A Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, its preparation method and application

Abstract

This invention belongs to the field of photocatalysis technology, and relates to a Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, its preparation method, and its application. The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material is obtained by calcining a mixture of rod-shaped carbon nitride precursor, niobium oxide, graphene, and optionally cobalt-doped BiOBr nanosheets in a mass ratio of 100:(1~3):(0.1~2):(0~2). The rod-shaped carbon nitride precursor is prepared by dissolving melamine and a cobalt-based compound in water and carrying out a hydrothermal polymerization reaction. The hydrothermal polymerization reaction conditions include a temperature of 160℃~220℃ and a time of 15h~20h. The resulting hydrothermal polymerization product is then filtered and the solid product is dried. The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by this invention exhibits good degradation rate and cycle stability when degrading antibiotic wastewater.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, its preparation method, and its application. Background Technology

[0002] Photocatalysis is based on the redox capabilities of photomaterials under light conditions, enabling the purification of pollutants and the synthesis and transformation of substances. Typically, photocatalytic reactions use semiconductors as catalysts and light as energy to degrade organic matter into carbon dioxide and water. Therefore, photocatalysis technology, as a highly efficient, safe, and environmentally friendly purification technology, has gained international recognition for its effectiveness in improving indoor air quality and water purification.

[0003] Photocatalysis, as an emerging advanced oxidation technology, has demonstrated unique advantages and broad application prospects in the degradation of antibiotic-containing wastewater. Photocatalysis utilizes light energy to drive the generation of highly oxidizing substances, mineralizing antibiotics and transforming them into harmless small molecules, effectively addressing environmental residue problems. However, while many photocatalysts possess suitable band gaps and photoresponsiveness, their high carrier recombination rates lead to a large number of recombinations between photogenerated electrons and holes before reaching the catalyst surface, reducing photocatalytic activity. This high recombination rate not only affects the initial degradation efficiency but also accelerates the performance degradation of the catalyst during recycling. Furthermore, some catalysts, due to their stable crystal structure and insufficient photocatalytic reaction sites, struggle to effectively decompose photogenerated carriers, resulting in a rapid decline in degradation efficiency and insufficient cycle stability during recycling. Summary of the Invention

[0004] The primary objective of this invention is to overcome the shortcomings of existing photocatalysts in terms of insufficient cycle stability when degrading high-concentration antibiotic wastewater, and to provide a novel Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material that exhibits good cycle stability when degrading high-concentration antibiotic wastewater.

[0005] A second objective of this invention is to provide a method for preparing the above-mentioned Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material.

[0006] A third objective of this invention is to provide the application of the above-mentioned Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material in the photocatalytic degradation of antibiotics in water.

[0007] The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by this invention is obtained by calcining a rod-shaped carbon nitride precursor, niobium oxide, graphene, and optionally cobalt-doped BiOBr nanosheets in a mass ratio of 100:(1~3):(0.1~2):(0~2). The rod-shaped carbon nitride precursor is prepared by dissolving melamine and cobalt-based compounds in water and carrying out a hydrothermal polymerization reaction. The conditions of the hydrothermal polymerization reaction include a temperature of 160℃~220℃ and a time of 15h~20h. The resulting hydrothermal polymerization product is then filtered and the solid product is dried to obtain the rod-shaped carbon nitride precursor.

[0008] The preparation method of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by the present invention includes mixing rod-shaped carbon nitride precursor, niobium oxide and graphene, and optionally cobalt-doped BiOBr nanosheets and then calcining them.

[0009] The key to this invention lies in first subjecting melamine to a hydrothermal polymerization reaction in the presence of a cobalt-based compound and strictly controlling the hydrothermal polymerization reaction conditions to form a rod-shaped carbon nitride precursor. Then, the rod-shaped carbon nitride precursor is mixed with niobium oxide and graphene and calcined. The resulting Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material can maintain a high degradation rate even after more than 10 cycles of degradation of antibiotic wastewater (especially tetracycline wastewater) with a concentration as high as 20~40 mol / L. The reasons for this are speculated to be as follows: Firstly, graphene can significantly improve the separation efficiency of photogenerated carriers. With its ultra-high electron mobility, it rapidly captures and transfers photogenerated electrons, effectively suppressing electron-hole recombination, extending carrier lifetime, and broadening the spectral response range. By constructing heterojunctions or surface plasmon effects, it reduces the band gap of the system, allowing the catalyst to expand from absorbing only ultraviolet light to absorbing visible light and even near-infrared light, significantly improving light source utilization. Simultaneously, its ultra-large specific surface area provides a large number of active sites and enhances catalyst stability. Secondly, the thermal condensation of melamine under the aforementioned specific conditions to generate a graphitic carbon nitride precursor, the ammonia gas released during the thermal condensation process has an etching effect on the material structure, promoting the formation of porous structures and obtaining rod-shaped carbon nitride precursors with porous structures. These precursors have significantly increased surface areas, providing more photocatalytic active sites (such as surface defects and edge sites), thereby enhancing the adsorption and degradation capacity of pollutants. Furthermore, this structure can shorten the charge transport path, making... Electrons and holes migrate to the surface more quickly to participate in the reaction. At the same time, the introduction of cobalt-based compounds can inhibit the aggregation of graphitic carbon nitride particles, further increasing its specific surface area. Furthermore, cobalt-based compounds can also promote the separation of photogenerated electrons and holes through the heterojunction structure, acting as active centers to activate oxidants, generating strong oxidizing free radicals, and directly degrading antibiotics. On the other hand, when rod-shaped carbon nitride precursors are combined with niobium oxide and graphene and then calcined, the rod-shaped carbon nitride precursors are transformed into rod-shaped carbon nitride. At the same time, rod-shaped carbon nitride, niobium oxide, and graphene form a heterojunction structure. The band gap structure of rod-shaped carbon nitride is suitable for absorbing the visible light portion, but it has the defect of rapid photogenerated electron-hole recombination. The doping of niobium oxide can adjust the band structure of rod-shaped carbon nitride, broaden the light absorption wavelength region, and improve the solar energy utilization rate. Graphene, as an electron transfer medium, can quickly export the photogenerated electrons generated by rod-shaped carbon nitride and niobium oxide, reducing recombination loss, retaining holes on the catalyst surface to participate in the oxidation reaction, shortening the reaction distance, and improving the degradation efficiency.Furthermore, the "confined effect" of rod-shaped carbon nitride can suppress carrier recombination and significantly improve quantum efficiency. After loading niobium oxide and graphene onto rod-shaped carbon nitride, the porous structure of the resulting Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material can generate a light scattering effect, extending the light transmission path within the material and increasing the probability of photon collisions with active sites. Simultaneously, during the photocatalytic degradation of antibiotics, the porous channels and open structure of the Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material are beneficial for the separation of pollutants and reaction products. Diffusion reduces mass transfer resistance, allowing the reaction to proceed more efficiently and continuously. Furthermore, rod-shaped carbon nitride prevents niobium oxide and graphene from agglomerating or separating during recycling. Niobium oxide doping stabilizes the crystal structure of rod-shaped carbon nitride, reducing oxidative damage to the catalyst itself caused by photogenerated holes. Graphene's rapid electron transfer capability reduces the concentration of photogenerated holes on the surface of rod-shaped carbon nitride, inhibiting photocorrosion. The synergistic use of these three elements can maintain the original morphology and active site distribution of the catalyst during antibiotic degradation, preventing catalyst breakage or activity reduction and extending its service life.

[0010] In a preferred embodiment, the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material further contains cobalt-doped BiOBr nanosheets, which is more conducive to improving the degradation efficiency of antibiotics in wastewater. The reason for this is presumably due to the following: cobalt-doped BiOBr nanosheets possess highly efficient charge separation capabilities, reducing the recombination of photogenerated electrons and holes and improving photocatalytic activity. Furthermore, combining cobalt-doped BiOBr nanosheets with rod-shaped carbon nitride and niobium oxide allows for the formation of a multi-component heterojunction structure, further promoting charge separation and transport, and improving photocatalytic efficiency. In addition, cobalt doping can modulate the electronic structure of the BiOBr nanosheets, introducing new cobalt active sites, improving adsorption and activation efficiency, promoting the adsorption and activation of antibiotic molecules, and altering the band structure of the BiOBr nanosheets, causing a redshift in their absorption edge, broadening the light absorption range, and improving the utilization rate of visible light. Attached Figure Description

[0011] Figure 1 This is a scanning electron microscope (SEM) image of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material obtained in Example 1. Figure 2 The nitrogen adsorption-desorption isotherm curve of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material obtained in Example 1 is shown. Figure 3 The cumulative pore volume distribution diagram and the differential pore volume distribution diagram are shown for the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material obtained in Example 1. Figure 4The image shows a SEM image of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material obtained in Example 2. Detailed Implementation

[0012] The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material provided by this invention is obtained by calcining a mixture of rod-shaped carbon nitride precursor, niobium oxide, graphene, and optionally cobalt-doped BiOBr nanosheets. The mass ratio of the rod-shaped carbon nitride precursor, niobium oxide, graphene, and optionally cobalt-doped BiOBr nanosheets is 100:(1~3):(0.1~2):(0~2). When the amount of niobium oxide and graphene is below the lower limit, their effect is limited; when the amount of niobium oxide, graphene, and cobalt-doped BiOBr nanosheets is above the upper limit, it leads to catalyst particle agglomeration, covering of active sites, reducing photon contact with active sites, and decreasing photocatalytic efficiency. Specifically, the mass ratio of the rod-shaped carbon nitride precursor to niobium oxide is 100:(1~3), such as 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, 100:2.2, 100:2.5, 100:2.8, 100:3, etc. The mass ratio of the rod-shaped carbon nitride precursor to graphene is 100:(0.1~2), such as 100:0.1, 100:0.2, 100:0.4, 100:0.6, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, etc. The mass ratio of the rod-shaped carbon nitride precursor to the cobalt-doped BiOBr nanosheets is 100:(0~2), preferably 100:(0.5~2), such as 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, etc.

[0013] In the aforementioned Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material, the rod-shaped carbon nitride precursor is prepared by the following method: melamine and a cobalt-based compound are dissolved in water and subjected to a hydrothermal polymerization reaction. The conditions for the hydrothermal polymerization reaction include a temperature of 160℃~220℃ and a time of 15h~20h. The resulting hydrothermal polymerization product is then filtered and the solid product is dried to obtain the rod-shaped carbon nitride precursor. The preferred mass ratio of melamine to the cobalt-based compound is 100:(5~10), such as 100:5, 100:5.5, 100:6, 100:6.5, 100:7, 100:7.5, 100:8, 100:8.5, 100:9, 100:9.5, 100:10, etc. Furthermore, the cobalt-based compound may include at least one of cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt nitrate. The conditions for the hydrothermal polymerization reaction include a temperature of 160℃~220℃, such as 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, etc.; and a time of 15h~20h, such as 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h, 20h, etc. When the hydrothermal polymerization reaction time is less than 15 hours, melamine molecules only undergo preliminary dissolution and weak interactions, resulting in insufficient polymerization and an inability to form a stable tubular framework structure. The product is mostly amorphous particles or irregular lumps. When the hydrothermal polymerization reaction time is greater than 20 hours, melamine molecules undergo over-polymerization, with molecular chains agglomerating or growing disorderly, which destroys the integrity of the tubular structure, leading to increased pipe diameter, thinning of the pipe wall, or even collapse. The preferred drying conditions include temperatures of 50℃ to 90℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, and 90℃; and times of 5 hours to 24 hours, such as 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, and 24 hours.

[0014] In the aforementioned Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material, the graphene is preferably prepared by the following method: Graphite powder is oxidized in a mixture of strong acid and strong oxidant for 0.5 h to 120 h; the resulting oxidized solution is then diluted with water and hydrogen peroxide is added; an organic flocculant is added to the resulting mixed aqueous solution containing graphene oxide and residual inorganic ions to precipitate and separate the graphene oxide from the residual impurities; the precipitate is collected, washed with water, and dried; then the dried precipitate is placed in a high-temperature furnace at a temperature above 300°C for 15 s to 7 h or irradiated in a microwave oven for 5 s to 5 min to obtain graphene. The organic flocculant is preferably at least one of cationic organic flocculants, amphoteric organic flocculants, and nonionic flocculants. The cationic organic flocculant may contain at least one of amino groups, quaternary ammonium groups, quinolinetonium ions, and pyridinium ions. The cationic groups in the amphoteric organic flocculant can be at least one of amino groups, quaternary ammonium groups, quinoline-onium ions, and pyridinium ions, and the anionic groups can be at least one of carboxyl groups, sulfate groups, and phosphate groups. The nonionic flocculant can be at least one of polyacrylamide, polyethylene oxide, polyvinyl alcohol, and gelatin. The specific preparation process of the graphene can be carried out according to CN102167311A. The graphene obtained by the above method is in a highly fluffy state. When the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material prepared by combining it with rod-shaped carbon nitride precursors, niobium oxide, and optionally cobalt-doped BiOBr nanosheets is used to degrade high-concentration antibiotic wastewater, it is more conducive to improving the degradation rate of antibiotics and the catalyst cycle stability. The reasons for this are speculated to be as follows: Firstly, highly porous graphene has a three-dimensional porous network structure with a specific surface area far exceeding that of traditional graphene sheets. This structure not only provides more adsorption sites for antibiotic molecules but also rapidly enriches pollutants to the catalyst surface through physical adsorption, shortening the reaction distance and improving degradation efficiency. Meanwhile, traditional graphene sheets are prone to stacking due to van der Waals forces, which can lead to the masking of active sites. The porous structure of highly porous graphene can effectively inhibit the aggregation of rod-shaped carbon nitride and niobium oxide through steric hindrance, maintaining the dispersion of the catalyst and ensuring that more active sites are exposed in the reaction system. Secondly, as an electron transport medium, highly porous graphene's three-dimensional conductive network can quickly export photogenerated electrons generated by photoexcitation of carbon nitride and niobium oxide, reducing the probability of electron-hole recombination. At the same time, highly porous graphene can further optimize the electron transport path, enabling photogenerated electrons to participate in the reduction reaction more efficiently, while holes directly oxidize antibiotic molecules, forming a synergistic degradation mechanism of "adsorption-photocatalysis-oxidation".

[0015] In the aforementioned Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material, the cobalt-doped BiOBr nanosheets are preferably prepared by the following method: bismuth salt, bromide salt, and cobalt salt are dissolved in water; the resulting mixed solution undergoes a hydrothermal reaction, and the precipitate is collected, washed, and dried to obtain the cobalt-doped BiOBr nanosheets. The hydrothermal reaction conditions preferably include a temperature of 160℃~180℃, such as 160℃, 162℃, 165℃, 168℃, 170℃, 172℃, 175℃, 178℃, 180℃, etc.; and a time of 12h~24h, such as 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc. The molar ratio of the bismuth salt, bromide salt, and cobalt salt is preferably 1:(0.9~1.1):(0.005~0.1). Specifically, the molar ratio of the bismuth salt to the bromide salt is preferably 1:(0.9~1.1), such as 1:0.9, 1:0.92, 1:0.95, 1:0.98, 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.1, etc. Examples of the bismuth salt include at least one selected from bismuth nitrate, bismuth phosphate, bismuth aluminate, bismuth subcarbonate, bismuth oxychloride, bismuthate salts, bismuth subsalicylate, and ranitidine citrate. Examples of the bromide salt include at least one selected from sodium bromide, potassium bromide, ammonium bromide, boron bromide, 1-octylpyridine bromide, cyclohexylamine hydrobromide, 1-butyl-3-methylimidazolium bromide, ethyltriphenylphosphine bromide, bromocresol purple sodium salt, 2-bromoethylamine hydrobromide, and 3-bromopropylamine hydrobromide. The cobalt salts may include at least one of cobalt sulfate, cobalt chloride, cobalt carbonate, cobalt nitrate, cobalt fluoride, cobalt iodide, cobalt oxide, cobalt hydroxide, cobalt naphthenate, cobalt stearate, cobalt neodecanoate, and cobalt borate.

[0016] The preparation method of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by the present invention includes mixing rod-shaped carbon nitride precursor, niobium oxide and graphene, and optionally cobalt-doped BiOBr nanosheets and then calcining them.

[0017] In the preparation process of the above-mentioned Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, the preferred calcination conditions include a heating rate of 4~6℃ / min, such as 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6℃ / min; a calcination temperature of 500℃~550℃, such as 500℃, 505℃, 510℃, 515℃, 520℃, 525℃, 530℃, 535℃, 540℃, 545℃, 550℃; and a calcination time of 2h~10h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h.

[0018] The present invention will be described in detail below through embodiments.

[0019] Preparation Example 1 This preparation example illustrates the preparation of cobalt-doped BiOBr nanosheets.

[0020] Bismuth nitrate, potassium bromide, and cobalt nitrate were added to deionized water in a molar ratio of 1:1:0.05 and stirred until completely dissolved. The mixture was then transferred to a reaction vessel and heated to 170°C for 20 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was collected by centrifugation. The precipitate was washed twice with deionized water and ethanol, respectively, and then dried at 70°C for 12 hours to obtain cobalt-doped BiOBr nanosheets, denoted as Co-BiOBr-1.

[0021] Preparation Example 2 This preparation example illustrates the preparation of cobalt-doped BiOBr nanosheets.

[0022] Bismuth nitrate, sodium bromide, and cobalt chloride were added to deionized water in a molar ratio of 1:1.1:0.1 and stirred until completely dissolved. The mixture was then transferred to a reaction vessel and heated to 160°C for 24 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was collected by centrifugation. The precipitate was washed twice with deionized water and ethanol, respectively, and then dried at 70°C for 12 hours to obtain cobalt-doped BiOBr nanosheets, denoted as Co-BiOBr-2.

[0023] Preparation Example 3 This preparation example illustrates the preparation of cobalt-doped BiOBr nanosheets.

[0024] Bismuth nitrate, ammonium bromide, and cobalt sulfate were added to deionized water in a molar ratio of 1:0.9:0.005 and stirred until completely dissolved. The mixture was then transferred to a reaction vessel and heated to 180°C for 12 hours. After the reaction was completed, the mixture was allowed to cool naturally, and the precipitate was collected by centrifugation. The precipitate was washed twice with deionized water and ethanol, respectively, and then dried at 70°C for 12 hours to obtain cobalt-doped BiOBr nanosheets, denoted as Co-BiOBr-3.

[0025] Example 1 This embodiment illustrates the preparation of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by the present invention.

[0026] S1. Add 400 mL of deionized water to 20 g of melamine and 1 g of cobalt nitrate, heat to 90 °C and stir until dissolved, then stir and heat to 180 °C for hydrothermal polymerization for 18 h. After the reaction is complete, allow to cool naturally to room temperature, centrifuge the obtained liquid product, wash the solid product twice with deionized water, and then dry it in a 70 °C oven for 5 h to obtain rod-shaped carbon nitride precursor.

[0027] S2. Rod-shaped carbon nitride precursor, niobium oxide (Nb2O5), graphene (prepared according to the method in Example 1 of CN102167311A), and cobalt-doped BiOBr nanosheets (Co-BiOBr-1) were mixed and ground thoroughly in an agate mortar at a mass ratio of 100:2:1:2. The mixture was then placed in a crucible and calcined in a muffle furnace at a heating rate of 5℃ / min for 6 hours at 520℃. The resulting yellow solid was thoroughly ground until homogeneous to obtain the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, denoted as Nb2O5 / G / g-C3N4-1. The SEM image of this Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material is shown below. Figure 1 ,from Figure 1 It can be seen that the rod-shaped carbon nitride contained in this Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material exhibits a short rod morphology. The nitrogen adsorption-desorption experimental results of this Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material are shown below. Figure 2 and Figure 3 ,in, Figure 2 This is a nitrogen adsorption-desorption isotherm curve. Figure 3 The blue curve in the diagram represents the cumulative pore volume distribution, and the green curve represents the differential pore volume distribution.

[0028] Depend on Figure 2 As can be seen, the isotherm exhibits typical Type IV isotherm characteristics. The adsorption capacity increases sharply in the medium-high pressure region, accompanied by a significant adsorption-desorption hysteresis loop, indicating that the sample is a typical mesoporous material. In the low-pressure region, the adsorption capacity increases slowly and steadily, without obvious micropore filling characteristics, indicating that the sample has almost no micropores and its pore structure is predominantly mesoporous, effectively avoiding molecular diffusion resistance caused by micropores and better meeting the mass transfer requirements of photocatalytic reactions. The adsorption capacity in the high-pressure region can reach 120 cm⁻¹. 3 With STP levels of / g and above, the sample possesses a good specific surface area and pore volume, providing ample surface active sites for photocatalytic reactions, which is beneficial for the effective separation of photogenerated carriers and the adsorption and activation of reactant molecules. Figure 3It is evident that the sample possesses a certain pore capacity, providing ample adsorption and reaction space for photocatalytic reactions. The differential pore volume distribution shows that the sample pore size is highly concentrated in the 90-100 nm range, forming a sharp main peak in this region, indicating that large mesopores are absolutely dominant, with almost no small mesopores or micropores. The cumulative pore volume curve further verifies this characteristic: the curve decreases slowly in the pore size <50 nm range, while rapidly decaying in the 50-120 nm range, indicating that large mesopores contribute the vast majority of the pore volume, while the contributions of small mesopores and micropores are negligible. This large mesopore-dominated pore structure has significant mass transfer advantages in photocatalytic reactions: the large pore channels of 90-100 nm can significantly reduce the diffusion resistance of macromolecular reactants and products in the liquid phase system, facilitating the rapid transport and degradation of pollutants, while reducing pore blockage caused by product accumulation and improving the stability of the catalytic cycle.

[0029] Example 2 This embodiment illustrates the preparation of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by the present invention.

[0030] S1. Add 400 mL of deionized water to 20 g of melamine and 2 g of cobalt nitrate, heat to 90 °C and stir until dissolved, then stir and heat to 160 °C for hydrothermal polymerization for 20 h. After the reaction is complete, allow to cool naturally to room temperature, separate the obtained liquid product in a centrifuge, wash the solid product twice with deionized water, and then dry it in an oven at 50 °C for 24 h to obtain rod-shaped carbon nitride precursor.

[0031] S2. Rod-shaped carbon nitride precursor, niobium oxide (Nb2O5), graphene (prepared according to the method in Example 1 of CN102167311A), and cobalt-doped BiOBr nanosheets (Co-BiOBr-2) were mixed and ground thoroughly in an agate mortar at a mass ratio of 100:3:0.1:0.5. The mixture was then placed in a crucible and calcined in a muffle furnace at a heating rate of 4℃ / min for 10 h at 500℃. The resulting yellow solid was thoroughly ground until homogeneous to obtain the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, denoted as Nb2O5 / G / g-C3N4-2. The SEM image of this Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material is shown below. Figure 4 ,from Figure 4 It can be seen that the rod-shaped carbon nitride contained in the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material is presented in a short rod morphology.

[0032] Example 3 This embodiment illustrates the preparation of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material provided by the present invention.

[0033] S1. Add 400 mL of deionized water to 20 g of melamine and 1.6 g of cobalt nitrate, heat to 90 °C and stir until dissolved, then stir and heat to 220 °C for hydrothermal polymerization for 15 h. After the reaction is complete, allow to cool naturally to room temperature, separate the obtained liquid product in a centrifuge, wash the solid product twice with deionized water, and then dry it in an oven at 90 °C for 10 h to obtain rod-shaped carbon nitride precursor.

[0034] S2. Rod-shaped carbon nitride precursor, niobium oxide (Nb2O5), graphene (prepared according to the method in Example 1 of CN102167311A), and cobalt-doped BiOBr nanosheets (Co-BiOBr-3) were thoroughly mixed and ground in an agate mortar at a mass ratio of 100:1:2:1. The mixture was then placed in a crucible and calcined in a muffle furnace at a heating rate of 6 °C / min for 2 h at 550 °C. The resulting yellow solid was thoroughly ground until homogeneous to obtain the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material, denoted as Nb2O5 / G / g-C3N4-3. The rod-shaped carbon nitride contained in this Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material exhibits a short rod morphology.

[0035] Example 4 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material was prepared according to the method of Example 1, except that the graphene (prepared according to the method in Example 1 of CN102167311A) was used in the same weight proportion as the graphene (prepared according to the method in Example 1 of CN107539973A). All other conditions were the same as in Example 1, resulting in the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material, denoted as Nb2O5 / G / g-C3N4-4. The rod-shaped carbon nitride contained in this Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material exhibits a short rod morphology.

[0036] Example 5 The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalyst material was prepared according to the method of Example 1, except that the cobalt-doped BiOBr nanosheets (Co-BiOBr-1) were replaced with niobium oxide in the same weight proportions. All other conditions were the same as in Example 1, resulting in the Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalyst material, denoted as Nb₂O₅ / G / g-C₃N₄-5. The rod-shaped carbon nitride contained in this Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalyst material exhibits a short rod morphology.

[0037] Comparative Example 1 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 5. The difference was that the hydrothermal polymerization reaction time was controlled at 12h during the preparation of rod-shaped carbon nitride, and the other conditions were the same as in Example 5. The resulting Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was denoted as DNb2O5 / G / g-C3N4-1.

[0038] Comparative Example 2 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 5. The difference was that the hydrothermal polymerization reaction time was controlled at 24 h during the preparation of rod-shaped carbon nitride, while the other conditions were the same as in Example 5. The resulting Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was denoted as DNb2O5 / G / g-C3N4-2.

[0039] Comparative Example 3 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 5, except that cobalt nitrate was not added in the preparation of rod-shaped carbon nitride, and the other conditions were the same as in Example 5. The resulting Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was denoted as DNb2O5 / G / g-C3N4-3.

[0040] Comparative Example 4 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 5, except that the rod-shaped carbon nitride precursor was directly replaced by the same weight of melamine. The other conditions were the same as in Example 5, and the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was obtained, denoted as DNb2O5 / G / g-C3N4-4.

[0041] Comparative Example 5 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 1, except that niobium oxide was replaced by rod-shaped carbon nitride precursor in the same weight proportions. The other conditions were the same as in Example 1, and the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was obtained, which was denoted as DNb2O5 / G / g-C3N4-5.

[0042] Comparative Example 6 The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was prepared according to the method of Example 1, except that graphene was replaced by rod-shaped carbon nitride precursor in the same weight proportions. The other conditions were the same as in Example 1, and the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material was obtained, denoted as DNb2O5 / G / g-C3N4-6.

[0043] Test case 50 mg of the Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalyst material obtained from the above examples and comparative examples was added to a quartz reaction flask containing a tetracycline hydrochloride solution (50 mL, tetracycline hydrochloride concentration 30 mg / L). The mixture was thoroughly mixed, and samples were taken. The resulting samples were filtered through a 0.22 μm filter, and the concentration of tetracycline hydrochloride (denoted as C) was then determined using a UV-Vis spectrophotometer. t0 The quartz reaction flask was placed in a photocatalysis workstation and stirred in the dark for 30 minutes to allow the photocatalytic material and tetracycline to reach adsorption-desorption equilibrium. After continuous irradiation with a xenon lamp (λ > 300W) for 30 minutes and 50 minutes, samples were taken. The obtained samples were filtered through a 0.22 μm filter, and the concentration of tetracycline hydrochloride in the liquid sample (denoted as C) was determined using a UV-Vis spectrophotometer. t1 To ensure the degradation process is unaffected by thermal effects, tetracycline hydrochloride must be degraded in circulating water at 25°C. According to Δ=(C t0- C t1 ) / C t0 Degradation rate is calculated as ×100%, where △ represents the tetracycline degradation rate, and C t0 C represents the initial concentration of tetracycline. t1 The concentration of tetracycline after photodegradation is shown in Table 1.

[0044] After the above photocatalysis is completed, the suspension is centrifuged to recover the catalyst. The separated catalyst is dried and used in the next photocatalytic cycle test. The process and conditions of each cycle are the same as those of the above photocatalyst. The degradation rate results after 10 cycles are shown in Table 1.

[0045] Table 1. Degradation effects of different photocatalysts on tetracycline

[0046] As shown in Table 1, when the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material provided by this invention degrades tetracycline hydrochloride solutions with a concentration as high as 30 mg / L, the degradation rate of tetracycline hydrochloride reaches over 85.9% after the first 30 min of catalyst use, and over 79.1% after 10 cycles of catalyst use; the degradation rate reaches over 91.6% after the first 50 min of catalyst use, and over 85.4% after 10 cycles of catalyst use. This demonstrates that the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalyst material provided by this invention exhibits a high degradation rate for tetracycline degradation in wastewater, and the degradation rate does not significantly decrease after multiple cycles, indicating high catalyst stability.

[0047] A comparison of Examples 1 and 4 shows that when graphene is in a highly fluffy state, the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material prepared by combining it with rod-shaped carbon nitride precursors, niobium oxide, and cobalt-doped BiOBr nanosheets is more conducive to improving the degradation rate of tetracycline and the catalyst cycle stability when used to degrade high-concentration tetracycline wastewater.

[0048] A comparison of Examples 1 and 5 shows that when the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material also contains cobalt-doped BiOBr nanosheets, it is more conducive to improving the degradation efficiency of tetracycline in wastewater.

[0049] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material, characterized in that, The Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material is obtained by calcining a mixture of rod-shaped carbon nitride precursor, niobium oxide, graphene, and optionally cobalt-doped BiOBr nanosheets in a mass ratio of 100:(1~3):(0.1~2):(0~2). The rod-shaped carbon nitride precursor is prepared by dissolving melamine and cobalt-based compounds in water and carrying out a hydrothermal polymerization reaction. The conditions of the hydrothermal polymerization reaction include a temperature of 160℃~220℃ and a time of 15h~20h. The resulting hydrothermal polymerization product is then filtered and the solid product is dried to obtain the rod-shaped carbon nitride precursor.

2. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 1, characterized in that, The mass ratio of melamine to cobalt-based compound is 100:(5~10).

3. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 1, characterized in that, The cobalt-based compound is selected from at least one of cobalt sulfate, cobalt chloride, cobalt carbonate, and cobalt nitrate.

4. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 1, characterized in that, The graphene was prepared by the following method: graphite powder was placed in a mixture of strong acid and strong oxidant and oxidized for 0.5 h to 120 h. The resulting oxidized solution was then diluted with water and hydrogen peroxide was added. An organic flocculant was added to the resulting mixed aqueous solution containing graphene oxide and residual inorganic ions to precipitate and separate the graphene oxide from the residual impurities. The precipitate was collected, washed with water, and dried. The dried precipitate was then placed in a high-temperature furnace at a temperature above 300°C for 15 s to 7 h or placed in a microwave oven for 5 s to 5 min to obtain graphene.

5. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 4, characterized in that, The organic flocculant is selected from at least one of cationic organic flocculants, amphoteric organic flocculants, and nonionic flocculants; the cation in the cationic organic flocculant is selected from at least one of amino groups, quaternary ammonium groups, quinoline ions, and pyridinium ions; the cationic group in the amphoteric organic flocculant is selected from at least one of amino groups, quaternary ammonium groups, quinoline ions, and pyridinium ions, and the anionic group is selected from at least one of carboxyl groups, sulfate groups, and phosphate groups; the nonionic flocculant is selected from at least one of polyacrylamide, polyethylene oxide, polyvinyl alcohol, and gelatin.

6. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 1, characterized in that, The mass ratio of the cobalt-doped BiOBr nanosheets to the rod-shaped carbon nitride precursor is (0.5~2):

100.

7. The Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 6, characterized in that, The cobalt-doped BiOBr nanosheets were prepared by the following method: bismuth salt, bromide salt and cobalt salt were dissolved in water, the resulting mixed solution was subjected to hydrothermal reaction, the precipitate was collected, washed and dried to obtain cobalt-doped BiOBr nanosheets.

8. The method for preparing the Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to any one of claims 1 to 7, characterized in that, The method involves calcining a mixture of rod-shaped carbon nitride precursors, niobium oxide and graphene, and optionally cobalt-doped BiOBr nanosheets.

9. The preparation method of the Nb₂O₅ / G / g-C₃N₄ ternary heterojunction photocatalytic material according to claim 8, characterized in that, The calcination conditions include a heating rate of 4~6℃ / min, a calcination temperature of 500℃~550℃, and a calcination time of 2h~10h.

10. The application of the Nb2O5 / G / g-C3N4 ternary heterojunction photocatalytic material according to any one of claims 1 to 7 in the photocatalytic degradation of antibiotics in water.

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