Photoactive polyoxometalate-based metal-organic framework composites, their preparation methods and applications

Abstract

This application relates to a photoactive polyoxometalate-based metal-organic framework composite material, its preparation method, and its application, belonging to the field of photocatalytic materials technology. The preparation method of this application's photoactive polyoxometalate-based metal-organic framework composite material includes the following steps: stirring copper salt, a photosensitive ligand, and silicotungstic acid in a mixed solvent, then carrying out a hydrothermal reaction, cooling to room temperature, crystal precipitation, and washing and drying to obtain the photoactive polyoxometalate-based metal-organic framework composite material. The photoactive polyoxometalate-based metal-organic framework composite material provided in this application exhibits excellent performance in the CDC reaction for the synthesis of benzo(naphthalene)thiazole, achieving moderate to high yields, and providing a promising heterogeneous photocatalytic strategy for the green and efficient synthesis of benzo(naphthalene)thiazole derivatives.

Description

Technical Field

[0001] This application relates to the field of photocatalytic materials technology, and in particular to a photoactive polyoxometalate-based metal-organic framework composite material, its preparation method, and its application. Background Technology

[0002] Benzothiazoles and their derivatives, due to their unique heterocyclic structures composed of fused benzene / naphthyl rings and thiazole rings, exhibit excellent optical, electronic, and biological activities. Because of these superior properties, they have been widely applied in key fields such as optoelectronic materials, medicinal chemistry, and industry, thus becoming one of the research hotspots in contemporary materials chemistry and medicinal chemistry. However, traditional methods suffer from drawbacks such as low conversion rates, high environmental pollution risks, and complex reagents and reaction conditions. In recent years, various functional materials have been developed, including transition metal Ru-, Ir-, or Cu-based polypyridine complexes, polyoxides, organic dyes, cadmium sulfide, and composite materials. Although these catalytic systems have significant advantages, these strategies still face some key challenges, such as high costs, cumbersome preparation processes of noble metals, and poor stability and durability of organic ligand-supported metal catalysts and organic molecules. Therefore, there is an urgent need to develop highly efficient heterogeneous photocatalysts to achieve rapid and green synthesis of complex benzothiazole molecular skeletons through efficient construction of N-S bonds.

[0003] Polyoxometalate-based metal-organic frameworks (POMOFs) are composite functional materials formed by the chemical assembly of polyoxometalates (POMs) and metal-organic frameworks (MOFs). POMs are characterized by their clear structure and excellent electronic / redox properties, while MOFs are crystalline porous materials with high specific surface area and tunable pore structure. In the field of photocatalysis, the performance advantages of POMOFs far exceed those of single POMs or single MOFs, thanks to the synergistic effect between their two components. For example, the synergistic effect of electronic structure facilitates the separation of charge carriers. This spatial separation significantly extends the lifetime of charge carriers, thereby improving the quantum efficiency of photocatalytic reactions. At the same time, the synergistic effect of optical properties can expand the light absorption range, and the synergistic effect of structural stability can improve recyclability. These synergistic effects compensate for the shortcomings of single POMs, such as small specific surface area, rapid charge carrier recombination, and weak redox activity and limited stability of single MOFs, making POMOFs a promising new catalyst in photocatalytic water splitting, carbon dioxide reduction, organic pollutant degradation, and photocatalytic synthesis.

[0004] Here, by using the electron acceptor [SiW] 12 O 40 ] 4-A novel photoactive POMOF, [Cu2(BTIz)3(H2O)5SiW, was successfully synthesized by incorporating it into a BTIz-based MOF. 12 O 40 ]·5H2O. BTIz is a typical donor-acceptor-donor type photosensitizer. Its inherent planar π-conjugated electron absorption core is a benzothiadiazole unit, which can extend the light absorption range into the visible light region. The linear structure of the donor and acceptor π series enables BTIz to achieve efficient electron transfer in photocatalysis. [SiW 12 O 40 ] 4- As an electron sponge, it forms a microstructure through strong coordination bonds or electrostatic interactions with MOFs, thereby achieving spatial separation of electrons and holes. Under illumination, BTIz orderly transfers charge to the metal / POM, which is conducive to the formation of O2. - CuW-BTIz was used to synthesize benzothiazolium compounds by photocatalytic oxidative cross-coupling of benzothiazolium and amine under white light at room temperature, with yields ranging from moderate to excellent. Summary of the Invention

[0005] In view of this, this application provides a photoactive polyoxometalate-based metal-organic framework composite material, its preparation method and application. This photoactive polyoxometalate-based metal-organic framework composite material exhibits excellent performance in the CDC reaction for the synthesis of benzo(naphthalene)thiazole, achieving medium to high yields. It provides a promising heterogeneous photocatalytic strategy for the green and efficient synthesis of benzo(naphthalene)thiazole derivatives, and can effectively overcome the defects of the above-mentioned prior art.

[0006] The first aspect of this application provides a method for preparing a photoactive polyoxometalate-based metal-organic framework composite material, comprising the following steps:

[0007] Copper salt, photosensitive ligand and silicotungstic acid were stirred in a mixed solvent and then subjected to a hydrothermal reaction. After cooling to room temperature, crystals precipitated, and after washing and drying, the photoactive polyoxometalate-based metal-organic framework composite material was obtained.

[0008] Preferably, the hydrothermal temperature is 120°C and the hydrothermal time is 4 days.

[0009] Preferably, the mixed solvent is composed of distilled water and methanol, wherein the volume ratio of distilled water to methanol is 4:2.

[0010] Preferably, the washing conditions are as follows: washing is performed using distilled water.

[0011] Preferably, the hydrothermal reaction is carried out in a reaction vessel.

[0012] Preferably, the copper salt is Cu(NO3)2·3H2O.

[0013] Preferably, the photosensitive ligand is BTIz; the silicotungstic acid is K8[α-SiW]. 11 O 39 ]·13H2O.

[0014] Preferably, the Cu(NO3)2·3H2O, BTIz, and K8[α-SiW 11 O 39 The mass ratio of 13H2O is 78:13:72.

[0015] A second aspect of this application also provides a photoactive polyoxometalate-based metal-organic framework composite material. The photoactive polyoxometalate-based metal-organic framework composite material prepared by the above method has the chemical formula [Cu2(BTIz)3(H2O)5SiW 12 O 40 5H₂O. Specifically, its molecular formula is: C 36 Cu2N 18 O 50 S3SiW 12 It is abbreviated as CuW-BTIz (BTIz = 4,7-bis(imidazolyl)benzothiazole). This compound belongs to the monoclinic crystal system. Space group. This material can efficiently catalyze the N-S coupling reaction to synthesize benzothiazole compounds.

[0016] The third aspect of this application also provides the application of the above-mentioned photoactive polyoxometalate-based metal-organic framework composite material in photocatalytic oxidative cross-coupling reactions to synthesize benzothiazole compounds.

[0017] Compared with the prior art, this application has the following advantages:

[0018] (1) This application will use polyacids [SiW] 12 O 40 ] 4- A novel photoactive polyoxometalate-based metal-organic framework (POMOF) catalyst [Cu2(BTIz)3(H2O)5SiW] was synthesized by integrating it into a BTIz-based MOF. 12 O 40 ]·5H2O (CuW-BTIz, BTIz = 4,7-bis(imidazolyl)benzothiazole);

[0019] (2) In this application, BTIz, as a donor-acceptor-donor photosensitive ligand, has broad visible light absorption and efficient electron transfer capability, while [SiW12 O 40 ] 4- As an electron acceptor, it promotes charge separation through coordination interactions;

[0020] (3) This application utilizes visible light-induced photocatalytic cross-dehydrogenation coupling reaction (CDC) as a green and efficient alternative method, which solves the limitations of high cost of precious metal catalysts, poor stability of organic-based catalysts and low bonding efficiency.

[0021] (4) The CuW-BTIz of this application exhibits excellent performance in the CDC reaction for the synthesis of benzo(naphthiazole), achieving medium to high yields, and provides a promising heterogeneous photocatalytic strategy for the green and efficient synthesis of benzo(naphthiazole) derivatives. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 (a) shows the asymmetric unit cell of CuW-BTIz in an ellipsoidal model; (b) shows a view of a one-dimensional chain with a grid; (c) shows the crystal structure of CuW-BTIz exhibiting a grid-like lamellar stacking mode; (d) shows the crystal structure of CuW-BTIz displaying [SiW 12 O 40 ] 4- The stacking pattern of anions embedded along the a-direction;

[0024] Figure 2 Infrared spectra of compounds CuW-BTIz and H2BTIz;

[0025] Figure 3 The XRD pattern of compound CuW-BTIz is shown below.

[0026] Figure 4 (a) is the compound CuW-BTIz, SiW 12 (a) UV-Vis diffuse reflectance spectra of CuW-BTIz and BTIz; (b) Tauc plots of CuW-BTIz and BTIz; (c) Schematic diagram of optical band gap; (d) Transient photocurrent spectrum of CuW-BTIz; (e) Electrochemical impedance spectroscopy of CuW-BTIz and BTIz; (f) Fluorescence emission spectrum of CuW-BTIz as illumination time increases.

[0027] Figure 5Thermogravimetric spectrum of CuW-BTIz;

[0028] Figure 6 IR spectra of CuW-BTIz in different solutions;

[0029] Figure 7 IR spectra of CuW-BTIz at different pH values;

[0030] Figure 8 (a) High-resolution XPS spectrum of Cu before 2p illumination; (b) High-resolution XPS spectrum of W before 4f illumination; (c) High-resolution XPS spectrum of Cu after 2p illumination; (d) High-resolution XPS spectrum of W after 4f illumination.

[0031] Figure 9 (a) is the reactive oxygen species quenching experiment; (b) is the EPR spectrum of singlet oxygen; (c) is the EPR spectrum of hydroxyl radical; (d) is the EPR spectrum of superoxide radical.

[0032] Figure 10 It is 2-(thiomorpholino)benzothiazole 1 H NMR spectrum. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] Unless otherwise specified, the experimental methods used in the embodiments of this application are all conventional methods.

[0035] In the following embodiments, unless otherwise specified, all raw materials can be obtained by commercial purchase or conventional methods.

[0036] Example 1

[0037] A photoactive polyoxometalate-based metal-organic framework composite material [Cu2(BTIz)3(H2O)5SiW 12 O 40 The synthesis method of ·5H2O specifically includes the following steps:

[0038] The compound CuW-BTIz was prepared by self-assembly under hydrothermal conditions, specifically by weighing 39 mg of Cu(NO3)2·3H2O, 6.5 mg of BTIz, and 36 mg of K8[α-SiW]. 11 O39 The compound CuW-BTIz was dissolved in a mixture of 4 mL distilled water and 2 mL methanol by stirring. The solution was then transferred to a reaction vessel and reacted at 120°C for 4 days. After cooling to room temperature, crystals precipitated. These crystals were washed with distilled water and dried to obtain green crystals, with a yield of 60%. The chemical formula of the above compound is: C 36 Cu2N 18 O 50 S3SiW 12 .

[0039] Crystal structure analysis: Crystallographic analysis of compound CuW-BTIz was performed, and the results are as follows.

[0040] Table 1. Crystallographic data of compound {CuW-BTIz}

[0041]

[0042] As can be seen from Table 1, the compound CuW-BTIz belongs to the monoclinic crystal system. Space group. From Figure 1 As can be seen from a, the asymmetric unit consists of one [Cu2(BTIz)3(H2O)5] 4+ Cation, 1 [SiW] 12 O 40 ] 4- Composed of anion and 5 H2O molecules ( Figure 1 a). Two crystallographically independent Cu(II) ions alternately connect three BTIz bridges, forming a 1D lattice structure. Furthermore, [SiW 12 O 40 ] 4- Anions are suspended outside the mesh ( Figure 1 b). Both Cu ions are in a distorted octahedral coordination environment, with the equatorial plane formed by three imidazole N atoms from three BTIz ligands and one O atom from a coordinated water molecule, and are associated with [SiW]. 12 O 40 ] 4- One terminal oxygen atom and one O atom in a coordinated water molecule, or two O atoms in coordinated water molecules, occupy the axial position. The Jahn-Teller effect weakens Cu. 2+ The axial coordination bonds in the complex facilitate the dissociation of coordinated water molecules. This process enables Cu... 2+ Vacancies appear at the coordination sites of Cu, allowing it to bind to amine substrates and lower the dissociation energy of the N-H bonds in the latter. This property endows Cu with... 2+ Its high efficiency as an active center for catalytic amine conversion makes it extremely valuable in organic synthesis and materials catalysis. Most interestingly, the [SiW] of adjacent molecules... 12 O40 ] 4- Anions are precisely housed in the gaps between adjacent molecular networks through anion-π and hydrogen bond interactions, resulting in an interpenetrating arrangement. This allows 1D networks to be further assembled into 3D architectures. Figure 1 c, d). POMs have abundant W 6+ Its redox active sites and relatively low conduction band energy level enable it to act as an effective electron-trapping center. Specifically, when the MOF component generates electrons (e) under photoexcitation... - ) and holes (h + During this process, photogenerated electrons rapidly transfer from the conduction band of MOFs to the reduction active sites of POMs. This process prevents electrons from being drawn from the MOFs. - and h + Direct compounding is beneficial for reactive oxygen species (ROS) and O2. - The formation of MOFs. In addition, in this structure, the organic ligand BTIz used to construct MOFs has a conjugated π-electron system and heteroatoms N and S, which can establish a continuous hole transport pathway to rapidly transfer photogenerated holes to catalytically active sites on the material surface, thereby participating in amine oxidation reactions.

[0043] Infrared spectroscopy: The infrared spectrum of compound CuW-BTIz is as follows Figure 2 As shown in the figure. The presence of POM and BTIz can be seen from the figure, located at 952 cm⁻¹. -1 920 cm -1 797 cm -1 There is a WO d Si-O a WO b,c Characteristic stretching vibration.

[0044] X-ray powder diffraction: The X-ray powder diffraction pattern of compound CuW-BTIz is as follows. Figure 3 As shown, "Simulated" represents the spectrum obtained through simulation, and "Experimental" represents the spectrum obtained through experimentation. The comparison shows that the peak shapes and positions of the experimental and theoretical values ​​are almost perfectly matched, indicating that the sample phase purity is very high and there are virtually no impurities.

[0045] UV-Vis diffuse reflectance spectrum: UV-Vis spectrum of CuW-BTIz as follows Figure 4 As shown in Figure a, CuW-BTIz exhibits two broad and strong adsorption bands in the 200–800 nm range, demonstrating its potential application in photocatalysis. The 200–500 nm range corresponds to the π-band of the conjugated system of the organic ligand BTIz itself. π* and n The π* transition. The main reason for the absorption in the visible region of 500–800 nm is attributed to the metal-to-ligand charge transfer transition (MLCT) between the highest occupied molecular orbital (HOMO) of the Cu(I) ion and the lowest unoccupied molecular orbital (LUMO) of the ligand BTIz. According to the Tauc diagram, the band gap energy (Eg) of CuW-BTIz is 2.59 eV. Figure 4 b). The LUMO at the CuW-BTIz site is more negative than that at the BTIz reduction site, indicating that they thermodynamically complete the O2 activation process (O2 / O2· - The feasibility of (-0.33 V vs. NHE) Figure 4 c). The LUMO of CuW-BTIz is -0.96 V (vs. NHE). According to formula E VB = E CB + Eg, further calculations show that the HOMO is 1.63 V (vs. NHE).

[0046] Photoelectric properties study: Transient photocurrent was measured under xenon lamp irradiation. The results showed that the catalyst has strong photogenerated electron-hole pair separation efficiency, making it suitable as a potential photocatalyst. Figure 4 d). Simultaneously, electrochemical impedance spectroscopy (EIS) measurements were performed to test the carrier transport efficiency of CuW-BTIz. The smaller the semicircle in the Nyquist plot of the test sample, the higher the separation and transfer efficiency of photoexcited electron-hole pairs. The diameter of the Nyquist semicircle of the CuW-BTIz electrode is smaller than that of the H2BTIz electrode. Lower impedance values ​​indicate easier electron transfer, which means a more favorable photocatalytic reaction on the catalyst surface. Figure 4 e). Furthermore, the fluorescence intensity of CuW-BTIz gradually decreased with increasing illumination time, indicating that the rapid recombination of electron-hole pairs was suppressed during this process. The gradual decrease in fluorescence intensity suggests the formation of photoinduced free radical anions, leading to the overlap of emission and absorption bands (e). Figure 4 f).

[0047] Thermal stability analysis: Thermogravimetric analysis of compound CuW-BTIz, such as Figure 5 As shown, the curves indicate that CuW-BTIz possesses good thermal stability. After immersing the sample in different organic solvents such as N,N-dimethylformamide, acetonitrile, methanol, dichloromethane, and aqueous solutions with pH values ​​of 2, 4, 8, and 12 for 24 hours, the infrared spectra showed that most peaks did not exhibit significant changes. Figure 6 , 7 It can be demonstrated that CuW-BTIz maintains its complete structure in different solvents and pH conditions, exhibiting high chemical and thermal stability, thus meeting the requirements for use as a heterogeneous catalyst.

[0048] In-situ XPS spectra: To investigate the electron transfer in the photocatalytic reaction, we conducted in-situ XPS measurements. The Cu2p XPS spectrum shows that the doped Cu only... + and Cu 2+ The form of existence ( Figure 8 a) After illumination, some Cu in the CuW-BTIz sample... + The ions lose electrons and transform into Cu. 2+ For samples exposed to light, Cu + The binding energy was determined to be 952.01 eV (2p). 1 / 2 ) and 932.02eV (2p 3 / 2 The corresponding satellite peaks are located at 962.83 eV and 942.48 eV. Meanwhile, Cu... 2+ The binding energy was determined to be 955.50 eV (2p). 1 / 2 ) and 934.37 eV (2p 3 / 2 )( Figure 8 c). The W 4f peak of CuW-BTIz fits two peaks at binding energies of approximately 37.67 eV and 35.51 eV, consistent with the oxidation state of W(VI). Figure 8 b). After illumination, the binding energy of W4f shifted negatively, reaching approximately 36.82 eV and 34.60 eV, respectively, indicating that W(VI) was partially reduced to W(V) during the photocatalytic process of CuW-BTIz. Figure 8 d).

[0049] Active species quenching experiment: To verify the active species in the catalytic reaction, we conducted a free radical quenching experiment. Figure 9 a) As expected, with the addition of electron scavenger K2S2O8 and hole trapping agent KI, the conversion rates of the reaction were 12% and 9%, respectively, further confirming that the reaction is related to photogenerated electrons and holes. Furthermore, when 1,4-benzoquinone was added as a superoxide radical scavenger, the conversion rate dropped sharply to 31.92%, demonstrating that superoxide radicals play a key role in this reaction. However, when 1,4-diazabicyclo[2.2.2]octane and isopropanol were added as scavengers of singlet oxygen and hydroxyl radicals, respectively, the reaction conversion rate hardly changed. This indicates that singlet oxygen and hydroxyl radicals have no effect on this reaction.

[0050] Electron paramagnetic resonance (EPR) assays of reactive oxygen species: To further verify the presence of reactive oxygen species in this photocatalytic system, we performed EPR assays on these species, such as... Figure 9 As shown in bc, neither singlet oxygen nor hydroxyl radical signals were detected. Conversely, a significant superoxide radical signal was observed. Figure 9 d).

[0051] Example 2: Photocatalysis Application Experiment

[0052] Photocatalytic oxidation cross-coupling of thiols: In a typical reaction system, benzothiadiazole (0.5 mmol), morpholine (0.6 mmol), CuW-BTIz (10 mg), and DMF (2 mL) were added to a 15 mL quartz tube. A 20 W LED lamp was used as the bottom illumination light source. The reaction temperature was 25 ± 5 °C. After reacting for 24 h, the mixture was centrifuged to remove the CuW-BTIz sample. The mixture was then extracted with dichloromethane and dried with anhydrous sodium sulfate. 1 H NMR and 13 Qualitative and quantitative analysis was performed using C10 NMR spectroscopy. The photocatalyst was collected in a cyclic experiment, washed three times with water and dichloromethane by centrifugation, and then dried at 60°C for 3 h. This experiment was repeated four times.

[0053] Photocatalytic properties study

[0054] Based on its unique photochemical properties, we used the cross-coupling reaction of 2-mercaptobenzothiadiazole with amines as a model reaction. Using 2-mercaptobenzothiadiazole (0.5 mmol) and morpholine (0.6 mmol) as starting materials, N,N-dimethylformamide as solvent, CuW-BTIz (10 mg) and 1 atm O2 as oxidants, the reaction was carried out at room temperature for 24 h under 20 W white LED light irradiation, achieving a thiol oxidative coupling conversion rate of 92% (Table 2, entry 1). To optimize the reaction conditions, different solvents were screened, including ethanol, methanol, and acetonitrile (Table 2, entries 2-4). No reaction occurred without a catalyst and without light, indicating that both are indispensable (Table 2, entries 5-6). When K4[SiW] was used alone... 12 O 40 When Cu(NO3)2·13H2O and BTIz are used as catalysts, the yields are significantly less than ideal under the same conditions (Table 2, entries 7-9). When nitrogen is used instead of oxygen, the reaction does not proceed, indicating that oxygen is essential for the reaction (Table 2, entry 10).

[0055] Table 2. Control experiments of photocatalytic SN cross-coupling reaction

[0056]

[0057] a. Standard conditions: CuW-BTIz 10 mg, benzothiadiazole (0.5 mmol), morpholine (0.6 mmol), DMF (2 mL), white light, room temperature, 24 h, O2. b. Yield was determined using 1H NMR spectroscopy.

[0058] To investigate the structure-activity relationship between the structure of amine substrate B and the reaction yield, a series of amines with different structural types were selected as substrates, and their reactivity in the target oxidative coupling reaction was evaluated (Table 3). In the oxidative coupling reaction, the initial step of amine radical generation is highly dependent on the electron density of the nitrogen atom in the amine substrate. When B is an aliphatic amine, the electron-donating effect of the alkyl group significantly enhances the electron density of the nitrogen atom, making it easier to lose a single electron under oxidative conditions to form the key amine radical intermediate (Table 3, Entries 1, 2, 5). At the same time, the high nucleophilicity of aliphatic amines also facilitates the nucleophilic attack of the amine radical on the coupling partner, promoting the subsequent formation of SN bonds. Correspondingly, the reaction yield remained at a high level (89-92%), and the yield of the cyclic tertiary amine piperidine reached 92% (Table 3, Entry 1). The cyclic structure of piperidine not only maintains the high electron density on the nitrogen atom, but also stabilizes the generated amine radical through the delocalization effect of the cyclic system, thus exhibiting the highest reactivity among all tested compounds. Conversely, when B is an aralkyl secondary / primary amine, the conjugation between the benzene ring and the lone pair of electrons of nitrogen reduces the electron density of the nitrogen atom, thereby hindering the single-electron oxidation process and the formation of amine radical intermediates (Table 3, entries 3, 4). Furthermore, the nucleophilicity of the nitrogen atom reduces the efficiency of the SN bond formation step, leading to a significant decrease in reaction yield (77–79%).

[0059] Table 3. Substrate expansion experiments for photocatalytic SN cross-coupling reactions

[0060]

[0061] A (0.5 mmol), B (0.6 mmol), DMF (2 mL), white light, room temperature, 24 h, O2.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a photoactive polyoxometalate-based metal-organic framework composite material, characterized in that, Includes the following steps: Copper salt, photosensitive ligand and silicotungstic acid were stirred in a mixed solvent and then subjected to a hydrothermal reaction. After cooling to room temperature, crystals precipitated, and after washing and drying, the photoactive polyoxometalate-based metal-organic framework composite material was obtained.

2. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 1, characterized in that, The hydrothermal temperature is 120℃, and the hydrothermal time is 4 days.

3. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 1, characterized in that, The mixed solvent is composed of distilled water and methanol, wherein the volume ratio of distilled water to methanol is 4:

2.

4. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 1, characterized in that, The specific conditions for washing are: washing with distilled water.

5. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 1, characterized in that, The hydrothermal reaction is completed in a reactor.

6. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 1, characterized in that, The copper salt is Cu(NO3)2·3H2O.

7. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 6, characterized in that, The photosensitive ligand is BTIz; the silicotungstic acid is K8[α-SiW] 11 O 39 ]·13H2O.

8. The method for preparing the photoactive polyoxometalate-based metal-organic framework composite material according to claim 7, characterized in that, The Cu(NO3)2·3H2O, BTIz and K8[α-SiW 11 O 39 The mass ratio of 13H2O is 78:13:

72.

9. A photoactive polyoxometalate-based metal-organic framework composite material, characterized in that, The photoactive polyoxometalate-based metal-organic framework composite material prepared by the method according to any one of claims 1 to 8 has the chemical formula [Cu2(BTIz)3(H2O)5SiW 12 O 40 ]·5H2O.

10. The application of the photoactive polyoxometalate-based metal-organic framework composite material of claim 9 in photocatalytic oxidative cross-coupling reactions to synthesize benzothiazole compounds.

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