Fluorinated carbon dot photocatalyst, preparation method thereof and application of fluorinated carbon dot photocatalyst in photocatalytic preparation of hydrogen peroxide

Abstract

The invention discloses a carbon fluoride dot photocatalyst, a preparation method thereof and application of the carbon fluoride dot photocatalyst in photocatalytic preparation of hydrogen peroxide. The carbon fluoride dot photocatalyst is synthesized by reacting tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine through a hydrothermal method, and has a graphene-like layered structure; c-F covalent bonds are formed in a carbon skeleton; the preparation method comprises the following steps: adding tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine into water, uniformly mixing, carrying out hydrothermal reaction, and filtering, purifying and drying a reaction product to obtain solid fluorinated carbon dot powder. According to the fluorinated carbon dot photocatalyst disclosed by the invention, through fluorination, the fluorinated carbon dot material has a wider light absorption range, more efficient carrier separation capability and more hydrophobic physical characteristics, so that the reaction efficiency of photocatalytic H2O2 production is improved.

Description

Technical Field

[0001] The invention relates to a photocatalyst, in particular to a fluorinated carbon point photocatalyst and a preparation method thereof and application thereof in photocatalytic preparation of hydrogen peroxide. Background Art

[0002] H 2 O 2 It is a green oxidant and is widely used in environmental governance, medical disinfection, chemical synthesis and other fields. Traditional industrial production mainly relies on the anthraquinone method, but there are problems such as high energy consumption and organic solvent pollution. 2 O 2 It uses water, oxygen and solar energy as raw materials and has the potential to be green and sustainable. Traditional catalysts (such as TiO 2 , metal complexes) have problems such as low visible light utilization, high carrier recombination rate, and the need for precious metal doping. Although some carbon-based materials have the advantage of low cost, their catalytic activity and selectivity are insufficient. Some carbon-based materials such as C 3 N 4 , gC 3 N 4 Although it has the advantage of low cost (Feng, B., Liu, Y., Wan, K., Zu, S., Pei, Y., Zhang, X., Qiao, M., Li, H., & Zong, B. (2024). Tailored Exfoliation of Polymeric Carbon Nitride for Photocatalytic H 2 O 2 Production and CH 4 Valorization Mediated by O 2 Activation.Angewandte Chemie International Edition, 63(18), e202401884.), but the catalytic activity and selectivity are insufficient, and the original C 3 N 4 The photocatalytic efficiency of hydrogen peroxide production was only 97.4 μmol·g -1 ·L -1In the prior art, fluorination doping technology is used to modify materials for photocatalysis, such as Wu, J., Liu, Z., Lin, X., Jiang, E., Zhang, S., Huo, P., Yan, Y., Zhou, P., & Yan, Y. (2022). Breaking through water-splitting bottlenecks over carbon nitride with fluorination. Nature Communications, 13 (1), 1-8. 3 N 4 Achieve complete decomposition of water. Han, W., Zhang, H., Li, D., Qin, W., Zhang, X., Wang, S., & Duan, X. (2024). Surface engineered carbon quantum dots for efficient photocatalytic hydrogen peroxide production. Applied Catalysis B: Environment and Energy, 350, 123918. used modified carbon dots as photocatalysts to prepare hydrogen peroxide, but did not involve the fluorine modification process. At present, there are few reports on the use of fluorine-modified carbon dot materials for photocatalytic preparation of hydrogen peroxide, and the catalytic efficiency needs to be further improved. Summary of the invention

[0003] Purpose of the invention: The first purpose of the present invention is to provide a fluorinated carbon dot photocatalyst that improves the photocatalytic efficiency of photocatalytic preparation of hydrogen peroxide; the second purpose of the present invention is to provide a method for preparing the fluorinated carbon dot photocatalyst; the third purpose of the present invention is to provide the use of the fluorinated carbon dot photocatalyst in the photocatalytic preparation of hydrogen peroxide.

[0004] Technical solution: The fluorinated carbon dot photocatalyst described in the present invention is synthesized by hydrothermal reaction of tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine, has a graphene-like layered structure, and forms CF covalent bonds in the carbon skeleton.

[0005] Preferably, the molar ratio of the total amount of tetrafluoroterephthalic acid and terephthalic acid to p-phenylenediamine is (1-4): 1. The fluorine doping amount in the fluorinated carbon dots is controlled by the addition ratio of tetrafluoroterephthalic acid to determine the optimal fluorine doping amount for preparing hydrogen peroxide.

[0006] Preferably, the molar ratio of tetrafluoroterephthalic acid to terephthalic acid is 1:(0-3).

[0007] More preferably, the molar ratio of tetrafluoroterephthalic acid to terephthalic acid is 1:(0-1 / 3), and the molar ratio of the total molar amount of tetrafluoroterephthalic acid and terephthalic acid to p-phenylenediamine is (1-2):1.

[0008] Preferably, the carbon dot particle size is within 10 nm. Small particle size increases the specific surface area of ​​the material, exposes more surface active sites, and increases oxygen (O 2 ) adsorption capacity. Further preferably, the particle size of the carbon dots is 2.0-4.5 nm.

[0009] The method for preparing the fluorinated carbon dot photocatalyst of the present invention comprises the following steps:

[0010] (1) dissolving tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine in water and mixing them uniformly;

[0011] (2) transferring the mixed solution to a reactor for hydrothermal reaction;

[0012] (3) The reaction product is filtered, purified, and dried to obtain solid fluorinated carbon dot powder.

[0013] During the hydrothermal reaction, the precursor reacts in a high-temperature and high-pressure aqueous solution, undergoes amide condensation and dehydration reactions, and then polymerizes into a carbon core, with unreacted functional groups (-COOH, -F) retained on its surface.

[0014] Preferably, in step (2), the hydrothermal reaction temperature is 160-200°C, and the reaction time is 2-10 hours. More preferably, the hydrothermal reaction temperature is 180-200°C, and the reaction time is 3-6 hours.

[0015] Preferably, in step (3), filtration is performed using a microporous membrane filter of 0.22 to 0.45 μm.

[0016] Preferably, in step (3), the purification is dialysis, and the dialysis is performed using a dialysis bag with a molecular weight cutoff of 500 to 3000 Da. The specific method is: dialyzing the filtrate with a dialysis bag, using pure water as the dialysis replacement fluid, replacing the dialysis replacement fluid every 3 to 5 hours, and the dialysis process lasts for 40 hours.

[0017] Preferably, in step (3), the drying is freeze drying, and the specific method is: freeze the dialyzed solution in a -80°C refrigerator for 8 to 10 hours, and then dry it in a freeze dryer under vacuum until it becomes powdery.

[0018] The invention relates to the use of the fluorinated carbon dot photocatalyst in the photocatalytic preparation of hydrogen peroxide.

[0019] The application comprises the following steps:

[0020] (1) dispersing the carbon dots in a solution;

[0021] (2) Oxygen is introduced into the solution, and a photocatalytic reaction is carried out under the irradiation of a xenon lamp.

[0022] Preferably, the dispersion ratio of the carbon dots in step (1) is 0.1 to 0.8 g / L to avoid the decrease in activity caused by carbon dot agglomeration at high concentrations. At the same time, a suitable dispersion concentration can also promote excellent light absorption efficiency.

[0023] Preferably, the solution in step (1) is an ethanol-water solution.

[0024] Invention mechanism:

[0025] The present invention is based on a controllable synthesis strategy of fluorinated carbon dots and realizes efficient photocatalytic synthesis of hydrogen peroxide (H2O2) through molecular structure design and interface reaction optimization. 2 O 2 ). Tetrafluoroterephthalic acid is used as a fluorine-containing precursor to directly participate in the synthesis of carbon dots. Tetrafluoroterephthalic acid provides abundant fluorine atoms. Its rigid benzene ring structure and strong electron-withdrawing effect promote the uniform doping of fluorine atoms in the carbon dot skeleton. Compared with the traditional fluorination method of adding additional sodium fluoride to the reaction system, it is more convenient and has higher fluorination efficiency.

[0026] Due to the high electronegativity and strong electron-withdrawing property of fluorine, the band gap structure of carbon dots can be regulated and the light absorption capacity of carbon dot materials can be enhanced. The high electronegativity of fluorine atoms (4.0) induces the formation of a directional built-in electric field on the surface of carbon dots, accelerates the migration of carriers to the catalyst surface, and improves the charge separation efficiency. After fluorination, the hydrophobicity of carbon dots is enhanced, and a hydrophobic microenvironment can be generated on the surface of nano-scale carbon dots, which promotes the absorption and utilization of oxygen and is conducive to the generation of hydrogen peroxide through the oxygen reduction process.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The fluorinated carbon dot photocatalyst of the present invention introduces fluorine, and the fluorinated carbon dot material has a wider light absorption range, more efficient carrier separation ability and more hydrophobic physical characteristics, which are conducive to photocatalytic H production. 2 O 2 reaction; (2) the preparation method is simple, the raw materials are cheap and readily available, the hydrophilicity is good, and the uniformity in the solution is good. The method is green and simple, and has the premise of being able to be put into large-scale production in the future, and has good application prospects in solving problems such as future energy shortages; (3) the fluorinated carbon dot photocatalyst is used in photocatalytic H production 2 O 2 Among them, the photocatalytic activity of the most preferred fluorinated group of carbon dots 1.5F-CD increased by 3.22 times, which is significantly better than that of the non-fluorinated group of carbon dots CD, and has broad prospects in the practical application of photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The synthetic route and product structure schematic diagram of the present invention;

[0029] Figure 2 This is a transmission electron microscopy image of the fluorinated photocatalyst 1.5F-CD prepared in Example 5;

[0030] Figure 3 This is a particle size distribution diagram of the fluorinated photocatalyst 1.5F-CD prepared in Example 5;

[0031] Figure 4 This is a high-resolution transmission electron microscopy image of the fluorinated carbon dots 1.5F-CD synthesized in Example 5;

[0032] Figure 5 , Figure 6 and Figure 7 They are the full XPS spectrum of the fluorinated photocatalyst 1.5F-CD prepared in Example 5 and the non-fluorinated carbon dots prepared in Comparative Example 1, the high-resolution XPS spectrum of C 1s, and the high-resolution XPS spectrum of F1s;

[0033] Figure 8 The H in the photocatalytic process of the fluorinated photocatalysts prepared in Examples 1 to 7 and the non-fluorinated carbon dots prepared in Comparative Example 1 2 O 2 Yield map;

[0034] Fig. 9 The photocatalytic H production of the fluorinated photocatalysts prepared in Examples 1 to 7 and the non-fluorinated carbon dots prepared in Comparative Example 1 2 O 2 Efficiency graph;

[0035] Fig.10 The contact angle test diagram of the fluorinated photocatalyst 1.5F-CD prepared in Example 5 and the non-fluorinated carbon point prepared in Comparative Example 1;

[0036] Fig.11 The UV-visible absorption spectra of the fluorinated photocatalysts prepared in Examples 1 to 7 and the non-fluorinated carbon dots prepared in Comparative Example 1;

[0037] Fig.12 The fluorescence emission spectra of the fluorinated photocatalysts prepared in Examples 1 to 7 and the non-fluorinated carbon dots prepared in Comparative Example 1 at an excitation wavelength of 330 nm;

[0038] Fig.13 This is a cyclic stability test chart of the fluorinated photocatalyst 1.5F-CD prepared in Example 5. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below in conjunction with embodiments.

[0040] Example 1

[0041] The preparation method of the fluorinated carbon dot photocatalyst of the present invention comprises the following steps:

[0042] (1) 1.08 g (10 mmol) of p-phenylenediamine was dissolved in 40 mL of pure water, and then 1.245 g (7.5 mmol) of terephthalic acid and 0.595 g (2.5 mmol) of tetrafluoroterephthalic acid were added. After stirring evenly, the entire solution was transferred to a 100 mL polytetrafluoroethylene liner, and reacted in a reactor at 200° C. for 3 h. After the reaction was completed, the reaction solution was allowed to stand at room temperature until it was completely cooled;

[0043] (2) The reaction solution in (1) was taken out and filtered with a 0.22 μm microporous filter membrane. The filtered solution was then placed in a pre-treated dialysis bag with a specification of 1000 Da. Pure water was used as the dialysis replacement fluid. The volume ratio of the reaction solution to the dialysis replacement fluid should be less than 1:100. During the dialysis process, the dialysis replacement fluid was replaced every 3 to 5 hours, and the dialysis was continued for about 40 hours.

[0044] (3) After the dialysis is completed, the solution in the dialysis bag is transferred to a 50 mL centrifuge tube, frozen in a -80°C refrigerator for 10 h, and dried in a freeze dryer to a powdery state, thereby obtaining fluorinated carbon dots 0.25F-CD.

[0045] Example 2

[0046] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0.83 g (5 mmol), and the mass of tetrafluoroterephthalic acid was changed to 1.19 g (5 mmol). The other conditions remained unchanged to obtain fluorinated carbon dots 0.5F-CD.

[0047] Example 3

[0048] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0.415 g (2.5 mmol), and the mass of tetrafluoroterephthalic acid was changed to 1.785 g (7.5 mmol). The other conditions remained unchanged to obtain fluorinated carbon dots 0.75F-CD.

[0049] Example 4

[0050] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0 g, and the mass of tetrafluoroterephthalic acid was changed to 2.38 g (10 mmol). The other conditions remained unchanged to obtain fluorinated carbon dots 1F-CD.

[0051] Example 5

[0052] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0 g, and the mass of tetrafluoroterephthalic acid was changed to 3.57 g (15 mmol). The other conditions remained unchanged to obtain the fluorinated carbon dots 1.5F-CD.

[0053] Example 6

[0054] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0 g, and the mass of tetrafluoroterephthalic acid was changed to 4.76 g (20 mmol). The other conditions remained unchanged to obtain fluorinated carbon dots 2F-CD.

[0055] Example 7

[0056] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 0 g, and the mass of tetrafluoroterephthalic acid was changed to 9.52 g (40 mmol). The other conditions remained unchanged to obtain fluorinated carbon dots 4F-CD.

[0057] Comparative Example 1

[0058] On the basis of Example 1, the mass of terephthalic acid in step (1) was changed to 1.66 g (10 mmol), tetrafluoroterephthalic acid was not added, and other conditions remained unchanged to obtain unfluorinated carbon dots CD.

[0059] Structural characterization

[0060] The structure of the fluorinated carbon dot 1.5F-CD synthesized in Example 5 was characterized.

[0061] Figure 2 This is a transmission electron microscope image of the fluorinated carbon dots 1.5F-CD synthesized in Example 5. Figure 2 It can be seen that the fluorinated carbon dots are uniformly quasi-spherical.

[0062] Figure 3 This is the particle size distribution diagram of the fluorinated carbon dots 1.5F-CD synthesized in Example 5. It can be seen from the figure that the particle size distribution of the fluorinated carbon dots is between 2.0 and 4.5 nm, and the average particle size is 2.91 nm.

[0063] Figure 4 This is a high-resolution transmission electron micrograph of the fluorinated carbon dots 1.5F-CD synthesized in Example 5. It can be seen from the figure that the lattice size of the fluorinated carbon dots is 0.22 nm, corresponding to the (100) crystal plane, indicating that the carbon dots contain a graphite-like structure.

[0064] Figure 5 This is the full XPS spectra of the fluorinated carbon dots 1.5F-CD synthesized in Example 5 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1. It can be seen from the figure that 1.5F-CD has an additional fluorine peak at about 688 eV relative to CD, which proves the successful loading of fluorine.

[0065] Figure 6 The XPS carbon spectra of the fluorinated carbon dots 1.5F-CD synthesized in Example 5 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1 are shown in the figure. As shown in the figure, the carbon spectrum of 1.5F-CD can be divided into four peaks, namely 284.8 eV (CC / C=C), 286.2 eV (CC / CO), 287.8 eV (C=O) and 289.6 eV (CF). Compared with the non-fluorinated CD, the CN / CO peak position shifts 0.2 eV toward the high binding energy direction, which indicates that the electron-withdrawing effect of fluorine atoms after fluorination changes the electronic environment of carbon. The appearance of the new CF peak also proves that fluorine is successfully doped into the carbon skeleton.

[0066] Figure 7 The XPS fluorine spectra of the fluorinated carbon dots 1.5F-CD synthesized in Example 5 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1 are as shown in the figure. An obvious CF peak appears in 1.5F-CD, while no obvious peak signal is detected in CD, which directly proves the successful doping of fluorine.

[0067] Performance Characterization

[0068] 1. Photocatalytic H production 2 O 2 Performance Testing

[0069] The photocatalytic H production of the fluorinated carbon dot photocatalysts synthesized in Examples 1 to 7 and the non-fluorinated carbon dot photocatalyst synthesized in Comparative Example 1 was 2 O 2 Performance tested.

[0070] Test method: The photocatalytic degradation performance was evaluated using a photocatalytic reactor equipped with a 500W xenon lamp. The temperature was controlled at 25°C during the reaction. 30 mg of the prepared photocatalyst was completely dispersed in 90 mL of pure water, and 10 mL of anhydrous ethanol was added as a hole sacrificial agent during the photocatalytic reaction, and ultrasonic treatment was performed for 5 minutes. The mixed reaction solution was stirred in the dark for 30 minutes, and oxygen was introduced at a ventilation rate of 30 mL / min to saturate the reaction solution with oxygen. After 2 hours of illumination, 1.5 mL of the reaction solution was filtered with a 0.22 μm filter every 15 minutes. Then, the H 2 O 2 Concentration. Specifically, 2.15 mL of the diluted sample solution was mixed with 0.40 mL of phosphate buffer. Then 50 μL of N, N-diethyl-1, 4-phenylenediamine sulfate solution (DPD) and 50 μL of horseradish peroxidase solution (POD) were added in sequence and stirred for 90 seconds. The absorbance of the solution was then measured at 551 nm using a UV-visible spectrophotometer.

[0071] Figure 8 , 9The H in the photocatalytic process of the fluorinated carbon dot photocatalysts synthesized in Examples 1 to 7 and the carbon dot photocatalyst synthesized in Comparative Example 1 are respectively 2 O 2 Yield graph and performance efficiency graph.

[0072] Depend on Figure 8 and 9 It can be seen that the photocatalyst of unfluorinated CD has a H 2 O 2 The concentration is 34.83 μmol·L -1 , the efficiency is 58.04μmol·g -1 ·h -1 ; 0.25F-CD photocatalyst H in 2 hours system 2 O 2 The concentration is 37.77 μmol·L -1 , the efficiency is 62.95μmol·g -1 ·h -1 ; 0.5F-CD photocatalyst H in 2 hours system 2 O 2 The concentration was 43.17 μmol·L -1 , the efficiency is 71.96μmol·g -1 ·h -1 ; 0.75F-CD photocatalyst H in 2 hours system 2 O 2 The concentration was 54.22 μmol·L -1 , the efficiency is 90.37μmol·g -1 ·h -1 ; 1F-CD photocatalyst H in 2 hours system 2 O 2 The concentration is 76.86 μmol·L -1 , the efficiency reached 128.10μmol·g -1 ·h -1 ; 1.5H in the F-CD photocatalyst system within 2 hours 2 O 2 The concentration is 112.32 μmol·L -1 , the efficiency reached 187.22μmol·g -1 ·h -1 ; 2F-CD photocatalyst H in 2 hours 2 O 2 The concentration is 69.87 μmol·L -1 , the efficiency is 116.45μmol·g -1 ·h -1 ; 4F-CD photocatalyst H in 2 hours system 2 O 2The concentration is 63.30 μmol·L -1 , the efficiency is 105.50μmol·g -1 ·h -1 Among them, the photocatalytic production of H by 1.5F-CD 2 O 2 The efficiency is the highest, which is 3.22 times that of the unfluorinated carbon point in the comparative example.

[0073] From the catalytic effect data of Examples 1 to 7, it can be seen that as the proportion of tetrafluoroterephthalic acid increases, the catalytic efficiency changes. From no tetrafluoroterephthalic acid to 1.5F-CD, the catalytic efficiency gradually increases and reaches the maximum in 1.5F-CD. After the tetrafluoroterephthalic acid is added again, the catalytic efficiency begins to decrease. The high electronegativity (4.0) of the fluorine atom in TFA forms a directional built-in electric field in the carbon dots, accelerating the migration of photogenerated electrons (e-) to the surface and promoting the effective separation and transfer of carriers. At the same time, fluorination also forms hydrophobic micro-areas on the surface of the carbon dots, promoting O 2 enrichment, forming an efficient "gas-liquid-solid" three-phase reaction interface.

[0074] 2. Contact angle test diagram

[0075] Fig.10 The contact angle test graphs of the fluorinated carbon dots 1.5F-CD synthesized in Example 5 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1 are shown.

[0076] Depend on Fig.10 It can be obtained that the contact angle of the unfluorinated carbon dot CD is 44.3°, and the contact angle of the fluorinated carbon dot 1.5F-CD is 83.2°. The hydrophobicity of the carbon dots is improved after fluorination, which is conducive to the formation of hydrophobic micro-regions around the carbon dots during the reaction, promoting the utilization of oxygen, so as to increase the production of hydrogen peroxide through the oxygen reduction process.

[0077] 3. Ultraviolet absorption spectrum test

[0078] Fig.11 The ultraviolet absorption spectra of the fluorinated carbon dots synthesized in Examples 2 and Examples 4 to 7 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1 are shown.

[0079] Depend on Fig.11 It can be seen that in the visible light range (400-700nm), the light absorption capacity of carbon dots is enhanced after fluorination, among which 1.5F-CD has the strongest light absorption capacity, which indicates that 1.5F-CD has stronger photocatalytic activity.

[0080] 4. Fluorescence emission spectrum test

[0081] Fig.12The fluorescence emission spectra of the fluorinated carbon dots synthesized in Examples 2 and Examples 4 to 7 and the non-fluorinated carbon dots CD synthesized in Comparative Example 1 at an excitation wavelength of 330 nm, the peak shapes of the carbon dots in each group are similar, the peak positions are close, and the peak intensity of the carbon dots after fluorination is significantly reduced, indicating that the fluorinated carbon dots have more excellent photogenerated carrier separation efficiency, improved light utilization and hydrogen peroxide production capacity.

[0082] 5. Catalyst stability test

[0083] Fig.13 This is a test graph of the cyclic stability of the fluorinated carbon dots 1.5F-CD synthesized in Example 5.

[0084] Depend on Fig.13 It can be seen that after 4 cycles of degradation experiments, the fluorinated carbon dots 1.5F-CD still maintained high photocatalytic activity, with the performance remaining above 95%, showing excellent stability and reliability.

Claims

1. A fluorinated carbon dot photocatalyst, characterized in that: It is synthesized by the hydrothermal reaction of tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine, has a graphene-like layered structure, and forms CF covalent bonds in the carbon skeleton.

2. The fluorinated carbon dot photocatalyst according to claim 1, characterized in that: The molar ratio of the total molar amount of tetrafluoroterephthalic acid and terephthalic acid to p-phenylenediamine is (1-4):

1.

3. The fluorinated carbon dot photocatalyst according to claim 2, characterized in that: The molar ratio of tetrafluoroterephthalic acid to terephthalic acid is 1:(0-3).

4. The fluorinated carbon dot photocatalyst according to claim 1, characterized in that The particle size of the carbon dots is within 10 nm.

5. The fluorinated carbon dot photocatalyst according to claim 1, characterized in that: The particle size of the carbon dots is 2.0 to 4.5 nm.

6. A method for preparing the fluorinated carbon dot photocatalyst according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) adding tetrafluoroterephthalic acid and terephthalic acid or tetrafluoroterephthalic acid and p-phenylenediamine into water and mixing them evenly; (2) transferring the mixed solution to a reactor for hydrothermal reaction; (3) The reaction product is filtered, purified, and dried to obtain solid fluorinated carbon dot powder.

7. The method for preparing the fluorinated carbon dot photocatalyst according to claim 6, characterized in that: In step (2), the hydrothermal reaction temperature is 160-200°C.

8. Use of the fluorinated carbon dot photocatalyst according to any one of claims 1 to 5 in the photocatalytic preparation of hydrogen peroxide.

9. The use according to claim 8, characterized in that: The following steps are involved: (1) dispersing the carbon dots in a solution; (2) Oxygen is introduced into the solution, and a photocatalytic reaction is carried out under the irradiation of a xenon lamp.

10. The use according to claim 9, characterized in that: In step (1), the dispersion ratio of carbon dots is 0.1 to 0.8 g / L.

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