Two-dimensional heterojunction piezoelectric material for water treatment and preparation method thereof

Abstract

The invention provides a two-dimensional heterojunction piezoelectric material for water treatment and a preparation method thereof, and belongs to the technical field of water treatment. The two-dimensional heterojunction piezoelectric material has a heterojunction structure formed by cobalt sulfide and molybdenum disulfide, and molybdenum disulfide has a 1T crystal phase and a 2H crystal phase. The two-dimensional heterojunction piezoelectric material has good conductivity, charge separation efficiency and stability, when the two-dimensional heterojunction piezoelectric material is applied to water treatment, the two-dimensional heterojunction piezoelectric material generates surface charges under the action of mechanical force and catalyzes and degrades various organic pollutants in water, application is flexible, and environmental adaptability is high.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a two-dimensional heterojunction piezoelectric material, its preparation method, and its application in water treatment. Background Technology

[0002] Piezoelectric catalytic degradation technology, as an environmentally friendly advanced oxidation water treatment technology, uses mechanical energy such as water flow vibration and ultrasound to drive the deformation of piezoelectric materials, causing the positive and negative charge centers inside the piezoelectric materials to separate and form a built-in electric field. The separated positive and negative charges can participate in oxidation-reduction reactions, generating superoxide anions (·O2) by activating dissolved oxygen in the water. - This technology utilizes reactive oxygen species such as hydroxyl radicals (·OH) to oxidize and degrade organic pollutants in water. It requires no additional oxidant and produces no toxic byproducts, making it a promising technology for water treatment.

[0003] However, the application of piezoelectric materials in water treatment is still subject to many limitations: existing piezoelectric materials generally suffer from problems such as easy charge recombination and poor intrinsic conductivity, which makes it difficult for the separated charges to migrate efficiently to the material surface to participate in the reaction. As a result, the amount of active oxygen species generated is low, and the catalytic degradation efficiency of piezoelectric materials is low. In addition, piezoelectric materials also suffer from problems such as insufficient long-term operational stability, poor environmental adaptability, and susceptibility to interference from water pH and complex components in actual water bodies, making it difficult to meet the needs of actual water treatment scenarios. Summary of the Invention

[0004] In view of this, the main objective of the present invention is to provide a two-dimensional heterojunction piezoelectric material that can be used for water treatment and a method for preparing the same, in order to at least partially solve at least one of the aforementioned technical problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] In one aspect of the present invention, a two-dimensional heterojunction piezoelectric material is provided, which has a heterojunction structure formed by cobalt sulfide and molybdenum disulfide, wherein the molybdenum disulfide has a 1T crystal phase and a 2H crystal phase.

[0007] In another aspect of the present invention, a method for preparing the above-mentioned two-dimensional heterojunction piezoelectric material is provided, comprising: mixing and stirring a molybdenum source, a sulfur source and a complexing agent in water to form a precursor solution; adding a cobalt source to the precursor solution and mixing, and carrying out a hydrothermal reaction at 180~220°C to obtain the two-dimensional heterojunction piezoelectric material.

[0008] In another aspect of the present invention, a method for piezoelectric catalytic water treatment is provided, comprising: adding the above-mentioned two-dimensional heterojunction piezoelectric material into the water body to be treated, and under the action of mechanical force, causing the two-dimensional heterojunction piezoelectric material to degrade organic pollutants in the water body to be treated through piezoelectric catalytic degradation.

[0009] Compared with the prior art, the technical solution provided by the embodiments of the present invention has at least the following beneficial effects: In the two-dimensional heterojunction piezoelectric material, cobalt sulfide and molybdenum disulfide can form a compact heterojunction structure, and the 1T and 2H crystal phases of molybdenum disulfide can work synergistically. Specifically, the 1T crystal phase can improve charge transport efficiency and enhance piezoelectric catalytic reaction kinetics, while the 2H crystal phase possesses good piezoelectricity and structural stability. The coexistence of these two phases solves the defects of low catalytic efficiency or insufficient stability of single-phase molybdenum disulfide. Simultaneously, the introduction of cobalt sulfide can regulate the band structure and built-in electric field of molybdenum disulfide, effectively suppressing piezoelectric charge recombination, improving charge separation and utilization efficiency, and also improving the stability of the 1T crystal phase by introducing local lattice distortion, promoting charge redistribution, and inducing crystal structure strain. This enhances the overall structural stability and conductivity of the two-dimensional heterojunction piezoelectric material and extends its service life.

[0010] The two-dimensional heterojunction piezoelectric material is used for piezoelectric catalytic water treatment. It can generate a piezoelectric effect driven by mechanical energy, effectively degrade a variety of organic pollutants, and has strong environmental adaptability. It can maintain good pollutant removal effect in a wide pH range (pH 3~9) and in actual domestic sewage and industrial wastewater. Moreover, the application method is flexible and it can maintain stable performance even after long-term operation (140 h). It simplifies the application process and broadens the adaptability to actual water treatment scenarios. Attached Figure Description

[0011] Figure 1 This is an X-ray diffraction pattern of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Embodiment 1 of the present invention;

[0012] Figure 2 These are transmission electron microscope (TEM) images and high-resolution TEM images of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention, wherein (a) is a TEM image of molybdenum disulfide; (b) is a TEM image of the two-dimensional heterojunction piezoelectric material in Example 1; (c) is a high-resolution TEM image of molybdenum disulfide; and (d) is a high-resolution TEM image of the two-dimensional heterojunction piezoelectric material in Example 1.

[0013] Figure 3 This refers to the two-dimensional heterojunction piezoelectric material and the molybdenum element in molybdenum disulfide in Embodiment 1 of the present invention. X-ray photoelectron spectrum of the orbit;

[0014] Figure 4This is the inductively coupled plasma atomic emission spectrum of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Embodiment 1 of the present invention;

[0015] Figure 5 These are Kelvin probe force microscope amplitude diagrams, electrochemical piezocurrent response diagrams, and electrical impedance diagrams of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention, wherein (a) is the Kelvin probe force microscope amplitude diagram of molybdenum disulfide; (b) is the Kelvin probe force microscope amplitude diagram of the two-dimensional heterojunction piezoelectric material in Example 1; (c) is the piezoelectric response capability test diagram of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1; and (d) is the electrical impedance diagram of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1.

[0016] Figure 6 This is a graph showing the cyclic degradation performance of the two-dimensional heterojunction piezoelectric material for sulfamethoxazole in Example 1 of this invention.

[0017] Figure 7 These are quenching experiment diagrams of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention, and electron paramagnetic resonance test diagrams of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention. Specifically, (a) is a quenching diagram of active species in the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention; (b) is an electron paramagnetic resonance test diagram of singlet oxygen in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention; (c) is an electron paramagnetic resonance test diagram of superoxide anions in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention; and (d) is an electron paramagnetic resonance test diagram of holes in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention.

[0018] Figure 8 This is a diagram showing the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention on sulfamethoxazole under different pH environmental conditions;

[0019] Figure 9 The graph shows the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention on sulfamethoxazole under different water conditions.

[0020] Figure 10 This is a diagram showing the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material for different organic pollutants in Example 1 of the present invention;

[0021] Figure 11 This is a schematic diagram of the operation of the two-dimensional heterojunction piezoelectric material-filled column in Embodiment 1 of the present invention;

[0022] Figure 12 This is a diagram showing the operational stability of the two-dimensional heterojunction piezoelectric material-filled column in Embodiment 1 of the present invention.

[0023] Figure 13These are X-ray diffraction comparison images of the two-dimensional heterojunction piezoelectric materials and molybdenum disulfide in Examples 1 to 3 of this invention;

[0024] Figure 14 This is a diagram showing the piezoelectric degradation performance of two-dimensional heterojunction piezoelectric materials and molybdenum disulfide on sulfamethoxazole in Examples 1 to 3 of this invention.

[0025] Figure 15 The graph shows the degradation performance of molybdenum disulfide and the composite piezoelectric materials in Comparative Examples 1 to 5 of this invention on chloramphenicol. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0027] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0029] In existing piezoelectric catalytic water treatment technologies, molybdenum disulfide (MoS2) is a commonly used piezoelectric material. However, it suffers from inherent defects such as easy recombination of internal piezoelectric charges and low carrier migration efficiency, which limit its catalytic activity and result in poor degradation of organic pollutants. Although constructing a mixture of 1T and 2H crystal phases of MoS2 can enhance charge separation ability to some extent, the 1T crystal phase itself is metastable and easily undergoes a phase transition during actual water treatment, transforming into the more stable 2H crystal phase. This causes the material's catalytic performance to decay rapidly, making it difficult to meet the requirements for long-term stable operation. Therefore, there is an urgent need to develop a piezoelectric catalytic material that combines high catalytic efficiency with good stability.

[0030] In the process of realizing this invention, it was discovered that if the high conductivity and structural stability of metallic conductor materials can be utilized, and a composite heterojunction structure can be constructed by rationally selecting modification materials and MoS2, then the stable heterojunction interface formed between the modification materials and MoS2 can be used to simultaneously solve the problems of low charge separation efficiency and insufficient material stability.

[0031] Based on this, this invention proposes a two-dimensional heterojunction piezoelectric material, its preparation method, and its application in water treatment. Through extensive experimental research, this invention has discovered that cobalt sulfide (CoS2) and MoS2 have a good lattice matching relationship. The spacing between the (200) crystal plane of CoS2 and the (100) crystal plane of MoS2 is well-matched. Simultaneously, the metallic conductor properties of CoS2 enable it to form a Schottky heterojunction with MoS2, thereby directionally guiding piezoelectric charge separation. Furthermore, utilizing the strong electronic coupling between the 1T crystal phases of CoS2 and MoS2, the metastable 1T crystal phase is effectively stabilized through interfacial charge transfer. This invention employs a one-step hydrothermal method, simultaneously achieving the generation of a mixed 1T and 2H crystal phase in the MoS2 crystal plane and the construction of the heterojunction interface between MoS2 and CoS2 by controlling the ratio of cobalt and molybdenum and the reaction conditions. The heterojunction structure of the two-dimensional heterojunction piezoelectric material not only effectively suppresses piezoelectric charge recombination by enhancing the built-in electric field, but also utilizes the interfacial stabilizing effect of CoS2 to maintain the stability of the 1T crystal phase during long-term (140 h) piezoelectric catalysis, thus solving the problem of balancing degradation efficiency and stability. When this two-dimensional heterojunction piezoelectric material is applied to water treatment, no carbon substrate support is required. Under mechanical force, the two-dimensional heterojunction piezoelectric material can degrade various organic pollutants in water through piezoelectric catalysis, ultimately achieving effective and stable removal of pollutants from water.

[0032] Specifically, according to one aspect of the present invention, a two-dimensional heterojunction piezoelectric material is provided, which has a heterojunction structure formed by cobalt sulfide and molybdenum disulfide, wherein the molybdenum disulfide has a 1T crystal phase and a 2H crystal phase.

[0033] According to embodiments of the present invention, in a two-dimensional heterojunction piezoelectric material, cobalt sulfide (CoS2) and molybdenum disulfide (MoS2) can form a tightly bonded heterojunction structure through lattice matching. This interfacial bonding effectively eliminates the charge transport barrier between the two materials, providing a smooth channel for rapid charge transfer between them, avoiding charge loss caused by loose interfacial bonding, and laying the structural foundation for the excellent piezoelectric catalytic performance of the two-dimensional heterojunction piezoelectric material. Meanwhile, the 1T and 2H crystal phases of MoS2 exhibit a synergistic effect: the 1T crystal phase, as the metallic phase of MoS2, has high electron mobility and good conductivity, which can accelerate the charge transport rate during the piezoelectric catalytic reaction, significantly enhance the kinetic characteristics of the piezoelectric catalytic reaction, and allow charges to migrate from the interior of the material to the surface active sites more quickly, reducing the residence time of charges inside the material; while the 2H crystal phase, as the semiconductor phase of MoS2, has excellent intrinsic piezoelectricity and structural stability. Its unique crystal structure can generate a stable piezoelectric potential when stimulated by mechanical force, providing sufficient power for the piezoelectric catalytic reaction. At the same time, its strong thermodynamic stability can effectively support the overall structure of the material and prevent the crystal structure from collapsing or breaking during long-term mechanical force or catalytic reaction. The coexistence of 1T and 2H crystal phases solves the inherent defects of single-phase MoS2: Although the single 1T crystal phase MoS2 has good electrical conductivity, it has poor thermodynamic stability and is prone to phase transformation, resulting in rapid decay of catalytic performance. Although the single 2H crystal phase MoS2 has stable structure and good piezoelectricity, it has poor electrical conductivity and low charge transport efficiency, which in turn limits the overall catalytic efficiency.

[0034] In addition, the introduction of CoS2 plays a regulatory role in the performance of MoS2, further enhancing the overall performance of the two-dimensional heterojunction piezoelectric material. On the one hand, as a conductive phase, CoS2, after forming a heterojunction with MoS2, can effectively regulate the band structure of MoS2, causing the bands of the two to shift and match, thereby optimizing the built-in electric field strength inside the heterojunction. The enhancement of the built-in electric field can significantly suppress the recombination loss of free electrons and holes during the piezoelectric catalytic reaction, improve the charge separation efficiency and utilization efficiency, and allow more free electrons and holes to participate in the catalytic degradation reaction, thereby enhancing the piezoelectric catalytic activity of the two-dimensional heterojunction piezoelectric material. On the other hand, the introduction of CoS2 interacts with the MoS2 lattice, inducing slight distortion of the local lattice of MoS2. This lattice distortion can promote the redistribution of charges inside the two-dimensional heterojunction piezoelectric material, breaking the uniformity of charge distribution and making it easier for charges to migrate to the surface active sites of the two-dimensional heterojunction piezoelectric material. Simultaneously, the lattice distortion of MoS2 induces crystal structure strain. This strain stabilizes the metastable 1T phase, inhibiting its transformation into the more thermodynamically stable 2H phase during long-term use. This maintains the ratio of the 1T to 2H phases, ensuring the charge transport efficiency and structural stability of the two-dimensional heterojunction piezoelectric material. Ultimately, through these multiple effects, the introduction of CoS2 effectively modulates the built-in electric field of the two-dimensional heterojunction piezoelectric material, enhancing its overall piezoelectric catalytic activity and structural stability, extending its service life, and enabling it to meet the application requirements of long-term (140 h) piezoelectric catalytic water treatment.

[0035] According to embodiments of the present invention, the relative content ratio of the 1T crystal phase and the 2H crystal phase in the two-dimensional heterojunction piezoelectric material is 1 to 0.7:1. For example, it can be 1:1, 0.95:1, 0.9:1, 0.85:1, 0.8:1, 0.7:1, etc., preferably 1:1. The coexistence of the 1T and 2H crystal phases in this ratio in the two-dimensional heterojunction piezoelectric material achieves synergistic complementarity and matching of the properties of the two crystal phases: the 1T crystal phase possesses high charge transport characteristics, which can fully utilize its advantages to enhance the piezoelectric catalytic reaction kinetics and significantly improve the piezoelectric charge migration efficiency inside the two-dimensional heterojunction piezoelectric material; the 2H crystal phase has good intrinsic piezoelectricity and structural stability, which can effectively ensure the basic piezoelectric performance and structural reliability of the two-dimensional heterojunction piezoelectric material. This crystal phase ratio range balances the piezoelectric catalytic activity and basic structural stability of the two-dimensional heterojunction piezoelectric material, successfully avoiding the defects of insufficient stability of the 1T crystal phase or low catalytic efficiency of the 2H crystal phase in single-phase MoS2. Meanwhile, this specific crystalline phase can adapt to the lattice matching requirements and interfacial bonding characteristics of CoS2, ensuring the tight construction of the cobalt sulfide and molybdenum disulfide heterojunction structure, thereby optimizing the built-in electric field strength inside the heterojunction and effectively suppressing the recombination loss of piezoelectric charges. Furthermore, this crystalline phase ratio provides a suitable structural basis for the strong electronic coupling between CoS2 and the 1T crystalline phase in MoS2, which is beneficial for CoS2 to stabilize the metastable 1T crystalline phase through interfacial charge transfer, inhibiting its transformation to the stable 2H crystalline phase, and significantly improving the long-term (140 h) piezoelectric catalytic stability of the two-dimensional heterojunction piezoelectric material. In summary, this mixed crystalline phase ratio, when combined with CoS2, can synergistically enhance the overall conductivity and catalytic activity of the two-dimensional heterojunction piezoelectric material. During piezoelectric catalytic degradation, it can promote the effective generation of free radical and non-free radical reactive oxygen species, significantly improving the catalytic degradation efficiency of organic pollutants.

[0036] In some specific embodiments, the ratio of the 1T crystal phase to the 2H crystal phase in the two-dimensional heterojunction piezoelectric material can be determined by the molybdenum element. Orbit (Mo) Quantitative characterization of Mo was performed using X-ray photoelectron spectroscopy (XPS). Specifically, in the XPS spectra, the crystal phases of Mo corresponding to the 1T and 2H phases were analyzed. The characteristic peaks are fitted separately, and the ratio of the peak areas of the two phases can be used to determine the ratio of the 1T phase to the 2H phase in the two-dimensional heterojunction piezoelectric material.

[0037] According to embodiments of the present invention, the molar ratio of cobalt to molybdenum in the two-dimensional heterojunction piezoelectric material is 1:1 to 20, for example, 1:1, 1:6, 1:8, 1:10, 1:20, etc. In the two-dimensional heterojunction piezoelectric material, cobalt mainly exists in the form of substitutional doping, that is, cobalt ions successfully occupy the lattice sites of molybdenum, forming a substitutional doped structure of molybdenum sites. This doping form can further optimize the lattice structure and electron distribution of the two-dimensional heterojunction piezoelectric material, enhance the interfacial interaction between cobalt and MoS2, and lay the foundation for the construction of the heterojunction structure and the improvement of the overall material performance.

[0038] According to embodiments of the present invention, the two-dimensional heterojunction piezoelectric material has a nanosphere structure or a nanofloral structure with a size of 300-500 nm, such as 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc. Pure MoS2 material has a loose nanosheet structure. The two-dimensional heterojunction piezoelectric material formed after introducing CoS2 exhibits a nanofloral morphology or a more dense nanosphere structure. The reason for this morphological difference is that the introduction of CoS2 changes the growth and assembly behavior of MoS2. Due to the lattice matching, CoS2 and MoS2 form a strong interfacial interaction, which promotes the formation of a tighter interlayer contact between MoS2 nanosheets, breaking the disordered and loosely stacked state of pure MoS2 sheets, causing the sheets to move closer to each other and undergo directional aggregation. The originally dispersed nanosheets complete the densification assembly under the bridging and induction effect of CoS2, ultimately forming a more dense nanofloral or nanosphere structure than pure MoS2 nanosheets. This avoids the structural loosening problem caused by excessive dispersion of pure MoS2 flakes, and constructs a more regular heterojunction morphology through tight interfacial bonding, which greatly increases the effective specific surface area of ​​the two-dimensional heterojunction piezoelectric material and fully exposes the active sites of the two-dimensional heterojunction piezoelectric material, thereby improving its piezoelectric catalytic reaction efficiency.

[0039] According to another embodiment of the present invention, a method for preparing the above-mentioned two-dimensional heterojunction piezoelectric material is provided, comprising: mixing and stirring a molybdenum source, a sulfur source and a complexing agent in water to form a precursor solution; adding a cobalt source to the precursor solution and mixing, and carrying out a hydrothermal reaction at 180~220°C to obtain the two-dimensional heterojunction piezoelectric material.

[0040] According to embodiments of the present invention, the preparation method of the two-dimensional heterojunction piezoelectric material is a one-step hydrothermal method. The overall process is simple and easy to operate, requiring no complex equipment or multi-step modification processes, and no need to introduce substrates such as carbon materials. This results in low preparation cost and ease of large-scale production. The addition of a complexing agent effectively inhibits the directional growth of MoS2 crystal nuclei, enabling control over the microstructure of the two-dimensional heterojunction piezoelectric material and inducing the formation of denser nanospheres or nanofloral structures. This facilitates the exposure of the specific surface area and piezoelectric catalytic active sites of the two-dimensional heterojunction piezoelectric material, thereby improving the utilization rate of active sites and charge transfer efficiency. The sulfur source can slowly release sulfur species during the hydrothermal process, which is beneficial for forming a more crystalline layered MoS2 structure. Simultaneously, the molybdenum source system can form a stable co-chelate system with the cobalt source. After thorough mixing, cobalt sulfide is uniformly loaded on the MoS2 surface, preventing localized aggregation of cobalt sulfide that covers the active sites. Adjusting the hydrothermal synthesis temperature and introducing a cobalt source helps to precisely control the ratio of the 1T and 2H phases in MoS2, resulting in a well-matched mixed phase with a relative content of 1 to 0.7:1. Simultaneously, the cobalt source can stabilize the metastable 1T phase through strong electronic coupling with it, inhibiting its transformation to the 2H phase and further enhancing the structural and catalytic stability of the two-dimensional heterojunction piezoelectric material.

[0041] The two-dimensional heterojunction piezoelectric material prepared by this method has good piezoelectric charge separation efficiency, conductivity and structural stability. It can effectively suppress piezoelectric charge recombination and significantly enhance the piezoelectric catalytic performance of the material, laying a good material foundation for its application in the field of water treatment.

[0042] In some specific embodiments, when the molybdenum source, sulfur source, and complexing agent are mixed in water, the stirring rate can be 1100 rpm, and the stirring time can be no less than 60 min to ensure that the raw materials are fully mixed and dispersed. The hydrothermal reaction can be carried out in a reactor. The precursor solution is transferred to the reactor and filled into the reactor at a ratio of 75% of the reaction volume. The hydrothermal reaction temperature is preferably 200℃, and the reaction time can be 24 h to achieve the construction of mixed crystal phases of 1T and 2H in MoS2 and the formation of a tight heterojunction structure between CoS2 and MoS2. The product obtained from the reaction is washed twice with deionized water and ethanol to remove residual impurities, and then dried in a vacuum environment at 60℃ for 6-8 h to obtain a two-dimensional heterojunction piezoelectric material with high purity and crystallinity.

[0043] According to embodiments of the present invention, the molybdenum source is a soluble molybdenum salt, selected from any one of ammonium molybdate and ammonium tetrathiomolybdate; the sulfur source is selected from any one of thiourea and L-cysteine. The present invention specifically selects the molybdenum and sulfur sources. Sodium molybdate is avoided as the molybdenum source to eliminate the influence of sodium metal ions, and the aforementioned molybdenum source system can form a more stable co-chelate system with CoS2, ensuring uniform loading of CoS2. The preferred sulfur source is thiourea, which can slowly decompose during the hydrothermal reaction, gradually releasing sulfur species, which is beneficial for the growth of MoS2 crystals and the formation of a more crystalline layered MoS2 structure.

[0044] The complexing agent is citric acid. Because citric acid molecules contain carboxyl and hydroxyl groups, they can regulate the microstructure of MoS2 through multiple mechanisms: First, citric acid can react with molybdenum ions (Mo2O3) dissociated from the molybdenum source. 6+ Formation of stable soluble complexes, delaying the formation of Mo 6+ The binding reaction with sulfur species slowly released from the sulfur source regulates the nucleation rate of MoS2 crystals, avoiding problems such as uneven crystal size and disordered agglomeration. At the same time, citric acid can selectively adsorb on the high surface energy dominant crystal face of MoS2 crystal nuclei, suppressing the intrinsic two-dimensional anisotropic directional growth characteristics of MoS2 and inducing the formation of nanofloral clusters or more dense nanosphere structures. In addition, the formed complex forms a steric barrier on the surface of MoS2 crystal nuclei, preventing irreversible agglomeration during crystal growth and ensuring the compactness and regularity of the obtained morphology. Moreover, citric acid has good water solubility, no impurity residue, and is suitable for hydrothermal synthesis systems, and will not interfere with the subsequent construction of heterojunction structures.

[0045] The cobalt source can be either cobalt nitrate or cobalt chloride. In practice, the types and adjustments of the molybdenum source, sulfur source, complexing agent, and cobalt source can be made according to the preparation requirements.

[0046] According to embodiments of the present invention, the molar ratio of molybdenum source to sulfur source is 1:5 to 25, for example, 1:5, 1:10, 1:15, 1:20, 1:25, etc. In the precursor solution, the supply rate of sulfur species in the hydrothermal reaction, the chemical environment for MoS2 nucleus growth, and the internal stress state during lattice formation are controlled by adjusting the ratio of molybdenum source to sulfur source. This, in turn, directionally controls the nucleation and growth of the MoS2 crystal phase, resulting in a mixed crystal phase of 1T and 2H phases in the molybdenum disulfide crystal facets, while taking into account the performance advantages of both phases. When the molar ratio of molybdenum source to sulfur source is adjusted within the suitable range of 1:5 to 25, the sulfur source can slowly and continuously release sulfur species during the hydrothermal process. This provides sufficient and suitable sulfur source for the growth of MoS2 crystal nuclei, ensuring the stable nucleation and growth of the 2H crystal phase and providing the basis for the piezoelectricity and structural stability of two-dimensional heterojunction piezoelectric materials. Furthermore, by adjusting the supply concentration of sulfur species, the MoS2 lattice can generate appropriate lattice distortion and internal stress during its formation, inducing the nucleation of the metastable 1T crystal phase and ensuring its stable existence in the lattice. This avoids the problem of low piezoelectric catalytic efficiency of the single 2H crystal phase MoS2.

[0047] If the ratio of molybdenum source to sulfur source is unbalanced, such as insufficient sulfur source (molar ratio of molybdenum source to sulfur source greater than 1:5), it will result in insufficient sulfur species supply, leading to excessive lattice defects in MoS2. This causes the generated 1T crystal phase to rapidly transform into the thermodynamically stable 2H crystal phase, preventing the formation of a stable biphase state. Conversely, if there is excessive sulfur source (molar ratio of molybdenum source to sulfur source less than 1:25), it will result in an excess of sulfur species, promoting the directional growth of MoS2 nuclei towards the 2H crystal phase, making it difficult to induce 1T crystal phase nucleation, and similarly preventing the formation of a biphase state. Therefore, by controlling the ratio of molybdenum source to sulfur source, the ratio of 1T crystal phase and 2H crystal phase in MoS2 can be optimized, obtaining a mixed-phase MoS2 that combines piezoelectric catalytic activity with basic structural stability.

[0048] The molar ratio of cobalt source to molybdenum source is 1:2 to 20, for example, 1:2, 1:4, 1:8, 1:10, 1:15, 1:20, etc. Based on obtaining a mixed crystalline phase MoS2, a heterojunction structure is constructed by screening the molar ratio of cobalt source to molybdenum source: on the one hand, the cobalt source can effectively regulate the band structure of MoS2 and optimize the overall piezoelectric catalytic degradation performance of the heterojunction piezoelectric material; on the other hand, an appropriate amount of cobalt source can stabilize the metastable 1T crystalline phase in MoS2 through the interaction between the formed CoS2 and the 1T crystalline phase, significantly improving the long-term (140 h) catalytic stability of the heterojunction piezoelectric material. If the amount of cobalt source added is too small (the molar ratio of cobalt source to molybdenum source is less than 1:20, for example, the molar ratio of cobalt source to molybdenum source is 1:40), cobalt is likely to exist in the form of single atomic sites, resulting in insufficient number of effective active sites in the two-dimensional heterojunction piezoelectric material. If the amount of cobalt source added is too large (the molar ratio of cobalt source to molybdenum source is greater than 1:2, for example, the molar ratio of cobalt source to molybdenum source is 1:1), it is easy to cause excessive aggregation of the generated CoS2, which will block the piezoelectric active sites on the surface of MoS2 and also affect the piezoelectric catalytic performance of the two-dimensional heterojunction piezoelectric material.

[0049] According to another aspect of the present invention, a method for piezoelectric catalytic water treatment is provided, comprising: adding the above-mentioned two-dimensional heterojunction piezoelectric material into the water body to be treated, and under the action of mechanical force, causing the two-dimensional heterojunction piezoelectric material to degrade organic pollutants in the water body to be treated through piezoelectric catalytic degradation.

[0050] According to an embodiment of the present invention, the piezoelectric catalytic water treatment method is based on band theory and the synergistic effect of heterojunctions. In the two-dimensional heterojunction piezoelectric material, MoS2 deforms under mechanical force, causing the internal charge centers to separate and form a built-in electric field. Positive and negative charges then directionally migrate to both ends of the two-dimensional heterojunction piezoelectric material. The positive charges can directly oxidize and degrade organic pollutants, while the negative charges can reduce oxygen (O2) in the water to generate superoxide anions (·O2). - The presence of free radicals such as CoS2 and MoS2 in the two-dimensional heterojunction piezoelectric material further degrades organic pollutants. Simultaneously, CoS2 in the two-dimensional heterojunction piezoelectric material optimizes the piezoelectric properties of MoS2, promoting the generation of more free positive and negative charges and O2 in the material. - It can also activate oxygen molecules to generate additional ·O2 through electrons on sulfur defects produced by its own mechanical force. - Furthermore, cobalt sulfide derivatives rich in sulfur defects (CoS...) 2-x High-valent cobalt species (Co) exposed on the surface 3+ ), can convert O2 - Rapidly converted to singlet oxygen ( 1O2), thereby constructing a synergistic degradation pathway of free radicals and non-free radicals. Compared with the pure MoS2 single free radical degradation pathway, the synergistic pathway of this invention significantly increases the types and quantities of reactive oxygen species generated, effectively improving the degradation efficiency of organic pollutants.

[0051] According to a further specific embodiment of the present invention, the piezoelectric catalytic degradation of organic pollutants in the water to be treated includes at least one of the following two methods.

[0052] (1) In the piezoelectric catalytic degradation process, the positive charge (hole: h) generated by the two-dimensional heterojunction piezoelectric material based on the piezoelectric effect is utilized. + Direct oxidation and degradation of organic pollutants.

[0053] Electron-hole (e - / h + The generation of the piezoelectric effect is based on the band structure theory of piezoelectricity. In this invention, when MoS2 in the two-dimensional heterojunction piezoelectric material is deformed under mechanical force, its internal charge centers separate, thereby forming a directional built-in electric field. Driven by this built-in electric field, positive and negative charges migrate directionally, with electrons (e) of the negative charge... - ) and positively charged holes (h + ) respectively move to the positive and negative electrodes of the two-dimensional heterojunction piezoelectric material and exist stably, among which holes (h + MoS2, possessing oxidizing properties, can directly oxidize and degrade organic pollutants to achieve a cleaning effect. In two-dimensional heterojunction piezoelectric materials, MoS2 exists as a mixed phase of 1T and 2H crystal phases, forming a lattice-matched heterojunction with CoS2. On one hand, the 1T crystal phase improves the charge transport efficiency of the two-dimensional heterojunction piezoelectric material, optimizing the reaction efficiency; on the other hand, the construction of the CoS2 heterojunction optimizes the band structure and overall conductivity of MoS2, further enhancing the built-in electric field strength and allowing more electrons and holes (electrons and holes) to pass through. - / h + The electron-hole composite material escapes the recombination trend and exists in a free state on the surface of a two-dimensional heterojunction piezoelectric material, becoming an active species that can directly participate in the degradation of organic pollutants. Compared with pure MoS2, the electron-hole composite material of this invention has a higher electron density and greater number of electrons and holes. - / h + The generation rate has been significantly improved.

[0054] (2) During the piezoelectric catalytic degradation process, the electrons (e) generated by the piezoelectric effect of the two-dimensional heterojunction piezoelectric material - This process can catalyze the production of reactive species from oxygen (O2) in the water to be treated, thereby utilizing these reactive species to degrade organic pollutants. These reactive species include superoxide anions (·O2). - Singlet oxygen () 1O2). Effective degradation of organic pollutants is achieved through a synergistic pathway of "free radicals + non-free radicals". The specific generation process of each active species is as follows.

[0055] Superoxide anion (·O2) - MoS2 is the main free radical reactive species in the catalytic process, and its generation occurs through two pathways: (1) the piezoelectric electron reduction pathway of MoS2. Free electrons (e) generated simultaneously with holes are generated. - Under the influence of the built-in electric field, it moves towards one end of the two-dimensional heterojunction piezoelectric material, e - It undergoes a reduction reaction with molecular oxygen in the water to directly generate ·O2. - The increased charge separation efficiency brought about by CoS2 significantly increases the electron supply in this pathway, leading to a higher O2 content. - The generation efficiency also increases accordingly; (2) CoS2 defect site activation pathway: CoS2 will generate sulfur defects under mechanical force. The unpaired electrons on the defect site can directly activate molecular oxygen in water and generate O2 independently without relying on the piezoelectric electrons of MoS2. - This achieved an additional replenishment of superoxide anions, significantly increasing the overall concentration of free radical species.

[0056] Singlet oxygen ( 1 CoS2 (O2) is the main non-radical reactive species in the catalytic process. In the two-dimensional heterojunction piezoelectric material of this invention, CoS2 undergoes lattice distortion due to mechanical forces, resulting in some sulfur atoms detaching from the lattice and forming sulfur defects, which in turn lead to the formation of sulfur-defect-rich cobalt sulfide derivatives (CoS2). 2-x CoS 2-x High-valent cobalt species (Co) with strong oxidizing properties exposed on the surface 3+ ), Co 3+ The superoxide anions (·O2) generated above can be used to... - It can be converted into singlet oxygen at a relatively fast rate. This conversion process is highly efficient and requires no additional conditions, enabling two-dimensional heterostructure piezoelectric materials to generate free radicals while simultaneously acquiring highly active non-radical species.

[0057] The two-dimensional heterojunction piezoelectric material of this invention achieves electron-hole vacancies through the synergistic effect of the piezoelectric effect and the heterojunction interface. - / h + ), superoxide anion (·O2) - Singlet oxygen () 1 The synergistic generation of O2 by multiple species. The generation pathways of each species complement and coordinate with each other, ensuring the effectiveness of the free radical degradation pathway while introducing the non-free radical degradation pathway, thus forming a degradation microenvironment with synergistic interaction of multiple active species on the surface of the two-dimensional heterojunction piezoelectric material.

[0058] According to embodiments of the present invention, the pH range of the water to be treated is 3-9, for example, it can be 3, 4, 5, 6, 7, 8, 9, etc., and the organic pollutants can include at least one of sulfamethoxazole (SMX), chloramphenicol (CAP), 4-chlorophenol (4-CP), bisphenol A (BPA), methylene blue (MB), rhodamine B (RhB), and methyl orange (MO). The two-dimensional heterojunction piezoelectric material of the present invention, relying on the synergistic degradation mechanism of "free radical + non-free radical" and structural stability, exhibits good environmental adaptability, is less affected by the anions and acidity / alkalinity of the water, and can maintain a relatively high degradation efficiency in acidic, neutral, and alkaline conditions, as well as in complex water bodies such as domestic sewage and industrial wastewater. It also has good universality for various recalcitrant organic pollutants such as sulfamethoxazole, bisphenol A, and various dyes.

[0059] According to embodiments of the present invention, the dosage of the two-dimensional heterojunction piezoelectric material is ≥0.5 g / L, for example, it can be 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, etc. Sufficient dosage can provide enough piezoelectric active sites for the piezoelectric catalytic reaction, avoiding the limitation of the generation efficiency of active species and the probability of contact with organic pollutants due to insufficient sites, thus ensuring the catalytic degradation efficiency of the two-dimensional heterojunction piezoelectric material.

[0060] According to embodiments of the present invention, the mechanical force can be applied through any one of mechanical vibration, mechanical stirring, or ultrasound. All of these methods can provide suitable mechanical energy to the two-dimensional heterojunction piezoelectric material, causing it to deform effectively. Based on band theory, this triggers the separation of internal charge centers and the formation of a built-in electric field, achieving efficient separation and directional migration of piezoelectric charges. This, in turn, generates active species such as superoxide anions, singlet oxygen, and electron-hole pairs through multiple pathways, meeting the energy requirements for the synergistic degradation of "free radicals + non-free radicals." Furthermore, different forms of mechanical force can be flexibly adapted to various water treatment applications, such as direct powder dispensing, catalytic membranes, and packed columns, ensuring efficient triggering of piezoelectric catalytic reactions in all scenarios.

[0061] In some specific embodiments, the piezoelectric catalytic water treatment method of the present invention can be carried out under oxygen aeration conditions in practical applications to improve degradation efficiency. Oxygen aeration can significantly increase the dissolved oxygen content in the water, providing a sufficient oxygen source for the catalytic generation of active species by the two-dimensional heterojunction piezoelectric material. This facilitates the reduction of oxygen in the water by piezoelectric electrons on the surface of the two-dimensional heterojunction piezoelectric material, generating more superoxide anions (·O2). - It can also activate molecular oxygen and ·O2 at CoS2 defect sites. - To singlet oxygen ( 1 The conversion of O2) supplements the raw materials, further strengthening the synergistic degradation pathway of "free radicals + non-free radicals".

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Unless otherwise specified, specific techniques or conditions in the embodiments are conventional methods, which can be performed according to the techniques or conditions described in the literature in this field or according to the product instructions. It should be noted that, unless otherwise specified, the methods provided by this invention are conventional methods, and the reactants and reagents can be obtained from publicly available commercial sources unless otherwise specified.

[0063] Example 1

[0064] This embodiment 1 provides a two-dimensional heterojunction piezoelectric material, and the preparation method of the two-dimensional heterojunction piezoelectric material is as follows.

[0065] 2.47 g of ammonium molybdate tetrahydrate and 3.8 g of thiourea were dissolved in 60 mL of ultrapure water, and 0.36 g of citric acid was added. The mixture was stirred at 1100 r / min for 60 min to form a precursor solution.

[0066] 0.5 g of cobalt nitrate hexahydrate (with a cobalt to molybdenum molar ratio of 1:8 and a Co:Mo ratio of 1:8) was added to the precursor solution, and the mixture was stirred until homogeneous to obtain a mixed solution. The mixed solution was transferred to an autoclave (working capacity 80 mL) and subjected to hydrothermal reaction at 200 °C for 24 hours. After the reaction mixture was allowed to cool naturally, the product was collected by filtration. The product was washed twice with ethanol and twice with ultrapure water. The washed product was then vacuum dried at 60 °C for 8 hours and ground to finally obtain a two-dimensional heterojunction piezoelectric material (CoS2 / MoS2).

[0067] The following performance characterization and analysis were performed on the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention.

[0068] (1) Characterization of material morphology and structure: After grinding the two-dimensional heterojunction piezoelectric material in Example 1 evenly, it was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS).

[0069] Figure 1 This is an X-ray diffraction pattern of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Embodiment 1 of the present invention.

[0070] like Figure 1 As shown, XRD enables qualitative and quantitative analysis of materials by measuring the 2θ (2-Theta) diffraction angle and intensity. Figure 1XRD results showed that, compared with the standard cards for cobalt sulfide (CoS2) (PDF#-83-0573) and molybdenum disulfide (MoS2) (PDF#-73-1508), both MoS2 and the two-dimensional heterojunction piezoelectric material (CoS2 / MoS2) exhibited obvious standard characteristic peaks of MoS2. Furthermore, the diffraction spectrum of the two-dimensional heterojunction piezoelectric material also corresponded to the characteristic peaks of the cobalt sulfide (CoS2) phase without any other impurity peaks, indicating that cobalt was successfully incorporated into MoS2, and that its phase was CoS2.

[0071] Figure 2 These are transmission electron microscope (TEM) images and high-resolution TEM images of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention, wherein (a) is a TEM image of molybdenum disulfide; (b) is a TEM image of the two-dimensional heterojunction piezoelectric material in Example 1; (c) is a high-resolution TEM image of molybdenum disulfide; and (d) is a high-resolution TEM image of the two-dimensional heterojunction piezoelectric material in Example 1.

[0072] like Figure 2 As shown in the transmission electron microscope images (a) and (b), the MoS2 material exhibits a nanosheet structure, while the presence of CoS2 leads to further aggregation of the two-dimensional heterojunction piezoelectric material into a nanofloral morphology. HRTEM images (c) and (d) clearly identify the unique lattice features of the 1T and 2T phases of MoS2 in both the MoS2 and the two-dimensional heterojunction piezoelectric material. Due to the different atomic coordination environments and lattice arrangements of the two phases, the 1T phase exhibits a triangular arrangement structure, while the 2T phase exhibits a typical hexagonal honeycomb structure. Furthermore, the (200) crystal plane of CoS2 can be identified in the two-dimensional heterojunction piezoelectric material, which establishes a close interfacial contact with the characteristic (002) crystal plane of MoS2, thus confirming the formation of a highly integrated CoS2 and MoS2 heterojunction structure.

[0073] Figure 3 This refers to the two-dimensional heterojunction piezoelectric material and the molybdenum element in molybdenum disulfide in Embodiment 1 of the present invention. X-ray photoelectron spectrum of the orbit.

[0074] like Figure 3 As shown, XPS spectra analysis of two-dimensional heterojunction piezoelectric materials and MoS2 were performed, revealing the molybdenum content in both. Orbit (Mo) The photoelectron spectroscopy peaks all exhibited characteristic peaks of Mo(IV) (228.5 eV), Mo(V) (228.8 eV), and Mo(VI) (232.2 eV). For Mo... Quantitative analysis of the peak areas of the 1T and 2H phases in the spectra of the two-dimensional heterojunction piezoelectric material and MoS2 revealed that the ratio of the 1T to 2H phases (1T / 2H) increased from 0.70 in pure MoS2 to 1.0 in the two-dimensional heterojunction piezoelectric material. This indicates that the introduction of CoS2 promotes the transformation of the 2H phase to the 1T phase in MoS2, thereby improving the conductivity of the two-dimensional heterojunction piezoelectric material and contributing to the improvement of piezoelectric charge transport efficiency.

[0075] (2) Chemical composition analysis of materials: The two-dimensional heterojunction piezoelectric material (about 2 mg) and molybdenum disulfide (about 2 mg) in Example 1 were heated and digested in 30% nitric acid, and the metal ion content was tested by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0076] Figure 4 This is the inductively coupled plasma atomic emission spectrum of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Embodiment 1 of the present invention.

[0077] like Figure 4 As shown, ICP-AES test results indicate that the molar ratio of cobalt to molybdenum in the two-dimensional heterojunction piezoelectric material of Example 1 is approximately 1:6, slightly higher than the ratio in the precursor solution (1:8). This suggests that cobalt mainly exists in the form of substitution doping during material preparation, meaning that cobalt ions successfully occupy the lattice sites of molybdenum, forming a substitution-type doped structure at the molybdenum sites.

[0078] (3) Surface potential distribution, piezoelectric response, and charge transport tests. The surface potential distribution and charge transport of the two-dimensional heterojunction piezoelectric material in Example 1 of this invention were tested using Kelvin probe force microscopy (KPFM amplitude) and electrochemical current response and electrical impedance (EIS) tests. The piezoelectric response capability was tested using electrochemical current-time (ECS)... Characterization Tests: Using carbon paper as the electrode substrate, molybdenum disulfide and the two-dimensional heterojunction piezoelectric material from Example 1 were dispersed in a mixture of isopropanol, water, and a perfluorosulfonic acid polymer solution (Nafion solution) to prepare two electrode dispersions. Equal amounts of each dispersion were then drop-coated onto the surface of carbon paper to prepare corresponding working electrodes. Under open-circuit voltage conditions, the ideal detection current was 0 mA when the ultrasound was not activated. The piezoelectric material can convert mechanical energy into electrical energy and generate free charges, thus forming a current. After the ultrasound was activated, the piezoelectric material on the working electrode deformed under the ultrasonic cavitation pressure, forming a built-in electric field that drives the directional transport of piezoelectric charges, which is then expressed as a current signal. This was used to test the strength of the material's piezoelectric response and the efficiency of charge separation and transport.

[0079] Figure 5These are Kelvin probe force microscope amplitude diagrams, electrochemical piezocurrent response diagrams, and electrical impedance diagrams of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention, wherein (a) is the Kelvin probe force microscope amplitude diagram of molybdenum disulfide; (b) is the Kelvin probe force microscope amplitude diagram of the two-dimensional heterojunction piezoelectric material in Example 1; (c) is the piezoelectric response capability test diagram of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1; and (d) is the electrical impedance diagram of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1.

[0080] like Figure 5 As shown in (a) and (b), under a 4 V AC bias, the two-dimensional heterojunction piezoelectric material in Example 1 exhibits a more significant amplitude response, indicating that the introduction of CoS2 endows the two-dimensional heterojunction piezoelectric material with stronger out-of-plane piezoelectric properties. Subsequently, electrochemical tests were used to evaluate the piezoelectric response and conductivity of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide under mechanical stress. In (c) The curves show a comparison of the piezoelectric response capabilities of the two-dimensional heterojunction piezoelectric material, molybdenum disulfide, and the blank group (without the two-dimensional heterojunction piezoelectric material and molybdenum disulfide) in Example 1. It can be observed that under ultrasonic irradiation, the piezoelectric response intensity of the two-dimensional heterojunction piezoelectric material in Example 1 is higher than that of MoS2, reflecting that the two-dimensional heterojunction piezoelectric material generates more piezoelectric excited carriers under mechanical excitation. Its average maximum piezoelectric current is calculated to be 1.7 times that of MoS2 over five consecutive cycles. It can be observed that the piezoelectric current decreases after several cycles, which is due to the ultrasonic excitation causing the two-dimensional heterojunction piezoelectric material to detach from the electrode surface. Furthermore, in the electrical impedance (EIS) plot (d), the horizontal axis represents the real resistivity (Z' / Ω) of the complex impedance of the electrochemical system, and the vertical axis represents the imaginary reactance (Z'' / Ω). Together, they constitute the complex impedance that varies with the AC signal frequency, which can be used to characterize the electrochemical behavior of the material, such as its electrical impedance. (d) The EIS diagram shows that the radius of the impedance spectrum of the two-dimensional heterojunction piezoelectric material in Example 1 is smaller than that of MoS2, indicating that the impedance of the two-dimensional heterojunction piezoelectric material is reduced, and efficient carrier transport can be achieved in the piezoelectric catalysis process.

[0081] (4) Performance of the material in piezoelectric degradation of sulfamethoxazole (SMX): 30 mg of the two-dimensional heterojunction piezoelectric material from Example 1 was ultrasonically dispersed in 60 mL of a 5 mg / L SMX solution. After stirring for 40 min to reach adsorption-desorption equilibrium, the mixture was transferred to an ultrasonic machine to start the reaction. During the reaction, a fixed amount of reaction solution was taken periodically, and methanol was added to terminate the reaction. The mixed solution was filtered through a 0.22 μm filter membrane and the remaining SMX concentration was tested by high performance liquid chromatography (HPLC). After the reaction was completed, a new round of SMX contaminant (high-concentration contaminant mother liquor, maintaining the initial SMX contaminant concentration at 5 mg / L) was directly added to the system, and a total of 5 cycles were performed (the reaction time for the first to fourth cycles was 3 h, and the reaction time for the fifth cycle was 4 h). The two-dimensional heterojunction piezoelectric material after the fifth cycle was collected, washed with methanol and water, dried, and the degradation experiment was repeated.

[0082] Figure 6 This is a graph showing the cyclic degradation performance of the two-dimensional heterojunction piezoelectric material for sulfamethoxazole in Example 1 of the present invention.

[0083] like Figure 6 As shown, the performance of the two-dimensional heterojunction piezoelectric material decreased after 5 cycles (cycles 1 to 5), but the catalytic performance could be basically restored after regeneration by removing residual pollutant intermediates on the surface of the two-dimensional heterojunction piezoelectric material through methanol cleaning. These results indicate that the two-dimensional heterojunction piezoelectric material of this invention exhibits good catalytic performance and stability in the piezoelectric degradation of organic pollutants.

[0084] (5) Test of piezoelectric catalytic reaction pathway of materials: p-benzoquinone, L-histidine and disodium ethylenediaminetetraacetate (EDTA-2Na) were selected as superoxide anions (·O2) - Singlet oxygen () 1 O2) and electron holes (e - / h + Quenching agents for 2,2,6,6-tetramethyl-4-piperidinone (TEMP), 5,5-dimethyl-1-pyrrolidone-N-oxide-methanol solution (DMPO-methanol), and tetramethylpiperidin nitroxide radical (TEMPO) are used as singlet oxygen ( 1 O2), superoxide anion (·O2) - ) and electron holes (e - / h + A quencher was added to the reaction system containing the two-dimensional heterojunction piezoelectric material from Example 1 for the degradation of sulfamethoxazole (SMX), and the type of active species was preliminarily determined by the inhibitory effect of the quencher on the degradation reaction. Electron paramagnetic resonance (EPR) tests were performed on both the two-dimensional heterojunction piezoelectric material and molybdenum disulfide reaction systems to further verify the active species generated during the catalytic reaction.

[0085] Figure 7 These are quenching experiment diagrams of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention, and electron paramagnetic resonance (EPR) test diagrams of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention. Specifically, (a) is a quenching diagram of active species in the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention; (b) is an EPR test diagram of singlet oxygen in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention; (c) is an EPR test diagram of superoxide anion in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention; and (d) is an EPR test diagram of holes in the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Example 1 of the present invention.

[0086] like Figure 7 As shown in Figure (a), the quenching experiment results of the two-dimensional heterojunction piezoelectric material system show that all three quenchers inhibited the degradation of SMX, indicating that superoxide anions (·O2) may exist in the system. - Singlet oxygen () 1 O2) and electron holes (e - / h + Multiple active species were detected. The presence of these active species was further confirmed by the EPR results of the two systems. In (b), a clear singlet oxygen signal was captured in the two-dimensional heterojunction piezoelectric material system using TEMP as a scavenger, while this signal was not observed in the MoS2 system, indicating that singlet oxygen was generated only in the two-dimensional heterojunction piezoelectric material system. 1 O2) active species. In (c), superoxide anions (·O2) were obtained in both systems via DMPO-methanol scavenging agent. - The characteristic peak signal of ) is present, but the signal in the two-dimensional heterostructure piezoelectric material system is more obvious in comparison. Finally, in (d), obvious electron-hole vacancies (e-holes) are captured in both systems by TEMPO. - / h + The signal was positive, but the signal change amplitude of the MoS2 group decreased over time. Compared with the blank control (the system without the addition of two-dimensional heterojunction piezoelectric material and MoS2), the two-dimensional heterojunction piezoelectric material system may have more electrons and holes to maintain the signal. In summary, when the two-dimensional heterojunction piezoelectric material in Example 1 is stimulated by mechanical force, due to its piezoelectricity, it can generate free electrons and holes to directly or indirectly participate in the degradation reaction and generate superoxide anions (·O2). - Singlet oxygen () 1 O2) reactive species participate in the reaction, degrading organic pollutants through a mixed and synergistic pathway of "free radicals + non-free radicals". Under the same conditions, only superoxide anions (·O2) were detected in MoS2. - ) and electron holes (e - / h +The EPR signal indicates that the degradation reaction involving MoS2 is dominated by the free radical pathway. From the above results, it can be seen that the two-dimensional heterojunction piezoelectric material system in Example 1 of this invention adds a non-free radical degradation pathway to the pure MoS2 degradation pathway, thereby effectively improving the overall piezoelectric catalytic reaction efficiency.

[0087] (6) Environmental tolerance test of the material: To evaluate the environmental tolerance of the two-dimensional heterojunction piezoelectric material in Example 1, the degradation rate of the material for sulfamethoxazole (SMX) was tested under different pH values ​​and different water conditions. The degradation efficiency of the material for other organic pollutants was also tested. During the tests, the concentration of the two-dimensional heterojunction piezoelectric material and the initial concentration of SMX were kept consistent with the concentrations set in the aforementioned performance test of the material's piezoelectric degradation of sulfamethoxazole (SMX).

[0088] Figure 8 This is a diagram showing the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention on sulfamethoxazole under different pH environmental conditions.

[0089] like Figure 8 As shown, the two-dimensional heterojunction piezoelectric material in Example 1 maintained a degradation performance of over 75% within a wide pH range (3-9), and the degradation efficiency even improved in acidic environments. However, its degradation performance decreased slightly with increasing pH; at pH 11, the SMX degradation efficiency decreased to 66%. This is presumably because alkaline environments reduce the number of free radical reactive species (such as ·O2) in the system. - The activity and amount of piezoelectric material generated by strong alkaline conditions may affect the crystal structure stability of the two-dimensional heterojunction piezoelectric material itself, thereby destroying the catalytic active sites on the material surface and weakening its piezoelectric catalytic degradation ability.

[0090] Figure 9 The diagram shows the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention on sulfamethoxazole under different water conditions.

[0091] like Figure 9 As shown, deionized water, domestic sewage (diluted 10 times for testing), and actual textile wastewater (diluted 20 times for testing) were used as background water bodies. SMX mother liquor was added to these water bodies to achieve an initial SMX concentration of 5 ppm. The performance of the two-dimensional heterojunction piezoelectric material in degrading SMX in different water bodies was tested. The experimental data showed that under different water quality conditions, the two-dimensional heterojunction piezoelectric material could achieve an SMX degradation rate of over 95% within 150 minutes, demonstrating that this two-dimensional heterojunction piezoelectric material has good environmental adaptability and promising prospects for water treatment applications.

[0092] The two-dimensional heterojunction piezoelectric material prepared in Example 1 was applied to organic pollutant systems containing sulfamethoxazole (SMX), 4-chlorophenol (4-CP), bisphenol A (BPA), and methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) dyes. The concentration of the two-dimensional heterojunction piezoelectric material added was consistent with the concentration set in the performance test of the piezoelectric degradation of sulfamethoxazole (SMX) by the aforementioned material.

[0093] Figure 10 This is a diagram showing the piezoelectric degradation performance of the two-dimensional heterojunction piezoelectric material in Example 1 of the present invention for different organic pollutants.

[0094] like Figure 10 As shown, this two-dimensional heterojunction piezoelectric material can effectively degrade various organic pollutants in the system, with particularly outstanding degradation efficiency for dye-based organic pollutants, achieving complete degradation within 10 minutes. It also exhibits good degradation effects on typical recalcitrant organic pollutants such as sulfamethoxazole, 4-chlorophenol, and bisphenol A. These results fully demonstrate that the two-dimensional heterojunction piezoelectric material of this invention possesses good piezoelectric catalytic degradation universality, is adaptable to complex mixed organic wastewater treatment scenarios, and has good practical application suitability.

[0095] (7) Material stability test: The continuous flow stability test was carried out using the two-dimensional heterojunction piezoelectric material filling column in Example 1 of the present invention.

[0096] Figure 11 This is a schematic diagram of the operation of the two-dimensional heterojunction piezoelectric material-filled column in Embodiment 1 of the present invention.

[0097] like Figure 11 As shown, the two-dimensional heterojunction piezoelectric material prepared in Example 1 was used as a packing material and mixed with alumina (Al2O3) at a mass ratio of 1:2 before being packed into a reaction column. Al2O3 was used to construct fluid channels within the packing bed to ensure smooth flow of the feed solution. After the feed solution was pumped into the reaction column and the catalytic reaction was completed, the effluent was collected and its degradation rate was measured. A sulfamethoxazole (SMX) solution with an initial concentration of 2.5 mg / L was used as the feed solution, and a dead-end continuous flow mode was used for catalytic degradation testing, with the feed solution flow rate set at 0.1 mL / min. By applying a reaction pressure of approximately 15 MPa as mechanical energy, the piezoelectric effect of the two-dimensional heterojunction piezoelectric material in the packing material was excited, achieving the degradation of organic pollutants in water under continuous flow conditions. The stability of the heterojunction piezoelectric material was then evaluated through the long-term operation of this continuous flow system.

[0098] Figure 12 This is a diagram showing the operational stability of the two-dimensional heterojunction piezoelectric material-filled column in Embodiment 1 of the present invention.

[0099] like Figure 12As shown, the two-dimensional heterojunction piezoelectric material-filled column from Example 1 of this invention was used in a cyclic experiment for the piezoelectric degradation of SMX. Continuous flow experiments showed that under a high pressure of approximately 15 MPa, the two-dimensional heterojunction piezoelectric material could achieve continuous stable operation for more than 140 hours, maintaining a degradation rate of nearly 100% for SMX, with no significant attenuation in catalytic performance. These experimental results fully demonstrate that the two-dimensional heterojunction piezoelectric material of this invention possesses good structural stability and reusability, and has broad potential for environmental engineering applications.

[0100] Example 2

[0101] This embodiment 2 provides a two-dimensional heterojunction piezoelectric material. The difference between the preparation method of this two-dimensional heterojunction piezoelectric material and that of embodiment 1 is that 2.0 g of cobalt nitrate hexahydrate (where the molar ratio of cobalt to molybdenum is 1:2, and Co:Mo = 1:2) is added to the precursor solution.

[0102] Example 3

[0103] This embodiment 3 provides a two-dimensional heterojunction piezoelectric material. The difference between the preparation method of this two-dimensional heterojunction piezoelectric material and that of embodiment 1 is that 0.2g of cobalt nitrate hexahydrate (where the molar ratio of cobalt to molybdenum is 1:20, and Co:Mo = 1:20) is added to the precursor solution.

[0104] Figure 13 These are X-ray diffraction comparison images of the two-dimensional heterojunction piezoelectric material and molybdenum disulfide in Examples 1 to 3 of this invention.

[0105] like Figure 13 As shown, XRD enables qualitative and quantitative analysis of materials by measuring the 2θ (2-theta) diffraction angle and intensity. Figure 13XRD results showed that the diffraction pattern of pure MoS2 exhibited characteristic diffraction peaks at approximately 14°, 32°, 36°, and 58°, corresponding to the (002), (100), (102), and (301) crystal planes, consistent with the characteristics of the hexagonal 2H phase of MoS2. Compared to pure MoS2, the XRD patterns of the two-dimensional heterojunction piezoelectric materials with different cobalt to molybdenum molar ratios in Examples 1-3 all retained the characteristic diffraction peaks of MoS2, indicating that the introduction of cobalt did not disrupt the main crystal structure of MoS2. Meanwhile, as the cobalt to molybdenum molar ratio increased, the intensity of the characteristic peaks of MoS2 gradually decreased, and the peak positions shifted slightly to higher angles. This indicates that the introduction of cobalt caused lattice distortion in MoS2, reducing the interplanar spacing, and confirming the strong interfacial interaction between CoS2 and MoS2. The above results show that by adjusting the molar ratio of cobalt to molybdenum in the precursor (1:2~20), two-dimensional heterojunction piezoelectric materials with different cobalt contents can be successfully prepared. Furthermore, the introduction of cobalt affects the crystal structure of MoS2, providing a structural basis for subsequent regulation of the piezoelectric catalytic performance of the materials.

[0106] Figure 14 This is a diagram showing the piezoelectric degradation performance of two-dimensional heterojunction piezoelectric materials and molybdenum disulfide on sulfamethoxazole in Examples 1 to 3 of this invention.

[0107] like Figure 14 As shown, under the same piezoelectric catalytic conditions, the catalytic degradation efficiency of pure MoS2 is relatively low, with a remaining SMX concentration of approximately 30% after 150 min. In contrast, the two-dimensional heterojunction piezoelectric materials with the introduction of cobalt exhibit better piezoelectric catalytic performance. When the molar ratio of cobalt to molybdenum during preparation is 1:8 (Example 1), the two-dimensional heterojunction piezoelectric material exhibits the best piezoelectric catalytic activity, reducing the remaining SMX concentration to approximately 5% after 150 min. When the molar ratio of cobalt to molybdenum during preparation is 1:2 (Example 2), the catalytic performance of the two-dimensional heterojunction piezoelectric material is second best, with a remaining SMX concentration of approximately 15% after 150 min. When the molar ratio of cobalt to molybdenum during preparation is 1:20 (Example 3), the catalytic performance of the material actually decreases, with a remaining SMX concentration of approximately 35% after 150 min. This may be due to insufficient active sites caused by the low cobalt content. The above results indicate that the introduction of cobalt can effectively improve the piezoelectric catalytic performance of MoS2. An appropriate molar ratio of cobalt to molybdenum can optimize the interface structure and charge separation efficiency of the heterojunction. However, excessive cobalt (molar ratio of cobalt to molybdenum greater than 1:2) may agglomerate on the surface of MoS2, covering the active sites and thus leading to a decrease in catalytic performance.

[0108] Comparative Examples 1 to 5 below provide various metal-modified MoS2 composite materials for screening modified metals with good piezoelectric catalytic performance. All comparative materials used pure MoS2 as a support were prepared by metal salt solution impregnation. Specific comparative examples and preparation methods are as follows.

[0109] Comparative Example 1

[0110] Comparative Example 1 provides a cobalt-molybdenum disulfide composite piezoelectric material (Co-MoS2). The preparation method of this cobalt-molybdenum disulfide heterojunction piezoelectric material differs from that of Example 1 in that: a homogeneous solution containing 20 mg of cobalt chloride powder is added to a homogeneous solution containing 200 mg of molybdenum disulfide (MoS2) powder, and after mixing and stirring for 2 h, the cobalt-molybdenum disulfide composite piezoelectric material is obtained by centrifugation.

[0111] Comparative Example 2

[0112] Comparative Example 2 provides a copper-molybdenum disulfide composite piezoelectric material (Cu-MoS2). The preparation method of this copper-molybdenum disulfide heterojunction piezoelectric material differs from that of Example 1 in that: a homogeneous solution containing 20 mg of copper chloride powder is added to a homogeneous solution containing 200 mg of molybdenum disulfide (MoS2) powder, and after mixing and stirring for 2 h, the copper-molybdenum disulfide composite piezoelectric material is obtained by centrifugation.

[0113] Comparative Example 3

[0114] Comparative Example 3 provides an iron-molybdenum disulfide composite piezoelectric material (Fe-MoS2). The preparation method of this iron-molybdenum disulfide heterojunction piezoelectric material differs from that of Example 1 in that: a homogeneous solution containing 20 mg of ferric chloride powder is added to a homogeneous solution containing 200 mg of molybdenum disulfide (MoS2) powder, and after mixing and stirring for 2 h, the iron-molybdenum disulfide composite piezoelectric material is obtained by centrifugation.

[0115] Comparative Example 4

[0116] Comparative Example 4 provides a nickel-molybdenum disulfide composite piezoelectric material (Ni-MoS2). The preparation method of this nickel-molybdenum disulfide heterojunction piezoelectric material differs from that of Example 1 in that: a homogeneous solution containing 20 mg of nickel chloride powder is added to a homogeneous solution containing 200 mg of molybdenum disulfide (MoS2) powder, and after mixing and stirring for 2 h, the nickel-molybdenum disulfide composite piezoelectric material is obtained by centrifugation.

[0117] Comparative Example 5

[0118] Comparative Example 5 provides a manganese-molybdenum disulfide composite piezoelectric material (Mn-MoS2). The preparation method of this manganese-molybdenum disulfide heterojunction piezoelectric material differs from that of Example 1 in that: a homogeneous solution containing 20 mg of manganese chloride powder is added to a homogeneous solution containing 200 mg of molybdenum disulfide (MoS2) powder, and after mixing and stirring for 2 h, centrifugation is performed to obtain the manganese-molybdenum disulfide composite piezoelectric material.

[0119] The piezoelectric degradation of chloramphenicol (CAP) was tested on MoS2 and the composite piezoelectric materials in Comparative Examples 1 to 5 to explore the catalytic effect of composite piezoelectric materials formed by combining different metals with MoS2.

[0120] Specific testing method: 30 mg of MoS2 and the piezoelectric materials from Comparative Examples 1 to 5 were ultrasonically dispersed in 60 mL of a 2 mg / L CAP solution. After stirring for 40 min to reach adsorption-desorption equilibrium, the mixture was transferred to an ultrasonic machine to start the reaction. During the reaction, a fixed amount of sample was periodically added to a methanol solution to terminate the reaction. After filtering through a 0.22 μm filter membrane, the remaining CAP concentration was determined by high-performance liquid chromatography (HPLC).

[0121] Figure 15 The graph shows the degradation performance of molybdenum disulfide and the composite piezoelectric materials in Comparative Examples 1 to 5 of this invention on chloramphenicol.

[0122] like Figure 15 As shown, under the same piezoelectric catalytic conditions, MoS2 and the piezoelectric materials in Comparative Examples 1 to 5 all achieved a certain amount of chloramphenicol (CAP) degradation. The remaining concentration of chloramphenicol gradually decreased with increasing reaction time. Specifically, the remaining concentration of chloramphenicol in pure MoS2 was approximately 40% at 120 min, while the piezoelectric performance of the composite piezoelectric materials with the introduction of transition metals copper, iron, nickel, and manganese decreased, possibly because some transition metals occupied the active sites of MoS2 during the material synthesis process. In contrast, the MoS2 material modified with cobalt showed superior catalytic activity, reducing the remaining concentration of chloramphenicol to below 30% at 120 min, with a significantly higher degradation efficiency than other transition metal-modified MoS2 piezoelectric materials. The test results indicate that the introduction of cobalt can effectively improve the piezoelectric catalytic performance of MoS2, suggesting that cobalt can optimize the piezoelectric catalytic activity of molybdenum disulfide, possibly through improvements in charge separation efficiency, interfacial interactions, and the synergistic degradation pathway of "free radical + non-free radical." This provides a basis for the design of the two-dimensional heterojunction material for efficient piezoelectric catalytic water treatment in this invention.

[0123] In summary, the two-dimensional heterojunction piezoelectric material of the present invention has at least the following significant advantages compared with existing molybdenum disulfide piezoelectric materials and piezoelectric water treatment technologies.

[0124] (1) This invention fully utilizes the heterostructure construction strategy, optimizing the built-in electric field of MoS2 by rationally controlling the structure of the two-dimensional heterojunction piezoelectric material. By leveraging the conductor CoS2 to effectively improve the interface state of MoS2 and control its band structure, the electron separation efficiency and transport rate of MoS2 during the piezoelectric process are significantly enhanced, successfully alleviating the problems of low charge separation efficiency and poor conductivity inherent in pure MoS2, thereby achieving superior piezoelectric response performance. Atomic force microscopy (KPFM) amplitude diagrams show that the piezoelectric amplitude of the two-dimensional heterojunction piezoelectric material of this invention is significantly greater than that of pure MoS2; current-time ( The spectrum further confirms that the two-dimensional heterojunction material has a stronger piezoelectric response current output capability; the electrical impedance (EIS) spectrum shows that the impedance of the two-dimensional heterojunction piezoelectric material of the present invention is less than that of pure MoS2 material, confirming that the introduction of CoS2 effectively optimizes the conductivity of the piezoelectric material itself and provides a guarantee for efficient charge transport.

[0125] (2) The two-dimensional heterojunction piezoelectric material of the present invention can effectively remove organic pollutants in water through a synergistic degradation pathway of "free radicals + non-free radicals". Electron paramagnetic resonance (EPR) spectroscopy results show that the two-dimensional heterojunction material system can effectively generate reactive oxygen species and charge carriers, specifically including superoxide anions (·O2). - Singlet oxygen () 1 O2) and electron holes (e - / h + Experimental data show that the two-dimensional heterojunction piezoelectric material can achieve a degradation rate of over 95% for the recalcitrant organic pollutant sulfamethoxazole (SMX) within 150 min, with a degradation rate constant k value as high as 0.014 min. -1 It is a pure MoS2 material (0.008 min). -1 The efficiency of this two-dimensional heterojunction material is 1.8 times that of the original material, which fully demonstrates its advantages in efficient catalytic degradation.

[0126] (3) The two-dimensional heterojunction piezoelectric material of the present invention has good environmental adaptability. Under different pH conditions and in various actual water quality scenarios (such as domestic wastewater and textile wastewater), it can maintain a good pollutant removal effect. At the same time, the two-dimensional heterojunction piezoelectric material exhibits good degradation efficiency for various types of organic pollutants (including antibiotics, phenols, dyes, etc.), effectively solving the problems of low degradation efficiency, serious interference from environmental factors, and narrow applicability of existing piezoelectric advanced oxidation technology.

[0127] (4) The two-dimensional heterojunction piezoelectric material of the present invention has good chemical stability and reusability: In the cyclic experiment of direct piezoelectric degradation of SMX, the material can still maintain more than 80% of its catalytic activity after being reused 4 times. Although the catalytic performance decreased to a certain extent in the 5th cycle due to the adsorption of pollutant intermediates on the material surface and blockage of active sites, the active sites can be re-exposed after the two-dimensional heterojunction piezoelectric material is collected and cleaned, and the catalytic performance is completely restored. In addition, the packed column continuous flow experiment shows that under the high-pressure excitation condition of about 15 MPa, the two-dimensional heterojunction piezoelectric material can achieve continuous and stable degradation for more than 140 hours, and the degradation rate of SMX is maintained at nearly 100%, with no significant decay in catalytic performance, further confirming its good reusability, structural stability and potential in environmental engineering applications.

[0128] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-dimensional heterojunction piezoelectric material, characterized in that, The heterojunction piezoelectric material has a heterojunction structure formed by cobalt sulfide and molybdenum disulfide, wherein the molybdenum disulfide has a 1T crystal phase and a 2H crystal phase.

2. The two-dimensional heterojunction piezoelectric material according to claim 1, characterized in that, The relative content ratio of 1T crystal phase and 2H crystal phase in the heterojunction piezoelectric material is 1~0.7:

1.

3. The two-dimensional heterojunction piezoelectric material according to claim 1, characterized in that, The molar ratio of cobalt to molybdenum in the heterojunction piezoelectric material is 1:1 to 20.

4. The two-dimensional heterojunction piezoelectric material according to claim 1, characterized in that, The heterojunction piezoelectric material has a nanosphere structure or a nanoflower cluster structure with a size of 300~500 nm.

5. A method for preparing a two-dimensional heterojunction piezoelectric material as described in any one of claims 1 to 4, characterized in that, The method includes: The molybdenum source, sulfur source, and complexing agent are mixed and stirred in water to form a precursor solution; A cobalt source is added to the precursor solution, and the mixture is thoroughly mixed and subjected to a hydrothermal reaction at 180~220℃ to obtain a two-dimensional heterojunction piezoelectric material.

6. The preparation method according to claim 5, characterized in that, The molybdenum source is a soluble molybdenum salt, selected from either ammonium molybdate or ammonium tetrathiomolybdate. The sulfur source is either thiourea or L-cysteine; The complexing agent is citric acid; The cobalt source is either cobalt nitrate or cobalt chloride.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the molybdenum source to the sulfur source is 1:5~25; The molar ratio of the cobalt source to the molybdenum source is 1:2~20.

8. A method for piezoelectric catalytic water treatment, characterized in that, The method includes: The two-dimensional heterojunction piezoelectric material according to any one of claims 1 to 4 is added to the water body to be treated, and under the action of mechanical force, the two-dimensional heterojunction piezoelectric material degrades the organic pollutants in the water body to be treated through piezoelectric catalysis.

9. The method according to claim 8, characterized in that, The piezoelectric catalytic degradation of organic pollutants in the water to be treated includes: In the piezoelectric catalytic degradation process, the two-dimensional heterojunction piezoelectric material is used to catalyze the oxygen in the water to be treated to generate active species, so as to use the active species to oxidize and degrade the organic pollutants. The active species include at least one of superoxide anion and singlet oxygen. And / or, the organic pollutants are oxidized and degraded using the positive charge generated by the piezoelectric effect of the two-dimensional heterojunction piezoelectric material.

10. The method according to claim 8, characterized in that, The pH range of the water to be treated is 3-9; The dosage of the two-dimensional heterojunction piezoelectric material is ≥0.5 g / L; The mechanical force can be applied in any one of the following ways: mechanical vibration, mechanical stirring, or ultrasound.

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