A hydrophobic mixed-valence metal-organic framework material, a preparation method thereof and a method for photocatalytic preparation of hydrogen peroxide

Abstract

The application discloses a hydrophobic mixed-valence metal organic framework material and a preparation method and a method for photocatalytically preparing hydrogen peroxide, the ligand of the metal organic framework material is bicarbazole, the bicarbazole group provides a larger conjugated structure, has wide absorption of visible light, forms a MOF structure with a large-aperture pore regular appearance, and has high light absorption conversion efficiency, high catalytic activity, and chemical stability and water stability. The hydrophobic mixed-valence metal organic framework material can be prepared through a solvothermal reaction, and synthesis is simple and convenient, and the hydrophobic mixed-valence metal organic framework material can be mass-produced without a complicated operation process. In the method for photocatalytically preparing hydrogen peroxide, the hydrophobic mixed-valence metal organic framework material is dispersed in an organic phase formed by benzyl alcohol, and does not need to be in contact with an aqueous solution, so that hydrophobicity and water instability of the catalyst are avoided; and the hydrogen peroxide generation rate can reach 4717.84 mu mol / g / h.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal organic framework functional materials, and relates to a hydrophobic mixed-valence metal organic framework material, a preparation method thereof and a method for photocatalytically preparing hydrogen peroxide. BACKGROUND

[0002] In recent years, with the development of industrialization, energy consumption is increasing, resources are exhausted, and environmental pollution is becoming increasingly serious, so it is imperative to develop a series of secondary and clean energy. Hydrogen peroxide (H2O2) is widely used in water environment remediation as an environmentally friendly strong oxidant. Many pollutants, including organic dyes, organochlorine pesticides, cyanide, phenols, antibiotics, can be treated with H2O2 and will not cause secondary pollution to the environment, so it can be used as an environmentally friendly disinfectant to inactivate pathogenic microorganisms.

[0003] The typical industrial production of H2O2 is based on the anthraquinone method, but this method needs to use expensive palladium-based catalysts and complex reactions such as catalyst hydrogenation and oxidation processes, and may also produce toxic by-products. Therefore, the process of producing H2O2 has high cost, huge energy consumption and is not sustainable for multi-step hydrogenation and oxidation reactions, and it is very important to develop an efficient, economical and environmentally friendly H2O2 production method. The photocatalytic production of H2O2 is considered to be a green, efficient and economical way to produce H2O2, but in the prior art, most of the photocatalysts used are water-unstable and the structure is easily destroyed; or the material is hydrophobic, so it cannot be combined with water well and has poor performance. SUMMARY

[0004] In order to overcome the deficiencies of the prior art, the first object of the present application is to provide a hydrophobic mixed-valence metal organic framework material, which has a regular appearance, high chemical stability and water stability, and can efficiently produce superoxide radicals through oxidation reaction.

[0005] The second object of the present application is to provide a preparation method of the hydrophobic mixed-valence metal organic framework material.

[0006] The third object of the present application is to provide a method for photocatalytically preparing hydrogen peroxide.

[0007] The first object of the present application can be achieved by adopting the following technical scheme:

[0008] A hydrophobic mixed-valence metal organic framework material, an organic ligand with a structure shown in formula I is coordinated with a Fe2M metal cluster to form a mixed-valence metal organic framework material; M in the Fe2M metal cluster is one of Ni, Fe, Mn or Co;

[0009] The four carboxyl groups of each organic ligand are connected to the Fe2M metal cluster respectively, wherein three carboxyl groups replace the acetic acid coordination groups on the Fe2M metal cluster; one carboxyl group is directly connected to the metal ion of the Fe2M metal cluster;

[0010] The six acetic acid coordination groups on each Fe2M metal cluster are replaced by the carboxyl groups of the ligand; one ligand carboxyl group is directly connected to one Fe ion or M ion of the Fe2M metal cluster;

[0011]

[0012] The second object of the present application can be achieved by adopting the following technical solutions:

[0013] The hydrophobic mixed-valence metal-organic framework material is prepared by solvothermal reaction of the organic ligand with the structure shown in formula I and the Fe2M metal cluster in an organic solvent under catalysis of acetic acid.

[0014] Further, the mass ratio of the organic ligand to the Fe2M metal cluster is 1:1-1.5.

[0015] Further, the organic solvent is a mixture of one or both of DMF and DEF.

[0016] Further, the volume ratio of acetic acid to the organic solvent is 1:(1-20).

[0017] Further, the mass-volume ratio of the organic ligand to the total volume of acetic acid and the organic solvent is 1:(0.15-0.8) mg / ml.

[0018] Further, the solvothermal reaction is performed at 100-170℃ for 24-72h.

[0019] Further, the preparation path of the organic ligand with the structure shown in formula I is as follows:

[0020]

[0021] Further, after the solvothermal reaction, cooling is performed, and the cooling is cooling to 15-35℃ under natural conditions.

[0022] Further, after the cooling, the obtained system is subjected to solid-liquid separation, and then the obtained solid substance is sequentially washed and dried to obtain the hydrophobic mixed-valence metal-organic framework material.

[0023] Further, the reagent used for the washing is acetone.

[0024] Further, the drying is air drying under natural conditions.

[0025] The third object of the present application can be achieved by adopting the following technical solution:

[0026] A method for photocatalytically preparing hydrogen peroxide, wherein the hydrophobic mixed-valence metal organic framework material or the hydrophobic mixed-valence metal organic framework material prepared by the method is used as a photocatalyst to prepare hydrogen peroxide through a photocatalytic reaction.

[0027] Further, the hydrophobic mixed-valence metal organic framework material is subjected to a photocatalytic reaction under light irradiation in a benzyl alcohol and potassium dihydrogen phosphate aqueous solution with oxygen being introduced to prepare hydrogen peroxide.

[0028] Further, the mass-volume ratio of benzyl alcohol to the mixed-valence metal organic framework material is 1:(0.5-2) mg / mL; the light irradiation condition is (0.1-0.15) W / cm 2 Xenon lamp irradiation;

[0029] Further, the volume ratio of the potassium dihydrogen phosphate aqueous solution to the benzyl alcohol is 1:(1-3); and the concentration of the potassium dihydrogen phosphate is (0.005-0.05) mol / L.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] 1. The hydrophobic mixed-valence metal organic framework material of the present application has a large conjugated structure provided by the double carbazole groups of the ligand, has a wide absorption of visible light, and forms a charge separation state; the macrocyclic structure is conducive to the formation of large-aperture pores, improves the contact probability of substrates and exposed catalytically active sites, and promotes the occurrence of photo-reactions; and the regular appearance of the hydrophobic mixed-valence metal organic framework material increases the chemical stability and water stability of the catalyst.

[0032] 2. The preparation method of the hydrophobic mixed-valence metal organic framework material of the present application can be prepared through a solvothermal reaction, is simple and convenient to synthesize, and can be mass-produced without complicated operation processes.

[0033] 3. The method for photocatalytically preparing hydrogen peroxide of the present application has the hydrophobic mixed-valence metal organic framework material dispersed in an organic phase formed by benzyl alcohol, does not need to be in contact with an aqueous solution, avoids the hydrophobicity and water instability of the catalyst, and can achieve a hydrogen peroxide production rate of 4717.84 μmol / g / h. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The connection structure between the ligand and the Fe2M metal cluster in the hydrophobic mixed-valence metal organic framework material prepared in Examples 1-4 of the present application is shown in the schematic diagram.

[0035] Figure 2NMR spectrum of the organic ligand of the structure shown in Formula I;

[0036] Figure 3 NMR spectrum of the organic ligand of the structure shown in Formula I;

[0037] Figure 4 Appearance of the hydrophobic mixed-valence metal-organic framework material prepared in Examples 1-4 of the present application;

[0038] Figure 5 NMR spectrum of the product of the photocatalytic reaction of Example 5;

[0039] Figure 6 X-ray powder diffraction pattern of the hydrophobic mixed-valence metal-organic framework material of the present application;

[0040] Figure 7 Infrared spectrum of the hydrophobic mixed-valence metal-organic framework material of the present application;

[0041] Figure 8 X-ray powder diffraction pattern of the hydrophobic mixed-valence metal-organic framework material of the present application after being soaked in different solvents for 36 h;

[0042] Figure 9 SEM image of Fe2NiBCTA prepared in Example 3;

[0043] Figure 10 Elemental mapping of Fe2NiBCTA prepared in Example 3;

[0044] Figure 11 UV absorption curve of the reaction solution after the hydrophobic mixed-valence metal-organic framework material of Examples 1-4 of the present application was used as a catalyst for 4 h;

[0045] Figure 12 Column chart of the rate of hydrogen peroxide production by the hydrophobic mixed-valence metal-organic framework material of Examples 1-4 of the present application as a catalyst;

[0046] Figure 13 UV absorption curve of the photocatalytic reaction solution under different reaction conditions;

[0047] Figure 14 Column chart of the rate of hydrogen peroxide production by the photocatalytic reaction under different reaction conditions;

[0048] Figure 15 UV absorption curve of the reaction solution after Fe2NiBCTA prepared in Example 3 was used as a catalyst for 4 h in a cycle for three times;

[0049] Figure 16 X-ray powder diffraction pattern of Fe2NiBCTA prepared in Example 3 after being used as a catalyst in a cycle for three times. DETAILED DESCRIPTION

[0050] The technical solutions of the present application will be clearly and completely described below in combination with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0051] In the prior art of photocatalytic preparation of hydrogen peroxide, most of the photocatalysts used are water-unstable and their structures are easily destroyed, or the materials are hydrophobic and cannot be combined with water well, so that the photocatalysts cannot be repeatedly used or the hydrogen peroxide production efficiency is not good. Therefore, the present application provides a hydrophobic mixed-valence metal organic framework material and a preparation method thereof and a method for photocatalytic preparation of hydrogen peroxide.

[0052] A hydrophobic mixed-valence metal organic framework material, an organic ligand with a structure shown in formula I is coordinated with Fe2M metal clusters to form a mixed-valence metal organic framework material; M in the Fe2M metal cluster is one of Ni, Fe, Mn or Co;

[0053] Four carboxyl groups of each organic ligand are connected with the Fe2M metal cluster, wherein three carboxyl groups replace the acetic acid coordination groups on the Fe2M metal cluster; one carboxyl group is directly connected to the metal ion of the Fe2M metal cluster;

[0054] Six acetic acid coordination groups on each Fe2M metal cluster are replaced by the carboxyl groups of the ligand; one Fe ion or M ion of the Fe2M metal cluster is directly connected with the carboxyl group of one ligand; a connection structure diagram of the ligand and the Fe2M metal cluster of the hydrophobic mixed-valence metal organic framework material is shown in Figure 1 .

[0055]

[0056] The hydrophobic mixed-valence metal organic framework material of the present application has a ligand of biscalbazole, and the biscalbazole group provides a large conjugated structure, has a wide absorption of visible light, and can effectively absorb light energy; four carboxyl groups are connected to each ligand unit to coordinate with different metal ions, so that efficient charge transfer in the catalyst is realized; the macrocyclic structure of the ligand is beneficial to the formation of large-aperture pore particles, improves the contact probability of substrates and exposed catalytically active sites, and promotes the occurrence of photo-reaction; and the regular appearance of the hydrophobic mixed-valence metal organic framework material increases the chemical stability and water stability of the catalyst.

[0057] As one of the embodiments, the structure formula of the Fe2M metal cluster is [Fe2M(μ3-O)(CH3COO)6], wherein one μ3-O connects two Fe 3+ and one M2+ two Fe 3+ and M 2+ are connected by two carboxyl groups of two acetic acid groups, and six acetic acid coordination groups form a triangular prism shape. The μ3-O connects two Fe 3+ and one M 2+ can increase the charge transfer between the three metal ions, and promote the redox reaction thereof.

[0058] The application further provides a preparation method of the hydrophobic mixed-valence metal organic framework material, which comprises the following steps: performing a solvothermal reaction on an organic ligand with a structure shown in formula I and a Fe2M metal cluster in an organic solvent under catalysis of acetic acid, so as to obtain the hydrophobic mixed-valence metal organic framework material.

[0059] The preparation method of the hydrophobic mixed-valence metal organic framework material provided by the application comprises the following steps: performing a solvothermal reaction on a ligand and a metal cluster, so as to obtain the hydrophobic mixed-valence metal organic framework material, and the reaction does not require special reaction conditions and processes.

[0060] As one of the embodiments, the mass ratio of the organic ligand to the Fe2M metal cluster is 1:1-1.5.

[0061] As one of the embodiments, the organic solvent is a mixture of one or two of DMF or DEF.

[0062] As one of the embodiments, the volume ratio of acetic acid to the organic solvent is 1:(1-20).

[0063] As one of the embodiments, the mass-to-volume ratio of the organic ligand to the total volume of acetic acid and the organic solvent is 1:(0.15-0.8) mg / ml.

[0064] As one of the embodiments, the condition of the solvothermal reaction is that the reaction is performed at 100-170 ℃ for 24-72 h. The material ratio of the reaction and the reaction condition can be adjusted according to the solvothermal reaction, but under the above reaction condition, the hydrophobic mixed-valence metal organic framework material can be obtained more stably.

[0065] As one of the embodiments, the solvothermal reaction is followed by cooling, and the cooling is cooling to 15-35 ℃ under natural conditions.

[0066] As one of the embodiments, after the cooling, the obtained system is further subjected to solid-liquid separation, and then the obtained solid substance is sequentially subjected to washing and drying, so as to obtain the hydrophobic mixed-valence metal organic framework material.

[0067] As one of the embodiments, the reagent used in the washing is acetone.

[0068] As one of the embodiments, the drying is air drying under natural conditions.

[0069] As one of the embodiments, the preparation path of the organic ligand with the structure shown in formula I is as follows:

[0070]

[0071] In the embodiment, the 3,6-dibromocarbazole is coupled at the N atom under the action of potassium permanganate in an organic solvent to obtain a bis-carbazole;

[0072] Then, the bromine atom is replaced by an acetonitrile group under the catalysis of cuprous cyanide and divalent palladium, preferably 1,1'-bis(diphenylphosphino) ferrocene palladium (II) dichloride; the reaction solvent is preferably super dry DMF; the reaction temperature is preferably 120-153 DEG C; and finally, the acetonitrile group is carboxylated under the action of an aqueous sodium hydroxide solution to obtain the organic ligand with the structure shown in formula I.

[0073] The application further provides a method for preparing hydrogen peroxide by photocatalysis, wherein the hydrophobic mixed-valence metal organic framework material or the hydrophobic mixed-valence metal organic framework material prepared by the method for preparing a hydrophobic mixed-valence metal organic framework material is used as a photocatalyst to prepare hydrogen peroxide by photocatalysis.

[0074] As one of the embodiments, the hydrophobic mixed-valence metal organic framework material is subjected to a photocatalytic reaction under the conditions of bubbling oxygen into benzyl alcohol and an aqueous potassium dihydrogen phosphate solution and irradiation to prepare hydrogen peroxide.

[0075] The photocatalytic system is a two-phase system of an organic phase and an aqueous phase in benzyl alcohol and an aqueous potassium dihydrogen phosphate solution; the hydrophobic mixed-valence metal organic framework material is used as a solid-phase catalyst and is hydrophobic and dense, so it is dispersed in the organic phase in the lower layer of the organic phase and the aqueous phase, and the benzyl alcohol is oxidized by photocatalysis at the same time that the superoxide free radical is generated, the superoxide free radical is transferred to the aqueous phase in the upper layer to form hydrogen peroxide. In this way, the hydrophobic mixed-valence metal organic framework material is used as a photocatalyst to perform a catalytic reaction in the organic phase, and does not need to contact the aqueous solution, thereby avoiding the problems of hydrophobicity and instability of the catalyst in water; at the same time, the Fenton-like effect of the Fe-based metal organic framework material on hydrogen peroxide is avoided, and the yield of hydrogen peroxide is improved. Moreover, the reaction does not need to add a photosensitizer or a sacrificial agent, which is conducive to environmental protection.

[0076] As one of the embodiments, the mass-to-volume ratio of benzyl alcohol to the mixed-valence metal organic framework material is 1:(0.5-2) mg / mL.

[0077] As one of the embodiments, the irradiation condition is (0.1-0.15) W / cm 2Xenon lamp irradiation; preferably, the light irradiation condition is 0.134 W / cm 2 Xenon lamp irradiation.

[0078] As one of the embodiments, the volume ratio of the aqueous potassium dihydrogen phosphate solution to benzyl alcohol is 1: (1-3).

[0079] As one of the embodiments, the concentration of the potassium dihydrogen phosphate is (0.005-0.05) mol / L.

[0080] The following is further illustrated by specific examples.

[0081] Preparation of the organic ligand of the structure shown in Formula I

[0082] 2g of 3,6-dibromocarbazole was weighed into a 100 mL round-bottom flask, dissolved in 40 mL of acetone, and then 2.5 g of potassium permanganate was added. The reaction was carried out at 65°C for 12 h to obtain tetrabromobiscarbazole;

[0083] 1g of tetrabromobiscarbazole, 1.4g of cuprous cyanide, and 0.1g of 1,1'-bis(diphenylphosphino) ferrocene dichloropalladium (II) were weighed, deoxygenated by bubbling, and then 30 mL of super-dry DMF was added. The reaction was carried out at 150°C for 2 days under nitrogen protection, and then DCM was passed through the column to obtain tetracyanobiscarbazole;

[0084] 2g of tetracyanobiscarbazole was weighed, 50 mL of ethanol and 30 mL of 10 M sodium hydroxide solution were added, and the reaction was carried out at 80°C for 12 h. After that, concentrated hydrochloric acid was added to acidify to pH = 2, and white solid was precipitated. After filtration, the solid was washed with water and methanol, and dried to obtain the white powder product, which is the organic ligand of the structure shown in Formula I. The nuclear magnetic hydrogen spectrum of the organic ligand of the structure shown in Formula I is shown in Figure 2 , and the nuclear magnetic carbon spectrum is shown in Figure 3 .

[0085] Example 2

[0086] 2mg of the ligand and 2mg of Fe2Fe metal cluster were added to a glass tube, 50μL of acetic acid and 0.5mL of DMF were added in sequence, and the glass tube was sealed by a hydrogen oxygen machine. The glass tube was placed in an ultrasonic wave for 10min, and then placed in an oven for heating at 140°C for 48h. After cooling to room temperature, the glass tube was opened, and the solid product was collected by centrifugation and washed with acetone for 3 times. After drying, the product was obtained, and the appearance is shown in Figure 4 b, which is named as Fe3BCTA.

[0087] Example 3

[0088] 2 mg of the ligand and 3 mg of Fe2Co metal cluster were added into a glass tube, 0.8 mL of acetic acid, 0.4 mL of DMF and 0.4 mL of DEF were added into the glass tube in sequence; the glass tube was sealed by hydrogen-oxygen mixture; the glass tube was put into ultrasonic wave for 10 min; the glass tube was put into an oven for heating at 120 °C for 60 h; after cooling to room temperature, the glass tube was opened, the solid product was collected by centrifugation, and the solid product was washed by acetone for 3 times; after air-drying, the product was obtained, and the appearance was as shown in Fig. Figure 4 d, and was named as Fe2CoBCTA.

[0089] Example 4

[0090] 2 mg of the ligand and 2.6 mg of Fe2Ni metal cluster were added into a glass tube, 100 μL of acetic acid and 1 mL of DEF were added into the glass tube in sequence; the glass tube was sealed by hydrogen-oxygen mixture; the glass tube was put into ultrasonic wave for 10 min; the glass tube was put into an oven for heating at 170 °C for 24 h; after cooling to room temperature, the glass tube was opened, the solid product was collected by centrifugation, and the solid product was washed by acetone for 3 times; after air-drying, the product was obtained, and the appearance was as shown in Fig. Figure 4 a, and was named as Fe2NiBCTA.

[0091] Example 5

[0092] 2 mg of the ligand and 2.3 mg of Fe2Mn metal cluster were added into a glass tube, 50 μL of acetic acid and 0.25 mL of DMF were added into the glass tube in sequence; the glass tube was sealed by hydrogen-oxygen mixture; the glass tube was put into ultrasonic wave for 10 min; the glass tube was put into an oven for heating at 100 °C for 72 h; after cooling to room temperature, the glass tube was opened, the solid product was collected by centrifugation, and the solid product was washed by acetone for 3 times; after air-drying, the product was obtained, and the appearance was as shown in Fig. Figure 4 c, and was named as Fe2MnBCTA.

[0093] Example 6

[0094] 5 mg of Fe2MBCTA prepared in the example was added into a photocatalytic reaction bottle, 5 mL of benzyl alcohol solution, 3 mL of 0.01 mol / L potassium dihydrogen phosphate solution, and oxygen was bubbled for 5 min. Then the reaction bottle was irradiated by a 0.134 W / (cm 2 ) xenon lamp for 4 h; the content of hydrogen peroxide in the photocatalytic reaction bottle was tested by iodometric method, and the reaction product was detected by nuclear magnetic resonance, and the results were as shown in Fig. Figure 5 .

[0095] Test Example:

[0096] 1. X-ray powder diffraction test

[0097] The hydrophobic mixed valence metal organic framework materials prepared in Examples 2-5 were respectively subjected to X-ray powder diffraction test, and the X-ray powder diffraction patterns are shown in Figure 6 .

[0098] From the results of the X-ray powder diffraction test of Figure 6 , it can be seen that the diffraction spectrum of the synthesized Fe2MBCTA is highly consistent with the simulated diffraction spectrum in peak position, indicating that the synthesized Fe2MBCTA is a pure phase, and the three different metal clusters of Fe2NiBCTA, Fe2CoBCTA and Fe2MnBCTA have the same main framework; and from the peak shape and intensity of the diffraction peak, it can be seen that the hydrophobic mixed valence metal organic framework material of the application has high crystallinity.

[0099] 2. Infrared spectrum test

[0100] The hydrophobic mixed valence metal organic framework materials prepared in Examples 2-5 were respectively subjected to infrared spectrum test, and the infrared spectrum test patterns are shown in Figure 7 .

[0101] From the infrared spectrum Figure 7 , it can be clearly observed that the characteristic peaks of carboxylic acid at 2644cm -1 and 2532cm -1 in the ligand disappear, and the characteristic peak of carbonyl group is shifted from 1685cm -1 to 1560cm -1 , indicating that the carboxylic acid functional group in the ligand is coordinated with the metal cluster. The stretching vibration peak of the metal cluster can still be seen in the fingerprint region, indicating that the metal cluster is well preserved during the synthesis process, and the carboxylic acid functional group in the ligand is coordinated with the metal cluster to form the main framework of Fe2MBCTA.

[0102] 3. Stability test

[0103] 5mg of the hydrophobic mixed valence metal organic framework material prepared in Examples 2-5 was respectively soaked in 5mL of different solvents and aqueous solutions with different pH values, and after 36h of soaking, centrifugal separation, and vacuum drying at 45℃, X-ray powder diffraction test was performed, and the test results are shown in Figure 8 .

[0104] From Figure 8 , it can be seen that after 36h of soaking in air, boiling water, DMF, ethanol, water, acetonitrile, methanol, THF, and 36h of soaking in aqueous solution with pH of 3-11, the XRD peaks of the hydrophobic mixed valence metal organic framework material of the application basically do not change, indicating that the MOF framework basically does not change, and indicating that the chemical stability and water stability are good.

[0105] 4. SEM characterization

[0106] The hydrophobic mixed valence metal-organic framework material Fe3BCTA prepared in Example 2 was subjected to scanning electron microscope (SEM) observation, and the results are shown in Figure 9 , and the element distribution is shown in Figure 10 .

[0107] As can be seen from the SEM image of Figure 9 , the hydrophobic mixed valence metal-organic framework material Fe3BCTA has a polyhedral structure and a relatively regular morphology. As can be seen from Figure 10 , the elements are uniformly distributed.

[0108] The hydrophobic mixed valence metal-organic framework materials prepared in Examples 2-5 were used as catalysts for photocatalytic reaction according to the photocatalytic reaction conditions of Example 6, and the amount of generated hydrogen peroxide was tested by iodometric method: 0.5 mL of aqueous phase solution was taken after centrifugation of the reaction solution, 2 mL of 0.1 mol / L aqueous potassium hydrogen phthalate (C8H5KO4) and 2 mL of 0.4 mol / L aqueous potassium iodide (KI) were added, and the mixture was kept for 30 min; H2O2 molecules react with iodine ions (I - ) under acidic conditions to generate triiodide ions (l3 - ), which have a very strong absorption near 350 nm; the absorbance of l3 - at 350 nm was measured by ultraviolet spectrophotometer (Shimadzu UV-2700i), and then the amount of H2O2 generated in each reaction was calculated; the curve of hydrogen peroxide concentration corresponding to its absorbance and the ultraviolet absorption curve of the reaction solution after 4 h reaction of the hydrophobic mixed valence metal-organic framework materials of Examples 2-5 as catalysts are shown in Figure 11 , and the column chart of the calculated hydrogen peroxide production rate is shown in Figure 12 .

[0109] As can be seen from the nuclear magnetic resonance hydrogen spectrum of the photocatalytic reaction of Figure 5 , there is an aldehyde group peak at 9.98 ppm, suggesting that benzaldehyde product is generated and benzyl alcohol is oxidized to benzaldehyde.

[0110] As can be seen from the results of Figure 11 , the concentration of hydrogen peroxide has a linear relationship with the absorbance at 350 nm, and the fitting degree is 0.9998. As can be seen from Figure 12 , the hydrogen peroxide production rate of Fe2NiBCTA is 4717.84 μmol / g / h, that of Fe3BCTA is 3236.80 μmol / g / h, and that of Fe2MnBCTA is 1744.66 μmol / g / h after 4 h light irradiation.

[0111] Fe2NiBCTA prepared in Example 3 was used as catalyst for reaction for 4 h under no light irradiation according to the photocatalytic reaction conditions of Example 6, and the results are shown in Figure 13 and Figure 14 as shown;

[0112] The ligand 2mg and 2.6mg Fe2Ni metal cluster shown in formula I were physically mixed, and the photocatalytic reaction was carried out according to the photocatalytic reaction conditions of Example 6 instead of Fe2NiBCTA, and the results are shown in Figure 13 and Figure 14 .

[0113] From the results of Figure 13 and Figure 14 , it can be seen that under no light, little hydrogen peroxide is produced, indicating that the catalytic reaction of Fe2NiBCTA is a photocatalytic reaction. Physical mixing of the ligand with the Fe2Ni metal cluster cannot produce good photocatalytic effect, and after the mixed valence metal organic framework material Fe2NiBCTA of the application is prepared by hydrothermal reaction, the photocatalytic reaction rate can be accelerated.

[0114] The Fe2NiBCTA prepared in Example 4 was used as a catalyst to carry out the reaction according to the reaction conditions of Example 6 to realize the first cycle, and the reaction liquid was centrifuged to collect the solid residue, and the solid residue was washed with acetone for 3 times, and the recovered Fe2NiBCTA was obtained after drying; the recovered Fe2NiBCTA was continuously reacted according to the reaction conditions of Example 6 to realize the second cycle; the recovered Fe2NiBCTA was recovered again after the reaction; the third reaction was carried out according to the reaction conditions of Example 6 to realize the third cycle, and the recovered catalyst was characterized each time. The results of the three photocatalytic reactions are shown in Figure 15 , and the PXRD pattern of the recovered Fe2NiBCTA after three cycles is shown in Figure 16 .

[0115] From Figure 15 , it can be seen that the hydrogen peroxide produced by each photocatalytic reaction is basically the same, indicating that the Fe2NiBCTA catalyst has the same effect in three reactions, and the catalytic performance of the recycled catalyst will not decrease. This can also be seen from the PXRD pattern of the recovered catalyst each time. Figure 16 The PXRD pattern of the recovered Fe2NiBCTA after three cycles is shown in

[0116] In summary, the hydrophobic mixed-valence metal organic framework material has excellent chemical stability and water stability. The synthesis steps are simple and convenient, the experimental period is short, the production time is effectively saved, and the material can be mass-produced without complicated operation process; as a catalyst for photocatalytic preparation of hydrogen peroxide, the material has excellent performance and maintains the stability of the framework, wherein the hydrogen peroxide production rate of the hydrophobic mixed-valence metal organic framework material formed by Fe2Ni metal clusters reaches 4717.84 μmol / g / h; and the crystal structure of the catalyst remains stable after use without change, and has recycling potential.

[0117] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the scope of protection of the present application. Any non-essential changes and substitutions made by those skilled in the art on the basis of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for preparing hydrogen peroxide by photocatalysis, characterized in that: A hydrophobic mixed-valence metal-organic framework material is used as a photocatalyst to prepare hydrogen peroxide through a photocatalytic reaction. The hydrophobic mixed-valence metal-organic framework material is formed by coordinating an organic ligand having a structure shown in Formula I with an Fe2M metal cluster. The Fe2M metal cluster has a structural formula of [Fe2M(μ3-O)(CH3COO)6], where M in the Fe2M metal cluster is one of Ni, Fe, or Mn. The four carboxyl groups of each organic ligand are connected to the Fe2M metal cluster respectively, three of which replace the acetic acid coordination groups on the Fe2M metal cluster; one carboxyl group is directly connected to the metal ion of the Fe2M metal cluster; The six acetic acid coordination groups on each Fe2M metal cluster are replaced by the carboxyl group of the organic ligand; an Fe ion or M ion of the Fe2M metal cluster is directly connected to the carboxyl group of an organic ligand; 2. The method for preparing hydrogen peroxide by photocatalysis according to claim 1, characterized in that: The preparation method of the hydrophobic mixed-valence metal organic framework material, The organic ligand with the structure shown in formula I and the Fe2M metal cluster are subjected to a solvothermal reaction in an organic solvent under the catalysis of acetic acid to prepare the hydrophobic mixed-valence metal organic framework material.

3. The method for preparing hydrogen peroxide by photocatalysis according to claim 2, characterized in that: The mass ratio of organic ligand to Fe2M metal cluster is 1:1-1.

5.

4. The method for preparing hydrogen peroxide by photocatalysis according to claim 2, wherein: The organic solvent is one of DMF and DEF or a mixture of the two; the volume ratio of acetic acid to the organic solvent is 1:(1-20); and the mass volume ratio of the organic ligand to the total volume of acetic acid and the organic solvent is 1:(0.15-0.8) mg / ml.

5. The method for preparing hydrogen peroxide by photocatalysis according to claim 2, characterized in that: The solvent thermal reaction conditions are: reaction at 100-170°C for 24-72 hours.

6. The method for preparing hydrogen peroxide by photocatalysis according to claim 2, characterized in that: The preparation path of the organic ligand of the structure shown in Formula I is:

7. A method for preparing hydrogen peroxide by photocatalysis according to any one of claims 2 to 6, characterized in that: After the solvent thermal reaction, the temperature is lowered to 15-35°C under natural conditions. After the cooling, the method further comprises: performing solid-liquid separation on the system obtained after the cooling, and then washing and drying the obtained solid matter in sequence to obtain a hydrophobic mixed-valence metal organic framework material. The reagent used for the washing is acetone, and the drying is drying under natural conditions.

8. The method for preparing hydrogen peroxide by photocatalysis according to claim 1, characterized in that: The hydrophobic mixed-valence metal organic framework material is placed in benzyl alcohol and potassium dihydrogen phosphate aqueous solution, oxygen is introduced, and a photocatalytic reaction occurs under light to prepare hydrogen peroxide.

9. The method for photocatalytically preparing hydrogen peroxide according to claim 8, characterized in that: The mass volume ratio of the mixed-valent metal organic framework material to benzyl alcohol was 1:1 mg / mL; the illumination condition was (0.1-0.15) W / cm 2 Xenon lamp irradiation; The volume ratio of the potassium dihydrogen phosphate aqueous solution to benzyl alcohol is 1:(1-3); the concentration of the potassium dihydrogen phosphate is (0.005-0.05) mol / L.

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