An efficient, green and universal melt synthesis method for covalent organic frameworks

Abstract

The present invention discloses a kind of efficient green and universal melt synthesis method of covalent organic framework, comprising the steps of: making organic monomer 1, organic monomer 2 and auxiliary agent melt polymerization reaction, and the product is activated to obtain a covalent organic framework; the auxiliary agent is containing amides, phosphoramides, acylhydrazones, hydrazides or phosphoramidites for synthesizing stable imines, hydrazones, acylhydrazones, polyimides, vinyls, vinylides, ketone-enols or pyrazines COFs with good applicability. The method is characterized by good applicability and process greening, and can achieve solvent-free, cyclic auxiliary agents, simple process, and simple equipment of multiple types of COFs. Batch synthesis has high specific surface area and higher crystallinity COFs. At the same time, the method breaks through the harsh conditions required for the solvent thermal synthesis common to traditional COFs and does not use harmful organic solvents, and is suitable for large-scale batch preparation of high-quality COFs materials.

Description

Technical Field

[0001] The present invention relates to the technical field of synthesis of covalent organic frameworks, and in particular to a highly efficient, green and universal melt synthesis method of covalent organic frameworks. Background Art

[0002] Covalent organic frameworks (COFs) are a type of porous crystalline polymer material with one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) long-range order formed by reversible covalent bonds of highly customizable organic small molecule monomers. Compared with traditional materials, it has the advantages of highly controllable crystalline structure, high specific surface area, good stability, easy modification and functionalization, low density, no harmful heavy metals, and adjustable and controllable pores. Therefore, covalent organic framework materials have great application potential in gas adsorption and separation, catalysis, batteries and energy storage, drug delivery, pollutant adsorption and treatment, sensing, luminescence, molecular sieving, membrane separation and other fields. However, due to the harsh synthesis conditions of covalent organic framework materials, the current synthesis method of COFs can only meet laboratory needs.

[0003] Currently, the most common and conventional method for synthesizing COFs is the solvothermal method, which is characterized by allowing organic monomers to condense and crystallize into solid COFs powder in an oxygen-free glass tube in a mixed organic solvent of appropriate proportions under the action of a catalyst at high temperature. Although this method is universal for the synthesis of most COFs, it is limited by the size of the glass tube and the use of toxic and volatile organic solvents. In addition, completely different organic solvent combinations may be used for different COFs. And the optimal catalyst for different types of COFs is also different. Therefore, this method can currently only prepare covalent organic framework materials at the level of tens or hundreds of milligrams, which is far from meeting the production requirements for industrialization.

[0004] With increasing concern about environmental issues, reducing the use of toxic, hazardous, and volatile organic solvents is an urgent task. Therefore, there is an urgent need to develop a universal synthetic method that can efficiently prepare covalent organic frameworks without the use of organic solvents.

[0005] Currently, researchers have developed some methods for the green, solvent-free synthesis of COFs. For example, the document J.Am.Chem.Soc.139,13083-13091 (2017) reports a method for preparing COFs synthesized from 1,3,5-triformyl-2,4,6-triphenol monomers using p-toluenesulfonic acid as a catalyst. Patent CN 114773556 A discloses a method for synthesizing alkenyl COFs using anhydrides or carboxylic acids as catalysts. Although these methods have solved the above problems to a certain extent, they all have the problem of universality, that is, these methods are often only effective for the synthesis of one or several specific COFs. In addition, the catalysts or additives used in these methods are often highly acidic and corrosive, which places more stringent requirements on industrial production equipment.

[0006] Therefore, developing a universal, efficient, green, solvent-free, recyclable, and easy-to-scale up and large-scale synthesis method for preparing various types of COFs is a difficult problem that needs to be solved urgently in the field of COFs. Summary of the Invention

[0007] The present invention addresses the problems in COFs synthesis methods and provides a solvent-free, green, efficient, and universal synthesis method for a variety of COFs. COFs are synthesized by a solvent-free melt method using compounds containing active amino groups as auxiliary agents. The requirements for reaction equipment are low, and the resulting covalent organic framework has good crystallinity and porosity.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A highly efficient, green and universal melt synthesis method for a covalent organic framework comprises the following steps: subjecting an organic monomer 1, an organic monomer 2 and an auxiliary agent to a melt polymerization reaction, and activating the product to obtain a covalent organic framework;

[0010] The auxiliary agent is a compound containing amides, phosphoramides, acylhydrazones, hydrazides or phosphoramidites;

[0011] The organic monomer 1 is an organic monomer containing one or more reactive functional groups selected from amino, hydrazine, hydrazide, active methyl / methylene, and o-diphenolic hydroxyl groups;

[0012] The organic monomer 2 is an organic monomer containing Y reactive functional groups selected from the group consisting of aldehyde, ketone, anhydride, carboxyl, carboxylate, and fluorobenzene;

[0013] Wherein, 2≤X≤8, 2≤Y≤12, and the reaction functional groups of the organic monomer 1 and the organic monomer 2 are different.

[0014] The present invention has found that solvent-free synthesis of COFs materials can be achieved by using compound additives containing amides, and high-yield and efficient green synthesis can be achieved through high-temperature melt polymerization. The additive can be recycled and reused. The additive has a melting point and boiling point of about 100-250°C and has an active amino group. This type of additive has dual functions, namely amino and acyl groups. The amino part can be used as an additive for the reaction of imine, imide, and hydrazide COFs, and can effectively regulate the reaction of amino ligands and aldehyde ligands to generate highly crystalline COFs materials. In the generation of alkenyl COFs, the acyl group in the additive can effectively interact with the nitrogen / oxygen in the active methyl / methylene monomer to further activate the methyl / methylene group, so that it can effectively react with the aldehyde group to generate highly crystalline alkenyl COFs.

[0015] Preferably, the auxiliary agent has one of the structures shown in the following I-VIII:

[0016]

[0017] Among them, R and R' in I to VIII are one or more of the following groups: substituted or position-substituted phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted condensed ring group, substituted or position-substituted alkyl, substituted or unsubstituted heterocyclic group, and R and R' groups may be the same or different.

[0018] Specifically, the amide compound is a compound having a structure shown in I; the hydrazide compound is a compound having a structure shown in II; the N-formylidene amide compound is a compound having a structure shown in III; the acylhydrazone compound is a compound having a structure shown in IV; the disubstituted hydrazide compound is a compound having a structure shown in V; the disubstituted amide compound is a compound having a structure shown in VI; the phosphoramide compound is a compound having a structure shown in VII; and the phosphoramidite compound is a compound having a structure shown in VIII.

[0019] Preferably, the organic monomer containing X amino reactive functional groups has one of the following structures:

[0020]

[0021] Preferably, the organic monomer containing X active methyl / methylene reactive functional groups has one of the following structures:

[0022]

[0023] wherein each occurrence of R1 is C or N; each occurrence of R2 is O, S or NH;

[0024] Preferably, the organic monomer containing X o-diphenolic hydroxyl reactive functional groups has one of the following structures:

[0025]

[0026] Preferably, the organic monomer containing Y aldehyde or ketone reactive functional groups has one of the following structures:

[0027]

[0028] Preferably, the organic monomer containing Y anhydride, carboxyl or carboxylate reactive functional groups has one of the following structures:

[0029]

[0030] Preferably, the organic monomer containing Y fluorobenzene reactive functional groups has one of the following structures:

[0031]

[0032] Each occurrence of Z is independently F or H, and Z in the above structure has at least one F.

[0033] Preferably, the melt synthesis method comprises the steps of grinding and mixing organic monomer 1, organic monomer 2 and an auxiliary agent, melt-polymerizing in a closed reaction vessel, and activating the organic framework to obtain the covalent organic framework.

[0034] Preferably, the reaction vessel can be one of a high-pressure reactor, a sealed hard glass tube, and a sealed thick-walled reaction bottle.

[0035] The melt polymerization temperature is 100-300° C., and the reaction time is 0.5-10 days. Preferably, the melt polymerization temperature is 120-250° C., and the reaction time is 2-5 days.

[0036] The method of the present invention is applicable to the synthesis of various COFs materials, including imine-linked, alkenyl-linked, alkenylene-linked, imide-linked, keto-enamine-linked, triazine-linked, pyrazine-linked, hydrazone / acylhydrazone-linked COFs, etc., and has wide universality.

[0037] Preferably, when organic monomer 1 is an organic monomer containing one or more reactive functional groups selected from amino, hydrazine, and hydrazide groups, organic monomer 2 is an organic monomer containing one or more reactive functional groups selected from aldehyde, ketone, anhydride, carboxyl, carboxylate, and fluorophenyl groups;

[0038] Preferably, when organic monomer 1 is an organic monomer containing an active methyl / methylene reactive functional group, organic monomer 2 is an organic monomer containing one or more reactive functional groups of an aldehyde group or a ketone group;

[0039] Preferably, when the organic monomer 1 is an organic monomer containing an o-diphenol hydroxyl reactive functional group, the organic monomer 2 is an organic monomer containing a fluorobenzene reactive functional group.

[0040] Further preferably, the organic monomer 1 is one or more of p-aniline, benzyl diamine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5-tris(4-aminophenyl)benzene, 1,3,5-trimethyl-2,4,6-triazine, tris(4-aminophenyl)amine, 2,4,6-trimethylpyridine, 2,4,6-tris(3-hydroxy-4-aminophenyl)-1,3,5-triazine, N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine, tetrakis-(4-aminophenyl)ethylene, 5,5'-dimethyl-3,3'-bipyridine, etc.;

[0041] Further preferably, the organic monomer 2 is one or more of 2,5-dimethoxyterephthalaldehyde, pyromellitic anhydride, 1,4,5,8-naphthalenetetracarboxylic acid, 1,3,5-tris(4'-formyl[1,1'-biphenyl]-4-yl)benzene, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 4,4'-biphenyldicarboxaldehyde, terephthalaldehyde, 1,2-bis(4'-formylphenyl)acetylene, tetrafluoroterephthalonitrile, etc.;

[0042] Further preferably, the auxiliary agent is one or more of 4-trifluoromethylbenzamide, 4-methylbenzamide, fluorobenzamide, diphenylphosphoramide, trifluoroacetamide, (bistrifluoromethanesulfonyl imide) amine, (bisfluorosulfonyl imide) amine, bistrifluoroacetamide, N-amino-bis(trifluoroacetamide), cyanobenzamide, and nitrobenzamide.

[0043] More preferably, the auxiliary agent is one or more of 4-trifluoromethylbenzamide, 4-methylbenzamide, fluorobenzamide, diphenylphosphoramide, and trifluoroacetamide;

[0044] The molar ratio of the organic monomer 1 to the organic monomer 2 is 1:8 to 8:1.

[0045] The molar ratio of the auxiliary agent to the organic monomer 1 is 0.5-90: 1. The amount of the auxiliary agent is preferably such that the reactive monomer can be substantially dissolved in a molten state.

[0046] The obtained covalent organic framework material is in powder, block, film or porous form.

[0047] The activation comprises: removing impurities from the product by Soxhlet extraction, sublimation, freeze drying or rotary evaporation to obtain a covalent organic framework and a recovered auxiliary agent. The recovered auxiliary agent can be put into use again.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention unexpectedly discovered a class of auxiliary agents that can efficiently synthesize COFs materials in a solvent-free manner. The auxiliary agents are applicable to a variety of covalent organic framework materials, have high synthesis efficiency, and the products have good crystallinity and porosity.

[0050] (2) The synthesis method of the present invention can achieve gram-kilogram-level preparation, has low equipment requirements, and has been used to prepare a variety of COFs on a large scale. It is very suitable for industrial production needs and has a very high prospect for promotion and application.

[0051] (3) The present invention not only does not use organic solvents that are toxic and harmful to the environment, but the additives used can also be recycled and reused, which is green, environmentally friendly and sustainable. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is the X-ray diffraction pattern of the COF material obtained in Example 1.

[0053] Figure 2 This is the Fourier transform infrared spectrum of the COF material obtained in Example 1.

[0054] Figure 3 This is the X-ray diffraction pattern of the COF material obtained in Example 2.

[0055] Figure 4 This is a scanning electron microscope image of the COF material obtained in Example 2.

[0056] Figure 5 This is a transmission electron microscope image of the COF material obtained in Example 2.

[0057] Figure 6 This is the X-ray diffraction pattern of the COF material obtained in Example 3.

[0058] Figure 7 This is the nitrogen adsorption-desorption curve of the COF material obtained in Example 3 at 77K.

[0059] Figure 8 This is the X-ray diffraction pattern of the COF material obtained in Example 4.

[0060] Figure 9 This is the Fourier infrared spectrum of the COF material obtained in Example 4.

[0061] Figure 10 This is the X-ray diffraction pattern of the COF material obtained in Example 5.

[0062] Figure 11 This is the Fourier infrared spectrum of the COF material obtained in Example 5.

[0063] Figure 12 This is the X-ray diffraction pattern of the COF material obtained in Example 6.

[0064] Figure 13 This is the X-ray diffraction pattern of the COF material prepared by reusing the auxiliary agent in Example 7. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0066] The raw materials used in the following specific embodiments are all purchased from the market.

[0067] Example 1

[0068] 1,3,5-Trimethyl-2,4,6-triazine (123.2 mg, 1.0 mmol), 4,4'-biphenyldicarboxaldehyde (315.3 mg, 1.5 mmol), and 4-trifluoromethylbenzamide (1.2 g, 6.0 mmol) were weighed and placed in a thick-walled glass tube connected to a vacuum line. When the pressure inside the tube dropped below 0.2 mmHg, the tube was sealed with a flame to isolate it from the air. The sealed tube was transferred to a forced air oven set at 200°C and allowed to stand for 4 days. The reaction yielded a dark red, blocky solid, which was crushed in a mortar and pestle and then washed in tetrahydrofuran in a Soxhlet extractor for 3 hours to yield an orange-yellow powder.

[0069] The powder is placed in a 100°C forced air oven (or placed in a rotary evaporator) and dried to obtain a product mass between 370 mg and 377 mg with a yield of 96% to 98% (the yield loss is mainly due to the scattering of powder during the pulverization process). The washed tetrahydrofuran solution can be separated from tetrahydrofuran and 4-trifluoromethylbenzamide by rotary evaporation. The recovered auxiliary agent 4-trifluoromethylbenzamide can be reused and can be reused at least 10 times; the recovered tetrahydrofuran solvent can also be used multiple times.

[0070] like Figure 1 As shown in Figure 2, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity. Figure 2 The Fourier transform infrared spectroscopy in the sample proves that the sample is an olefinically connected COFs material.

[0071] Example 2

[0072] Weigh pyromellitic anhydride (327.3 mg, 1.5 mmol), tris(4-aminophenyl)amine (290.4 mg, 1.0 mmol), and 4-trifluoromethylbenzamide (1.7 g, 9 mmol). Place the above raw materials in a stainless steel reactor lined with tetrafluoroethylene in a glove box (O2≤0.1 ppm, H2O≤0.1 ppm) and tighten the seal. After the above reactor is placed in a 180°C blast oven for 5 days, a powder is obtained with a yield of 90% to 95%. After Soxhlet extraction with tetrahydrofuran, it is dried in a 100°C blast oven. The auxiliary agent 4-trifluoromethylbenzamide and the detergent tetrahydrofuran can be separated and recovered by rotary evaporation. The recovered auxiliary agent and tetrahydrofuran can be used for the next synthesis, and the auxiliary agent can be recycled at least 10 times. Figure 3 As shown in Figure 2, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity. Figure 4 is a scanning electron microscope image of the COF. Figure 5 : is a transmission electron microscope image of the COF, which shows that the COF has good crystallinity.

[0073] Example 3

[0074] Weigh 2,5-dimethoxyterephthalaldehyde (291.3 mg, 1.5 mmol), 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (531.6 mg, 1.0 mmol), and 4-trifluoromethylbenzamide (1.2 g, 6 mmol). Place the above raw materials in a stainless steel reactor lined with tetrafluoroethylene in a glove box (O2≤0.1 ppm, H2O≤0.1 ppm) and tighten the seal. After the above reactor was placed in a 160°C blast oven for 5 days, a powder was obtained with a yield of 90% to 95%. After Soxhlet extraction with tetrahydrofuran, it was dried in a 100°C blast oven. The auxiliary agent 4-trifluoromethylbenzamide and the detergent tetrahydrofuran can be separated and recovered by rotary evaporation. The recovered auxiliary agent and tetrahydrofuran can be used for the next synthesis, and the auxiliary agent can be recycled at least 10 times. Figure 6 As shown, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity. Figure 7 The nitrogen isothermal adsorption / desorption curve of the material at 77K, and its BET specific surface area is 1700m 2 g -1 .

[0075] Example 4

[0076] 1,3,5-Trimethyl-2,4,6-triazine (123.2 mg, 1.0 mmol), 4,4'-biphenyldicarboxaldehyde (315.3 mg, 1.5 mmol), and diphenylphosphoramide (2.0 g, 9.0 mmol) were weighed and placed in a thick-walled glass tube connected to a vacuum line. When the pressure inside the tube dropped below 0.2 mmHg, the tube was sealed with a flame to isolate it from the air. The sealed tube was transferred to a forced air oven set at 200°C and allowed to stand for 4 days. The reaction yielded a dark red, blocky solid. This was ground in a mortar and pestle and then washed in tetrahydrofuran in a Soxhlet extractor for 3 hours to yield an orange-yellow powder.

[0077] The powder is dried in a 100°C forced air oven (or on a rotary evaporator) to obtain a product mass of between 370 mg and 377 mg with a yield of 96% to 98% (the yield loss is mainly due to the scattering of powder during the pulverization process). The resulting tetrahydrofuran solution is washed and then rotary evaporated to separate tetrahydrofuran and diphenylphosphoramide. The recovered auxiliary agent diphenylphosphoramide can be reused and reused at least 10 times; the recovered tetrahydrofuran solvent can also be used multiple times.

[0078] like Figure 8 As shown in Figure 2, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity. Figure 9 The Fourier transform infrared spectroscopy in the sample proves that the sample is an olefinically connected COFs material.

[0079] Example 5

[0080] 1,3,5-Trimethyl-2,4,6-triazine (123.2 mg, 1.0 mmol), terephthalaldehyde (201.2 mg, 1.5 mmol), and diphenylphosphoramide (1.2 g, 6.0 mmol) were weighed and placed in a thick-walled glass tube connected to a vacuum line. When the pressure inside the tube dropped below 0.2 mmHg, the tube was sealed with a flame to isolate it from the air. The sealed tube was transferred to a forced air oven set at 200°C and allowed to stand for 4 days. The reaction yielded a dark red, blocky solid. This was ground in a mortar and pestle and then washed in tetrahydrofuran in a Soxhlet extractor for 3 hours to yield an orange-yellow powder.

[0081] like Figure 10 As shown in Figure 2, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity. Figure 11 The Fourier transform infrared spectroscopy in the sample proves that the sample is an olefinically connected COFs material.

[0082] Example 6

[0083] Scale-up synthesis: Weigh 2,4,6-trimethylpyridine (30.3 g, 250 mmol), 4,4'-biphenyldicarboxaldehyde (78.8 g, 375 mmol), and trifluoroacetamide (250 g, 2.3 mol). Add these raw materials to a sealed, Teflon-lined reactor (500 mL x 2) in a glove box (O₂ ≤ 0.1 ppm, H₂O ≤ 0.1 ppm). Heat the reactor at 180°C in a forced-air oven for 5 days to yield a dark red, blocky solid. The solid was pulverized and initially washed with N,N-dimethylformamide. Then, Soxhlet extraction with tetrahydrofuran (THF) was performed for 1 day. After drying in a forced-air oven, approximately 86.7 g of powder was obtained, with a yield of 91.0%. Figure 12 The X-ray diffraction pattern of the sample obtained in this example proves that the obtained sample is a COF material with high crystallinity.

[0084] Example 7

[0085] Recycling of auxiliary agents for resynthesis: Weigh out pyromellitic anhydride (327.3 mg, 1.5 mmol), tris(4-aminophenyl)amine (290.4 mg, 1.0 mmol), and 4-trifluoromethylbenzamide (1.7 g, 9 mmol) recovered in Example 2. Place the above raw materials in a stainless steel reactor lined with tetrafluoroethylene in a glove box (O2≤0.1 ppm, H2O≤0.1 ppm) and tighten the seal. After the above reactor was placed in a 180°C blast oven for 5 days, a powder was obtained with a yield of 90% to 95%. After Soxhlet extraction with tetrahydrofuran, it was dried in a 100°C blast oven. The auxiliary agent 4-trifluoromethylbenzamide and the detergent tetrahydrofuran can be separated and recovered by rotary evaporation, and the recovered auxiliary agent and tetrahydrofuran can be used for the next synthesis. As Figure 13 As shown, the powder X-ray diffraction test results show that the sample obtained by this method has high crystallinity.

[0086] Comparative Example 1

[0087] 2,5-Dimethoxyterephthalaldehyde (291.3 mg, 1.5 mmol), 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (531.6 mg, 1.0 mmol), and benzoic anhydride (1.3 g, 5.5 mmol) were weighed. These raw materials were placed in a tetrafluoroethylene-lined stainless steel reactor in a glove box (O₂ ≤ 0.1 ppm, H₂O ≤ 0.1 ppm) and sealed tightly. The reactor was placed in a forced air oven at 160°C for 5 days and then washed with N,N-dimethylformamide. No solid product remained, indicating that 2,5-Dimethoxyterephthalaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine could not form COF when benzoic anhydride was used as an auxiliary agent.

Claims

1. A highly efficient, green and universal melt synthesis method for covalent organic frameworks, characterized in that: The method comprises the following steps: allowing organic monomer 1, organic monomer 2 and an auxiliary agent to undergo melt polymerization reaction, and activating the product to obtain a covalent organic framework; The auxiliary agent is a compound containing amides or phosphoramides; The organic monomer 1 is an organic monomer containing one or more reactive functional groups selected from amino, hydrazine, hydrazide, active methyl / methylene, and o-diphenolic hydroxyl groups; The organic monomer 2 is an organic monomer containing Y reactive functional groups selected from the group consisting of aldehyde, ketone, anhydride, carboxyl, carboxylate, and fluorobenzene; wherein 2≤X≤8, 2≤Y≤12, and the reactive functional groups of organic monomer 1 and organic monomer 2 are different; When organic monomer 1 is an organic monomer containing one or more reactive functional groups selected from amino, hydrazine, and hydrazide groups, organic monomer 2 is an organic monomer containing one or more reactive functional groups selected from aldehyde, ketone, anhydride, carboxyl, carboxylate, and fluorophenyl groups; When organic monomer 1 is an organic monomer containing an active methyl / methylene reactive functional group, organic monomer 2 is an organic monomer containing one or more reactive functional groups of an aldehyde group or a ketone group; When the organic monomer 1 is an organic monomer containing an o-diphenol hydroxyl reactive functional group, the organic monomer 2 is an organic monomer containing a fluorobenzene reactive functional group.

2. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The auxiliary agent has one of the structures shown in the following I or VII: Wherein, R and R' in I or VII are one or more of the following groups: substituted or position-substituted phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted condensed ring group, substituted or position-substituted alkyl, substituted or unsubstituted heterocyclic group, and R and R' groups may be the same or different.

3. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The organic monomer containing X amino reactive functional groups has one of the following structures: The organic monomer containing X active methyl / methylene reactive functional groups has one of the following structures: wherein each occurrence of R1 is C or N; each occurrence of R2 is O, S or NH; The organic monomer containing X o-diphenol hydroxyl reactive functional groups has one of the following structures:

4. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The organic monomer containing Y aldehyde or ketone reactive functional groups has one of the following structures: The organic monomer containing Y anhydride, carboxyl or carboxylate reactive functional groups has one of the following structures: The organic monomer containing Y fluorobenzene reactive functional groups has one of the following structures: Each occurrence of Z is independently F or H, and Z in the above structure has at least one F.

5. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The organic monomer 1 is one or more of p-aniline, benzyl diamine, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, 1,3,5-tris(4-aminophenyl)benzene, 1,3,5-trimethyl-2,4,6-triazine, tris(4-aminophenyl)amine, 2,4,6-trimethylpyridine, 2,4,6-tris(3-hydroxy-4-aminophenyl)-1,3,5-triazine, N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine, tetrakis-(4-aminophenyl)ethylene, and 5,5'-dimethyl-3,3'-bipyridine; The organic monomer 2 is one or more of 2,5-dimethoxyterephthalaldehyde, pyromellitic anhydride, 1,4,5,8-naphthalenetetracarboxylic acid, 1,3,5-tris(4'-formyl[1,1'-biphenyl]-4-yl)benzene, 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 4,4'-biphenyldicarboxaldehyde, terephthalaldehyde, 1,2-bis(4'-formylphenyl)acetylene, and tetrafluoroterephthalonitrile.

6. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The auxiliary agent is one or more of 4-trifluoromethylbenzamide, 4-methylbenzamide, fluorobenzamide, diphenylphosphoramide, trifluoroacetamide, bistrifluoroacetamide, N-amino-bis(trifluoroacetamide), cyanobenzamide, and nitrobenzamide.

7. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The melt synthesis method comprises the steps of grinding and mixing organic monomer 1, organic monomer 2 and an auxiliary agent, melt-polymerizing in a closed reaction vessel, and activating the covalent organic framework to obtain the covalent organic framework.

8. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The melt polymerization temperature is 100-300°C and the reaction time is 0.5-10 days; and / or, the molar ratio of the organic monomer 1 to the organic monomer 2 is 1:8 to 8:1; And / or, the molar ratio of the auxiliary agent to the organic monomer 1 is 0.5-90:

1.

9. The efficient, green and universal melt synthesis method of covalent organic framework according to claim 1, characterized in that: The activation comprises: removing impurities from the product through Soxhlet extraction, sublimation technology, freeze drying or rotary evaporation technology to obtain a covalent organic framework and recover a reusable auxiliary agent.

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