MnIn2S4-coated Co9S8 heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a MnIn2S4-coated Co9S8 heterojunction photocatalyst and a preparation method and application thereof, and belongs to the technical field of photocatalytic materials.The preparation method comprises the steps that firstly, urea, cobalt chloride, water and ethylene glycol serve as raw materials to prepare a Co9S8 precursor; carrying out high-temperature calcination, namely firstly carrying out heat preservation at 350-420 DEG C for 1-2 hours, then heating to 440-460 DEG C, carrying out heat preservation for 3-4 hours, then heating to 580-610 DEG C, and carrying out heat preservation for 3-4 hours, so as to obtain a Co9S8 hollow nanotube; and then growing the MnIn2S4 nanosheet on the surface of the Co9S8 hollow nanotube in situ. The photocatalyst prepared through a hydrothermal-calcination combined strategy has a larger specific surface area and a wider light absorption range, and the migration distance of current carriers can be effectively shortened through a special three-dimensional hollow structure, so that better photocatalytic performance is shown, and the photocatalyst has a large application prospect in the fields of energy and environment.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and in particular to a MnIn2S4@Co9S8 heterojunction photocatalyst and a preparation method and application thereof. Background Art

[0002] Humans and animals often fail to fully absorb the antibiotics they take, resulting in large amounts of antibiotics being excreted into the environment as metabolites or even in their original form. This pollution is known as antibiotic pollution. Antibiotics are now ubiquitous in water environments worldwide, posing a major challenge facing humanity. Efficiently removing antibiotics from water has long been a vexing problem. Photocatalytic technology is an emerging technology that harnesses solar energy to generate highly reactive free radicals and holes to degrade various pollutants in mineralized environments. Consequently, the urgent need to control antibiotic pollution and develop clean energy is driving the development of photocatalytic technology towards higher efficiency and multifunctionality.

[0003] Metal sulfides have become a research hotspot due to their narrow band gap (<3eV) and visible light response properties. MnIn2S4, a typical ternary sulfide, has a layered structure and tunable electronic properties, but is limited by issues such as high recombination rate of photogenerated carriers, low mobility, and a narrow light absorption range, making it difficult to meet the needs of practical applications. Existing technologies often use a single modification strategy. For example, heterostructure construction can improve charge separation efficiency but sacrifices redox capacity; while morphology control can optimize material transport pathways, it cannot effectively suppress charge recombination. Therefore, there is an urgent need to overcome the limitations of a single strategy through collaborative design.

[0004] In recent years, the construction of heterojunctions has become an important means to optimize photocatalytic performance. In the existing technology, there are designs that combine heterostructure construction with morphology control, such as combining heterostructure construction with hollow nanostructures to prepare photocatalysts. However, this strategy is not ideal for improving charge separation efficiency and heterojunction construction. This is mainly because the performance of photocatalytic materials is highly dependent on their micromorphology and crystal structure characteristics. In particular, hollow nanostructures have attracted much attention due to their high specific surface area, short carrier transport paths and abundant reaction sites. However, the methods for preparing hollow nanostructures in the existing technology still have the following key problems:

[0005] First, the ability to control the morphology is insufficient. Taking the preparation of Co9S8 (CS) hollow nanotubes as an example, in the traditional two-step hydrothermal method, when pure water is used as a solvent to prepare the CS precursor in the first step, due to the high polarity of water, it is difficult to effectively control the aspect ratio of the precursor, resulting in the product being short rods (low aspect ratio). This type of morphology limits the uniformity of the tube wall during the subsequent hollowing process, and easily forms a hollow structure with uneven thickness, thereby reducing the specific surface area and the separation efficiency of photogenerated carriers. In addition, sodium sulfide as a liquid sulfur source can easily induce local oversulfurization of the CS precursor in the second-step hydrothermal reaction, leading to the formation of amorphous impurities, further hindering carrier migration.

[0006] Second, the hollow structure has poor stability. For example, the patent document with publication number CN109411239B discloses a simple preparation method for Cu-doped Co9S8 nanotube arrays for supercapacitors. Although the Cu-doped CS nanotubes reported therein improve the capacitance performance by solvent thermal method, the mechanical stability of the hollow structure is still insufficient and the structure is prone to degradation after recycling. Similarly, the patent document with publication number CN119406430A discloses a sulfur-rich vacancy ZnIn2S4@FeNi 0.48 S 1.71 Heterojunction photocatalyst and its preparation method and application, the patent uses "solvothermal method + two-step high temperature calcination method" to synthesize FeNi 0.48 S 1.71 Because the material forming process and the vulcanization reaction proceed simultaneously in a solvothermal method, the hollow nanospheres (FNS) are prone to skeleton collapse due to uncontrollable reaction kinetics. Furthermore, the closed spherical structure of the FNS material cannot effectively utilize the internal space, and residual surfactant (polyvinyl pyrrolidone) may shield the active sites, thereby affecting the photocatalytic performance of the composite material.

[0007] Third, there is a contradiction between crystallinity and carrier separation efficiency. High-temperature calcination is a common method to improve the crystallinity of materials, but high temperature usually also damages the interface of heterojunction composite materials. The high-temperature calcination method in the prior art is difficult to take into account both crystal integrity and charge separation efficiency. For example, the patent document with publication number CN117680164A discloses a MnIn2S4-MoO2 heterojunction photocatalyst and its preparation method. It reports that although the MnIn2S4-MoO2 heterojunction prepared by the hydrothermal method improves the carrier separation efficiency through the S-Mo bond, the high temperature conditions in its preparation process easily destroy the heterojunction interface, resulting in a decrease in photocatalytic activity.

[0008] In summary, although the existing technology adopts multi-strategy collaborative design, such as combining heterostructure construction with morphology control, there are still many technical problems such as low charge separation efficiency and unsatisfactory heterointerface construction effect.

[0009] In view of this, this patent application is filed. Summary of the Invention

[0010] In order to solve the above-mentioned technical problems, the present invention provides a MnIn2S4@Co9S8 heterojunction photocatalyst, and also provides a preparation method and application thereof.

[0011] The first object of the present invention is to provide a method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst, comprising the following steps:

[0012] (1) Preparation of Co9S8 hollow nanotubes: urea, cobalt chloride, water and ethylene glycol are mixed as raw materials to obtain a mixed solution, and the mixed solution is reacted in a reactor to obtain a Co9S8 precursor;

[0013] The Co9S8 precursor is calcined at high temperature to obtain Co9S8 hollow nanotubes;

[0014] The high-temperature calcination process is as follows: first, keep the temperature at 350-420°C for 1-2 hours, then increase the temperature to 440-460°C and keep the temperature for 3-4 hours, and then increase the temperature to 580-610°C and keep the temperature for 3-4 hours;

[0015] (2) MnIn2S4 nanosheets were in situ grown on the surface of Co9S8 hollow nanotubes to obtain Mnln2S4@Co9S8 heterojunction photocatalyst with a hollow tube structure.

[0016] Among the currently disclosed technologies, Co9S8 and MnIn2S4 are usually used in the fields of electrocatalysis and lithium batteries, but there are few reports in the field of photocatalysis, and there is a lack of corresponding research on the application of the two composite materials in heterojunction photocatalysis in the field of photocatalysis.

[0017] The present invention adopts a strategy that combines heterostructure construction with morphology control, and utilizes the synergistic optimization of S-type heterojunctions and hollow structures to in-situ grow MnIn2S4 nanosheets on the surface of Co9S8 hollow nanotubes, thereby obtaining a Mnln2S4@Co9S8 heterojunction photocatalytic material with a hollow tube structure. In the MnIn2S4@Co9S8 system of the present invention, the matching relationship between its conduction band (CB) and valence band (VB) drives electrons to migrate from the VB of Co9S8 to the CB of MnIn2S4, and holes to transfer in the opposite direction, forming an efficient charge transfer path. Combined with the three-dimensional hollow structure (electrons only need to migrate from the shell), the photogenerated carrier recombination rate is significantly reduced, and the hydrogen production rate is increased to 6.35mmol·h -1 ·g -1 In addition, the lattice matching and chemical bonding at the interface enhance the stability of the heterojunction and further optimize the charge transfer efficiency, which has great application prospects in the field of photocatalysis.

[0018] Among them, the Co9S8 hollow nanotube structure has a significant impact on the photocatalytic performance of the obtained Mnln2S4@Co9S8 heterojunction photocatalytic material. The present invention optimizes the preparation method of the Co9S8 hollow nanotube structure, which can accurately control the aspect ratio of the hollow nanotubes, improve the stability of the hollow structure skeleton, and enhance the crystallinity. It solves the technical problems in the existing preparation method, such as insufficient morphology control ability, poor hollow structure stability, and the contradiction between crystallinity and carrier separation efficiency. Therefore, when compounded with MnIn2S4, a composite material with significantly improved photocatalytic and pollutant degradation capabilities is obtained.

[0019] Specifically, the advantage of the present invention in the first step of preparing the Co9S8 precursor material using a solvothermal method with a water-ethanol mixed solvent (rather than the traditional hydrothermal method with pure water as the solvent or the solvothermal method with ethylene glycol as the solvent) is that: since the polarity of water is greater than that of ethylene glycol, and the viscosity of ethylene glycol is greater than that of water, the addition of ethylene glycol can weaken the polarity of the solvent and increase the viscosity, slow down the ion diffusion rate, and prolong the nucleation stage, thereby generating Co9S8 precursor nanorods with a high aspect ratio, laying a better structural foundation for the subsequent vulcanization to form hollow tubes.

[0020] The present invention adopts a three-step high-temperature gradient calcination method to prepare Co9S8 hollow nanotube materials, replacing the traditional hydrothermal method or simple calcination process. By precisely controlling the three key temperature stages of 350-420°C to start the sulfurization reaction, 440-460°C to promote the full reaction, and 580-610°C to optimize the crystal structure and the corresponding holding time, the material structure and performance can be finely controlled. Compared with the existing preparation method, the material's specific surface area, carrier transport performance, structural stability, and photoelectric and photocatalytic properties can be more effectively improved.

[0021] The first stage, calcined in a tube furnace at 350-420°C for 1-2 hours, allows the sulfur powder to sublime and diffuse evenly into the Co9S8 precursor. This allows the initial Co-S bonds to form through a gas-solid reaction, resulting in a porous sulfurized layer and initiating the sulfurization reaction. If the temperature is too low, the sulfur powder will not sublime sufficiently and will not react effectively with the precursor, leading to incomplete sulfurization and affecting the material's composition and structure. If the temperature is too high, the sulfur powder will sublime rapidly, causing an overly vigorous reaction and potentially causing localized high concentrations, uneven tube shell thickness, or even damage to the precursor structure. The second stage, calcined in a tube furnace at 440-460°C for 3-4 hours, further promotes the sulfurization reaction, achieving deep sulfurization and inducing lattice reorganization, resulting in a more stable and uniform material structure. If the temperature is too low, the sulfurization reaction will be incomplete, and residual precursor residue will result in low crystallinity, unstable structural growth, and suboptimal material performance. If the temperature is too high, excessive grain growth and reduced specific surface area may occur, impairing the material's photocatalytic performance. The third stage, calcination in a tubular furnace at 580-610°C and holding for 3-4 hours, optimizes the material's crystallinity and stability. High temperatures promote further regularization of atoms within the material, forming a more complete crystal structure and enhancing its structural stability. If the temperature is too low, incomplete crystallization leads to grain refinement, grain boundary scattering increases carrier transport resistance, and the material becomes unstable. Excessively high temperatures can cause sintering, collapse the pore structure, significantly reduce the specific surface area, and severely degrade photocatalytic performance.

[0022] In summary, the present invention adopts a three-step high-temperature calcination method when preparing Co9S8 hollow nanotube materials. Compared with the traditional hydrothermal method for preparing Co9S8 hollow nanotube materials, its advantages are: ① The Co9S8 material lattice can be repaired by gradient heating, which promotes grain growth and reduces grain boundary scattering, thereby reducing carrier transmission resistance and forming a denser crystalline skeleton, thereby improving mechanical strength and thermal stability; while the hydrothermal method (such as 180℃ secondary hydrothermal) has a lower temperature, and the hollow structure mainly depends on the precursor dissolution-recrystallization process, and the structure is not good. The crystallinity and structural compactness are relatively weak, and the hollow structure often collapses locally due to solvent thermal stress; ② The original three-step high-temperature gradient calcination (350-420℃ to start gas-solid sulfurization, 440-460℃ structural transformation, 580-610℃ crystallization strengthening) avoids local corrosion caused by liquid sulfurizing agent (the traditional hydrothermal method uses Na2S as the sulfur source, which will ionize to generate a large amount of sulfur ions when dissolved in water, which can easily cause excessive local reaction rate, form amorphous impurities, and reduce carrier migration efficiency), so as to achieve controllable tube wall thickness and porosity. In particular, the vulcanization step of "440-460℃ and keeping warm for 3-4h" can effectively avoid insufficient vulcanization in the low-temperature section and excessive sulfur loss in the high-temperature section, and more finely control the vulcanization reaction and structural evolution process to ensure sufficient diffusion of sulfur atoms and lattice ordering. Each temperature gradient has a clear reaction purpose and function, which can gradually optimize the crystal structure and pore structure of the material, thereby improving the specific surface area of ​​the material to a certain extent and achieving precise control of crystal quality. This has not been reported in the existing technology.

[0023] Furthermore, the present invention selects MnIn2S4 and Co9S8 as raw materials for compounding, which is because MIS and CS have unique advantages in terms of band structure, interface interaction, catalytic active site synergy, etc., and are not comparable to any other sulfides of the same series. Specifically, Mn 2+ The d orbital energy level of In 3+ The p-orbital hybridization makes the conduction band (CB) and valence band (VB) positions of MIS more suitable for the band structure of CS, and theoretically can form a type II heterojunction. On the other hand, as a transition metal, the unpaired electrons in the 3d orbital of Mn can enhance the adsorption and activation ability of reactants such as H2O and O2, while the Zn in the same series of sulfides such as ZnIn2S4 2+ The d orbital is fully filled, and the active site density is low. In addition, by consulting the periodic table, it is found that Mn and Zn belong to the same period element, and Mn has a stronger metallic property, with an electronegativity of 1.7, while Zn has an electronegativity of 1.2. Therefore, when forming sulfides with S, Mn 2+ With S 2- The bonding energy is higher than that of Zn 2+ With S 2- , which will make the sulfide skeleton of MIS more resistant to light corrosion. Therefore, the present invention achieves the purpose of the invention by introducing the Mn element.

[0024] Preferably, in step (1), the reaction temperature of the raw materials in the reactor is 80-140° C., and the reaction time is 6-12 h.

[0025] Preferably, when preparing the Co9S8 precursor, the molar ratio of urea to cobalt chloride is 2:(0.6-1), and the volume ratio of water to ethylene glycol is 1:(1-2);

[0026] And / or, the metal ion concentration in the mixed solution is 0.08 to 0.2 mol / L. If the metal ion concentration is too low, the reaction rate will be slow, increasing the time cost. If the metal ion concentration is too high, the reaction rate will be too fast, resulting in an excessively rapid crystallization rate, which may cause poor material crystallinity. This metal ion concentration range is set by comprehensively considering the above two factors.

[0027] In the present invention, the aspect ratio of the Co9S8 precursor is effectively regulated by changing the ratio of water and ethylene glycol in the solvent, thereby affecting the hollow nanotube structure (such as tube wall thickness, pore size uniformity) formed by subsequent calcination. A single solvent, such as a hydrothermal method with pure water as a solvent or a solvent thermal method with ethylene glycol as a solvent, cannot achieve this regulation effect. For example, a high ethylene glycol ratio (low polarity environment) has high viscosity, slow ion diffusion, and a more uniform supersaturation distribution, which is conducive to the formation of slender Co9S8 precursor rods of uniform size. After calcination, thin-walled, high aspect ratio hollow tubes are formed, which is conducive to improving specific surface area and carrier transport efficiency; while in a high water ratio (high polarity environment), ions diffuse quickly and supersaturation fluctuates greatly, which can easily lead to irregular growth or short and thick Co9S8 precursor rods. After calcination, thick-walled hollow tubes are formed, which are suitable for scenarios requiring structural stability. This regulation strategy provides a flexible preparation path for designing photocatalytic materials with specific morphology and performance.

[0028] Preferably, during high-temperature calcination, the heating rate during the heating process is 3-6°C / min. If the heating rate is too slow, <3°C / min, and the residence time in the low-temperature zone is too long, it may lead to incomplete decomposition of the precursor, residual impurities or unreacted components, affecting the purity of the final product, and the time cost is high. If the heating rate is too fast, >6°C / min, it will lead to large temperature differences within the material, uneven thermal expansion, and stress concentration, which may cause material breakage, cracks, or structural collapse.

[0029] Preferably, during high-temperature calcination, the Co9S8 precursor is placed in a tube furnace filled with argon, and sulfur powder is placed upstream of the tube furnace.

[0030] Preferably, the process of in-situ growth is:

[0031] Co9S8 hollow nanotubes are added to an acid solution, followed by manganese chloride, indium chloride tetrahydrate and thioacetamide to obtain a solid-liquid mixture;

[0032] The solid-liquid mixture was reacted at 80-90° C. in an oil bath for 2-3 hours, cooled, washed and dried to obtain the Mnln2S4@Co9S8 heterojunction photocatalyst.

[0033] In the present invention, a low-temperature oil bath method is used to compound the materials. The low-temperature oil bath method can form a heterojunction in a relatively mild environment, avoiding high temperature damage to the heterojunction interface. Preferably, the pH value of the acid solution is 2 to 4;

[0034] And / or, the mass ratio of Co9S8 hollow nanotubes to manganese chloride in the solid-liquid mixture is 1:(0.2-1.2), and the molar ratio of manganese chloride, indium chloride tetrahydrate, and thioacetamide is 1:2:(4-6). For MIS@CS composite samples, if the proportion of MIS nanosheets is too high, a shielding effect will occur, where the MIS nanosheets completely block the CS, and the MIS also block each other. On the other hand, if the MIS proportion is too low, light utilization efficiency will be low. Therefore, this ratio can maintain the composite material's light absorption performance at a relatively good level.

[0035] And / or, the washing is to wash the sample alternately with deionized water and anhydrous ethanol for 3 times or more, the drying temperature is 60-90° C., and the drying time is 8-12 hours.

[0036] In summary, the preparation method of the present invention has made the following breakthrough improvements: First, the synergistic optimization of the S-type heterojunction and the hollow structure, the enhancement of charge separation efficiency through the energy band gradient and the built-in electric field, combined with the hollow structure to shorten the migration distance, breaking through the limitations of a single modification strategy; through the combination of gradient heating and hydrothermal-calcination strategy, urea and ethylene glycol form a tubular precursor in the hydrothermal reaction, and its internal pores reserve a hollow template for the subsequent sulfurization process; staged tubular furnace calcination realizes uniform sublimation of sulfur powder and lattice reconstruction, and finally forms a regular hollow tube structure under the action of the Kirkendall effect. MnIn2S4 nanosheets are in situ grown on the surface of the Co9S8 hollow tube. The close contact at the interface and the special three-dimensional spatial structure enhance the stability of the heterojunction, forming a specific surface area of ​​264.5m 2 / g of three-dimensional hollow structure, which is 3.7 times higher than that of pure Co9S8, providing an efficient channel for reactant adsorption and material transfer; secondly, the use of low-toxic water-ethylene glycol solvent and gradient calcination strategy avoids the use of strong acid / base and structural collapse caused by local excess sulfur; thirdly, it achieves complete water decomposition (simultaneous generation of H2 and O2) without precious metal loading, and exhibits efficient degradation ability for pollutants such as tetracycline hydrochloride.

[0037] The second object of the present invention is to provide a MnIn2S4@Co9S8 heterojunction photocatalyst, which is prepared by the preparation method described in any of the above items, in which MnIn2S4 nanosheets are in situ grown on the surface of Co9S8 hollow nanotubes to form a MnIn2S4@Co9S8 heterojunction composite material with a hollow structure.

[0038] Preferably, the size of the MnIn2S4 nanosheets is 150-600 nm, the thickness of the nanosheets is 20-80 nm, and the size of the formed micron flowers is 1000-4000 nm;

[0039] And / or, the length of the Co9S8 hollow nanotube is 3500-6000 nm, the radius is 70-350 nm, and the hollowness degree of the hollow nanotube is 60%-80%;

[0040] And / or, the photocatalyst has a length of 3700 to 6600 nm and a radius of 200 to 600 nm.

[0041] The third object of the present invention is to provide an application of the MnIn2S4@Co9S8 heterojunction photocatalyst described in any one of the above items, which is used for photocatalytic decomposition of water to produce hydrogen, full decomposition of water and degradation of organic pollutants;

[0042] Preferably, the organic pollutant is at least one of tetracycline hydrochloride, phenol, methylene blue, and rhodamine B.

[0043] This paper proposes for the first time the use of a water-ethylene glycol mixed solvent to control the precursor morphology and combine it with a three-step gradient high-temperature calcination to prepare Co9S8 hollow nanotubes. This is combined with a low-temperature oil bath method to produce MnIn2S4@Co9S8 heterojunction composite materials under mild conditions. This process has not been reported in the prior art. Experimental data show that the optimal composite material has a specific surface area of ​​264.5m 2 / g, pore volume 0.454cm 3 / g, compared with the Co9S8 sample prepared by the traditional two-step hydrothermal method (28.3m 2 / g,0.051cm 3 / g) increased by 9.3 times and 8.9 times respectively, providing an efficient channel for material transmission.

[0044] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0045] 1. The present invention adopts a solvothermal method with a water-ethylene glycol mixed solvent to regulate the precursor morphology, combines a three-step gradient to precisely control high-temperature calcination to prepare Co9S8 hollow nanotubes, and combines a low-temperature oil bath method to obtain MnIn2S4@Co9S8 heterojunction composite materials under mild conditions. This solves the problems of low specific surface area, unstable hollow structure, and low carrier transport efficiency of the traditional hydrothermal method hollow structure, and realizes directional optimization of structure-performance.

[0046] Specifically, the hollow Co9S8 material prepared by a solvothermal method combined with a three-step high-temperature calcination method exhibited multi-dimensional photocatalytic application advantages: in terms of water decomposition and hydrogen production, the composite sample produced 19050 μmol·g of hydrogen within 3 hours. -1 , which are 2.3 and 5.3 times that of the Co9S8-based composite material and MnIn2S4 material prepared by the two-step traditional hydrothermal method, respectively. In terms of pollutant degradation, the sample has excellent degradation performance for tetracycline hydrochloride, which is 1.7 and 1.58 times that of the Co9S8-based composite material and MnIn2S4 material prepared by the two-step traditional hydrothermal method, respectively. In addition, the full decomposition performance of water by MnIn2S4@Co9S8 without precious metal loading reached 9810μmol·g in 3 hours. -1 (H2) and 4840 μmol·g -1 (O2), and the degradation rates of Rhodamine B (RhB), Methylene Blue (MB), and Phenol (Phenol) reached 5.12h -1 , 6.73h -1 and 1.15h -1 , demonstrating its good photocatalytic multifunctionality.

[0047] 2. The material of the present invention has outstanding performance in photocatalytic performance and structural stability. The cyclic hydrogen production data show that the yield of the MnIn2S4@Co9S8 heterojunction composite material prepared by the solvent thermal method and the three-step high-temperature calcination method remains above 98% after 15 hours, and the XRD before and after the hydrogen production experiment is compared. It is found that its structure has almost no change, confirming that it has a strong and stable skeleton structure during the photocatalytic reaction, which is significantly better than the Co9S8-based composite material prepared by the two-step traditional hydrothermal method (the hydrogen production performance attenuation amplitude is 37.2%, and the XRD characteristic peak is missing after the hydrogen production experiment). The above results show that the hollow structure Co9S8 material of the present invention has not only broken through the bottleneck of the traditional photocatalyst activity and stability through its unique pore design and interface synergistic effect, but also shows great potential for industrial application in the field of multi-pollutant synergistic degradation and full water decomposition to produce hydrogen, providing an efficient and sustainable solution for green energy conversion and environmental governance.

[0048] 3. The present invention utilizes the unique Co9S8 hollow nanotube material prepared and uses it as a carrier to grow MnIn2S4 nanosheets on it, which solves the technical bottleneck of MnIn2S4, which is limited by the high recombination rate of photogenerated carriers, low mobility and narrow light absorption range despite its layered structure and controllable electronic properties, and meets the needs of practical applications.

[0049] Among them, since CS (i.e. Co9S8) has a narrow band gap and is black, and MIS (i.e. MnIn2S4) has a wide band gap and is orange-yellow, the composite material formed by the two is black. Since all visible light is absorbed, it appears black. Therefore, after adding CS to MIS, the light absorption performance is improved, which expands the light absorption range of MIS.

[0050] 4. The MnIn2S4@Co9S8 heterojunction photocatalyst provided by the present invention, MIS and CS show unique advantages in terms of band structure, interface interaction, catalytic active site coordination, etc. 2+ The d orbital energy level of In 3+ The hybridization of the p-orbital of MIS makes the conduction band (CB) and valence band (VB) positions more compatible with the band structure of CS, theoretically enabling the formation of a type II heterojunction. Furthermore, as a transition metal, the unpaired electrons in the 3d orbital of Mn can enhance the adsorption and activation of reactants such as H2O and O2, making the sulfide skeleton of MIS more resistant to photocorrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0052] Figure 1 These are the X-ray diffraction (XRD) patterns of the photocatalytic materials prepared in Example 1 and Comparative Examples 1 to 7 of the present invention, wherein (a) is the XRD pattern of the photocatalytic materials prepared in Comparative Examples 4 to 7, and (b) is the XRD pattern of the photocatalytic materials prepared in Example 1 and Comparative Examples 1 to 3.

[0053] Figure 2 These are scanning electron microscope (SEM) morphologies of the photocatalytic materials prepared in Example 1 and Comparative Examples 6 and 8 to 10 of the present invention, wherein (a), (b), (c), (d) and (e) are SEM images of the photocatalytic materials prepared in Comparative Example 8, Comparative Example 9, Comparative Example 6, Example 1 and Comparative Example 10, respectively.

[0054] Figure 3 1 to 7 and 10 of the present invention, wherein (a) is a current density curve of the photocatalytic material prepared in Comparative Examples 4 to 7; (b) is a current density curve of the photocatalytic material prepared in Example 1, Comparative Examples 1 to 3 and 10 of the present invention.

[0055] Figure 4 These are electrochemical impedance spectroscopy (EIS) graphs of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 7, and Comparative Example 10 of the present invention, wherein (a) is the EIS curve graph of the photocatalytic materials prepared in Comparative Examples 4 to 7; (b) is the EIS curve graph of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3, and Comparative Example 10.

[0056] Figure 5 Graphs showing the photocatalytic performance of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3, and Comparative Example 10 of the present invention, wherein (a) is a graph showing the hydrogen production rate, and (b) is a bar graph showing the comparison of the rate constants for tetracycline hydrochloride degradation by the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3, and Comparative Example 10.

[0057] Figure 6 Graphs showing the photocatalytic performance of the photocatalytic material prepared in Example 1, wherein (a) and (b) are respectively a graph showing the rate of simultaneous hydrogen and oxygen production by dual water decomposition of the photocatalytic material prepared in Example 1, and a bar graph showing the reaction rate constants for the degradation of different substances (tetracycline hydrochloride, rhodamine B, methylene blue, and phenol).

[0058] Figure 7 These are photocatalytic stability test diagrams of the photocatalytic materials prepared in Example 1 and Comparative Example 1, wherein (a) and (b) are hydrogen production cycle test diagrams of the photocatalytic materials prepared in Comparative Example 1 and Example 1, respectively, and a hydrogen production experiment was carried out for 3 hours in each cycle.

[0059] Figure 8 3 and 4. These are XRD comparison diagrams of the photocatalytic materials prepared in Example 1 and Comparative Example 1 before and after the hydrogen production experiment, wherein (a) and (b) are XRD comparison diagrams of the photocatalytic materials prepared in Comparative Example 1 and Example 1 before and after the hydrogen production experiment, respectively. DETAILED DESCRIPTION

[0060] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0061] Example 1:

[0062] This embodiment provides a method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst controlled by a three-step high-temperature calcination method, comprising the following steps:

[0063] S1. Dissolve 16mmol urea and 8mmol cobalt chloride in a mixed solvent of 30mL deionized water and 30mL ethylene glycol, stir and dissolve to obtain solution ①;

[0064] S2. Transfer ① to a 100 mL reactor and heat at 80–140°C for 6–12 h. Cool to room temperature. Centrifuge the resulting sample, rinse several times with deionized water and anhydrous ethanol, and dry in a drying oven at 60–90°C for 12 h to obtain Co9S8 precursor ②.

[0065] S3. Place ② in a ceramic boat, which is then placed in an argon-filled tube furnace. Place sufficient sulfur powder upstream of the tube furnace (approximately 1.2 g; the target product, Co9S8, requires 8 mmol of sulfur source, approximately 0.256 g. Considering the loss of sulfur powder upstream, 1.2 g is appropriate). Heat the mixture to 350-420°C and maintain for 1-2 hours. Then, heat the mixture to 440-460°C and maintain for 3-4 hours. Finally, heat the mixture to 580-610°C and maintain for 3-4 hours. Cool the mixture naturally to obtain Co9S8 hollow nanotubes. The heating rate during this process is 3-6°C / min.

[0066] S4. 150 mg of Co9S8 hollow nanotube material was added to an acid solution having a pH of 2 to 4, followed by the addition of 0.5 mmol of manganese chloride, 1 mmol of indium chloride tetrahydrate, and 2 mmol of thioacetamide to obtain a solid-liquid mixture;

[0067] S5. The solid-liquid mixture was reacted in an oil bath at 80-90°C for 2-3 hours, cooled to room temperature, centrifuged, and washed multiple times with deionized water and anhydrous ethanol. The sample was then dried in a drying oven at 60-90°C for 12 hours to obtain a MnIn2S4@Co9S8 heterojunction photocatalytic material with a hollow structure.

[0068] Comparative Example 1:

[0069] This comparative example provides a method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst regulated by a hydrothermal method, comprising the following steps:

[0070] S1. Dissolve 16mmol urea and 8mmol cobalt chloride in 60mL deionized water and stir to dissolve to obtain solution ①;

[0071] S2. Transfer ① to a 100 mL reactor and heat at 80–140°C for 6–12 h. Cool to room temperature. Centrifuge the resulting sample, rinse several times with deionized water and anhydrous ethanol, and dry in a drying oven at 60–90°C for 12 h to obtain Co9S8 precursor ②.

[0072] S3. Dissolve ② in 60 mL of deionized water and ultrasonically disperse. Then, add 3 g of sodium sulfide nonahydrate, stir thoroughly, transfer to a 100 mL reactor, heat at 160-180°C for 6-12 h, cool to room temperature, centrifuge the resulting sample, rinse several times with deionized water and anhydrous ethanol, and dry in a drying oven at 60-90°C for 12 h to obtain Co9S8 hollow nanotubes.

[0073] S4. 150 mg of Co9S8 hollow nanotube material was added to an acid solution having a pH of 2 to 4, followed by the addition of 0.5 mmol of manganese chloride, 1 mmol of indium chloride tetrahydrate, and 2 mmol of thioacetamide to obtain a solid-liquid mixture;

[0074] S5. The solid-liquid mixture was reacted in an oil bath at 80-90°C for 2-3 hours, cooled to room temperature, centrifuged, and washed multiple times with deionized water and anhydrous ethanol. The sample was then dried in a drying oven at 60-90°C for 12 hours to obtain a MnIn2S4@Co9S8 heterojunction photocatalytic material with a hollow structure.

[0075] Comparative Example 2:

[0076] This comparative example provides a preparation method of a MnIn2S4@Co9S8 heterojunction photocatalyst regulated by a three-step high-temperature calcination method. The difference from Example 1 is that the mixed solvent of 30 mL of deionized water and 30 mL of ethylene glycol in step S1 is changed to 60 mL of deionized water, and the remaining steps and parameters remain unchanged.

[0077] Comparative Example 3:

[0078] This comparative example provides a preparation method of a MnIn2S4@Co9S8 heterojunction photocatalyst regulated by a two-step high-temperature calcination method. The difference from Example 1 is that the 440-460°C and 3-4h insulation in step S3 are omitted, and the remaining steps and parameters remain unchanged.

[0079] Comparative Example 4:

[0080] This comparative example provides a preparation method of Co9S8 photocatalyst regulated by a hydrothermal method, which differs from comparative example 1 in that only steps S1 to S3 are retained, while steps S4 to S5 are omitted.

[0081] Comparative Example 5:

[0082] This comparative example provides a preparation method of Co9S8 photocatalyst regulated by a three-step high-temperature calcination method, which differs from comparative example 2 in that only steps S1 to S3 are retained, while steps S4 to S5 are omitted.

[0083] Comparative Example 6:

[0084] This comparative example provides a preparation method of Co9S8 photocatalyst regulated by a three-step high-temperature calcination method, which differs from Example 1 in that only steps S1 to S3 are retained, and steps S4 to S5 are omitted.

[0085] Comparative Example 7:

[0086] This comparative example provides a preparation method of Co9S8 photocatalyst regulated by a two-step high-temperature calcination method, which differs from comparative example 3 in that only steps S1 to S3 are retained, while steps S4 to S5 are omitted.

[0087] Comparative Example 8:

[0088] This comparative example provides a preparation method of a Co9S8 photocatalyst precursor regulated by a hydrothermal method, which differs from comparative example 1 in that only steps S1 to S2 are retained, while steps S3 to S5 are omitted.

[0089] Comparative Example 9:

[0090] This comparative example provides a method for preparing a Co9S8 photocatalyst precursor regulated by a solvent thermal method, which differs from Example 1 in that only steps S1 to S2 are retained, and steps S3 to S5 are omitted.

[0091] Comparative Example 10:

[0092] This comparative example provides a method for preparing an untreated MnIn2S4 photocatalyst, which differs from Example 1 in that only steps S4 to S5 are retained, wherein the Co9S8 material is not added in step S4, and the remaining steps and parameters remain unchanged.

[0093] The photocatalysts prepared in the above Example 1 and Comparative Examples 1 to 10 are respectively recorded as MIS@CS-solvent + 3 (Example 1), MIS@CS-water + water (Comparative Example 1), MIS@CS-water + 3 (Comparative Example 2), MIS@CS-solvent + 2 (Comparative Example 3), CS hollow tube-water + water (Comparative Example 4), CS hollow tube-water + 3 (Comparative Example 5), CS hollow tube-solvent + 3 (Comparative Example 6), CS hollow tube-solvent + 2 (Comparative Example 7), CS precursor-water (Comparative Example 8), CS precursor-solvent (Comparative Example 9) and MIS (Comparative Example 10).

[0094] Among them, "Solvent + 3" refers to the CS hollow nanotubes formed by 3-step calcination in a tube furnace after the CS precursor is prepared by the solvent thermal method (the solvent is deionized water and ethylene glycol); "Water + Water" refers to the CS hollow nanotubes prepared by the hydrothermal method (the solvent is deionized water) after the CS precursor is prepared by the hydrothermal method (the solvent is deionized water); "Water + 3" refers to the CS hollow nanotubes formed by 3-step calcination in a tube furnace after the CS precursor is prepared by the hydrothermal method (the solvent is deionized water); "Solvent + 2" refers to the CS hollow nanotubes formed by 2-step calcination in a tube furnace after the CS precursor is prepared by the solvent thermal method (the solvent is deionized water and ethylene glycol).

[0095] Table 1 shows the structural information such as specific surface area, pore volume and average pore diameter of the samples prepared in Example 1 and Comparative Examples 1 to 10 of this patent. After specific surface area test (BET) characterization, it can be seen that the specific surface area of ​​the CS hollow tube-water + 3 (Comparative Example 5) sample is significantly higher than that of the CS hollow tube-water + water (Comparative Example 4), which shows that compared with the hydrothermal vulcanization process of the CS precursor, the three-step high-temperature calcination vulcanization can make the final CS sample more hollow. In addition, the pore volume of the CS hollow tube-water + 3 (Comparative Example 5) sample has more than doubled, while the average pore diameter has shrunk by 61.4%, which shows that the CS hollow tube under high temperature calcination has a denser hollow skeleton, which means that its mechanical structure strength and stability are improved. On the other hand, compared with the CS hollow tube-water + 3 material (Comparative Example 5), the specific surface area and pore volume of the CS hollow tube-solvent + 3 (Comparative Example 6) sample are further increased. This is because when the CS precursor is prepared by the solvothermal method, the addition of ethylene glycol weakens the polarity of the solvent and increases the viscosity, slows down the ion diffusion rate, and prolongs the nucleation stage, thereby generating CS precursor nanorods with a high aspect ratio, laying a better structural foundation for the subsequent vulcanization to form hollow tubes. The specific surface area of ​​the CS hollow tube-solvent + 2 (Comparative Example 7) sample is slightly larger than that of the CS hollow tube-water + 3 (Comparative Example 5), and slightly smaller than that of the CS hollow tube-solvent + 3 (Comparative Example 6). This is because the CS precursor prepared by the solvent thermal method has a larger aspect ratio, and thus has a larger specific surface area during further high-temperature calcination and hollowing. The three-step calcination and sulfurization of the CS hollow tube-solvent + 3 (Comparative Example 6) sample is compared with the two-step calcination of the CS hollow tube-solvent + 2 (Comparative Example 7) sample. It can more finely control the sulfurization reaction and structural evolution process, gradually optimize the crystal structure and pore structure of the material, and improve the specific surface area of ​​the material to a certain extent. After the MIS material is in situ grown on the surface of the CS hollow nanotube, the specific surface area of ​​the MIS@CS composite sample is significantly improved, and its size pattern is consistent with that of the CS hollow nanotube. The optimal MIS@CS-solvent + 3 (Example 1) composite material exhibits a surface area of ​​264.5m 2 / g and a maximum specific surface area of ​​0.454 cm 3The maximum pore volumes of CS@C@MS / ...

[0096] Table 1 Specific surface area, pore volume and average pore diameter of CS, MIS and their composite samples prepared by different processes

[0097]

[0098]

[0099] Figure 1 The X-ray diffraction (XRD) patterns of the photocatalytic materials prepared in Example 1 and Comparative Examples 1 to 7 of the present invention are shown in Figure 1, wherein (a) is the XRD pattern of the photocatalytic materials prepared in Comparative Examples 4 to 7, and (b) is the XRD pattern of the photocatalytic materials prepared in Example 1 and Comparative Examples 1 to 3. Figure 1 (a) It can be seen that the characteristic peaks of the four CS materials prepared at 29.8°, 31.2°, 47.6° and 52.1° correspond to the (311), (222), (511) and (440) crystal planes, respectively, which are consistent with the standard XRD cards, indicating that CS was successfully prepared. The half-height width of the characteristic peak of the CS hollow tube-water + water sample is wider than that of the CS hollow tube-water + 3, and the peak intensity is also weaker, which indicates that for the same CS precursor material, the crystallinity of the CS hollow tube material after three-step high-temperature calcination and sulfurization is better than that after hydrothermal sulfurization. In addition, the characteristic peaks of the CS hollow tube-solvent + 3 material and the CS hollow tube-water + 3 material are almost the same, indicating that the preparation of CS precursors by solvothermal and hydrothermal methods does not affect their crystal quality. Furthermore, the half-height width of the characteristic peak at 31.2° of the CS hollow tube-solvent + 2 material is wider than that of the CS hollow tube-solvent + 3 material, which indicates that the structure of the material cannot be further improved and stabilized if the step of "440-460℃ and heat preservation for 3-4h" is omitted during the high-temperature calcination and sulfurization process. Figure 1 (b) It can be seen that the four MIS@CS composites exhibit characteristic peaks of MIS and CS at the same time, which indicates that MIS does not affect its structure when it is in situ grown on CS hollow nanotubes, and the two are successfully composited.

[0100] Figure 2 The scanning electron microscope (SEM) morphology images of the photocatalytic materials prepared in Example 1 and Comparative Examples 6 and 8-10 of the present invention are shown, wherein (a), (b), (c), (d) and (e) are SEM images of the photocatalytic materials prepared in Comparative Example 8, Comparative Example 9, Comparative Example 6, Example 1 and Comparative Example 10, respectively. Figure 2(ab) It can be seen that both the CS precursor-water and CS precursor-solvent materials exhibit nanorod morphology, and the CS precursor-solvent material is more "slender", which confirms that the aspect ratio of the CS precursor can be regulated by changing the polarity of the solvent by adding ethylene glycol. Figure 2 (c) shows the hollow tube morphology of CS hollow tube-soluble + 3 material. From the enlarged illustration, it can be seen that the degree of hollowing of the material is very high. The high aspect ratio and the special hollow structure mean that during the photocatalytic process, water or pollutants can pass through the entire hollow nanotube, and the increased contact area accelerates the reaction process. Figure 2 (d) is the SEM image of the MIS@CS-solvent+3 heterojunction composite material. It can be seen that the thin MIS nanosheets are tightly wrapped on the surface of the CS hollow tube, thus showing a special three-dimensional spatial morphology with a length of nearly 10 μm and a radius of about 200 to 600 nm. Figure 2 (e) is the SEM image of the MIS material, which shows a flower-like structure morphology composed of nanosheets, where the size of the nanosheets is 150-600 nm, the thickness of the nanosheets is 20-80 nm, and the size of the formed microflowers is 1000-4000 nm.

[0101] Figure 3 The current density curves of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 7 and Comparative Example 10 of the present invention are shown in FIG. 1 , wherein (a) is a current density curve of the photocatalytic materials prepared in Comparative Examples 4 to 7; (b) is a current density curve of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3 and Comparative Example 10. Figure 3 (a) As can be seen, the CS hollow tube-solvent + 3 material prepared by the solvothermal method and three-step high-temperature calcination exhibits the highest current density, slightly higher than the CS hollow tube-water + 3 material prepared by the hydrothermal method and three-step high-temperature calcination method. This is due to the solvothermal method manipulating the aspect ratio of the CS hollow tube material, resulting in a larger specific surface area and, therefore, a higher carrier concentration under the same conditions. On the other hand, the current density of the CS hollow tube-solvent + 2 material and the CS hollow tube-water + water material is lower. This indicates that while the solvothermal method increases the specific surface area of ​​the CS hollow tube, the high-temperature calcination and sulfurization process effectively repairs the lattice of the CS hollow tube material, thus dominating the internal charge separation efficiency of the material. Furthermore, compared to the two-step high-temperature calcination method, the addition of a pre-sulfurization step (440-460°C for 3-4 hours) in the three-step high-temperature calcination method effectively avoids insufficient sulfurization at low temperatures and rapid sulfur loss at high temperatures, enabling precise control of crystal quality. Figure 3(b) shows that the current density of MIS@CS composite materials is higher than that of MIS materials. Among them, the current density of the optimal heterojunction composite material MIS@CS-solvent+3 is 3.7 and 11.5 times that of the MIS@CS-water+water composite material prepared by the two-step hydrothermal method and the uncompounded MIS material, respectively. This indicates that the MIS@CS composite material has a higher carrier separation efficiency under the synergistic effect of regulating the aspect ratio of the CS hollow tube by the solvothermal method, optimizing and repairing the lattice by high-temperature heat treatment, and the hollow structure and heterojunction.

[0102] Figure 4 The electrochemical impedance spectroscopy (EIS) graphs of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 7, and Comparative Example 10 of the present invention are shown, wherein (a) is the EIS graph of the photocatalytic materials prepared in Comparative Examples 4 to 7; (b) is the EIS graph of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3, and Comparative Example 10. Figure 4 (a) It can be seen that the CS hollow tube-solvent + 3 material has the smallest EIS curvature radius. After only changing the precursor preparation method from solvent thermal method to hydrothermal method, the EIS curvature radius of the CS hollow tube-water + 3 material increases, but it is smaller than the CS hollow tube-solvent + 2 material prepared by retaining the solvent thermal method and changing the three-step calcination method to a two-step calcination method. In addition, the CS hollow tube-water + water material prepared by the two-step hydrothermal method has the largest internal electron migration resistance, which indicates that the three-step high-temperature calcination can significantly promote the growth of CS hollow tube grains, reduce its grain boundary scattering, and thus reduce the resistance of electrons in the migration process. From Figure 4 (b) It can be seen that the EIS radius and Figure 4 The corresponding CS hollow tube materials in (a) show the same rules and are generally smaller than MIS materials, which shows that heterojunctions and hollow structures can effectively promote charge transfer.

[0103] Figure 5 The photocatalytic performance diagram of the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3 and Comparative Example 10 of the present invention, wherein (a) is a hydrogen production rate curve, and (b) is a comparative bar graph of the rate constants of tetracycline hydrochloride degradation by the photocatalytic materials prepared in Example 1, Comparative Examples 1 to 3 and Comparative Example 10. Figure 5 (ab) It can be seen that the photocatalytic hydrogen production of the MIS@CS-solvent+3 heterojunction composite after solvothermal regulation, high-temperature heat treatment, and low-temperature in-situ growth of MIS nanosheets reached 19.05 mmol·g in 3 hours. -1 , which are 1.4, 1.8, 2.3 and 5.3 times that of MIS@CS-water+3, MIS@CS-solvent+2, MIS@CS-water+water and MIS material respectively. The degradation rate of tetracycline hydrochloride is 1.89h -1, 1.2, 1.3, 1.7, and 15.8 times those of MIS@CS-water+3, MIS@CS-solvent+, MIS@CS-water+water, and MIS materials, respectively. This indicates that the MIS@CS-solvent+3 heterojunction composite, synergistically controlled by the solvothermal method and the three-step high-temperature calcination method, exhibits faster carrier dynamics. The solvothermal method modulates the aspect ratio of the CS precursor by changing the polarity of the solution. The three-step high-temperature calcination method repairs the interfacial defects of the CS hollow nanotube material and significantly promotes carrier migration and transfer. Subsequently, the heterojunction composite is formed by in situ growth of MIS nanosheets in the relatively mild environment of the low-temperature oil bath method, avoiding further high-temperature damage to the crystal structure. The synergistic effect of these processes results in the MIS@CS-solvent+3 heterojunction composite exhibiting superior photocatalytic performance.

[0104] Figure 6 Figure 1 shows the photocatalytic performance of the photocatalytic material prepared in Example 1, where (a) and (b) are graphs showing the rates of hydrogen and oxygen production from dual water splitting and histograms showing the reaction rate constants for the degradation of different substances (tetracycline hydrochloride, rhodamine B, methylene blue, and phenol), respectively. It can be seen that by regulating the hollow structure, crystal quality, and the synergistic effects of the heterojunction, the MIS@CS-solubilized + 3 heterojunction composite material achieved a hydrogen production of 9810 μmol·g within 3 hours. -1 , oxygen production reached 4840 μmol·g -1 , and the degradation rates of rhodamine B, methylene blue and phenol reached 5.12h -1 , 6.73h -1 and 1.15h -1 , demonstrating its multifunctionality in photocatalysis.

[0105] Figure 7 The photocatalytic stability test diagrams of the photocatalytic materials prepared in Example 1 and Comparative Example 1 are shown in Figures (a) and (b) are the hydrogen production cycle test diagrams of the photocatalytic materials prepared in Comparative Example 1 and Example 1, respectively. Each cycle was a continuous 3-hour hydrogen production experiment. It can be seen that the MIS@CS-water+water composite material produced 2.73 mmol·h of hydrogen in the first hydrogen production cycle. -1 ·g -1 , while the hydrogen production in the fifth cycle was only 1.99 mmol·h -1 ·g -1 , with a performance degradation of 37.2%. On the other hand, the MIS@CS-solvent+3 heterojunction composite material maintained 98% of its initial hydrogen production after 15 hours of continuous hydrogen production. This clearly demonstrates that by adjusting the polarity of the solvent to control the hollow structure, the unique three-step high-temperature sulfurization and calcination design, and the interfacial synergistic effect, it has successfully overcome the bottleneck of traditional photocatalysts in balancing activity and stability.

[0106] Figure 8 XRD comparison diagrams of the photocatalytic materials prepared in Example 1 and Comparative Example 1 before and after the hydrogen production experiment. Among them, (a) and (b) are the XRD comparison diagrams of the photocatalytic materials prepared in Comparative Example 1 and Example 1 before and after the hydrogen production experiment, respectively. It can be seen that although the full width at half maximum of the characteristic peaks belonging to CS is relatively wide and the peak intensity decreases before the hydrogen production experiment for the MIS@CS-water + water composite material, the characteristic peaks of CS (the sun symbol in the figure) and MIS (the pentagram symbol in the figure) exist simultaneously, indicating that the structure is relatively stable at this time. After the hydrogen production experiment, the relative intensities of the characteristic peaks of MIS located at 27.6° and 33.4° changed. That is, the intensity of the characteristic peak at 27.6° was greater than that at 33.4° before the hydrogen production experiment, but it was exactly the opposite after the hydrogen production experiment. In addition, the characteristic peak of CS located at 52.1° not only became weaker and wider, but the characteristic peak at 31.2° disappeared directly. In contrast, the XRD patterns of the MIS@CS-solvent + 3 heterojunction composite material before and after the hydrogen production experiment were almost the same. This further indicates that compared with the CS hollow nanotube material prepared by the hydrothermal method, after being treated by the three-step high-temperature calcination method, the framework of the CS hollow nanotube material in the MIS@CS-solvent + 3 heterojunction composite material is more solid and not prone to collapse, thus showing better structural stability during the photocatalytic reaction.

[0107] The above specific embodiments further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst, characterized in that: The following steps are involved: (1) Preparation of Co9S8 hollow nanotubes: urea, cobalt chloride, water and ethylene glycol are mixed as raw materials to obtain a mixed solution, and the mixed solution is reacted in a reactor to obtain a Co9S8 precursor; The Co9S8 precursor is calcined at high temperature to obtain Co9S8 hollow nanotubes; The high-temperature calcination process is as follows: first, keep the temperature at 350-420°C for 1-2 hours, then increase the temperature to 440-460°C and keep the temperature for 3-4 hours, and then increase the temperature to 580-610°C and keep the temperature for 3-4 hours; (2) MnIn2S4 nanosheets were in situ grown on the surface of Co9S8 hollow nanotubes to obtain Mnln2S4@Co9S8 heterojunction photocatalyst with a hollow tube structure.

2. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 1, characterized in that: In step (1), the reaction temperature of the raw materials in the reactor is 80-140° C., and the reaction time is 6-12 h.

3. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 1, characterized in that: When preparing the Co9S8 precursor, the molar ratio of urea to cobalt chloride is 2:(0.6-1), and the volume ratio of water to ethylene glycol is 1:(1-2); And / or, in the mixed solution, the concentration of metal ions is 0.08 to 0.2 mol / L.

4. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 1, characterized in that: During high-temperature calcination, the heating rate of the heating process is 3 to 6°C / min.

5. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 1, characterized in that: During high-temperature calcination, the Co9S8 precursor is placed in a tube furnace filled with argon, and sulfur powder is placed upstream of the tube furnace.

6. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 1, characterized in that: The process of in situ growth is: Co9S8 hollow nanotubes are added to an acid solution, followed by manganese chloride, indium chloride tetrahydrate and thioacetamide to obtain a solid-liquid mixture; The solid-liquid mixture was reacted at 80-90° C. in an oil bath for 2-3 hours, cooled, washed and dried to obtain the Mnln2S4@Co9S8 heterojunction photocatalyst.

7. The method for preparing a MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 6, characterized in that: The pH value of the acid solution is 2 to 4; And / or, the mass ratio of Co9S8 hollow nanotubes to manganese chloride in the solid-liquid mixture is 1:(0.2-1.2), and the molar ratio of manganese chloride, indium chloride tetrahydrate, and thioacetamide is 1:2:(4-6); And / or, the washing is to wash the sample alternately with deionized water and anhydrous ethanol for 3 times or more, the drying temperature is 60-90° C., and the drying time is 8-12 hours.

8. A MnIn2S4@Co9S8 heterojunction photocatalyst, characterized in that: By adopting the preparation method according to any one of claims 1 to 7, MnIn2S4 nanosheets are in-situ grown on the surface of Co9S8 hollow nanotubes to form a MnIn2S4@Co9S8 heterojunction composite material with a hollow structure.

9. The MnIn2S4@Co9S8 heterojunction photocatalyst according to claim 8, characterized in that: The size of the MnIn2S4 nanosheets is 150-600 nm, the thickness of the nanosheets is 20-80 nm, and the size of the formed micron flowers is 1000-4000 nm; And / or, the length of the Co9S8 hollow nanotube is 3500-6000 nm, the radius is 70-350 nm, and the hollowness degree of the hollow nanotube is 60%-80%; And / or, the photocatalyst has a length of 3700 to 6600 nm and a radius of 200 to 600 nm.

10. Use of the MnIn2S4@Co9S8 heterojunction photocatalyst according to any one of claims 8 to 9 for photocatalytic water decomposition to produce hydrogen, complete water decomposition, and degradation of organic pollutants; Preferably, the organic pollutant is at least one of tetracycline hydrochloride, phenol, methylene blue, and rhodamine B.

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