A graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst, its preparation method and application

Abstract

The present invention discloses a graphene quantum dots (GQDs)-loaded iron-doped titanium-based metal-organic framework photocatalyst, a preparation method thereof, and an application thereof. The preparation includes the following steps: Step 1, dissolving a titanium source, an iron source, and 2-aminoterephthalic acid in a mixed solution of N,N-dimethylformamide and methanol for a mixed reaction, and washing and drying the product to obtain an iron-doped titanium-based metal-organic framework; Step 2, mixing and pyrolyzing citric acid monohydrate and graphite powder to obtain GQDs; Step 3, obtaining the iron-doped titanium-based metal-organic framework photocatalyst by ball-milling and mixing the iron-doped titanium-based metal-organic framework with the GQDs. Based on the support of the metal ion doping strategy, GQDs can further improve the photocatalytic performance of MOFs. The obtained catalyst has excellent catalytic activity and photo-stability. Moreover, the preparation method of the present invention is simple and easy to implement, providing a new option for the screening of catalysts for removing pollutants in the water environment and an important reference for the preparation of efficient photocatalytic materials.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and particularly relates to a graphene quantum dots (GQDs)-loaded iron-doped titanium-based metal-organic framework photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Norfloxacin (NOR) is a quinolone antibiotic widely used in the treatment of diseases in humans and animals. It has the characteristics of a broad antibacterial spectrum, strong effect, and long half-life. It has good stability in nature. Continuous input and accumulation will cause serious harm to the natural environment and human health. Therefore, effectively eliminating antibiotics such as NOR has become an urgent public interest issue. The photocatalytic / persulfate oxidation system has received extensive attention due to its advantages of low cost and low energy consumption. In recent years, many research works have been devoted to developing catalysts such as metal-organic frameworks (MOFs), carbon materials, transition metals, etc. for the photocatalytic / persulfate oxidation hybrid system.

[0003] Among these materials, MOFs have received extensive attention due to their large specific surface area, permanent pores, and a large number of active metal sites. However, single MOFs have the disadvantage of fast electron (e - )-hole (h + ) recombination, which limits their application in photocatalytic reactions. The metal ion doping strategy can effectively inhibit the recombination of photo-generated e - -h + by creating a shorter electron migration path and a Metal to Metal Charge Transfer (MMCT) process, thereby improving the catalytic efficiency.

[0004] In 2020, this research group prepared NH 2 -MIL-68(In α Fe 1-α ) for photocatalytic reduction of Cr(VI) (Applied Surface Science, 2020, 528: 147053..). The removal rate reached 99.29% after 120 min. The introduction of Fe generates an MMCT process, promotes the transfer of photo-generated carriers, and reduces the recombination of photo-generated e - -h + , thereby improving the photocatalytic effect. Loading photosensitizers is another commonly used method for modifying MOFs, which can increase the light response range of MOFs and reduce the band gap (E g) to improve the structural stability and photo-stability. Graphene quantum dots (GQDs) have quantum confinement effect and boundary effect, breaking the special zero-bandgap structure of GO (graphene oxide), which can excite stable fluorescence, and have good biocompatibility, low toxicity and stable fluorescence characteristics. GQDs have few layers and a surface size of less than 100 nm, combining the advantages of GO and QDs (quantum dots), and can regulate the pore structure of MOFs from a finer nano-microstructure perspective.

[0005] In 2018, Lin et al. prepared CQDs / MIL-53(Fe) composite materials for photocatalytic removal of Cr(VI) (Inorganic Chemistry Frontiers, 2018, 5(12): 3170 - 3177.). The introduction of CQDs significantly improved the photocatalytic ability of MIL-53(Fe). The photocatalytic ability of the composite material can be adjusted by controlling the content of CQDs. The main reason for the enhanced photocatalytic activity of the composite material is that CQDs can act as electron acceptors to promote the separation of photo-generated carriers. In addition, CQDs also play the role of photosensitizers, absorbing long-wavelength visible light (λ > 570 nm) and transferring the energy to MIL-53(Fe), enhancing the light absorption in the long-wavelength visible light region, thereby improving the photocatalytic performance. Summary of the Invention

[0006] Aiming at the problem that the photocatalytic activity of single MOFs in the prior art needs to be improved, the present invention provides a preparation method of a GQDs-loaded iron-doped titanium-based MOFs photocatalyst. The prepared catalyst can efficiently remove NOR in the water environment in a photocatalytic / persulfate oxidation system and has good structural stability and photo-stability.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A preparation method of a graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst, comprising the following steps:

[0009] Step 1, dissolving a titanium source, an iron source, and 2-aminoterephthalic acid in a mixed solution of N,N-dimethylformamide and methanol, mixing, and after microwave reaction, washing and drying the product to obtain an iron-doped titanium-based metal-organic framework;

[0010] Step 2, pyrolyzing a mixture of citric acid monohydrate and graphite powder to obtain GQDs;

[0011] Step 3, ball-milling and mixing the iron-doped titanium-based metal-organic framework with the GQDs to obtain the iron-doped titanium-based metal-organic framework photocatalyst.

[0012] The GQDs-loaded iron-doped titanium-based metal-organic framework photocatalyst prepared by the present invention has iron doped in NH 2 -MIL-125(Ti). Through the potential energy difference between metal centers, photo-generated e - is separated and transferred through the MMCT process, thus effectively suppressing the problem of easy recombination of e - -h + in the material. At the same time, it brings a higher specific surface area, which is conducive to the dispersion of active sites, thereby increasing the photocatalytic activity. The loading of GQDs improves the light response ability of MOFs, while reducing the E g of MOFs, improving the structural stability and light stability, making it have better recyclability, and providing the possibility for the further development and utilization of photocatalysts for removing pollutants in the water environment.

[0013] The titanium source includes one or more of isobutyl titanate and isopropyl titanate;

[0014] The iron source includes one or more of ferric chloride, ferric nitrate and their hydrates;

[0015] In step 1, the molar ratio of the titanium source to the iron source is 8:1 - 2:1.

[0016] In the mixed solution of N,N-dimethylformamide and methanol in step 1, the molar ratio of N,N-dimethylformamide to methanol is 1:1.5 - 1:2. When the proportion of methanol increases, the morphology of NH2-MIL-125(Ti) will change slightly, from round cake shape to square-round shape, and the photocatalytic effect changes little.

[0017] The microwave reaction conditions include: placing the precursor solution in a microwave reactor, microwave conditions: 100 - 300 W, 2 - 3 GHz, reacting for 1 - 3 h.

[0018] In step 2, the mass ratio of citric acid monohydrate to graphite powder is 1:1 - 3:1. As the proportion of graphite powder increases, the size of graphene quantum dots gradually increases, and the loading effect with MOF becomes worse, and the photocatalytic effect decreases.

[0019] In step 2, the pyrolysis temperature is 150 - 180 °C and the pyrolysis time is 10 - 30 min.

[0020] In step 3, the mass ratio of the iron-doped titanium-based metal-organic framework to the GQDs is 1:5 - 15. As the loading amount of GQDs increases, the catalytic effect of CPPA improves, but as the loading amount continues to increase, the catalytic effect decreases. This is because the loading of more GQDs leads to the aggregation of quantum dots, blocking part of the pore structure of the organic framework, resulting in a decrease in its adsorption of TC-HCl and the loss of more reactive sites.

[0021] The washing and drying process in Step 1 specifically includes: washing the product with N,N-dimethylformamide and ethanol successively for 1 - 3 times, and drying it under vacuum at 50 - 80 °C for 3 - 5 h to obtain iron-doped titanium-based metal-organic framework.

[0022] The present invention also provides a graphene quantum dots-loaded iron-doped titanium-based metal-organic framework photocatalyst prepared according to the described preparation method. The GQDs-loaded iron-doped titanium-based MOF photocatalyst provided by the present invention has high photocatalytic activity and good stability in NOR wastewater. At pH = 3.2, with a catalyst dosage of 10 mg and a persulfate dosage of 4 mM, the removal rate of 20 mg L -1 of NOR reaches up to 80.1% at most within 120 min and remains stable after multiple cycles.

[0023] The present invention also provides the application of the described graphene quantum dots-loaded iron-doped titanium-based metal-organic framework photocatalyst in photocatalytic reactions, such as norfloxacin, tetracycline hydrochloride, etc.

[0024] Through the metal ion doping and in-situ loading strategy, the present invention designs and prepares a GQDs-loaded iron-doped titanium-based MOF photocatalyst, which realizes the efficient removal of NOR in the photocatalytic / persulfate oxidation hybrid system. The doping of Fe and the loading of the photosensitizer GQDs can effectively inhibit the rapid recombination of e - -h + , increase the light response range, thereby improving the photocatalytic removal performance and realizing the efficient removal of NOR in the water environment, which is of great significance for protecting the environment and human health.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) Through the metal ion doping and in-situ loading strategy, the present invention designs and prepares a GQDs-loaded iron-doped titanium-based MOF photocatalyst, which realizes the efficient removal of NOR in the photocatalytic / persulfate oxidation hybrid system. The doping of Fe and the loading of the photosensitizer GQDs can effectively inhibit the rapid recombination of e - -h + , increase the light response range, thereby improving the photocatalytic removal performance and realizing the efficient removal of NOR in the water environment, which is of great significance for protecting the environment and human health.

[0027] (2) The GQDs-loaded iron-doped titanium-based MOFs photocatalyst provided by the present invention has high photocatalytic activity and good stability in NOR wastewater and can be recycled and reused multiple times.

[0028] (3) The GQDs-loaded iron-doped titanium-based MOFs photocatalyst provided by the present invention is synthesized by ball milling. The method is simple and can be used for small-scale operations in the laboratory as well as for large-scale industrial production. Description of the Drawings

[0029] Figure 1 X-ray diffraction patterns (XRD) of the composite photocatalytic materials prepared in the examples and comparative examples.

[0030] Figure 2 Scanning electron micrographs of the composite photocatalytic materials prepared in the examples and comparative examples.

[0031] Figure 3 X-ray photoelectron spectroscopy of the composite photocatalytic materials prepared in the examples and comparative examples.

[0032] Figure 4 DRS spectra and band gap energies of the composite photocatalytic materials prepared in the examples and comparative examples.

[0033] Figure 5 Photocatalytic degradation effect of the composite photocatalytic materials prepared in the examples and comparative examples on tetracycline hydrochloride.

[0034] Figure 6 Photocatalytic degradation effect diagram of the composite photocatalytic materials prepared in the examples and comparative examples on norfloxacin.

[0035] Figure 7 For Fe 0.2 Photocatalytic degradation effect diagram of the Fe

[0036] Figure 8 For Fe 0.2 XRD and FT-IR characterizations of the Fe Detailed Description of the Invention

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent substitutions on the basis of understanding the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0038] The raw materials used in the following detailed description are all purchased from the market. The specific examples of the present invention will be described in detail below in combination with the technical solutions and the drawings.

[0039] Example 1:

[0040] Step 1, Dissolve isobutyl titanate, ferric chloride hexahydrate, and 2-aminoterephthalic acid in a mixed solution of N,N-dimethylformamide and methanol. The molar ratio of isobutyl titanate to ferric chloride hexahydrate is 8:2, and the molar ratio of N,N-dimethylformamide to methanol is 30:57. Stir and mix evenly to obtain a precursor solution of iron-doped titanium-based metal-organic framework;

[0041] Step 2, Transfer the precursor solution prepared in Step 1 to a microwave reactor for reaction. Microwave conditions: 150W, 2.5GHz, 2.5 hours. Wash the obtained product 3 times each with N,N-dimethylformamide and ethanol, and vacuum dry it at 60°C for 5h. Control the vacuum degree between -25 mmHg to obtain iron-doped titanium-based metal-organic framework, denoted as 20% Fe-NH 2 -MIL-125(Ti);

[0042] Step 3, Pyrolyze citrate monohydrate and graphite powder in a ratio of 1:1 at a pyrolysis temperature of 180°C for 30 min to obtain orange-yellow GQDs;

[0043] Step 4, Mix the iron-doped titanium-based metal-organic framework prepared in Step 2 and the GQDs obtained in Step 3 in a mass ratio of 1:10. Through ball milling, the ball milling conditions are: the rotation speed is set at 300 rpm / min, and the grinding time is 3 hours. The rotation speed is set at 300 rpm and continued at room temperature for 3 hours. Change the rotation direction once every 30 minutes, 10 minutes each time, to obtain the photocatalyst Fe of GQDs-loaded iron-doped titanium-based metal-organic framework 0.2 TiGQDs-10.

[0044] Example 2

[0045] Synthesize a series of catalysts according to the method of Example 1. Change the mass ratio of the iron-doped titanium-based metal-organic framework in Step 2 to the GQDs obtained in Step 3 to 1:5 and 1:15. The obtained catalysts are respectively labeled as Fe 0.2 TiGQDs-5, Fe 0.2 TiGQDs-15.

[0046] Comparative Example 1

[0047] Step 1, Dissolve isobutyl titanate (0.515 mL) and 2-aminoterephthalic acid (0.545 g) in a mixed solution of N,N-dimethylformamide and methanol. The molar ratio of N,N-dimethylformamide to methanol is 30:57. Stir and mix evenly to obtain a precursor solution of titanium-based metal-organic framework;

[0048] Step 2: Transfer the precursor solution prepared in Step 1 to a microwave reactor for reaction. Microwave conditions: 150 W, 2.5 GHz, 2.5 hours. Wash the obtained product three times each with N,N-dimethylformamide and ethanol, and then dry it under vacuum at 60 °C for 5 h, with the vacuum degree controlled between -25 mmHg to obtain titanium-based metal-organic framework NH 2 -MIL-125(Ti).

[0049] Step 3: Pyrolyze the citrate monohydrate and graphite powder in a ratio of 1:1 at a pyrolysis temperature of 180 °C for 30 min to obtain orange GQDs;

[0050] Step 4: Mix the titanium-based metal-organic framework prepared in Step 2 with the GQDs obtained in Step 3 in a mass ratio of 1:10. Through ball milling, the ball milling conditions are as follows: the rotation speed is set at 300 rpm / min, and the grinding time is 3 hours. The rotation speed is set at 300 rpm and continued for 3 hours at room temperature, changing the rotation direction every 30 minutes for 10 minutes each time to obtain the photocatalyst NMGQDs-10 of GQDs-loaded iron-doped titanium-based metal-organic framework.

[0051] Characterization and testing

[0052] The XRD patterns of the Fe 0.2 TiGQDs-10, Fe 0.2 TiGQDs-5, Fe 0.2 TiGQDs-15, 20% Fe-NH 2 -MIL-125(Ti), NH 2 -MIL-125(Ti) photocatalysts are as Figure 1 shown. By comparing with the standard cards, it is found that the XRD pattern of Fe 0.2 TiGQD s-10 is the same as that of NH 2 -MIL-125(Ti); no other crystal phases related to Fe and GQDs are found, and no peak shift occurs, indicating that appropriate loading of Fe and GQDs does not damage the crystal structure of NH 2 -MIL-125(Ti).

[0053] Figure 2 For the SEM images of NH 2 -MIL-125(Ti) (a), 20% Fe-NH 2 -MIL-125(Ti) (b), the TEM image (c) and HRTEM image (d) of the Fe 0.2 TiGQDs-10 composite photocatalyst. As observed from the scanning electron microscope, NH 2The crystal morphology of -MIL-125(Ti) (a) is a circular cake with a particle size of about 500 nm. Compared with NH 2 -MIL-125(Ti), 20% Fe-NH 2 -MIL-125(Ti) has a thinner crystal form and a larger particle size, about 1 μm, as shown in Figure 2 (b).

[0054] Figure 2 (c) shows that the quantum dots are loaded on the organic framework. Among them, (d) is the HR-TEM image of the Fe 0.2 TiGQD s-10 composite photocatalyst. The lattice fringe spacing d = 0.21 nm belongs to GQDs, further proving that GQDs are successfully loaded on Fe-NH 2 -MIL-125(Ti). This is consistent with the analysis results of XRD.

[0055] Figure 3 XPS spectrum of the Fe 0.2 TiGQD s-10 composite photocatalyst prepared in Example 1. Figure 3 XPS survey spectrum of the prepared Fe 0.2 TiGQD s-10 composite photocatalyst. It can be seen from the survey spectrum that the sample mainly contains C, N, O, Ti, and Fe elements. This result is consistent with the composition of the Fe-NH 2 -MIL-125(Ti)@GQDs composite photocatalyst.

[0056] The surface element composition and chemical state of Fe 0.2 TiGQD s-10 were analyzed by XPS characterization technology. As shown in Figure 3 (a) is the XPS survey spectrum of Fe 0.2 TiGQD s-10. It can be observed that Fe 0.2 TiGQD s-10 contains five elements: C, N, O, Ti, and Fe. The high-resolution spectrum of C 1s is shown in Figure 3 (b). The peaks at 288.1, 285.8, and 284.2 eV are attributed to C=O in carboxyl groups and C-C, C=C in the benzene ring skeleton respectively. The high-resolution spectrum of N 1s has two peaks. The peak at 402.5 eV indicates the formation of low-electron nitrogen, and the peak at 398.9 eV belongs to the -NH 2 group, as shown in Figure 3 c). From the high-resolution spectrum of O 1s ( Figure 3 (d)), it can be seen that the two main peaks at 531.3 and 529.8 eV belong to the C=O bond and the Ti-O bond respectively.

[0057] The high-resolution Ti 2p spectrum is as shown in Figure 3 (e). The binding energy at 464.1 eV corresponds to the characteristic peak of Ti 2p 1 / 2 , and the binding energy at 458.3 eV corresponds to the characteristic peak of Ti 2p 3 / 2 , which are respectively attributed to Fe 0.2 TiGQD s-10 containing trivalent and tetravalent Ti. The high-resolution Fe 2p spectrum is as shown in Figure 3 (f). Among them, 715.5 eV is the satellite peak of Fe(III), and Fe(III) is the main form of Fe in 20% Fe-NH 2 -MIL-125(Ti). The main peaks are located at 711.5 eV and 725.5 eV respectively, corresponding to Fe 2p 3 / 2 and Fe 2p 1 / 2 . The XPS results indicate that Fe 0.2 TiGQD s-10 is successfully synthesized.

[0058] Figure 4 DRS spectra (a) and band gap energy calculation (b) of the Fe 0.2 TiGQD s-10 composite photocatalyst prepared in Example 1. As can be seen from Figure 4(s), the Fe 0.2 TiGQD s-10 composite photocatalyst has better visible light response performance compared with Fe-NH 2 -MIL-125(Ti). As can be seen from Figure 4 (b), Fe 0.2 TiGQD s-10 has a smaller Eg value. The DRS characterization results show that the introduction of GQDs increases the visible light response performance of the Fe-NH 2 -MIL-125(Ti) composite photocatalytic material, and is expected to further improve the visible light catalytic ability.

[0059] The Fe-NH 2 -MIL-125(Ti)@GQDs composite photocatalytic material prepared in Example 1 has visible light activity and can be excited by visible light. Through the synergistic modification strategy of loading photosensitizers and metal ion doping, the degradation ability of pollutants is effectively improved. The Fe-NH 2 -MIL-125(Ti)@GQDs composite photocatalytic material prepared in the present invention has potential application prospects in the fields of sewage treatment, air purification, etc.

[0060] Application Example 1: Photocatalytic degradation of TC-HCl (tetracycline hydrochloride) by the catalyst:

[0061] Using 100 mg / L tetracycline hydrochloride as the pollutant, 50 mL of the pollutant was taken and placed in a photocatalytic reactor. The pH was adjusted to 3.2 with 0.2 mol / L HCl. 3 mL of the reaction solution was taken as the zero point for ultraviolet spectrophotometry testing. 10 mg of the catalysts prepared in Example 1 and Example 2 were added respectively, and dark adsorption was carried out for 1 h to reach dark equilibrium. During this period, 3 mL of the reaction solution was taken every 20 min for centrifugation, and the catalyst was filtered off with a 0.22-μm aqueous filter membrane for subsequent ultraviolet testing.

[0062] The photocatalytic degradation effect of tetracycline hydrochloride is as Figure 5 shown. (a) is the change in degradation efficiency over time, and (b) is the total removal efficiency of different catalysts. Among them, the photocatalytic removal rate of tetracycline hydrochloride (TC-HCl) by Fe 0.2 TiGQDs-10 is 75.6%, and that of Fe 0.2 TiGQDs-5 is 64.8%, and that of Fe 0.2 TiGQDs-15 is 69.5%.

[0063] Application Example 2: Photocatalytic degradation of NOR (norfloxacin) by the catalyst:

[0064] Using 100 mg / L norfloxacin as the pollutant, 10 mL was taken and diluted to 20 mg / L of the target pollutant, and water was added to 50 mL and placed in a photocatalytic reactor. The pH was adjusted to 3.2 with 0.2 mol / L HCl. 3 mL of the reaction solution was taken as the zero point for ultraviolet spectrophotometry testing. 10 mg of the catalyst was added, and dark adsorption was carried out for 1 h to reach dark equilibrium. During this period, 3 mL of the reaction solution was taken every 20 min for centrifugation, and the catalyst was filtered off with a 0.22-μm aqueous filter membrane for subsequent ultraviolet testing.

[0065] Figure 6 is the photocatalytic degradation effect diagram of norfloxacin. (a) is the change in degradation efficiency over time, and (b) is the total removal efficiency of different catalysts. Among them, the photocatalytic removal rate of norfloxacin by NH2-MIL-125(Ti) is 15.3%, that of NMGQDs-10 is 33.7, and that of Fe 0.2 TiGQD s-10 is 80.1%, and that of 20% Fe-NH2-MIL-125(Ti) is 56.7%. Fe 0.2 TiGQD s-10 has the best effect

[0066] This shows that there is a synergistic effect between metal ion doping and GQDs loading, which is manifested as: Fe 3+ doping improves Fe-NH 2The visible-light response performance and PDS activation performance of -MIL-125(Ti), and the MMCT process between Ti-O-Fe effectively promotes the transfer of photo-generated carriers. GQDs have excellent visible-light adsorption ability and electron transfer ability, providing another path for carrier transport, which can further enhance the separation and transfer of photo-generated carriers and inhibit photo-generated e - -h + pair recombination. Electrons on Ti may be transferred through two paths. One is transferred to Fe through the MMCT process between Ti-O-Fe, and the other is first transferred to GQDs and then transferred from GQDs to Fe, ultimately improving the activity of Fe active sites to activate PDS for NOR removal.

[0067] Application Example 3

[0068] Cyclic test: To investigate the repeated catalytic performance and recycling stability of Fe 0.2 TiGQDs-10, a cyclic test experiment was carried out on it. As Figure 7 shown, after five cyclic experiments, Fe 0.2 TiGQDs-10 still showed good CPPA catalytic performance for NOR removal, and its removal rate still reached 70.3%. Figure 8 XRD and FT-IR characterizations of Fe 0.2 TiGQDs-10 before and after use were carried out. The results showed that the crystal structure and framework structure of the catalyst did not change significantly before and after use, indicating that Fe 0.2 TiGQDs-10 has good recycling stability.

Claims

1. Preparation method of graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst, characterized in that, it comprises the following steps: Step 1, dissolve a titanium source, an iron source, and 2-aminoterephthalic acid in a mixed solution of N,N-dimethylformamide and methanol and mix them. After microwave reaction, the product is washed and dried to obtain an iron-doped titanium-based metal-organic framework; Step 2, mix citric acid monohydrate and graphite powder and pyrolyze them to obtain GQDs; Step 3, obtain the iron-doped titanium-based metal-organic framework photocatalyst by ball-milling and mixing the iron-doped titanium-based metal-organic framework and the GQDs; In Step 1, the molar ratio of the titanium source to the iron source is 8:1 - 4:1; in the mixed solution of N,N-dimethylformamide and methanol in Step 1, the molar ratio of N,N-dimethylformamide to methanol is 1:1.5 - 1:2; In Step 2, the mass ratio of citric acid monohydrate to graphite powder is 1:1 - 3:1; In Step 3, the mass ratio of the iron-doped titanium-based metal-organic framework to the GQDs is 1:5 - 15.

2. The preparation method of the graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst according to claim 1, characterized in that, the titanium source includes one or more of isobutyl titanate and isopropyl titanate; the iron source includes one or more of ferric chloride, ferric nitrate, and their hydrates.

3. The preparation method of the graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst according to claim 1, characterized in that, in Step 2, the pyrolysis temperature is 150 - 180 °C and the pyrolysis time is 10 - 30 min.

4. The preparation method of the graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst according to claim 1, characterized in that, the washing and drying process in Step 1 specifically includes: Wash the product with N,N-dimethylformamide and ethanol successively for 1 - 3 times, and vacuum-dry it at 50 - 80 °C for 3 - 5 h to obtain the iron-doped titanium-based metal-organic framework.

5. The graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst prepared by the preparation method according to any one of claims 1 - 4.

6. Application of the graphene quantum dot-loaded iron-doped titanium-based metal-organic framework photocatalyst according to claim 5 in photocatalytic reaction.

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