Heterojunction nanocomposites and their preparation methods and applications

Abstract

The present invention provides a heterojunction nanocomposite and its preparation method and application. The heterojunction nanocomposite includes C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles, and the C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles are MoS2 / titanium dioxide hybrids with layered C3N4 coated on the surface. Among them, in the MoS2 / titanium dioxide hybrids, the titanium dioxide nanotubes are highly oriented; the MoS2 nanosheets are in the shape of petal flakes and are evenly distributed on the surface of the titanium dioxide nanotubes. This material has a stable structure and a high removal efficiency for organic pollutants; its preparation method is safe, simple, has a mild reaction, low toxicity, has the advantages of environmental friendliness, safety and controllability, is easy to scale up production, brings major innovations to future new energy development and environmental governance, and is suitable for large-area popularization and application.

Description

Technical Field

[0001] The present invention relates to the field of environmental treatment and remediation materials, and particularly to a heterojunction nanocomposite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of industrialization, various persistent organic pollutants, such as p-nitrophenol, methyl orange, methylene blue, phenol, rhodamine, fluorescein, 2,4-dichlorophenoxyacetic acid, etc., are over-emitted into the environment. According to a large number of studies, these chemical substances are persistent and have the ability of long-distance migration and bioaccumulation, and thus may pose potential hazards to the ecosystem and human health.

[0003] TiO2 is a direct wide-bandgap semiconductor material (3.2 eV). In order to promote the research of TiO2 materials in the field of light energy conversion, it is necessary to perform various sensitizations on it to expand the light response range of the material and ultimately improve the light conversion efficiency. Commonly used photosensitizers in the prior art are narrow-band semiconductor materials, such as CdS, CdSe, Fe2O3, and CdTe; noble metal semiconductors, such as Bi2MoO6, BiOBr, Ag3PO4, etc. However, they all have problems such as poor stability and high production costs due to the inclusion of noble metal elements.

[0004] Research has confirmed that co-modifying with different sensitizers can not only expand the light response range of the material to the visible and near-infrared regions but also provide a well-ordered bandgap structure to promote the transport of carriers, and is applied to the removal of organic pollutants. However, the existing modified materials have low light utilization efficiency, poor organic pollutant removal efficiency, and high synthesis difficulty. Summary of the Invention

[0005] The main object of the present invention is to provide a heterojunction nanocomposite material, a preparation method thereof, and an application thereof, aiming to solve the problems of low efficiency in treating organic pollutants and high synthesis difficulty of the photocatalytic composite material in the prior art.

[0006] To achieve the above object, the present invention provides a heterojunction nanocomposite material, which includes C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles. The C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles are MoS2 / titanium dioxide hybrids with a layered C3N4 coated on the surface. Among them, in the MoS2 / titanium dioxide hybrids, the titanium dioxide nanotubes grow highly directionally; the MoS2 nanosheets are in a petal-like morphology and are evenly distributed on the surface of the titanium dioxide nanotubes.

[0007] The present invention also provides a method for preparing the heterojunction nanocomposite as described above, comprising the steps of: providing a molybdenum sulfide solution; the molybdenum sulfide solution being an aqueous solution containing a molybdenum source substance and a sulfur source substance; wherein, the molar ratio of molybdenum element to sulfur element in the molybdenum sulfide solution is 1-3:15-20.

[0008] Adding titanium dioxide nanotubes to the molybdenum sulfide solution for hydrothermal reaction to obtain a MoS2 / titanium dioxide hybrid; wherein, in the MoS2 / titanium dioxide hybrid, the titanium dioxide nanotubes are highly oriented; the MoS2 nanosheets are in a petal-like morphology and are uniformly distributed on the surface of the titanium dioxide nanotubes.

[0009] Providing a C3N4 dispersion; immersing the MoS2 / titanium dioxide hybrid in the C3N4 dispersion for high-temperature treatment to obtain a heterojunction nanocomposite; wherein, the temperature of the high-temperature treatment is 150-200 °C; the duration of the high-temperature treatment is 4-6 h.

[0010] Further, the molybdenum source substance includes one or more of molybdenum trioxide, ammonium molybdate, and sodium molybdate.

[0011] Further, the sulfur source substance is C2H5NS.

[0012] Further, the temperature of the hydrothermal reaction is 180-220 °C; the duration of the hydrothermal reaction is 6-24 h.

[0013] Further, the C3N4 dispersion is obtained by successively performing high-temperature calcination treatment, grinding treatment, protonation treatment, and ultrasonic dispersion treatment on a nitrogen-containing organic substance to obtain the C3N4 dispersion; wherein, the nitrogen-containing organic substance includes one or more of melamine, cyanuric acid, melamine resin, and urea.

[0014] Further, the temperature of the high-temperature calcination treatment is 450-550 °C; the duration of the high-temperature calcination treatment is 12-24 h.

[0015] Further, after the high-temperature treatment step, it further includes washing and vacuum drying the product after high-temperature treatment to obtain the heterojunction nanocomposite.

[0016] The present invention also provides an application of the heterojunction nanocomposite as described above or the heterojunction nanocomposite prepared by the preparation method as described in any one of the above. Inserting the heterojunction nanocomposite as a working electrode into an organic pollutant solution and performing visible light irradiation treatment to obtain a solution after pollutant decomposition; wherein, the light band of the visible light is 400-800 nm, and the duration of the visible light irradiation treatment is 30-80 min.

[0017] Further, the concentration of the organic pollutant solution is 10 - 50 mg / L; the organic pollutant solution includes one or more of p-nitrophenol, methyl orange, methylene blue, phenol, rhodamine, fluorescein, 2,4-dichlorophenoxyacetic acid.

[0018] Beneficial effects achieved by the present invention:

[0019] The heterojunction nanocomposite provided by the present invention can utilize the light source in the visible light band to realize the transfer of charge and energy of the heterojunction nanocomposite. MoS2 in the heterojunction nanocomposite has a strong adsorption capacity, and the heterostructure of the formed heterojunction nanocomposite has a stepwise energy level structure with energy matching. The formation of the energy bands among MoS2 nanosheets, C3N4 and titanium dioxide nanotubes is more conducive to the transport of charge carriers, reduces the recombination of electron-hole pairs, and solves the problem of carrier transport limitation. Moreover, the structure of the heterojunction nanocomposite is stable, which is beneficial to the efficient removal of organic pollutants.

[0020] The preparation method of the heterojunction nanocomposite provided by the present invention simply and efficiently prepares a high-performance optoelectronic material (heterojunction nanocomposite) with the optimal matching of multi-element energy bands on the premise of low production cost. The preparation yield of this preparation method is relatively high, the product morphology is uniform, and the stability is relatively high. It solves the problems of complex nanometerization process, easy agglomeration of products, large particle size, etc. Moreover, the equipment used in the preparation process is inexpensive, the operation steps are safe and simple, the reaction is mild, and the toxicity is small. It has the advantages of environmental friendliness, safety and controllability, and is easy to be mass-produced, bringing a major innovation to future new energy development and environmental governance.

[0021] When the heterojunction nanocomposite provided by the present invention is applied to treat the organic pollutant solution, the material is directly used as the working electrode and inserted into the organic pollutant solution, and then irradiated with visible light (the light band is 400 - 800) for 30 - 80 min. The treatment process is simple, the reaction time is short, the energy consumption is low, and the removal efficiency of organic pollutants is high, which is suitable for large-area popularization and application. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0023] Figure 1 It is a characterization analysis diagram of the heterojunction nanocomposite prepared in Example 1 of the present invention; wherein, Figure 1(a) is a transmission electron microscope (TEM) image of the material at a scale of 100 nm; Figure 1 (b) is Figure 1 a magnified image of (a) by a factor of 2; Figure 1 (c) is a scanning electron microscope (SEM) image of the material at a scale of 500 nm; Figure 1 (d) is Figure 1 a magnified image of (c) by a factor of 2.5; Figure 1 (e) is a high-resolution transmission electron microscope (HRTEM) image of the material;

[0024] Figure 2 is an X-ray photoelectron spectroscopy (XPS) image of the heterojunction nanocomposite prepared in Example 2 of the present invention; among them, Figure 2(a) is the full X-ray photoelectron spectroscopy (XPS) image of the material; Figure 2(b) is the high-resolution X-ray photoelectron spectroscopy (XPS) image of C1s, O 1s, Ti 2p, N 1s, Mo 3d, and S 2p of the material;

[0025] Figure 3 is an energy-dispersive X-ray (EDX) spectroscopic analysis image of the heterojunction nanocomposite prepared in Example 1 of the present invention;

[0026] Figure 4 is the catalytic degradation effect diagram of the heterojunction nanocomposite on Rh B in Example 3 of the present invention;

[0027] Figure 5 is the comparison diagram of the catalytic degradation effect of different materials on Rh B in Example 3 of the present invention; among them, Figure 5 (a) is the comparison diagram of the catalytic degradation effect of each material on Rh B at different times; Figure 5 (b) is the comparison diagram of the degradation kinetic rate of each material on Rh B;

[0028] Figure 6 is the four-cycle comparison diagram of the catalytic degradation of Rh B by the heterojunction nanocomposite in Example 3 of the present invention;

[0029] Figure 7 is the catalytic degradation effect diagram of the heterojunction nanocomposite on PNP in Example 4 of the present invention;

[0030] Figure 8 is the comparison diagram of the catalytic degradation effect of different materials on PNP in Example 4 of the present invention; among them, Figure 8 (a) is the comparison diagram of the catalytic degradation effect of each material on PNP at different times; Figure 8 (b) is the comparison diagram of the degradation kinetic rate of each material on PNP;

[0031] Figure 9It is the comparison diagram of four cycles of heterogeneous junction nanocomposite catalyzing the degradation of PNP in Example 4 of the present invention;

[0032] Figure 10 It is the comparison diagram of ultraviolet-visible absorption spectra analysis of heterogeneous junction nanocomposite, TiO2, TiO2 / MOS2, and TiO2 / C3N4 in Analysis Example 4 of the present invention; among them, Figure 10 (a) is the comparison diagram of ultraviolet-visible (UV-vis) absorption spectra of each material; Figure 10 (b) is the comparison diagram of the corresponding Kubelka-Munk transformed reflection spectra.

[0033] The realization, functional features, and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. It should also be understood that the terms used in the embodiments of the present invention are for the purpose of describing specific specific implementation manners, rather than for limiting the protection scope of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used in the present invention are the same as those understood by those of ordinary skill in the art of the present technology and the records of the present invention. Any methods, devices, and materials similar or equivalent to the methods, devices, and materials described in the embodiments of the present invention can also be used to implement the present invention. Those skilled in the art should know that, as an explanation of this application document, without affecting the actual understanding of the technical solution of this application, "Binding Energy" can be expressed as binding energy, "Intensity" can be expressed as intensity, "Wavelength" can be expressed as wavelength, "Absorbance" can be expressed as absorbance, "Removal efficiency of Rh B" can be expressed as the catalytic degradation efficiency of Rh B, "In(C0 / C t )" can be expressed as the relationship between the reactant concentration and time (especially in the first-order kinetic process, the concentration of the reactant decays exponentially with time, and at this time In(C0 / C t ) is proportional to the reaction time t), "C t" / C0" can be expressed as the instantaneous concentration / original concentration, and "Removal efficiency of PNP" can be expressed as the removal efficiency of PNP.

[0037] When the embodiments give numerical ranges, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. For the test methods without specific conditions noted in the following embodiments, they are generally carried out under conventional conditions or according to the conditions recommended by each manufacturer. The materials or reagents required in the following embodiments are commercially available unless otherwise specified.

[0038] In order to solve the problems existing in the prior art, such as low efficiency in treating organic pollutants and high difficulty in material synthesis when using photocatalytic composite materials, the present invention provides a heterojunction nanocomposite material. The heterojunction nanocomposite material includes C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles. The C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles are a MoS2 / titanium dioxide hybrid body with layered C3N4 coated on the surface. Among them, in the MoS2 / titanium dioxide hybrid body, the titanium dioxide nanotubes are highly oriented; the MoS2 nanosheets have a petal-like morphology and are evenly distributed on the surface of the titanium dioxide nanotubes.

[0039] Specifically, the titanium dioxide nanotubes are highly oriented, with a diameter of about 80 nm and a wall thickness of about 10 nm. The petal-like MoS2 nanosheets are thinly and evenly distributed on the surface of the titanium dioxide nanotubes. The MoS2 nanosheets are mainly attached to the junction areas between the titanium dioxide nanotubes. Although the loading amount is large, the titanium dioxide nanotube array maintains the characteristic of having open ends at the top. This structure is beneficial to the transport of photo-generated electrons and the adsorption of substances to be degraded.

[0040] It should be noted that the heterojunction nanocomposite material is composed of petal-like MoS2 and layered C3N4. Two semiconductor material thin films with different electronic band structures are sequentially deposited on the titanium dioxide nanotubes to form a heterojunction nanocomposite material.

[0041] Research findings show that the electron mobility of MoS2 is higher than that of titanium dioxide. A variety of MoS2 nanostructures can be directly grown on a TiO2 substrate through a simple and low-cost chemical route. For example, zero-dimensional nanospheres, one-dimensional nanowires, two-dimensional nanoplates, and three-dimensional porous multi-layer nanoplates. However, for zero-dimensional nanospheres: the preparation process is complex, and it is difficult to control the particle size and morphology. For one-dimensional nanowires: they are prone to agglomeration during the preparation process, resulting in a decline in performance. For two-dimensional nanoplates: high temperature and high pressure are required during the preparation process, and the cost is relatively high. For three-dimensional porous multi-layer nanoplates: the preparation process is complex, and special equipment and technology are needed. "In the MoS2 / titanium dioxide hybrid, titanium dioxide nanotubes are highly oriented; MoS2 nanosheets have a petal-like morphology and are evenly distributed on the surface of titanium dioxide nanotubes." The titanium dioxide nanotube array maintains the characteristic of an open top, and this structure is conducive to the transport of photo-generated electrons and the adsorption of substances to be degraded. It effectively improves the composite efficiency of MoS2 and titanium dioxide and enhances the interaction between the two; the petal-like MoS2 nanosheets and the embedded titanium dioxide nanotubes form a unique structure, which is conducive to improving the photocatalytic performance; the MoS2 / titanium dioxide hybrid can effectively separate and transfer electron-hole pairs, reduce the recombination probability, and improve the quantum efficiency; MoS2 and titanium dioxide in the hybrid can act synergistically to improve the selectivity and activity of the photocatalytic reaction. C3N4 (graphitic carbon nitride) is a non-metallic semiconductor material. It is an organic polymer with a unique two-dimensional layered structure, composed of carbon and nitrogen atoms connected by covalent bonds. It can generate electron-hole pairs under visible light irradiation for reactions such as catalytic water decomposition to produce hydrogen and degradation of organic pollutants. C3N4 is also a direct bandgap semiconductor, and its bandgap width is about 2.9 eV, which means it can only absorb photons with energy higher than its bandgap. In the visible light range, the energy of most photons is lower than the bandgap energy of C3N4, so the efficiency of C3N4 in photocatalytic reactions under visible light is relatively low.

[0042] However, the heterojunction nanocomposite material (C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles) of the present invention obtained through research can significantly improve the photocatalytic efficiency; the reasons are analyzed as follows:

[0043] (1) Synergistic effect of energy band structure: The energy band structures of MoS2 and titanium dioxide work in synergy with that of C3N4, enabling the composite material to absorb light in a wider wavelength range. The bandgap width of MoS2 is approximately 1.9 eV, while that of titanium dioxide is approximately 3.2 eV. By combining C3N4 with MoS2 and titanium dioxide, MoS2 can be utilized to absorb visible light, while C3N4 and titanium dioxide can only absorb near-ultraviolet light, thereby causing a redshift in the light absorption range and extending it to the visible light absorption range. Visible light accounts for approximately 50% of the total solar radiation energy, while ultraviolet light accounts for approximately 7% of the total solar radiation energy. This composite material improves the utilization efficiency of solar energy.

[0044] (2) Separation of electron-hole pairs: The combination of C3N4, MoS2, and titanium dioxide can improve the separation efficiency of electron-hole pairs. During the photocatalysis process, the separation of electron-hole pairs is the key to improving the catalytic efficiency. The composite of C3N4, MoS2, and titanium dioxide (heterojunction nanocomposite) can provide an effective electron-hole pair separation mechanism, reducing the charge recombination within the composite and thus enhancing the catalytic activity.

[0045] (3) Enhanced light absorption and light scattering: Different materials in the composite material can interact with each other to enhance light absorption and scattering. This helps to improve the light utilization rate and further enhance the photocatalytic efficiency.

[0046] (4) Synergistic catalysis: The synergistic effect among C3N4, MoS2, and titanium dioxide can promote specific catalytic reactions. For example, MoS2 can act as an electron donor to help C3N4 and titanium dioxide accelerate specific redox reactions, thereby improving the catalytic performance.

[0047] By combining C3N4 with MoS2 and titanium dioxide, the respective advantages can be utilized to overcome the limitations of single materials, thereby achieving more efficient and comprehensive photocatalytic performance.

[0048] The heterojunction nanocomposite provided by the present invention can utilize a light source in the visible light band to achieve the transfer of charge and energy of the heterojunction nanocomposite. MoS2 in the heterojunction nanocomposite has a strong adsorption capacity, and the heterostructure of the formed heterojunction nanocomposite has a stepwise energy level structure that matches its energy. The formation of the energy bands among MoS2 nanosheets, C3N4, and titanium dioxide nanotubes is more conducive to the transport of charge carriers, reducing the recombination of electron-hole pairs and solving the problem of carrier transport limitation. Moreover, the structure of the heterojunction nanocomposite is stable, which is beneficial for the efficient removal of organic pollutants.

[0049] The present invention also provides a method for preparing the above heterogeneous junction nanocomposite, comprising the steps of: providing a molybdenum sulfide solution; the molybdenum sulfide solution being an aqueous solution containing a molybdenum source substance and a sulfur source substance; wherein, the molar ratio of molybdenum element to sulfur element in the molybdenum sulfide solution is 1-3:15-20. Specifically, a chemical reaction occurs between the source substance and the sulfur source substance in the molybdenum sulfide solution: Mo 4+ +2S 2- →MoS2. When the molar ratio of molybdenum element to sulfur element in the molybdenum sulfide solution is 1-3:15-20, it can ensure that the reactants react fully, avoiding excessive or insufficient sulfur, thereby affecting the formation and purity of molybdenum disulfide. If the molar ratio of molybdenum element to sulfur element is too high, excessive sulfur may lead to too high sulfur content in the generated molybdenum disulfide, affecting its performance; if the molar ratio is too low, excessive molybdenum may lead to too high molybdenum content in the generated molybdenum disulfide, also affecting its performance.

[0050] Adding titanium dioxide nanotubes to the molybdenum sulfide solution for hydrothermal reaction to obtain a MoS2 / titanium dioxide hybrid; wherein, in the MoS2 / titanium dioxide hybrid, the titanium dioxide nanotubes are highly oriented; the MoS2 nanosheets are in a petal-like morphology and are evenly distributed on the surface of the titanium dioxide nanotubes.

[0051] Specifically, the petal-like MoS2 nanosheets have good visible light absorption ability, while the titanium dioxide nanotubes have good response in the ultraviolet region. The energy band structure of MoS2 matches the energy band structure of the titanium dioxide nanotubes, enabling the effective transfer and separation of photo-generated electrons and holes; the combination of the two can broaden the light absorption range and improve the photocatalytic efficiency.

[0052] Moreover, a heterojunction is formed between the MoS2 nanosheets and the titanium dioxide nanotubes, generating a built-in electric field to promote charge separation. Among them, the interfacial contact between the MoS2 nanosheets and the titanium dioxide nanotubes is conducive to the rapid separation and transmission of charges, reducing charge recombination, thereby further enhancing the photocatalytic activity and improving charge separation and transmission.

[0053] The petal-like morphology of the MoS2 nanosheets may introduce certain surface defects, and these defects can serve as active sites to promote the photocatalytic reaction. Therefore, the embedding of the MoS2 nanosheets can also enhance the structural stability of the composite material, enabling it to maintain good performance during long-term use and enhancing stability. Moreover, the petal-like MoS2 nanosheets increase the specific surface area of the material, contributing to the adsorption of pollutants and improving the rate of the photocatalytic reaction.

[0054] In addition, it was found during the experiment that if the morphology of MoS2 is not petal-like, it may not be able to form a good embedding structure with titanium dioxide nanotubes, affecting charge transport and synergy. Under certain extreme conditions, MoS2 and titanium dioxide may undergo a chemical reaction, damaging the structure and properties of the composite material, resulting in chemical compatibility problems. Moreover, MoS2 nanosheets with non-petal-like morphologies will affect the loading amount. Either too high or too low loading amount of MoS2 nanosheets may affect the performance of the final composite material. An excessively high loading amount may lead to agglomeration, reducing the specific surface area and light transmittance; an excessively low loading amount will not be able to fully exert the synergy.

[0055] In an optional embodiment, a sheet-like metal titanium sheet is etched by wet chemical etching to obtain titanium dioxide nanotubes with a vertically growing three-dimensional porous structure. The three-dimensional porous structure of the titanium dioxide nanotubes endows them with a relatively high specific surface area, which is beneficial to enhancing their catalytic, adsorption, and sensing properties. Moreover, the porous structure provides more active sites, enabling the titanium dioxide nanotubes to have excellent catalytic activity and good biocompatibility in catalytic reactions. And this kind of porous structure can change the propagation path of light in the material, enhancing the light absorption and luminescence properties of the composite material.

[0056] In addition, the three-dimensional porous structure of the titanium dioxide nanotubes can provide certain mechanical support, making the finally prepared composite material more durable during application. The porous structure of the titanium dioxide nanotubes also facilitates the introduction of MoS2 nanosheets and C3N4 in subsequent preparation process steps, thereby realizing the functionalization of the composite material.

[0057] Among them, wet chemical etching is environmentally friendly and does not produce harmful organic solvents and gases. And the preparation is simple, can be carried out under laboratory conditions, and is easy to scale up production. Moreover, using metal titanium as a precursor has a low cost, and the wet chemical etching process does not require expensive equipment.

[0058] Provide a C3N4 dispersion; immerse the MoS2 / titanium dioxide hybrid in the C3N4 dispersion and perform high-temperature treatment to obtain a heterojunction nanocomposite; wherein, the temperature of the high-temperature treatment is 150 - 200 °C; the duration of the high-temperature treatment is 4 - 6 h. Specifically, in order to obtain a well-dispersed C3N4 dispersion, concentrated hydrochloric acid solution is used to protonate C3N4. Protonated C3N4 is beneficial to the coating of C3N4 on the surface of titanium dioxide nanotubes due to the stacking fracture and the formation of small C3N4 particles. After loading MoS2 and C3N4 nanoparticles, the structural integrity and morphology of TiO2 NTAs remain unchanged.

[0059] Among them, at 150-200 °C, the molecules in the C3N4 dispersion can penetrate to the surface or inside of the MoS2 / titania hybrid, forming chemical bonding or physical adsorption, thereby promoting the interaction between materials. This interfacial interaction can enhance the bonding strength of the materials and improve the performance of the composite material.

[0060] The temperature of 150-200 °C helps to eliminate the internal defects of the material, promote the phase transition process, and form a more stable crystal structure. For MoS2 and titania, it may help to form a more stable phase in this temperature range, improving the thermal stability of the material. Moreover, since both MoS2 and titania are semiconductor materials, the adjustment of their energy band structures is crucial for the optoelectronic properties of the composite material. High-temperature treatment may optimize the energy band structure by changing the electron state density on the material surface, thereby improving the optoelectronic conversion efficiency of the composite material. Finally, the internal defects of the prepared material are reduced, and the bonding force between grains is enhanced, thus improving the mechanical properties of the composite material, such as strength and toughness; the optimized energy band structure and interfacial state can significantly improve the optoelectronic properties of the composite material, such as light absorption efficiency and optoelectronic conversion efficiency; the internal structure of the material is optimized, improving the thermal stability of the composite material so that it can still maintain good performance in high-temperature environments.

[0061] If the temperature is too high, it may cause irreversible chemical reactions in the material, such as the decomposition of C3N4 or the oxidation of MoS2, thus destroying the structure of the final composite material. If the treatment time is too long, it may cause overheating on the material surface, resulting in thermal damage and affecting the performance of the material. The compatibility between the C3N4 dispersion and the MoS2 / titania hybrid is also an important factor for the success of this preparation step. Incompatible materials may undergo harmful reactions during high-temperature treatment, destroying the structure of the composite material. In summary, by reasonably selecting the temperature (150-200 °C) and treatment duration (4-6 h) of high-temperature treatment, a heterojunction nanocomposite material with enhanced mechanical properties, improved optoelectronic properties, and enhanced thermal stability can be effectively prepared.

[0062] The preparation method of the heterojunction nanocomposite material provided by the present invention simply and efficiently prepares a high-performance optoelectronic material (heterojunction nanocomposite material) with an optimal match of multi-element energy bands on the premise of low production cost. This preparation method has a high preparation yield, uniform product morphology, and high stability, solving problems such as complex nanometerization process, easy agglomeration of products, and large particle size. Moreover, the equipment used in the preparation process is inexpensive, the operation steps are safe and simple, the reaction is mild, and the toxicity is small, having the advantages of environmental friendliness, safety and controllability, being easy for large-scale production, and bringing a major innovation to future new energy development and environmental governance.

[0063] Furthermore, the molybdenum source material includes one or more of molybdenum trioxide, ammonium molybdate, and sodium molybdate. Preferably, the molybdenum source material is sodium molybdate (Na2MoO4·2H2O). Sodium molybdate (Na2MoO4·2H2O) is a high-purity molybdenum compound that can provide a high-purity molybdenum source, and the prepared MoS2 has high purity; and under the experimental conditions of the present invention, using sodium molybdate is more conducive to promoting the formation of petal-like MoS2. Moreover, sodium molybdate is easily soluble in solution, facilitating mixing with other reactants, thus simplifying the preparation process. Sodium molybdate is usually easily separated from the solution by simple filtration or centrifugation after the reaction, facilitating subsequent washing and drying steps. This ease of handling makes sodium molybdate a preferred raw material for synthesizing MoS2. Using sodium molybdate as the molybdenum source can be carried out under relatively mild reaction conditions, such as lower temperature and pressure, which helps reduce energy consumption and simplify equipment requirements. And sodium molybdate has good solubility in water, which is conducive to using the aqueous phase synthesis method, which is usually environmentally friendly and reduces the need for waste generation and treatment. It also has a relatively low price, and using sodium molybdate as the raw material has high cost-effectiveness.

[0064] Furthermore, the sulfur source material is C2H5NS. Specifically, in the process of synthesizing MoS2, the choice and addition amount of the sulfur source have a great influence on the quality of the final product; sodium molybdate can react with C2H5NS to provide a uniform and controllable sulfur source, which helps to precisely control the composition and structure of MoS2.

[0065] Furthermore, the temperature of the hydrothermal reaction is 180 - 220 °C; the duration of the hydrothermal reaction is 6 - 24 h.

[0066] Furthermore, the C3N4 dispersion is obtained by successively performing high-temperature calcination treatment, grinding treatment, protonation treatment, and ultrasonic dispersion treatment on the nitrogen-containing organic matter to obtain the C3N4 dispersion; wherein, the nitrogen-containing organic matter includes one or more of melamine, cyanuric acid, melamine resin, and urea. Specifically, in an optional embodiment, melamine is calcined at high temperature in a muffle furnace, and the obtained yellow agglomerates are ground into powder. Protonation treatment is carried out by treating with hydrochloric acid at room temperature for 4 - 6 h. Then the protonated C3N4 is washed with deionized water until neutral conditions and dried. Ultrasonic dispersion is carried out with deionized water for 6 - 8 h to obtain a uniformly dispersed C3N4 dispersion.

[0067] Furthermore, the temperature of the high-temperature calcination treatment is 450 - 550 °C; the duration of the high-temperature calcination treatment is 12 - 24 h.

[0068] Furthermore, after the high-temperature treatment step, it also includes washing treatment and vacuum drying treatment on the product after high-temperature treatment to obtain the heterojunction nanocomposite material. Specifically, the product after high-temperature treatment is washed three times with deionized water and vacuum dried to obtain the heterojunction nanocomposite material.

[0069] The present invention also provides an application of the heterojunction nanocomposite as described above or the heterojunction nanocomposite prepared by the preparation method of any one of the above. The heterojunction nanocomposite is inserted into an organic pollutant solution as a working electrode and subjected to visible light irradiation treatment to obtain a solution after the pollutants are decomposed. Among them, the light band of the visible light is 400-800 nm, and the duration of the visible light irradiation treatment is 30-80 min.

[0070] Specifically, 50-100 mL of the organic pollutant solution can be taken and added to a cubic quartz cup. The heterojunction nanocomposite is inserted into the quartz cup as a working electrode and irradiated with visible light having a light band of 400-800 nm. The solution is stirred at room temperature, the rotor speed is 50-200 rpm, and sampling is performed every 10 min, and the sampling volume is 250 μL-350 μL. It is detected by an ultraviolet spectrophotometer, and an organic pollutant removal curve is drawn according to the results. Specifically, the visible light source: a simulated sunlight xenon lamp (500 W Xe lamp, Beijing Changtuo) + a UV-cut filter, and the light band is 400-800 nm. Light intensity: 100 mW / cm 2 , and the measuring instrument is NOVA Oriel 70260. Applying the heterojunction nanocomposite provided by the present invention to treat an organic pollutant solution, directly inserting the material into the organic pollutant solution as a working electrode and performing visible light irradiation treatment for 30-80 min is sufficient. The treatment process is simple, the reaction time is short, the energy consumption is low, the removal efficiency of organic pollutants is high, and it is suitable for large-scale popularization and application.

[0071] Furthermore, the concentration of the organic pollutant solution is 10-50 mg / L; the organic pollutant solution includes one or more of p-nitrophenol, methyl orange, methylene blue, phenol, rhodamine, fluorescein, 2,4-dichlorophenoxyacetic acid.

[0072] For further understanding of the present invention, examples are given below for illustration:

[0073] Example 1

[0074] A molybdenum-sulfur solution is prepared by using sodium molybdate and C2H5NS in a molar ratio of 1:15;

[0075] Titanium dioxide nanotubes are added to the molybdenum-sulfur solution for hydrothermal reaction (180 °C; 24 h) to obtain a MoS2 / titanium dioxide hybrid;

[0076] Melamine is used for high-temperature roasting treatment (450 °C; 24 h), grinding treatment, protonation treatment, and ultrasonic dispersion treatment in sequence to provide a C3N4 dispersion;

[0077] Immerse the MoS2 / titanium dioxide hybrid in the C3N4 dispersion and perform high-temperature treatment (150 °C; 6 h), then wash and vacuum-dry the product after high-temperature treatment to obtain a heterojunction nanocomposite.

[0078] Example 2

[0079] Prepare a molybdenum-sulfur solution with sodium molybdate and C2H5NS in a molar ratio of 3:20;

[0080] Add titanium dioxide nanotubes to the molybdenum-sulfur solution and carry out a hydrothermal reaction (220 °C; 6 h) to obtain a MoS2 / titanium dioxide hybrid;

[0081] Use melamine to perform high-temperature calcination treatment (550 °C; 12 h), grinding treatment, protonation treatment, and ultrasonic dispersion treatment in sequence to provide a C3N4 dispersion;

[0082] Immerse the MoS2 / titanium dioxide hybrid in the C3N4 dispersion and perform high-temperature treatment (200 °C; 4 h), then wash and vacuum-dry the product after high-temperature treatment to obtain a heterojunction nanocomposite.

[0083] Analysis Example 1

[0084] Characterize and analyze the heterojunction nanocomposite prepared in Example 1 to obtain a transmission electron microscope (TEM) image at a scale of 100 nm, as shown in Figure 1 (a); Figure 1 (b) is a magnified image 2 times that of Figure 1 (a); Figure 1 (c) is a scanning electron microscope (SEM) image of the heterojunction nanocomposite at a scale of 500 nm; Figure 1 (d) is a magnified image 2.5 times that of Figure 1 (c); Figure 1 (e) is a high-resolution transmission electron microscope (HRTEM) image of the heterojunction nanocomposite.

[0085] From Figure 1 (a), it can be seen that the flaky petals are MoS2, and the middle black layer is C3N4. Figure 1 (b) shows that the MoS2 nanosheets are evenly and thinly distributed on the surface of the TiO2 nanotubes. The MoS2 nanosheets are mainly attached to the junction areas between the nanotubes, maintaining the characteristics of the open ends at the top of the TiO2 nanotube array. This structure is beneficial to the transmission of photo-generated electrons and the adsorption of substances to be degraded. Protonated C3N4 is coated on the surface of the TiO2 nanotubes. After loading MoS2 and C3N4 nanoparticles, the structural integrity and morphology of the TiO2NTAs remain unchanged.

[0086] Figure 1 (c) depicts the scanning electron microscope (SEM) image of the heterojunction nanocomposite, indicating that the MoS₂ nanosheets are thinly and evenly distributed on the surface of TiO₂ nanotubes. The MoS₂ nanosheets are mainly attached to the junction areas between the nanotubes, maintaining the characteristic of the open top of the TiO₂ nanotube array. This structure is beneficial to the transport of photo-generated electrons and the adsorption of pollutants to be degraded. Protonated C₃N₄ is coated on the surface of TiO₂ nanotubes. After loading MoS₂ and C₃N₄ nanoparticles, the structural integrity and morphology of TiO₂ NTAs remain unchanged. As Figure 1 (d) shows, the TiO₂ nanotubes are magnified. The obtained TiO₂ nanotubes are highly oriented in growth, with a tube diameter of about 80 nm and a tube wall thickness of about 10 nm.

[0087] Figure 1 (e) depicts the high-resolution transmission electron microscope (HRTEM) image of the heterojunction nanocomposite. The measured lattice spacing is 0.269 nm, corresponding to the crystal plane of MoS₂. The lattice spacing of 0.356 nm corresponds to the crystal plane of C₃N₄. The lattice fringe spacing of 0.241 nm can be attributed to the crystal plane of anatase TiO₂. The lattice fringes of TiO₂, MoS₂, and C₃N₄ can be clearly observed from this HRTEM image, indicating the well-defined crystal structure of the heterojunction nanocomposite.

[0088] Analysis Example 2

[0089] The full X-ray photoelectron spectroscopy (XPS) spectrum of the heterojunction nanocomposite prepared in Example 2 is shown in Fig. 2(a).

[0090] The characteristic peaks of all major elements in the sample can be observed from Fig. 2(a), C 1s, N 1s, O 1s, Ti 2p, Mo 3d, and S 2p. The characteristic peak positions of each element can help determine its presence and possible chemical states in the sample (heterojunction nanocomposite). Among them, the peaks of C and N indicate the presence of C₃N₄, while the peaks of Mo and S confirm the presence of MoS₂. The peaks of Ti and O indicate the presence of TiO₂.

[0091] The high-resolution X-ray photoelectron spectroscopy (XPS) spectra of C 1s, O 1s, Ti 2p, N 1s, Mo 3d, and S 2p of the heterojunction nanocomposite prepared in Example 2 are shown in Fig. 2(b).

[0092] As shown in Fig. 2(b), the sample (heterojunction nanocomposite) is mainly composed of elements C, N, Mo, S, Ti, and O. The characteristic peaks of these elements (C 1s, N 1s, Mo 3d, S 2p, Ti 2p, and O 1s) can be clearly observed in the full spectrum of Fig. 2(a). Among them: the XPS peak positions of MoS2: the peak of Mo 3d 3 / 2 is located at 232.0 eV; the peak of Mo 3d 5 / 2 is located at 228.1 eV; the peak of S 2p is located at 163.0 eV. The positions of these peaks indicate the presence of Mo 4+ ions. The C 1s peak is located at 285.4 eV. The N 1s spectrum belongs to C=N-C (394.9 eV). The O 1s peak corresponds to the Ti-O bond (529.8 eV). The Ti 2p spectrum shows two peaks, located at 459.1 eV (Ti 2p3 / 2) and 464.9 eV (Ti 2p1 / 2) respectively.

[0093] Analysis Example 3

[0094] Energy-dispersive X-ray (EDX) spectroscopy analysis was performed on the products at each stage (titanium dioxide nanotubes, MoS2 / titanium dioxide hybrid, heterojunction nanocomposite) during the preparation process of Example 1, and the analysis results are as Figure 3 shown. According to Figure 3 it can be seen that this spectrum shows characteristic peaks corresponding to the elements C (carbon), N (nitrogen), O (oxygen), Ti (titanium), Mo (molybdenum), and S (sulfur). The elemental composition of the sample was determined, which is consistent with the analysis results of XPS in Analysis Example 2.

[0095] Among them, the analysis data of Spectrum 11 are shown in Table 1:

[0096] Table 1 Analysis Data of Spectrum 11

[0097]

[0098] The analysis data of Spectrum 12 are shown in Table 2:

[0099] Table 2 Analysis Data of Spectrum 12

[0100]

[0101] Example 3

[0102] 1. Use the heterojunction nanocomposite (TiO2 / MoS2 / C3N4) to catalytically degrade Rh B (rhodamine B)

[0103] (1) Take 100 mL of 20 mg / L Rh B solution and add it to a cubic quartz cup, and insert the heterojunction nanocomposite prepared in Example 1 as the working electrode into the quartz cup.

[0104] (2) Irradiate the cubic quartz cell with light having wavelengths of 400 - 800 nm respectively, light intensity: 100 mW / cm 2 . And stir the solution at room temperature, the rotor speed is 200 rpm, take samples every 10 min until 60 min, and the sampling volume is 300 μL.

[0105] (3) Use an ultraviolet spectrophotometer to detect the sampling results, and draw the Rh B removal curve according to the results, specifically as Figure 4 shown.

[0106] As can be seen from Figure 4 , the heterojunction nanocomposite electrode shows high catalytic efficiency for Rh B molecules. Rh B can be completely decomposed by 60 min of light irradiation, and the highest degradation kinetic rate k = 0.3056 min -1 .

[0107] 2. Under simulated solar radiation and other same experimental conditions, use TiO2, TiO2 / MOS2, TiO2 / C3N4, TiO2 / MOS2 / C3N4 (heterojunction nanocomposite) to catalytically degrade Rh B respectively, and the degradation comparison results are as Figure 5 shown; among them, Figure 5 (a) is the comparison chart of the catalytic degradation effects of each material on Rh B at different times; Figure 5 (b) is the comparison chart of the degradation kinetic rates of each material on Rh B.

[0108] As Figure 5 shown, under the same conditions, the activity of the TiO2 / MOS2 / C3N4 electrode is significantly higher than that of other electrodes: TiO2 / C3N4, TiO2 / MOS2, TiO2. Under 60 min of light irradiation, the degradation rates of the above photocatalysts on RhB are 100%, 78.3%, 69.7%, and 38.2% respectively. It shows that the enhanced photocatalytic activity of TiO2 / MOS2 / C3N4 is not only attributed to the strong adsorption ability of the composite material, but also to the formation of a heterostructure with matching energy bands between C3N4, MOS2 and TiO2 nanotubes.

[0109] 3. Under simulated solar radiation and other same experimental conditions, use TiO2 / MOS2 / C3N4 (heterojunction nanocomposite) to catalytically degrade Rh B for four cycles. The comparison chart of the catalytic degradation performance of the heterojunction nanocomposite for four cycles (1st, 2nd, 3rd, 4th) is as Figure 6 shown.

[0110] According to Figure 6As shown, after being used multiple times (four cycles), the photocatalytic degradation performance of the heterojunction nanocomposite did not show a significant decline, indicating that the material has good stability and durability and strong practical applicability.

[0111] Example 4

[0112] 1. Use the heterojunction nanocomposite (TiO2 / MOS2 / C3N4) to catalyze the degradation of PNP (nitrophenol)

[0113] (1) Take 100 mL of 20 mg / L PNP solution and add it to a cubic quartz cup. Insert the heterojunction nanocomposite prepared in Example 2 as the working electrode into the quartz cup.

[0114] (2) Irradiate the cubic quartz cup with light of wavelengths from 200 to 800 nm, and stir the solution at room temperature with a rotor speed of 200 rpm. Take samples every 10 min until 40 min, and the sample volume is 300 μL.

[0115] (3) Use a UV spectrophotometer to detect the sampling results, and draw a PNP removal curve according to the results, as specifically shown in Figure 7 as follows.

[0116] As can be seen from Figure 7 , after 40 min of continuous visible light radiation, the characteristic peak of the PNP model molecule disappeared, indicating that the pollutants had been completely eliminated. And the highest degradation kinetic rate k = 0.1317 min -1 .

[0117] 2. Under the conditions of light radiation with wavelengths from 200 to 800 nm and other same experimental conditions, use TiO2, TiO2 / MOS2, TiO2 / C3N4, and TiO2 / MOS2 / C3N4 (heterojunction nanocomposite) to catalyze the degradation of PNP respectively. The degradation comparison results are as shown in Figure 8 as follows; among them, Figure 8 (a) is a comparison chart of the catalytic degradation effects of each material on PNP at different times; Figure 8 (b) is a comparison chart of the degradation kinetic rates of each material on PNP.

[0118] As shown in Figure 8As shown, under the same conditions, the activity of the TiO2 / MOS2 / C3N4 electrode is significantly higher than that of other electrodes: TiO2 / C3N4, TiO2 / MOS2, and TiO2. Under 40 minutes of light irradiation, the degradation rates of PNP by the above photocatalysts are 100%, 76.2%, 54.9%, and 29.8%, respectively. This shows that the enhanced photocatalytic activity of TiO2 / MOS2 / C3N4 is not only attributed to the strong adsorption ability of the composite material but also to the formation of a heterostructure with a matched energy band among C3N4, MOS2, and TiO2 nanotubes.

[0119] 4. Under light radiation with a wavelength of 200 - 800 nm and other same experimental conditions, TiO2 / MOS2 / C3N4 (heterojunction nanocomposite) was used to catalytically degrade PNP for four cycles. The comparative diagram of the catalytic degradation performance of the heterojunction nanocomposite for four cycles (1st, 2nd, 3rd, 4th) is as Figure 9 shown.

[0120] According to Figure 9 shown, during the process of degrading 20 mg / L of PNP by the heterojunction nanocomposite, this experiment was repeated four times, and the heterojunction nanocomposite showed extremely strong photocatalytic stability and broad application prospects.

[0121] Analysis Example 4

[0122] The heterojunction nanocomposite prepared in Example 2, TiO2, TiO2 / MOS2, and TiO2 / C3N4 used in Example 4 were subjected to ultraviolet-visible absorption spectroscopy analysis, and the results are as Figure 10 shown. Among them, Figure 10 (a) is the comparative diagram of the ultraviolet-visible (UV-vis) absorption spectra of each material; Figure 10 (b) is the comparative diagram of the corresponding Kubelka-Munk transformed reflection spectra.

[0123] Compared with TiO2, TiO2 / MOS2, and TiO2 / C3N4, the absorption curve of the heterojunction nanocomposite shows a significant enhancement in the visible light region. The absorption edge of the heterojunction nanocomposite has a significant red shift towards a higher wavelength of about 440 nm. The band gap energy of a semiconductor can be estimated by the Kubelka-Munk transformation and is calculated to be 1.50, 2.01, 2.80, and 3.20 electron volts, respectively.

[0124] In summary, in the above technical solutions of the present invention, the above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for preparing a heterojunction nanocomposite material, characterized in that, Including the steps: Providing a molybdenum-sulfur solution; the molybdenum-sulfur solution is an aqueous solution containing a molybdenum source substance and a sulfur source substance; wherein, the molar ratio of molybdenum element to sulfur element in the molybdenum-sulfur solution is 1-3:15-20; Adding titanium dioxide nanotubes to the molybdenum-sulfur solution for hydrothermal reaction to obtain a MoS2 / titanium dioxide hybrid; wherein, in the MoS2 / titanium dioxide hybrid, the titanium dioxide nanotubes are highly oriented and the titanium dioxide nanotubes keep the top openings; the MoS2 nanosheets are in a petal-like morphology and are uniformly distributed on the surface of the titanium dioxide nanotubes; Providing a C3N4 dispersion; Immersing the MoS2 / titanium dioxide hybrid in the C3N4 dispersion for high-temperature treatment to obtain a heterojunction nanocomposite; wherein, the temperature of the high-temperature treatment is 150-200 °C; the duration of the high-temperature treatment is 4-6 h; The heterojunction nanocomposite includes C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles, and the C3N4 / MoS2 / titanium dioxide nanotube heterojunction nanoparticles are MoS2 / titanium dioxide hybrids with layered C3N4 coated on the surface.

2. The preparation method according to claim 1, characterized in that, The molybdenum source substance includes one or more of molybdenum trioxide, ammonium molybdate, and sodium molybdate.

3. The preparation method according to claim 1, characterized in that, The sulfur source substance is C2H5NS.

4. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 180-220 °C; the duration of the hydrothermal reaction is 6-24 h.

5. The preparation method according to claim 1, characterized in that, The C3N4 dispersion is obtained by successively performing high-temperature calcination treatment, grinding treatment, protonation treatment, and ultrasonic dispersion treatment on a nitrogen-containing organic substance to obtain the C3N4 dispersion; Wherein, the nitrogen-containing organic substance includes one or more of melamine, cyanuric acid, melamine resin, and urea.

6. The preparation method according to claim 5, characterized in that The temperature of the high-temperature calcination treatment is 450-550 °C; the duration of the high-temperature calcination treatment is 12-24 h.

7. The preparation method according to claim 1, characterized in that, After the step of the high-temperature treatment, it further includes washing treatment and vacuum drying treatment on the product after the high-temperature treatment to obtain the heterojunction nanocomposite.

8. Use of the heterojunction nanocomposite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that, Inserting the heterojunction nanocomposite as a working electrode into an organic pollutant solution and performing visible light irradiation treatment to obtain a solution after the pollutant is decomposed; wherein, the light band of the visible light is 400-800 nm, and the duration of the visible light irradiation treatment is 30-80 min.

9. The application according to claim 8, characterized in that, The concentration of the organic pollutant solution is 10-50 mg / L; The organic pollutant solution includes one or more of p-nitrophenol, methyl orange, methylene blue, phenol, rhodamine, fluorescein, and 2,4-dichlorophenoxyacetic acid.

Images