A sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst, its preparation method, and pesticide degradation application

Abstract

The present invention discloses a sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst, its preparation method and pesticide degradation application, and relates to related technical fields such as coal-based solid waste recycling, inorganic chemistry, and photocatalytic materials. The present invention uses coal chemical solid waste gasification fine slag as a precursor, adds copper salt, indium salt and thioacetamide, and synthesizes the heterojunction composite catalyst by a one-step hydrothermal method. During the hydrothermal process, coal gasification fine slag nanoparticles are first uniformly deposited on the surface of sulfur-indium-copper nanorods, and then the sulfur-indium-copper nanorods self-assemble to form nanotubes with a length of 5-10 μm and a diameter of 1-2 μm. The catalyst of the present invention has excellent catalytic performance in the photocatalytic degradation reaction of the pesticide thiamethoxam. The present invention utilizes the adsorption capacity of coal gasification fine slag, the rapid photogenerated charge transfer of one-dimensional nanorods and nanotubes, and the mutual synergistic effect of heterogeneous interfaces to promote the separation and transfer of electrons and holes, thereby achieving efficient degradation of the photocatalytic degradation reaction of thiamethoxam.

Description

Technical Field

[0001] The present invention relates to the fields of coal-based solid waste recycling, inorganic chemistry, photocatalytic materials and other related technical fields, and in particular to a sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst, a preparation method thereof, and pesticide degradation application. Background Art

[0002] Coal gasification technology is a core technology for the clean and efficient utilization of coal. All coal gasification technologies use coal as a feedstock and decompose it under high-temperature conditions using steam or oxygen as a gasification medium to produce syngas. This syngas can be further used to generate downstream products such as coal-to-liquids, coal-to-olefins, coal-to-ethylene glycol, and coal-to-methanol. However, the gasification process produces a large amount of fine gasification slag. Currently, the comprehensive utilization rate of fine gasification slag is very low. The accumulation and landfill of large quantities of this slag not only consumes land resources but also has a permanent impact on the environment.

[0003] Copper indium sulfide (CuInS2) has a chalcopyrite structure and a band gap of 1.55 eV, allowing it to absorb the visible portion of sunlight and improve solar energy utilization.

[0004] Thiamethoxam, a new generation of highly effective, low-toxic thiononicotinoid insecticides, is widely used in agricultural production. Current methods for treating thiamethoxam wastewater in China, such as incineration and triple-effect evaporation, are characterized by high energy consumption, high costs, and large waste residue production, leading to increased incineration costs. Photocatalytic oxidation technology, a novel pollutant treatment technology developed in recent years, offers the advantages of efficient and comprehensive pollutant degradation. This technology utilizes catalysts for in-situ activation to generate large amounts of reactive oxygen species (ROS), disrupting the stable structure of pollutants, breaking down large polymers into smaller molecules, and even further mineralizing them into carbon dioxide and water. Therefore, the development of high-performance catalysts for efficient photocatalytic degradation of thiamethoxam is crucial. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for preparing a sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst and its application, and to use it in the photocatalytic degradation of thiamethoxam.

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

[0007] The present invention provides a sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst, wherein the components of the composite catalyst include coal gasification fine slag and sulfur-indium-copper; the morphology of the composite catalyst is that coal gasification fine slag nanoparticles are deposited on sulfur-indium-copper nanorods, and the sulfur-indium-copper nanorods self-assemble to form nanotubes; the percentage of the coal gasification fine slag in the composite catalyst does not exceed 80wt%.

[0008] In the above technical solution, further, the length of the nanorods is 100-300 nm, the diameter of the coal gasification slag nanoparticles is 20-50 nm; the length of the nanotubes is 5-10 µm and the diameter is 1-2 µm; the percentage of the coal gasification slag in the heterojunction composite catalyst is 50-75 wt%.

[0009] The present invention also provides a method for preparing a sulfur-indium-copper nanotube-loaded coal gasification slag heterojunction composite catalyst. The catalyst is synthesized using coal gasification slag as a precursor, copper salt, indium salt, and thioacetamide via a one-step hydrothermal method. The hydrothermal method is performed at a temperature of 120-180°C for 10-18 hours. This method, based on the comprehensive utilization of coal-based solid waste and transforming waste into treasure, uses coal gasification slag as a raw material and utilizes innovative controllable construction and structural regulation strategies to synthesize the sulfur-indium-copper nanotube-loaded coal gasification slag heterojunction composite catalyst via a one-step hydrothermal method.

[0010] In the above technical solution, further, the preparation method comprises the following steps:

[0011] (1) Dissolve coal gasification slag, copper salt, indium salt and thioacetamide in deionized water at room temperature. After stirring evenly, transfer the aqueous solution to a reaction vessel, place it in an oven at 120-180°C for 10-18 hours, and then cool it naturally to room temperature.

[0012] (2) The product obtained in step (1) is washed and centrifuged, and dried in an oven to obtain a black sulfur-indium copper and coal gasification fine slag heterojunction composite catalyst.

[0013] In the above technical solution, further, the coal gasification fine slag used is collected from the coal-based carbon-containing solid waste generated in the coal gasification process of Inner Mongolia Zhuozheng Coal Chemical Co., Ltd. It has a graphene-like structure and high specific surface area, a unique pore structure, rich surface functional groups and microcrystalline structure, and is a very good functional carbon-based nanomaterial.

[0014] In the above technical solution, further, the step (1) requires stirring for 20 to 40 minutes to achieve uniform mixing, followed by ultrasonication for 5 to 10 minutes.

[0015] In the above technical solution, further, in the step (1), the molar ratio of the three compounds of copper salt, indium salt and thioacetamide is (0.5~1.5): (0.5~1.5): (1.5~3), preferably 1:1:2; based on 1mmol of copper salt, the amount of the coal gasification fine slag added is <1g, preferably 300~500mg.

[0016] In the above technical solution, further, the copper salt is Cu(NO3)2·3H2O or anhydrous CuCl2; the indium salt is InCl3·4H2O or In(NO3)3·xH2O.

[0017] In the above technical solution, further, in step (1), after the temperature is raised to 120-180°C at a rate of 5-7°C / min, the oven is kept at a constant temperature for 10-18 hours.

[0018] In the above technical solution, further, in step (2), the washing is performed with deionized water, centrifuged three times, and then washed with anhydrous ethanol and centrifuged three times; the drying temperature in step (2) is 50-80°C, and the drying time is 10-15 hours.

[0019] The present invention also provides the aforementioned indium-sulfur-copper nanotube-loaded coal gasification slag heterojunction composite catalyst for the photocatalytic degradation of thiamethoxam. Using coal gasification slag as a precursor, the indium-sulfur-copper nanotube-loaded coal gasification slag heterojunction composite catalyst is synthesized via a one-step hydrothermal method. The catalyst utilizes the adsorption capacity of coal gasification slag, the rapid photogenerated charge transport between one-dimensional nanorods and nanotubes, and the synergistic interaction of the heterojunction interface to promote the separation and transfer of electrons and holes, achieving efficient photocatalytic degradation of thiamethoxam.

[0020] The coal gasification slag used in the present invention is a coal-based carbonaceous solid waste with a graphene-like structure and high specific surface area. Compared to fly ash, coal gangue, and other materials, the coal gasification slag has a unique pore structure, abundant surface functional groups, and a microcrystalline structure. By modifying the coal gasification slag, the present invention has developed a high-performance carbon-based composite catalytic material. Using the coal gasification slag as a precursor, the present invention utilizes a one-step hydrothermal method to rationally construct a sulfur-indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst. By leveraging the adsorption properties of the coal gasification slag and the effective synergy of the heterojunction interface, the catalyst promotes the separation and transfer of photogenerated electrons and holes, achieving photocatalytic degradation of thiamethoxam.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention uses coal gasification slag as a precursor, along with copper salts, indium salts, and thioacetamide, to synthesize a sulfur-indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst via a one-step hydrothermal method. During the hydrothermal process, coal gasification slag nanoparticles first uniformly deposit on the surface of the sulfur-indium copper nanorods. The nanorods then self-assemble into nanotubes with lengths of 5-10 µm and diameters of 1-2 µm. This catalyst exhibits excellent catalytic performance in the photocatalytic degradation of the pesticide thiamethoxam, achieving a thiamethoxam degradation rate of 83.94% at 25°C for 1 h. This result demonstrates that the adsorption capacity of coal gasification slag, the rapid photogenerated charge transport between the one-dimensional nanorods and nanotubes, and the synergistic interaction at the heterojunction interface promote the separation and transfer of electrons and holes, resulting in efficient photocatalytic degradation of thiamethoxam. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD and FTIR characterization of coal gasification slag, sulfur-indium copper, and sulfur-indium copper nanotube-loaded coal gasification slag heterojunction composite catalysts; Figure 1 a is XRD characterization, Figure 1 b is FTIR characterization.

[0024] Figure 2 This is the SEM image of coal gasification fine slag.

[0025] Figure 3 This is the SEM image of the sulfur indium copper nanotube catalyst.

[0026] Figure 4 This is the SEM image of the sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst.

[0027] Figure 5 This is a locally enlarged SEM image of the sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst.

[0028] Figure 6 The research is about the photocatalytic degradation of thiamethoxam by using coal gasification fine slag, sulfur-indium copper, and sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst.

[0029] Figure 7 This is an SEM image of a composite catalyst of coal gasification fine slag, in which the proportion of fine slag is over 80%, and indium sulfur copper nanotubes are loaded.

[0030] Figure 8 The UV-vis DRS characterization, Tauc plot, Mott-Schottky curve, EIS spectrum and transient photocurrent response curve of coal gasification fine slag, sulfur-indium copper and sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite catalysts; Figure 8 a is the Uv-vis DRS characterization, Figure 8 b is the Tauc plot, Figure 8 c is the Mott-Schottky curve of copper indium sulfide, Figure 8 d is the CC-0.5 Mott-Schottky curve, Figure 8 e is the EIS spectrum of coal gasification slag, sulfur-indium copper and sulfur-indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst, Figure 8 f is the transient photocurrent response curve of copper indium sulfide and CC-0.5. DETAILED DESCRIPTION

[0031] To facilitate a better understanding of the technical solutions of the present invention by those skilled in the art, the following detailed description, combined with examples, describes the preparation method and application of a sulfur-indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst provided by the present invention. The following examples are intended to illustrate the present invention only and are not intended to limit its scope. The coal gasification slag used in these examples was derived from coal-based carbonaceous solid waste generated during the coal gasification process of Inner Mongolia Zhuozheng Coal Chemical Co., Ltd.

[0032] Example 1 Preparation of Sulfur-Indium-Copper Nanotube-Loaded Coal Gasification Fine Slag Heterojunction Composite Catalyst

[0033] At 25 ℃, 20 mL of deionized water and 10 mL of anhydrous ethanol were added to a 50 mL beaker. 500 mg of coal gasification fine slag, 1.0 mmol Cu(NO3)2•3H2O, 1.0 mmol InCl3•4H2O and 2.0 mmol thioacetamide were added under stirring. After stirring evenly, the solution was transferred to a polytetrafluoroethylene reactor and the reactor was sealed. The reactor was kept at a constant temperature of 150 ℃ for 15 h and naturally cooled to room temperature. The obtained product was washed with deionized water and anhydrous ethanol, centrifuged three times, and dried at 70 ℃ for 12 h to obtain sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst (CC-0.5).

[0034] The anhydrous ethanol used in the present invention is analytically pure with a purity of ≥99.7%, the copper nitrate trihydrate is analytically pure with a purity of ≥99.0%, the indium trichloride tetrahydrate is analytically pure with a purity of ≥99.9%, and the thioacetamide is analytically pure with a purity of ≥98.0%.

[0035] The copper indium sulfide catalyst (CuInS2) was prepared by adopting the above preparation method without adding coal gasification fine slag.

[0036] The above preparation method was used to prepare indium sulfur copper nanotube-loaded coal gasification fine slag heterojunction composite catalysts (CC-0.1, CC-0.3, CC-1.0) with different coal gasification fine slag contents by changing the amount of added coal gasification fine slag to 100 mg, 300 mg and 1.0 g, respectively.

[0037] The sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst, sulfur-indium-copper catalyst, and coal gasification fine slag with different coal gasification fine slag contents prepared by the above method are marked as CC-0.1, CC-0.3, CC-0.5, CC-1.0, CuInS2, and Coal cinder, respectively.

[0038] Figure 1 a is the XRD of the synthesized catalyst and coal gasification slag. The sulfur indium copper sample gave diffraction peaks at 27.81°, 32.21°, 46.39° and 54.92°, corresponding to the (111), (200), (220) and (311) crystal planes of the cubic system of sulfur indium copper, respectively, indicating that the synthesized sample is pure sulfur indium copper. The coal gasification slag sample gave a diffraction peak at 26.54° corresponding to the carbon of the isometric system, indicating that the coal gasification slag contains carbon. The sulfur indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst spectrum only showed diffraction peaks corresponding to single-phase sulfur indium copper and coal gasification slag, and no other diffraction peaks appeared, indicating that a sulfur indium copper nanotube-loaded coal gasification slag heterojunction composite catalyst was formed.

[0039] Figure 1 b shows the FTIR analysis results of the three catalysts. The pure phase copper indium sulfide has a wavelength of 592.9 cm -1 The characteristic absorption peak is attributed to the symmetrical stretching vibration mode of the S-In-S bond. In the FTIR spectrum of coal gasification fine slag, 988.9 cm -1 and 1597.8cm -1 Obvious signals were detected at 592.9 cm and 100 cm, corresponding to the CH bond and CO bond, respectively. It is worth noting that the lattice vibration peak of copper indium sulfide (592.9 cm) was also retained in the infrared spectrum of CC-0.5 composite material. -1 ) and the characteristic peaks of coal gasification fine slag (988.9 cm -1 / 1597.8 cm -1 ), this spectral superposition phenomenon confirms the successful construction of the sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite material.

[0040] Figure 2 This is the SEM picture of coal gasification fine slag. Figure 3 This is the SEM image of the sulfur indium copper nanotube catalyst. Figure 4 This is the SEM image of the sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst (CC-0.5). Figure 5 for Figure 4 A partially enlarged SEM image of the S-In-Cu nanotube-loaded coal gasification slag heterojunction composite catalyst. From the image, we can clearly see that the coal gasification slag nanoparticles are evenly deposited on the surface of the S-In-Cu nanorods, which self-assemble into nanotubes with a length of 5-10 µm and a diameter of 1-2 µm. Figure 3 and Figure 4 , you can clearly see Figure 3 The tubular morphology of copper indium sulfide is less, while Figure 4 After being doped with coal gasification fine slag, medium sulfur indium copper mostly forms relatively regular hollow tubes, indicating that the doping of coal gasification fine slag is beneficial to promoting sulfur indium copper to maintain its tubular morphology.

[0041] Example 2 Photocatalytic Degradation of Thiamethoxam

[0042] The photocatalytic degradation of thiamethoxam was carried out in a double-jacketed beaker. The thiamethoxam concentration used in the reaction was 5 mg·L -1 Accurately measure 100 mL of 5 mg•L -1 To a thiamethoxam solution, 10 mg of different catalysts (composite catalyst from Example 1, copper indium sulfide, and coal gasification slag) were added. The mixture was stirred with a magnetic stirrer for 30 minutes, then placed under a xenon lamp and reacted for 60 minutes. The stock solution and the different reaction solutions were analyzed using a double-beam UV-visible spectrophotometer (TU-1901, Beijing Puxi General Instrument Co., Ltd.) to calculate the absorbance and degradation rate of thiamethoxam.

[0043] from Figure 6 As can be seen, the thiamethoxam degradation rate of the synthesized catalyst gradually increased with increasing reaction time. The copper indium sulfide nanotube-loaded coal gasification slag heterojunction composite catalyst exhibited enhanced reactivity compared to the single-phase copper indium sulfide and coal gasification slag, achieving a thiamethoxam degradation rate of 83.94% after a single hour of reaction. The figure shows that increasing the amount of coal gasification slag doped with it increases the catalytic degradation activity. However, excessive amounts of coal gasification slag doping can actually reduce the degradation activity, as excessive amounts of slag can disrupt the tubular morphology.

[0044] The present invention synthesizes a sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst through a one-step hydrothermal method. The adsorption capacity of the coal gasification fine slag, the rapid photogenerated charge transfer of one-dimensional nanorods and nanotubes, and the synergistic effect of the heterogeneous interface are utilized to promote the separation and transfer of electrons and holes, thereby achieving efficient degradation of the thiamethoxam photocatalytic degradation reaction.

[0045] Comparative Example 1

[0046] The preparation method of Example 1 was followed, except that the amount of coal gasification fine slag added was 1 g. The SEM image of the prepared composite catalyst is shown in FIG. Figure 7 As shown, from Figure 7 The results show that when the percentage of coal gasification fine slag in the composite catalyst exceeds 80wt%, the sulfur indium copper nanorods disintegrate and accumulate into nanogroups, and cannot maintain the nanorod-like morphology.

[0047] Example 3 Energy band structure of the synthesized catalyst

[0048] The energy band structures of the synthesized catalysts were determined by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Mott-Schottky curve (MS curve) using Lambda 355 and CHI760D, respectively.

[0049] UV-visible diffuse reflectance spectroscopy analysis showed that ( Figure 8 a), coal gasification slag exhibits typical conductor material properties, with continuous absorption characteristics in the entire spectral range and no obvious absorption edge is observed, which indicates that the material itself lacks effective photogenerated carrier generation capability. However, the material has significant light capture capability, and the absorbed photon energy is mainly converted into thermal energy through non-radiative pathways (molecular vibration relaxation and exciton recombination), resulting in low photon conversion efficiency. Comparative analysis found that the absorption edge of pure indium sulfide copper is located near 600 nm, corresponding to a wider semiconductor band gap structure. It is worth noting that the absorption edge of the CC-0.5 composite material is significantly red-shifted to the 780 nm region, which is due to the heterojunction interface effect: when indium sulfide copper forms a close interface contact with coal gasification slag, the disorder of the lattice atomic arrangement in the interface region increases significantly, inducing energy level diffusion, thereby achieving band gap compression (from 2.01 eV to 1.72 eV) and spectral response range expansion ( Figure 8 b). Tauc curve analysis confirms that the formation of the heterojunction effectively improves the photoelectric properties of the material.

[0050] The slope characteristics of the MS curves of copper indium sulfide and CC-0.5 indicate that both exhibit n-type semiconductor characteristics ( Figure 8 c. Figure 8 d). The flat band potentials measured by linear region tangent extrapolation show that the Ef of CuInS is -0.45 V (vs. SSC), while that of CC-0.5 shifts negatively to -0.69 V (vs. SSC). Based on the 0.2 V negative offset between the conduction band potential (ECB) and the flat band potential of n-type semiconductors, the ECB of CC-0.5 is calculated to be -0.89 V (vs. SSC). This value is converted to -0.69 V (vs. NHE) through electrode potential conversion (SSC → NHE). Furthermore, combined with the band gap of CuInS (2.01 eV), the valence band potential of CC-0.5 is deduced to be EVB = 1.03 V (vs. NHE). Similarly, the EVB of pristine CuInS is 1.56 V (vs. NHE). This potential evolution confirms that the heterostructure effectively optimizes the material's band structure.

[0051] Example 4 Photoelectric Performance of Synthesized Catalyst

[0052] The photoelectrochemical performance of the catalyst was characterized using a CHI 760E electrochemical workstation. A three-electrode test system was constructed: a Pt electrode served as the counter electrode, an Ag / AgCl electrode served as the reference electrode, and a catalyst-modified FTO glass served as the working electrode. A 0.5 M sodium sulfate (Na2SO4) solution served as the electrolyte. The working electrode was prepared as follows: 40 mg of catalyst powder and 30 μL of perfluorosulfonic acid resin (Nafion) were weighed and dispersed in 3 mL of anhydrous ethanol. The mixture was continuously ground in an agate mortar to form a uniform and viscous slurry. The slurry was evenly applied to the conductive surface of the FTO glass using a pipette. The mixture was then infrared dried at 200°C for 20 minutes.

[0053] The catalysts used were the sulfur-indium-copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst (CC-0.5) and the sulfur-indium-copper catalyst prepared in Example 1.

[0054] Figure 8 Figure e shows the electrochemical impedance spectroscopy characteristics of the synthesized catalyst. Experimental data show that there are significant differences in the charge transfer characteristics of different catalysts. The Nyquist arc curvature radius of the coal gasification fine slag is the largest, indicating that the material has a high photogenerated carrier recombination efficiency; in contrast, the indium copper sulfide catalyst exhibits the smallest curvature radius, confirming its excellent charge transport performance. It is worth noting that the impedance response of the composite CC-0.5 composite material shows intermediate state characteristics, which is attributed to the effective charge transfer channel formed at the heterojunction interface, thereby significantly improving the spatial separation efficiency of photogenerated carriers. Figure 8 The transient photocurrent response test further verified that the photocurrent density of CC-0.5 was about 2 times higher than that of the indium copper sulfide catalyst. This enhancement effect originated from the directional migration mechanism of photogenerated electron-hole pairs under the action of the interfacial electric field, which prompted more high-energy electrons to participate in the surface catalytic reaction kinetics.

[0055] The examples of the present invention are described in detail above in conjunction with the embodiments, but the present invention is not limited to the above examples. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of the present invention, and should also be regarded as the scope of protection of the present invention.

Claims

1. A sulfur-indium copper nanotube-supported coal gasification fine slag heterojunction composite catalyst, characterized in that: The components of the heterojunction composite catalyst include coal gasification slag and indium copper sulfide; the morphology of the heterojunction composite catalyst is that coal gasification slag nanoparticles are deposited on indium copper sulfide nanorods, and the indium copper sulfide nanorods self-assemble to form nanotubes; the percentage of the coal gasification slag in the heterojunction composite catalyst does not exceed 80wt%.

2. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 1, characterized in that: The length of the nanorods is 100-300 nm, and the diameter of the coal gasification fine slag nanoparticles is 20-50 nm; The nanotubes have a length of 5-10 μm and a diameter of 1-2 μm; The percentage of the coal gasification fine slag in the heterojunction composite catalyst is 50-75 wt %.

3. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 1, characterized in that: The preparation method of the heterojunction composite catalyst comprises: using coal gasification fine slag as a precursor, adding copper salt, indium salt and thioacetamide, and synthesizing it by a one-step hydrothermal method; the temperature of the one-step hydrothermal method is 120-180°C, and the time is 10-18 hours.

4. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 3, characterized in that: The preparation method comprises the following steps: (1) Dissolve coal gasification slag, copper salt, indium salt, and thioacetamide in deionized water at room temperature, stir evenly, react at 120-180 °C for 10-18 h, and cool naturally to room temperature. (2) The product obtained in step (1) is washed, centrifuged, and dried to obtain the composite catalyst.

5. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, characterized in that: The step (1) requires stirring for 20 to 40 minutes to mix evenly, followed by ultrasonication for 5 to 10 minutes.

6. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, characterized in that: In the step (1), the molar ratio of the three compounds, copper salt, indium salt and thioacetamide, is (0.5-1.5): (0.5-1.5): (1.5-3); based on 1 mmol of copper salt, the amount of the coal gasification fine slag added is less than 1 g.

7. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, characterized in that: The copper salt is Cu(NO3)2·3H2O or anhydrous CuCl2; the indium salt is InCl3·4H2O or In(NO3)3·xH2O.

8. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, characterized in that: In step (1), the temperature is raised to 120-180°C at a rate of 5-7°C / min and then maintained at a constant temperature for 10-18 hours.

9. The sulfur-indium-copper nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, characterized in that: In step (2), the product is washed with deionized water, centrifuged, and then washed with anhydrous ethanol and centrifuged; In step (2), the drying temperature is 50-80°C and the drying time is 10-15 hours.

10. Use of the sulfur-indium copper nanotube-loaded coal gasification fine slag heterojunction composite catalyst according to any one of claims 1 to 9 in photocatalytic degradation of thiamethoxam.

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