A method for in-situ hydrothermal construction of g-C3N5 / SrTiO3 heterojunction composite photocatalyst and its application

Abstract

The application provides a method for constructing a g-C3N5 / SrTiO3 heterojunction composite photocatalyst in situ by a hydrothermal method and application thereof, and relates to the technical field of composite photocatalytic materials.The composite material is composed of g-C3N5 and SrTiO3, and is prepared by using an in-situ hydrothermal method, and the preparation process is simple.The g-C3N5 / SrTiO3 heterojunction composite photocatalyst prepared by the preparation method has a closely combined interface, is beneficial to the efficient transmission and separation of photo-generated carriers, overcomes the deficiency that photo-generated electron-hole pairs of single g-C3N5 and SrTiO3 are prone to recombination, and simultaneously overcomes the deficiency that SrTiO3 only has ultraviolet light response.The g-C3N5 / SrTiO3 heterojunction composite photocatalyst has good visible light degradation performance on various dye pollutants.

Description

Technical Field

[0001] This invention belongs to the field of composite photocatalytic materials technology, specifically relating to a method for in-situ hydrothermal construction of g-C3N5 / SrTiO3 heterojunction composite photocatalysts and their applications. Background Technology

[0002] Strontium titanate (SrTiO3) is a perovskite-structured material with a cubic lattice parameter of 3.905 Å. Its lattice structure is formed by a tightly bound network of octahedral TiO6 units sharing corners. SrTiO3 has a high melting point of 2080 °C and is commonly used as a substrate for the epitaxial growth of high-temperature superconductors. Furthermore, SrTiO3 exhibits a high dielectric constant at ambient temperature, making it applicable to macroscopic electronics, ferroelectrics, and optoelectronics. While SrTiO3 is an electronic insulator at room temperature, it undergoes a metal-insulator transition after photodoping, thus being considered a hybrid electron-ion conductor. Due to its excellent photoelectric properties and high thermal and chemical stability, SrTiO3 can also be used as a photocatalyst in processes such as water splitting, exhibiting a photocatalytic activity in the ultraviolet region with an indirect band gap of approximately 3.2 eV. However, single SrTiO3 samples only show activity under ultraviolet light, and the easy recombination of photogenerated electrons and holes limits its further applications. Ion doping, controlling sample morphology, and adjusting crystal planes are common methods to overcome this defect and improve its catalytic performance.

[0003] In addition, constructing a heterojunction system using binary semiconductor composites to bend the band structure on the sample surface is also a conventional method to accelerate carrier migration rate. Another semiconductor can not only provide special active centers for the adsorption / reaction of reactants / reaction intermediates, but also change the composite band structure to help change the band gap absorption and separate photoexcited electron-hole pairs. The band bending between the two semiconductors is affected by a variety of factors, such as doping type and concentration, particle size, surface structure, etc. The structure of a heterojunction composed of two semiconductor oxides can be roughly divided into two types. The first type is the pn structure. The pn junction is a structure that effectively promotes charge separation. Generally speaking, when n-type and p-type semiconductors are in contact, the carriers form a space charge region at their interface, thereby generating a built-in electric field that can guide electrons and holes to migrate to different positions. The photocatalytic process in this pn heterostructure has the following advantages: (1) more efficient charge separation; (2) rapid charge transfer to the catalyst interface; (3) longer lifetime of charge carriers; (4) separation of oxidation and reduction reactions in a very small space.

[0004] Sharma et al. synthesized SrTiO3-coated modified Cu2O nanofilms of varying thicknesses and used them as photoelectrodes in photoelectrochemical water splitting. The formation of the composite structure effectively improved the separation of electrons and holes (10.1021 / jp507039n). Che et al. prepared a novel SrTiO3 / Bi2O3 heterostructure photocatalyst using a simple microwave process and studied its photocatalytic activity for visible light-driven tetracycline degradation. Compared with the original SrTiO3 and Bi2O3, the prepared SrTiO3 / Bi2O3 sample showed significantly enhanced photocatalytic activity for tetracycline degradation. The enhanced photocatalytic activity was attributed to the formation of a heterojunction between SrTiO3 and Bi2O3, which can greatly improve the transfer and separation of charge carriers at the interface between the two phases (10.1016 / j.jallcom.2016.07.311). Kanagaraj et al. synthesized SrTiO3 nanocubes and three-dimensional mesoporous BiOBr catalysts using the sol-gel method and precipitation method, respectively. SrTiO3-BiOBr heterojunction composite catalysts with different weight percentages were synthesized by impregnation method. The electron-hole recombination rate of the heterojunction catalyst was lower than that of SrTiO3 and BiOBr alone, and the electron transfer resistance was also reduced. Under visible light and sunlight irradiation, its photocatalytic activity against carcinogenic reactive dyes such as Reactive Blue 198, Reactive Black 5, and Reactive Yellow 145 was enhanced (10.1016 / j.apcatb.2017.01.084). Chinese patent ZL202410593845.X combines foamed PZT ceramics and SrTiO3 as a novel photocatalytic degradation material, effectively reducing material costs and environmental pollution risks. Chinese patent ZL202410123487.6 describes a one-step hydrothermal synthesis of SrTiO3-TiO2-CaTiO3, followed by NaBH4 reduction to load a layer of Cu2O particles onto its surface, thus preparing a double pn heterojunction and double type II heterojunction composite photocatalyst SrTiO3-TiO2-CaTiO3 / Cu2O. This method is simple to prepare, significantly improves the photoelectric conversion efficiency of the material, and exhibits highly efficient photocatalytic water splitting for hydrogen production, applicable to hydrogen production from deionized water and natural water.

[0005] Combining SrTiO3 with carbon and nitride compounds to form binary composites is a common method for modifying the properties of SrTiO3. Konstas et al. prepared SrTiO3 / g-C3N4 composites with different ratios using an ultrasonic mixing method, successfully loading spherical SrTiO3 particles onto the g-C3N4 plane to form heterojunction composites. The composites exhibited good photocatalytic activity for methylene blue (MB) dye (10.3390 / catal8110554). Luo et al. prepared g-C3N4 / SrTiO3 nanocomposites through a two-step mechanical grinding and calcination process. These composites exhibited the highest hydrogen evolution activity under visible light, superior to pure g-C3N4 and SrTiO3. This is mainly due to the strong built-in electric field at the g-C3N4 / SrTiO3 interface, which facilitates the flow of photogenerated electrons from g-C3N4 to SrTiO3, resulting in efficient electron separation and greater photoreduction of H2O molecules to H2 (10.1016 / j.apcatb.2019.01.089). Chinese patent CN117000284A discloses a doped SrTiO3@g-C3N4 nanopowder composite material, which combines La, Rh co-doped SrTiO3 with g-C3N4 via electrostatic self-assembly.

[0006] It should be noted that although both g-C3N5 and g-C3N4 are carbon-nitrogen compounds in terms of chemical composition, their nitrogen content and carbon-nitrogen ratio differ, resulting in significant differences in their band structure, conduction band / valence band positions, and electronic structure. g-C3N5 is prepared by thermal polycondensation using 3-amino-1,2,4-triazole as a precursor. Compared to g-C3N4 prepared using urea or melamine as precursors, g-C3N5 has a narrower band gap, stronger visible light absorption, and a higher nitrogen content, providing more active sites and facilitating the generation and transport of photogenerated carriers. When g-C3N5 is combined with SrTiO3, its unique band position will form a different heterojunction type and electron transfer path with SrTiO3 than the g-C3N4 / SrTiO3 system, thus producing different photocatalytic effects. Furthermore, in existing technologies, the composite of g-C3N4 and SrTiO3 is mostly achieved through physical mixing, mechanical grinding, or electrostatic self-assembly, which makes it difficult to achieve a tight bond between the two phases and limits further improvement in the interface charge transfer efficiency.

[0007] However, to date, there have been no reports on the materials, preparation methods, and applications of g-C3N5 / SrTiO3 heterojunction composite photocatalysts formed by combining g-C3N5 and SrTiO3.

[0008] In view of the above background and current research status, this invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a g-C3N5 / SrTiO3 heterojunction composite photocatalyst. This method employs in-situ hydrothermal synthesis, hydrothermally growing SrTiO3 nanoparticles on the surface of g-C3N5, which enables a tight interfacial bond between g-C3N5 and SrTiO3, thereby facilitating the transport and separation of photogenerated carriers. Simultaneously, the highly efficient visible light response characteristics of g-C3N5 overcome the limitation of SrTiO3, which can only absorb ultraviolet light, thus enhancing the material's utilization rate of visible light and ultimately achieving a significant improvement in photocatalytic activity.

[0010] Another objective of this invention is to provide an application of g-C3N5 / SrTiO3 heterojunction composite photocatalyst in the removal of environmental pollutants and other fields.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing g-C3N5 / SrTiO3 composite material, comprising the following steps: (1) 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace to obtain g-C3N. 5； (2) Weigh the titanium source and add it to ethylene glycol, stir until completely dissolved, and record it as solution A; weigh the strontium source and add it to deionized water, stir until completely dissolved, and record it as solution B; then add solution B dropwise to solution A under continuous stirring to obtain a mixture, and adjust the pH to 12 with alkaline hydroxide; add g-C3N5 obtained in step (1), continue stirring for 3 hours, and then transfer the above mixture into a hydrothermal reactor for hydrothermal reaction, so that SrTiO3 nanoparticles grow in situ on the surface of g-C3N5. The product after the reaction is washed with acetic acid, ethanol and deionized water and then vacuum dried to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0012] In some embodiments, the calcination temperature in the muffle furnace is 500-520°C, and the calcination time is 2-4 hours. In some embodiments, the reaction temperature in the hydrothermal reactor is 120-240°C, and the reaction time is 2-72 hours.

[0013] The titanium source is one of tetrabutyl titanate, tetraisopropyl titanate, titanium tetrachloride, titanium sulfate, and titanium dioxide.

[0014] The strontium source is one of hydrated strontium chloride, hydrated strontium hydroxide, strontium nitrate, and strontium acetate.

[0015] The alkaline hydroxide is either sodium hydroxide or potassium hydroxide.

[0016] The molar ratio of titanium and strontium in the titanium source and the strontium source is 1:1 to 1:1.2.

[0017] Secondly, the present invention provides an application of the g-C3N5 / SrTiO3 heterojunction composite photocatalyst obtained by the above preparation method in the removal of environmental pollutants.

[0018] The environmental pollutants include at least one of Rhodamine B, methylene blue, and methyl orange dye.

[0019] As a preferred embodiment, a method for preparing a g-C3N5 / SrTiO3 heterojunction composite photocatalyst includes the following steps: (1) 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace to obtain g-C3N. 5； (2) Weigh the titanium source and add it to ethylene glycol, stir until completely dissolved, and record it as solution A; weigh the strontium source and add it to deionized water, stir until completely dissolved, and record it as solution B; then add solution B dropwise to solution A under continuous stirring to obtain a mixture, and adjust the pH to 12 with alkaline hydroxide; add g-C3N5 obtained in step (1), continue stirring for 3 hours, and then transfer the above mixture into a hydrothermal reactor for hydrothermal reaction, so that SrTiO3 nanoparticles grow in situ on the surface of g-C3N5. The product after the reaction is washed with acetic acid, ethanol and deionized water and then vacuum dried to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0020] In this step, the muffle furnace calcination temperature is 520℃, and the calcination time is 2 hours. The hydrothermal reactor reaction temperature is 200℃, and the reaction time is 8 hours.

[0021] In this step, the titanium source is tetrabutyl titanate.

[0022] In this step, the strontium source is hydrated strontium chloride.

[0023] In this step, the alkaline hydroxide is sodium hydroxide.

[0024] In this step, the molar ratio of titanium and strontium in the titanium source and the strontium source is 1:1.

[0025] The beneficial effects of the technical solution provided by this invention are as follows: This invention employs in-situ hydrothermal synthesis, resulting in a simple preparation process and low cost. During the reaction, SrTiO3 nanoparticles are hydrothermally grown on the surface of g-C3N5, achieving a tight bond between the g-C3N5 and SrTiO3 interfaces. This promotes the efficient transport and separation of photogenerated carriers. Simultaneously, the efficient visible light response characteristics of g-C3N5 extend the light utilization rate of SrTiO3, ultimately leading to a significant improvement in photocatalytic activity. Compared to existing g-C3N4 / SrTiO3 composite materials prepared using physical mixing or electrostatic self-assembly, the in-situ growth strategy of this invention transforms the two-phase interface from a simple physical contact into a tight heterojunction interface formed through chemical bonding and lattice matching. This significantly reduces the interfacial charge transfer resistance and improves the separation efficiency of photogenerated electron-hole pairs. Meanwhile, this invention introduces g-C3N5 into a composite system with SrTiO3 for the first time. By utilizing the narrower band gap, stronger visible light absorption, and unique band position of g-C3N5 compared to g-C3N4, a heterojunction type and carrier migration path different from g-C3N4 / SrTiO3 are formed, resulting in excellent photocatalytic effects that are difficult for those skilled in the art to predict, especially for the efficient removal of environmental pollutants such as Rhodamine B, methylene blue, and methyl orange. Attached Figure Description

[0026] Figure 1 The image shown is the XRD pattern of the sample obtained in Example 1 of this invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0029] The reagents and raw materials used in this invention are shown in Table 1 below: Table 1. Reagents and raw materials used in this invention 3-Amino-1,2,4-triazole <![CDATA[C2H4N4]]> Analytical Pure Shanghai McLean Biochemical Technology Co., Ltd. Tetrabutyl titanate <![CDATA[C 16 H 36 O4Ti]]> Analytical Pure Shanghai Aladdin Biochemical Technology Co., Ltd. Strontium chloride hexahydrate <![CDATA[SrCl2·6H2O]]> Analytical Pure Shanghai McLean Biochemical Technology Co., Ltd. Sodium hydroxide NaOH Analytical Pure Sinopharm Chemical Reagent Co., Ltd. Deionized water <![CDATA[H2O]]> <![CDATA[S<5 μs·cm -1 ]]> Hangzhou Wahaha Group Co., Ltd. Example 1

[0030] 5 g of 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace at 520 °C for 2 hours to obtain g-C3N5 for later use. 0.01 mol of tetrabutyl titanate was weighed and added to 50 mL of ethylene glycol, stirred until completely dissolved, and labeled as solution A. 0.01 mol of strontium chloride hexahydrate was weighed and added to deionized water, stirred until completely dissolved, and labeled as solution B. Then, solution B was added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 1.5 g of g-C3N5 prepared in the above steps was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 200 °C for 8 hours. The product after reaction was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0031] 100 mg of the prepared g-C3N5 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 100 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated for 60 minutes with a 300 W xenon lamp at a distance of 20 cm from the liquid surface under stirring. After degradation, the absorbance of the solution at 554 nm was measured by a UV-Vis spectrophotometer after centrifugation. The degradation rate of Rhodamine B was calculated to be 98.2%. Example 2

[0032] 5 g of 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace at 520 °C for 2 hours to obtain g-C3N5 for later use. 0.01 mol of tetrabutyl titanate was weighed and added to 50 mL of ethylene glycol, stirred until completely dissolved, and labeled as solution A. 0.01 mol of strontium chloride hexahydrate was weighed and added to deionized water, stirred until completely dissolved, and labeled as solution B. Then, solution B was added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 1.5 g of g-C3N5 prepared in the above steps was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 200 °C for 8 hours. The product after reaction was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0033] 100 mg of the prepared g-C3N5 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 10 mL of a 10 mg / L methylene blue solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated for 60 minutes with a 300 W xenon lamp at a distance of 20 cm from the liquid surface under stirring. After degradation, the solution was centrifuged and the absorbance at 664 nm was measured by a UV-Vis spectrophotometer. The degradation rate of methylene blue was calculated to be 90.3%. Example 3

[0034] 5 g of 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace at 520 °C for 2 hours to obtain g-C3N5 for later use. 0.01 mol of tetrabutyl titanate was weighed and added to 50 mL of ethylene glycol, stirred until completely dissolved, and labeled as solution A. 0.01 mol of strontium chloride hexahydrate was weighed and added to deionized water, stirred until completely dissolved, and labeled as solution B. Then, solution B was added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 1.5 g of g-C3N5 prepared in the above steps was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 200 °C for 8 hours. The product after reaction was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0035] 100 mg of the prepared g-C3N5 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 10 mL of methyl orange solution with a concentration of 10 mg / L. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated with a 300 W xenon lamp source at a distance of 20 cm from the liquid surface for 60 minutes under stirring. After degradation, the solution was centrifuged and the absorbance at 460 nm was measured by a UV-Vis spectrophotometer. The degradation rate of methyl orange was calculated to be 80.5%. Example 4

[0036] 5 g of 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace at 500 °C for 3 hours to obtain g-C3N5 for later use. 0.01 mol of tetrabutyl titanate was weighed and added to 50 mL of ethylene glycol, stirred until completely dissolved, and labeled as solution A. 0.01 mol of strontium chloride hexahydrate was weighed and added to deionized water, stirred until completely dissolved, and labeled as solution B. Then, solution B was added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 1.5 g of g-C3N5 prepared in the above steps was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 120 °C for 72 hours. The product after reaction was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0037] 100 mg of the prepared g-C3N5 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 100 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated with a 300 W xenon lamp at a distance of 20 cm from the liquid surface for 60 minutes with stirring. After degradation, the solution was centrifuged and the absorbance at 554 nm was measured by a UV-Vis spectrophotometer. The degradation rate of Rhodamine B was calculated to be 87.6%. Example 5

[0038] 5 g of 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace at 500 °C for 4 hours to obtain g-C3N5 for later use. 0.01 mol of tetrabutyl titanate was weighed and added to 50 mL of ethylene glycol, stirred until completely dissolved, and labeled as solution A. 0.01 mol of strontium chloride hexahydrate was weighed and added to deionized water, stirred until completely dissolved, and labeled as solution B. Then, solution B was added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 2 g of the g-C3N5 prepared in the above steps was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 240 °C for 2 hours. The product after reaction was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst.

[0039] 100 mg of the prepared g-C3N5 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 10 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated for 60 minutes with a 300 W xenon lamp at a distance of 20 cm from the liquid surface under stirring. After degradation, the absorbance of the solution at 554 nm was measured by a UV-Vis spectrophotometer after centrifugation. The degradation rate of Rhodamine B was calculated to be 90.4%. Comparative Example 1

[0040] 0.01 mol of tetrabutyl titanate was added to 50 mL of ethylene glycol and stirred until completely dissolved, denoted as solution A. 0.01 mol of strontium chloride hexahydrate was added to deionized water and stirred until completely dissolved, denoted as solution B. Solution B was then added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. After stirring for 3 hours, the mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 200°C for 8 hours. The product was washed with acetic acid, ethanol, and deionized water and then vacuum dried at 60°C to obtain the SrTiO3 monomer material.

[0041] 100 mg of the prepared SrTiO3 monomer material was placed in a beaker containing 10 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated with a 300 W xenon lamp at a distance of 20 cm from the liquid surface for 60 minutes with stirring. After degradation, the solution was centrifuged and the absorbance at 554 nm was measured by a UV-Vis spectrophotometer. The degradation rate of Rhodamine B was calculated to be 26.7%. Comparative Example 2

[0042] Add 5 g of 3-amino-1,2,4-triazole to a crucible, and calcine it in a muffle furnace at 520 °C for 2 hours to obtain g-C3N5 monomer.

[0043] 100 mg of the prepared g-C3N5 monomer was placed in a beaker containing 100 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated with a 300 W xenon lamp at a distance of 20 cm from the liquid surface for 60 minutes with stirring. After degradation, the solution was centrifuged and the absorbance at 554 nm was measured by a UV-Vis spectrophotometer. The degradation rate of Rhodamine B was calculated to be 55.9%. Comparative Example 3

[0044] 0.01 mol of tetrabutyl titanate was added to 50 mL of ethylene glycol and stirred until completely dissolved, denoted as solution A. 0.01 mol of strontium chloride hexahydrate was added to deionized water and stirred until completely dissolved, denoted as solution B. Solution B was then added dropwise to solution A under continuous stirring to obtain a mixture. The pH of the mixture was adjusted to 12 with sodium hydroxide. 1.5 g of g-C3N4 was added, and stirring was continued for 3 hours. The mixture was then transferred to a hydrothermal reactor and hydrothermally reacted at 200 °C for 8 hours. The product was washed with acetic acid, ethanol, and deionized water, and then vacuum dried at 60 °C to obtain the product g-C3N4 / SrTiO3 heterojunction composite photocatalyst.

[0045] 100 mg of the prepared g-C3N4 / SrTiO3 heterojunction composite photocatalyst was placed in a beaker containing 100 mL of a 10 mg / L Rhodamine B solution. After sonication for 2 minutes and dark adsorption for 30 minutes, the solution was irradiated for 60 minutes with a 300 W xenon lamp at a distance of 20 cm from the liquid surface under stirring. After degradation, the absorbance of the solution at 554 nm was measured by a UV-Vis spectrophotometer after centrifugation. The degradation rate of Rhodamine B was calculated to be 70.8%.

[0046] As can be seen from Comparative Examples 1 and 2, the prepared SrTiO3 monomer and g-C3N5 monomer materials showed a significant decrease in the degradation effect of Rhodamine B under the same conditions compared with the g-C3N5 / SrTiO3 composite material. This is mainly because the photogenerated electrons and holes of the SrTiO3 monomer and g-C3N5 monomer materials are more likely to recombine, and there are not enough photogenerated charge carriers required for efficient photocatalytic reaction.

[0047] As shown in Comparative Example 3, the g-C3N5 / SrTiO3 heterojunction composite photocatalyst exhibits significantly improved Rhodamine B degradation performance under the same conditions compared to the g-C3N4 / SrTiO3 heterojunction composite photocatalyst. This is mainly due to the differences in band gap width, conduction band, and valence band position between g-C3N5 and g-C3N4: g-C3N5 has a narrower band gap than g-C3N4, enabling it to absorb visible light more effectively and generate more photogenerated carriers; simultaneously, the heterojunction formed by g-C3N5 and SrTiO3 has a different band arrangement structure than g-C3N4 / SrTiO3, resulting in higher separation efficiency of photogenerated electron-hole pairs and a better carrier transport path. Furthermore, the in-situ hydrothermal growth method employed in this invention creates a tight chemical interface between g-C3N5 and SrTiO3, rather than the loose contact of conventional physical mixing, further reducing the interfacial charge transfer resistance and thus achieving a significant improvement in photocatalytic activity. The results indicate that replacing g-C3N4 with g-C3N5 in the composite of SrTiO3 is not a simple material substitution, but rather a fundamental change in the band structure and interface properties of the heterojunction, achieving technical effects that are difficult for those skilled in the art to anticipate.

[0048] Characterization of g-C3N5 / SrTiO3 heterojunction materials: In this invention, a Bruker D8 Advance X-ray diffractometer was used to analyze the g-C3N5 / SrTiO3 heterojunction composite photocatalyst prepared in Example 1 and the g-C3N5 monomer prepared in Comparative Example 2. The results are as follows: Figure 1 As shown, the test conditions were: Cu target Kα line, λ = 0.15406 nm, 2θ 10°–80°, and scan rate 5° / min. Figure 1 It can be seen that the diffraction peaks of 2θ at 12.8° and 27.5° correspond to the (100) and (002) crystal planes, respectively. The diffraction peaks of 2θ at 22.8°, 32.4°, 39.9°, 46.5°, 52.3°, 57.8°, 67.8°, 72.6° and 77.2° correspond to the (100), (110), (111), (200), (210), (211), (220), (221) and (310) crystal planes of SrTiO3 (PDF card 79-0174), with space group Pm-3m, a=b=c=3.905. The diffraction peaks of the g-C3N5 / SrTiO3 heterojunction composite photocatalyst were all attributed to g-C3N5 and SrTiO3, with no other impurity peaks, indicating that the composite material is composed of g-C3N5 and SrTiO3, and the sample has high purity and good crystallinity.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a g-C3N5 / SrTiO3 composite material, characterized in that, Includes the following steps: (1) 3-amino-1,2,4-triazole was added to a crucible and calcined in a muffle furnace to obtain g-C3N5; (2) Weigh the titanium source and add it to ethylene glycol, stir until completely dissolved, and record it as solution A; weigh the strontium source and add it to deionized water, stir until completely dissolved, and record it as solution B; then add solution B dropwise to solution A under continuous stirring to obtain a mixture, and adjust the pH to 12 with alkaline hydroxide; add g-C3N5 obtained in step (1), continue stirring for 3 hours, and then transfer the above mixture into a hydrothermal reactor for hydrothermal reaction, so that SrTiO3 nanoparticles grow in situ on the surface of g-C3N5. The product after the reaction is washed with acetic acid, ethanol and deionized water and then vacuum dried to obtain the product g-C3N5 / SrTiO3 heterojunction composite photocatalyst; In step (1), the calcination temperature of the muffle furnace is 500~520℃ and the calcination time is 2~4 hours; in step (2), the reaction temperature of the hydrothermal reactor is 120~240℃ and the reaction time is 2~72 hours.

2. The preparation method according to claim 1, characterized in that, The titanium source is one of tetrabutyl titanate, tetraisopropyl titanate, titanium tetrachloride, titanium sulfate, and titanium dioxide.

3. The preparation method according to claim 1, characterized in that, The strontium source is one of hydrated strontium chloride, hydrated strontium hydroxide, strontium nitrate, and strontium acetate.

4. The preparation method according to claim 1, characterized in that, The alkaline hydroxide is either sodium hydroxide or potassium hydroxide.

5. The preparation method according to claim 1, characterized in that, The molar ratio of titanium to strontium in the titanium source and strontium source is 1:1 to 1:1.

2.

6. The application of a g-C3N5 / SrTiO3 heterojunction composite photocatalyst obtained by any one of claims 1 to 5 in the removal of environmental pollutants.

7. The application according to claim 6, characterized in that, The environmental pollutants include at least one of Rhodamine B, methylene blue, and methyl orange dye.

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