of Ni species on Au / AlOOH. SAC / AlOOH-2 has the lowest fluorescence intensity, indicating that it has the best effect on the separation of photogenerated carriers. In order to further study the dynamic characteristics of photoinduced carriers in photocatalysts, time-resolved photoluminescence spectroscopy (TRPL) was used to study the fluorescence decay lifetime (τ) of photogenerated carriers. Figure 7 b shows the time-resolved photoluminescence spectra of all catalyst samples and the corresponding average lifetime of carriers. SAC / AlOOH-1、AuNi-Ni SAC / AlOOH-2 and AuNi-Ni SAC The average fluorescence decay lifetime (τ Ave ) are 3.43, 4.14, 4.65, 4.71 and 4.27 ns respectively. SAC The average fluorescence decay lifetime of Au / AlOOH is higher than that of Au / AlOOH and Ni / AlOOH, indicating that the introduction of Ni species increases the lifetime, and AuNi-Ni SAC Au / AlOOH-2 exhibits the longest fluorescence lifetime. This increased lifetime, τ, increases the likelihood that these sites participate in the photocatalytic reaction before recombination. This further demonstrates the contribution of Ni sites to the enhanced charge separation efficiency, consistent with the activity trend. Therefore, from the above analysis, the decreased PL intensity and increased fluorescence lifetime provide strong evidence that Ni modification on the Au / AlOOH surface accelerates electron transfer and inhibits carrier recombination.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a single-atom Ni-modified AuNi alloy catalyst, characterized in that: The following steps are involved: Step 1: adding an AlOOH carrier to an Au nanoparticle solution, sequentially subjecting the Au nanoparticles to ultrasound and mechanical stirring to allow the AlOOH and Au nanoparticles to self-assemble under electrostatic interaction, and then collecting the precipitate by centrifugal washing; freeze-drying the precipitate and then annealing it to obtain an Au nanoparticle-loaded AlOOH composite material, denoted as Au / AlOOH; Step 2: Add the Au / AlOOH composite material obtained in step 1 to deionized water and disperse it evenly by ultrasonication, then add the Ni salt solution and methanol under vigorous stirring to obtain a suspension; irradiate the suspension with ultraviolet light under an inert gas atmosphere, and reduce the Ni salt by electrons synergistically generated by the photoexcitation of Au nanoparticles and AlOOH; after the irradiation, the obtained solution is centrifuged and washed to collect the precipitate and dry it to obtain a single-atom Ni-modified AuNi alloy photocatalyst.

2. The preparation method according to claim 1, characterized in that In step 1, the concentration of the Au nanoparticle solution is 0.1-1 mM, and the usage ratio of the AlOOH carrier to the Au nanoparticle solution is 0.1-2.5 g / 103 mL.

3. The preparation method according to claim 1, characterized in that In step 1, the particle size of the Au nanoparticles is 4-12 nm.

4. The preparation method according to claim 1, characterized in that In step 2, the Ni salt is selected from any one of Ni(NO3)2, NiCl2, NiSO4 and Ni(acac)2.

5. The preparation method according to claim 1, characterized in that In step 2, the concentration of the Ni salt solution is set to 10 g / L, and the usage ratio of the Au / AlOOH composite material, deionized water, Ni salt solution, and methanol is 1.0 g: 50-150 mL: 10-100 mL: 30-100 mL.

6. The preparation method according to claim 1, characterized in that In step 2, the wavelength of the ultraviolet light is 250 to 350 nm, and the illumination time is 60 to 300 minutes.

7. A single-atom Ni-modified AuNi alloy catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. The single-atom Ni-modified AuNi alloy catalyst according to claim 7, characterized in that: The catalyst comprises an AlOOH carrier and a metal active component supported on the AlOOH carrier, wherein the metal active component consists of AuNi nano alloy particles and single-atom Ni.

9. The single-atom Ni-modified AuNi alloy catalyst according to claim 8, characterized in that: The particle size of the AuNi nano alloy particles is 5-15 nm.

10. Use of the single-atom Ni modified AuNi alloy catalyst according to claim 7, 8 or 9, characterized in that: Used for photocatalytic CO2 reduction reaction to convert CO2 into CH4.

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