Universal synthesis and atmospheric water collection application of covalent organic framework aerogel

Abstract

The invention provides a simple, universal and extensible method for preparing the covalent organic framework aerogel by utilizing a plurality of group protection strategies. The COF gel material is generated through the aldehyde amine condensation reaction of the group-protected amino monomer and the aldehyde group monomer, so that the molding of the non-melting COF material is realized. The COF aerogel material can be obtained only through a simple freeze-drying method, the preparation method is simple, the prepared material has the characteristics of high crystallinity, high porosity and the like, and the COF organic hydrogel can be very conveniently subjected to structure and function design and can easily load various functional groups. A water vapor adsorption determination experiment is carried out, and the COF aerogel material can realize good solar energy absorption and photo-thermal conversion, has good atmospheric water collection performance, and has a great industrial practical application prospect.

Description

Technical Field

[0001] The invention belongs to the field of porous organic materials, and in particular relates to the universal synthesis of a class of covalent organic framework aerogel materials and their application in the field of atmospheric water collection. Background Art

[0002] Water is an important resource for human survival, but the global water shortage problem has become increasingly serious with the rapid growth of the global population, rapid socio-economic development, and accelerated industrialization. Recently, the new technology of using porous adsorbents as physical adsorbents to collect water vapor in the atmosphere (atmospheric water harvesting (AWH)) to prepare pure water has attracted widespread attention from the scientific and industrial communities. However, traditional porous adsorbents (such as activated carbon and polymer resins) lack structural order (crystallinity) and have disordered functional units. It is impossible to study the relationship between water collection performance and material structure based on a clear and definite structure, so it is difficult to better design and synthesize high-performance water collection materials based on structure-activity relationship research. In recent years, crystalline porous materials with regular and ordered structures, such as zeolites and metal-organic frameworks (MOFs), have shown great potential in water collection. However, zeolite materials have problems with high regeneration temperature and high energy consumption during water collection, which limits their use in practical applications. MOF materials have poor stability, especially poor water stability, which restricts large-scale application in real scenarios. The development of new crystalline porous materials has important theoretical and practical significance, because they can replace traditional water collection materials and have the characteristics of low price, high stability, easy molding and regeneration. This will help improve the utilization efficiency of water resources and make our lives more sustainable. As a new type of crystalline porous polymer material, covalent organic framework (COF) has become an ideal atmospheric water collection material due to its clear structure, customizable functions, adjustable pore size, high porosity, high chemical and thermal stability. The low skeleton density, high specific surface area and easy-to-adjust pore size of COF can increase the adsorption capacity of COF materials on water vapor; COF's clear and regular structure is convenient for studying structure-activity relationships to guide material design; COF's easy modification of functional groups can adjust the pore environment (such as hydrophilicity / hydrophobicity, etc.) and water vapor adsorption / desorption rate of COF materials, thereby achieving rapid adsorption and desorption of water vapor; COF materials have high structural stability, which can enhance the recycling performance of COF materials. However, the research on using COF for atmospheric water collection is still in its infancy. There are very few reported COF examples, and there are problems with the formation of COFs, which restricts their large-scale practical applications in the future.

[0003] Gels have many advantages such as good adjustability, strong stability and good adsorption performance. Gels have good adjustability, and their physical properties, such as hardness, elasticity, shape, etc., can be adjusted as needed to meet different application requirements. In addition, gels can be given specific chemical properties, such as hydrophilicity, lipophilicity, etc., to cope with different application environments. Gels have high stability, and their properties are not easy to change at different temperatures, pH values ​​and ion concentrations, maintaining a relatively stable adsorption and separation effect. This makes gels perform well in various practical applications. The surface of gel materials has rich functional groups, which are easy to react with other biomolecules and form chemical bonds, thereby showing a high adsorption capacity. Gels can be mainly divided into organic gels, hydrogels, organic hydrogels and aerogels. Among them, organic hydrogels can be transformed into aerogels through solvent exchange and freeze drying, thus breaking the gap between different types of gels. It is of great significance to develop new gel materials with high versatility. Summary of the invention

[0004] The purpose of the present invention is to adopt a universal group protection strategy to prepare COFs aerogels. This type of material has the advantages of high crystallinity, high porosity, and very convenient structural and functional design.

[0005] Another object of the present invention is to conduct water vapor adsorption and desorption measurement experiments for application in atmospheric water collection. COFs aerogel can achieve good solar energy absorption, photothermal conversion and atmospheric water collection performance, which is comparable to the most advanced materials and has great industrial practical application prospects. Other objects of the present invention are clear to those skilled in the art from the above and following descriptions.

[0006] The first aspect of the present invention is to propose a universal group protection strategy for preparing COFs aerogel, characterized in that the group protection strategy is used to construct the COFs aerogel material in one step by covalently linking imines.

[0007] Preferably, the synthesis method 1 is to directly add the group-protected di-linked and tri-linked amino monomers, the tri-linked monomers containing aldehyde groups and the catalyst into the reactor, condense the aldehyde amine under closed conditions to obtain the COFs gel material, and then wash and purify it.

[0008] Preferably, the monomer 1 is a group-protected di-linked and tri-linked amino monomer.

[0009] More preferably, the monomer 2 is a three-linked monomer containing an aldehyde group.

[0010] In a preferred embodiment of the present invention, the group-protected amino monomer is any one of benzyloxycarbonyl (Cbz)-protected, tert-butyloxycarbonyl (Boc)-protected, methyloxycarbonyl (Fmoc)-protected p-phenylenediamine, 4,4'-biphenylenediamine, p-diaminoazobenzene, 1,3,5-tris(4-aminophenyl)benzene, and 2,4,6-tris(4-aminophenyl)diazenyl)benzene-1,3,5-triol.

[0011] In a preferred embodiment of the present invention, the aldehyde monomer is any one of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde, 2,4-dihydroxy-1,3,5-benzenetricarboxaldehyde and 2-hydroxy-1,3,5-benzenetricarboxaldehyde.

[0012] Preferably, the catalyst is a compound containing an acidic functional group.

[0013] More preferably, the catalyst is one of concentrated hydrochloric acid, concentrated sulfuric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and trifluoroacetic acid.

[0014] Preferably, the obtained COFs gel is an imine-linked COFs gel block.

[0015] Preferably, the pore size of the COFs material is 1.0-2.1 nm.

[0016] Preferably, the specific surface area of ​​the COFs material is 322-1625 m 2 / g.

[0017] Preferably, the molar ratio of organic monomer 1 to organic monomer 2 is 3:2 or 1:1.

[0018] Preferably, in the reaction system, the amount of the catalyst acid used is 60-150 μL, more preferably 60 μL.

[0019] Preferably, in the reaction system, the amount of water used is 0.1-0.9 mL, more preferably 0.4 mL.

[0020] Preferably, the temperature of the reaction system is 120-150°C.

[0021] Preferably, in the reaction system, the solvent is o-dichlorobenzene, n-butanol, mesitylene, dioxane, tetrachloroethane, tetrahydrofuran, or n-heptane.

[0022] Preferably, the reaction time is 1-5 days, more preferably 3 days.

[0023] Preferably, the closed reaction vessel is a steel high-pressure reactor with a polytetrafluoroethylene lining.

[0024] Preferably, the COFs material cleaning and purification steps are: soaking the obtained COFs gel sample in DMF to wash the unreacted precursor, then using THF Soxhlet extraction to further remove the unreacted monomers, followed by solvent exchange, and finally freeze-drying for 12 h to obtain a highly crystalline COFs aerogel.

[0025] The synthesis method of the present invention is to construct an imine-based COFs gel material through a group protection strategy, and the relevant general formula can be expressed as: In the general formula: organic monomer 1 mainly includes: any one of benzyloxycarbonyl (Cbz) protected, tert-butyloxycarbonyl (Boc) protected, methyloxycarbonyl (Fmoc) protected p-phenylenediamine, 4,4'-biphenylenediamine, p-diaminoazobenzene, 1,3,5-tris(4-aminophenyl)benzene, 2,4,6-tris(4-aminophenyl)diazenyl)benzene-1,3,5-triol. Organic monomer 2 mainly includes: any one of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde, 2,4-dihydroxy-1,3,5-benzenetricarboxaldehyde, 2-hydroxy-1,3,5-benzenetricarboxaldehyde. The above-mentioned monomers 1 and 2 can be combined arbitrarily, and the target COFs can be prepared under any one of the conditions of the catalyst. The catalyst is any one of concentrated hydrochloric acid, concentrated sulfuric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and trifluoroacetic acid.

[0026] Preferably, in the COF gel water adsorption performance test, the sample is degassed at 120°C for 24 h.

[0027] Preferably, the atmospheric water collection experiment is carried out in a K2CO3 saturated salt solution atmosphere (25°C, about 43%RH). Compared with the prior art inventions, the present invention has the following innovations: 1. For the first time, the group-protected amino monomer is used as the building block of the imine-based COFs, successfully realizing the universal synthesis of COF aerogels, greatly improving the formability of COFs, and having a relatively wide range of universality. 2. For the first time, COFs aerogels based on the group protection strategy are applied to the field of atmospheric water collection, and their adsorption performance is good, with great prospects for practical industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : The present invention is used to construct a group protection strategy monomer structure formula and a COF gel structure formula of a covalent organic framework gel material.

[0029] Figure 2 : Schematic diagram of the synthesis route of the covalent organic framework gel material prepared by the present invention.

[0030] Figure 3: Powder diffraction pattern of a representative covalent organic framework gel material prepared in the present invention.

[0031] Figure 4 : Infrared spectrum of a representative covalent organic framework gel material prepared by the present invention.

[0032] Figure 5 : 77K nitrogen isothermal adsorption-desorption curve of the representative covalent organic framework gel material prepared by the present invention.

[0033] Figure 6 : 298 K isothermal water vapor adsorption and desorption curves of representative covalent organic framework aerogel materials prepared in the present invention.

[0034] Figure 7 : Diagram of an atmospheric water collection device of a representative covalent organic framework aerogel material prepared in the present invention.

[0035] Figure 8 : Water adsorption test diagram of the representative covalent organic framework aerogel material TpPa COF prepared in the present invention. Specific implementation methods Unless otherwise specified in the context of this application, the technical terms and abbreviations used in this application have the conventional meanings known to those skilled in the art; unless otherwise specified, the raw material compounds used in the following examples are commercially available. Example 1 is a method for synthesizing the material, and Example 2 is a test of the representative material for solar thermal seawater evaporation.

[0036] According to the present invention, the general synthesis of a class of covalent organic framework aerogel materials and the relevant performance characterization tests of their applications in the field of atmospheric water collection are described in detail below. On the contrary, the following examples are only used to further explain and invent the present invention and should not be considered as limiting the scope of the present invention.

[0037] Embodiment 1: According to the above general formula, benzyloxycarbonyl (Cbz) protected, tert-butyloxycarbonyl (Boc) protected, or methyloxycarbonyl (Fmoc) protected p-phenylenediamine (0.09 mmol), 4,4'-biphenylenediamine (0.09 mmol), p-diaminoazobenzene (0.09 mmol), 1,3,5-tris(4-aminophenyl)benzene (0.06 mmol), 2,4,6-tris(4-aminophenyl)diazenyl)benzene-1,3,5-triol (0.06 mmol), 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (0.06 mmol, 12.60 mg), 2,4-dihydroxy-1,3,5-benzenetricarboxaldehyde (0.06 mmol, 11.60 mg), 2-hydroxy-1,3,5-benzenetricarboxaldehyde (0.06 mmol, 1 10.60 mg), add 4mL of o-dichlorobenzene, n-butanol, mesitylene, one or more of dioxane, tetrachloroethane, tetrahydrofuran, n-heptane, and one of concentrated hydrochloric acid (60 μL), concentrated sulfuric acid (30 μL), p-toluenesulfonic acid (140 mg), trifluoromethanesulfonic acid (60 μL), trifluoroacetic acid (60 μL), carefully put into a steel high-pressure reactor with a polytetrafluoroethylene lining, put it in a 120 ℃ oven for reaction for 3 days, and obtain a dark reddish brown to black COF gel after the reaction. After soaking it in DMF and CH3OH, Soxhlet extraction in THF lasts for 48 hours, followed by solvent exchange, and finally freeze-dried for 12 hours to obtain a highly crystalline COFs aerogel material with a yield of about 77.8%-95.3%. Figure 3 As shown in Figure 2, the powder X-ray diffraction pattern shows that the synthesized COFs material has high crystallinity. Figure 4 Infrared spectroscopy test further proved that the material is an imine-linked COFs material, where 1571 cm -1 The characteristic peak at 2 corresponds to the stretching vibration of the carbon-oxygen double bond of enol tautomerism. Figure 5 is the nitrogen isothermal adsorption-desorption curve of TpPa gel material at 77K, and its BET surface area is 901 m 2 / g, and the pore size is 1.2 nm.

[0038] Example 2: The prepared COF gel is subjected to sufficient water exchange to ensure that no organic solvent is present, and then freeze-dried to obtain an aerogel. Figure 7 As shown, a saturated salt solution of K2CO3 was added to the dryer, and the hygrometer displayed the changes in temperature and humidity in the system. The activated COF aerogel was placed in the dryer for water collection test. The test showed that TpPa COF exhibited good water collection performance, and the water collection amount was about (0.11 g / g, 43% RH).

[0039] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention in any form. Any researcher and technician familiar with the field, without departing from the scope of the technical solution of the present invention, using the above content to make non-innovative changes and modifications to the technical solution of the present invention, such as only changing the addition ratio of raw materials and reagents, reaction time and operation process, etc., should be included in the protection scope of the present invention.

Claims

1. A method for preparing aerogel based on covalent organic framework material, characterized in that The following steps are included: (1) directly adding the group-protected di-linked and tri-linked amino monomers, tri-linked monomers containing aldehyde groups and a catalyst into a reactor, condensing the aldehyde amine under closed conditions to obtain a COFs gel material, which is then cleaned and purified; (2) The obtained COFs gel sample was immersed in an organic solvent to wash the unreacted precursor, followed by solvent exchange, and finally freeze-dried for 12 h to obtain a highly crystalline COFs aerogel.

2. The method according to claim 1, characterized in that The obtained COFs gel sample was immersed in DMF to wash the unreacted precursor, and then extracted with THF to further remove the unreacted monomers, followed by solvent exchange, and finally freeze-dried for 12 h to obtain highly crystalline COFs aerogel.

3. The aerogel prepared as claimed in claims 1-2.

4. Use of aerogel according to claim 3, characterized in that COFs aerogels for atmospheric water harvesting.

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