TiO2 / CNQDs / fluorescein composite photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of composite photocatalysts, and discloses a TiO2 / CNQDs / fluorescein composite photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing mesoporous TiO2 with a nano porous structure; the preparation method comprises the following steps: uniformly mixing urea and trisodium citrate, and carrying out low-temperature solid-phase reaction to obtain a solid mixture containing CNQDs; dispersing the CNQDs in ethanol for dialysis and purification to obtain a CNQDs ethanol solution; the preparation method comprises the following steps: dispersing a fluorescein compound, a CNQDs ethanol solution and mesoporous TiO2 in a mixed solution, stirring for reaction, and drying to obtain the TiO2 / CNQDs / fluorescein composite photocatalyst. According to the TiO2 / CNQDs / fluorescein composite photocatalyst prepared by the invention, an independent nano space is used as an active reaction site, a carrier migration path is shortened through a nano confinement effect, light scattering is increased for multiple times, the light energy utilization rate is increased, and reactants are enriched; meanwhile, the photocatalytic hydrogen evolution efficiency and stability are remarkably improved under the conditions of wide light response range, strong interfacial force and good wettability and being independent of noble metals.

Description

Technical Field

[0001] This application relates to the field of composite photocatalyst technology, and in particular to a TiO2 / CNQDs / fluorescein composite photocatalyst, its preparation method and application. Background Technology

[0002] Against the backdrop of "carbon peaking" and "carbon neutrality," the global energy system is shifting from a fossil fuel-dominated structure to a clean energy structure based on renewable energy. In current international energy strategies, the combination of solar energy and hydrogen energy has attracted significant attention and is considered one of the core pathways to achieving deep decarbonization. This method uses solar energy to decompose water and produce hydrogen, effectively converting intermittent electricity into storable hydrogen energy, forming a true renewable energy closed loop. It not only solves the problems of intermittent solar energy and difficulty in storage, but also alleviates the issues of excessive reliance on fossil fuel production, high pollution, and difficulty in widespread implementation of hydrogen energy.

[0003] TiO2 is a relatively mature inorganic semiconductor in the field of photocatalytic hydrogen evolution. Due to its unparalleled photochemical stability, suitable bandgap position, and mature physicochemical properties, it has become an indispensable structural pillar and functional carrier unit in photocatalytic hydrogen production research. Current research on high-performance modified TiO2 photocatalytic materials mainly includes microstructure control, defect engineering, doping modification, and heterostructure construction, aiming to enhance its photocatalytic performance by improving light absorption capacity, carrier separation efficiency, and surface reactivity. For example, patent CN119909664A uses a heterometallic doping-molten salt-mediated high-temperature heat treatment method to control the crystal planes and defects of TiO2, preparing rutile TiO2 with selective exposure of {101} and {110} crystal planes and low defect concentration doping. This achieves synergistic control of the microstructure and surface and bulk defects of rutile titanium dioxide, thereby improving the separation efficiency of photogenerated charges in the bulk phase of rutile titanium dioxide, improving surface activity, and increasing the photocatalytic hydrogen production activity by tens of times. However, its photocatalytic efficiency is low, with the best photocatalytic efficiency being only ~280 μmol·g. -1 ·h -1 Patent CN118874461A describes the preparation of gold (Au)-modified TiO2 composite photocatalytic materials via a solvothermal method. The Au doping effectively improves the absorption of visible light by TiO2, increasing the photocatalytic efficiency to 3379 μmol·g. -1 ·h -1However, Au is a precious metal, which greatly increases the cost of its application in photocatalytic water splitting. Furthermore, this type of nano-Au is usually loaded onto the TiO2 surface in the form of nanoclusters, resulting in low atom economy. Patent CN118874464A first prepared np-type homojunction TiO2 using a hydrothermal and sintering method, and then uniformly dispersed Cu2O particles on TiO2 using a chemical precipitation method, successfully constructing an npp-type ternary heterojunction. This not only extended the photoresponse range to 400 nm, but also increased the photocatalytic hydrogen production rate by 100% compared to the original nP-type homojunction TiO2 material, to approximately 5020 μmol·g. -1 ·h -1 However, the preparation process of this composite photocatalytic material is complex, and its response to visible light remains limited. Furthermore, Cu2O is susceptible to photocorrosion, exhibits poor stability, and the dissolution of transition metal ions can lead to secondary pollution. Although some progress has been made in the research of TiO2-based photocatalytic materials, problems remain, including a narrow light absorption range, insufficient stability, easy recombination of photogenerated carriers, dependence on noble / transition metals, and photoelectrocatalysis. Therefore, the construction of stable, efficient, and environmentally friendly TiO2-based photocatalytic hydrogen evolution materials is urgently needed.

[0004] Graphitic carbon nitride quantum dots (CNQDs) have great potential for improving the hydrogen production performance of TiO2-based photocatalytic materials through water splitting due to their low cost, resistance to photocorrosion, non-toxicity, ease of preparation, and significant quantum confinement and edge effects. The matched and tunable band structure of CNQDs allows them to form type II or Z-type heterojunctions with TiO2 to improve carrier separation efficiency. Furthermore, the abundant surface states of CNQDs can provide active / adsorption sites for composite photocatalysts. However, there are few reports on the photocatalytic water splitting of TiO2 / CNQDs heterojunction composites. The main limitations are: 1) CNQDs have poor wettability, which limits the adsorption and activation of water molecules and hinders the transfer of photocarriers after loading them onto the TiO2 surface; 2) Although CNQDs can be used as photosensitizers to sensitize TiO2, their energy level modulation is limited, and their absorption of visible light is still weak; 3) The preparation process is cumbersome and lacks stability. For example, the TiO2 / CNQDs heterojunction composite prepared by vapor deposition requires harsh conditions such as high temperature and high pressure, and it relies on van der Waals forces as interfacial forces. CNQDs are prone to desorption, which also reduces the separation and migration efficiency of photogenerated carriers; or the high-temperature sintering method is not only energy-intensive, but also prone to introducing uncontrollable defects, resulting in poor reproducibility; 4) It relies on noble / transition metals, which is costly and poses environmental pollution problems.

[0005] Therefore, there is an urgent need to develop novel, highly efficient TiO2 / CNQDs heterojunction photocatalytic composite materials. Summary of the Invention

[0006] This application provides a TiO2 / CNQDs / fluorescein composite photocatalyst, its preparation method, and its application, aiming to solve the technical problems of narrow light response range, weak interfacial interaction, and high cost of existing TiO2 / CNQDs heterojunction photocatalytic composite materials.

[0007] To achieve the above objectives, the present application adopts the following technical solution.

[0008] A first aspect of this application provides a method for preparing a TiO2 / CNQDs / fluorescein composite photocatalyst, comprising:

[0009] S1, Prepare mesoporous TiO2 with a nanoporous structure;

[0010] S2, urea and trisodium citrate are mixed evenly and reacted under low temperature to obtain a solid mixture containing CNQDs; the mixture is then dispersed in ethanol and purified by dialysis to obtain a CNQDs ethanol solution;

[0011] S3, a fluorescein-based compound, a CNQDs ethanol solution, and mesoporous TiO2 are dispersed in a mixed solution, stirred and reacted, and then dried to obtain a TiO2 / CNQDs / fluorescein composite photocatalyst.

[0012] Preferably, the fluorescein-like compound includes any one of fluorescein, sodium fluorescein, or dihydrofluorescein.

[0013] Preferably, the molar ratio of urea to trisodium citrate is (6~48):1.

[0014] Preferably, the mass-to-volume ratio of the fluorescein compound, CNQDs ethanol solution, and mesoporous TiO2 is (0.1~0.75) mg:(0.1~10) mL:100 mg.

[0015] Preferably, the temperature of the low-temperature solid-phase reaction is 160~220°C, and the reaction time is 2~8h;

[0016] The dialysis time is 12-48 hours.

[0017] Preferably, the mixed solution is a solution of ethanol and water in a volume ratio of 1:1.

[0018] Preferably, the mesoporous TiO2 with a nanoporous structure is prepared by the following method:

[0019] Polyoxyethylene polyoxypropylene ether, tetrahydrofuran, acetic acid and hydrochloric acid are mixed to form a transparent solution, then tetrabutyl titanate is added and stirred until a completely homogeneous solution is obtained.

[0020] The completely homogeneous solution was dried at low temperature to obtain F127 / TiO2 hydrogel;

[0021] The F127 / TiO2 hydrogel was dried at high temperature to obtain precursor powder;

[0022] The precursor powder was calcined to obtain mesoporous TiO2.

[0023] More preferably, the mass-to-volume ratio of polyoxyethylene polyoxypropylene ether to tetrahydrofuran is 4 g / (20~28) mL;

[0024] The volume ratio of tetrahydrofuran, acetic acid, and hydrochloric acid is 100:(20~25):(10~20);

[0025] The mass ratio of polyoxyethylene polyoxypropylene ether to tetrabutyl titanate is 8:(15~25);

[0026] The temperature for the low-temperature drying is 35~55°C;

[0027] The high-temperature drying temperature is 75~85°C;

[0028] The calcination temperature is 300~500°C, and the calcination time is 1~5h.

[0029] A second aspect of this application provides a TiO2 / CNQDs / fluorescein composite photocatalyst prepared by the above-described preparation method.

[0030] A third aspect of this application provides the application of the above-mentioned TiO2 / CNQDs / fluorescein composite photocatalyst in photocatalytic water splitting for hydrogen production.

[0031] Compared with the prior art, the beneficial effects of this application are as follows:

[0032] This application utilizes a solvent-promoted dispersion method to facilitate the entry of extremely small-sized CNQDs and small-molecule fluorescein compounds into the pores of mesoporous TiO2. The independent nanospace of mesoporous TiO2 serves as the active reaction site, laying the foundation for the "nanoconfinement effect." The CNQDs, with their extremely small quantum size, carry an opposite charge to the surface of the mesoporous TiO2. This shortens the carrier migration distance and, in conjunction with the multi-channel carrier migration pathway of the mesoporous structure, greatly promotes the separation and transport efficiency of photogenerated charges and enhances the stability of the composite material through strong interfacial forces. The fluorescein-based sensitizer can effectively improve the absorption of visible light by the TiO2 / CNQDs heterojunction photocatalytic composite material, and the dual effects of the anchoring (-COOH) group of the fluorescein-based compound and electrostatic adsorption can stably load it onto the mesoporous TiO2. Through the synergistic effect of the three, the hydrophobicity and phase separation caused by the adsorption of a large number of CNQDs on the TiO2 surface are significantly reduced. At the same time, the reactants / intermediates are enriched by the "nano confinement effect", which enhances the adsorption and activation of water molecules and improves the light energy utilization rate.

[0033] The TiO2 / CNQDs / fluorescein composite photocatalyst prepared in this application uses an independent nanospace as the active reaction site. Through the "nano confinement effect", it shortens the carrier migration path, increases multiple light scattering to improve light energy utilization and enriches reactants. At the same time, it has a wide photoresponse range, strong interfacial forces, good wettability, and significantly improves the photocatalytic hydrogen evolution efficiency and stability without relying on noble metals. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 TEM test results of the mesoporous TiO2, CNQDs and TCN5 / FL-Na0.5 composite photocatalyst prepared in Example 1;

[0036] Figure 2 The image shows the EDX energy dispersive spectroscopy results of TCN5 / FL-Na0.5 in Example 1.

[0037] Figure 3 The image shows the XRD results of TCN5 / FL-Na0.5 in Example 1.

[0038] Figure 4The UV-Vis absorption spectra of mesoporous TiO2, CNQDs, TCN5 / FL-Na0.5, and FL-Na prepared in Example 1 are shown in the figure.

[0039] Figure 5 The image shows the photocatalytic hydrogen production effect of the TCN5 / FL-Na0.5 composite photocatalyst of Example 1, the mesoporous TiO2 of Comparative Example 1, and the TCN5 composite photocatalyst of Comparative Example 3 under a xenon lamp. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0041] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0042] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0043] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0044] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0045] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0046] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0048] In a first aspect, this application provides a method for preparing a TiO2 / CNQDs / fluorescein composite photocatalyst, comprising:

[0049] S1, Prepare mesoporous TiO2 with a nanoporous structure.

[0050] The mesoporous TiO2 with a nanoporous structure is prepared by the following method:

[0051] Polyoxyethylene polyoxypropylene ether, tetrahydrofuran, acetic acid and hydrochloric acid are mixed to form a transparent solution, then tetrabutyl titanate is added and stirred until a completely homogeneous solution is obtained.

[0052] The preferred mass-to-volume ratio of polyoxyethylene polyoxypropylene ether to tetrahydrofuran is 4 g / (20~28) mL; the preferred volume ratio of tetrahydrofuran, acetic acid and hydrochloric acid is 100:(20~25):(10~20); and the preferred mass ratio of polyoxyethylene polyoxypropylene ether to tetrabutyl titanate is 8:(15~25).

[0053] The completely homogeneous solution was dried at a low temperature of 35~55°C to obtain F127 / TiO2 hydrogel;

[0054] The F127 / TiO2 hydrogel was dried at 75~85°C to obtain the precursor powder.

[0055] The precursor powder is heated to 300-500°C at a heating rate of 1°C / min and calcined for 1-5 hours to obtain mesoporous TiO2.

[0056] S2, urea and trisodium citrate are mixed evenly and reacted under low temperature to obtain a solid mixture containing CNQDs; the mixture is then dispersed in ethanol and purified by dialyzing for 12-48 hours to obtain a CNQDs ethanol solution.

[0057] In this application, the preferred molar ratio of urea to trisodium citrate is (6~48):1; the temperature of the low-temperature solid-phase reaction is 160~220°C, and the reaction time is 2~8h.

[0058] S3, a fluorescein-based compound, a CNQDs ethanol solution, and mesoporous TiO2 are dispersed in a mixed solution, stirred and reacted, and then dried to obtain a TiO2 / CNQDs / fluorescein composite photocatalyst.

[0059] In this application, the fluorescein compound is selected from any one of fluorescein, sodium fluorescein, or dihydrofluorescein; the preferred mass-to-volume ratio of the fluorescein compound, CNQDs ethanol solution, and mesoporous TiO2 is (0.1~0.75) mg:(0.1~10) mL:100 mg.

[0060] The mixed solution is a solution of ethanol and water in a volume ratio of 1:1.

[0061] This application utilizes a solvent-promoted dispersion method to facilitate the entry of extremely small-sized CNQDs and small organic molecule fluorescein compounds into the pores of mesoporous TiO2. Through the synergistic effect of the three, the hydrophobicity and phase separation phenomena caused by the adsorption of a large number of CNQDs on the TiO2 surface are significantly reduced. At the same time, the reactants / intermediates are enriched through the "nano confinement effect", which enhances the adsorption and activation capacity of water molecules and improves the light energy utilization rate.

[0062] Specifically, the independent nanospace of mesoporous TiO2 serves as an active reaction site, laying the foundation for the "nanoconfinement effect." CNQDs prepared by the low-temperature solid-state method have extremely small quantum sizes and their surfaces carry charges opposite to those on the surface of mesoporous TiO2. This shortens the carrier migration distance and, in conjunction with the multi-channel carrier migration pathways of the mesoporous structure, greatly promotes the separation and transport efficiency of photogenerated charges and enhances the stability of the composite material through strong interfacial forces. Furthermore, the use of readily available and economical fluorescein compounds as sensitizers can effectively improve the absorption of visible light by the TiO2 / CNQDs heterojunction photocatalytic composite material. The dual effects of the anchoring and electrostatic adsorption of the carboxyl groups (-COOH) of fluorescein compounds can stably load them onto mesoporous TiO2.

[0063] The TiO2 / CNQDs / fluorescein composite photocatalyst prepared in this application utilizes independent nanospaces as active reaction sites. Through the "nano confinement effect," it shortens the carrier migration path, increases multiple light scattering to improve light energy utilization, and enriches reactants. Simultaneously, it exhibits a wide photoresponse range, strong interfacial forces, good wettability, and significantly improves photocatalytic hydrogen evolution efficiency and stability without relying on noble metals. The TiO2 / CNQDs / fluorescein composite photocatalyst of this application can be used for photocatalytic water splitting to produce hydrogen, exhibiting a wide light absorption range, strong interfacial forces, low cost, and high catalytic efficiency.

[0064] The present application will be further illustrated by the following embodiments. In the embodiments:

[0065] F127 is polyoxyethylene polyoxypropylene ether.

[0066] THF is tetrahydrofuran, AcOH is acetate, TBOT is tetrabutyl titanate.

[0067] FL stands for fluorescein, FL-Na for sodium fluorescein, and FL-2H for dihydrofluorescein.

[0068] CNQDs are graphitic carbon nitride quantum dots.

[0069] Example 1

[0070] This embodiment provides a method for preparing a TiO2 / CNQDs / fluorescein composite photocatalyst, including:

[0071] S1, add 1.6g of F127 to 10mL of THF, then add 2.4mL of AcOH solution and 1.5mL of HCl solution, and stir to obtain a transparent solution; then quickly add 3.4g of TBOT, stir for 30min, and obtain a golden yellow completely homogeneous solution.

[0072] The completely homogenized solution was dried in an oven at 45°C for 24 hours to obtain F127 / TiO2 hydrogel;

[0073] The F127 / TiO2 hydrogel was dried in an oven at 80°C for 15 hours to obtain the precursor powder.

[0074] The precursor powder was transferred to a covered alumina crucible and placed in a muffle furnace. The temperature was increased to 400°C at a rate of 1°C / min and calcined for 3 hours. After cooling to room temperature, mesoporous TiO2 was obtained.

[0075] S2, urea and trisodium citrate were ground evenly at a molar ratio of 24:1, added to a high-pressure reactor and reacted at 180°C for 4 hours to obtain a reddish-brown solid containing CNQDs; 0.24 g of the reddish-brown solid was dispersed in 100 mL of ethanol, ultrasonically filtered and dialyzed for 24 hours to obtain an ethanol solution of CNQDs.

[0076] S3, 0.5 mg of FL-Na, 5 mL of CNQDs in ethanol solution and 100 mg of mesoporous TiO2 were dispersed in 20 mL of a mixed solution of ethanol and water (volume ratio 1:1), stirred for 24 h and then dried to obtain TiO2 / CNQDs / fluorescein composite photocatalyst, denoted as TCN5 / FL-Na0.5.

[0077] Example 2

[0078] The difference between Example 2 and Example 1 is that in S1, the amount of THF is 8 mL, the amount of AcOH solution is 1.6 mL, the amount of HCl is 0.8 mL, and the amount of TBOT is 3 g. All other aspects are the same as in Example 1.

[0079] Example 3

[0080] The difference between Example 3 and Example 1 is that in S1, the amount of THF is 12 mL, the amount of AcOH solution is 3.4 mL, the amount of HCl is 2.4 mL, and the amount of TBOT is 4 g. All other aspects are the same as in Example 1.

[0081] Example 4

[0082] The difference between Example 4 and Example 1 is that the drying temperature of the completely homogenized solution in S1 is 35°C, while the rest are the same as in Example 1.

[0083] Example 5

[0084] The difference between Example 5 and Example 1 is that the drying temperature of the completely homogenized solution in S1 is 55°C, while the rest are the same as in Example 1.

[0085] Example 6

[0086] The difference between Example 6 and Example 1 is that the drying temperature of the F127 / TiO2 hydrogel in S1 is 75°C, while the rest are the same as in Example 1.

[0087] Example 7

[0088] The difference between Example 7 and Example 1 is that the drying temperature of the F127 / TiO2 hydrogel in S1 is 85°C, while the rest are the same as in Example 1.

[0089] Example 8

[0090] The difference between Example 8 and Example 1 is that the calcination temperature of the precursor powder in S1 is 300°C and the time is 5h, while the rest are the same as in Example 1.

[0091] Example 9

[0092] The difference between Example 9 and Example 1 is that the calcination temperature of the precursor powder in S1 is 500°C and the time is 1 hour, while the rest are the same as in Example 1.

[0093] Example 10

[0094] The difference between Example 10 and Example 1 is that the molar ratio of urea to trisodium citrate in S2 is 6:1, while the rest are the same as in Example 1.

[0095] Example 11

[0096] The difference between Example 11 and Example 1 is that the molar ratio of urea to trisodium citrate in S2 is 12:1, while the rest are the same as in Example 1.

[0097] Example 12

[0098] The difference between Example 12 and Example 1 is that the molar ratio of urea to trisodium citrate in S2 is 36:1, while the rest are the same as in Example 1.

[0099] Example 13

[0100] The difference between Example 13 and Example 1 is that the molar ratio of urea to trisodium citrate in S2 is 48:1, while the rest is the same as in Example 1.

[0101] Example 14

[0102] The difference between Example 14 and Example 1 is that the reaction temperature in S2 is 160°C, while the rest is the same as in Example 1.

[0103] Example 15

[0104] The difference between Example 15 and Example 1 is that the reaction temperature in S2 is 200°C, while the rest is the same as in Example 1.

[0105] Example 16

[0106] The difference between Example 16 and Example 1 is that the reaction temperature in S2 is 220°C, while the rest is the same as in Example 1.

[0107] Example 17

[0108] The difference between Example 17 and Example 1 is that the reaction time in S2 is 2 hours, while the rest is the same as in Example 1.

[0109] Example 18

[0110] The difference between Example 18 and Example 1 is that the reaction time in S2 is 6 hours, while the rest is the same as in Example 1.

[0111] Example 19

[0112] The difference between Example 19 and Example 1 is that the reaction time in S2 is 8 hours, while the rest is the same as in Example 1.

[0113] Example 20

[0114] The difference between Example 20 and Example 1 is that the dialysis time in S2 is 12 hours, while the rest is the same as in Example 1.

[0115] Example 21

[0116] The difference between Example 21 and Example 1 is that the dialysis time in S2 is 36 hours, while the rest is the same as in Example 1.

[0117] Example 22

[0118] The difference between Example 22 and Example 1 is that the dialysis time in S2 is 48 hours, while the rest is the same as in Example 1.

[0119] Example 23

[0120] The difference between Example 23 and Example 1 is that the fluorescein compound used in S3 is FL-2H, while the rest are the same as in Example 1.

[0121] Example 24

[0122] The difference between Example 24 and Example 1 is that the fluorescein compound used in S3 is FL, while the rest are the same as in Example 1.

[0123] Example 25

[0124] The difference between Example 25 and Example 1 is that the amount of FL-Na used in S3 is 0.1 mg, while the rest is the same as in Example 1.

[0125] Example 26

[0126] The difference between Example 26 and Example 1 is that the amount of FL-Na used in S3 is 0.25 mg, while the rest is the same as in Example 1.

[0127] Example 27

[0128] The difference between Example 27 and Example 1 is that the amount of FL-Na used in S3 is 0.75 mg, while the rest is the same as in Example 1.

[0129] Example 28

[0130] The difference between Example 28 and Example 1 is that the amount of ethanol solution of CNQDs used in S3 is 2.5 mL, and the rest is the same as in Example 1.

[0131] Example 29

[0132] The difference between Example 29 and Example 1 is that the amount of ethanol solution of CNQDs used in S3 is 7.5 mL, and the rest is the same as in Example 1.

[0133] Example 30

[0134] The difference between Example 30 and Example 1 is that the amount of ethanol solution of CNQDs used in S3 is 10 mL, and the rest is the same as in Example 1.

[0135] Comparative Example 1

[0136] Comparative Example 1 is the mesoporous TiO2 photocatalyst prepared in step S1 of Example 1.

[0137] Comparative Example 2

[0138] Comparative Example 2 is the CNQDs photocatalyst prepared in step S2 of Example 1.

[0139] Comparative Example 3

[0140] Comparative Example 3 is a TiO2 / CNQDs photocatalyst, denoted as TCN5. Its preparation method differs from Example 1 in that FL-Na is not added in S3; otherwise, it is the same as Example 1.

[0141] The mesoporous TiO2, CNQDs, and TCN5 / FL-Na0.5 composite photocatalyst prepared in Example 1 were tested by transmission electron microscopy (TEM), and the results are as follows: Figure 1 As shown; simultaneously, EDX energy dispersive spectroscopy analysis was performed on TCN5 / FL-Na0.5 from Example 1, and the results are as follows. Figure 2 As shown.

[0142] in, Figure 1 a is CNQDs, Figure 1 b represents mesoporous TiO2. Figure 1 c is TCN5 / FL-Na0.5. (From...) Figure 1 It can be seen that the mesoporous TiO2 is in the form of nanoparticles with a distinct and uniformly distributed mesoporous structure, indicating the successful preparation of nanoporous TiO2; the average particle size of CNQDs is 4.75±0.07 nm, and there is no obvious agglomeration phenomenon; after the mesoporous TiO2 is composited by solvent-promoted dispersion method, CNQDs successfully enter the pores and are loaded on the pore walls. Figure 2 The EDX energy dispersive spectroscopy analysis results show that the characteristic elements titanium (Ti), oxygen (O), carbon (C), nitrogen (N), and sodium (Na) of the composite photocatalyst are uniformly distributed, indicating that CNQDs and FL-Na are uniformly distributed on mesoporous TiO2, and the composite photocatalyst has been successfully prepared.

[0143] X-ray diffraction (XRD) analysis was performed on TCN5 / FL-Na0.5 from Example 1, and the results are as follows: Figure 3 As shown. The diffraction peaks of the mesoporous TiO2 prepared in Example 1 are consistent with the characteristic diffraction peaks of pure TiO2 (PDF#21-1272), indicating that its crystal form is anatase phase; while the XRD diffraction peaks of TCN5 / FL-Na0.5 are consistent with the diffraction peaks of single mesoporous TiO2, indicating that the introduction of CNQDs and FL-Na did not change the crystal structure of mesoporous TiO2.

[0144] The mesoporous TiO2, CNQDs, and TCN5 / FL-Na0.5 composite photocatalyst prepared in Example 1, as well as FL-Na, were subjected to ultraviolet-visible absorption spectroscopy (UV-Vis). The results are as follows: Figure 4 As shown, the TCN5 / FL-Na0.5 composite photocatalyst exhibits significantly enhanced light absorption in the visible light region compared to single mesoporous TiO2, indicating that the introduction of FL-Na effectively addresses the issue of the narrow light absorption range of mesoporous TiO2.

[0145] The hydrogen production performance of the TCN5 / FL-Na0.5 composite photocatalyst prepared in Example 1, the mesoporous TiO2 photocatalyst of Comparative Example 1, and the TCN5 composite photocatalyst prepared in Comparative Example 3 was studied. The specific methods are as follows:

[0146] A xenon lamp was used as the hydrogen production light source with a wavelength range of ≥320nm; the catalyst dosage was 1.5g / L, the sacrificial agent was 20mL triethanolamine, and 60mL water was added; the reaction cell was evacuated, argon was used as the carrier gas, and the H2 generated in the gas chromatography system was detected. A hydrogen production experiment was conducted for 4 hours, and the hydrogen data in the system was collected every 1 hour.

[0147] The photocatalytic hydrogen production effects of the TCN5 / FL-Na0.5 composite photocatalyst in Example 1, the mesoporous TiO2 photocatalyst in Comparative Example 1, and the TCN5 composite photocatalyst in Comparative Example 3 under a xenon lamp are as follows: Figure 5 As shown, the horizontal axis represents time, the vertical axis represents hydrogen production, and the curve represents the hydrogen production of the above catalyst under a xenon lamp with triethanolamine as a sacrificial agent as a function of time.

[0148] from Figure 5 It can be seen that the TCN5 composite photocatalyst achieves a hydrogen production rate of 2336 μmol·g within 4 hours. -1 ·h -1 The hydrogen production rate is significantly higher than that of mesoporous TiO2 photocatalysts (984 μmol·g⁻¹). -1 ·h -1This indicates that CNQDs successfully entered the mesoporous TiO2 pores to construct a heterostructure, and synergistically achieved improved photocatalytic hydrogen evolution through the "nano confinement effect"; while the TCN5 / FL-Na0.5 composite photocatalyst further increased the hydrogen production rate to 6625 μmol·g within 4 h. -1 ·h -1 This indicates that the FL-Na photosensitizer further improved the hydrogen evolution performance of the photocatalytic system by enhancing its light absorption capacity.

[0149] The composite photocatalysts prepared in Examples 2-30 have similar performance to the TCN5 / FL-Na0.5 composite photocatalyst in Example 1, and both exhibit good photocatalytic effects.

[0150] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for preparing a TiO2 / CNQDs / fluorescein composite photocatalyst, characterized in that, include: S1, Prepare mesoporous TiO2 with a nanoporous structure; S2, urea and trisodium citrate are mixed evenly and reacted under low temperature to obtain a solid mixture containing CNQDs; the mixture is then dispersed in ethanol and purified by dialysis to obtain a CNQDs ethanol solution; S3, a fluorescein-based compound, a CNQDs ethanol solution, and mesoporous TiO2 were dispersed in a mixed solution, stirred and reacted, and then dried to obtain a TiO2 / CNQDs / fluorescein composite photocatalyst.

2. The preparation method according to claim 1, characterized in that, The fluorescein compounds include any one of fluorescein, sodium fluorescein, or dihydrofluorescein.

3. The preparation method according to claim 1, characterized in that, The molar ratio of urea to trisodium citrate is (6~48):

1.

4. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the fluorescein compound, CNQDs ethanol solution, and mesoporous TiO2 is (0.1~0.75) mg:(0.1~10) mL:100 mg.

5. The preparation method according to claim 1, characterized in that, The temperature of the low-temperature solid-phase reaction is 160~220°C, and the reaction time is 2~8h; the dialysis time is 12~48h.

6. The preparation method according to claim 1, characterized in that, The mixed solution is a solution of ethanol and water in a volume ratio of 1:

1.

7. The preparation method according to claim 1, characterized in that, The mesoporous TiO2 with a nanoporous structure is prepared by the following method: Polyoxyethylene polyoxypropylene ether, tetrahydrofuran, acetic acid and hydrochloric acid are mixed to form a transparent solution, then tetrabutyl titanate is added and stirred until a completely homogeneous solution is obtained. The completely homogeneous solution was dried at low temperature to obtain F127 / TiO2 hydrogel; The F127 / TiO2 hydrogel was dried at high temperature to obtain precursor powder; The precursor powder was calcined to obtain mesoporous TiO2.

8. The preparation method according to claim 7, characterized in that, The mass-to-volume ratio of polyoxyethylene polyoxypropylene ether to tetrahydrofuran is 4 g / (20~28) mL; The volume ratio of tetrahydrofuran, acetic acid, and hydrochloric acid is 100:(20~25):(10~20); The mass ratio of polyoxyethylene polyoxypropylene ether to tetrabutyl titanate is 8:(15~25); The temperature for the low-temperature drying is 35~55°C; The high-temperature drying temperature is 75~85°C; The calcination temperature is 300~500°C, and the calcination time is 1~5h.

9. The TiO2 / CNQDs / fluorescein composite photocatalyst prepared by the preparation method according to any one of claims 1-8.

10. The application of the TiO2 / CNQDs / fluorescein composite photocatalyst according to claim 10 in photocatalytic water splitting for hydrogen production.

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