Carbon dot-anatase titanium dioxide composite photocatalyst and preparation method and application thereof

Abstract

This invention relates to a carbon dot-anatase titanium dioxide composite photocatalyst, its preparation method, and its application. The preparation method includes adding a titanium source to a carbon dot dispersion and adjusting the pH to obtain a mixed system; stirring the mixed system to react and obtain the carbon dot-anatase titanium dioxide composite photocatalyst. The preparation method of this invention achieves one-pot in-situ composite formation of carbon dots and titanium dioxide during the initial hydrolysis of the titanium source and the pre-crystallization stage of titanium dioxide, unlike the stepwise loading method of the prior art which first prepares titanium dioxide and then loads carbon dots. It eliminates the need for high-temperature calcination and has the advantages of mild preparation conditions, simple process, and low energy consumption. This invention, through low-temperature in-situ construction, allows carbon dots to stably bind to the surface of titanium dioxide and form a defect coupling interface structure, thereby enhancing the visible light absorption capacity of the composite material and the separation and transport efficiency of photogenerated carriers, and improving the visible light photocatalytic activity of titanium dioxide.

Description

Technical Field

[0001] This invention relates to the field of carbon dot-titanium dioxide composite catalyst technology, specifically to a carbon dot-anatase titanium dioxide composite photocatalyst, its preparation method, and its application. Background Technology

[0002] Compared with traditional physical adsorption and chemical precipitation technologies, semiconductor photocatalysis technology can use light energy to drive redox reactions under normal temperature and pressure conditions, degrading or reducing pollutants into small molecules with lower toxicity or even harmlessness, and has good application prospects in the field of environmental pollution control.

[0003] Titanium dioxide (TiO2) has become one of the most widely used photocatalytic materials due to its advantages such as low toxicity, high chemical stability, low cost, and readily available raw materials. Among them, anatase TiO2 has attracted widespread attention due to its high photocatalytic activity. However, anatase TiO2 still suffers from drawbacks such as a large band gap, narrow visible light response range, and rapid recombination rate of photogenerated electron-hole pairs, which severely limit its solar energy utilization efficiency and practical application effects. To improve the photocatalytic performance of TiO2, existing technologies typically employ methods such as metal doping, semiconductor composites, or carbon material modification to expand its visible light absorption range and promote the separation and transport of photogenerated carriers. However, these methods generally suffer from complex preparation processes, reliance on high-temperature calcination or energy-intensive hydrothermal treatment processes, insufficient interfacial bonding, and the risk of metal leaching in some modified systems, making it difficult to simultaneously achieve green and low-energy preparation and high-efficiency photocatalytic performance.

[0004] Carbon quantum dots (CDOs), as a novel type of carbon-based nanomaterial, possess excellent light absorption properties, electron transport capabilities, and abundant surface functional groups, making them an effective modifying component for improving the visible light response and interfacial charge separation efficiency of TiO2. Biomass-derived CDOs, in particular, have attracted widespread attention in recent years due to their wide availability, low cost, and good biocompatibility. However, most existing CDO-TiO2 composite technologies involve preparing CDOs and TiO2 separately, followed by impregnation, adsorption, hydrothermal composite treatment, or calcination to achieve subsequent loading. Essentially, these methods still belong to post-assembly or stepwise construction approaches. These methods not only have lengthy processes, but the interaction between CDOs and TiO2 is primarily physical adsorption or surface adhesion, making it difficult to form stable and tight interfacial chemical coupling under mild conditions. This limits the visible light utilization efficiency and photogenerated carrier separation efficiency of the composite material.

[0005] Therefore, there is an urgent need to develop a yeast-derived carbon dot-titanium dioxide composite photocatalyst and its preparation method that does not require high-temperature calcination or precious metal co-catalysts, has mild preparation conditions, and is suitable for large-scale preparation, in order to meet the application needs of water pollution control such as organic pollutant degradation and heavy metal ion reduction. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of long process flow, insufficient interfacial bonding and reliance on high-temperature calcination in the preparation of existing carbon dot-titanium dioxide composite materials.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst, comprising, After adding the titanium source to the carbon dot dispersion, the pH was adjusted to obtain a mixed system; The mixture was stirred and reacted to obtain a carbon dot-anatase titanium dioxide composite photocatalyst.

[0008] Furthermore, the concentration of the titanium source is 1-3 mol / L; The concentration of the carbon dot dispersion is 1-1.5 g / L; The volume ratio of the titanium source to the carbon dot dispersion is 1:5-10.

[0009] Furthermore, the titanium in the titanium source is derived from at least one of titanium tetrachloride, titanium oxysulfate, titanium ester, and titanium alkoxide.

[0010] Furthermore, the mass ratio of carbon dots in the carbon dot dispersion to titanium dioxide theoretically generated from the titanium source is 0.02-0.1:1.

[0011] Furthermore, the pH of the mixture is 1.5-3.0.

[0012] Furthermore, the stirring reaction is carried out at a temperature of 20-60℃ and a rotation speed of 200-500 rpm for 24-72 hours.

[0013] Furthermore, the methods for preparing carbon dots include, The carbon source is dispersed in a solvent, followed by a solvothermal reaction. After the reaction, the carbon is separated, filtered, dialyzed, concentrated, and dried to obtain carbon dots.

[0014] Furthermore, the mass-to-volume ratio of the carbon source to the solvent is 1g:5-20mL; The solvothermal activity is maintained at 180-220℃ for 8-12 hours; The average particle size of the carbon dots is 3-4 nm.

[0015] This invention also provides a carbon dot-anatase titanium dioxide composite photocatalyst, which is prepared by the above-described method.

[0016] This invention also provides the application of the above-mentioned carbon dot-anatase titanium dioxide composite photocatalyst in photocatalytic degradation of organic matter and reduction removal of heavy metal elements.

[0017] Compared with the prior art, the beneficial effects of the present invention include: The preparation method of the present invention achieves one-pot in-situ composite of carbon dots and titanium dioxide in the initial hydrolysis of titanium source and the pre-crystallization stage of titanium dioxide. Unlike the stepwise loading method of the prior art which first prepares titanium dioxide and then loads carbon dots, it does not require high-temperature calcination and has the advantages of mild preparation conditions, simple process and low energy consumption.

[0018] This invention utilizes a low-temperature in-situ construction method to stably bond carbon dots to the surface of titanium dioxide and form a defect coupling interface structure, thereby enhancing the visible light absorption capacity of the composite material and the separation and transport efficiency of photogenerated carriers, and improving the visible light photocatalytic activity of titanium dioxide.

[0019] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0021] Figure 1 A flowchart of the preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst of the present invention is shown; Figure 2 The transmission electron microscope image of the yeast-derived carbon dots prepared according to the present invention is shown; Figure 3 A transmission electron microscope (TEM) image of the composite catalyst prepared in Example 1 is shown. Figure 4 A high-resolution transmission electron microscope image of the composite catalyst prepared in Example 1 is shown; Figure 5 Transmission electron microscopy (TEM) image and average particle size distribution of UC-TiO2 prepared in Comparative Example 2 are shown. Figure 6 The XRD patterns of the catalysts obtained in Examples 1-3 and Comparative Examples 1-3 are shown. Figure 7 The FTIR spectra of the catalysts obtained in Examples 1-3 and Comparative Examples 1-3 are shown. Figure 8 The UV-vis DRS spectra of the catalysts obtained in Examples 1-3 and Comparative Examples 2-3 are shown. Figure 9The TRPL spectra of the catalysts obtained in Examples 1-3 and Comparative Examples 2-3 are shown. Figure 10 Visible light photocatalytic degradation curves of RhB by the catalysts of the examples and comparative examples are shown. Figure 11 The photocatalytic reduction curves of Cr(VI) by the catalysts of the examples and comparative examples are shown; Figure 12 The graph shows the cycle stability test results of the catalyst in Example 1 for the photocatalytic degradation efficiency of RHB; Figure 13 The graph shows the cycle stability test results of the catalyst of Example 1 for the photocatalytic reduction efficiency of Cr(VI); Figure 14 The FTIR spectra of the catalyst of Example 1 before and after cyclic testing of RHB photocatalytic degradation and Cr(VI) photocatalytic reduction are shown. Figure 15 XPS spectra of the catalyst of Example 1 before and after cyclic testing of RHB photocatalytic degradation and Cr(VI) photocatalytic reduction are shown. Detailed Implementation

[0022] Titanium dioxide possesses many unique advantages, including stable chemical properties, excellent photoelectrochemical properties, resistance to photocorrosion, non-toxicity to organisms, and abundant sources, making it commonly used in photocatalysis. However, due to its wide band gap (3.0 eV for rutile and 3.2 eV for anatase), titanium dioxide generally only absorbs short-wavelength ultraviolet light, resulting in low solar energy utilization (only 3%-5%). Furthermore, the recombination of electrons and holes generated by photoexcitation leads to low quantum efficiency, limiting its applications. Carbon dots possess unique photoinduced electron transfer and electron storage properties. Numerous studies have demonstrated that carbon dot-carbon dioxide composites can broaden the photoresponse range, enhance the photoresponse current, and extend the lifetime of photogenerated electrons. However, due to the weak crystallinity of titanium dioxide prepared in low-temperature liquid phases, the preparation of carbon dot-carbon dioxide composites typically involves combining high-temperature calcined titanium dioxide with carbon dots, or preparing carbon dots with titanium precursors under high temperature and high pressure hydrothermal conditions. These methods not only have a long process flow, but also rely mainly on physical adsorption or surface adhesion between carbon dots and titanium dioxide, making it difficult to form a stable and tight interfacial chemical coupling under mild conditions.

[0023] Therefore, the present invention provides a method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst, comprising, After adding the titanium source to the carbon dot dispersion, the pH was adjusted to obtain a mixed system; The mixture was stirred and reacted to obtain a carbon dot-anatase titanium dioxide composite photocatalyst.

[0024] As some preferred embodiments, the concentration of the titanium source is 1-3 mol / L; the concentration of the carbon dot dispersion is 1-1.5 g / L; the volume ratio of the titanium source to the carbon dot dispersion is 1:5-10.

[0025] In some preferred embodiments, the pH of the mixed system is 1.5-3.0. Preferably, 20%-28% ammonia is used to adjust the pH. This avoids rapid hydrolysis and local precipitation of titanium tetrachloride caused by strong alkali, facilitating slow nucleation and growth of titanium dioxide under slightly acidic conditions. Furthermore, ammonia, as a volatile alkali source, introduces fewer other impurities (Na₂O₃). + K + This is beneficial for obtaining carbon dot / anatase TiO2 composite materials with better dispersion and tighter interfacial bonding.

[0026] As some preferred embodiments, the stirring reaction is carried out at a temperature of 20-60°C and a rotation speed of 200-500 rpm for 24-72 hours.

[0027] The titanium source is prepared by dissolving a titanium-containing substance in a first solvent. The type of titanium-containing substance is not strictly limited, but can be at least one of titanium tetrachloride, titanium oxysulfate, titanate ester, titanium alkoxide, etc., with titanium tetrachloride being the most preferred. The first solvent for dissolving the titanium-containing substance is also not strictly limited, but can be at least one of water, ethanol, acetone, etc. Some titanium-containing substances are easily hydrolyzed, and the first solvent only needs to ensure the stability of the reaction.

[0028] The carbon dot dispersion is prepared by dispersing carbon dots in a second solvent. The second solvent for dispersing carbon dots does not need to be strictly limited. For example, it can be at least one of water, ethanol, acetone, etc. The second solvent needs to ensure that the carbon dots are well dispersed and will not cause severe hydrolysis of titanium after mixing with the titanium source.

[0029] Methods for preparing carbon dots include, The carbon source was dispersed in a third solvent at a mass-volume ratio of 1g:5-20mL, followed by a solvothermal reaction at 180-220℃ for 8-12 hours. After the reaction, the carbon source was separated, filtered, dialyzed, concentrated and dried to obtain carbon dots.

[0030] The type of carbon source is not strictly limited, but can be, for example, at least one of sugars and small molecule organic compounds (glucose, sucrose, citric acid, dicarboxylic acid, glutathione, etc.), natural biomass (pine needles, leaves, traditional Chinese medicine, soybean residue, shiitake mushrooms, shrimp shells, etc.), natural polymers and derivatives (chitosan, gelatin, etc.), and other complexes (such as yeast powder). The third solvent can be selected from at least one of water, ethanol, N,N-dimethylformamide, ethylene glycol, glycerol, etc.

[0031] The separation is performed by centrifugation; the filtration is performed using a 0.22μm filter membrane; the dialysis is performed using a dialysis bag with a molecular weight cutoff of 1000Da, and the dialysis time is 48-72h.

[0032] As some preferred embodiments, the mass ratio of carbon dots in the carbon dot dispersion to titanium dioxide theoretically generated from the titanium source is 0.02-0.1:1.

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] The highly active dry yeast used in the examples and comparative examples was purchased from Angel Yeast Co., Ltd. (Yichang, Hubei Province), and the titanium tetrachloride solution was purchased from Thermo Fisher Scientific (China) Co., Ltd. (Shanghai) with a concentration of 2 mol / L and was used directly.

[0037] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0038] Example 1 like Figure 1 As shown, a method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst includes the following steps: Step 1: Preparation of yeast-derived carbon dots: Weigh 2g of yeast powder and disperse it in 20mL of deionized water. Sonicate for 15min to break up the cell walls. Transfer the mixture to a 50mL PTFE-lined stainless steel reactor and react at 200℃ for 10h. After the reaction, filter through a 0.22μm membrane. Place the filtrate in a dialysis bag with a molecular weight cutoff of 1000Da and dialyze in the dark for 72h, changing the deionized water periodically. After dialysis, concentrate by rotary evaporation and freeze-dry to obtain yeast-derived carbon dot powder, denoted as Y-CD.

[0039] Step 2, Preparation of the composite photocatalyst: Weigh 50 mg of yeast-derived carbon dot powder and add it to 40 mL of deionized water, stirring to disperse. Slowly add 6.25 mL of a 2 mol / L TiCl4 solution to the resulting dispersion, and adjust the pH of the system to 2.0 with 20% ammonia water to obtain a mixed system. Place the mixed system at 40℃ and stir continuously at 300 rpm for 48 h. After the reaction is complete, centrifuge at 10000 rpm for 10 min, collect the precipitate, wash it with deionized water until the supernatant is nearly neutral, and dry it at 60℃ to obtain the composite photocatalyst. In this example, the mass ratio of carbon dots to titanium dioxide theoretically generated from the titanium source is 0.05:1, so the composite catalyst is denoted as 0.05Y-CD / UC-TiO2.

[0040] Example 2 Compared with Example 1, the difference is that in step 2, the amount of yeast-derived carbon dot powder is changed to 20 mg, and the composite catalyst is recorded as 0.02Y-CD / UC-TiO2.

[0041] Example 3 Compared with Example 1, the difference is that in step 2, the amount of yeast-derived carbon dot powder is changed to 100 mg, and the composite catalyst is recorded as 0.10Y-CD / UC-TiO2.

[0042] Comparative Example 1 A method for preparing yeast-derived carbon dots is the same as step 1 in Example 1, and will not be repeated here.

[0043] Comparative Example 2 A method for preparing anatase titanium dioxide is the same as step 2 in Example 1, and will not be repeated here. The prepared material will be referred to as UC-TiO2.

[0044] Comparative Example 3 Commercial P25 titanium dioxide.

[0045] Comparative Example 4 A method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst includes the following steps: Step 1: Preparation of yeast-derived carbon dots: Weigh 2g of yeast powder and disperse it in 20mL of deionized water. Sonicate for 15min to break up the cell walls. Transfer the mixture to a 50mL PTFE-lined stainless steel reactor and react at 200℃ for 10h. After the reaction, filter through a 0.22μm membrane. Place the filtrate in a dialysis bag with a molecular weight cutoff of 1000Da and dialyze in the dark for 72h, changing the deionized water periodically. After dialysis, concentrate by rotary evaporation and freeze-dry to obtain yeast-derived carbon dot powder, denoted as Y-CD.

[0046] Step 2, Preparation of anatase titanium dioxide: 6.25 mL of a 2 mol / L TiCl4 solution was slowly added dropwise to 40 mL of deionized water. The pH of the system was adjusted to 2.0 with 20% ammonia solution to obtain a mixed system. The mixed system was placed at 40℃ and stirred continuously at 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged at 10000 rpm for 10 min, the precipitate was collected, washed with deionized water until the supernatant was nearly neutral, and dried at 60℃ to obtain uncalcined anatase titanium dioxide.

[0047] Step 3: Preparation of the composite photocatalyst: Weigh 50 mg of yeast-derived carbon dot powder and 1000 mg of uncalcined anatase titanium dioxide, add them to 40 mL of deionized water, and sonicate for 30 min to ensure uniform dispersion. Stir continuously at 40 °C for 48 h to ensure sufficient contact between the yeast-derived carbon dots and titanium dioxide. After the reaction, centrifuge at 10000 rpm for 10 min, collect the precipitate, wash it 2-3 times with deionized water, and dry it at 60 °C to obtain the composite photocatalyst, denoted as 0.05Y-CD / UC-TiO2 (post-adsorption).

[0048] Comparative Example 5 A method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst includes the following steps: 50 mg of yeast-derived carbon dot powder and 1000 mg of commercial P25 titanium dioxide were added to 40 mL of deionized water and sonicated for 30 min to ensure uniform dispersion. The mixture was then stirred continuously at 300 rpm for 48 h at 40 °C to ensure sufficient contact between the yeast-derived carbon dots and titanium dioxide. After the reaction was complete, the mixture was centrifuged at 10000 rpm for 10 min, the precipitate was collected, washed 2-3 times with deionized water, and dried at 60 °C to obtain the composite photocatalyst, denoted as 0.05Y-CD / P25 (post-adsorption).

[0049] Test case like Figure 2 As shown, transmission electron microscopy reveals that the Y-CD prepared in Example 1 consists of zero-dimensional spherical nanoparticles with an average particle size of approximately 3.55 nm, exhibiting good size uniformity. This indicates that the method of the present invention can successfully prepare yeast-derived carbon dots. Figure 3 As shown, the average particle size of the 0.05Y-CD / UC-TiO2 prepared in Example 1 is approximately 4.97 nm, and significant agglomeration is observed between the particles. Figure 4 High-resolution transmission electron microscopy images show that smaller Y-CD particles are dispersed on a larger UC-TiO2 surface, indicating that yeast-derived carbon dots and uncalcined anatase titanium dioxide have achieved effective composite. In addition, obvious (101) lattice fringes of anatase TiO2 can be seen, indicating that it has good crystallinity. Figure 5 The microstructure and average particle size distribution of UC-TiO2 prepared in Comparative Example 2 are shown. Its average size is 4.38 nm, and there is some agglomeration. Compared with commercial P25 titanium dioxide (average particle size of about 21 nm), UC-TiO2 has relatively low crystallinity, but smaller particle size, which is beneficial to provide more exposed active sites.

[0050] Figure 6 The XRD patterns of the materials obtained in Examples 1-3 and Comparative Examples 1-3 are shown. It can be seen that the UC-TiO2 prepared in Comparative Example 2 is anatase crystal. The positions of the diffraction peaks of the composite catalysts in Examples 1-3 are basically the same as those in Comparative Example 2, indicating that the introduction of yeast-derived carbon dots did not destroy the crystal structure of titanium dioxide. Figure 7 The infrared spectra of the materials obtained in Examples 1-3 and Comparative Examples 1-3 are shown. It can be seen that the composite catalysts of Examples 1-3 have changed in the position or intensity of the relevant absorption peaks compared with Comparative Example Y-CD and Comparative Example 2 UC-TiO2, indicating that there is a strong interfacial interaction between yeast-derived carbon dots and titanium dioxide.

[0051] Figure 8The UV-Vis diffuse reflectance spectra of the materials obtained in Examples 1-3 and Comparative Examples 2-3 are shown. It can be seen that the composite catalysts of Examples 1-3 exhibit stronger visible light absorption capacity compared with UC-TiO2 in Comparative Example 2 and commercial P25 titanium dioxide in Comparative Example 3. This indicates that the introduction of yeast-derived carbon dots helps to expand the light response range of the materials. In addition, the amount of yeast-derived carbon dots can further optimize and adjust the absorption performance of the composite catalyst for visible light. Figure 9 The time-resolved photoluminescence spectra of the materials obtained in Examples 1-3 and Comparative Examples 2-3 are shown. It can be seen that the transient fluorescence decay behavior of the composite catalysts in Examples 1-3 is significantly different from that in Comparative Examples 2-3, indicating that the introduction of Y-CD is beneficial to improving the interfacial charge separation and carrier migration process of the composite material.

[0052] To investigate the photocatalytic performance of the materials in the examples and comparative examples, Rhodamine B was degraded and hexavalent chromium was reduced and removed under simulated visible light. The simulated visible light was achieved using a 300W xenon lamp equipped with a cutoff filter with a wavelength greater than 420 nm.

[0053] Rhodamine B degradation test: 100 mg of catalyst was dispersed in 100 mL of a 30 mg / L Rhodamine B (RhB) solution. After adsorption by stirring in the dark for 30 min, a photocatalytic reaction was carried out. Samples were taken every 10 min, and the absorbance at 554 nm was measured. The degradation rate was calculated using the following formula:

[0054] Degradation rate (%) = (A0 - A) t ) / A0×100%; Where A0 is the initial absorbance, A t denoted as absorbance at time t.

[0055] Hexavalent chromium reduction test: 100 mg of catalyst was dispersed in 100 mL of 20 mg / L Cr(VI) solution, stirred and adsorbed in the dark for 30 min, and then subjected to light irradiation. Samples were taken at regular intervals, and the absorbance at 540 nm was measured using the diphenylcarbazide method, and the Cr(VI) reduction rate was calculated.

[0056] The blank control group (labeled as control) is the experimental result obtained under the same photocatalytic reaction conditions as in Example 1, but without the addition of a catalyst.

[0057] Figure 10 and Figure 11The visible light photocatalytic degradation performance of RhB and the visible light photocatalytic reduction performance of Cr(VI) are shown in the examples and comparative examples, respectively. It can be seen that the 0.05Y-CD / UC-TiO2 composite photocatalyst obtained in Example 1 exhibits the best photocatalytic performance under visible light irradiation conditions, with a degradation rate of over 99% after reacting with 30 mg / L RhB solution for 30 min and a reduction rate of over 99% after reacting with 20 mg / L Cr(VI) solution for 60 min. Kinetic fitting results show that its apparent reaction rate constants for RhB degradation and Cr(VI) reduction are 29.5 times and 60.2 times that of commercial P25, respectively. However, the photocatalytic performance of Comparative Example 1 (Y-CD), Comparative Example 2 (UC-TiO2), Comparative Example 3 (commercial P25), and Comparative Example 4 [0.05Y-CD / UC-TiO2 (post-adsorption)] and Comparative Example 5 [0.05Y-CD / P25 (post-adsorption)] were all lower than that of the composite catalysts of Examples 1-3 of this invention. This indicates that the improvement in the photocatalytic performance of the composite photocatalyst of this invention does not originate from the simple post-adsorption or mixing of yeast-derived carbon dots, but is related to the interfacial binding state formed by low-temperature in-situ construction.

[0058] Figure 12 and Figure 13 The cycle stability test results of the composite catalyst in Example 1 for the visible light photocatalytic degradation of RhB and the visible light photocatalytic reduction of Cr(VI) are shown respectively. It can be seen that after 5 cycles, it still maintains high RhB degradation efficiency and Cr(VI) reduction efficiency. The FTIR and XPS characterization results of the samples before and after cycling are shown below. Figure 14 and Figure 15 As shown, no obvious abnormal changes were observed in the spectrum, indicating that the composite photocatalyst has good structural stability and recyclability.

[0059] Overall, the preparation method of the present invention achieves one-pot in-situ composite of carbon dots and titanium dioxide during the initial hydrolysis of titanium source and the pre-crystallization stage of titanium dioxide. This is different from the stepwise loading method of the prior art, which first prepares titanium dioxide and then loads carbon dots. It does not require high-temperature calcination and has the advantages of mild preparation conditions, simple process and low energy consumption.

[0060] This invention utilizes a low-temperature in-situ construction method to stably bond carbon dots to the surface of titanium dioxide and form a defect coupling interface structure, thereby enhancing the visible light absorption capacity of the composite material and the separation and transport efficiency of photogenerated carriers, and improving the visible light photocatalytic activity of titanium dioxide.

[0061] In summary, the preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst provided by this invention has mild preparation conditions, does not require high-temperature calcination, and the obtained material has excellent visible light photocatalytic activity, good cycle stability, and promising application prospects.

[0062] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a carbon dot-anatase titanium dioxide composite photocatalyst, characterized by, include, After adding the titanium source to the carbon dot dispersion, the pH was adjusted to obtain a mixed system; The mixture was stirred and reacted to obtain a carbon dot-anatase titanium dioxide composite photocatalyst.

2. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1, characterized in that, The concentration of the titanium source is 1-3 mol / L; The concentration of the carbon dot dispersion is 1-1.5 g / L; The volume ratio of the titanium source to the carbon dot dispersion is 1:5-10.

3. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1, characterized in that, The titanium in the titanium source is derived from at least one of titanium tetrachloride, titanium oxysulfate, titanium ester, and titanium alkoxide.

4. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1 or 2, characterized in that, The mass ratio of carbon dots in the carbon dot dispersion to titanium dioxide theoretically generated from the titanium source is 0.02-0.1:

1.

5. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1, characterized in that, The pH of the mixture is 1.5-3.

0.

6. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1, characterized in that, The stirring reaction was carried out at a temperature of 20-60℃ and a rotation speed of 200-500 rpm for 24-72 hours.

7. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 1, characterized in that, Methods for preparing carbon dots include, The carbon source is dispersed in a solvent, followed by a solvothermal reaction. After the reaction, the carbon is separated, filtered, dialyzed, concentrated, and dried to obtain carbon dots.

8. The preparation method of the carbon dot-anatase titanium dioxide composite photocatalyst according to claim 7, characterized in that, The mass-to-volume ratio of the carbon source to the solvent is 1g:5-20mL; The solvothermal activity is maintained at 180-220℃ for 8-12 hours; The average particle size of the carbon dots is 3-4 nm.

9. A carbon dot-anatase titanium dioxide composite photocatalyst, characterized in that, It is obtained by the preparation method according to any one of claims 1-8.

10. The application of the carbon dot-anatase titanium dioxide composite photocatalyst as described in claim 9 in the photocatalytic degradation of organic matter and the reduction and removal of heavy metal elements.

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