Composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a composite photocatalyst as well as 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, and adding an aqueous solution of alkyl alcohol into the mixed solution for reaction to obtain a suspension; 2) carrying out heat treatment on the suspension to prepare TiO2 hollow spheres; (3) adding salt of rare earth elements, salt of iron series elements and carboxylic acid into water, adding alkanediol and the TiO2 hollow spheres, and heating to prepare gel; (4) carrying out heat treatment on the gel to prepare a TiO2 hollow sphere with a core-shell structure; and 5) sequentially adding the TiO2 hollow spheres with the core-shell structure and the carbon quantum dots into mixed alcohol of alkanediol and alkyl alcohol for reaction to prepare the composite photocatalyst. The composite photocatalyst disclosed by the invention is high in visible light absorptivity and relatively good in antibiotic photocatalytic degradation performance.

Description

Technical Field

[0001] The present invention relates to a composite photocatalyst, a preparation method thereof, and uses thereof. Background Art

[0002] Antibiotics, as a class of widely used chemical substances, play an important role in multiple fields such as agricultural production, medical and health care, and food processing. However, the widespread use of these compounds has also caused a series of environmental problems, especially the increasingly severe impact on the situation of organic matter pollution. In recent years, with the continuous increase in the usage amount of antibiotics, the problem of their residue and accumulation in the environment has become more prominent. These compounds often have a long half-life and are difficult to degrade rapidly under natural conditions, resulting in a continuous increase in the residue amount of antibiotics in ecological environments such as soil and water bodies. This kind of organic matter pollution not only disrupts the balance of the ecosystem but also poses a serious threat to biodiversity.

[0003] To address the increasingly severe antibiotic pollution, scientific researchers are actively exploring efficient and environmentally friendly solutions. Compared with 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 harm caused by antibiotic residues. Photocatalysts mainly based on titanium dioxide (TiO 2 ) have characteristics such as chemical stability, thermal stability, and availability, and can be used to degrade antibiotics. However, since the band gap of titanium dioxide is between 3.0 and 3.2 eV, it can only absorb light in the ultraviolet region, and the utilization of sunlight is extremely 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 synthesizing a composite nano-photocatalyst by using a hydrothermal method to prepare a carbon quantum dot solution. The method includes: using vitamin C as a carbon source, and preparing carbon quantum dots (CQDs) with up-conversion characteristics by a hydrothermal method in a mixed solution of absolute ethanol and deionized water. 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, and after drying, 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 obtained by this method is mainly spherical particles of TiO 2 , and the specific surface area needs to be improved. Moreover, it is used for the degradation of methylene blue dye. At the same time, this method uses dichloromethane for extraction, and the preparation process is not environmentally friendly.

[0005] CN107099287A discloses a hydrothermal preparation method of carbon quantum dots used as a visible light catalytic photosensitizer. This method uses larch as the raw material. After being treated by the high-temperature and high-pressure hydrothermal method, the dark brown solid product is removed by centrifugation and filtration to obtain a light yellow liquid product. The liquid product is centrifuged at high speed, and the centrifugation speed and time are controlled to remove insoluble small particle impurities. A dialysis bag with a certain molecular weight is used for dialysis to remove unreacted sugars, salts, etc. Then, the target product - water-soluble fluorescent carbon quantum dots is obtained by concentration. Mix it with TiO 2 to prepare a photocatalytic composite system. Using antibiotics as the model substance, the photocatalytic degradation performance of the composite system on the model substance and the action efficiency of carbon dots as the photosensitizer are investigated. This method mainly focuses on the preparation of the photosensitizer carbon quantum dots and does not mention how the carbon quantum dots and TiO 2 are combined to prepare the photocatalyst. This method still uses solid TiO 2 particles as the main catalyst, and there are still problems such as too fast recombination of electron-hole pairs and low specific surface area.

[0006] CN118616032A The present invention discloses a TiO 2 -CQDs nanoflower photocatalyst and its preparation method. This catalyst includes TiO 2 and CQDs doped with TiO 2 ; the CQDs are derived from aloe extract. The preparation method of this catalyst uses the extract obtained from natural aloe as the carbon source to provide CQDs, and modifies TiO 2 to obtain a nanoflower catalyst and a catalytic film with excellent ability to catalytically degrade polycyclic aromatic hydrocarbons. The TiO 2 -CQDs nanoflower photocatalyst prepared by this method is a solid structure, and there are still problems such as 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 its preparation method. This photocatalyst is a composite photon crystal grain formed by covalently connecting silylated carbon quantum dots and hollow titanium dioxide, and the optimal use concentration is 0.3 - 0.5 g / L. The preparation method of this photocatalyst is as follows: S1: Using citric acid as the carbon source and 3-aminopropyltriethoxysilane as the coupling agent, prepare a silylated carbon quantum dot solution; S2: Carbonize the glucose solution at 180 - 220 °C to prepare nano-carbon spheres; S3: Using the nano-carbon spheres as the inner core template and tetrabutyl titanate as the raw material, prepare hollow TiO 2 ; S4: Covalently bind carbon quantum dots and hollow TiO 2 to prepare a CQDs / TiO 2 nano-composite photocatalyst. This photocatalyst uses silylated carbon quantum dots to modify hollow TiO 2Perform surface modification to narrow its bandgap, reduce the electron-hole recombination rate, and extend the spectral response range of TiO 2 , increasing the sunlight utilization rate from 6% to 35% and enhancing the photocatalytic activity. It is applied to the degradation of methyl orange. SUMMARY OF THE INVENTION

[0008] In view of this, an object of the present invention is to provide a preparation method of a composite photocatalyst. The obtained composite photocatalyst is a core-shell structure formed by wrapping a salt of an iron-based element of a rare earth element around a TiO 2 hollow sphere; the core-shell structure is modified with carbon quantum dots. The composite photocatalyst has high utilization efficiency for visible light and can effectively degrade antibiotics. Another object of the present invention is to provide a composite photocatalyst prepared by the above preparation method. Still another object of the present invention is to provide a use of the above composite photocatalyst.

[0009] The present invention adopts the following technical solutions to achieve the above objects.

[0010] On the one hand, the present invention provides a preparation method of a composite photocatalyst, including the following steps:

[0011] 1) Mix carbon nanospheres, alkyl alcohols from C1 to C5, and alkyl titanates to obtain a mixed solution; add an aqueous solution of alkyl alcohols from C1 to C5 to the mixed solution at 40 - 90 °C for reaction to obtain a suspension; wherein, based on 100 mg of carbon nanospheres, 1 - 20 mL of alkyl titanates are added;

[0012] 2) Separate the solid and liquid of the suspension obtained in step 1), dry the obtained solid to obtain a powder; heat-treat the powder at 300 - 1000 °C to prepare TiO 2 hollow spheres;

[0013] 3) Add a salt of a rare earth element, a salt of an iron-based element, and a carboxylic acid to water to prepare a mixed solution; adjust the pH value of the mixed solution to 6 - 8, then add an alkylene glycol from C2 to C5 to the mixed solution; then add the TiO 2 hollow spheres prepared in step 2), and heat and 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); in the mixed solution, the concentration of the salt of the rare earth element is 0.01 - 0.1 mol / L; based on 1 mL of the mixed solution, 5 - 20 mg of TiO 2 hollow spheres are added;

[0014] 4) Dry the gel prepared in step 3), and then heat-treat it at 300 - 1000 °C to prepare a core-shell structured TiO 2 hollow sphere;

[0015] 5) Add the core-shell structured TiO 2 hollow spheres and carbon quantum dots to the mixed alcohol of C2-C5 alkylene glycol and C1-C5 alkyl alcohol in sequence to obtain an alcohol solution of the mixture; react the alcohol solution of the mixture at 100-500 °C to obtain a composite photocatalyst; wherein, the addition amount of the carbon quantum dots is 2.5-10 wt% of the mass of the core-shell structured TiO 2 hollow spheres.

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

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

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

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

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

[0021] According to the preparation method of the present invention, preferably:

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

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

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

[0025] According to the preparation method of the present invention, preferably:

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

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

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

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

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

[0031] S3) Perform dialysis treatment on the product solution obtained 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 of the present invention, preferably:

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

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

[0035] On the other hand, the present invention also provides a composite photocatalyst prepared by any of the above preparation methods.

[0036] On yet another aspect, the present invention also provides the use of the above composite photocatalyst in photocatalytic degradation of antibiotics.

[0037] The composite photocatalyst of the present invention has a stable structure, uniform nanoparticle size, high absorption rate of visible light, and good performance in photocatalytic degradation of antibiotics. Description of the 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 during 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-visible diffuse reflection spectrum diagram of Experimental Example 5.

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

[0045] Figure 8 It is the result diagram of tetracycline degradation in Experimental Example 7. Detailed implementation manners

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

[0047] <Preparation method of composite photocatalyst>

[0048] The preparation method of the composite photocatalyst of the present invention includes a suspension preparation step, a TiO 2 hollow sphere preparation step, a rare earth element coating step, a TiO 2 hollow sphere preparation step of core-shell structure and a modification step of carbon quantum dots. Optionally, it further includes a carbon nanosphere preparation step and a carbon quantum dot preparation step. The following is a detailed description.

[0049] Preparation steps of carbon nanospheres

[0050] In the present invention, the carbon nanospheres can be commercially available products or can be prepared by oneself. The present invention preferably prepares them by oneself.

[0051] According to a specific implementation manner of the present invention, the preparation method of the carbon nanospheres includes the following steps:

[0052] a) Heat-treat the sugar solution at 100-500 °C to obtain a heat-treated product;

[0053] b) Wash and dry the heat-treated product obtained in step a) to prepare carbon nanospheres.

[0054] According to a specific implementation manner of the present invention, 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 an implementation manner of the present invention, the sugar can be selected from at least one of monosaccharides and polysaccharides, preferably at least one of glucose, fructose, galactose, mannose, sucrose, maltose, trehalose, dextran, and starch; more preferably at least one of glucose, fructose, sucrose, maltose, and starch.

[0056] According to an implementation manner of the present invention, the heat treatment temperature of the sugar solution can be 100-500 °C, preferably 120-400 °C, and more preferably 150-300 °C. 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 invention, the heat treatment can be carried out in any high-temperature reaction equipment well-known in the art, preferably in a high-temperature reaction kettle with a polytetrafluoroethylene lining.

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

[0059] In the present invention, C1-C5 alkyl alcohols can include, but are not limited to, methanol, ethanol, propanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, isopentanol, sec-pentanol, neopentanol, etc.

[0060] The present invention does not make any special limitation on the number of washing times, and it is subject to the clarification of the washing waste liquid. The washing method can be to wash with one detergent or to use different detergents in different washing times, and no special limitation is made here.

[0061] According to an embodiment of the present invention, 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 invention, the drying time can be 1-24 h, preferably 2-20 h, and more preferably 5-18 h.

[0063] Limiting the reactant ratio and reaction conditions within the above ranges is beneficial to the stable progress of the hydrothermal carbonization method and more beneficial to the formation of carbon nanospheres.

[0064] Preparation steps of suspension

[0065] Mix carbon nanospheres, C1-C5 alkyl alcohols, and alkyl titanate to obtain a mixed solution; add an aqueous solution of C1-C5 alkyl alcohols to the mixed solution at 40-90 °C for reaction to obtain a suspension.

[0066] According to an embodiment of the present invention, the C1-C5 alkyl alcohol can be a C1-C3 alkyl alcohol, preferably a C1-C3 normal alkyl alcohol, and more preferably methanol or ethanol.

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

[0068] In the present invention, after adding carbon nanospheres to C1-C5 alkyl alcohols, the mixed solution can be ultrasonically treated.

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

[0070] Ultrasonic is beneficial to the uniform dispersion of carbon nanospheres into C1-C5 alkyl alcohols. At the same time, it can greatly reduce the binding force between nanoparticles and effectively prevent the occurrence of agglomeration phenomenon.

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

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

[0073] According to a specific embodiment of the present invention, the alkyl titanate can be dropped into the mixture of carbon nanospheres and C1-C5 alkyl alcohols under stirring.

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

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

[0076] According to a specific embodiment of the present invention, the aqueous solution of C1-C5 alkyl alcohol can be dropped under stirring conditions, and the dropping time is the reaction time.

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

[0078] TiO 2 Preparation steps of hollow 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 to 1000 °C to prepare TiO 2 hollow spheres.

[0080] In the present invention, solid-liquid separation can be achieved by any filtration method well-known in the art, and no special limitation is made herein. For example, it can be gravity filtration, pressure filtration, centrifugal filtration, vacuum filtration, etc. All kinds of filtration methods can be realized by equipment well-known in the art.

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

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

[0083] Reasonable heat treatment conditions are beneficial to the formation of the TiO 2 hollow structure.

[0084] In the present invention, the heat treatment can be carried out in any type of high-temperature heat treatment furnace well-known in the art, and no special limitation is made herein. For example but not limited to, it can be a high-temperature sintering furnace, such as a muffle furnace.

[0085] Coating step of rare earth elements

[0086] Add the salts of rare earth elements, the salts of iron-based elements and carboxylic acid into water to obtain a mixed solution; adjust the pH value of the mixed solution, and then add a C2 - C5 alkanediol into the mixed solution; then add TiO 2 hollow spheres, and heat and react to obtain a gel.

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

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

[0089] According to an embodiment of the present invention, the salt of the rare earth element can be selected from at least one of nitrates, sulfates, phosphates, acetates, carbonates, and halides of the rare earth element, preferably at least one of nitrates, sulfates, carbonates, and halides of the rare earth element, and more preferably at least one of nitrates, sulfates, and halides of the rare earth element. The salt of the rare earth element of the present invention can be either an anhydrous salt or a hydrated salt.

[0090] According to an embodiment of the present invention, the salt of the iron-based element can be selected from at least one of nitrates, sulfates, phosphates, acetates, carbonates, and halides of the iron-based element, preferably at least one of nitrates, sulfates, carbonates, and halides of the iron-based element, and more preferably at least one of nitrates, sulfates, and halides of the iron-based element. The salt of the iron-based element of the present invention can be either an anhydrous salt or a hydrated salt.

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

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

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

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

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

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

[0097] According to an embodiment of the present invention, based on the sum of rare earth elements and iron-based elements being 1 mol, the volume of C2-C5 alkylene diol added can be 0.5-5 mL, preferably 1-5 mL, more preferably 1-3 mL.

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

[0099] In the present invention, as a chelating agent, the C2-C5 alkylene diol 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 invention, based on the sum of rare earth elements and iron-based elements being 1 mol, TiO 2 The mass of the hollow spheres can be 100-600 mg, preferably 150-550 mg, more preferably 200-500 mg.

[0101] In the present invention, after adding TiO 2 hollow spheres, the mixed solution can be ultrasonically treated. The ultrasonication time can be 10-90 min, preferably 15-80 min, more preferably 20-60 min.

[0102] Ultrasonication is beneficial for the uniform dispersion of TiO 2 hollow spheres into the mixed solution. At the same time, it can greatly reduce the binding force between nanoparticles, effectively prevent the occurrence of agglomeration, and thus improve the microstructure and properties of the subsequently prepared core-shell structured TiO 2 hollow spheres.

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

[0104] In the present invention, the mixed solution can also be stirred during the heat treatment process.

[0105] Limiting the reaction product and reaction conditions within the above ranges is beneficial for the stable progress of the in-situ sol-gel deposition method and the formation of a gel, and is more beneficial for the formation of subsequent core-shell structured TiO 2 hollow spheres.

[0106] TiO with core-shell structure 2 Preparation steps of hollow spheres

[0107] The gel is dried and then heat-treated at 300-1000 °C to obtain TiO with a core-shell structure 2 hollow spheres.

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

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

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

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

[0112] Reasonable heat treatment conditions are beneficial to the formation of TiO with a core-shell structure 2 hollow spheres.

[0113] Preparation steps of carbon quantum dots

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

[0115] S1) Place the carbon source material in water, add liquid diamine to obtain a suspension;

[0116] S2) React the suspension obtained in step S1) at 100-500 °C to obtain a product solution;

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

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

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

[0120] According to an embodiment of the present invention, based on 1 g of the carbon source material, the amount of water used can be 2 to 10 mL, preferably 3 to 10 mL, and more preferably 3 to 9 mL;

[0121] According to an embodiment of the present invention, based on 1 g of the carbon source material, the addition amount of the liquid diamine can be 0.1 to 1 mL, preferably 0.2 to 0.8 mL, and more preferably 0.3 to 0.6 mL.

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

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

[0124] A reasonable reactant ratio and reaction conditions are beneficial to the stable progress of the hydrothermal method and more beneficial to the formation of carbon quantum dots.

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

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

[0127] A reasonable dialysis bag is more beneficial to efficiently dialyze out carbon quantum dots.

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

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

[0130] Modification steps of carbon quantum dots

[0131] Add the core-shell structured TiO 2 hollow spheres and carbon quantum dots to the mixed alcohol of C2-C5 alkylene glycol and C1-C5 alkyl alcohol in sequence to prepare an alcohol solution of the mixture; react the alcohol solution of the mixture at 100 to 500 °C to prepare a composite photocatalyst.

[0132] According to one embodiment of the present invention, the C2-C5 alkylene glycol can be a C2-C4 alkylene glycol, 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 invention, the C1-C5 alkyl alcohol can be a C1-C3 alkyl alcohol, preferably a C1-C3 normal alkyl alcohol, and more preferably at least one of methanol, ethanol, and n-propanol.

[0134] In the present invention, the C1-C5 alkyl alcohol may include, but is not limited to, methanol, ethanol, propanol, 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 invention, the volume ratio of the C2-C5 alkylene glycol to the C1-C5 alkyl alcohol can be 1:1 to 5, preferably 1:1 to 3, and more preferably 1:2 to 3.

[0136] In the present invention, based on 100 mg of the core-shell structured TiO 2 hollow spheres, the amount of the mixed alcohol used can be 10 to 100 mL, preferably 20 to 80 mL, and more preferably 20 to 50 mL.

[0137] According to one embodiment of the present invention, the addition amount of the carbon quantum dots can be 2.5 to 10 wt% of the mass of the core-shell structured TiO 2 hollow spheres, preferably 3 to 8 wt%, and more preferably 3 to 5 wt%.

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

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

[0140] A reasonable reactant ratio and reaction conditions are beneficial for the carbon quantum dots to be better modified on the core-shell structured TiO 2 hollow spheres to form a composite photocatalyst.

[0141] According to a specific embodiment of the present invention, it may further include the steps of centrifuging and drying the reaction product.

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

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

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

[0145] <Composite photocatalyst>

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

[0147] According to an embodiment of the present invention, the composite photocatalyst is a core-shell structure formed by wrapping a salt of an iron-based element acid of a rare earth element with TiO 2 hollow spheres as the core; the core-shell structure is modified with carbon quantum dots.

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

[0149] The specific surface area of the composite photocatalyst can be at least 12 m 2 / g, preferably 12 to 30 m 2 / g, more preferably 13 to 25 m 2 / g, even more preferably 15 to 20 m 2 / g.

[0150] The core-shell structure of the composite photocatalyst of the present invention optimizes the electronic structure, improves the separation of photo-generated carriers, enhances light absorption and extends the spectral response range in photocatalysis, thereby improving the activity and efficiency of the catalyst. The outer shell material can enhance the stability and durability of the catalyst, reduce side reactions, and increase the selectivity of the photocatalytic reaction. The outer 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 extend the service life of the catalyst and enhance its application effect in a complex reaction environment.

[0151] The salt of the iron-based element acid of the rare earth element (LaFeO 3 ) in Example 1 is a p-type semiconductor with a band gap of about 2.3 eV. It plays a role in promoting the separation and transfer of carriers in the ternary system of the composite catalyst, especially in the electron migration process of TiO 2 and CQDs. The salt of the iron-based element acid of the rare earth element can not only effectively capture TiO 2The electrons generated on it can also participate in the reaction through its own catalytic properties, further reducing the recombination of carriers and improving the migration efficiency of electrons. This can significantly enhance the efficiency of the photocatalytic reaction. The introduction of the salts of iron-based elements of rare earth elements effectively inhibits the recombination of electrons and holes and enhances the anti-recombination ability of the photocatalyst by providing additional electron-accepting sites, further improving the catalytic performance.

[0152] As an iron-based element compound, the salts of iron-based elements of rare earth elements have good thermal stability and corrosion resistance. It can improve the stability of the photocatalyst and prevent the decline of surface active sites of TiO 2 . In addition, the salts of iron-based elements of rare earth elements themselves have strong anti-pollution ability, which helps to prevent the catalyst surface from being covered by pollutants and maintain catalytic activity for a longer time.

[0153] The addition of the salts of iron-based elements of rare earth elements introduces an additional catalytic effect, which can not only improve the separation efficiency of photo-generated carriers, but also promote the progress of redox reactions through its oxygen reduction characteristics. The incorporation of the salts of iron-based elements of rare earth elements makes the working mechanism of the catalyst more diverse, forms a stronger synergistic effect, and significantly improves the overall photocatalytic performance.

[0154] As an electron acceptor, carbon quantum dots (CQDs) can promote electron transfer and significantly improve the light absorption and electron transport rates. In addition, CQDs have excellent up-conversion characteristics, which are also beneficial to the absorption of visible light, thereby enhancing the photocatalytic ability of TiO 2 .

[0155] <Use>

[0156] The present invention also provides the use of the above composite photocatalyst in the photocatalytic degradation of antibiotics.

[0157] According to an embodiment of the present invention, the degradation rate of antibiotics in antibiotic wastewater by the composite photocatalyst under visible light irradiation within 2 h is at least 90%.

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

[0159] <Testing method>

[0160] XRD determination: It is carried out using an X'Pert PRO type XRD powder diffractometer produced by Panalytical Company.

[0161] SEM determination: It is carried out using a Sigma500 type field emission scanning electron microscope produced by ZEISS Company.

[0162] TEM measurement: Conducted using a Thermo Fisher Talos F200i transmission electron microscope from the United States.

[0163] BET measurement: Conducted using a Beckman Coulter SA3100 specific surface area and pore size analyzer from the United States.

[0164] XPS measurement: Conducted using a Thermo Scientific ESCALAB QXi X-ray photoelectron spectrometer.

[0165] UV-Vis diffuse reflectance spectroscopy measurement: Conducted using a Hitachi UH4150 UV-Vis spectrophotometer from Japan.

[0166] Absorbance measurement: Conducted using a Hitachi UH4150 UV-Vis spectrophotometer from Japan.

[0167] <Raw material description>

[0168] Other raw materials in the following examples are all commercially available products unless otherwise specified. Among them, commercial TiO 2 photocatalyst was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0169] Preparation Example 1

[0170] Carbon nanospheres were prepared by 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 to a polytetrafluoroethylene-lined autoclave, seal it, and heat-treat it at 170 °C for 10 h. Centrifuge the heat-treated solution at a speed of 8000 rpm to obtain a dark brown heat-treated product. Then wash the heat-treated product alternately with deionized water and absolute ethanol 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] Carbon quantum dots (CQDs) were prepared by hydrothermal method.

[0174] Weigh 8 g of straw powder and place it in 60 mL of deionized water. Add 3 mL of ethylenediamine dropwise under stirring to obtain a suspension. Transfer the suspension to a polytetrafluoroethylene-lined autoclave, seal it, and heat-treat it at 180 °C for 10 h. Centrifuge the heat-treated solution at a speed of 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: Using carbon nanospheres as a template, prepare TiO by the sol-gel method 2 hollow spheres

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

[0178] Filter the suspension by suction filtration, and 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 TiO 2 hollow spheres (denoted as h-TiO 2 ).

[0179] Step 2: Prepare core-shell structured TiO by the in-situ sol-gel deposition method 2 hollow spheres

[0180] Dissolve La(NO 3 ) 3 ·6H 2 O (0.433 g, 1.0 mmol), Fe(NO 3 ) 3 ·9H 2 O (0.404 g, 1.0 mmol), and citric acid monohydrate (0.420 g, 2.0 mmol) in 50 mL of distilled water to obtain a mixed solution. After continuously stirring for 2 h, add ammonia water (concentration of 1 mol / L) dropwise to the mixed solution to adjust the pH value to 7.5, and then add 3 mL of ethylene glycol. Then add 600 mg of TiO 2 hollow spheres (h-TiO 2 ) for dispersion, and ultrasonically treat for 30 min to obtain a dispersion. Then heat-treat the dispersion by stirring at 90 °C for 3 h to obtain a gel.

[0181] Dry the gel in an oven at 105 °C for 5 h to obtain a powder. Place the powder in a muffle furnace and heat-treat at 600 °C for 4 h to prepare core-shell structured TiO 2 hollow spheres. The core-shell structured TiO 2 hollow spheres are TiO 2 hollow spheres (h-TiO 2 ) as the core and LaFeO 3(Denoted as LFO) The shell is formed (denoted as TLFO (TiO 2 @LaFeO 3 ))

[0182] Step 3: Prepare the composite photocatalyst

[0183] Disperse 100 mg of TLFO into a mixed alcohol of 10 mL of ethylene glycol and 20 mL of ethanol. Under stirring, add the carbon quantum dot solution prepared in Preparation Example 2 according to 3 wt% of the mass of carbon quantum dots to the mass of TLFO, and continuously stir for 12 h to obtain an alcohol solution of the mixture. Place the alcohol solution of the mixture in a high-pressure autoclave with a polytetrafluoroethylene lining, react at 180 °C for 12 h, then naturally cool the reaction product and centrifuge at a speed of 8000 rpm, discard the supernatant, and dry the precipitate in an oven at 80 °C for 10 h to obtain the composite photocatalyst (denoted as CDs-TLFO (CDs@TiO 2 @LaFeO 3 ))

[0184] Example 2

[0185] The difference from Example 1 is only that the addition amount of carbon quantum dots is different. In this example, the carbon quantum dot solution prepared in Preparation Example 2 is added according to 5 wt% of the mass of carbon quantum dots to the mass of TLFO.

[0186] Comparative Example 1

[0187] The difference from Example 1 is only that the addition amount of carbon quantum dots is different. In this example, the carbon quantum dot solution prepared in Preparation Example 2 is added according to 0.5 wt% of the mass of carbon quantum dots to the mass of TLFO.

[0188] Comparative Example 2

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

[0190] Comparative Example 3

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

[0192] Experimental Example 1

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

[0194] As can be seen from Figure 2 , the diffraction peaks of h-TiO 2 at 2θ = 25.2°, 37.8°, 48.0°, 53.8°, 55.0° and 62.6° match the (101), (004), (200), (105), (211) and (204) crystal planes respectively, mainly showing the anatase phase of TiO 2 (JCPDS No.21-1272). In the XRD pattern of h-TiO 2 , diffraction peaks of trace rutile TiO 2 phase (JCPDS No.21-1276) can also be observed. The inventors believe that this is due to the formation of trace rutile from anatase during heat treatment. At the same time, when the anatase phase and rutile phase coexist, a heterojunction will be formed, which helps to promote the separation of photogenerated carriers, thereby enhancing the photocatalytic activity of the composite photocatalyst. In addition, the strongest diffraction peaks are shown in the XRD pattern of LFO. The diffraction peaks at 2θ = 22.6°, 32.2°, 39.7°, 46.2°, 57.4° and 67.3° correspond to the (100), (110), (111), (202), (210) and (220) crystal planes (JCPDS No.37-1493) respectively. This indicates that a binary heterojunction of TiO 2 and LFO has been successfully constructed on TLFO. Compared with the diffraction peaks of 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 hardly change. 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 during the preparation process are as Figure 3 shown.

[0197] As can be seen from Figure 3 (a), the average diameter of the carbon nanospheres used as templates is about 500 nm, and the size and distribution are very uniform. In Figure 3 (b), the size of h-TiO 2 has shrunk to a certain extent. The inventors believe that this is due to the release of CO 2 during the calcination process, and the structure of h-TiO 2 is not damaged. In Figure 3 (c), when LFO is introduced, a tightly connected framework is presented between the TLFO particles, and the diameter of the TLFO particles is about 450 nm. As can be seen from Figure 3As can be seen from (d), with the deposition of CQDs during the hydrothermal process, the spherical structure of CDs-TLFO becomes more regular.

[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 hollow core-shell structure with uniform size and dimensions, 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, thus showing better adsorption and providing more active sites.

[0199] Figure 3 (g) is the size distribution diagram of CQDs, from which many black quantum dots with a size of about 10 nm can be observed (shown by the red circles in the figure). Figure 3 (h) shows the HRTEM image of CDs-TLFO. The lattice spacings of 0.35 nm, 0.32 nm, and 0.28 nm are attributed to TiO 2 (101), CQDs, and LFO(110), respectively.

[0200] As Figure 3 (i) - (n) shows, the elements La, Fe, O, Ti, and C can be detected in CDs-TLFO by elemental 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 TiO 2 and the loading of CQDs.

[0202] Experimental Example 3

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

[0204] As Figure 4 can be seen, the specific surface areas of h-TiO 2 and CDs-TLFO are 10.98 m 2 / g and 14.63 m 2 / g, respectively. Compared with h-TiO 2 , CDs-TLFO has a larger specific surface area and a denser porous structure, which is beneficial to the transfer and separation of carriers. Therefore, the inventor believes that CDs-TLFO obtains more active sites, thus further improving the photocatalytic activity of the composite photocatalyst.

[0205] Experimental Example 4

[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 the elements in TiO 2 and LFO (La, Fe, Ti, and O), which is consistent with the results of elemental analysis. The C1s peak at a binding energy of 284.8 eV was used for 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, while the peak at a binding energy of 288.6 eV is attributed to Ti-O-C, indicating that amorphous carbon is incorporated into the TiO 2 lattice. Figure 5 shows 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 the oxygen in the hydroxyl group of adsorbed water molecules, absorbed oxygen, and lattice oxygen, respectively. Among them, the absorbed oxygen at a binding energy of 531.0 eV coincides with the oxygen vacancy caused by surface oxygen defects, indicating the presence of oxygen vacancies in CDs-TLFO. Figure 5 shows 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 , shake-up satellite peaks, and Fe2p 1 / 2 . The peaks at binding energies of 711.4 eV and 727.4 eV correspond to the Fe(III) state, while the peaks at binding energies of 709.8 eV and 723.9 eV correspond to the Fe(II) state, indicating the presence of 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 the Ti2p 2 and Ti2p 3 / 2 of the hollow-structured TiO 1 / 2 , and the spin-orbit splitting of Ti2p is 5.7 eV, indicating the presence of the Ti(IV) oxidation state in CDs-TLFO. In addition, the peak at a binding energy of 459.9 eV is attributed to the Ti-C bond on TiO 2 , indicating that CQDs have been successfully incorporated into the TiO 2 lattice synthesized using carbon nanospheres as a template. Figure 5 In the La3d spectrum of 5 / 2 , the two peaks at binding energies of 834.7 eV and 851.4 eV are La3d 3 / 2。By measurement, the average difference between the two peaks is about 17 eV, indicating the presence of La(III) ions in the composite photocatalyst CDs-TLFO prepared in Example 1.

[0208] Experimental Example 5

[0209] The ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS) of the composite photocatalyst CDs-TLFO prepared in Example 1, the intermediate products h-TiO 2 , LFO, and TFLO during the preparation process were detected respectively, and the results are as Figure 6 shown.

[0210] Figure 6 shows the light absorption capabilities of CDs-TLFO, h-TiO 2 , LFO, and TFLO. As can be seen from Figure 6 , CDs-TLFO, h-TiO 2 , LFO, and TFLO all have strong absorption in the wavelength range of 250 - 620 nm. Hollow h-TiO 2 shows the maximum absorption at about 340 nm in the ultraviolet region, and the absorption edge is around 400 nm. After combining LFO with h-TiO2, TLFO shows an obvious red-shifted absorption edge, about 540 nm, indicating that its light absorption ability 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 light and near-ultraviolet regions. It can be clearly seen from the figure that the light absorption intensity of CDs-TLFO in the visible light and near-ultraviolet regions is significantly higher than that of the intermediate products h-TiO2, LFO, and TFLO. This improvement mainly utilizes the unique upconversion properties of CQDs, and this enhanced light absorption helps to improve the photocatalytic activity of the catalyst.

[0211] Experimental Example 6

[0212] Using a 300 W xenon lamp equipped with a filter as the light source and an ethanol circulation system to maintain the temperature at 20 °C, the photocatalytic degradation of tetracycline was tested. The specific method is as follows:

[0213] Dissolve 20 mg of tetracycline (TC) in 1 L of water, stir vigorously until completely dissolved, and prepare a tetracycline solution with a concentration of 20 mg / L. Then, take 40 mg of commercially available TiO 2 catalyst, h-TiO 2 , LFO, TFLO, and the composite photocatalyst prepared in Example 1 and disperse them in 50 mL of the tetracycline solution, which are respectively denoted as TiO 2 group, h-TiO 2The groups include the LFO group, the TFLO group, and the CDs-TLFO group.

[0214] The five groups of tetracycline solutions were stirred on a magnetic stirrer in the dark for 40 min to achieve adsorption equilibrium. During the photocatalysis process, 3 mL of the supernatant was aspirated 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 from the absorbance. The degradation rate of tetracycline at different time points was calculated using the following formula:

[0215]

[0216] where C 0 is the initial concentration of the solution, and C is the concentration of the solution after the reaction.

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

[0218] According Figure 7 to the calculation results, the degradation rates of tetracycline in 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] Experimental Example 7

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

[0221] 20 mg of tetracycline (TC) was dissolved in 1 L of water and stirred vigorously until completely dissolved to prepare a tetracycline solution with a concentration of 20 mg / L. Then, 40 mg of the composite photocatalysts prepared in Examples 1-2 and Comparative Examples 1-3 were respectively dispersed in 50 mL of the tetracycline solution, and were denoted as the 3CDs-TLFO group, the 5CDs-TLFO group, the 0.5CDs-TLFO group, the 1CDs-TLFO group, and the 2CDs-TLFO group, respectively.

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

[0223]

[0224] Among them, C 0 is the initial concentration of the solution, and C is the concentration of the solution after the reaction.

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

[0226] Depend on Figure 8 It can be seen that the tetracycline degradation rates of the five groups of tetracycline solutions within 2 hours are 65.6%, 76.4%, 85.5%, 92.8% and 98.6% respectively. It can be seen that the tetracycline degradation effect of the composite photocatalyst prepared in the embodiment is significantly better than that of the comparative example, and the composite photocatalyst prepared in the present invention has excellent photocatalytic degradation performance of antibiotics.

[0227] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for preparing a composite photocatalyst, comprising the following steps: 1) mixing carbon nanospheres, C1-C5 alkyl alcohols, 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 react to obtain a suspension; wherein 1-20 mL of alkyl titanate is added based on 100 mg of carbon nanospheres; 2) separating the suspension obtained in step 1) from solid and liquid, and drying the obtained solid to obtain powder; heat treating the powder at 300-1000° C. to obtain TiO2 hollow spheres; 3) adding a salt of a rare earth element, a salt of an iron element and a carboxylic acid into water to obtain a mixed solution; adjusting the pH value of the mixed solution to 6-8, and then adding a C2-C5 alkanediol into the mixed solution; then adding the TiO2 hollow spheres obtained in step 2), heating and reacting to obtain a gel; wherein the molar ratio of the rare earth element, the iron element and the carboxylic acid is (1-5):(1-5):(5-20); in the mixed solution, the concentration of the salt of the rare earth element is 0.01-0.1 mol / L; adding 5-20 mg of the TiO2 hollow spheres to 1 mL of the mixed solution; 4) drying the gel obtained in step 3), and then heat-treating it at 300-1000° C. to obtain TiO2 hollow spheres with a core-shell structure; 5) The core-shell structured TiO2 hollow spheres and carbon quantum dots obtained in step 4) are sequentially added to a mixed alcohol of C2-C5 alkanediol and C1-C5 alkyl alcohol to obtain an alcohol solution of the mixture; the alcohol solution of the mixture is reacted at 100-500°C to obtain a composite photocatalyst; wherein the amount of carbon quantum dots added is 2.5-10wt% of the mass of the core-shell structured TiO2 hollow spheres.

2. The preparation method according to claim 1, characterized in that: The preparation method of the carbon nanospheres comprises the following steps: a) heat treating the sugar solution at 100-500° C. 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 carbon nanospheres.

3. The preparation method according to claim 2, characterized in that: The sugar is selected from at least one of monosaccharides and polysaccharides.

4. The preparation method according to claim 1, characterized in that: The alkyl titanate is tetraalkyl titanate.

5. The preparation method according to claim 1, characterized in that: In step 3), the rare earth element is selected from at least one of lanthanum, cerium, neodymium, praseodymium, terbium and dysprosium; In step 3), the iron-based element is selected from at least one of iron, cobalt and nickel; In step 3), the carboxylic acid is selected from at least one of citric acid, tartaric acid, malic acid, oxalic acid and ascorbic acid.

6. The preparation method according to claim 1, characterized in that: In step 3), the salt of the rare earth element is selected from at least one of nitrates, sulfates, phosphates, acetates, carbonates and halides of the rare earth element; In step 3), the salt of the iron-based element is selected from at least one of nitrates, sulfates, phosphates, acetates, carbonates and halides of the iron-based element.

7. The preparation method according to claim 1, characterized in that: The method for preparing carbon quantum dots comprises the following steps: S1) placing a carbon source in water and adding a liquid diamine to obtain a suspension; wherein 0.1 to 1 mL of the liquid diamine is added based on 1 g of the carbon source; S2) reacting the suspension obtained in step S1) at 100-500° C. to obtain a product solution; S3) dialyzing the product solution obtained in step S2) in a dialysis bag with a molecular weight cutoff of 1000 to 5000 Da to obtain carbon quantum dots.

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

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

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

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