Sulfur indium copper nanotube loaded coal gasification fine slag heterojunction composite catalyst and preparation method and pesticide degradation application thereof

Abstract

The invention discloses a copper indium sulfide nanotube loaded coal gasification fine slag heterojunction composite catalyst as well as a preparation method and pesticide degradation application thereof, and relates to the related technical fields of coal-based solid waste recycling, inorganic chemistry, photocatalytic materials and the like. According to the invention, coal chemical industry solid waste gasification fine slag is used as a precursor, copper salt, indium salt and thioacetamide are added, and the heterojunction composite catalyst is synthesized by a one-step hydrothermal method. In the hydrothermal process, coal gasification fine slag nanoparticles are firstly uniformly deposited on the surface of a sulfur indium copper nanorod, and then the sulfur indium copper nanorod is self-assembled to form a nanotube with the length of 5-10 m and the diameter of 1-2 m. The catalyst provided by the invention has excellent catalytic performance in photocatalytic degradation of pesticide thiamethoxam. By utilizing the adsorption capacity of the coal gasification fine slag, the rapid photogenerated charge transfer of the one-dimensional nanorods and the nanotubes and the mutual synergistic effect of heterogeneous interfaces, the separation and transfer of electrons and holes are promoted, and the efficient degradation of the reaction of photocatalytic degradation of thiamethoxam is realized.

Description

Technical Field

[0001] The present invention relates to related technical fields such as coal-based solid waste recycling, inorganic chemistry, photocatalytic materials, etc., and particularly relates to a copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst, a preparation method thereof, and an application in pesticide degradation. Background Art

[0002] Coal gasification technology is the core technology for the clean and efficient utilization of coal. All coal gasification technologies use coal as raw material, and under high-temperature conditions, steam or oxygen is used as the gasification medium to decompose coal to generate syngas. The generated syngas is further extended to downstream products, such as coal-to-oil, coal-to-olefins, coal-to-ethylene glycol, coal-to-methanol, etc. However, a large amount of fine slag of coal gasification is generated during the coal gasification process. At present, the comprehensive utilization rate of the fine slag of coal gasification is very low. A large amount of stacking and landfill not only occupy land resources, but also cause permanent impacts on the environment.

[0003] As a material with important application value, copper indium sulfide has gradually attracted wide attention. Copper indium sulfide (CuInS2) has a chalcopyrite structure and a band gap of 1.55 eV, which enables it to absorb the visible light part in sunlight and improve the solar energy utilization rate.

[0004] Thiamethoxam, as a new generation of highly efficient and low-toxic thiamine nicotine insecticide, is widely used in agricultural production. In China, in the treatment of thiamethoxam wastewater, the current main methods such as incineration method and triple-effect evaporation method have problems such as high energy consumption, high cost, and large amount of waste residue production, resulting in an increase in incineration cost. Photocatalytic oxidation technology is a new type of pollutant treatment technology developed in recent years, which has the advantages of efficient and comprehensive degradation of pollutants. This technology can utilize the catalyst to in-situ activate a large number of reactive oxygen species (ROS), break the stable structure of pollutants, decompose macromolecular polymers into small molecule substances, and even further mineralize them into carbon dioxide and water. Therefore, it is particularly important to develop catalysts with excellent performance to achieve efficient photocatalytic degradation of thiamethoxam. Summary of the Invention

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

[0006] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions: The present invention provides a copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst, and the components of the composite catalyst include the fine slag of coal gasification and copper indium sulfide; the morphology of the composite catalyst is that the fine slag nanoparticles of coal gasification are deposited on the copper indium sulfide nanorods, and the copper indium sulfide nanorods self-assemble to form nanotubes; the percentage content of the fine slag of coal gasification in the composite catalyst does not exceed 80 wt%.

[0007] In the above technical solution, further, the length of the nanorods is 100 - 300 nm, and the diameter of the fine slag nanoparticles of coal gasification is 20 - 50 nm; the length of the nanotubes is 5 - 10 µm and the diameter is 1 - 2 µm; the percentage content of the coal gasification fine slag in the heterojunction composite catalyst is 50 - 75 wt%.

[0008] The present invention also provides a preparation method of a copper indium sulfide nanotube supported coal gasification fine slag heterojunction composite catalyst, which is synthesized by a one-step hydrothermal method using coal gasification fine slag as a precursor and adding copper salt, indium salt and thioacetamide; the temperature of the one-step hydrothermal synthesis is 120 - 180 °C and the time is 10 - 18 h. Based on the comprehensive utilization of coal-based solid waste, turning waste into treasure, using coal gasification fine slag as raw material, through the innovation of controllable construction and structure regulation strategies, a copper indium sulfide nanotube supported coal gasification fine slag heterojunction composite catalyst is synthesized by a one-step hydrothermal method.

[0009] In the above technical solution, further, the preparation method includes the following steps: (1) At room temperature, dissolve the coal gasification fine slag, copper salt, indium salt and thioacetamide in deionized water, after stirring evenly, transfer the aqueous solution to a reaction vessel, place it in an oven at 120 - 180 °C and react for 10 - 18 hours, and then naturally cool to room temperature; (2) Wash and centrifuge the product obtained in step (1), and dry it in an oven to obtain a black copper indium sulfide and coal gasification fine slag heterojunction composite catalyst.

[0010] In the above technical solution, further, the used coal gasification fine slag 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, a high specific surface area, a unique pore structure, rich surface functional groups and a microcrystalline structure, and is a good functional carbon-based nanomaterial.

[0011] In the above technical solution, further, the mixing in step (1) needs to be stirred for 20 - 40 min and then ultrasonicated for 5 - 10 min.

[0012] In the above technical solution, further, the molar ratio of the three compounds of copper salt, indium salt and thioacetamide in step (1) is (0.5 - 1.5):(0.5 - 1.5):(1.5 - 3), preferably 1:1:2; taking 1 mmol of copper salt as an example, the addition amount of the coal gasification fine slag < 1 g, preferably 300 - 500 mg.

[0013] 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.

[0014] In the above technical solution, further, in step (1), the temperature is raised to 120-180 °C at a rate of 5-7 °C / min, and then the oven is kept at a constant temperature for 10-18 h.

[0015] In the above technical solution, further, in step (2), it is washed with deionized water and centrifuged 3 times, and then washed with anhydrous ethanol and centrifuged 3 times; the drying temperature in step (2) is 50-80 °C, and the drying time is 10-15 h.

[0016] The present invention also provides the above-mentioned copper indium sulfide nanotube-supported coal gasification fine slag heterojunction composite catalyst for photocatalytic degradation of thiamethoxam. Using coal gasification fine slag as a precursor, a copper indium sulfide nanotube-supported coal gasification fine slag heterojunction composite catalyst is synthesized by a one-step hydrothermal method. By utilizing 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 the heterojunction interface, the separation and transfer of electrons and holes are promoted, and the efficient degradation of the photocatalytic degradation of thiamethoxam reaction is achieved.

[0017] The coal gasification fine slag used in the present invention is a coal-based carbon-containing solid waste, which has a graphene-like structure and a high specific surface area. Compared with fly ash, coal gangue, etc., the coal gasification fine slag has a unique pore structure, rich surface functional groups and a microcrystalline structure. The present invention develops a carbon-based composite catalytic material with excellent performance through modification of the coal gasification fine slag. The present invention uses coal gasification fine slag as a precursor and rationally constructs a copper indium sulfide nanotube-supported coal gasification fine slag heterojunction composite catalyst by a one-step hydrothermal method. By utilizing the adsorption performance of coal gasification fine slag and the effective synergy of the heterojunction interface, the separation and transfer of photogenerated electrons and holes are promoted, and the photocatalytic degradation of thiamethoxam is achieved.

[0018] Compared with the prior art, the beneficial effects of the present invention are: The present invention uses gasification fine slag as a precursor, adds copper salt, indium salt and thioacetamide, and synthesizes a copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst by a one-step hydrothermal method. During the hydrothermal process, the gasification fine slag nanoparticles are first uniformly deposited on the surface of the copper indium sulfide nanorods, and then the copper indium sulfide nanorods self-assemble to form nanotubes with a length of 5-10 µm and a diameter of 1-2 µm. This catalyst shows excellent catalytic performance in the photocatalytic degradation of the pesticide thiamethoxam. At 25 °C and after 1 h of reaction, the degradation rate of thiamethoxam can reach 83.94%. This result indicates that by utilizing the adsorption capacity of the gasification fine slag, the rapid photogenerated charge transport of the one-dimensional nanorods and nanotubes, and the mutual synergistic effect of the heterointerfaces, the separation and transfer of electrons and holes are promoted, achieving efficient degradation of the photocatalytic degradation of thiamethoxam reaction. Description of the Drawings

[0019] Figure 1 are the XRD and FTIR characterizations of gasification fine slag, copper indium sulfide, and copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst; Figure 1 a is the XRD characterization, Figure 1 b is the FTIR characterization.

[0020] Figure 2 is the SEM image of gasification fine slag.

[0021] Figure 3 is the SEM image of copper indium sulfide nanotube catalyst.

[0022] Figure 4 is the SEM image of copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst.

[0023] Figure 5 is the SEM image of the locally enlarged copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst.

[0024] Figure 6 are the reaction performances of gasification fine slag, copper indium sulfide, and copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst in the photocatalytic degradation of thiamethoxam.

[0025] Figure 7 is the SEM image of the copper indium sulfide nanotube-supported gasification fine slag composite catalyst with the gasification fine slag accounting for more than 80%.

[0026] Figure 8 are the Uv-vis DRS characterization, Tauc plot, Mott-Schottky curve, EIS spectrum, and transient photocurrent response curve of gasification fine slag, copper indium sulfide, and copper indium sulfide nanotube-supported gasification fine slag heterojunction composite catalyst; 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 Mott-Schottky curve of CC-0.5 Figure 8 e is the EIS spectrum of the composite catalyst of gasification fine slag, copper indium sulfide and gasification fine slag supported copper indium sulfide nanotubes Figure 8 f is the transient photocurrent response curve of copper indium sulfide and CC-0.5 Detailed implementation mode

[0027] To enable those skilled in the art to better understand the technical solutions of the present invention, the following describes in detail a preparation method and application of a composite catalyst of copper indium sulfide nanotubes supported on gasification fine slag provided by the present invention in combination with embodiments. The following embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The gasification fine slag used in the embodiments is a coal-based carbon-containing solid waste generated from the gasification process of Inner Mongolia Zhuozheng Coal Chemical Co., Ltd.

[0028] Example 1 Preparation of a composite catalyst of copper indium sulfide nanotubes supported on gasification fine slag At 25 °C, 20 mL of deionized water and 10 mL of absolute ethanol were added to a 50 mL beaker. Under stirring, 500 mg of gasification fine slag, 1.0 mmol of Cu(NO3)2•3H2O, 1.0 mmol of InCl3•4H2O and 2.0 mmol of thioacetamide were added. After stirring evenly, the solution was transferred to a polytetrafluoroethylene reaction kettle and the kettle was sealed. It was kept at a constant temperature of 150 °C for 15 h and then naturally cooled to room temperature. The obtained product was washed and centrifuged 3 times with deionized water and absolute ethanol respectively, and dried at 70 °C for 12 h to prepare a composite catalyst of copper indium sulfide nanotubes supported on gasification fine slag (CC-0.5).

[0029] The absolute ethanol used in the present invention is of analytical grade with a purity of ≥99.7%, copper nitrate trihydrate is of analytical grade with a purity of ≥99.0%, indium trichloride tetrahydrate is of analytical grade with a purity of ≥99.9%, and thioacetamide is of analytical grade with a purity of ≥98.0%.

[0030] Using the above preparation method, without adding gasification fine slag, a copper indium sulfide catalyst (CuInS2) was prepared.

[0031] Using the above preparation method, the amount of gasification fine slag added was changed to 100 mg, 300 mg and 1.0 g respectively to prepare composite catalysts of copper indium sulfide nanotubes supported on gasification fine slag with different gasification fine slag contents (CC-0.1, CC-0.3, CC-1.0).

[0032] The CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite catalysts, CuInS₂ catalysts, and coal gasification fine slags with different coal gasification fine slag contents prepared by the above method were respectively labeled as CC-0.1, CC-0.3, CC-0.5, CC-1.0, CuInS₂, and Coal cinder.

[0033] Figure 1 a is the XRD of the synthesized catalysts and coal gasification fine slag. The CuInS₂ 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 cubic CuInS₂, respectively, indicating that the synthesized sample was pure-phase CuInS₂. A diffraction peak at 26.54° corresponding to isometric carbon was given in the coal gasification fine slag sample, indicating that the coal gasification fine slag contained carbon. Only the diffraction peaks corresponding to single-phase CuInS₂ and coal gasification fine slag appeared in the spectrum of the CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite catalyst, and no other diffraction peaks appeared, indicating the formation of the CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite catalyst.

[0034] Figure 1 b shows the FTIR analysis results of the three catalysts. Pure-phase CuInS₂ presented a characteristic absorption peak at 592.9 cm -1 , attributed to the symmetric stretching vibration mode of the S-In-S bond. In the FTIR spectrum of the coal gasification fine slag, obvious signals were detected at 988.9 cm -1 and 1597.8 cm -1 , corresponding to the C-H bond and C-O bond, respectively. It is worth noting that the infrared spectrum of the CC-0.5 composite material retained both the lattice vibration peak of CuInS₂ (592.9 cm -1 ) and the characteristic peaks of the coal gasification fine slag (988.9 cm -1 / 1597.8 cm -1 ). This spectral superposition phenomenon confirmed the successful construction of the CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite material.

[0035] Figure 2 is the SEM image of the coal gasification fine slag, Figure 3 is the SEM image of the CuInS₂ nanotube catalyst, Figure 4 is the SEM image of the CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite catalyst (CC-0.5), Figure 5 is Figure 4 the SEM image of the locally magnified CuInS₂ nanotube-supported coal gasification fine slag heterojunction composite catalyst. From the figure, we can clearly see that the coal gasification fine slag nanoparticles were uniformly deposited on the surface of the CuInS₂ nanorods, and the CuInS₂ nanorods self-assembled to form nanotubes with a length of 5 - 10 µm and a diameter of 1 - 2 µm. ComparisonFigure 3 and Figure 4 , it can be clearly seen that Figure 3 the tubular morphology of copper indium sulfide is less, while Figure 4 after doping with coal gasification fine slag, copper indium sulfide is mostly regular hollow tubes, indicating that the doping of coal gasification fine slag is beneficial to promoting copper indium sulfide to maintain its tubular morphology.

[0036] Example 2 Photocatalytic Degradation of Thiamethoxam Reaction The photocatalytic degradation of thiamethoxam reaction was carried out in a double-layer jacketed beaker. The concentration of thiamethoxam used in this reaction was 5 mg•L -1 . Accurately measure 100 mL of 5 mg•L -1 thiamethoxam solution, add 10 mg of different catalysts (the composite catalyst of Example 1, copper indium sulfide, coal gasification fine slag), stir with a magnetic stirrer, and place it under a xenon lamp source after 30 min for 60 minutes of reaction. Use a double-beam ultraviolet-visible spectrophotometer (TU-1901 of Beijing Purkinje General Instrument Co., Ltd.) to detect the original solution and different reaction solutions respectively, and calculate the absorbance and degradation rate of thiamethoxam.

[0037] From Figure 6 it can be seen that with the increase of reaction time, the degradation rate of thiamethoxam by the synthesized catalyst gradually increases. The heterojunction composite catalyst of copper indium sulfide nanotubes loaded with coal gasification fine slag shows enhanced reaction activity compared with single-phase copper indium sulfide and coal gasification fine slag. After 1 h of reaction, its degradation rate of thiamethoxam can reach 83.94%. It can be seen from the figure that when the amount of doped coal gasification fine slag is larger, the catalytic degradation activity is higher, but when the amount of doped coal gasification fine slag is too high, it will instead reduce its degradation activity, which is because the excessive coal gasification fine slag will destroy its tubular morphology.

[0038] The present invention synthesizes a heterojunction composite catalyst of copper indium sulfide nanotubes loaded with coal gasification fine slag by a one-step hydrothermal method. Utilizing the adsorption capacity of coal gasification fine slag, the rapid photogenerated charge transfer of one-dimensional nanorods and nanotubes, and the mutual synergy of the heterojunction interface, it promotes the separation and transfer of electrons and holes, and realizes the efficient degradation of the photocatalytic degradation of thiamethoxam reaction.

[0039] Comparative Example 1 According to the preparation method of Example 1, the difference is only that the addition amount of coal gasification fine slag is 1 g. The SEM image of the prepared composite catalyst is as shown in Figure 7 . It can be seen from the Figure 7 results that when the percentage content of coal gasification fine slag in the composite catalyst exceeds 80 wt%, the copper indium sulfide nanorods disintegrate and accumulate into nano groups, and the nanorod-like morphology cannot be maintained.

[0040] Example 3 Energy Band Structure of the Synthesized Catalyst The energy band structure of the synthesized catalyst was determined by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and Mott-Schottky curves (MS curve), using Lambda 355 and CHI760D respectively.

[0041] Ultraviolet-visible diffuse reflectance spectroscopy analysis showed that Figure 8 a), the fine slag of coal gasification exhibited typical conductor material characteristics, showing continuous absorption characteristics in the whole spectral range and no obvious absorption edge was observed, indicating that the material itself lacked the ability to generate effective photo-generated carriers. However, this material had significant light trapping ability, and the absorbed photon energy was mainly converted into heat energy through non-radiative pathways (molecular vibrational relaxation and exciton recombination), resulting in a low photon conversion efficiency. Comparative analysis found that the absorption edge of pure copper indium sulfide was located near 600 nm, corresponding to a relatively wide semiconductor band gap structure. It should be noted that the absorption edge of the CC-0.5 composite material was significantly red-shifted to the 780 nm region, which was due to the heterojunction interface effect: when copper indium sulfide formed a close interface contact with the fine slag of coal gasification, the degree of lattice atom arrangement disorder in the interface region increased significantly, inducing energy level dispersion, and then achieving band gap compression (from 2.01 eV to 1.72 eV) and spectral response range expansion ( Figure 8 b). Tauc curve analysis confirmed that the formation of the heterojunction effectively improved the optoelectronic properties of the material.

[0042] The slope characteristics of the MS curves of copper indium sulfide and CC-0.5 could determine that both showed n-type semiconductor characteristics ( Figure 8 c, Figure 8 d). The flat band potential values measured by the linear region tangent extrapolation method showed that the Ef value of copper indium sulfide was -0.45 V (vs. SSC), while the Ef of CC-0.5 was negatively shifted to -0.69 V (vs. SSC). Based on the 0.2V negative offset relationship between the conduction band potential (ECB) and the flat band potential of n-type semiconductors, the ECB of CC-0.5 was calculated to be -0.89 V (vs. SSC). After electrode potential conversion (SSC→NHE), this value was converted to -0.69 V (vs. NHE). Further combined with the band gap value of copper indium sulfide (2.01 eV), the valence band potential EVB of CC-0.5 was deduced to be 1.03 V (vs. NHE). Similarly, the EVB of the original copper indium sulfide was 1.56 V (vs. NHE). This potential evolution confirmed that the construction of the heterostructure effectively optimized the energy band structure of the material.

[0043] Example 4 Optoelectronic properties of the synthesized catalyst The photoelectrochemical properties of the catalyst were characterized using a CHI 760E electrochemical workstation. A three-electrode test system was constructed: a Pt electrode was used as the counter electrode, Ag / AgCl as the reference electrode, and the FTO glass modified with the catalyst as the working electrode. A 0.5 M sodium sulfate (Na2SO4) solution was used as the electrolyte. The preparation process of the working electrode was as follows: Weigh 40 mg of catalyst powder and 30 μL of perfluorosulfonic acid resin (Nafion), and disperse them in 3 mL of absolute ethanol. Continuously grind the mixture in an agate mortar to form a uniform and viscous slurry. Use a pipette to evenly coat the slurry on the conductive surface of the FTO glass. Conduct infrared drying at 200 °C for 20 minutes.

[0044] The catalysts used were the copper indium sulfide nanotube-supported coal gasification fine slag heterojunction composite catalyst (CC-0.5) prepared in Example 1 and the copper indium sulfide catalyst.

[0045] Figure 8 Figure e shows the electrochemical impedance spectroscopy characteristics of the synthesized catalysts. The 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 this material has a high photogenerated carrier recombination efficiency; in contrast, the copper indium sulfide catalyst shows the smallest curvature radius, confirming its excellent charge transfer performance. It is worth noting that the impedance response of the composite material CC-0.5 presents intermediate-state characteristics, which is attributed to the effective charge transfer channels formed at the heterojunction interface, thus significantly improving the spatial separation efficiency of photogenerated carriers. Figure 8 Figure f further verified through transient photocurrent response tests that the photocurrent density of CC-0.5 is about twice that of the copper indium sulfide catalyst. This enhancement effect stems from the directional migration mechanism of photogenerated electron-hole pairs under the action of the interfacial electric field, which promotes more high-energy electrons to participate in the surface catalytic reaction kinetic process.

[0046] The above has described the examples of the present invention in detail in combination with the embodiments. However, the present invention is not limited to the above examples. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes made without departing from the gist of the present invention should also be regarded as the protection scope of the present invention.

Claims

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

2. The copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst according to claim 1, characterized in that, The length of the nanorods is 100 - 300 nm, and the diameter of the fine 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 content of the fine coal gasification slag in the heterojunction composite catalyst is 50 - 75 wt%.

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

4. The copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst according to claim 3, wherein, The preparation method includes the following steps: (1) At room temperature, dissolve fine coal gasification slag, copper salt, indium salt and thioacetamide in deionized water, stir evenly, react at 120 - 180 °C for 10 - 18 h, and naturally cool to room temperature; (2) Wash, centrifuge the product obtained in step (1), and dry to obtain the composite catalyst.

5. The copper indium sulfide nanotube-supported coal gasification fine slag heterojunction composite catalyst according to claim 4, wherein, In step (1), the mixture needs to be stirred for 20 - 40 min and then sonicated for 5 - 10 min to be evenly mixed.

6. The copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst according to claim 4, characterized in that, In 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); taking 1 mmol of copper salt as an example, the addition amount of the fine coal gasification slag is < 1 g.

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

8. The copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst according to claim 4, wherein, In step (1), after heating to 120 - 180 °C at a rate of 5 - 7 °C / min, keep the temperature constant for 10 - 18 h.

9. The copper indium sulfide nanotube-supported fine slag of coal gasification heterojunction composite catalyst according to claim 4, wherein, In step (2), wash and centrifuge with deionized water and then wash and centrifuge with absolute ethanol; In step (2), the drying temperature is 50 - 80 °C and the drying time is 10 - 15 h.

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

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