A Bi4TaO8Cl@g-C3N4 composite nanomaterial, its preparation method and application

Abstract

This invention relates to a Bi4TaO8Cl@g-C3N4 composite nanomaterial, its preparation method, and its application. The method includes the following steps: BiOCl, Bi2O3, and Ta2O5 are pretreated by calcination; the pretreated BiOCl, Bi2O3, and Ta2O5 are then mixed; a molten salt additive is added and the mixture is homogeneously mixed before calcination; the calcined product is washed to obtain Bi4TaO8Cl nanosheets; g-C3N4 and Bi4TaO8Cl nanosheets are dispersed in water and ultrasonically composited to obtain the Bi4TaO8Cl@g-C3N4 composite nanomaterial. When the material of this invention is subjected to mechanical vibration and generates a piezoelectric potential, electrons and holes can be effectively separated under the action of an electric field and migrate in different directions, thereby significantly reducing the recombination rate of electrons and holes, allowing more charge carriers to participate in the catalytic reaction to generate H2O2, and greatly improving the catalytic efficiency.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric catalysis technology, specifically to a Bi4TaO8Cl@g-C3N4 composite nanomaterial, its preparation method, and its application. Background Technology

[0002] In the field of catalysis, the core to improving reaction efficiency lies in achieving effective separation and efficient transport of photogenerated or piezoelectric charge carriers, while suppressing rapid recombination of electron-hole pairs as much as possible. This requires optimization through various strategies, including precise control of band structure, constructing heterojunctions to form built-in electric fields to enhance interfacial charge separation capabilities, increasing the exposure ratio of active sites on the material surface, and optimizing the application of external fields (such as mechanical vibrations or electric fields). In recent years, piezoelectric catalysis technology has gradually become a research hotspot in the design of high-efficiency catalysts due to its ability to drive reactions by generating piezoelectric potential through mechanical vibration without the need for an external light source. Piezoelectric potential can not only provide long-range driving forces to promote charge carrier separation, but also suppress charge carrier recombination through electrostatic shielding effects and extend their lifetime, providing a more efficient energy utilization pathway for catalytic reactions. In addition, the charge accumulation and depletion effects induced by piezoelectric potential can optimize the surface band distribution of materials, further enhancing the adsorption capacity of polar molecules or ions.

[0003] Bi4TaO8Cl, as a layered perovskite oxide material, is an ideal candidate for studying piezoelectric catalysis due to its excellent piezoelectric properties and unique structural characteristics. Its structure consists of (Bi2O2) 2+ Layers and (TaO4Cl) 2- The alternating layers form a layered perovskite structure, providing not only natural charge migration channels but also exhibiting high spontaneous polarization and ferroelectric properties. In particular, the coherent off-center displacement of Bi₄TaO₈Cl results in a more uniform internal charge distribution, thereby enhancing the material's spontaneous polarization effect and piezoelectric response. Under mechanical vibration or externally applied strain, this structural characteristic can further disrupt the electrostatic shielding effect within the material, significantly increasing the piezoelectric potential and thus driving charge separation and migration more efficiently, promoting catalytic reactions.

[0004] Despite Bi₄TaO₈Cl's theoretically large piezoelectric potential and strong redox capabilities, its practical application in piezoelectric catalysis still faces significant limitations. First, its band gap of approximately 3.0 eV limits its catalytic efficiency across a broader energy range, as it only exhibits strong absorption in the ultraviolet region. Second, the random orientation of its spontaneous polarization may cancel each other out after nanosheet aggregation, significantly reducing the piezoelectric induction intensity. Furthermore, while the conduction band position of Bi₄TaO₈Cl (-1.05 eV, relative to NHE) is sufficient to drive some oxygen reduction reactions, its high valence band position (1.85 eV) restricts charge separation efficiency, affecting overall catalytic performance. Therefore, through rational design and optimization, such as constructing heterojunctions or introducing external strain, its catalytic performance can be further improved, allowing it to realize greater potential in piezoelectric catalysis.

[0005] Bi4TaO8Cl, as a ferroelectric material, has achieved remarkable results in piezoelectric catalysis. For example, studies have shown that Bi4TaO8Cl can be used for highly efficient seawater splitting in piezoelectric catalysis. Under conditions requiring no co-catalysts or scavengers, its hydrogen production rate reaches 1.5 mmol g / L. -1 h -1 The process generates hydrogen simultaneously, producing the value-added chemical H2O2. Although the hydrogen production rate using seawater as the reaction medium is slightly lower, it still outperforms most oxide catalysts and piezoelectric catalysts in photocatalytic H2 production. This study elucidates the reaction mechanism using a bilayer model, providing important theoretical support for future material optimization.

[0006] However, this system still has shortcomings: the band gap width of Bi4TaO8Cl (~3.0 eV) limits its energy utilization efficiency, while the random aggregation of nanosheets and the cancellation of spontaneous polarization effects lead to insufficient piezoelectric induction intensity, further limiting its catalytic performance improvement. In addition, Bi4TaO8Cl has also been used for piezoelectric photocatalytic wastewater treatment. For example, single-crystal Bi4TaO8Cl nanoplates exhibit visible light response and significant piezoelectric behavior, producing 0.35% crystal deformation and band bending exceeding 2.5 eV under applied pressure. Using this material to treat five typical pollutants from the textile and pharmaceutical industries, studies have found that it exhibits excellent performance in piezoelectric catalysis, photocatalysis, and a combined piezoelectric photocatalysis method, achieving mineralization of all pollutants. This indicates that combining piezoelectric and photocatalytic effects can produce a synergistic effect exceeding 45%. However, this system still suffers from insufficient material stability and band structure matching. Especially in the single Bi4TaO8Cl system, the high recombination rate of electron-hole pairs leads to a decrease in efficiency under specific reaction conditions. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a Bi4TaO8Cl@g-C3N4 composite nanomaterial, its preparation method, and its application.

[0008] The objective of this invention can be achieved through the following technological inventions:

[0009] One objective of this invention is to provide a method for preparing Bi4TaO8Cl@g-C3N4 composite nanomaterials, comprising the following steps:

[0010] S1. BiOCl, Bi2O3 and Ta2O5 were pretreated by calcination, and then the pretreated BiOCl, Bi2O3 and Ta2O5 were mixed. Molten salt additive was added and mixed evenly before calcination. The calcined product was washed to obtain Bi4TaO8Cl nanosheets.

[0011] Specifically, all components are thoroughly mixed by mechanical grinding; after the mixture is ground uniformly, it is transferred to an alumina crucible and calcined at high temperature; after calcination, the crucible is naturally cooled to room temperature, and the product is repeatedly washed with a large amount of deionized water to completely remove the residue of the molten salt additive, and finally dried to obtain Bi4TaO8Cl nanosheets.

[0012] S2. Disperse g-C3N4 and Bi4TaO8Cl nanosheets in water and ultrasonically composite them to obtain Bi4TaO8Cl@g-C3N4 composite nanomaterials.

[0013] Specifically, appropriate amounts of Bi4TaO8Cl and g-C3N4 are weighed according to a certain mass ratio and added to deionized water. The composite treatment is carried out by ultrasonic equipment. The appropriate ultrasonic frequency, power and time are adjusted to allow the two materials to be fully mixed and interact to form a stable heterojunction structure. After ultrasonic treatment, the sample is dried to finally obtain the Bi4TaO8Cl@g-C3N4 composite material.

[0014] Further, the molar ratio of BiOCl, Bi2O3, and Ta2O5 is (1-3):(1-2):1. Preferably, the molar ratio of BiOCl, Bi2O3, and Ta2O5 is 3:2:1.

[0015] Further, the molten salt additive is NaCl and KCl in a mass ratio of (1-3):(1-3). Preferably, the molten salt additive is NaCl and KCl in a mass ratio of 1:1.

[0016] Further, the calcination temperature is 700–800℃, the calcination time is 14–28 h, and the heating rate is 3–5℃ / min. Preferably, the calcination temperature is 700℃, the calcination time is 14 h, and the heating rate is 5℃ / min.

[0017] Furthermore, the preparation method of g-C3N4 is as follows: using a nitrogen-containing organic compound as a precursor, g-C3N4 is obtained through intermolecular condensation reaction under high temperature conditions. In addition, g-C3N4 can also be prepared by methods such as template method and pyrolysis nitridation method.

[0018] Furthermore, the nitrogen-containing organic compound is any one or more of melamine, urea, and dicyandiamide.

[0019] Furthermore, the frequency of the ultrasound is 40±2kHz, the power is 500~600W, and the duration is 20~60min.

[0020] Preferably, the ultrasonic power is 540W and the duration is 30min.

[0021] The second objective of this invention is to provide a Bi4TaO8Cl@g-C3N4 composite nanomaterial, which is prepared by the method described above. The composite nanomaterial is a heterojunction composite material formed by Bi4TaO8Cl nanosheets and g-C3N4, wherein the mass of g-C3N4 is 1 to 4 wt% of the heterojunction composite material, preferably 1 wt%, 2 wt%, 3 wt%, or 4 wt%.

[0022] Furthermore, the particle size of the composite nanomaterial is 100-800 nm.

[0023] The third objective of this invention is the application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial described above, which is used in piezoelectric catalysts.

[0024] Mechanism of action:

[0025] In the Bi4TaO8Cl@g-C3N4 heterojunction, the band gap of g-C3N4 is approximately 2.7 eV, with a conduction band position of -1.13 eV and a valence band position of 1.57 eV, while the conduction band position of Bi4TaO8Cl is -1.05 eV (relative to NHE) and the valence band position is 1.85 eV. Compared to Bi4TaO8Cl, g-C3N4 has higher conduction and valence band positions and a lower work function. When these two semiconductor materials are in close contact, electrons in g-C3N4 spontaneously diffuse into Bi4TaO8Cl, forming an electron depletion layer and an electron accumulation layer near the interface, respectively, making Bi4TaO8Cl negatively charged and g-C3N4 positively charged. Under applied mechanical stress, an internal piezoelectric field is generated at the interface of this heterojunction, pointing from g-C3N4 to Bi4TaO8Cl. This piezoelectric field effectively promotes charge separation while suppressing charge recombination.

[0026] Furthermore, when Bi4TaO8Cl and g-C3N4 come into contact, their Fermi levels adjust to the same level. This causes the Fermi level of Bi4TaO8Cl to shift upward and the Fermi level of g-C3N4 to shift downward, forming band bending at the interface. This band bending further enhances the driving force of the piezoelectric field on the directional migration of charge carriers. Although g-C3N4 itself does not usually possess piezoelectric properties due to its two-dimensional layered structure symmetry, it can be induced to exhibit certain elastomerism through modification. Specifically, urea is subjected to two-step high-temperature heat treatment to form the basic structure of g-C3N4, followed by ultrasonic exfoliation to enhance polarization performance. Under applied mechanical stress, the electron distribution of the modified g-C3N4 may change, exhibiting an elastomerism effect, thereby synergizing with the piezoelectric effect of Bi4TaO8Cl to further improve the charge separation efficiency of the heterojunction. Under the combined action of the piezoelectric field and band bending, the polarization charge induced by mechanical stress accumulates near the interface. This polarization effect, by modulating the interfacial barrier of the heterojunction, facilitates the directional separation and migration of piezoelectric charges, thus avoiding ineffective recombination of charges.

[0027] Therefore, electrons accumulated in g-C3N4 and holes accumulated in Bi4TaO8Cl are retained and participate in the piezoelectric catalytic reaction. This mechanism significantly enhances catalytic performance, demonstrating the importance of the synergistic effect of piezoelectricity and interfacial charge separation. The layered structure and chemical stability of g-C3N4 effectively reduce the random aggregation of Bi4TaO8Cl nanosheets, thus avoiding performance degradation due to polarization effect cancellation. This composite material optimizes the migration paths of electrons and holes through band modulation, maximizing the efficiency of interfacial charge separation.

[0028] Furthermore, the excellent optical response of g-C3N4 significantly expands the light absorption range of the composite material, enabling more efficient utilization of light energy and achieving synergistic utilization of optical and mechanical energy. Optimized bandgap matching further enhances carrier migration efficiency, ensuring improved overall performance of the heterojunction across multiple scales. This performance improvement is attributed to the built-in electric field formed by the heterojunction, which not only promotes charge separation but also enhances charge transport efficiency and material stability. By constructing the Bi4TaO8Cl@g-C3N4 heterojunction material, the limitations of Bi4TaO8Cl were successfully overcome. Optimized bandgap modulation and significantly improved charge transport efficiency result in excellent performance in the H2O2 generation reaction.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) The Bi4TaO8Cl@g-C3N4 composite nanomaterial provided by this invention is constructed by heterojunctioning Bi4TaO8Cl nanosheets with g-C3N4 to form a Bi4TaO8Cl@g-C3N4 composite nanomaterial. A built-in electric field is formed between the Bi4TaO8Cl nanosheets and g-C3N4. When the material is subjected to mechanical vibration to generate a piezoelectric potential, electrons and holes can be effectively separated under the action of the electric field and migrate in different directions, thereby significantly reducing the recombination rate of electrons and holes, allowing more charge carriers to participate in the catalytic reaction to generate H2O2, and greatly improving the catalytic efficiency. Under one hour of piezoelectric catalysis, the H2O2 yield of Bi4TaO8Cl is 34 μmol / L, that of g-C3N4 is 16 μmol / L, while the yield of the Bi4TaO8Cl@g-C3N4 composite material is as high as 493 μmol / L, which is 15 times that of Bi4TaO8Cl alone.

[0031] (2) The preparation method of Bi4TaO8Cl@g-C3N4 composite nanomaterials provided by the present invention is simple, environmentally friendly and low cost.

[0032] (3) The Bi4TaO8Cl@g-C3N4 composite nanomaterial provided by the present invention has excellent catalytic efficiency when used as a piezoelectric catalyst to generate hydrogen peroxide. Attached Figure Description

[0033] Figure 1 The XRD patterns of g-C3N4, Bi4TaO8Cl, and CNBi-2 powders in this invention are obtained by X-ray diffraction.

[0034] Figure 2 The image shows the field emission scanning electron microscope morphology of CNBi-2 powder in this invention.

[0035] Figure 3This is an elemental mapping analysis diagram of CNBi-2 powder in this invention;

[0036] Figure 4 This is a comparison of the absorption spectra of g-C3N4, Bi4TaO8Cl, and CNBi-2 powders in the visible light range in this invention.

[0037] Figure 5 This is a comparison chart of the piezoelectric catalytic performance of g-C3N4, Bi4TaO8Cl, and CNBi-2 materials in this invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical invention of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0040] 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.

[0041] Bi4TaO8Cl, as a ferroelectric material, has achieved remarkable results in piezoelectric catalysis. For example, studies have shown that Bi4TaO8Cl can be used for highly efficient seawater splitting in piezoelectric catalysis. Under conditions requiring no co-catalysts or scavengers, its hydrogen production rate reaches 1.5 mmol g / L. -1 h -1 The process generates hydrogen simultaneously, producing the value-added chemical H2O2. Although the hydrogen production rate using seawater as the reaction medium is slightly lower, it still outperforms most oxide catalysts and piezoelectric catalysts in photocatalytic H2 production. This study elucidates the reaction mechanism using a bilayer model, providing important theoretical support for future material optimization.

[0042] However, this system still has shortcomings: the band gap width of Bi4TaO8Cl (~3.0 eV) limits its energy utilization efficiency, while the random aggregation of nanosheets and the cancellation of spontaneous polarization effects lead to insufficient piezoelectric induction intensity, further limiting its catalytic performance improvement. In addition, Bi4TaO8Cl has also been used for piezoelectric photocatalytic wastewater treatment. For example, single-crystal Bi4TaO8Cl nanoplates exhibit visible light response and significant piezoelectric behavior, producing 0.35% crystal deformation and band bending exceeding 2.5 eV under applied pressure. Using this material to treat five typical pollutants from the textile and pharmaceutical industries, studies have found that it exhibits excellent performance in piezoelectric catalysis, photocatalysis, and a combined piezoelectric photocatalysis method, achieving mineralization of all pollutants. This indicates that combining piezoelectric and photocatalytic effects can produce a synergistic effect exceeding 45%. However, this system still suffers from insufficient material stability and band structure matching. Especially in the single Bi4TaO8Cl system, the high recombination rate of electron-hole pairs leads to a decrease in efficiency under specific reaction conditions.

[0043] Therefore, the present invention provides a method for preparing Bi4TaO8Cl@g-C3N4 composite nanomaterials, comprising the following steps:

[0044] S1. BiOCl, Bi2O3 and Ta2O5 were pretreated by calcination, and then the pretreated BiOCl, Bi2O3 and Ta2O5 were mixed. Molten salt additive was added and mixed evenly before calcination. The calcined product was washed to obtain Bi4TaO8Cl nanosheets.

[0045] Specifically, all components are thoroughly mixed by mechanical grinding; after the mixture is ground uniformly, it is transferred to an alumina crucible and calcined at high temperature; after calcination, the crucible is naturally cooled to room temperature, and the product is repeatedly washed with a large amount of deionized water to completely remove the residue of the molten salt additive, and finally dried to obtain Bi4TaO8Cl nanosheets.

[0046] S2. Disperse g-C3N4 and Bi4TaO8Cl nanosheets in water and ultrasonically composite them to obtain Bi4TaO8Cl@g-C3N4 composite nanomaterials.

[0047] Specifically, appropriate amounts of Bi4TaO8Cl and g-C3N4 are weighed according to a certain mass ratio and added to deionized water. The composite treatment is carried out by ultrasonic equipment. The appropriate ultrasonic frequency, power and time are adjusted to allow the two materials to be fully mixed and interact to form a stable heterojunction structure. After ultrasonic treatment, the sample is dried to finally obtain the Bi4TaO8Cl@g-C3N4 composite material.

[0048] In this embodiment, the molar ratio of BiOCl, Bi2O3 and Ta2O5 is (1-3):(1-2):1;

[0049] Preferably, the molar ratio of BiOCl, Bi2O3 and Ta2O5 is 3:2:1.

[0050] In this embodiment, the molten salt additive is NaCl and KCl in a mass ratio of (1-3):(1-3); preferably, the molten salt additive is NaCl and KCl in a mass ratio of 1:1.

[0051] In this embodiment, the calcination temperature is 700–800°C, the calcination time is 14–28 h, and the heating rate is 3–5°C / min.

[0052] Preferably, the calcination temperature is 700℃, the calcination time is 14h, and the heating rate is 5℃ / min.

[0053] In this embodiment, the preparation method of g-C3N4 is as follows: using a nitrogen-containing organic compound as a precursor, g-C3N4 is obtained through intermolecular condensation reaction under high temperature conditions.

[0054] Specifically, urea is placed in a crucible and gradually heated to a higher temperature and held for a period of time to induce a preliminary thermal decomposition reaction, generating intermediate products. After the reaction cools to room temperature, it is heated again to an appropriate temperature and held to further promote the decomposition and recombination of urea, ultimately forming the basic structure of g-C3N4. Subsequently, the obtained sample is placed in a tube furnace and subjected to high-temperature heat treatment under an inert atmosphere. Before use, the prepared g-C3N4 needs to undergo ultrasonic exfoliation treatment, which disperses it in deionized water. Through prolonged ultrasonic action, the particles or flakes are fully dispersed. The ultrasonically treated suspension is then dried to obtain the g-C3N4 sample.

[0055] In this embodiment, the nitrogen-containing organic compound is any one or more of melamine, urea, and dicyandiamide.

[0056] In this embodiment, the frequency of the ultrasound is 40±2kHz, the power is 500~600W, and the duration is 20~60min. Preferably, the power is 540W and the duration is 30min.

[0057] This embodiment also provides a Bi4TaO8Cl@g-C3N4 composite nanomaterial, which is prepared by the method described above. The composite nanomaterial is a heterojunction composite material formed by Bi4TaO8Cl nanosheets and g-C3N4, wherein the mass of g-C3N4 is 1-4 wt% of the heterojunction composite material. The particle size of the composite nanomaterial is 100-800 nm.

[0058] This embodiment also provides an application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial as described above, which is used in piezoelectric catalysts.

[0059] Mechanism of action:

[0060] In the Bi4TaO8Cl@g-C3N4 heterojunction, the band gap of g-C3N4 is approximately 2.7 eV, with a conduction band position of -1.13 eV and a valence band position of 1.57 eV, while the conduction band position of Bi4TaO8Cl is -1.05 eV (relative to NHE) and the valence band position is 1.85 eV. Compared to Bi4TaO8Cl, g-C3N4 has higher conduction and valence band positions and a lower work function. When these two semiconductor materials are in close contact, electrons in g-C3N4 spontaneously diffuse into Bi4TaO8Cl, forming an electron depletion layer and an electron accumulation layer near the interface, respectively, making Bi4TaO8Cl negatively charged and g-C3N4 positively charged. Under applied mechanical stress, an internal piezoelectric field is generated at the interface of this heterojunction, pointing from g-C3N4 to Bi4TaO8Cl. This piezoelectric field effectively promotes charge separation while suppressing charge recombination.

[0061] Furthermore, when Bi4TaO8Cl and g-C3N4 come into contact, their Fermi levels tune to the same level. This causes the Fermi level of Bi4TaO8Cl to shift upward and the Fermi level of g-C3N4 to shift downward, resulting in band bending at the interface. This band bending further enhances the driving force of the piezoelectric field on the directional migration of charge carriers.

[0062] Although g-C3N4 itself typically lacks piezoelectric properties due to its two-dimensional layered structure symmetry, modification can induce a certain elastomeric effect. Specifically, urea undergoes two-step high-temperature heat treatment to form the basic g-C3N4 structure, followed by ultrasonic exfoliation to enhance polarization performance. Under applied mechanical stress, the electron distribution of the modified g-C3N4 may change, exhibiting an elastomeric effect. This, in conjunction with the piezoelectric effect of Bi4TaO8Cl, further improves the charge separation efficiency of the heterojunction. Under the combined action of the piezoelectric field and band bending, mechanically stress-induced polarization charges accumulate near the interface. This polarization effect, by modulating the interface barrier of the heterojunction, facilitates the directional separation and migration of piezoelectric charges, avoiding ineffective charge recombination.

[0063] Therefore, electrons accumulated in g-C3N4 and holes accumulated in Bi4TaO8Cl are retained and participate in the piezoelectric catalytic reaction. This mechanism significantly enhances catalytic performance, demonstrating the importance of the synergistic effect of piezoelectricity and interfacial charge separation. The layered structure and chemical stability of g-C3N4 effectively reduce the random aggregation of Bi4TaO8Cl nanosheets, thus avoiding performance degradation due to polarization effect cancellation. This composite material optimizes the migration paths of electrons and holes through band modulation, maximizing the efficiency of interfacial charge separation.

[0064] Furthermore, the excellent optical response of g-C3N4 significantly expands the light absorption range of the composite material, enabling it to utilize light energy more efficiently and achieve synergistic utilization of optical and mechanical energy. Optimization of bandgap matching further enhances carrier migration efficiency, thereby ensuring improved overall performance of the heterojunction across multiple scales.

[0065] This invention further verifies the superior performance of the Bi4TaO8Cl@g-C3N4 heterojunction material. In the H2O2 generation reaction, the H2O2 yields of single Bi4TaO8Cl and g-C3N4 are 34 μmol / L and 16 μmol / L, respectively, while the H2O2 yield of Bi4TaO8Cl@g-C3N4 reaches as high as 493 μmol / L, a significant increase of approximately 15 times. This performance improvement is attributed to the built-in electric field formed by the heterojunction, which not only promotes charge separation but also enhances charge transport efficiency and material stability. By constructing the Bi4TaO8Cl@g-C3N4 heterojunction material, the limitations of Bi4TaO8Cl are successfully overcome. Optimized band modulation and significantly improved charge transport efficiency enable it to exhibit excellent performance in the H2O2 generation reaction.

[0066] Example 1

[0067] This embodiment provides the preparation of Bi4TaO8Cl@g-C3N4 composite nanomaterials:

[0068] (1) Weigh 0.3141g BiOCl, 0.6530g Bi2O3 and 0.2210g Ta2O5 respectively, and place each raw material in a muffle furnace for calcination pretreatment. The temperature is slowly raised to 300℃ at a heating rate of 5K / min and held at that temperature for 5 hours.

[0069] After the calcination pretreatment is completed, the dried BiOCl, Bi2O3 and Ta2O5 are mixed in a molar ratio of 3:2:1, and 2.9279g NaCl and 3.7463g KCl are added as molten salt additives. The molar ratio of molten salt additives is 1:1. All components are placed together in an agate mortar and thoroughly mixed by mechanical grinding.

[0070] Carefully transfer the uniformly ground mixture into an alumina crucible, place it in a muffle furnace for high-temperature calcination, slowly raise the temperature to 700°C at a heating rate of 5 K / min, and hold it at that temperature for 14 hours.

[0071] After calcination, turn off the power to the muffle furnace and allow the sample to cool naturally to room temperature inside the furnace. After the sample has cooled, remove the crucible and transfer the sample to a beaker. Add a large amount of deionized water and wash the sample multiple times. Stir the sample thoroughly each time to ensure that the molten salt is completely dissolved in the water. Then collect the precipitate by centrifugation. Repeat the washing process at least 5 times to ensure that all NaCl and KCl impurities are removed.

[0072] After washing, the product was dried in a vacuum drying oven at 60°C for 5 hours to finally obtain high-quality Bi4TaO8Cl nanosheets.

[0073] (2) Accurately weigh 10g of urea, put it into a clean crucible, cover the crucible, put the crucible into a muffle furnace, set the heating program, and make the furnace heat up to 550℃ within 120min, and keep it at this temperature for 2h.

[0074] After the heat preservation is completed, turn off the power of the muffle furnace and let the sample cool naturally to room temperature inside the furnace. After the sample has cooled, carefully remove the crucible lid, readjust the parameters of the muffle furnace, and heat the furnace to 500℃ within 120 minutes, and keep it at that temperature for 2 hours.

[0075] After the reaction is complete, the sample is collected and transferred into a ceramic boat. The ceramic boat is placed in a tube furnace, and the tube furnace parameters are set to heat it to 500°C within 100 min and keep it at that temperature for 2 h under a nitrogen atmosphere. The nitrogen flow rate is controlled at 20-50 mL / min.

[0076] Finally, g-C3N4 sample was obtained; 50 mg of the prepared g-C3N4 was added to 100 mL of deionized water, and the solution was placed in an ultrasonic cleaner. The ultrasonic frequency was set to 40 kHz and the power to 540 W, and the ultrasonic treatment was carried out for 10 h.

[0077] After ultrasonic treatment, the solution is transferred to a vacuum drying oven and dried at 100°C until all the water in the beaker has evaporated. The dried sample is then collected for later use.

[0078] (3) According to the mass of g-C3N4 being 2wt% of the heterojunction composite material, accurately weigh 98mg Bi4TaO8Cl and 2mg g-C3N4 respectively, place them in a clean beaker, add an appropriate amount of deionized water to the beaker so that the sample is completely submerged in the water to form a uniform suspension, place the beaker in an ultrasonic cleaner, set the ultrasonic frequency to 40±2kHz, the power to 540W, and ultrasonically treat for 30 minutes.

[0079] After ultrasonic treatment, the solution was centrifuged to collect the precipitate, which was then transferred to a vacuum drying oven and dried at 60°C for 6 hours to obtain the Bi4TaO8Cl@g-C3N4 composite material.

[0080] Application Example 1

[0081] In this application example, the Bi4TaO8Cl@g-C3N4 composite material obtained in Example 1 was used to conduct a piezoelectric catalysis experiment. The specific steps are as follows:

[0082] (1) Accurately weigh 50 mg of the prepared Bi4TaO8Cl@g-C3N4 composite material and disperse it in 100 mL of pure water to form a uniform dispersion.

[0083] (2) Transfer the above dispersion to a reaction flask and place the reaction flask in an ultrasonic bath. Set the ultrasonic frequency to 40 kHz and conduct the experiment.

[0084] During ultrasonic vibration, the temperature of the reaction system is precisely controlled at 15℃ using a circulating water cooling system. The water flow rate of the circulating water cooling system should be controlled within an appropriate range, generally 100-200 mL / min, to ensure good cooling effect.

[0085] (3) During the reaction, every 20 minutes, 3 ml of the reaction solution was taken out using a syringe, filtered through a 0.22 μm organic filter, and the filtrate was collected. Samples were taken at three time points for subsequent analysis.

[0086] (4) For the detection of hydrogen peroxide, the filtered sample is mixed with 1 mL of 0.4 M KI solution and 1 mL of 0.1 M potassium hydrogen phthalate solution.

[0087] Then, the KI / H ratio was measured using a UV-Vis spectrometer. 32 Mo7N6O 28 The absorbance at 351 nm is combined. Before measuring absorbance, the UV-Vis spectrometer must be calibrated to ensure the accuracy of the measurement results.

[0088] Based on a pre-plotted standard curve, the concentration of H2O2 in the sample is calculated using absorbance values, thereby evaluating the piezoelectric catalytic performance of the composite material at different ultrasonic frequencies.

[0089] Figure 1 X-ray diffraction (XRD) patterns of g-C3N4, Bi4TaO8Cl, and CNBi-2 powders are shown. XRD analysis of Bi4TaO8Cl nanosheets, g-C3N4, and Bi4TaO8Cl@g-C3N4 composites was performed using a Rigaku Ultima IV diffractometer. Cu Kα radiation was used during the measurements, with a wavelength of [wavelength missing]. The scanning range was set at 5-80°, with a precise step size of 0.02°. The X-ray diffraction (XRD) pattern of Bi4TaO8Cl nanosheets obtained under these measurement conditions clearly reveals their crystal structure characteristics. The position, intensity, and shape of each diffraction peak can be compared with standard cards to accurately determine the phase purity, crystallinity, and crystal structure integrity of the prepared Bi4TaO8Cl nanosheets. The XRD pattern of g-C3N4 also reflects its unique crystal structure information, helping to understand the structure formation process during its preparation. The XRD pattern of the Bi4TaO8Cl@g-C3N4 composite material is a key basis for judging the composite effect. In this pattern, characteristic diffraction peaks of both Bi4TaO8Cl and g-C3N4 can be observed, and the position and intensity of the peaks may change compared to the single material. These changes can provide important clues for studying the interaction between the two components in the composite material, changes in crystal structure, and the formation of heterojunctions.

[0090] Figure 2 Field emission scanning electron microscopy (FEM) images of CNBi-2 powder. The morphology of the Bi4TaO8Cl@g-C3N4 composite material was observed using FEM, and the obtained FEM images are shown below. Figure 2The images provide a clear visual representation of the microstructure of the composite material. High-resolution images clearly show that the Bi4TaO8Cl nanosheets exhibit a sheet-like structure with a relatively flat surface, uniform thickness, and regular edges. The g-C3N4 nanosheets, on the other hand, are thin films that tightly wrap around the Bi4TaO8Cl nanosheets. This unique microstructure allows for a large contact area between the two, facilitating charge transfer and separation at the interface and laying a solid foundation for improving the material's catalytic performance. Further analysis of the images reveals details such as the uniformity of the g-C3N4 film coverage on the Bi4TaO8Cl nanosheet surface and the tightness of the bonding between the two, all of which are closely related to the composite material's performance.

[0091] Figure 3 The elemental mapping analysis diagram of CNBi-2 powder is shown. The elemental distribution mapping analysis of the Bi4TaO8Cl@g-C3N4 composite material was performed using energy-scattered X-ray spectroscopy (EDS) combined with field emission scanning electron microscopy (FESEM) to further explore the elemental distribution characteristics in the material. Figure 3 The EDS spectrum (a) clearly shows the presence of the main elements Bi, Ta, Cl, C, O, and N in the composite material, indicating that the composition of the composite material is consistent with the design. Mapping diagrams (bh) show that Bi (Figure c) highly overlaps with Ta and Cl (Figures d and g), demonstrating the uniform distribution of Bi4TaO8Cl nanosheets. The distribution of C (Figure e) and N (Figure h) corresponds to the presence of g-C3N4, appearing as a thin film uniformly covering the surface of the Bi4TaO8Cl nanosheets. The distribution of O (Figure f) shows its uniform presence throughout the composite material, consistent with the oxide portion of the Bi4TaO8Cl structure. Overall, the mapping analysis further confirms the good bonding between the Bi4TaO8Cl nanosheets and the g-C3N4 film. The close contact and uniform elemental distribution provide ideal conditions for charge separation and transport at the interface, thereby enhancing the photocatalytic performance of the material. This result is highly consistent with the design goals of the composite material and provides experimental basis for further optimization of its photoelectric properties.

[0092] Figure 4 The graph shows a comparison of the absorption spectra of g-C3N4, Bi4TaO8Cl, and CNBi-2 powders in the visible light range. The absorption spectra of Bi4TaO8Cl nanosheets, g-C3N4, and Bi4TaO8Cl@g-C3N4 composite materials in the visible light range were measured using a UV-Vis spectrometer, and the results are plotted as follows. Figure 4For Bi4TaO8Cl nanosheets, their absorption spectra reflect the light absorption characteristics of the material in the visible light region. By analyzing the position, intensity, and absorption edge of the absorption peaks, we can understand their absorption capacity for different wavelengths of light, and thus infer their electronic structure and optical properties. The absorption spectrum of g-C3N4 reflects its unique absorption behavior in the visible light range, typically exhibiting strong absorption peaks within a certain wavelength range, which is closely related to its electronic transitions and band structure. The absorption spectrum of the Bi4TaO8Cl@g-C3N4 composite material is an important basis for studying the changes in optical properties after the two materials are combined. Compared with the single material, the absorption spectrum of the composite material may exhibit redshift or blueshift phenomena, and the absorption intensity may also change. These changes may be due to the redistribution of electronic states and the adjustment of the band structure caused by the formation of the heterojunction structure, thereby affecting the material's light absorption and utilization efficiency.

[0093] Figure 5 A comparison of the piezoelectric catalytic performance of g-C3N4, Bi4TaO8Cl, and CNBi-2 materials. Based on... Figure 5 This paper compares the performance of Bi4TaO8Cl nanosheets, g-C3N4, and Bi4TaO8Cl@g-C3N4 composite materials prepared in this invention in terms of H2O2 production per unit time. Under the same reaction conditions, piezoelectric catalysis experiments were conducted on the three materials to produce H2O2, and the H2O2 concentration was measured at different reaction time points. These data were plotted as curves to form a performance graph. The graph clearly shows that under the piezoelectric catalytic effect for one hour, the yield of Bi4TaO8Cl is 34 μmol / L, the yield of g-C3N4 is 16 μmol / L, while the yield of the Bi4TaO8Cl@g-C3N4 composite material reaches as high as 493 μmol / L, which is 15 times that of Bi4TaO8Cl alone. This fully demonstrates the significant advantage of heterojunction structures in improving the piezoelectric catalytic performance of materials. By analyzing the trend of H2O2 production rate changes of different materials at different reaction times, the catalytic activity and stability of the materials can be further understood, providing a strong reference for optimizing material performance and reaction conditions. For example, if the composite material maintains a high H2O2 generation rate over a long period of time, it indicates that it has good stability and sustained catalytic ability, which is beneficial for large-scale production and long-term operation in practical applications.

[0094] In summary, the Bi4TaO8Cl@g-C3N4 composite material prepared in this invention exhibits excellent catalytic activity in the hydrogen peroxide generation reaction, along with high stability and a long lifespan. By combining Bi4TaO8Cl nanosheets with good photoelectric properties with g-C3N4, a highly efficient charge separation interface is formed, significantly improving the catalytic efficiency of the material. The heterojunction structure between Bi4TaO8Cl and g-C3N4 promotes carrier migration within the material, enhancing its performance in catalytic reactions. This composite material holds great potential in the field of catalysis, particularly suitable for reactions requiring efficient charge separation and high catalytic efficiency.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the invention shall still fall within the protection scope of the present invention.

Claims

1. An application of a Bi4TaO8Cl@g-C3N4 composite nanomaterial, characterized in that, This material is used in piezoelectric catalysts; The method for preparing this material includes the following steps: S1. BiOCl, Bi2O3 and Ta2O5 were pretreated by calcination, and then the pretreated BiOCl, Bi2O3 and Ta2O5 were mixed. Molten salt additive was added and mixed evenly before calcination. The calcined product was washed to obtain Bi4TaO8Cl nanosheets. S2. Disperse g-C3N4 and Bi4TaO8Cl nanosheets in water and ultrasonically composite them to obtain Bi4TaO8Cl@g-C3N4 composite nanomaterials. The basic structure of g-C3N4 is formed by two-step high-temperature heat treatment of urea. The g-C3N4 is then placed in a tube furnace and subjected to high-temperature heat treatment under an inert atmosphere. Before use, the prepared g-C3N4 undergoes ultrasonic exfoliation treatment.

2. The application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial according to claim 1, characterized in that, The molar ratio of BiOCl, Bi2O3 and Ta2O5 is (1~3): (1~2):

1.

3. The application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial according to claim 1, characterized in that, The molten salt additive is NaCl and KCl in a mass ratio of (1~3): (1~3).

4. The application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial according to claim 1, characterized in that, The calcination temperature is 700~800℃, the calcination time is 14~28h, and the heating rate is 3~5℃ / min.

5. The application of the Bi4TaO8Cl@g-C3N4 composite nanomaterial according to claim 1, characterized in that, In S2, the frequency of the ultrasound is 40±2kHz, the power is 500~600W, and the duration is 20~60min.

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