A graphite phase carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material, a preparation method and application thereof

Abstract

The application provides a graphite phase carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material, and the photocatalyst is a layered nanosheet structure, which takes graphite phase carbon nitride as a skeleton, is doped with vanadium disulfide nanosheets and carbon nanotubes, and the graphite phase carbon nitride, the vanadium disulfide nanosheets and the carbon nanotubes are interwoven to form a heterojunction. The graphite phase carbon nitride, the vanadium disulfide and the carbon nanotube cooperate with each other to construct an efficient photocatalytic system, which can simultaneously drive oxidation (tetracycline hydrochloride degradation) and reduction (hydrogen peroxide generation) processes.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, specifically to a graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Hydrogen peroxide is widely used in organic synthesis, medical disinfection, wastewater treatment, and other fields, and its demand is increasing. Currently, the industrial production of hydrogen peroxide via the anthraquinone process has many drawbacks, such as complex processes, high energy consumption, and severe pollution.

[0004] Meanwhile, tetracycline hydrochloride (TCH), as a typical antibiotic, is difficult to metabolize after being ingested by the human body, and most of it is excreted in the form of the parent compound.

[0005] Photocatalysis, as a green and efficient advanced redox process, can achieve the synthesis of hydrogen peroxide and the degradation of antibiotics driven by sunlight. Graphitic carbon nitride is a non-metallic photocatalyst with a unique graphitic layered structure. Using triazine rings as structural units, it exhibits chemical stability, high corrosion resistance, and a unique electronic and band structure. Furthermore, graphitic carbon nitride demonstrates photoresponsiveness, making it one of the hot research materials in the field of visible light photocatalysis.

[0006] However, graphitic carbon nitride suffers from drawbacks such as insufficient absorption in the visible light region, low electrical conductivity, small specific surface area, and rapid recombination of photogenerated electron-hole pairs, limiting its efficiency in driving redox reactions. To improve its photocatalytic activity, graphitic carbon nitride is doped with other substances to form binary heterojunctions, such as CN / TiO2 and CN / MOFs. However, current binary heterojunction photocatalytic effects are unsatisfactory, only enabling the synthesis of hydrogen oxide or the degradation of antibiotics, and failing to achieve multifunctional composites. Summary of the Invention

[0007] To overcome the above problems, this invention provides a ternary heterojunction composite material of graphitic carbon nitride / vanadium disulfide / carbon nanotubes, its preparation method, and its application.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a ternary heterojunction composite material of graphitic carbon nitride / vanadium disulfide / carbon nanotubes. The composite material has a layered nanosheet structure with graphitic carbon nitride (CN) as the framework and doped with vanadium disulfide (VS2) nanosheets and carbon nanotubes (CNTs). The graphitic carbon nitride, vanadium disulfide nanosheets and carbon nanotubes are interwoven to form a heterojunction.

[0010] In one or more embodiments, the particle size of the nanosheet structure is 3~9 μm, preferably 3.6~8.6 μm.

[0011] In one or more embodiments, the particle size of vanadium disulfide nanosheets is 1~4 μm, preferably 1.92~3.5 μm.

[0012] A second aspect of the present invention provides a method for preparing the graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material described in the first aspect, comprising the following steps:

[0013] (1) Disperse melamine and ammonium metavanadate in an ammonia solution, then add thioacetamide, mix well, then add carbon nanotubes, and mix well again;

[0014] (2) The mixture in step (1) is subjected to hydrothermal treatment, and then the solid is collected and calcined to obtain the graphite phase carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material.

[0015] In one or more embodiments, in step (1), the molar ratio of melamine to ammonium metavanadate is (18~22):1, preferably 20:1.

[0016] In one or more embodiments, in step (1), the concentration of the ammonia solution is 1.4 wt% to 1.6 wt%.

[0017] In one or more embodiments, in step (1), the concentration of ammonium metavanadate in the ammonia solution is 0.1~0.2 mol / L, preferably 0.125 mol / L.

[0018] In one or more embodiments, in step (1), the molar ratio of ammonium metavanadate to thioacetamide is 2:(13~16), preferably 2:15.

[0019] In one or more embodiments, in step (1), the mass ratio of melamine to carbon nanotubes is 1:(5~15), preferably 1:10.

[0020] In one or more embodiments, in step (2), the temperature of the hydrothermal treatment is 160~200 ℃, preferably 180 ℃; the time of the hydrothermal treatment is 18~24 h, preferably 20 h.

[0021] In one or more embodiments, in step (3), the calcination temperature is 350~500 ℃, preferably 400 ℃; the calcination time is 1.5~4 h, preferably 2 h.

[0022] A third aspect of the present invention provides the application of the graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material described in the first aspect or the graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material prepared by the preparation method described in the second aspect as a photocatalyst.

[0023] In one or more embodiments, the application includes: catalyzing the synthesis of hydrogen peroxide from water and oxygen under visible light.

[0024] In one or more embodiments, the application includes: catalytically degrading antibiotics under visible light;

[0025] Preferably, the antibiotic includes tetracycline hydrochloride (TCH).

[0026] The beneficial effects of this invention are as follows:

[0027] (1) This invention provides a ternary heterojunction composite material of graphitic carbon nitride / vanadium disulfide / carbon nanotubes. The photocatalyst has a layered nanosheet structure, with graphitic carbon nitride (CN) as the framework, doped with vanadium disulfide (VS2) nanosheets and carbon nanotubes (CNTs). The graphitic carbon nitride, vanadium disulfide nanosheets, and carbon nanotubes intertwine to form a heterojunction. The graphitic carbon nitride, vanadium disulfide, and carbon nanotubes work together to construct a highly efficient photocatalytic system that can simultaneously drive oxidation (degradation of tetracycline hydrochloride) and reduction (generation of hydrogen peroxide). Vanadium disulfide has a layered two-dimensional structure, high electrical conductivity, and redox activity. 4+ / V 5+ Yes, it can significantly enhance carrier separation and promote the selective two-electron oxygen reduction (ORR) pathway, thereby improving the generation efficiency of hydrogen peroxide. At the same time, its surface activity is conducive to the generation of reactive oxygen species (ROS), which are essential for the mineralization of stubborn pollutants such as tetracycline hydrochloride. The contribution of carbon nanotubes lies in their conductive framework, which can accelerate electron transport, minimize charge recombination, and provide a high surface area with strong π-π interactions, thereby increasing the local pollutant concentration at the catalyst interface and enhancing degradation kinetics.

[0028] (2) In this invention, a graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material was obtained by hydrothermal reaction and calcination of the precursor material. The hydrothermal treatment promoted the nucleation and anchoring of vanadium disulfide nanosheets in the carbon nanotube matrix. At the same time, the carbon nanotubes and nanosheets intertwined with each other and formed a strong interfacial contact through π-π stacking and van der Waals forces. The subsequent calcination improved the crystallinity, removed residual organic matter, and activated the surface, ultimately forming a structurally complete and highly stable composite material. This stable structure effectively inhibited photocorrosion and maintained an efficient charge transfer path, exhibiting excellent durability and stable photocatalytic performance.

[0029] (3) The introduction of vanadium disulfide into graphitic carbon nitride and carbon nanotubes can significantly enhance light absorption, especially in the visible light region, making the photocatalytic process more effective under natural sunlight. This is because vanadium disulfide exhibits absorption at approximately 596 nm and 640 nm due to the action of photoexcitons, which is generated by spin-orbit-induced valence band splitting. Most conventional photocatalysts require ultraviolet (UV) light to achieve efficient photocatalytic activity, which poses a significant limitation to practical applications because UV light only accounts for a small portion of the solar spectrum; however, most sunlight is located in the visible light region. Therefore, developing photocatalysts that can effectively utilize visible light is crucial for enhancing solar energy conversion and practical applications. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 Characterization of photocatalytic hydrogen peroxide synthesis: a) represents the photocatalytic hydrogen peroxide synthesis yields of the original CN, VS2, binary heterojunction composites CN@VS2 and CNTs@VS2, and ternary heterojunction composites CVCN-1, CVCN-2, and CVCN-3; b) represents the photocatalytic hydrogen peroxide synthesis yield of the ternary heterojunction composite CVCN-2 using various quenching and trapping ions; c) represents the hydrogen peroxide synthesis yield of the ternary heterojunction composite CVCN-2 in different solvents; d) represents the hydrogen peroxide synthesis yield of the ternary heterojunction composite CVCN-2 over four consecutive reaction cycles; e) represents the hydrogen peroxide synthesis yield of the ternary heterojunction composite CVCN-2 in different atmospheres; f) represents the kf and kd values ​​of the ternary heterojunction composite CVCN-2.

[0032] Figure 2The photocatalytic degradation effect of ternary heterojunction composite material CVCN-2 on TCH is shown in Figure a, where a represents the photocatalytic degradation effect of the original CN, VS2, binary heterojunction composite materials CN@VS2 and CNTs@VS2, and ternary heterojunction composite materials CVCN-1, CVCN-2, and CVCN-3 on TCH; b represents the photocatalytic degradation effect of ln(C) on TCH. t The relationship between / C0) and time and the fitting results; c represents the effect of reactive oxygen species, OH substances, and photogenerated electron-hole pairs on TCH degradation; d represents the effect of the ternary heterojunction composite material CVCN-2 on TCH degradation over three consecutive reaction cycles;

[0033] Figure 3 Characterization of the ternary heterojunction composite material CVCN-2: a) SEM image of CVCN-2, b) TEM image of CVCN-2, c) HAADF-STEM image of CVCN-2, d) X-ray diffraction (XRD) patterns of the original CN, VS2, binary heterojunction composites CN@VS2 and CNTs@VS2, and CVCN-2, and e) FTIR spectra of the original CN, VS2, and CVCN-2.

[0034] Figure 4 Characterization of the ternary heterojunction composite material CVCN-2, where a) is the UV-Vis spectrum of the original CN, VS2, and the ternary heterojunction composite material CVCN-2; b) is the bandgap diagram of the original CN, VS2, and the ternary heterojunction composite material CVCN-2; c) is the characterization of the ternary heterojunction composite material CVCN-2. Figure 3 Time-resolved photoluminescence (TRPL) spectrum of the CVCN-2 heterojunction composite material; d and e are electron spin resonance (ESR) spectra. Detailed Implementation

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] The following are the standardized Chinese translations of chemical reagent names:

[0039] p-Benzoquinone (p-BQ)

[0040] Silver nitrate (AgNO3)

[0041] Sodium oxalate (Na2C2O4)

[0042] Ethylenediaminetetraacetic acid (EDTA)

[0043] Benzoquinone (BQ)

[0044] Isopropyl alcohol (IPA)

[0045] The carbon nanotubes used in this invention were purchased from Suzhou Hengqiu Graphene Technology Co., Ltd., with product number HQNANO-CNTs-010-0. They have an inner diameter of 3~5 nm, an outer diameter of 8~15 nm, and a length of 3~12 μm.

[0046] Example 1

[0047] Preparation of graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite materials:

[0048] (1) Dissolve 5 g of melamine and 2 mmol of ammonium metavanadate (NH4VO3) in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia is 15:1) and stir vigorously for 30 min to ensure complete dissolution; then add 15 mmol of thioacetamide (TAA), stir for another 1 h at room temperature, mix evenly, add 25 mg of carbon nanotubes, disperse by ultrasonication, let stand for 2 h, and then stir at room temperature for 12 h to ensure uniform mixing.

[0049] (2) The well-mixed mixture was transferred to a stainless steel autoclave lined with 50 mL of polytetrafluoroethylene and heated at 180 °C for 20 h. After naturally cooling to room temperature, the dark precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and vacuum dried at 80 °C overnight. Finally, the obtained material was heated to 400 °C at a heating rate of 5 °C / min under an inert atmosphere and calcined at this temperature for 2 h. After natural cooling, the composite material was collected and named CVCN-1 according to the increase in CNT content.

[0050] Example 2

[0051] Preparation of graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite materials:

[0052] (1) Dissolve 5 g of melamine and 2 mmol of ammonium metavanadate (NH4VO3) in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia is 15:1) and stir vigorously for 30 min to ensure complete dissolution; then add 15 mmol of thioacetamide (TAA), stir for another 1 h at room temperature, mix evenly, add 50 mg of carbon nanotubes, disperse by ultrasonication, let stand for 2 h, and then stir at room temperature for 12 h to ensure uniform mixing.

[0053] (2) The well-mixed mixture was transferred to a stainless steel autoclave lined with 50 mL of polytetrafluoroethylene and heated at 180 °C for 20 h. After naturally cooling to room temperature, the dark precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and vacuum dried at 80 °C overnight. Finally, the obtained material was heated to 400 °C at a heating rate of 5 °C / min under an inert atmosphere and calcined at this temperature for 2 h. After natural cooling, the composite material was collected and named CVCN-2 according to the increase in CNT content.

[0054] Example 3

[0055] Preparation of graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite materials:

[0056] (1) Dissolve 5 g of melamine and 2 mmol of ammonium metavanadate (NH4VO3) in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia is 15:1) and stir vigorously for 30 min to ensure complete dissolution; then add 15 mmol of thioacetamide (TAA), stir for another 1 h at room temperature, mix evenly, add 75 mg of carbon nanotubes, disperse by ultrasonication, let stand for 2 h, and then stir at room temperature for 12 h to ensure uniform mixing.

[0057] (2) The well-mixed mixture was transferred to a stainless steel autoclave lined with 50 mL of polytetrafluoroethylene and heated at 180 °C for 20 h. After naturally cooling to room temperature, the dark precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and vacuum dried at 80 °C overnight. Finally, the obtained material was heated to 400 °C at a heating rate of 5 °C / min under an inert atmosphere and calcined at this temperature for 2 h. After natural cooling, the composite material was collected and named CVCN-3 according to the increase in CNT content.

[0058] Comparative Example 1

[0059] Graphitic carbon nitride (CN): 5 g of melamine was placed in an alumina crucible, which was then transferred to a muffle furnace and heated to 400 °C at a heating rate of 5 °C per minute under air conditions. The sample was held at this temperature for 2 hours. After naturally cooling to room temperature, the resulting pale yellow powder was collected, thoroughly ground, and stored for later use.

[0060] Comparative Example 2

[0061] Vanadium disulfide (VS2) nanosheets: First, 2 mmol of ammonium metavanadate (NH4VO3) was dissolved in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia was 15:1), and the solution was stirred vigorously for 30 min to ensure complete dissolution. Then, 15 mmol of thioacetamide (TAA) was added, and the mixture was stirred for another 1 h at room temperature. After mixing thoroughly, the homogeneous mixture was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 180 °C for 20 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and dried overnight under vacuum at 80 °C.

[0062] Comparative Example 3

[0063] The binary heterojunction composite material CN@VS2 was prepared by dissolving 5 g of melamine and 2 mmol of ammonium metavanadate (NH4VO3) in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia was 15:1) and stirring vigorously for 30 min to ensure complete dissolution. Then, 15 mmol of thioacetamide (TAA) was added, and the mixture was stirred for another 1 h at room temperature until homogeneous. The mixture was then transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 180 °C for 20 h. After natural cooling to room temperature, the dark precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and vacuum dried overnight at 80 °C. Finally, the resulting material was heated to 400 °C at a heating rate of 5 °C / min under an inert atmosphere and calcined at this temperature for 2 h. After natural cooling, the composite material was collected.

[0064] Comparative Example 4

[0065] Binary heterojunction composite material CNTs@VS2: First, 2 mmol of ammonium metavanadate (NH4VO3) was dissolved in 16 mL of ammonia solution (the volume ratio of deionized water to commercially available ammonia was 15:1), and stirred vigorously for 30 min to ensure complete dissolution; then, 15 mmol of thioacetamide (TAA) was added, and stirred for another 1 h at room temperature; after mixing evenly, 25 mg of carbon nanotubes were added, ultrasonically dispersed, and then allowed to stand for 2 h, followed by stirring at room temperature for 12 h to ensure uniform mixing; the mixed mixture was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and heated at 180 °C for 20 h; after naturally cooling to room temperature, the dark precipitate was collected by centrifugation, thoroughly washed with deionized water and ethanol, and vacuum dried overnight at 80 °C; finally, the obtained material was heated to 400 °C at a heating rate of 5 °C / min under an inert atmosphere and calcined at this temperature for 2 h, and the composite material was collected after natural cooling.

[0066] Experimental Example 1

[0067] (1) Photocatalytic synthesis of hydrogen peroxide:

[0068] 25 mg of photocatalyst was ultrasonically dispersed in 50 mL of an ethanol-water solution (ethanol to deionized water volume ratio 9:1), and oxygen was continuously introduced for 15 min to ensure O2 saturation. Then, simulated sunlight (AM 1.5G, 100 mW·cm⁻¹) was used. -2 The photocatalytic activity was evaluated by irradiating the suspension with a monochromatic LED light source (420 nm). During irradiation, 1.0 mL of the reaction mixture was collected at predetermined time intervals and immediately filtered through a 0.22 µm microporous membrane to remove catalyst particles. The concentration of hydrogen peroxide generated was determined by iodometric titration. Specifically, 0.5 mL of 0.4 mol / L potassium iodide (KI) solution and 0.5 mL of 0.1 mol / L potassium hydrogen phthalate (KPH) solution were added to the filtrate. The reaction mixture was then allowed to stand in the dark for 30 min, and the absorbance was recorded at approximately 352 nm. The stability and reusability of the photocatalyst for hydrogen peroxide generation were tested using the same method. After each cycle, the catalyst was recovered by centrifugation, thoroughly washed with water and ethanol, and dried at 80 °C for reuse.

[0069] (2) Photocatalytic degradation of TCH:

[0070] Tetracycline hydrochloride (TCH) was used as an antibiotic contaminant model to evaluate the photocatalytic performance of the photocatalyst under visible light irradiation. A 35 mg / L TCH aqueous solution (50 mL) was used as the test contaminant. For each photocatalytic test, 25 mg of catalyst was dispersed in the TCH solution and then sonicated for 5 minutes to ensure uniform dispersion. Photocatalytic degradation was initiated under visible light irradiation (λ ≥ 420 nm) using an 80 W LED light source equipped with a cutoff filter. At predetermined time intervals, 3 mL of the suspension was immediately filtered through a 0.22 µm microporous membrane to remove catalyst particles. The concentration of TCH was measured using a UV-Vis spectrophotometer, and the absorbance at 358 nm, corresponding to the characteristic absorbance peak of TCH, was recorded. To explore catalytic stability and reusability, after each cycle, the photocatalyst was recovered by centrifugation, thoroughly washed with water and ethanol, dried at 80 °C, and reused in subsequent runs under the same conditions.

[0071] Results explanation:

[0072] The photocatalytic synthesis of hydrogen peroxide and degradation of TCH prepared in this invention were evaluated under visible light (λ ≥ 420 nm).

[0073] Figure 1 The results showed that, compared with the original CN, VS2, and the binary heterojunction composites CN@VS2 and CNTs@VS2, the ternary heterojunction composite CVCN-2 exhibited the best catalytic synthesis of hydrogen peroxide, with a hydrogen peroxide yield of 2525 mmol / L. -1 h -1 Furthermore, various quenching and trapping ion tests were used on the photocatalyst to confirm reactive oxygen species, electron-hole pairs, and hydroxyl substances, such as... Figure 1 As shown in Figure b, in the capture experiment, p-benzoquinone (p-BQ), silver nitrate (AgNO3), sodium oxalate (Na2C2O4), and isopropanol (IPA) were used as capture agents for superoxide anion (O2•⁻), electron (e⁻), hole (h⁺), and hydroxyl radical (•OH), respectively, with corresponding hydrogen peroxide generation amounts of 77.41 mmol L⁻¹. -1 h -1 873.41 mmol / L -1 h -1 1300.3 mmol / L -1 h -1 and 724.38 mmol L -1 h -1 The yield of hydrogen peroxide synthesized from the ternary heterojunction composite material CVCN-2 in different atmospheres and solvents is as follows: Figure 1As shown in Figures c and e, the amount of hydrogen peroxide generated in water is 187.8 mmol L. -1 h -1 The concentration of formaldehyde was 1250.84 mmol / L. -1 h -1 The concentration in isopropanol was 724 mmol / L. -1 h -1 Under different atmospheres, the concentration was 515.79 mmol / L under nitrogen conditions. -1 h -1 In the open environment, it was 757.71 mmol L. -1 h -1 This study demonstrates the effectiveness of the material in photocatalytic hydrogen peroxide synthesis under different atmospheres and solvents. The stability and recyclability of the photocatalyst are crucial for industrial applications. Repeated tests were conducted on the optimal ternary heterojunction composite material CVCN-2 for the same duration. It is clear that the ternary heterojunction composite material CVCN-2 maintained significant hydrogen peroxide evolution stability over four consecutive reaction cycles. Figure 1 As shown in Figure d. In the catalytic reaction process, the generation and decomposition of hydrogen peroxide play a crucial role in practical applications. Fitting results for various photocatalysts show that the ternary heterojunction composite material CVCN-2 exhibits the highest kf value and the second lowest kd value, such as... Figure 1 As shown in f, the ternary heterojunction composite material CVCN-2 exhibits the highest hydrogen peroxide yield in the photocatalytic reaction. In summary, all the above results indicate that the graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction photocatalyst has high photocatalytic efficiency, exhibits excellent hydrogen peroxide yield under various conditions, and demonstrates stable reproducibility.

[0074] The photodegradation of TCH using the ternary heterojunction composite material CVCN-2 was tested, and its application in environmental protection was evaluated. The results are as follows: Figure 2 As shown. The photocatalytic degradation effects of pristine CN, VS2, binary heterojunction composites CN@VS2 and CNTs@VS2, and ternary heterojunction composite CVCN-2 on TCH were investigated under visible light irradiation. Under dark conditions, the degradation ability of the standard samples was achieved, and an adsorption-desorption equilibrium was reached between TCH and CVCN-2, with negligible TCH removal. However, under visible light irradiation, the ternary heterojunction composite CVCN-2 showed a 94% removal rate of TCH within 1 hour, while the removal rate of pristine CN for TCH was approximately 49%. Figure 2 As shown in Figure a. The time-dependent kinetics of TCH degradation were also investigated for pristine CN, VS2, and binary heterojunction composites CN@VS2 and CNTs@VS2, as well as ternary heterojunction composites CVCN-1, CVCN-2, and CVCN-3, using ln(Ct The relationship between / C0) and time and the fitting results are as follows: Figure 2 As shown in Figure b, the degradation process follows pseudo-first-order kinetics. During the experiment, the effects of reactive oxygen species, OH substances, and photogenerated electron-hole pairs on TCH degradation were investigated, as shown below. Figure 2 As shown in Figure c. To elucidate the major reactive species responsible for the photocatalytic degradation of tetracycline (TC), a systematic quenching experiment was conducted using selective scavengers. Isopropanol (IPA) was used to quench hydroxyl radicals (•OH), and ethylenediaminetetraacetic acid (EDTA) was used to capture photogenerated holes (h). + p-BQ (p-BQ) scavenges superoxide radicals (O2•) ⁻ Without any scavenger, the TC degradation efficiency reached approximately 95% after 1 hour of irradiation, indicating high photocatalytic activity. After the introduction of IPA, the degradation efficiency decreased to approximately 68%, indicating that hydroxyl radicals participate in the degradation process, although they are not the dominant reactive species. EDTA showed a more significant inhibitory effect, reducing the degradation to approximately 36%, implying the important role of photogenerated holes in the oxidation mechanism. Notably, the addition of p-BQ resulted in the greatest suppression of photocatalytic activity, with the degradation rate dropping to approximately 23%. This sharp decline clearly indicates that superoxide radicals are the dominant reactive species promoting TC degradation in the current system. These results collectively demonstrate a hierarchical structure of reactive species, with superoxide radicals playing the most critical role, followed by photogenerated holes, and then hydroxyl radicals. These insights provide strong evidence for mixed redox degradation pathways, with superoxide-driven processes being the most influential. To obtain better catalytic efficiency and stability, the ternary heterojunction composite material CVCN-2 underwent three consecutive cycles of testing. After each cycle, the sample was washed with water and dried at 80 °C before use. The relevant results are as follows: Figure 2 As shown in Figure d. Considering the above results, the combination of CNTs, CN, and VS2 forms a multi-interface heterostructure through van der Waals forces and electronic coupling. CN anchors the VS2 nanosheets, while CNTs bridge the layers, forming a conductive network that enables rapid electron transport. At the interfaces, band bending and local electric fields drive the directional flow of electrons between CN and VS2, while CNTs effectively extract and shuttle charges. This unique structure promotes the development of ROS (O2) - The formation of ·OH groups enhances the degradation of TCH. The synergistic structure ensures efficient light capture, rapid charge separation, and abundant active sites, thereby achieving high photocatalytic activity.

[0075] Example 4

[0076] Figure 3SEM images in image a reveal that the ternary heterojunction composite CVCN-2 exhibits a highly textured and layered morphology, consisting of randomly stacked layered nanosheets. These sheet-like structures are based on CN as a framework. The observable roughness and porosity are likely due to the incorporation of VS2 and CNTs. The presence of interconnected flakes and embedded particles indicates its high specific surface area and porous network, which is highly advantageous for catalysis and electron transport applications. Figure 3 The TEM image in b provides further insight into the internal nanostructure, revealing ultrathin, wrinkled, and translucent flakes—characteristics typical of exfoliated CN and VS2 nanosheets. Darker contrast in certain areas indicates overlapping or denser regions, possibly where CNTs are interwoven with layered CN and VS2. This wrinkled yet flexible structure ensures close contact between the three components, promoting efficient charge migration and structural cohesion at the nanoscale. On the other hand, ... Figure 3 HAADF-STEM images of CVCN-2 provide high-resolution elemental contrast, with brighter areas representing heavier atoms (e.g., vanadium and sulfur in VS2) and darker areas corresponding to lighter elements (carbon and nitrogen in CN and CNTs). The images confirm the uniform and well-dispersed distribution of VS2 within the CN-CNT matrix. This uniform dispersion enhances interfacial contact and ensures strong electronic coupling between components. Combined SEM, TEM, and HAADF-STEM analyses reveal that the ternary heterojunction composite CVCN-2 exhibits a layered, porous, and well-dispersed morphology; the combination of ultrathin CN and VS2 nanosheets with CNTs forms a three-dimensional conductive and catalytic network, providing abundant active sites, improved charge transport pathways, and mechanical robustness.

[0077] X-ray diffraction (XRD) Figure 3(d) provides key insights into the structural characteristics and composite formation of CN, VS2, and the binary heterojunction composites CN@VS2 and CNTs@VS2, and the ternary heterojunction composite CVCN-2. Pure VS2 exhibits sharp, clear peaks pointing to the (001), (100), (102), (103), (110), and (112) planes, confirming its hexagonal phase and high crystallinity. In contrast, CN shows two typical reflections: a weak peak (100) at 13.1° due to in-plane triazine stacking, and a strong peak (002) at 27.4° due to interlayer stacking of its conjugated layers, indicating a layered, partially amorphous structure. In the CN@VS2 composite, the (002) CN peak becomes broader and slightly shifted, while the intensity of the VS2 peak decreases, indicating reduced crystallinity and the presence of strong interfacial interactions such as electrostatic attraction, van der Waals forces, hydrogen bonding, and potential VN coordination. The nitrogen-rich surface of CN facilitates the anchoring and uniform dispersion of VS2, thereby promoting better charge transfer and structural integration. CNTs@VS2 retain VS2 reflection, albeit slightly broadened, indicating good dispersibility and small domain size. Due to their partial graphitic properties, CNTs contribute a broad background, and interactions with VS2 occur through π-π stacking and hydrogen bonding. These conductive scaffolds enhance electronic connectivity and support a uniform VS2 distribution. The ternary heterojunction composite CVCN-2 combines the characteristics of CN, CNTs, and VS2, exhibiting a broadened (002)CN peak and severely suppressed VS2 signal, reflecting nanoscale mixing and structural disorder. This suggests that all components are tightly bound with increasing carbon content, and crystallinity decreases due to the encapsulation and exfoliation of VS2 within the CN-CNT matrix; here, CN provides abundant N sites for coordination, CNTs provide the conductive backbone, and VS2 provides active catalytic sites. The formation of the composite is driven by synergistic non-covalent π-π stacking, van der Waals forces and hydrogen bonding, as well as possible covalent (VN, SN) interactions. All structural analyses indicate the successful fabrication of the ternary heterojunction CVCN-2 composite material. The broadening and suppression of XRD peaks, particularly in CVCN-2, suggest reduced crystallinity, finer particle size, and more uniform dispersion, indicators of closer contact between components. Furthermore, FTIR spectroscopy (…) Figure 3 (e) reveals the shifts and intensity variations of characteristic bonds, confirming the presence of strong interfacial interactions and chemical bonds. These synergistic effects, structural coherence from XRD, and bonding evidence from FTIR highlight the efficient integration of CN, CNTs, and VS2, forming a stable photocatalytic system with improved charge transfer, light absorption, and reactivity.

[0078] The UV-Vis spectra and corresponding band gaps of photocatalysts and raw materials are as follows: Figure 4As shown in a and b, the efficiency of semiconductors in photocatalysis depends on their ability to efficiently generate hole pairs during excitation, which is controlled by their band gap and light absorption characteristics. UV-Vis diffuse reflectance spectroscopy (DRS) was used to evaluate the light absorption capacity and band gap of the prepared materials. Notably, all materials exhibited efficient absorption of visible light. Pure CN showed an absorption edge at 450 nm. The UV-Vis absorption spectra of VS2 nanosheets showed absorption near 596 nm and 640 nm, likely due to photoexcitons; photoexcitons are bound states of electron-hole pairs that behave similarly to hydrogen atoms; photoexciton transitions in transition metal sulfides (TMDCs) originate from valence band energy splitting caused by spin-orbit coupling. Exciton peaks are generated directly from the split valence band at the Brillouin zone K-point, while loading of CNTs produces non-covalent π-π stacking and possible covalent (VN, SN) interactions. The Tauc equation (αhѵ) was employed. 2 =A(hv-Eg) 1 / 2 The band gap of the prepared materials was determined, and a reduction in the band gap was observed in the ternary heterojunction composite CVCN-2. The results indicate that the absorption shifts to the near-infrared region, which is beneficial for better catalytic activity and provides more reaction sites. Time-resolved photoluminescence (TRPL) spectroscopy results show that photoexcited electrons are effectively suppressed and utilized more efficiently. Furthermore, analysis of the ternary heterojunction composite CVCN-2 compared to pure CN shows an extended lifetime for photoexcited carriers. This phenomenon implies a reduced recombination rate in the heterojunction formed by the combination of CN, VS2, and CNTs. Specifically, compared to CN, the ternary heterojunction composite CVCN-2 exhibits a shorter lifetime and a faster and longer decay lifetime for photoexcited hole pairs. These findings collectively indicate that electron transport is enhanced, carrier separation is promoted, and hydrogen production is improved due to CN modification, as shown in the results. Figure 4 As shown in Figure c. Electron spin resonance (ESR) is crucial for confirming the generation of active species and understanding the photocatalytic mechanism at the molecular level. Using ESR testing to identify the major active species in the photocatalytic process provides more information about the degradation mechanism of TCH and the production of hydrogen peroxide on the ternary heterojunction composite CVCN-2. Figure 4 As shown in figures d and e, the typical peaks of DMPO-O2- and DMPO-OH disappear under dark conditions. After 5 minutes of illumination, the characteristic peaks of DMPO-O2- and DMPO-OH reappear; after 10 minutes of illumination, these peaks intensify, indicating that O2... - ·OH and ·OH are the main active species. ESR further confirms that O2 - The formation of ·OH active species facilitates the decomposition of TCH and reactive oxygen species, thereby improving the catalytic efficiency of hydrogen peroxide.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material as a photocatalyst, characterized in that, The application is to catalyze the synthesis of hydrogen peroxide from water and oxygen under visible light; The composite material has a layered nanosheet structure with graphitic carbon nitride as the framework and vanadium disulfide nanosheets and carbon nanotubes as dopants. The graphitic carbon nitride, vanadium disulfide nanosheets and carbon nanotubes are interwoven to form a heterojunction.

2. The application as described in claim 1, characterized in that, The particle size of the nanosheet structure is 3~9 μm.

3. The application as described in claim 2, characterized in that, The particle size of the nanosheet structure is 3.6~8.6 μm.

4. The application as described in claim 1, characterized in that, The particle size of vanadium disulfide nanosheets is 1~4μm.

5. The application as described in claim 4, characterized in that, The vanadium disulfide nanosheets have a particle size of 1.92~3.5 μm.

6. The application as described in claim 1, characterized in that, The preparation method of the graphitic carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material includes the following steps: (1) Disperse melamine and ammonium metavanadate in an ammonia solution, then add thioacetamide, mix well, then add carbon nanotubes, and mix well again; (2) The mixture in step (1) is subjected to hydrothermal treatment, and then the solid is collected and calcined to obtain the graphite phase carbon nitride / vanadium disulfide / carbon nanotube ternary heterojunction composite material.

7. The application as described in claim 6, characterized in that, In step (1), the molar ratio of melamine to ammonium metavanadate is (18~22):

1.

8. The application as described in claim 7, characterized in that, In step (1), the molar ratio of melamine to ammonium metavanadate is 20:

1.

9. The application as described in claim 6, characterized in that, In step (1), the concentration of the ammonia solution is 1.4 wt% to 1.6 wt%.

10. The application as described in claim 6, characterized in that, In step (1), the concentration of ammonium metavanadate in the ammonia solution is 0.1~0.2 mol / L.

11. The application as described in claim 10, characterized in that, In step (1), the concentration of ammonium metavanadate in the ammonia solution is 0.125 mol / L; 12. The application as described in claim 6, characterized in that, In step (1), the molar ratio of ammonium metavanadate to thioacetamide is 2:(13~16).

13. The application as described in claim 12, characterized in that, In step (1), the molar ratio of ammonium metavanadate to thioacetamide is 2:

15.

14. The application as described in claim 6, characterized in that, In step (1), the mass ratio of melamine to carbon nanotubes is 1:(5~15).

15. The application as described in claim 14, characterized in that, In step (1), the mass ratio of melamine to carbon nanotubes is 1:

10.

16. The application as described in claim 6, characterized in that, In step (2), the temperature of the hydrothermal treatment is 160~200 ℃; the time of the hydrothermal treatment is 18~24 h.

17. The application as described in claim 16, characterized in that, In step (2), the temperature of the hydrothermal treatment is 180 °C and the time of the hydrothermal treatment is 20 h.

18. The application as described in claim 6, characterized in that, In step (3), the calcination temperature is 350~500 ℃; the calcination time is 1.5~4 h.

19. The application as described in claim 18, characterized in that, In step (3), the calcination temperature is 400 ℃ and the calcination time is 2 h.

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