Nickel-loaded nitrogen-sulfur double-doped carbon material photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a nickel-loaded nitrogen-sulfur double-doped carbon material photocatalyst and a preparation method and application thereof.The preparation method includes the steps that 5-amino-1H-tetrazole, 2-mercaptoimidazole and nickel salt serve as raw materials and are mixed with a lithium chloride / potassium chloride molten salt medium, the mixture is ground, pyrolyzed in the inert atmosphere and then subjected to acid pickling, water washing, organic solvent washing and drying, and the nickel-loaded nitrogen-sulfur double-doped carbon material photocatalyst is obtained. The method disclosed by the invention is simple in process, environment-friendly and easy for large-scale production; the obtained photocatalyst has a rich mesoporous structure, the BET specific surface area is 20-30 m < 2 > / g, the average pore size is 14-25 nm, high dispersion of metal nickel atoms can be achieved, the metal nickel atoms, nitrogen and sulfur form a co-doped structure, the light absorption spectrum range of the photocatalyst is remarkably widened, and the charge separation efficiency and the activity of converting carbon dioxide into C2 are improved.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst material preparation, specifically to a nickel-loaded nitrogen-sulfur dual-doped carbon photocatalyst, its preparation method, and its application. Background Technology

[0002] Converting carbon dioxide into high-value-added chemicals or fuels is a key pathway to achieving carbon resource recycling and alleviating energy and environmental pressures. Photocatalysis, which utilizes solar energy to drive CO2 reduction reactions, is considered a promising solution. Among numerous photocatalytic materials, graphitic carbon nitride has been extensively studied due to its suitable band structure, good chemical stability, and simple preparation. However, unmodified graphitic carbon nitride inherently suffers from limited visible light absorption, small specific surface area, and easy recombination of photogenerated electron-hole pairs, severely restricting its catalytic efficiency.

[0003] To overcome these limitations, researchers have proposed various modification strategies, among which the introduction of metal species such as nickel, cobalt, and iron for doping is considered to effectively modulate the electronic structure, broaden the light absorption range, and promote charge separation. However, traditional metal doping methods often fail to achieve a high degree of dispersion of metal active centers, easily leading to nanoparticle aggregation and significantly reducing the available active sites. More importantly, most existing modified photocatalysts, including metal-doped carbon nitride materials, generally exhibit a high selectivity for C1 compounds such as carbon monoxide and methane in CO2 reduction reactions, while showing very low selectivity or even no formation of high-value C2 products such as ethylene and ethane, which require carbon-carbon coupling. This bottleneck mainly stems from the fact that traditional doping methods easily lead to the aggregation of metal nanoparticles, reducing the available active sites; unmodified materials have a high photogenerated electron-hole recombination rate and a narrow visible light absorption range; and the catalyst surface struggles to simultaneously and efficiently activate multiple CO2 molecules and guide the directional coupling of reaction intermediates.

[0004] Therefore, developing a novel photocatalyst that can achieve high metal dispersion, well-defined active site structure, and efficient carbon-carbon coupling capability is of urgent practical significance for improving the selectivity and efficiency of CO2 reduction to prepare multi-carbon products and promoting the practical development of this technology. Summary of the Invention

[0005] The present invention aims to provide a nickel-loaded nitrogen-sulfur co-doped carbon photocatalyst, its preparation method, and its application. The preparation method is simple, environmentally friendly, and easy to scale up. The resulting photocatalyst has a rich mesoporous structure, enabling high dispersion of metallic nickel and co-doping with nitrogen and sulfur, significantly improving the visible light absorption spectrum range, charge separation efficiency, and carbon dioxide to C2 conversion activity of the photocatalyst.

[0006] To achieve the above objectives, the present invention proposes the following technical solution:

[0007] A method for preparing a nickel-supported nitrogen-sulfur dual-doped carbon photocatalyst includes the following steps:

[0008] (1) The first component and the second component are mixed and ground at a mass ratio of 1:(5-10) to obtain a precursor mixture; wherein the first component is composed of a nitrogen-containing organic precursor, a sulfur-containing organic precursor and a nickel salt, and the second component is a molten salt medium;

[0009] (2) Under an inert atmosphere, the precursor mixture obtained in step (1) is heated to 500-600°C at a heating rate of 1-5°C / min and kept at this temperature for 2-6 hours to complete the pyrolysis reaction and obtain the pyrolysis product; (3) The pyrolysis product obtained in step (2) is impregnated with an acid solution to remove the molten salt medium and some unstable nickel species; then it is washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst.

[0010] As a preferred embodiment of the present invention, the second component is a mixture of lithium chloride and potassium chloride in a mass ratio of (0.5-1):1.

[0011] As a preferred embodiment of the present invention, the mass ratio of the nitrogen-containing organic precursor to the sulfur-containing organic precursor in the first component is (1-4):1.

[0012] As a preferred embodiment of the present invention, the nickel salt accounts for 5%-8% of the total mass of the nitrogen-containing organic precursor and the sulfur-containing organic precursor.

[0013] As a preferred embodiment of the present invention, the nitrogen-containing organic precursor is 5-amino-1H-tetrazole.

[0014] As a preferred embodiment of the present invention, the sulfur-containing organic precursor is 2-mercaptoimidazole.

[0015] As a preferred embodiment of the present invention, the nickel salt is any one of nickel chloride, nickel nitrate, and nickel acetate.

[0016] The present invention also provides a nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst, which is prepared by the preparation method of the nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst.

[0017] As a preferred embodiment of the present invention, the photocatalyst has a mesoporous structure; its specific surface area is 20-30 m². 2 / g, porosity 0.05-0.07cm3 / g, with an average pore size of 14-25nm.

[0018] The present invention also provides an application of a nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst, wherein the photocatalyst is applied in a photocatalytic CO2 reduction reaction, and the product of the photocatalytic CO2 reduction reaction includes C2 alkanes.

[0019] As can be seen from the above technical solutions, the technical solution of the present invention provides a nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst, its preparation method and application, which has the following advantages compared with the prior art:

[0020] The photocatalyst prepared in this invention introduces nickel species into a sulfur-doped carbon nitride framework and modulates the precursor ratio, resulting in a significant red shift in the light absorption edge of the material. The narrower band gap and wider absorption range directly enhance the light-harvesting ability of the catalyst, thereby increasing the concentration of photogenerated carriers (electrons and holes) and providing more energy sources for driving the reaction.

[0021] Nickel species act as electron traps, capturing photogenerated electrons and transferring them to CO2 molecules, thus reducing electron-hole recombination. Nitrogen-sulfur doping introduces defect energy levels that serve as electron transition platforms, extending carrier lifetime and improving quantum efficiency. Photoluminescence spectroscopy shows a significant decrease in the emission peak intensity of Example 1, confirming that electron-hole recombination is effectively suppressed.

[0022] Nickel species are atomically dispersed in the photocatalyst, coordinating with nitrogen and sulfur to form single-atom active centers, providing a high density of sites for CO2 adsorption and activation. Sub-nanometer nickel clusters promote electron transfer and coupling with intermediates, which is key to C / C bond formation. Nanoscale nickel particles act as electron collectors, enhancing overall conductivity and stabilizing reaction intermediates. The gradient distribution of nickel species of different sizes within the mesoporous carbon framework forms continuous electron transport pathways, optimizing reaction kinetics.

[0023] The method of this invention achieves high dispersion and efficient utilization of nickel species in a nitrogen-sulfur co-doped carbon framework, resulting in high atom utilization. Simultaneously, the unique electronic structure optimizes the material's light absorption range and charge separation efficiency, jointly promoting enhanced photocatalytic performance and enabling the efficient conversion of CO2 resources into high-value chemicals.

[0024] Furthermore, unlike traditional photocatalysts which typically generate C1 products such as CO or CH4, this invention, through precise design of multi-scale nickel active sites, successfully guides the reaction pathway toward C-C coupling, achieving selective generation of C2 hydrocarbons such as ethylene and ethane.

[0025] This invention employs a one-step molten salt pyrolysis method, which is simple in process, requires no complex templates or post-processing steps, is easy to scale up, and yields high output. The raw materials used are inexpensive and readily available, and the reaction process does not require the use of toxic or harmful reagents, making it environmentally friendly.

[0026] The photocatalyst prepared by this invention has a well-developed mesoporous structure and a BET specific surface area of ​​20-30 m². 2 / g, with an average pore size of 14-25nm. This structure facilitates the diffusion and mass transfer of reactants and products, and exposes more active sites, thereby improving catalytic efficiency.

[0027] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0028] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0029] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0030] Figure 1 The XRD patterns are of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalysts prepared in Examples 1, 2, and 3 of this invention, and the photocatalysts obtained in Comparative Examples 1 and 2.

[0031] Figure 2 Transmission electron microscope (TEM) images of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalysts prepared in Examples 1 and 2 of this invention, and the photocatalysts obtained in Comparative Examples 1 and 2.

[0032] Figure 3 This is a comparison chart of the CO2 reduction reaction yields of the nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalysts prepared in Examples 1, 2, and 3 of the present invention and the photocatalysts obtained in Comparative Examples 1 and 2.

[0033] Figure 4 The image shows a cycle test diagram of the reduction of CO2 to C2H4 and C2H6 of the nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst prepared in Example 1 of this invention.

[0034] Figure 5 The N2 adsorption curve and embedded pore diagram of the nickel-loaded nitrogen-sulfur dual-doped carbon material prepared in Example 1 of this invention are shown.

[0035] Figure 6 The N2 adsorption curve and embedded pore diagram of the nickel-loaded nitrogen-sulfur dual-doped carbon material prepared in Example 2 of this invention are shown.

[0036] Figure 7 The N2 adsorption curve and embedded pore diagram of the nickel-loaded nitrogen-sulfur dual-doped carbon material prepared in Example 3 of this invention are shown.

[0037] Figure 8 Fourier transform infrared (FTIR) spectra of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalysts prepared in Examples 1, 2, and 3 of this invention, and the photocatalysts obtained in Comparative Examples 1 and 2.

[0038] Figure 9 The photoluminescence spectra of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalyst prepared in Example 1 of this invention and the photocatalyst obtained in Comparative Example 3 are shown below.

[0039] Figure 10 The ultraviolet-visible diffuse reflectance spectra of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalyst prepared in Example 1 of this invention and the photocatalysts obtained in Comparative Examples 1 and 2 are shown.

[0040] Figure 11 This is a comparison of the yield of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalyst prepared in Example 1 of the present invention and the photocatalyst obtained in Comparative Example 3. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art.

[0042] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" indicate that the element or object preceding "comprising" encompasses the features, wholes, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or sets thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0043] To address the shortcomings of existing photocatalysts in terms of visible light absorption range, charge separation efficiency, and catalytic selectivity for C2 olefins, this invention provides a nickel-loaded nitrogen-sulfur dual-doped carbon material photocatalyst. When applied in the photocatalytic CO2 reduction reaction, the photocatalyst produces not only C1 products such as CO or CH4, but also C2 hydrocarbon products such as ethylene and ethane.

[0044] The specific preparation method of the photocatalyst in this embodiment of the invention includes the following steps:

[0045] (1) The first component and the second component are thoroughly mixed and ground in a mass ratio of 1:(5-10) to obtain a precursor mixture. Defect energy levels are introduced by nitrogen-sulfur dual doping to capture photogenerated electrons; nickel species act as an electron transfer bridge to rapidly transfer electrons to CO2 molecules.

[0046] The first component includes a nitrogen-containing organic precursor, a sulfur-containing organic precursor, and a nickel salt, wherein the mass ratio of the nitrogen-containing organic precursor to the sulfur-containing organic precursor is (1-4):1; and the nickel salt accounts for 5%-8% of the mass of the nitrogen-containing organic precursor and the sulfur-containing organic precursor.

[0047] The nitrogen-containing organic precursor is 5-amino-1H-tetrazole. This molecule has an extremely high nitrogen-to-carbon ratio (N / C=5) and can efficiently form triazine or heptaazine ring units during pyrolysis, making it an excellent nitrogen source for constructing the main framework of photocatalysts.

[0048] The sulfur-containing organic precursor is 2-mercaptoimidazole. Its molecular structure contains both an imidazole ring and a thiol group. During pyrolysis, it can not only serve as a sulfur doping source, but its nitrogen-containing heterocycle can also participate in the construction of the carbon nitride framework, thereby enabling sulfur atoms to be embedded into the carbon-nitrogen network in a more uniform and stable manner, avoiding the uneven doping or structural damage that may be caused by using an external sulfur source alone.

[0049] The nickel salt is any one of nickel chloride, nickel nitrate, and nickel acetate. This embodiment of the invention selects any one of these three nickel salts as the nickel source based on their comprehensive reaction characteristics in the molten salt pyrolysis system, aiming to achieve high dispersion of metallic nickel atoms and effective coordination with nitrogen and sulfur atoms, while avoiding the introduction of difficult-to-remove impurity anions. During the grinding process, it easily forms a homogeneous mixture at the molecular level with nitrogen-containing organic precursors, sulfur-containing organic precursors, and the molten salt medium. This initial homogeneity is a key prerequisite for ensuring that nickel substances can migrate and disperse from the atomic level during subsequent pyrolysis, rather than directly agglomerating into larger nanoparticles. All three nickel salts can undergo effective thermal decomposition or transformation within the pyrolysis temperature range of 500-600℃. Their anions (Cl... - NO3 - CH3COO - At this temperature, it can completely decompose or exist in gaseous form (such as HCl, NO). X (CO2) escapes from the reaction system, or forms soluble complexes in the molten salt medium and is thus effectively removed.

[0050] This invention does not employ mixed nickel salts because the decomposition temperatures, rates, and interactions with molten salts of different anions vary, potentially leading to uneven local reaction environments and interfering with the directional dispersion and coordination of nickel species. Furthermore, the core reason for selecting these three specific nickel salts is that their anions do not form unstable or difficult-to-remove residues in the final carbon material framework.

[0051] The second component is a molten salt medium, a mixture of lithium chloride and potassium chloride in a mass ratio of 0.5-1:1. Potassium chloride (KCl) alone has a melting point of approximately 770°C, while lithium chloride (LiCl) has a melting point of approximately 610°C. When the two are mixed in a specific mass ratio (preferably 0.5:1 to 1:1 in this invention), a eutectic mixture can be formed, with a eutectic point much lower than the melting point of the single component (down to approximately 350°C). This allows the pyrolysis reaction to proceed at a relatively low temperature (500-600°C in this invention), where the molten salt becomes liquid. This not only significantly reduces energy consumption but also lowers the high-temperature resistance requirements of the reaction equipment, making the process more economical, safer, and easier to scale up.

[0052] (2) Under the protection of nitrogen or argon inert atmosphere with a purity of 99.99%, the precursor mixture is subjected to a programmed temperature rise pyrolysis reaction, wherein the heating rate is 1-5℃ / min, and when the temperature is raised to 500-600℃, it is held for 2-6h to obtain the pyrolysis product.

[0053] (3) The pyrolysis product is soaked in an acidic solution such as dilute hydrochloric acid for 12-24 hours to remove the residual molten salt medium. Then, it is washed with organic solvents such as deionized water and anhydrous ethanol to remove the residual organic matter. After drying, the photocatalyst is obtained.

[0054] The molar concentration of the acid solution is 2-3 M. The pyrolysis products are impregnated with the acid solution to remove inactive nickel species and residual molten salt media formed during pyrolysis, exposing atomically dispersed nickel active sites; at the same time, the carbon framework can be partially etched to enhance pore connectivity and further improve the specific surface area and pore size distribution uniformity.

[0055] First, anhydrous ethanol is used to remove residual acid solution and organic matter from the surface. Then, deionized water is used to wash away the acid solution and anhydrous ethanol from the product surface to prevent pore blockage and passivation of active sites.

[0056] The photocatalyst prepared in the embodiments of this invention has a typical mesoporous structure. The mesoporous channels provide spatial confinement for the CO intermediate, increasing its local concentration and promoting dimerization. The nickel-nitrogen-sulfur active sites on the pore surface provide directional adsorption configurations, guiding the intermediate towards the C2 product pathway. Its BET specific surface area is 20-30 m². 2 / g, porosity 0.05-0.07cm 3 / g, with an average pore size of 14-25nm. This porous structure facilitates the diffusion and mass transfer of reactants and products, while also exposing more active sites, thereby improving catalytic efficiency.

[0057] Example 1

[0058] (1) Place 0.5g of 5-amino-1H-tetrazole (5-AT), 0.125g of 2-mercaptoimidazole (S-Im), 0.05g of nickel chloride hexahydrate (NiCl2·6H2O), and 6.25g of lithium chloride / potassium chloride mixed molten salt (LiCl to KCl mass ratio of 1:1) in an agate mortar and grind and mix thoroughly for 30 minutes to obtain a homogeneous precursor mixture. The mass ratio of nitrogen-containing organic precursor to sulfur-containing organic precursor is 4:1, the nickel salt accounts for 8% of the mass of nitrogen-containing organic precursor and sulfur-containing organic precursor, and the ratio of the total mass of the molten salt medium to the total mass of the two precursor compounds and the nickel salt is approximately 9:1.

[0059] (2) Transfer the precursor mixture obtained in step (1) to an alumina crucible and place it in a tube furnace. Purge with high-purity nitrogen (purity ≥ 99.99%) to purge air and maintain a nitrogen atmosphere. Proceed from room temperature to 550°C at a heating rate of 2.5°C / min and hold at that temperature for 4 hours. After the reaction is complete, allow it to cool naturally to room temperature.

[0060] (3) The pyrolysis block product obtained in step (2) was taken out and crushed, and then immersed in 60 mL of dilute hydrochloric acid solution (molar concentration of 2.5 M) and left to stand overnight (about 12 hours) at room temperature. Subsequently, it was repeatedly washed with deionized water until the filtrate was neutral, and then washed three times with anhydrous ethanol. Finally, the solid product was dried in a vacuum drying oven at 60 °C for 12 hours to obtain a brown final photocatalyst sample, denoted as CNS. 4 / 1 -Ni.

[0061] Example 2

[0062] (1) 0.5g 5-AT, 0.5g S-Im, 0.05g nickel chloride hexahydrate and 5.25g lithium chloride / potassium chloride mixed molten salt (LiCl to KCl mass ratio of 0.9:1) were thoroughly mixed and ground evenly. Among them, the mass ratio of 5-AT to S-Im was 1:1, the nickel salt accounted for 5% of the mass of nitrogen-containing organic precursor and sulfur-containing organic precursor, and the ratio of the total mass of the molten salt medium to the total mass of the two precursors and the nickel salt was approximately 5:1.

[0063] (2) Under the protection of argon atmosphere (purity ≥ 99.99%), the precursor mixture is heated to 500℃ at a rate of 3℃ / min and kept at this temperature for 3 hours.

[0064] (3) The cooled pyrolysis product was impregnated with dilute hydrochloric acid (3 M molar concentration) for 24 hours, then washed with deionized water and anhydrous ethanol, and dried under vacuum at 70 °C to obtain the photocatalyst, denoted as CNS. 1 / 1 -Ni.

[0065] Example 3

[0066] (1) 0.5g 5-AT, 0.25g S-Im, 0.05g nickel nitrate and 7.2g lithium chloride / potassium chloride mixed molten salt (LiCl to KCl mass ratio of 0.7:1) were thoroughly mixed and ground evenly. Among them, the mass ratio of 5-AT to S-Im was 2:1, the nickel salt accounted for 6.6% of the mass of nitrogen-containing organic precursor and sulfur-containing organic precursor, and the ratio of the total mass of the molten salt medium to the total mass of the two precursors and nickel salt was 9:1.

[0067] (2) Under the protection of nitrogen (purity ≥ 99.99%) atmosphere, the precursor mixture is heated to 600℃ at a rate of 5℃ / min and kept at this temperature for 4.5 hours.

[0068] (3) The cooled pyrolysis product was impregnated with dilute hydrochloric acid (2M molar concentration) for 15 hours, then washed with deionized water and anhydrous ethanol, and dried under vacuum at 50°C to obtain the photocatalyst, denoted as CNS. 2 / 1 -Ni.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that 2-mercaptoimidazolium is not added; only 5-amino-1H-tetrazole and nickel chloride are used. The remaining steps and parameters are exactly the same as in Example 1. The resulting photocatalyst is denoted as Ni-5AT.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 1 is that 5-amino-1H-tetrazole is not added; only 2-mercaptoimidazolium and nickel chloride are used. The remaining steps and parameters are exactly the same as in Example 1. The resulting photocatalyst is denoted as Ni-SM.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 1 is that no mixed molten salt of LiCl and KCl is added. All other steps and parameters are exactly the same as in Example 1. The resulting catalyst is denoted as CNS. 4 / 1 -Ni(ns).

[0075] The photocatalysts obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing. The specific testing procedures are as follows:

[0076] (1) Weigh 5 mg of the photocatalyst powder obtained in Examples 1, 2 and 3 respectively. Add 5 mL of deionized water and 15 mL of acetonitrile to each portion of photocatalyst powder as solvents, add 5 mL of triethanolamine (TEOA) as a sacrificial agent, and add C 30 H 24 Cl2N6Ru·6H2O was used as a photosensitizer, and a uniformly dispersed photocatalyst suspension was obtained by sonication at room temperature for 0.5 hours.

[0077] This invention selects acetonitrile as a solvent for photocatalysts based on its physicochemical properties, which has the following advantages:

[0078] CO2 has a much higher solubility in acetonitrile than in water or other common organic solvents. This is because the moderate polarity of acetonitrile and its weak interaction with CO2 molecules provide an ideal environment for accommodating CO2 molecules. Higher CO2 solubility means a higher concentration of reactants near the photocatalyst surface, which is a key factor in increasing the reaction rate.

[0079] Acetonitrile exhibits high chemical stability under photocatalytic reaction conditions, especially in the presence of photosensitizers and sacrificial agents. It is not easily oxidized by photogenerated holes and does not undergo side reactions with highly reactive reaction intermediates. This ensures that photogenerated charge carriers are maximized for the target reaction rather than being consumed in solvent decomposition.

[0080] Furthermore, acetonitrile effectively wets and disperses the nickel-loaded nitrogen-sulfur dual-doped carbon material, ensuring uniform suspension of the photocatalyst particles and full exposure of active sites. In addition, in this test system, the ruthenium-based complex exhibits good solubility and photochemical stability in acetonitrile, effectively absorbing light energy and generating excited-state electrons. Triethanolamine, on the other hand, dissolves effectively in a mixture of acetonitrile and water, thus functioning as an electron donor.

[0081] (2) Weigh 5 mg of the catalyst powder obtained from Comparative Example 1, Comparative Example 2 and Comparative Example 3 respectively. Add 5 mL of deionized water and 15 mL of acetonitrile to each part of photocatalyst powder, and add 5 mL of triethanolamine (TEOA) as a sacrificial agent, and add C 30 H 24 Cl2N6Ru·6H2O was used as a photosensitizer, and a uniformly dispersed photocatalyst suspension was obtained by sonication at room temperature for 0.5 hours.

[0082] (3) In the CO2 reduction reaction performance test, the suspensions obtained in steps (1) and (2) were compared and tested. The specific experimental method is as follows: First, the suspension was poured into a high-transmittance quartz reactor. Then, the sealed reactor was evacuated for 10 min, and an appropriate amount of Ar (purity ≥ 99.99%) was added. After mixing for 15 min, the reactor was evacuated again. The above operation was repeated twice to clean the impurities. Then, an appropriate amount of CO2 (99.999%) was added and mixed for 15 min. The reactor was irradiated with sunlight for 4 hours using a 300W xenon lamp to establish the photocatalytic CO2 reduction reaction system of the photocatalyst.

[0083] Every hour, the gas produced in the reactor in step (3) is extracted, and then the collected gas is qualitatively and quantitatively analyzed using a detector in a gas chromatograph, such as... Figure 3 The figures show the catalytic effects of the photocatalysts in Examples 1-3 and Comparative Examples 1-2. Whether preparing C1 gases such as methane and carbon monoxide, or C2 gases such as ethylene and ethane, Example 1 is better than Examples 2 and 3. Figure 3 As shown in (b), the C2 yields of the photocatalysts in Examples 1-3 were significantly higher than those in Comparative Examples 1 and 2, with the C2 yield of the photocatalyst in Example 1 being significantly higher. 4 / 1 The yield of Ni in C2H6 was 31.05 μmol·g. -1 ·h -1 The yield of C2H4 was 1.75 μmol·g. -1 ·h -1 The yield of CH4 was 30.95 μmol·g. -1 ·h -1 The CO yield was 133.95 μmol·g.-1 ·h -1 The yields of other photocatalysts are shown in Table 1 below.

[0084] like Figure 4 The figure shows a cyclic test diagram of CO2 reduction to C2H4 and C2H6 of the nickel-loaded nitrogen-sulfur dual-doped carbon photocatalyst prepared in Example 1 of this invention. 4 / 1 After multiple cycles of reaction, the yield of C2H6 decreased to 84.4%, demonstrating good structural stability and catalytic durability.

[0085] Table 1. Photocatalytic performance test results of the photocatalysts in the examples and comparative examples.

[0086] Conclusions and analysis of the above photocatalysts:

[0087] (1) such as Figure 2 The diagram shows the morphological characteristics of the photocatalysts obtained in various embodiments and comparative examples of the present invention. Figure 2 (a) Corresponding to Example 1, Figure 2 (b) Corresponding to Example 2, Figure 2 (c) Corresponding to ratio 1, Figure 2 (d) Corresponding ratio 2; of which Figure 2 (a) The sample exhibits a clear layered structure with a large number of small pores with a diameter between 14 and 25 nm distributed on its surface, while Comparative Example 1 and Comparative Example 2 do not have a similar structure.

[0088] Compared to Example 1, Comparative Example 1 contains only a nitrogen precursor and a nickel salt, lacking a sulfur precursor. This results in a simpler electronic structure of the carbon framework and lower photogenerated charge separation efficiency. Furthermore, the nickel species only coordinate with nitrogen, exhibiting poor dispersion and a tendency to aggregate into larger particles, thus reducing active sites. As shown in Table 1, the ethane yield of Comparative Example 1 is only 0.18 μmol·g. -1 ·h -1 This indicates that sulfur doping is key to CC coupling, and its UV-Vis spectrum shows a blue shift at the absorption edge, indicating a decrease in visible light utilization.

[0089] Compared to Example 1, Comparative Example 2 contains only sulfur precursor and nickel salt, lacking nitrogen precursor. This results in the inability to form a graphitic carbon nitride framework, leading to a disordered material structure and extremely low specific surface area. Although sulfur doping alone provides electron donors, the lack of nitrogen electron acceptors results in an unreasonable band structure. As shown in Table 1, its ethylene yield is only 0.35 μmol·g. -1 ·h -1 This indicates that nitrogen doping is the basis for stabilizing the structure and controlling the energy band.

[0090] The combined results of Comparative Examples 1 and 2 demonstrate that neither nitrogen nor sulfur doping alone can achieve excellent C2 product formation activity. Nitrogen and sulfur doping are indispensable in this invention; their synergistic effect, together with highly dispersed nickel species, constructs a unique and efficient electronic structure and reaction microenvironment, which is crucial for achieving highly selective C2 product formation.

[0091] (2) such as Figure 5-7 The figures shown are the N2 adsorption curves and embedded pore diagrams for Examples 1, 2, and 3, respectively. Specific surface areas and pore structure parameters are shown in Table 2. The specific surface areas of each photocatalyst range from 20-30 m². 2 The material has a porosity between 14-25 nm and a pore size between 1 / g. Its pore size distribution map shows that the pore size distribution is relatively concentrated. The material constructs a regular narrow mesoporous structure, which provides an ideal channel for low-resistance diffusion for efficient mass transfer of reactants and products, reduces mass transfer limitations, and is also conducive to exposing more active sites and promoting light absorption. The high porosity ensures that the reactants fully contact the active sites and improves the photocatalytic CO2 reduction activity.

[0092] Table 2. Specific surface area and pore structure parameters of the photocatalysts obtained in Examples 1-3

[0093]

[0094] (3) such as Figure 8 The image shows the Fourier transform infrared (FTIR) spectra of the photocatalysts prepared in Examples 1, 2, and 3, and Comparative Examples 1 and 2. All samples are in the range of 2900-3600 cm⁻¹. -1 A broad absorption band is observed across the entire range, attributed to the stretching vibration of the NH bond, indicating the presence of amine groups or uncondensed terminal amine groups in the material. At 2160 cm⁻¹... -1 Near the 1200-1600 cm⁻¹, Comparative Examples 1 and 2 show distinct sharp absorption peaks, which can be attributed to the stretching vibrations of the residual cyano group (-C≡N) in the structure; -1 The series of absorption peaks within this range correspond to the skeletal stretching vibrations of the C=N and CN bonds in the s-triazine heterocyclic unit, representing a characteristic absorption region for graphitic carbon nitride materials; located at 810 cm⁻¹ -1 The characteristic absorption peak at that location originates from the out-of-plane bending vibration mode of the triazine ring.

[0095] (4) such as Figure 9 The image shows the photoluminescence spectra of the photocatalyst prepared in Example 1 and Comparative Example 3. All samples exhibit a strong emission peak near 470 nm, which originates from the intrinsic radiative recombination of photogenerated electrons and holes in the carbon nitride matrix; while the modification in Example 1 effectively suppressed the simple recombination of electron-hole pairs, thereby directing more photogenerated electrons to the surface catalytic reaction.

[0096] (5) such as Figure 10 The image shows the UV-Vis diffuse reflectance spectra of the photocatalyst prepared in Example 1 and the photocatalysts obtained in Comparative Examples 1 and 2. All samples exhibit strong absorption in the UV region (200 < λ < 400 nm), but there are significant differences in the absorption edge and absorption intensity in the visible region (λ > 400 nm). The absorption edge of Example 1 is red-shifted and extends to approximately the orange-red region (approximately 600 nm), and the absorption intensity across the entire visible region is significantly improved. This wider spectral response allows for the utilization of more light energy, resulting in better catalytic efficiency.

[0097] (6) For example Figure 11 The figure shows a comparison of the yields of the photocatalyst prepared in Example 1 and the photocatalyst obtained in Comparative Example 3. The left side represents the product of Comparative Example 3, and the right side represents the product of Example 1. The photocatalyst yield of Example 1 was 281.47 mg, while the photocatalyst yield of Comparative Example 3 was 56.02 mg. The yield of Example 1 was 5.02 times that of Comparative Example 3, indicating promising mass production potential. Without the molten salt method, direct heating of the solid precursor is prone to over-reaction due to uneven heating and poor mass transfer, resulting in reduced yield. The molten salt method forms a uniform liquid phase environment at high temperatures, making the pyrolysis process more stable and controllable, and reducing precursor loss. This demonstrates that molten salt, as a liquid template and reaction medium, is a key component in ensuring uniform mixing of the precursor and the formation of regular mesopores during pyrolysis.

[0098] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing a nickel-loaded nitrogen-sulfur co-doped carbon material photocatalyst, characterized in that, The method comprises the following steps: (1) mixing and grinding the first component and the second component at a mass ratio of 1:(5-10) to obtain a precursor mixture; wherein the first component is composed of a nitrogen-containing organic precursor, a sulfur-containing organic precursor and a nickel salt, and the second component is a molten salt medium; (2) under the protection of an inert atmosphere, the precursor mixture obtained in step (1) is programmed to heat to 500-600℃ at a heating rate of 1-5℃ / min, and is kept at this temperature for 2-6 hours to complete the pyrolysis reaction, to obtain a pyrolysis product; (3) the pyrolysis product obtained in step (2) is immersed in an acid solution to remove the molten salt medium and part of the unstable nickel species; then it is washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the nitrogen and sulfur double-doped carbon material photocatalyst loaded with nickel.

2. The method for preparing a nickel-loaded nitrogen-sulfur co-doped carbon material photocatalyst according to claim 1, characterized by, The second component is a mixture of lithium chloride and potassium chloride at a mass ratio of (0.5-1):

1.

3. The method for preparing a nickel-loaded nitrogen-sulfur co-doped carbon material photocatalyst according to claim 2, characterized by, The mass ratio of the nitrogen-containing organic precursor to the sulfur-containing organic precursor in the first component is (1-4):

1.

4. The method for preparing a nickel-loaded nitrogen-sulfur co-doped carbon material photocatalyst according to claim 3, characterized by, The nickel salt in the first component accounts for 5%-8% of the total mass of the nitrogen-containing organic precursor and the sulfur-containing organic precursor.

5. The method for preparing a nickel-loaded, nitrogen-sulfur co-doped carbon material photocatalyst according to claim 1, characterized by, The nitrogen-containing organic precursor is 5-amino-1H-tetrazole.

6. The method for preparing a nickel-loaded, nitrogen-sulfur co-doped carbon material photocatalyst according to claim 1, characterized by, The sulfur-containing organic precursor is 2-mercaptoimidazole.

7. The method for preparing a nickel-loaded, nitrogen-sulfur co-doped carbon material photocatalyst according to claim 1, characterized by, The nickel salt is any one of nickel chloride, nickel nitrate and nickel acetate.

8. A nickel-loaded nitrogen-sulfur co-doped carbon material photocatalyst, characterized in that, Prepared by the method of any one of claims 1 to 7. 9.The Ni-loaded N and S co-doped carbon material photocatalyst according to claim 8, characterized in that, The photocatalyst has a mesoporous structure; its specific surface area is 20-30 m 2 / g, porosity 0.05-0.07 cm 3 / g, average pore diameter 14-25 nm.

10. Use of a nickel-loaded, nitrogen-sulfur co-doped material photocatalyst as claimed in claim 8 or 9, characterized in that, The photocatalyst is applied to a photocatalytic CO2 reduction reaction, and the product of the photocatalytic CO2 reduction reaction contains C2 alkanes.

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