Composite photocatalyst, method for preparing the same, and use thereof

Abstract

The application discloses a composite photocatalyst and a preparation method and application thereof. The preparation method of the composite photocatalyst comprises the following steps: 1) mixing carbon nanospheres, alkyl alcohol and alkyl titanate, adding an aqueous solution of the alkyl alcohol into the mixed solution to react, and obtaining a suspension; 2) heat-treating the suspension to prepare TiO2 hollow spheres; 3) adding a salt of a rare earth element, a salt of an iron-based element and carboxylic acid into water, adding an alkylene glycol and the TiO2 hollow spheres, and heating to prepare a gel; 4) heat-treating the gel to prepare TiO2 hollow spheres with a core-shell structure; and 5) sequentially adding the TiO2 hollow spheres with the core-shell structure and carbon quantum dots into a mixed alcohol of the alkylene glycol and the alkyl alcohol to react, and preparing the composite photocatalyst. The composite photocatalyst has a high visible light absorption rate and has a good performance of photocatalytic degradation of antibiotics.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite photocatalyst and a preparation method and use thereof. BACKGROUND

[0002] Antibiotic agents, as a class of widely used chemicals, play an important role in various fields such as agricultural production, medical health, food processing, etc. However, the widespread use of these compounds has also led to a series of environmental problems, especially the increasingly serious impact on organic pollution. In recent years, with the increasing use of antibiotic agents, their residues and accumulation in the environment have become increasingly prominent. These compounds often have a long half-life and are difficult to degrade rapidly under natural conditions, leading to a continuous increase in the residue of antibiotic agents in the ecological environment such as soil and water. This organic pollution not only disrupts the balance of the ecosystem, but also poses a serious threat to biodiversity.

[0003] To cope with the increasingly serious antibiotic pollution, researchers are actively exploring efficient and environmentally friendly solutions. Compared to traditional adsorption methods, microbial degradation methods, etc., photocatalytic degradation can remove macromolecular organic components in the solution and degrade them into small molecules, thereby effectively removing the hazards caused by antibiotic residues. Titanium dioxide (TiO2) based photocatalysts have chemical stability, thermal stability, and availability, and can be used to degrade antibiotics. However, due to the band gap of titanium dioxide being between 3.0-3.2 eV, it can only absorb ultraviolet light, and the utilization of sunlight is very low. At the same time, titanium dioxide as a photocatalyst also has problems such as rapid recombination of electron-hole pairs and low specific surface area.

[0004] CN103480353A discloses a method for preparing a composite nano-photocatalyst using a hydrothermal method to synthesize a carbon quantum dot solution. The method includes: using vitamin C as a carbon source, preparing carbon quantum dots (CQDs) with up-conversion characteristics in a mixed solution of anhydrous ethanol and deionized water by a hydrothermal method. Then, spherical titanium dioxide powder is prepared by a sol-gel method. The spherical titanium dioxide powder is mixed with the carbon quantum dot solution, dried, and then a composite nano-photocatalyst is prepared. This method uses the up-conversion characteristics of carbon quantum dots to modify titanium dioxide to prepare a composite photocatalyst. However, the catalyst prepared by this method is mainly TiO2 spherical particles, and the specific surface area needs to be improved. Moreover, it is used for the degradation of methyl blue dye. At the same time, dichloromethane is used for extraction in this method, and the preparation process is not environmentally friendly.

[0005] CN107099287A discloses a hydrothermal preparation method of carbon quantum dots as visible light catalytic photosensitizer. The method uses larch as raw material, after high temperature and high pressure hydrothermal treatment, centrifugal filtration is used to remove dark brown solid product, and light yellow liquid product is obtained. The liquid product is high-speed centrifuged, the centrifugal speed and time are controlled, and the insoluble small particle impurities are removed. The unreacted sugar, salt and the like are removed by dialysis with a dialysis bag of a certain molecular weight, and then concentrated to obtain the target product-water-soluble fluorescent carbon quantum dots. The carbon dots are compounded with TiO2 to prepare a photocatalytic composite system. The photocatalytic degradation performance of the composite system on the model substance is investigated, and the efficiency of the carbon dots as photosensitizer is investigated. The method is mainly for the preparation of photosensitizer carbon quantum dots, and does not mention how the carbon quantum dots and TiO2 are compounded to prepare the photocatalyst. The method is still a solid TiO2 particle-based catalyst, and the problems of too fast recombination of electron-hole pairs and low specific surface area still exist.

[0006] CN118616032A discloses a TiO2-CQDs nanoflower photocatalyst and a preparation method. The catalyst comprises TiO2 and CQDs doped with TiO2; the CQDs are derived from aloe extract. The preparation method of the catalyst uses the extract obtained from natural aloe as a carbon source to provide CQDs, and modifies TiO2 to obtain a nanoflower catalyst and a catalytic film with excellent catalytic degradation of polycyclic aromatic hydrocarbons. The TiO2-CQDs nanoflower photocatalyst prepared by the method is of solid structure, and still has the problems of low specific surface area and too fast recombination of electron-hole pairs. More importantly, it catalytically degrades polycyclic aromatic hydrocarbons under ultraviolet light irradiation.

[0007] CN108855242A discloses a photocatalyst and a preparation method. The photocatalyst is a composite photonic crystal particle covalently connected by silanized carbon quantum dots and hollow titanium dioxide, and the optimal use concentration is 0.3-0.5 g / L. The preparation method of the photocatalyst is as follows: S1: using citric acid as a carbon source and 3-aminopropyl triethoxysilane as a coupling agent, a silanized carbon quantum dot solution is prepared; S2: carbonizing a glucose solution at 180-220°C to prepare a nanocarbon ball; S3: using the nanocarbon ball as an inner core template and tetrabutyl titanate as a raw material, hollow TiO2 is prepared; S4: carbon quantum dots are covalently combined with hollow TiO2 to prepare a CQDs / TiO2 nanocomposite photocatalyst. The photocatalyst uses silanized carbon quantum dots to modify the surface of hollow TiO2, narrows the band gap, reduces the recombination rate of electrons and holes, extends the spectral response range of TiO2, increases the solar light utilization rate from 6% to 35%, and enhances the photocatalytic activity. It is applied to the degradation of p-methyl orange. SUMMARY

[0008] Therefore, one object of the present application is to provide a preparation method of a composite photocatalyst, wherein the composite photocatalyst has a core-shell structure with TiO2 hollow spheres as the core and a salt of an iron-based element acid of a rare earth element as the shell, and carbon quantum dots are modified on the core-shell structure; the composite photocatalyst has high visible light utilization efficiency and can effectively degrade antibiotics. Another object of the present application is to provide the composite photocatalyst prepared by the above preparation method. Still another object of the present application is to provide a use of the composite photocatalyst.

[0009] The above objects are achieved by the present application using the following technical solutions.

[0010] In one aspect, the present application provides a preparation method of a composite photocatalyst, comprising the following steps:

[0011] 1) mixing carbon nanospheres, C1-C5 alkyl alcohol and alkyl titanate to obtain a mixed solution; adding an aqueous solution of C1-C5 alkyl alcohol to the mixed solution at 40-90°C to obtain a suspension; wherein, 1-20 mL of alkyl titanate is added based on 100 mg of carbon nanospheres;

[0012] 2) solid-liquid separation of the suspension obtained in step 1) and drying the obtained solid to obtain a powder; heat treating the powder at 300-1000°C to prepare TiO2 hollow spheres;

[0013] 3) adding a salt of a rare earth element, a salt of an iron-based element and a carboxylic acid into water to prepare a mixed solution; adjusting the pH value of the mixed solution to 6-8, then adding C2-C5 alkane diol into the mixed solution; then adding the TiO2 hollow spheres prepared in step 2) and heating to react to prepare a gel; wherein, the molar ratio of the rare earth element, the iron-based element and the carboxylic acid is (1-5):(1-5):(5-20); the concentration of the salt of the rare earth element in the mixed solution is 0.01-0.1 mol / L; 5-20 mg of TiO2 hollow spheres is added based on 1 mL of the mixed solution;

[0014] 4) drying the gel prepared in step 3) and then heat treating at 300-1000°C to prepare TiO2 hollow spheres with a core-shell structure;

[0015] 5) sequentially adding the TiO2 hollow spheres with a core-shell structure prepared in step 4) and carbon quantum dots into a mixed alcohol of C2-C5 alkane diol and C1-C5 alkyl alcohol to prepare an alcohol solution of the mixture; reacting the alcohol solution of the mixture at 100-500°C to prepare a composite photocatalyst; wherein, the amount of the carbon quantum dots added is 2.5-10 wt% of the mass of the TiO2 hollow spheres with a core-shell structure.

[0016] According to the preparation method of the present application, preferably, the preparation method of the carbon nanospheres comprises the following steps:

[0017] a) heat treating a sugar solution at 100-500 ℃ to obtain a heat-treated product; wherein the mass concentration of the sugar solution is 0.01-1 g / mL;

[0018] b) washing and drying the heat-treated product obtained in step a) to obtain carbon nanospheres.

[0019] According to the preparation method, preferably, the sugar is at least one selected from monosaccharides and polysaccharides.

[0020] According to the preparation method, preferably, the alkyl titanate is tetraalkyl titanate.

[0021] According to the preparation method, preferably:

[0022] In step 3), the rare earth element is at least one selected from lanthanum, cerium, neodymium, praseodymium, terbium and dysprosium;

[0023] In step 3), the iron-based element is at least one selected from iron, cobalt and nickel;

[0024] In step 3), the carboxylic acid is at least one selected from citric acid, tartaric acid, malic acid, oxalic acid and ascorbic acid.

[0025] According to the preparation method, preferably:

[0026] In step 3), the salt of the rare earth element is at least one selected from nitrate, sulfate, phosphate, acetate, carbonate and halide of the rare earth element;

[0027] In step 3), the salt of the iron-based element is at least one selected from nitrate, sulfate, phosphate, acetate, carbonate and halide of the iron-based element.

[0028] According to the preparation method, preferably, the preparation method of the carbon quantum dots comprises the following steps:

[0029] S1) placing a carbon source substance in water, adding liquid diamine to obtain a suspension; wherein, based on 1 g of the carbon source substance, the amount of the liquid diamine added is 0.1-1 mL;

[0030] S2) reacting the suspension obtained in step S1) at 100-500 ℃ to obtain a product solution;

[0031] S3) dialyzing the product solution prepared in step S2) in a dialysis bag with a molecular weight cut-off of 1000-5000 Da to obtain carbon quantum dots.

[0032] According to the preparation method, preferably:

[0033] In step S1), the water is used in an amount of 2-10 mL based on 1 g of the carbon source substance.

[0034] In step S1), the liquid binary amine is a liquid C2-C6 alkanediamine.

[0035] In another aspect, the present application also provides a composite photocatalyst prepared by any of the above preparation methods.

[0036] In still another aspect, the present application also provides a use of the above composite photocatalyst in photocatalytic degradation of antibiotics.

[0037] The composite photocatalyst of the present application has a stable structure, uniform nanoparticle size, high visible light absorption rate, and good performance in photocatalytic degradation of antibiotics. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a schematic diagram of the preparation process of the composite photocatalyst of Example 1.

[0039] Figure 2 It is the XRD standard spectrum of the composite photocatalyst prepared in Example 1.

[0040] Figure 3 It is the SEM and TEM images of the composite photocatalyst prepared in Example 1 and the intermediate products in the preparation process.

[0041] Figure 4 It is the BET calculation diagram of the composite photocatalyst prepared in Example 1.

[0042] Figure 5 It is the XPS spectrum of the composite photocatalyst prepared in Example 1.

[0043] Figure 6 It is the UV-Vis diffuse reflectance spectrum of Experimental Example 5.

[0044] Figure 7 It is the tetracycline degradation result graph of Experimental Example 6.

[0045] Figure 8 It is the tetracycline degradation result graph of Experimental Example 7. DETAILED DESCRIPTION

[0046] The present application will be further described below in conjunction with specific embodiments, but the scope of protection of the present application is not limited thereto.

[0047] Preparation method of composite photocatalyst

[0048] The preparation method of the composite photocatalyst of the present application comprises a suspension preparation step, a TiO2 hollow sphere preparation step, a rare earth element coating step, a TiO2 hollow sphere with core-shell structure preparation step and a carbon quantum dot modification step. Optionally, it also comprises a carbon nanosphere preparation step and a carbon quantum dot preparation step. The following will be described in detail.

[0049] Preparation steps of carbon nanospheres

[0050] In the present application, the carbon nanospheres can be commercially available products or self-made. The present application preferably is self-made.

[0051] According to one specific embodiment of the present application, the preparation method of the carbon nanospheres comprises the following steps:

[0052] a) heat treating a sugar solution at 100-500℃ to obtain a heat-treated product;

[0053] b) washing and drying the heat-treated product obtained in step a) to obtain carbon nanospheres.

[0054] According to one specific embodiment of the present application, the mass concentration of the sugar solution can be 0.01-1 g / mL, preferably 0.02-0.8 g / mL, and more preferably 0.05-0.5 g / mL.

[0055] According to one embodiment of the present application, the sugar can be at least one selected from monosaccharides and polysaccharides, and preferably at least one selected from glucose, fructose, galactose, mannose, sucrose, maltose, trehalose, dextran and starch; and more preferably at least one selected from glucose, fructose, sucrose, maltose and starch.

[0056] According to one embodiment of the present application, the heat treatment temperature of the sugar solution can be 100-500℃, preferably 120-400℃, and more preferably 150-300℃. The heat treatment time of the sugar solution can be 1-20 h, preferably 2-18 h, and more preferably 5-15 h.

[0057] In the present application, the heat treatment can be carried out in any high-temperature reaction equipment known in the art, and preferably in a high-temperature reaction kettle containing a polytetrafluoroethylene lining.

[0058] According to one specific embodiment of the present application, the washing agent for washing the heat-treated product can be at least one selected from water and C1-C5 alkyl alcohol, preferably at least one selected from water and C1-C3 alkyl alcohol, more preferably at least one selected from water and C1-C3 n-alkyl alcohol, and most preferably at least one selected from deionized water, methanol, ethanol and n-propanol.

[0059] In the present application, the C1-C5 alkyl alcohol can include, but is not limited to, methanol, ethanol, propanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, sec-pentanol, neopentanol, and the like.

[0060] The present application does not particularly limit the number of washing, and the washing is performed until the washing waste liquid is clear. The washing method can use one washing agent or different washing agents in different washing times, which is not particularly limited herein.

[0061] According to one embodiment of the present application, the drying temperature can be 40-100°C, preferably 45-90°C, and more preferably 50-85°C.

[0062] According to another embodiment of the present application, the drying time can be 1-24h, preferably 2-20h, and more preferably 5-18h.

[0063] Limiting the reactant ratio and reaction conditions in the above range is beneficial to the stable performance of the hydrothermal carbonization method, and is more beneficial to the generation of carbon nanospheres.

[0064] Preparation steps of suspension

[0065] The carbon nanospheres, C1-C5 alkyl alcohol, and alkyl titanate are mixed to obtain a mixed solution; the C1-C5 alkyl alcohol aqueous solution is added to the mixed solution at 40-90°C to perform a reaction, and a suspension is obtained.

[0066] According to one embodiment of the present application, the C1-C5 alkyl alcohol can be C1-C3 alkyl alcohol, preferably C1-C3 n-alkyl alcohol, and more preferably methanol or ethanol.

[0067] According to one embodiment of the present application, the amount of C1-C5 alkyl alcohol can be 10-200mL, preferably 20-180mL, and more preferably 50-150mL, based on 100mg of carbon nanospheres.

[0068] In the present application, the carbon nanospheres can be mixed with the C1-C5 alkyl alcohol by ultrasonic treatment after being added to the C1-C5 alkyl alcohol.

[0069] According to one specific embodiment of the present application, the ultrasonic treatment time can be 10-90min, preferably 15-80min, and more preferably 20-60min.

[0070] The ultrasonic treatment is beneficial to the uniform dispersion of the carbon nanospheres in the C1-C5 alkyl alcohol, and can greatly reduce the binding force between the nanoparticles, effectively preventing the occurrence of agglomeration.

[0071] According to one embodiment of the present application, the alkyl titanate can be a tetraalkyl titanate, preferably at least one of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate.

[0072] According to one embodiment of the present application, the amount of the alkyl titanate added can be 1-20 mL, preferably 2-18 mL, more preferably 5-15 mL, based on 100 mg of the carbon nanospheres.

[0073] According to one specific embodiment of the present application, the alkyl titanate can be added dropwise to the mixture of the carbon nanospheres and the C1-C5 alkyl alcohol under stirring.

[0074] According to one embodiment of the present application, the volume ratio of the C1-C5 alkyl alcohol to water in the aqueous solution of the C1-C5 alkyl alcohol can be 1-10:1, preferably 2-8:1, more preferably 3-6:1.

[0075] According to one embodiment of the present application, the reaction temperature can be 40-90°C, preferably 45-85°C, more preferably 50-80°C. The reaction time can be 0.5-10 h, preferably 1-8 h, more preferably 2-5 h.

[0076] According to one specific embodiment of the present application, the aqueous solution of the C1-C5 alkyl alcohol can be added dropwise under stirring, and the time for the dropwise addition is the reaction time.

[0077] Limiting the proportions of the reactants and the reaction conditions to the above ranges is more conducive to complete hydrolysis of the alkyl titanate and adsorption of the alkyl titanate on the surface of the carbon nanospheres, and is conducive to stable performance of the sol-gel method using the carbon nanospheres as a template.

[0078] Preparation steps of TiO2hollow spheres

[0079] The suspension is subjected to solid-liquid separation, and the obtained solid is dried to obtain a powder. The powder is heat-treated at 300-1000°C to prepare the TiO2 hollow spheres.

[0080] In the present application, the solid-liquid separation can be achieved using any filtration method known in the art, which is not particularly limited herein, and can be, for example, gravity filtration, pressure filtration, centrifugal filtration, vacuum filtration, etc. The various filtration methods can be achieved using devices known in the art.

[0081] According to one embodiment of the present application, the temperature for the drying can be 40-100°C, preferably 45-90°C, more preferably 50-85°C. The time for the drying can be 1-24 h, preferably 2-20 h, more preferably 5-18 h.

[0082] According to one embodiment of the present application, the temperature of the heat treatment can be 300-1000℃, preferably 350-900℃, and more preferably 400-800℃. The time of the heat treatment can be 1-12h, preferably 1-10h, and more preferably 2-8h.

[0083] The reasonable heat treatment condition is beneficial to the formation of the TiO2 hollow structure.

[0084] In the present application, the heat treatment can be carried out in any type of high-temperature heat treatment furnace known in the art, which is not particularly limited herein. For example, but not limited to, it can be a high-temperature sintering furnace, such as a muffle furnace.

[0085] Rare earth element coating step

[0086] The salt of the rare earth element, the salt of the iron-based element and the carboxylic acid are added into water to prepare a mixed solution; the pH value of the mixed solution is adjusted, and then C2-C5 alkane diol is added into the mixed solution; then TiO2 hollow spheres are added, heated and reacted to prepare a gel.

[0087] According to one embodiment of the present application, the rare earth element can be selected from at least one of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), terbium (Tb) and dysprosium (Dy), preferably at least one of lanthanum, cerium, neodymium, praseodymium and terbium, and more preferably at least one of lanthanum, cerium and neodymium.

[0088] According to one embodiment of the present application, the iron-based element can be selected from at least one of iron (Fe), cobalt (Co) and nickel (Ni), preferably one or two of iron, cobalt and nickel, and more preferably one of iron, cobalt and nickel.

[0089] According to one embodiment of the present application, the salt of the rare earth element can be selected from at least one of nitrate, sulfate, phosphate, acetate, carbonate and halide of the rare earth element, preferably at least one of nitrate, sulfate, carbonate and halide of the rare earth element, and more preferably at least one of nitrate, sulfate and halide of the rare earth element. The salt of the rare earth element in the present application can be an anhydrous salt or a hydrated salt.

[0090] According to one embodiment of the present application, the salt of the iron-based element can be selected from at least one of nitrate, sulfate, phosphate, acetate, carbonate and halide of the iron-based element, preferably at least one of nitrate, sulfate, carbonate and halide of the iron-based element, and more preferably at least one of nitrate, sulfate and halide of the iron-based element. The salt of the iron-based element in the present application can be an anhydrous salt or a hydrated salt.

[0091] According to one embodiment of the present application, the carboxylic acid can be at least one selected from the group consisting of citric acid, tartaric acid, malic acid, oxalic acid, ascorbic acid, preferably one of citric acid, tartaric acid, malic acid, ascorbic acid, and more preferably one of citric acid, tartaric acid, and malic acid. The carboxylic acid of the present application can be either anhydrous carboxylic acid or hydrated carboxylic acid.

[0092] According to one embodiment of the present application, the molar ratio of the rare earth element, the iron-based element, and the carboxylic acid can be (1-5):(1-5):(5-20), preferably (1-5):(1-5):(5-18), and more preferably (1-5):(1-5):(5-15).

[0093] In the present application, the concentration of the salt of the rare earth element in the mixed solution can be 0.01-0.1 mol / L, preferably 0.01-0.08 mol / L, and more preferably 0.02-0.05 mol / L.

[0094] In the present application, the pH of the mixed solution can be adjusted to 6-8, preferably 6.2-7.8, and more preferably 6.5-7.5.

[0095] According to one embodiment of the present application, the mixed solution can be stirred before adjusting the pH of the mixed solution. The stirring time can be 0.5-5 h, preferably 1-5 h, and more preferably 1-3 h.

[0096] In the present application, any basic solution can be used to adjust the pH, such as but not limited to at least one of aqueous ammonia, alkali hydroxide solution, and alkali carbonate solution; preferably at least one of aqueous ammonia, aqueous sodium hydroxide solution, and aqueous sodium carbonate solution; and more preferably aqueous ammonia.

[0097] According to one embodiment of the present application, based on 1 mol of the sum of the rare earth element and the iron-based element, the volume of the C2-C5 alkane diol added can be 0.5-5 mL, preferably 1-5 mL, and more preferably 1-3 mL.

[0098] In the present application, the C2-C5 alkane diol can be at least one of C2-C4 alkane diol, preferably at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol, and more preferably at least one of ethylene glycol, 1,2-propanediol, and 1,4-butanediol.

[0099] In the present application, the C2-C5 alkane diol, as a chelating agent, can stabilize the solution system, adjust the solution viscosity, and improve the subsequent calcination performance by forming a complex with metal ions.

[0100] In the present application, the mass of the TiO2 hollow sphere added can be 100-600 mg, preferably 150-550 mg, and more preferably 200-500 mg, based on 1 mol of the sum of the rare earth element and the iron-based element.

[0101] In the present application, the mixed solution can also be subjected to ultrasonic treatment after the TiO2 hollow sphere is added. The ultrasonic treatment time can be 10-90 min, preferably 15-80 min, and more preferably 20-60 min.

[0102] The ultrasonic treatment is beneficial to the uniform dispersion of the TiO2 hollow sphere in the mixed solution, and can greatly reduce the binding force between the nanoparticles, effectively preventing the occurrence of agglomeration, thereby improving the microstructure and performance of the subsequently prepared core-shell structure TiO2 hollow sphere.

[0103] According to one embodiment of the present application, the heating reaction temperature can be 50-120°C, preferably 60-110°C, and more preferably 65-100°C. The heating reaction time can be 1-10 h, preferably 2-8 h, and more preferably 2-6 h.

[0104] In the present application, the mixed solution can also be subjected to stirring during the heat treatment.

[0105] The reaction product and reaction conditions are limited to the above ranges, which is beneficial to the stable in-situ sol-gel deposition and the formation of the gel, and more beneficial to the subsequent formation of the core-shell structure TiO2 hollow sphere.

[0106] Preparation steps of core-shell structure TiO2hollow spheres

[0107] The gel is dried and then subjected to heat treatment at 300-1000°C to obtain the core-shell structure TiO2 hollow sphere.

[0108] According to one embodiment of the present application, the drying temperature can be 50-150°C, preferably 60-120°C, and more preferably 80-110°C.

[0109] According to another embodiment of the present application, the drying time can be 1-24 h, preferably 2-20 h, and more preferably 5-15 h.

[0110] According to one embodiment of the present application, the heat treatment temperature can be 300-1000°C, preferably 350-950°C, and more preferably 500-800°C.

[0111] According to another embodiment of the present application, the heat treatment time can be 1-20 h, preferably 2-15 h, and more preferably 3-10 h.

[0112] Reasonable heat treatment condition is favorable to formation of TiO2 hollow sphere with core-shell structure.

[0113] Preparation steps of carbon quantum dots

[0114] According to one embodiment of the present application, the preparation method of carbon quantum dots comprises the following steps:

[0115] S1) placing a carbon source substance in water, adding liquid diamine to obtain a suspension;

[0116] S2) reacting the suspension obtained in step S1) at 100-500 DEG C to prepare a product solution;

[0117] S3) dialyzing the product solution prepared in step S2) in a dialysis bag with a molecular weight cut-off of 1000-5000 Da to prepare carbon quantum dots.

[0118] In the present application, the carbon source substance can be any carbon-containing substance known in the art, including but not limited to straw powder, sugar substance, organic acid, lignin, elemental carbon, etc., preferably at least one of straw powder, sugar substance, organic acid, elemental carbon, more preferably at least one of straw powder, glucose, sucrose, starch, cellulose, citric acid, ascorbic acid, carbon black, carbon nanotube.

[0119] According to one embodiment of the present application, the liquid diamine can be liquid C2-C6 alkane diamine, preferably liquid C2-C4 alkane diamine, more preferably at least one of ethylenediamine, 1,2-propanediamine, 1,3-propanediamine.

[0120] According to one embodiment of the present application, the amount of water can be 2-10 mL, preferably 3-10 mL, more preferably 3-9 mL, based on 1 g of carbon source substance.

[0121] According to one embodiment of the present application, the amount of liquid diamine can be 0.1-1 mL, preferably 0.2-0.8 mL, more preferably 0.3-0.6 mL, based on 1 g of carbon source substance.

[0122] In the present application, the liquid diamine can be added dropwise under stirring.

[0123] According to one embodiment of the present application, the reaction temperature can be 100-500 DEG C, preferably 120-450 DEG C, more preferably 150-400 DEG C. The reaction time can be 1-20 h, preferably 2-18 h, more preferably 3-15 h.

[0124] Reasonable reactant ratio and reaction condition are favorable to stable hydrothermal process, and more favorable to generation of carbon quantum dots.

[0125] In the present application, the heat treatment can be carried out in any high-temperature reaction equipment known in the art, preferably in a high-temperature reaction kettle containing a polytetrafluoroethylene lining.

[0126] According to one specific embodiment of the present application, the molecular weight cut-off of the dialysis bag can be 1000-5000 Da, preferably 2000-5000 Da, and more preferably 2000-4000 Da.

[0127] A reasonable dialysis bag is more conducive to efficient dialysis of carbon quantum dots.

[0128] In the present application, the product solution can be centrifuged before dialysis treatment. This is more conducive to the rapid progress of dialysis and saves time.

[0129] In the present application, the product obtained after dialysis treatment is a solution of carbon quantum dots. The concentration of the solution can be 1-20 mg / mL, preferably 2-18 mg / mL, and more preferably 5-15 mg / mL.

[0130] Modification steps of carbon quantum dots

[0131] The core-shell structured TiO2 hollow spheres and carbon quantum dots are sequentially added to a mixed alcohol of C2-C5 alkanediol and C1-C5 alkyl alcohol to prepare an alcohol solution of the mixture; and the alcohol solution of the mixture is reacted at 100-500℃ to prepare a composite photocatalyst.

[0132] According to one embodiment of the present application, the C2-C5 alkanediol can be C2-C4 alkanediol, preferably at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol, and more preferably at least one of ethylene glycol, 1,2-propanediol, and 1,4-butanediol.

[0133] According to one embodiment of the present application, the C1-C5 alkyl alcohol can be C1-C3 alkyl alcohol, preferably C1-C3 n-alkyl alcohol, and more preferably at least one of methanol, ethanol, and n-propanol.

[0134] In the present application, the C1-C5 alkyl alcohol can include, but is not limited to, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, isopentanol, sec-pentanol, neopentanol, etc.

[0135] According to one embodiment of the present application, the volume ratio of the C2-C5 alkanediol to the C1-C5 alkyl alcohol can be 1:1-5, preferably 1:1-3, and more preferably 1:2-3.

[0136] In the present application, the amount of mixed alcohol can be 10-100 mL, preferably 20-80 mL, and more preferably 20-50 mL, based on 100 mg of the TiO2 hollow sphere with core-shell structure.

[0137] According to one embodiment of the present application, the amount of carbon quantum dots can be 2.5-10 wt%, preferably 3-8 wt%, and more preferably 3-5 wt%, based on the mass of the TiO2 hollow sphere with core-shell structure.

[0138] According to one embodiment of the present application, the reaction temperature can be 100-500°C, preferably 120-450°C, and more preferably 150-400°C.

[0139] According to another embodiment of the present application, the reaction time can be 1-20 h, preferably 2-18 h, and more preferably 3-15 h.

[0140] Reasonable reactant ratio and reaction conditions are conducive to better modification of carbon quantum dots on the TiO2 hollow sphere with core-shell structure to generate the composite photocatalyst.

[0141] According to one specific embodiment of the present application, the reaction product can be further subjected to the steps of centrifugation and drying.

[0142] In the present application, the drying temperature can be 40-100°C, preferably 45-90°C, and more preferably 50-85°C.

[0143] The drying time can be 1-24 h, preferably 2-20 h, and more preferably 5-18 h.

[0144] The water used in the present application can be at least one selected from the group consisting of distilled water, deionized water, and ultrapure water; and preferably distilled water or deionized water.

[0145] <Composite photocatalyst>

[0146] The present application also provides a composite photocatalyst obtained by the above method.

[0147] According to one embodiment of the present application, the composite photocatalyst is a core-shell structure with the TiO2 hollow sphere as the core and the salt of the acid of the iron-based element of the rare earth element wrapped thereon; and the carbon quantum dots are modified on the core-shell structure.

[0148] According to one embodiment of the present application, the particle diameter of the composite photocatalyst can be 300-600 nm, preferably 350-550 nm, and more preferably 400-500 nm.

[0149] The specific surface area of the composite photocatalyst can be at least 12 m 2 / g, preferably 12-30 m 2 / g, more preferably 13-25 m 2 / g, more preferably 13-25 m 2 / g, more preferably 13-25 m

[0150] The core-shell structure of the composite photocatalyst of the present application optimizes the electronic structure, improves the separation of photo-generated carriers, enhances light absorption, and expands the spectral response range, thereby improving the activity and efficiency of the catalyst. The shell material can improve the stability and durability of the catalyst, reduce side reactions, and increase the selectivity of the photocatalytic reaction. The shell layer can also improve the hydrophilicity and dispersibility of the catalyst, thereby increasing its contact area with the reactants. In addition, the core-shell structure helps to prolong the service life of the catalyst and enhance its application effect in complex reaction environments.

[0151] The salt of the rare earth element iron series element acid (LaFeO3 in Example 1) is a p-type semiconductor with a band gap of about 2.3 eV. It plays a role in promoting carrier separation and transfer in the ternary system of the composite catalyst, especially in the electron migration process of TiO2 and CQDs. The salt of the rare earth element iron series element acid not only effectively captures the electrons generated on TiO2, but also participates in the reaction through its own catalytic properties, further reducing the recombination of carriers and improving the migration efficiency of electrons. This can significantly improve the efficiency of the photocatalytic reaction. The introduction of the salt of the rare earth element iron series element acid effectively suppresses the recombination of electrons and holes by providing additional electron accepting sites, enhances the anti-recombination ability of the photocatalyst, and further improves the catalytic performance.

[0152] As an iron series element-based compound, the salt of the rare earth element iron series element acid has good thermal stability and corrosion resistance. It can improve the stability of the photocatalyst and prevent the degradation of the active sites on the surface of TiO2. In addition, the salt of the rare earth element iron series element acid itself has strong anti-pollution ability, which helps to prevent the catalyst surface from being covered by pollutants and maintains longer catalytic activity.

[0153] The addition of the salt of the rare earth element iron series element acid introduces additional catalytic effects, not only improving the separation efficiency of photo-generated carriers, but also promoting redox reactions through its oxygen reduction properties. The incorporation of the salt of the rare earth element iron series element acid makes the working mechanism of the catalyst more diverse, forms a stronger synergistic effect, and significantly improves the overall photocatalytic performance.

[0154] Carbon quantum dots (CQDs) as electron acceptors can promote electron transfer and significantly improve light absorption and electron transport rates. In addition, CQDs have excellent upconversion properties, which are also beneficial to the absorption of visible light, thereby improving the photocatalytic ability of TiO2.

[0155] <Use>

[0156] The application further provides a use of the composite photocatalyst in photocatalytic degradation of antibiotics.

[0157] According to one embodiment of the application, the degradation rate of the composite photocatalyst to the antibiotics in antibiotic wastewater under visible light irradiation within 2 hours is at least 90%.

[0158] According to one specific embodiment of the application, the degradable antibiotics include, but are not limited to, at least one of tetracyclines, β-lactams and quinolones, preferably tetracyclines.

[0159] <Testing method>

[0160] XRD measurement: X'Pert PRO XRD powder diffractometer produced by Panalytical Company is used.

[0161] SEM measurement: Sigma500 field emission scanning electron microscope produced by ZEISS Company is used.

[0162] TEM measurement: Thermo Fisher Talos F200i transmission electron microscope produced by the United States is used.

[0163] BET measurement: SA3100 specific surface area and pore size analyzer produced by Beckman Coulter of the United States is used.

[0164] XPS measurement: Thermo Scientific ESCALAB QXi X-ray photoelectron spectrometer is used.

[0165] UV-visible diffuse reflectance spectrum measurement: UH4150 ultraviolet-visible spectrophotometer produced by Hitachi of Japan is used.

[0166] Absorbance measurement: UH4150 ultraviolet-visible spectrophotometer produced by Hitachi of Japan is used.

[0167] <Raw material description>

[0168] The other raw materials in the following examples are commercially available products, unless otherwise specified. Among them, the commercial TiO2 photocatalyst is purchased from Sinopharm Chemical Reagent Co., Ltd.

[0169] Preparation Example 1

[0170] The carbon nanospheres are prepared by a hydrothermal carbonization method.

[0171] Dissolve 6 g of glucose in 60 mL of deionized water to form a sugar solution. Then transfer the sugar solution into a Teflon-lined autoclave, seal, and heat treat at 170 °C for 10 h. Centrifuge the heat-treated solution at 8000 rpm to obtain a dark brown heat-treated product, and then wash the heat-treated product with deionized water and anhydrous ethanol alternately until the washing waste liquid is clear. Dry the washed heat-treated product in a vacuum oven at 80 °C for 10 h to prepare carbon nanospheres.

[0172] Preparation Example 2

[0173] Prepare carbon quantum dots (CQDs) by a hydrothermal method.

[0174] Weigh 8 g of straw powder into 60 mL of deionized water, and add 3 mL of ethylenediamine dropwise under stirring to obtain a suspension. Transfer the suspension into a Teflon-lined autoclave, seal, and heat treat at 180 °C for 10 h. Centrifuge the heat-treated solution at 8000 rpm to obtain a product solution. Then dialyze the product solution with a dialysis bag with a molecular weight cut-off of 3500 Da for 24 h to obtain a carbon quantum dot solution with a concentration of 10 mg / mL.

[0175] Example 1

[0176] Step 1, prepare TiO2 hollow spheres using carbon nanospheres as templates by a sol-gel method

[0177] Disperse 100 mg of carbon nanospheres prepared in Preparation Example 1 into 100 mL of anhydrous ethanol, and ultrasonically treat for 30 min. Then add 9 mL of n-butyl titanate (TBOT) dropwise under stirring to obtain a mixture. Add an aqueous solution of ethanol (volume ratio of anhydrous ethanol to water is 5:1) to the mixture at 60 °C under stirring for 3 h to react, so that the TBOT can be completely hydrolyzed and adsorbed on the surface of the carbon spheres, and the reaction is completed after the addition is completed to obtain a suspension.

[0178] Perform suction filtration on the suspension, dry the obtained filter cake in an oven at 80 °C for 10 h to obtain a powder. Heat treat the powder in a muffle furnace at 600 °C for 3 h to prepare TiO2 hollow spheres (denoted as h-TiO2).

[0179] Step 2, prepare TiO2 hollow spheres with core-shell structure by an in-situ sol-gel deposition method

[0180] La(NO3)3.6H2O (0.433 g, 1.0 mmol), Fe(NO3)3.9H2O (0.404 g, 1.0 mmol), and citric acid monohydrate (0.420 g, 2.0 mmol) were dissolved in 50 mL of distilled water to obtain a mixed solution, and ammonia water (1 mol / L) was added dropwise to the mixed solution after continuous stirring for 2 h to adjust the pH to 7.5, followed by the addition of 3 mL of ethylene glycol. Then, 600 mg of TiO2hollow spheres (h-TiO2) were added to the solution, and ultrasonic treatment was performed for 30 min to obtain a dispersion liquid. The dispersion liquid was then subjected to heat treatment at 90°C for 3 h with stirring to obtain a gel.

[0181] The gel was dried in an oven at 105°C for 5 h to obtain a powder. The powder was heat-treated in a muffle furnace at 600°C for 4 h to obtain TiO2hollow spheres with a core-shell structure. The TiO2hollow spheres with a core-shell structure were TiO2hollow spheres (h-TiO2) as a core wrapped with a shell of LaFeO3(referred to as LFO) (referred to as TLFO (TiO2@LaFeO3)).

[0182] Step 3, preparation of a composite photocatalyst

[0183] The TLFO (100 mg) was dispersed in a mixed alcohol of 10 mL of ethylene glycol and 20 mL of ethanol, and the carbon quantum dot solution prepared in Preparation Example 2 was added in an amount of 3 wt% based on the mass of the TLFO with stirring. The stirring was continued for 12 h to obtain an alcohol solution of a mixture. The alcohol solution of the mixture was placed in a polytetrafluoroethylene-lined autoclave, and reaction was performed at 180°C for 12 h. Subsequently, the reaction product was naturally cooled, and centrifugation was performed at a rotation speed of 8000 rpm, and the supernatant was discarded. The precipitate was dried in an oven at 80°C for 10 h to obtain a composite photocatalyst (referred to as CDs-TLFO (CDs@TiO2@LaFeO3)).

[0184] Example 2

[0185] The difference from Example 1 is only in the amount of the carbon quantum dots added. In this example, the carbon quantum dot solution prepared in Preparation Example 2 was added in an amount of 5 wt% based on the mass of the TLFO.

[0186] Comparative Example 1

[0187] The difference from Example 1 is only in the amount of the carbon quantum dots added. In this example, the carbon quantum dot solution prepared in Preparation Example 2 was added in an amount of 0.5 wt% based on the mass of the TLFO.

[0188] Comparative Example 2

[0189] The difference from Example 1 is only that the amount of carbon quantum dots added is different. In this example, the carbon quantum dot solution prepared in Preparation Example 2 is added in an amount of 1wt% of the mass of TLFO.

[0190] Comparative Example 3

[0191] The difference from Example 1 is only that the amount of carbon quantum dots added is different. In this example, the carbon quantum dot solution prepared in Preparation Example 2 is added in an amount of 2wt% of the mass of TLFO.

[0192] Experimental Example 1

[0193] The XRD standard pattern of the composite photocatalyst prepared in Example 1 is shown in Figure 2 .

[0194] As can be seen from Figure 2 , the XRD of h-TiO2 has diffraction peaks at 2θ = 25.2°, 37.8°, 48.0°, 53.8°, 55.0° and 62.6°, which are matched with (101), (004), (200), (105), (211) and (204) crystal faces, respectively, and mainly show the anatase phase of TiO2(JCPDS No. 21-1272). In the XRD pattern of h-TiO2, diffraction peaks of a small amount of rutile TiO2 phase (JCPDS No. 21-1276) can also be observed, and the inventors believe that this is because a small amount of anatase is formed into rutile during heat treatment. At the same time, when the anatase phase and the rutile phase coexist, a heterojunction is formed, which helps to promote the separation of photo-generated carriers, so as to enhance the photocatalytic activity of the composite photocatalyst. In addition, the XRD pattern of LFO shows the strongest diffraction peak, and the diffraction peaks at 2θ = 22.6°, 32.2°, 39.7°, 46.2°, 57.4° and 67.3° correspond to (100), (110), (111), (202), (210) and (220) crystal faces (JCPDS No. 37-1493), respectively. This indicates that a binary heterojunction of TiO2 and LFO is successfully constructed on TLFO. When CQDs are introduced, no characteristic diffraction peaks of CQDs are found in the XRD pattern, and the diffraction peaks of the composite photocatalyst CDs-TLFO are almost unchanged. This indicates that the introduction of CQDs does not affect the crystal structure of the composite photocatalyst.

[0195] Experimental Example 2

[0196] The SEM and TEM images of the composite photocatalyst prepared in Example 1 and the intermediate products in the preparation process are shown in Figure 3 .

[0197] From Figure 3 (a), it can be seen that the average diameter of the carbon nanospheres as templates is about 500 nm, and the size and distribution are very uniform. In Figure 3 (b), the size of h-TiO2 is shrunk to some extent, which the inventors believe is due to the release of CO2 during calcination, and the structure of h-TiO2 is not destroyed. In Figure 3 (c), when LFO is introduced, the TLFO particles exhibit a close connection framework, and the diameter of the TLFO particles is about 450 nm. From Figure 3 (d), it can be seen that the spherical structure of CDs-TLFO is more regular with the deposition of CQDs during the hydrothermal process.

[0198] Due to the small size of CQDs, it is difficult to observe their existence by SEM. Therefore, the microstructure of the catalyst CDs-TLFO was further studied by TEM. In Figure 3 (e), it can be clearly seen that the composite photocatalyst CDs-TLFO exhibits a uniform size and size of hollow core-shell structure, and the diameter of each hollow core-shell structure is about 450 nm. Figure 3 (f) further reveals the hollow core-shell structure of the composite photocatalyst CDs-TLFO particles. The catalyst with a hollow core-shell structure can expose a larger area, so as to exhibit better adsorption and provide more active sites.

[0199] Figure 3 (g) is a size distribution diagram of CQDs, from which it can be observed that there are many black quantum dots with a size of about 10 nm (shown by the red circles in the figure). Figure 3 (h) shows the HRTEM image of CDs-TLFO, and the lattice spacing of 0.35 nm, 0.32 nm and 0.28 nm are attributed to TiO2(101), CQDs and LFO(110), respectively.

[0200] As Experimental Example 3 (i)-(n) show that La, Fe, O, Ti and C elements can be detected in CDs-TLFO by element mapping, and the hollow core-shell structure is obvious.

[0201] The experimental results of Example 2 provide strong evidence for the close combination of LFO and TiO2 and the loading of CQDs.

[0202] Figure 4

[0203] The BET calculation diagram of the composite photocatalyst prepared in Example 1 is shown in FIG. 4.

[0204] From Experimental Example 4It can be seen that the specific surface areas of h-TiO2 and CDs-TLFO are 10.98 m 2 / g and 14.63 m 2 / g, respectively. Compared with h-TiO2, the specific surface area of CDs-TLFO is increased, and the porous structure is more compact, which is beneficial to the transfer and separation of carriers. Therefore, the inventors believe that CDs-TLFO obtains more active sites, so as to further improve the photocatalytic activity of the composite photocatalyst.

[0205] Figure 5

[0206] The XPS spectrum of the composite photocatalyst prepared in Example 1 is shown in Figure 5.

[0207] Figure 5 It can be seen that the full spectrum of CDs-TLFO contains all elements (La, Fe, Ti and O) in TiO2 and LFO, which is consistent with the elemental analysis results. The C1s peak at a binding energy of 284.8 eV is used as energy calibration. In the C1s spectrum of CDs-TLFO, the peaks at binding energies of 284.8 eV and 286.4 eV are attributed to C-O and C=O, and the peak at a binding energy of 288.6 eV is attributed to Ti-O-C, which indicates that amorphous carbon is doped in the TiO2 lattice. Figure 5 It is shown that there are three peaks in the O1s spectrum at binding energies of 532.8 eV, 531.0 eV and 529.1 eV, which can be attributed to oxygen in the hydroxyl group of adsorbed water molecules, absorbed oxygen and lattice oxygen, respectively. Among them, the absorbed oxygen appearing at a binding energy of 531.0 eV is consistent with the oxygen vacancy caused by surface oxygen defects, indicating that there is an oxygen vacancy in CDs-TLFO. Figure 5 It is shown that in the Fe2p spectrum, the three peaks at binding energies of 710.0 eV, 718.9 eV and 724.0 eV are Fe2p 3 / 2 , satellite peak and Fe2p 1 / 2 , respectively. The peaks at binding energies of 711.4 eV and 727.4 eV correspond to Fe(III) state, and the peaks at binding energies of 709.8 eV and 723.9 eV correspond to Fe(II) state, which indicates that there are two mixed oxidation states of Fe(III) and Fe(II) in CDs-TLFO. In Figure 5 , the peaks at binding energies of 458.3 eV and 464.0 eV are Ti2p 3 / 2 and Ti2p 1 / 2 of hollow structure TiO2, respectively, and the spin-orbit splitting of Ti2p is 5.7 eV, indicating that there is Ti(IV) oxidation state in CDs-TLFO. In addition, the peak at a binding energy of 459.9 eV is attributed to Ti-C bond on TiO2, indicating that CQDs are successfully doped in the TiO2 lattice synthesized with carbon nanospheres as templates.Experimental Example 5 The two peaks with binding energy at 834.7 eV and 851.4 eV in the La 3d spectrum are La 3d 5 / 2 The two peaks with binding energy at 838.4 eV and 855.3 eV are La 3d 3 / 2 The average difference between the two peaks is about 17 eV, indicating that the composite photocatalyst CDs-TLFO prepared in Example 1 contains La(III) ions.

[0208] Figure 6

[0209] The UV-Vis-DRS of the composite photocatalyst CDs-TLFO prepared in Example 1, the intermediate product h-TiO2, LFO and TFLO in the preparation process were detected, and the results are shown in Figure 6

[0210] Figure 6 The light absorption capacity of CDs-TLFO, h-TiO2, LFO and TFLO is shown. As can be seen from Experimental Example 6 CDs-TLFO, h-TiO2, LFO and TFLO all have strong absorption in the wavelength range of 250-620 nm. Hollow h-TiO2 shows a maximum absorption at about 340 nm in the ultraviolet region, and the absorption edge is about 400 nm. After combining LFO with h-TiO2, TLFO shows a significantly red-shifted absorption edge at about 540 nm, indicating that its absorption capacity in the visible light range has been enhanced. The introduction of carbon quantum dots (CQDs) further enhances the light absorption of CDs-TLFO in the visible and near ultraviolet regions. As can be seen from the figure, the light absorption intensity of CDs-TLFO in the visible and near ultraviolet regions is significantly higher than that of the intermediate products h-TiO2, LFO and TFLO. This improvement mainly takes advantage of the unique upconversion characteristics of CQDs. This enhanced light absorption helps to improve the photocatalytic activity of the catalyst.

[0211] Figure 7

[0212] A 300W xenon lamp equipped with a filter was used as a light source, and an ethanol circulation system was used to maintain the temperature at 20℃, and a photocatalytic degradation test of tetracycline was carried out. The specific method is as follows:

[0213] ​A tetracycline solution with a concentration of 20 mg / L was prepared by dissolving 20 mg of tetracycline (TC) in 1 L of water and stirring vigorously until completely dissolved. Then, 40 mg of commercially available TiO2catalyst, h-TiO2, LFO, TFLO and the composite photocatalyst prepared in Example 1 were dispersed in 50 mL of the tetracycline solution, respectively, and were recorded as the TiO2group, the h-TiO2group, the LFO group, the TFLO group and the CDs-TLFO group, respectively.

[0214] The five groups of tetracycline solutions were stirred on a magnetic stirrer in the dark for 40 min to reach adsorption equilibrium. During the photocatalytic process, 3 mL of supernatant was taken out every 20 min and filtered through a 0.22 μm microporous filter head. The filtered supernatant was detected using a UV-visible spectrophotometer, and the composite photocatalyst and the tetracycline solution were analyzed. According to the Beer-Lambert Law, the concentration of the tetracycline solution was calculated by the absorbance. The tetracycline degradation rate at different time points was calculated using the following formula:

[0215]

[0216] wherein C0is the initial concentration of the solution and C is the concentration of the solution after reaction.

[0217] The tetracycline degradation results of the five groups of tetracycline solutions are shown in Table 1. Figure 7

[0218] According to the results calculated, Experimental Example 7 the tetracycline degradation rates of the five groups of tetracycline solutions within 2 h were 11.8%, 25.4%, 31.4%, 52.9% and 98.6%, respectively. The tetracycline degradation effect of the CDs-TLFO group was significantly better than that of the other four groups.

[0219] Figure 8

[0220] A 300 W xenon lamp equipped with a filter was used as a light source, and an ethanol circulation system was used to maintain the temperature at 20°C to perform photocatalytic degradation of tetracycline. The specific method was as follows:

[0221] A tetracycline solution with a concentration of 20 mg / L was prepared by dissolving 20 mg of tetracycline (TC) in 1 L of water and stirring vigorously until completely dissolved. Then, 40 mg of commercially available TiO2catalyst, h-TiO2, LFO, TFLO and the composite photocatalyst prepared in Example 1 were dispersed in 50 mL of the tetracycline solution, respectively, and were recorded as the TiO2group, the h-TiO2group, the LFO group, the TFLO group and the CDs-TLFO group, respectively.

[0222] ​Five groups of tetracycline solutions were stirred on a magnetic stirrer in the dark for 40 minutes to reach adsorption equilibrium. During the photocatalysis process, 3 mL of supernatant was aspirated every 20 minutes and filtered through a 0.22 μm microporous filter. The filtered supernatant was analyzed using a UV-Vis spectrophotometer, and the composite photocatalyst and tetracycline solution were analyzed. The concentration of the tetracycline solution was calculated from the absorbance using the Beer-Lambert Law. The tetracycline degradation rate at different time points was calculated using the following formula:

[0223]

[0224] Where C0 is the initial concentration of the solution, and C is the concentration of the solution after the reaction.

[0225] The tetracycline degradation results of the five tetracycline solutions are shown in the figure. Figure 8 .

[0226] Depend on ​ It can be seen that the tetracycline degradation rates of the five tetracycline solutions within 2 hours were 65.6%, 76.4%, 85.5%, 92.8%, and 98.6%, respectively. This demonstrates that the composite photocatalyst prepared in the examples exhibits significantly better tetracycline degradation performance than the comparative examples, and the composite photocatalyst prepared in this invention possesses excellent photocatalytic degradation performance for antibiotics.

[0227] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing a composite photocatalyst, comprising the following steps: 1) mixing carbon nanospheres, C1-C5 alkyl alcohol and alkyl titanate to obtain a mixed solution; adding an aqueous solution of C1-C5 alkyl alcohol to the mixed solution at 40-90 ℃ to obtain a suspension; wherein, 1-20 mL of alkyl titanate is added based on 100 mg of carbon nanospheres; 2) solid-liquid separating the suspension obtained in step 1), drying the obtained solid to obtain a powder; and heat treating the powder at 300-1000 ℃ to obtain TiO 2 hollow spheres; 3) adding a salt of a rare earth element, a salt of an iron-based element and a carboxylic acid into water to obtain a mixed solution; adjusting the pH value of the mixed solution to 6-8, then adding C2-C5 alkanediol into the mixed solution; then adding the TiO 2 hollow spheres prepared in step 2) and heating to react to obtain a gel; wherein, the molar ratio of the rare earth element, the iron-based element and the carboxylic acid is (1-5) :(1-5) :(5-20); the concentration of the salt of the rare earth element in the mixed solution is 0.01-0.1 mol / L; and 5-20 mg of the TiO 2 hollow spheres is added based on 1 mL of the mixed solution; 4) drying the gel prepared in step 3) and heat treating at 300-1000 ℃ to obtain TiO 2 hollow spheres with core-shell structure; 5) sequentially adding the TiO 2 hollow spheres with core-shell structure prepared in step 4) and carbon quantum dots into a mixed alcohol of C2-C5 alkanediol and C1-C5 alkyl alcohol to obtain an alcohol solution of the mixture; and reacting the alcohol solution of the mixture at 100-500 ℃ to obtain the composite photocatalyst; wherein, the amount of the carbon quantum dots added is 2.5-10 wt% of the mass of the TiO 2 hollow spheres with core-shell structure. 6) a method for preparing the carbon nanospheres, comprising the following steps: a) heat treating a sugar solution at 100-500 ℃ to obtain a heat-treated product; wherein, the mass concentration of the sugar solution is 0.01-1 g / mL; b) washing and drying the heat-treated product obtained in step a) to obtain the carbon nanospheres. 7) the sugar is at least one selected from monosaccharides and polysaccharides. 8) the alkyl titanate is tetraalkyl titanate. 9) in step 3), the rare earth element is at least one selected from lanthanum, cerium, neodymium, praseodymium, terbium and dysprosium; in step 3), the iron-based element is at least one selected from iron, cobalt and nickel; and in step 3), the carboxylic acid is at least one selected from citric acid, tartaric acid, malic acid, oxalic acid and ascorbic acid. 10) in step 3), the salt of the rare earth element is at least one selected from nitrate, sulfate, phosphate, acetate, carbonate and halide of the rare earth element; and in step 3), the salt of the iron-based element is at least one selected from nitrate, sulfate, phosphate, acetate, carbonate and halide of the iron-based element. 11) a method for preparing the carbon quantum dots, comprising the following steps: a) mixing a sugar solution and a reducing agent to obtain a mixed solution; b) adding a salt of a rare earth element into the mixed solution to obtain a reaction solution; c) adjusting the pH value of the reaction solution to 6-8; d) adding C2-C5 alkanediol into the reaction solution; e) heating to react to obtain a gel; f) drying the gel; and g) heat treating at 300-1000 ℃ to obtain the carbon quantum dots. ​ ​ ​ ​ ​ 2. The production method according to claim 1, characterized by, ​ ​ ​ 3. The production method according to claim 2, characterized by, ​ 4. The method of claim 1, wherein, ​ ​ ​ ​ ​ ​ ​ ​ 7. The preparation method according to claim 1, characterized in that, ​ S1) placing a carbon source substance in water, adding a liquid binary amine to obtain a suspension; wherein, based on 1 g of the carbon source substance, 0.1-1 mL of the liquid binary amine is added; S2) reacting the suspension obtained in step S1) at 100-500 ℃ to prepare a product solution; S3) dialyzing the product solution prepared in step S2) in a dialysis bag with a molecular weight cut-off of 1000-5000 Da to prepare carbon quantum dots.

8. The preparation method according to claim 7, characterized in that: in step S1), the amount of water is 2-10 mL based on 1 g of the carbon source substance; in step S1), the liquid binary amine is a liquid C2-C6 alkanediamine.

9. A composite photocatalyst prepared by the preparation method according to any one of claims 1-8.

10. Use of the composite photocatalyst according to claim 9 in photocatalytic degradation of antibiotics.

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