Preparation method of covalent organic framework TFP-DAAQ and application of covalent organic framework TFP-DAAQ in catalysis of cracking of C-C bonds in lignin

Abstract

The invention discloses a preparation method of a covalent organic framework TFP-DAAQ and application of the covalent organic framework TFP-DAAQ in catalysis of cracking of C-C bonds in lignin. The catalyst is utilized to efficiently catalyze and convert the lignin model compound under a mild condition to obtain the aromatic compound, the preparation method is environment-friendly, the reaction condition is mild, noble metal is not needed, the heterogeneous phase is realized, the separation process is simple, the cost is lower, and fewer by-products are generated. The conversion rate of the typical beta-O-4 model compound 2-phenoxy-1-phenyl-ethanol reaches 85.6-97.0%, the selectivity of the main product benzaldehyde can reach 66.2%-69.1%, the product is easy to separate, and the method has a good industrial production cost advantage.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a preparation method of a covalent organic framework TFP-DAAQ and application of the covalent organic framework TFP-DAAQ in catalyzing C—C bond cleavage in lignin. Background Art

[0002] Lignocellulosic biomass is currently the most abundant natural renewable source of organic carbon. It is mainly composed of three components (cellulose, hemicellulose and lignin). It has many advantages such as abundant resources and carbon neutrality, and is an ideal raw material for providing chemicals and energy. The utilization of renewable carbon resources of biomass provides exciting prospects for sustainable chemical supply. Among them, lignin is the only natural renewable aromatic chemical raw material in nature, accounting for 10-35% of lignocellulosic biomass. Currently, only a very small amount of lignin is given high value. About 50 million tons of lignin are produced each year, of which 98% are used for direct combustion to provide heat, resulting in a waste of resources. This is mainly due to the irregular structure and complex composition of natural lignin. Therefore, it is a huge challenge to develop an efficient catalytic system to convert it from a cheap raw material to a high-value chemical.

[0003] Currently used catalytic methods often rely on demanding conditions such as high temperature and high pressure. For example, traditional thermal catalysis methods typically require temperatures exceeding 150°C and stoichiometric amounts of oxidants, which limits their efficiency. Furthermore, the harsh reaction conditions make them unsustainable.

[0004] Chinese invention patent CN202410572726 discloses a method for preparing a metal oxide / ruthenium tungsten composite catalyst and its application in catalyzing the cleavage of CO bonds in lignin. This technology uses a lignin model compound as a substrate, a small molecule alcohol as a solvent, and a metal oxide / ruthenium tungsten composite catalyst as a catalyst in the reaction. After stirring evenly in a closed high-pressure reactor, H2 or N2 is filled to make the pressure in the reactor 0.1-2.0 MPa, and the temperature in the reactor is adjusted to 165-380°C. This reaction catalyst requires the use of metal elements, and the reaction requires a high pressure, and high temperature is required for the reaction to occur and generate small molecule aromatic compounds. However, the catalyst synthesis process of this technology is complicated and the catalytic reaction conditions are harsh, which limits its industrial application.

[0005] Heterogeneous photocatalytic reactions driven by visible light are considered to be a renewable and environmentally friendly technology. High-value-added chemicals obtained by traditional thermal catalysis methods can be obtained under mild conditions, and the products and catalysts can be easily separated and recycled.

[0006] Prior art document 1 (Xu, X.; Dai, S.; Xu, S.; Zhu, Q.; & Li, Y. Efficient Photocatalytic Cleavage of Lignin Models by a Soluble Perylene Diimide / Carbon Nitride S-Scheme Heterojunction. Angewandte Chemie 2023, 135(44), e202309066.) discloses a polycarbonate nitride / polyhedral oligomeric silsesquioxane PDI (p-CN / P-PDI) S-type heterojunction photocatalyst prepared by solvent evaporation deposition method for selective cleavage of CC bonds in lignin β-O-4 model. According to the material characterization results, the synergistic effect of polyhedral oligomeric silsesquioxane (POSS) and S-type heterojunction maintains appropriate aggregation domains, achieving better sunlight utilization, faster charge transfer efficiency and greater redox capacity. However, this photocatalyst requires an oxygen atmosphere, the reaction environment is relatively harsh, and the catalyst synthesis method is relatively complicated. Moreover, the selectivity of the reaction products is not high enough, and the main products are benzaldehyde and phenyl formate.

[0007] Prior art document 2 (Rao, CH; Wei, HR; Miao, XL; Jia, MZ; Yao, XR; Zheng, XY,; & Zhang, J.; Selective cleavage of Cα–Cβ bonds in lignin models using abifunctional pyridinium photocatalyst via a PCET process. Green Chemistry 2023, 25(10), 3974-3981.) discloses an effective pyridine-based photocatalyst that selectively cleaves C–C bonds of β-O-4 and β-1 lignin model compounds under mild conditions. The strong electron accepting ability of the pyridine core unit and the neutral nitrogen atom provide a proton-coupled electron transfer (PCET) channel to promote hydrogen dissociation or the formation of corresponding free radical intermediates, thereby directly triggering the cleavage of the C–C bond through the β-scission process. Although the catalyst of this technology is a metal-free catalyst, it is a homogeneous catalyst, and it is difficult to separate the catalyst and the product after the reaction. The products mainly include benzaldehyde, benzoic acid, phenyl formate, 2-phenoxy-1-phenylethanone, and benzene ring. The product distribution is relatively mixed. The yields of the main products benzaldehyde, benzoic acid, and phenyl formate are 25 mol%, 24 mol%, and 23 mol%, respectively. The selectivity is not high, which is not conducive to industrial application and production. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a method for catalyzing the cleavage of C-C bonds in lignin using a covalent organic framework TFP-DAAQ, which can achieve the cleavage of C-C bonds in lignin under mild conditions, efficiently catalytically convert them into aromatic compounds, and obtain benzaldehyde, phenyl formate, and phenol after purification. The reaction conditions are mild, environmentally friendly, no precious metals are required, the process is heterogeneous, the separation process is simple, the cost is low, and there are fewer by-products.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] The present invention provides a method for preparing a covalent organic framework TFP-DAAQ, comprising the following steps:

[0011] S1 weighed the ligand raw materials 2,6-diaminoanthraquinone and 1,3,5-triformylphloroglucinol;

[0012] S2: Add the two raw materials into a mortar and grind them at room temperature. Before grinding, add 1,4-dioxane and mesitylene dropwise. Grind for a while and then add glacial acetic acid solution dropwise to continue grinding.

[0013] S3 collects the mixture and adds it to a polytetrafluoroethylene liner, then sequentially adds 1,4-dioxane and mesitylene solvent to the liner, and then ultrasonically disperses it and adds glacial acetic acid solution;

[0014] S4 is drying the reaction solution;

[0015] S5 After the reaction is completed, the solid in the liner is collected, centrifuged and washed, and filtered;

[0016] S6 obtains a solid and dries it to obtain the covalent organic framework TFP-DAAQ.

[0017] Furthermore, in step S1, the molar ratio of 2,6-diaminoanthraquinone to 1,3,5-triformylphloroglucinol is 3:1 to 2:1; in step S3, the volume ratio of 1,4-dioxane to mesitylene solvent is 1:1, and the concentration of glacial acetic acid solution is 6 mol / L -1 The volume ratio of the first two solvents to glacial acetic acid solution is 5:3 to 5:5.

[0018] Furthermore, the grinding process in step S2 is as follows: 1,4-dioxane and mesitylene are added dropwise in a volume ratio of 1:1, and 6 mol L is added dropwise after grinding for 10 to 20 minutes. -1 The volume ratio of the glacial acetic acid solution to the other two solvents is 5:3 to 5:5. Grind for another 10 to 20 minutes. After the solvent is basically evaporated, add the three solutions and repeat this operation.

[0019] Furthermore, in step S4, the oven temperature is set to 120°C to 150°C for reaction for 60 to 84 hours; in step S5, the solid in the lining is collected and centrifuged and washed in sequence with deionized water, N,N-dimethylformamide, ethanol, acetone and dichloromethane; the drying treatment in step S6 adopts an ordinary oven, the drying temperature is 60 to 80°C; and the drying time is 12 to 24 hours.

[0020] The present invention provides a covalent organic framework TFP-DAAQ, which is prepared by the above method.

[0021] The present invention also provides a method for catalyzing the cleavage of CC bonds in lignin using the above-mentioned covalent organic framework TFP-DAAQ. The method comprises mixing a lignin raw material, a covalent organic framework TFP-DAAQ catalyst and a polar aprotic solvent, reacting the mixture at 20-30° C. under light conditions in air for 5-6 hours, and obtaining an aromatic monomer product after purification.

[0022] Furthermore, the lignin raw material is a lignin model compound or an organosoluble lignin; the lignin model compound includes 2-phenoxy-1-phenyl-ethanol, 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol or 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol; the organosoluble lignin is obtained by extracting bagasse.

[0023] Furthermore, the amount of the covalent organic framework TFP-DAAQ is 20%-50% of the mass of the lignin raw material.

[0024] Furthermore, the polar aprotic solvent is acetonitrile.

[0025] Furthermore, the illumination conditions are: wavelength of 365-385nm, illumination intensity of 70%-100%; the purification method is to wash away the remaining substrate with N,N-dimethylformamide, then use dichloromethane or ethanol solvent to centrifuge and wash to remove the remaining N,N-dimethylformamide, and then filter.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) The synthesis of the covalent organic framework TFP-DAAQ catalyst of the present invention is a non-metallic strategy that does not require the use of toxic or precious metals. The covalent organic framework TFP-DAAQ catalyst of the present invention has higher selectivity than other catalysts, mainly due to its ability to activate C-H or OH bonds at specific sites. After the reaction of the present invention is completed, the TFP-DAAQ covalent organic framework catalyst can be separated from the reaction solution by simple filtration, and the operation method is simple.

[0028] (2) The present invention adopts a photocatalytic method with relatively mild conditions. The reaction can be completed only by irradiation with light. Compared with the prior art, the present invention does not require high temperature and high pressure conditions. The reaction conditions of the present invention increase safety and can also reduce energy consumption.

[0029] (3) Compared with other catalysts, the catalyst of the present invention can be reused, and its performance does not decrease but slightly increases after repeated use, which has obvious production cost advantages.

[0030] (4) The covalent organic framework TFP-DAAQ catalyst prepared by the present invention has a strong ability to efficiently separate and migrate photogenerated carriers when catalyzing the cleavage of CC bonds in lignin. It also constructs a catalytic system in which a hole quencher and a catalyst act synergistically, so that the system can be applied to real lignin. For example, it has a good effect on organic soluble lignin, and the mass fraction of the depolymerization yield can reach 5.16wt%. The products are mainly aromatic monomers, among which benzofuran (1.93wt%) has a higher yield, accounting for 37.4% of the total monomer yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the synthesis of the covalent organic framework TFP-DAAQ of the present invention.

[0032] Figure 2 This is the scanning electron microscope (SEM) image of the covalent organic framework TFP-DAAQ.

[0033] Figure 3 This is the transmission electron microscopy (TEM) image of the covalent organic framework TFP-DAAQ.

[0034] Figure 4 This is the XRD pattern of the covalent organic framework TFP-DAAQ.

[0035] Figure 5 This is the FT-IR spectrum of the covalent organic framework TFP-DAAQ.

[0036] Figure 6 This is the XPS spectrum of the covalent organic framework TFP-DAAQ. Figure 6 a, carbon spectrum Figure 6 b and nitrogen spectrum Figure 6 c.

[0037] Figure 7 This is the solid EPR test result of oxygen-centered free radicals in the covalent organic framework TFP-DAAQ.

[0038] Figure 8 This is a diagram showing the depolymerization results of the photocatalytic lignin model compound 2-phenoxy-1-phenylethanol in Example 1.

[0039] Figure 9 This is the GC-MS chart of benzaldehyde in Example 1.

[0040] Figure 10 This is the GC-MS chart of phenyl formate in Example 1.

[0041] Figure 11 This is the GC-MS chart of phenol in Example 1.

[0042] Figure 12 This is a diagram of the cyclic depolymerization results of Example 10.

[0043] Figure 13 This is a GC-MS chart of the depolymerization of 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol in Example 11.

[0044] Figure 14 This is a GC-MS chart of the depolymerization of 2-(2,6-dimethoxyphenyl)oxy-1-(4-methoxyphenyl)-ethanol in Example 12.

[0045] Figure 15 This is a diagram showing the photocatalytic depolymerization results of organolytic lignin in Example 13.

[0046] Figure 16 The UV absorption spectra of the catalysts in Example 1 and Comparative Examples 3 and 4 are shown.

[0047] Figure 17 It is the band gap width diagram of the catalyst in Example 1 and Comparative Examples 3 and 4. DETAILED DESCRIPTION

[0048] For a better understanding of the present invention, the present invention is further described below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0049] The structural formula of the covalent organic framework TFP-DAAQ is as follows Figure 1 , is an emerging class of organic porous crystalline materials connected by covalent bonds. TFP-DAAQ has high crystallinity, a high specific surface area, good thermal stability, a regular layered stacking structure, and strong light absorption and charge separation capabilities, and is considered to be an ideal medium for the separation and migration of photogenerated carriers. Currently, it is being studied and applied in hydrazine absorption due to its high specific surface area, in pseudocapacitive energy storage due to its good layered stacking structure and high electrochemical performance, and in photocatalytic oxygen and photocatalytic synthesis of hydrogen peroxide in alkaline water due to its strong light absorption and charge separation capabilities.

[0050] like Figure 1 As shown, the preparation method of the covalent organic framework TFP-DAAQ includes the following steps:

[0051] S1 Weigh 1 mmol of 2,6-diaminoanthraquinone and 0.5 mmol of 5-triformylphloroglucinol.

[0052] S2: Add the two raw materials to a mortar and grind them at room temperature. Before grinding, add 100 μL of 1,4-dioxane and 100 μL of mesitylene solution. Grind for 15 minutes, then add 100 μL of 6 mol L-1 glacial acetic acid solution. Grind for another 15 minutes. Once the solvent has evaporated, repeat the process with the three solutions. 1,4-dioxane and mesitylene serve as solvents to dissolve the DAAQ and TFP ligands, and glacial acetic acid serves as a catalyst.

[0053] The collected mixture in step S3 was added to a polytetrafluoroethylene liner, to which 10 mL of 1,4-dioxane and 10 mL of mesitylene solvent were added in sequence. The mixture was then ultrasonically dispersed for 30 minutes before the addition of 6 mL of a 6 mol L-1 glacial acetic acid solution.

[0054] S4 puts the reaction solution into the reactor, tightens it, and then puts it into an oven for reaction at 120°C for 72 hours.

[0055] After the reaction is completed, the solid in the liner is collected and centrifuged and washed with deionized water, N,N-dimethylformamide, ethanol, acetone, and dichloromethane in sequence at a speed of 10000 r min. -1 .

[0056] The solid obtained in S6 was placed in an oven at 60°C and dried for 12 h to obtain the covalent organic framework TFP-DAAQ.

[0057] A reddish-brown solid TFP-DAAQ is obtained, wherein N,N-dimethylformamide mainly removes the substrate that does not participate in the reaction.

[0058] Structural characterization:

[0059] Please refer to Figure 2-6 ,like Figure 2 As shown in Figure 2, the TFP-DAAQ sample exhibits a unique regular flower-like nanostructure formed by orderly stacking of nanorods with uniform unit sizes. Figure 3 The average length and width of these nanorods are 4 μm and 0.8 μm respectively. The XRD pattern was used to analyze the phase structure of COF in depth. Figure 4 As shown in the figure, strong characteristic diffraction peaks of (100), (110), (200), (210) and (001) crystal planes were observed at 2θ = 3.4°, 6.0°, 7.0°, 9.1° and 27.0°, indicating that the material synthesized based on the Schiff base reaction has high crystallinity and a long-range ordered hexagonal pore structure. Figure 5FT-IR shows that by comparing with TFP-DAAQ, the original DAAQ is at 3100-3500cm -1 The stretching vibration of amino group (-NH2) and TFP at 1644cm -1 The disappearance of the stretching vibration of the carbonyl (HC=O) in the aldehyde group indicates that the original monomer has completely reacted to form TFP-DAAQ. -1 The stretching vibration of carbonyl (-C=O) and 1582cm -1 The stretching vibration of the carbon-carbon double bond (-C=C) at 1245 cm -1 The stretching vibration of the carbon-nitrogen single bond (-CN) at 1659 cm -1 The -C=N bending vibration at the position indicates the formation of a new bond. The simultaneous presence of -CN and -C=N indicates that the synthesis was successful via the Schiff base reaction, and the synthesized COF contains two tautomers, ketoamine and enolimine. Figure 6 It is the XPS test. Figure 6 a The full spectrum shows that all samples have characteristic signals of C, N, and O, confirming the basic composition of the materials. Figure 6 b is the C1s fine spectrum. The quinone C=O and TFP unit C=O (289.6 eV), the TFP unit CO bond (286.6 eV), and the aromatic ring CC (284.8 eV) components account for 3.6%, 35.8%, and 60.6%, respectively. The CC component accounts for a significantly higher percentage than the combined oxygen-containing functional groups (CO, C=O) (39.4%), indicating that the COF framework of TFP-DAAQ is fully constructed. Figure 6 c is the N1s fine spectrum, π-π* satellite peak (404.7 eV), CNH (keto linkage, 400.4 eV), C=N (enol linkage, 399.7 eV) The above results fully demonstrate the successful synthesis of TFP-DAAQ.

[0060] In order to explore the key active species and their mechanism of action of TFP-DAAQ covalent organic framework material catalytic depolymerization of lignin model compounds, such as Figure 7 EPR characterization was carried out. In the solid EPR test, under the excitation of light, TFP-DAAQ showed a significantly enhanced characteristic signal of oxygen-centered organic free radicals (OCORs) at g=2.0046, proving that OCORs are important active substances in the system.

[0061] Example 1-3:

[0062] The covalent organic framework TFP-DAAQ catalyst prepared above was used to catalyze the cleavage of CC bonds in the lignin β-O-4 model compound (2-phenoxy-1-phenyl-ethanol) to obtain aromatic compounds (benzaldehyde, phenyl formate and phenol), and the reaction solvent was set to change for testing.

[0063] Take 0.1 mmol of 2-phenoxy-1-phenyl-ethanol as the substrate, and use 5 mL of acetonitrile, dichloromethane, and acetone as the reaction solvents, respectively. The concentration of 2-phenoxy-1-phenyl-ethanol is controlled to be 0.02 mol / L. 5 mg of the covalent organic framework TFP-DAAQ is added as the catalyst. In the photocatalytic reactor, stirring is started, the light intensity is set to 4 W, and the wavelength of the LED lamp is 385 nm. The reaction temperature is set to 25 ° C. The reaction is carried out for 5 hours. The test results are shown in Table 1. Figure 8 The spectrum of the typical β-O-4 model compound 2-phenoxy-1-phenyl-ethanol after photocatalytic depolymerization in acetonitrile after gas chromatography reaction, corresponding to the GC-MS matching results are shown in Figure 9 、 Figure 10 as well as Figure 11 . It is calculated by the peak area in its GC graph. The calculation formula is as follows:

[0064] Conversion rate (%) = (1 - amount of remaining reactants / amount of initial reactants) × 100% (1) Benzaldehyde yield (mol%) = (amount of benzaldehyde produced / amount of initial reactants) × 100% (2) Phenyl formate yield (mol%) = (amount of phenyl formate produced / amount of initial reactants) × 100% (3) Phenol yield (mol%) = (amount of phenyl formate produced / amount of initial reactants) × 100% (4)

[0065] Table 1 The conversion rate of each solvent and the yield of the product in the optimization of the reaction solvent in Example 1

[0066]

[0067] Example 4-9:

[0068] The covalent organic framework TFP-DAAQ catalyst prepared above was used to catalyze the cleavage of CC bonds in a lignin model compound (2-phenoxy-1-phenyl-ethanol) to produce aromatic compounds (benzaldehyde, phenyl formate, and phenol), and the test was performed with varying catalyst dosages.

[0069] 0.1 mmol of 2-phenoxy-1-phenyl-ethanol was used as the substrate, and 5 mL of acetonitrile was used as the reaction solvent. The concentration of 2-phenoxy-1-phenyl-ethanol was controlled at 0.02 mol / L. The covalent organic framework TFP-DAAQ catalyst was added in amounts of 1 mg, 3 mg, 5 mg, 7 mg, 9 mg, and 11 mg, respectively. Stirring was initiated in a photocatalytic reactor. A 4 W LED light with a wavelength of 385 nm was used for illumination. The reaction temperature was set to 20°C and the reaction was allowed to react for 5 h. The test results are shown in Table 2.

[0070] Table 2 Conversion rate of each catalyst dosage and product yield in the optimization of catalyst dosage in Example 1

[0071]

[0072] Example 10:

[0073] The covalent organic framework TFP-DAAQ catalyst prepared above was used to catalyze the cleavage of CC bonds in the lignin model compound (2-phenoxy-1-phenyl-ethanol) to obtain aromatic compounds (benzaldehyde, phenyl formate and phenol), and a cyclic experiment was carried out. Take 0.1mmol of 2-phenoxy-1-phenyl-ethanol as the substrate, 5mL of acetonitrile as the reaction solvent, control the concentration of 2-phenoxy-1-phenyl-ethanol to 0.02mol / L, add 9mg of covalent organic framework TFP-DAAQ as the catalyst, and in the photocatalytic reactor, start stirring, turn on the light intensity and set the LED lamp with a wavelength of 4W and 385nm, set the reaction temperature to 25℃, and react for 5h. After the reaction, the solid and liquid parts are separated by vacuum filtration, and the obtained solid catalyst is washed with acetonitrile. It is then placed in a 60℃ oven and dried for 12h, and the recovered catalyst is directly used in the cyclic reaction. A total of five cyclic reactions are carried out as follows Figure 12 , the performance is almost unchanged, indicating that the photocatalytic material has good cycle stability.

[0074] Example 11:

[0075] The covalent organic framework TFP-DAAQ catalyst prepared above was used to catalyze the cracking of the CC bond in 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol to obtain aromatic compounds.

[0076] Take 0.1 mmol of 0.02 mol / L 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol as the substrate, and use 5 mL of acetonitrile as the reaction solvent. Control the concentration of 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol to be 0.02 mol / L. Add 9 mg of the covalent organic framework TFP-DAAQ as the catalyst. In a photocatalytic reactor, start stirring, turn on the light intensity of a 5W LED lamp with a wavelength of 365nm, set the reaction temperature to 20°C, and react for 5 hours.

[0077] After the reaction, 1,3,5-trimethoxybenzene was added as an internal standard, filtered, and then subjected to gas chromatography-mass spectrometry (GC-MS) testing. GC-MS data showed that the CC bond in 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol was broken, and the substrate conversion rate reached 100%, obtaining the main products p-anisaldehyde, p-anisylbenzoic acid, 1-methoxy-4-propylbenzene, and 2-hydroxy-1-(4-methoxyphenyl)ethan-1-one in yields of 14.1 mol%, 14.1 mol%, 13.4 mol%, and 10.1 mol%, respectively. Other products included o-methoxyphenylformate, methyl 4-methoxybenzoate, methyl 3-(2-methoxyphenyl)propionate, deoxy-p-anisylbenzene, tetramethoxystilbene, etc. The GC-MS results of the main products are shown in FIG. Figure 13 .

[0078] Example 12:

[0079] The covalent organic framework TFP-DAAQ catalyst prepared above was used to catalyze the cracking of the CC bond in 2-(2,6-dimethoxyphenyl)oxy-1-(4-methoxyphenyl)-ethanol to obtain aromatic compounds.

[0080] Take 0.1 mmol of 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol as the substrate, use 5 mL of acetonitrile as the reaction solvent, and control the concentration of 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol to 0.02 mol / L. Add 9 mg of the covalent organic framework TFP-DAAQ as the catalyst. In a photocatalytic reactor, stir and illuminate with a 5 W LED light with a wavelength of 365 nm. Set the reaction temperature to 20°C and react for 5 hours. After the reaction, 1,3,5-trimethoxybenzene was added as an internal standard, filtered, and then subjected to gas chromatography-mass spectrometry (GC-MS) testing. GC-MS data showed that the CC bond in 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol was broken, and the substrate conversion rate reached 100%, obtaining the main products p-anisaldehyde, p-anisylbenzoic acid, 1-methoxy-4-propylbenzene, 4'-methoxyphenylpropiotone, and 2-hydroxy-1-(4-methoxyphenyl)ethan-1-one in corresponding yields of 7.7 mol%, 13.3 mol%, 8.6 mol%, 6.5 mol%, and 3.2 mol%, respectively. Other products included 2,6-dimethoxyphenylformate, methyl 4-methoxybenzoate, methyl 3-(2-methoxyphenyl)propionate, deoxy-p-anisylbenzene, tetramethoxystilbene, etc. The GC-MS results of the main products are shown in FIG. Figure 14 .

[0081] Example 13:

[0082] The prepared covalent organic framework TFP-DAAQ catalyst was used to catalyze the CC bonds in organolytic lignin to obtain aromatic compounds.

[0083] The extraction steps for organosoluble lignin from bagasse are as follows: 10.0 g of dried bagasse, 120 mL of ethanol, and 30 mL of H2SO4 (0.3 M) aqueous solution are added to a 200 mL lined stainless steel hydrothermal kettle. The mixture is heated and stirred at 120°C for 4 hours, then the reactor is cooled to room temperature, filtered, and washed with anhydrous ethanol to obtain a filtrate containing the lignin fraction. Deionized water (5 times the volume of the filtrate) is added to the filtrate to precipitate the lignin fraction. This fraction is filtered, washed with deionized water, and vacuum dried at 60°C for 12 hours to obtain the organosoluble lignin from the bagasse, which is then stored for future use.

[0084] Take 50 mg of bagasse organosoluble lignin, use 10 mL of acetonitrile as the reaction solvent, control the concentration of bagasse organosoluble lignin to 5 g / L, add 18 mg of covalent organic framework TFP-DAAQ as catalyst, add 1 mL of EDTA-2Na (0.4 molL -1) aqueous solution, in a photocatalytic reactor, start stirring, turn on the light intensity set to 4W and the wavelength of the LED lamp at 385nm, set the reaction temperature to 25℃, and react for 5h. After the reaction is completed, add the internal standard 1,3,5-trimethoxybenzene as the internal standard, filter it, and perform gas chromatography-mass spectrometry (GC-MS) test. According to the data, the total yield is 5.16wt%, and the main product has a higher yield of benzofuran (1.93wt%), accounting for 37.4% of the total monomer yield. And 3,5-dimethoxy-4-hydroxybenzaldehyde (0.60wt%) and p-hydroxybenzaldehyde (0.32wt%) and peroxidation products dimethyl phthalate (0.39wt%) and dibutyl phthalate (0.32wt%). The GC-FID spectrum after the reaction and the GC-MS matching results are shown in Figure 15 . Calculated by the peak area in its GC-FID graph.

[0085] Comparative Example

[0086] To demonstrate that the introduction of electron donor 1,3,5-triformylphloroglucinol (TFP) effectively promotes the transfer of photogenerated electrons to the acceptor 2,6-diaminoanthraquinone (DAAQ) unit, which is beneficial to the increase of oxygen-centered organic radicals (OCORs) and O2 -· To investigate the photocatalytic performance of the main active substance, DAAQ and TFP monomers were selected for catalytic performance testing. To demonstrate the importance of the anthraquinone structure as an electron acceptor for enhanced photogenerated charge separation, TFP-DAAC (DAAC replacing DAAQ) was used for performance testing. To demonstrate the importance of the TFP unit as an electron donor and to reveal that the conjugated electron channel formed between the carbonyl group in TFP and the anthraquinone in DAAQ may be a necessary condition for triggering the photocatalytic reaction, electron-deficient TFB was used to replace the electron-rich TFP and TFB-DAAQ was used for performance testing.

[0087] Comparative Example 1: Using 2,6-diaminoanthraquinone (DAAQ) as a photocatalyst and performing a photocatalytic reaction

[0088] Take 0.1mmol of 2-phenoxy-1-phenyl-ethanol with a concentration of 0.02mol / L as the substrate, 5mL of acetonitrile as the reaction solvent, and control the concentration of 2-phenoxy-1-phenyl-ethanol to 0.02mol / L; add 9mg of DAAQ purchased by Anaiji as a catalyst, in a photocatalytic reactor, start stirring, turn on the light intensity set to 4W LED lamp with a wavelength of 385nm, set the reaction temperature to 25°C, and react for 5h. After the reaction is completed, internal standard 1,3,5-trimethoxybenzene is added as an internal standard, filtered, and tested by gas chromatography-mass spectrometry (GC-MS). According to GC-MS data, the C-C bond in 2-phenoxy-1-phenyl-ethanol is broken, the substrate conversion rate is about 45.6%, and the product peaks of benzaldehyde, phenyl formate, and phenol appear, with corresponding yields of 36.5mol%, 2.7mol%, and 4.0mol%, respectively.

[0089] Comparative Example 2: Using 1,3,5-triformylphloroglucinol (TFP) as a photocatalyst and performing a photocatalytic reaction

[0090] Take 0.1mmol of 2-phenoxy-1-phenyl-ethanol as the substrate, use 5mL of acetonitrile as the reaction solvent, and control the concentration of 2-phenoxy-1-phenyl-ethanol to 0.02mol / L; add 9mg of TFP purchased by Anaiji as a catalyst, start stirring in a photocatalytic reactor, turn on the light intensity set to 4W and the wavelength of 385nm LED light, set the reaction temperature to 25°C, and react for 5h. After the reaction is completed, the internal standard 1,3,5-trimethoxybenzene is added as an internal standard. After filtration, gas chromatography-mass spectrometry (GC-MS) testing is performed. According to the GC-MS data, the C-C bond in 2-phenoxy-1-phenyl-ethanol is broken, the substrate conversion rate is about 8.9%, and almost no product peak appears.

[0091] Compared with TFP-DAAQ, the catalytic results of DAAQ monomer and TFP monomer are very low, with conversion rates of only 45.6% and 8.9% respectively. This is because the introduction of electron donor TFP effectively promotes the transfer of photogenerated electrons to the acceptor (anthraquinone unit), which is beneficial to increase the oxygen-centered free radicals and O2 -· The photocatalytic performance of the main active material.

[0092] Comparative Example 3: Preparation of covalent organic framework TFP-DAAC photocatalyst and photocatalytic reaction (1) Preparation of covalent organic framework TFP-DAAC photocatalyst

[0093] S1: Weigh 2 mmol of 2,6-diaminoanthracene (DAAC) and 1 mmol of 1,3,5-triformylphloroglucinol (TFP).

[0094] S2: Add the two raw materials into a mortar and grind them at room temperature. During the process, add 200 μL of 1,4-dioxane and 200 μL of mesitylene solution and grind for 15 minutes. Then add 200 μL of 6 mol L-1 glacial acetic acid solution and grind for another 15 minutes. After the solvent is basically evaporated, repeat this operation once more.

[0095] The collected mixture in step S3 was added to a polytetrafluoroethylene liner, to which 20 mL of 1,4-dioxane and 20 mL of mesitylene solvent were added in sequence. The mixture was then ultrasonically dispersed for 30 minutes before the addition of 12 mL of a 6 mol L-1 glacial acetic acid solution.

[0096] S4 puts the reaction solution into the reactor, tightens it, and then puts it into an oven for reaction at 120°C for 72 hours.

[0097] After the reaction is completed, the solid in the liner is collected and centrifuged and washed with deionized water, N,N-dimethylformamide, ethanol, acetone, and dichloromethane at a speed of 10000 r min. -1 .

[0098] The solid obtained in S6 was placed in an oven at 60° C. and dried for 24 h to obtain the covalent organic framework TFP-DAAC.

[0099] (2) The covalent organic framework TFP-DAAC catalyst prepared in Comparative Example 3 was used to catalyze the cleavage of the CC bond in 2-phenoxy-1-phenyl-ethanol to obtain aromatic compounds (benzaldehyde, phenyl formate and phenol).

[0100] 0.1 mmol of 0.02 mol / L 2-phenoxy-1-phenyl-ethanol was used as the substrate, 5 mL of acetonitrile was used as the reaction solvent, and 9 mg of TFP-DAAC catalyst was added. Stirring was initiated in a photocatalytic reactor, and the light intensity was set to 4 W using a 385 nm LED lamp. The reaction temperature was set to 25°C and the reaction was allowed to react for 5 h. After the reaction, 1,3,5-trimethoxybenzene was added as an internal standard. After filtration, gas chromatography-mass spectrometry (GC-MS) analysis was performed. GC-MS data showed that the C-C bond in 2-phenoxy-1-phenyl-ethanol was cleaved, and the substrate conversion was approximately 69.0%. Product peaks of benzaldehyde, phenyl formate, and phenol appeared, with corresponding yields of 63.7 mol%, 11.6 mol%, and 6.7 mol%, respectively.

[0101] Comparative Example 4: Preparation of covalent organic framework TFB-DAAQ photocatalyst and photocatalytic reaction (1) Preparation of covalent organic framework TFB-DAAQ photocatalyst

[0102] S1 Weigh 2 mmol of 2,6-diaminoanthraquinone (DAAQ) and 1 mmol of trimesaldehyde (TFB).

[0103] S2: Add the two raw materials into the mortar and grind them at room temperature. During the process, 200 μL of 1,4-dioxane and 200 μL of mesitylene solution are added dropwise. Grind for 15 minutes and then add 200 μL of 6 mol L -1 Grind with glacial acetic acid solution for another 15 minutes, and repeat this operation once the solvent has evaporated.

[0104] S3 collected the mixture and added it to a polytetrafluoroethylene liner. 20 mL of 1,4-dioxane and 20 mL of mesitylene solvent were added to the liner in sequence. Then, 6 mol L -1 12mL of glacial acetic acid solution.

[0105] S4 puts the reaction solution into the reactor, tightens it, and then puts it into an oven for reaction at 120°C for 72 hours.

[0106] After the reaction is completed, the solid in the liner is collected and centrifuged and washed with deionized water, N,N-dimethylformamide, ethanol, acetone, and dichloromethane at a speed of 10000 r min. -1 .

[0107] The solid obtained in S6 was placed in an oven at 60°C and dried for 24 h to obtain the covalent organic framework TFB-DAAQ.

[0108] (2) The covalent organic framework TFB-DAAQ catalyst prepared in Comparative Example 4 was used to catalyze the cleavage of the CC bond in 2-phenoxy-1-phenyl-ethanol to obtain aromatic compounds (benzaldehyde, phenyl formate and phenol).

[0109] A 0.1 mmol (0.02 mol / L) 2-phenoxy-1-phenyl-ethanol substrate was added to 5 mL of acetonitrile as the reaction solvent, along with 9 mg of TFB-DAAQ catalyst. Stirring was initiated in a photocatalytic reactor, and illumination was set to 4 W using a 385 nm LED light. The reaction temperature was set at 25°C and the reaction was allowed to react for 5 hours. After the reaction, 1,3,5-trimethoxybenzene was added as an internal standard. After filtration, the product was analyzed by gas chromatography-mass spectrometry (GC-MS). GC-MS data indicated that the C-C bond in the 2-phenoxy-1-phenyl-ethanol was cleaved, resulting in a substrate conversion of approximately 8.0%, with virtually no product peaks present.

[0110] The catalysts in Comparative Examples 1 and 2, respectively, replaced 2,6-diaminoanthracene (DAAC) with 2,6-diaminoanthraquinone (DAAQ) and trimesicaldehyde (TFB) with 1,3,5-triformylphloroglucinol (TFP) to synthesize two other covalent organic framework catalysts, TFP-DAAC and TFB-DAAQ. The performance of these two catalysts was significantly lower than that of the catalyst of the present invention. These results indicate that the anthraquinone group is an essential active site for the HAT reaction, demonstrating the importance of the active site of TFP-DAAQ in the photocatalytic depolymerization of lignin.

[0111] The test results of Example 1 and the test results of Comparative Examples 1-4 are shown in Table 3. The test results show that there is a large gap in catalytic performance between the comparative example and TFP-DAAQ. Compared with TFP-DAAQ, the catalytic performance of DAAQ monomer and TFP monomer is weaker, with conversion rates of only 45.6% and 8.9%, respectively. This shows that the catalyst TFP-DAAQ synthesized with TFP and DAAQ as ligands significantly improves the depolymerization efficiency of substrate 1. Subsequently, DAAC was used to replace DAAQ, and TFB was used to replace TFP to synthesize two other covalent organic framework catalysts, TFP-DAAC and TFB-DAAQ. The catalytic performance was reduced, with conversion rates of only 69.0% and 8.0%, respectively, proving the excellent catalytic effect of TFP-DAAQ.

[0112] Table 3 Conversion rate of catalyst at different reaction times and product yield in Comparative Examples 1-4

[0113]

[0114] Figure 16 and Figure 17 They are the characterization of the photocurrent and electrochemical impedance of the catalysts in Comparative Examples 3, 4 and Example 1, respectively. The separation of photogenerated carriers in COF was studied by measuring transient photocurrent and electrochemical impedance. The photocurrents of these COFs did not decay rapidly after being activated, indicating that the electrons and holes did not recombine rapidly after separation, showing their photostability. Comparing TFB-DAAQ and TFP-DAAC, the photocurrent density of TFP-DAAQ is stronger, which strongly proves that the carrier mobility in COF can be effectively adjusted by changing the ligand. It is worth noting that such results further demonstrate the importance of the conjugated structure of the carbonyl and anthraquinone units in TFP-DAAQ compared to TFB-DAAQ, as well as the conclusion that the enol structure in COF is partially converted into a keto structure after the reaction, and TFP-DAAQ* increases the ability to transfer photogenerated electrons. These results are also supported by electrochemical impedance spectroscopy (EIS) studies ( Figure 14 ), the wider the radius of the semicircle in the Nyquist plot, the greater the charge transfer resistance.

Claims

1. A method for preparing a covalent organic framework TFP-DAAQ, characterized in that: The following steps are involved: S1 weighed the ligand raw materials 2,6-diaminoanthraquinone and 1,3,5-triformylphloroglucinol; S2: Add the two raw materials into a mortar and grind them at room temperature. Before grinding, add 1,4-dioxane and mesitylene dropwise. Grind for a while and then add glacial acetic acid solution dropwise to continue grinding. S3 collects the mixture and adds it to a polytetrafluoroethylene liner, then sequentially adds 1,4-dioxane and mesitylene solvent to the liner, and then ultrasonically disperses it and adds glacial acetic acid solution; S4 is drying the reaction solution; S5 After the reaction is completed, the solid in the liner is collected, centrifuged and washed, and filtered; S6 obtains a solid and dries it to obtain the covalent organic framework TFP-DAAQ.

2. The method for preparing a covalent organic framework TFP-DAAQ according to claim 1, wherein: In step S1, the molar ratio of 2,6-diaminoanthraquinone to 1,3,5-triformylphloroglucinol is 3:1 to 2:1; in step S3, the volume ratio of 1,4-dioxane to mesitylene solvent is 1:1, and the concentration of glacial acetic acid solution is 6 mol L -1 The volume ratio of the first two solvents to glacial acetic acid solution is 5:3 to 5:

5.

3. The method for preparing a covalent organic framework TFP-DAAQ according to claim 1, wherein: Step S2 grinding process, specifically: before grinding, add 1,4-dioxane and mesitylene in a volume ratio of 1:1, grind for 10 to 20 minutes, then add 6 mol L -1 The volume ratio of glacial acetic acid solution to the other two solvents is 5:3 to 5:

5. Grind for another 10 to 20 minutes. After the solvent is basically evaporated, repeat this operation once more.

4. The method for preparing a covalent organic framework TFP-DAAQ according to claim 1, wherein: In step S4, the oven temperature is set to 120°C to 150°C and the reaction is carried out for 60 to 84 hours; in step S5, the solid in the lining is collected and centrifuged and washed in sequence with deionized water, N,N-dimethylformamide, ethanol, acetone and dichloromethane; in step S6, the drying treatment is carried out in a conventional oven at a drying temperature of 60 to 80°C; and the drying time is 12 to 24 hours.

5. A covalent organic framework TFP-DAAQ, characterized in that The method is prepared by any one of claims 1 to 4.

6. A method for catalyzing the cleavage of CC bonds in lignin using the covalent organic framework TFP-DAAQ according to claim 5, characterized in that: The lignin raw material, the covalent organic framework TFP-DAAQ catalyst and the polar aprotic solvent are mixed, reacted at 20-30° C. for 5-6 hours under light conditions in air, and the aromatic monomer product is obtained after purification.

7. The method according to claim 6, wherein The lignin raw material is a lignin model compound or an organic soluble lignin; the lignin model compound includes 2-phenoxy-1-phenyl-ethanol, 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol or 2-(2-methoxyphenyl)oxy-1-(4-methoxyphenyl)ethanol; the organic soluble lignin is obtained by extracting bagasse.

8. The method according to claim 7, wherein The amount of the covalent organic framework TFP-DAAQ is 20%-50% of the mass of the lignin raw material.

9. The method according to claim 8, wherein The polar aprotic solvent is acetonitrile.

10. The method according to claim 9, wherein The illumination conditions are as follows: the wavelength is 365-385nm and the illumination intensity is 70%-100%; the purification method is to wash away the remaining substrate with N,N-dimethylformamide, then use dichloromethane and ethanol solvents to centrifuge and wash in sequence to remove the remaining N,N-dimethylformamide, and then filter.

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