Preparation method of covalent organic framework and cellulose composite aerogel and application thereof

Abstract

This invention discloses a method for preparing a covalent organic framework-cellulose composite aerogel and its application, belonging to the field of porous functional materials and solar energy utilization technology. The composite aerogel uses cellulose nanofibers as a framework, constructs a cross-linked network through γ-glycidoxypropyltrimethoxysilane and polyethyleneimine, and introduces a covalent organic framework material as a functional component. Through directional freeze-drying and lyophilization, an aerogel material with a directional continuous pore structure is formed. The covalent organic framework material has tunable molecular structure and optical properties, enabling the composite aerogel to simultaneously possess light absorption, photothermal conversion, and photocatalytic reaction activity. The directional pore structure facilitates rapid water transport and vapor escape, and inhibits salt accumulation, thereby improving the solar interfacial evaporation efficiency. By controlling the structural type and loading content of the covalent organic framework, the synergistic process of photothermal evaporation and photocatalytic hydrogen peroxide production can be achieved, improving the overall solar energy utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of porous functional materials and solar energy utilization technology, specifically to an aerogel material constructed from a covalent organic framework and cellulose and its preparation method, and particularly to the application of this composite aerogel in photothermal-photocatalytic reactions. Background Technology

[0002] Global freshwater scarcity has become one of the most pressing issues facing the 21st century. Among existing technologies, solar-driven interfacial evaporation technology has been widely studied due to its ability to achieve low-energy water treatment. Simultaneously, the use of solar energy for photocatalytic reactions to produce high-value-added chemicals such as hydrogen peroxide is also gaining attention. However, existing solar-driven interfacial evaporation systems generally suffer from the following shortcomings: Firstly, most systems only achieve photothermal evaporation, failing to effectively utilize ultraviolet-visible light from sunlight for photocatalytic reactions within the same system, resulting in a relatively singular approach to solar energy utilization. Secondly, existing evaporators often employ random porous structures, leading to discontinuous water transport paths, limited steam escape efficiency, and a tendency for salt accumulation and even blockage within the pores during long-term operation. Furthermore, some systems rely on inorganic photothermal materials, which suffer from problems such as photocorrosion, ion dissolution, and strong thermal diffusion, hindering the long-term stable operation of the device.

[0003] Covalent organic frameworks (COFs) possess characteristics such as designable structure, tunable band structure, and ordered pores, demonstrating application potential in solar energy utilization and photocatalysis. Through molecular structure modulation, COFs can simultaneously possess photothermal conversion capabilities and photocatalytic active sites, providing a material basis for realizing the multifunctional utilization of solar energy. However, COFs typically exist in powder form, exhibiting poor dispersibility and formability, making them difficult to directly apply in interfacial evaporation systems and limiting their widespread adoption in practical applications.

[0004] Cellulose aerogels, as biomass-derived porous materials, possess advantages such as wide availability, renewability, biodegradability, and tunable structure. Through structural construction methods such as directional freezing, oriented continuous pore structures can be formed on a macroscopic scale, which helps reduce water transport resistance, promotes rapid vapor escape, and inhibits salt accumulation, providing a reliable foundation for constructing structurally ordered solar interfacial evaporation systems. However, existing cellulose aerogels mainly focus on structure and mass transfer functions, lacking photocatalytic activity and thus failing to meet the requirements for the synergistic operation of photothermal evaporation and photocatalytic reactions.

[0005] Therefore, how to introduce active components with photocatalytic functions while maintaining the structural stability and orientation mass transfer advantages of aerogels, and construct a composite material system that can synergistically achieve photothermal evaporation and photocatalytic reaction under the same light conditions, remains a technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing covalent organic framework and cellulose composite aerogel and its application. Through structural design and component synergy, the material can be used for both photothermal evaporation of water and photocatalytic hydrogen peroxide generation under the same light conditions.

[0007] To achieve the above objectives, this invention constructs a cellulose aerogel framework at the macroscopic structural level using a directional cryogenic molding method, resulting in an oriented, continuous pore structure arranged along the freezing direction. This oriented pore structure provides continuous channels for moisture transport and vapor emission, which helps reduce moisture transport resistance and maintain stable operation of the interfacial evaporation process.

[0008] Based on this, the present invention introduces COFs into the oriented cellulose aerogel framework, enabling the resulting composite aerogel to simultaneously possess light absorption, photothermal conversion, and photocatalytic reaction functions. The structural type of the COFs is not limited; its structure can be controlled by selecting different building blocks to meet the needs of synergistic operation of photothermal evaporation and photocatalytic reaction.

[0009] In some embodiments, the COFs are nitrogen-containing, and different nitrogen source structures are constructed by selecting different amine monomers to regulate the hydrophilic properties and photocatalytic reaction performance of the composite aerogel.

[0010] This invention achieves a synergistic configuration between the material structure orientation and functional components by combining a cellulose aerogel framework with a covalent organic framework material and adjusting the loading content of the COF material, enabling the composite aerogel to simultaneously meet the application requirements of photothermal evaporation and photocatalytic reaction.

[0011] In some embodiments, a photothermal conversion layer can be introduced onto the surface of the composite aerogel to enhance the material's ability to absorb sunlight. The photothermal conversion layer is preferably a carbon nanotube layer, used to improve the stability and efficiency of the photothermal evaporation process.

[0012] By controlling the freezing method and the loading content of COFs materials, the composite aerogel can achieve the synergistic operation of photothermal evaporation of water and hydrogen peroxide generation under solar-driven conditions, and maintain stable performance during continuous operation.

[0013] Compared with existing technologies, the composite aerogel provided by this invention has comprehensive advantages in terms of structural stability, mass transfer capacity and multifunctional synergy, and is suitable for application scenarios where solar interfacial evaporation and photocatalytic reaction are coupled. Attached Figure Description

[0014] The following is a brief explanation of the content depicted in the accompanying drawings:

[0015] Figure 1 This is a schematic diagram of the preparation process of COFs and COFs@CNF composite aerogel in this invention;

[0016] Figure 2 The images are SEM images along the longitudinal direction of (a) Comparative Example 1 and (b) Example 2 in this invention;

[0017] Figure 3 The images are (a) SEM images of Example 1 and (b) Example 2 along the longitudinal direction in this invention.

[0018] Figure 4 The PXRD spectra of COFs and COFs@CNF aerogels in Examples 1-2 of this invention are shown.

[0019] Figure 5 The FTIR spectra of COFs and COFs@CNF aerogels in Examples 1-2 of this invention are shown.

[0020] Figure 6 XPS spectra of COFs and COFs@CNF aerogels in Examples 1-2 of this invention;

[0021] Figure 7 The fatigue performance of Examples 1-2 in this invention after 20 consecutive cycles at 80% strain;

[0022] Figure 8 This is a comparison of the photocatalytic rates of the evaporators corresponding to Examples 1-2 and Comparative Examples 3-4 in this invention;

[0023] Figure 9 This invention provides a comparison of the evaporation rates of the evaporators corresponding to Examples 1-2 and Comparative Examples 3-4.

[0024] Figure 10 This is a performance change test of the evaporator corresponding to Example 2 of the present invention after 10 cycles of photothermal-photocatalytic coupling process. Detailed Implementation

[0025] The embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the embodiments described below are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or modifications made by those skilled in the art based on the content of the present invention without creative effort should all fall within the scope of protection of the present invention.

[0026] The covalent organic framework material used in this embodiment of the invention is a covalent organic framework material prepared by condensation reaction of 1,3,5-tricarboxyphenol (Tp) with melamine (Tt) or melamine (Ht), respectively, and denoted as TpTt and TpHt. The covalent organic framework material is then combined with cellulose nanofibers (CNF), γ-glycidoxypropyltrimethoxysilane (GPTMS), and polyethyleneimine (PEI) to prepare COF@CNF composite aerogel, the preparation process of which is illustrated below. Figure 1 As shown.

[0027] Example 1: Preparation of directional triazine-based COF@CNF composite aerogel

[0028] This embodiment provides a method for preparing directional triazine-based COF@CNF composite aerogel, comprising the following steps:

[0029] (1) Preparation of triazine-based covalent organic framework materials 1,3,5-Triformylphenol (Tp) and melamine (Tt) were added in an equimolar ratio to a mixed solvent consisting of dimethyl sulfoxide and acetic acid. The mixture was heated under sealed conditions to induce a condensation reaction between the aldehyde and amino groups, forming a covalent organic framework structure with triazine units as nodes. After the reaction was complete, the mixture was sequentially cooled, separated from its liquid state, washed with solvent, and dried to obtain powdered triazine-based covalent organic framework material TpTt.

[0030] (2) Construction of cellulose nanofiber crosslinking system Cellulose nanofiber dispersion was mixed with GPTMS, and the silane coupling agent was reacted with the hydroxyl groups on the surface of cellulose under stirring conditions; then PEI was added to form a stable and uniform CNF / GPTMS / PEI crosslinking system.

[0031] (3) Preparation of composite precursor solution The TpTt powder obtained in step (1) is added to the crosslinking system described in step (2) and mixed thoroughly under stirring conditions to uniformly disperse the covalent organic framework material and load it into the cellulose network, thereby obtaining the composite precursor liquid.

[0032] (4) Directional freeze forming and freeze drying The composite precursor liquid was shaped by directional freezing, and the ice crystals were induced to grow in a single direction by controlling the freezing direction. Subsequently, freeze-drying was performed to remove the ice crystal template, and finally, a directional triazine-based COF@CNF composite aerogel with an oriented continuous pore structure was obtained.

[0033] Example 2: Preparation of Directed Heptaazine-based COF@CNF Composite Aerogel

[0034] This embodiment provides a method for preparing a directional heptaazine-based COF@CNF composite aerogel. The difference between this embodiment and Example 1 lies in the molecular structure of the covalent organic framework material used; the remaining preparation steps and process conditions are the same.

[0035] Specifically, 1,3,5-triformylphenol (Tp) and melamine (Ht) were added to a mixed solvent composed of dimethyl sulfoxide and acetic acid, and a condensation reaction was carried out under heating conditions to form a covalent organic framework structure with heptaazine units as nodes. After the reaction was completed, the material was cooled, separated, washed, and dried to obtain powdered heptaazine-based covalent organic framework material TpHt.

[0036] The obtained TpHt powder was introduced into the CNF / GPTMS / PEI crosslinking system according to the method described in Example 1 to prepare a composite precursor solution. The composite precursor solution was then subjected to directional freezing and lyophilization to obtain a directional heptaazine-based COF@CNF composite aerogel with an oriented pore structure.

[0037] Comparative Example 1: Preparation of Non-directional Cellulose Aerogels

[0038] This comparative example provides a method for preparing cellulose aerogels without introducing covalent organic framework materials. A precursor solution is prepared by constructing a crosslinking system between cellulose nanofibers and GPTMS and PEI, followed by non-directional freeze-drying to obtain non-directional pure cellulose aerogels.

[0039] Comparative Example 2: Preparation of Directed Cellulose Aerogel

[0040] The only difference between this comparative example and Comparative Example 1 is the molding method. Without introducing covalent organic framework materials, the CNF / GPTMS / PEI precursor solution was molded by directional freezing and then freeze-dried to obtain directional pure cellulose aerogel.

[0041] Comparative Example 3: Preparation of Non-directional Triazine-based COF@CNF Composite Aerogel

[0042] In this comparative example, a triazine-based covalent organic framework material TpTt was prepared using the same method as in Example 1, and then introduced into a CNF / GPTMS / PEI crosslinking system to obtain a composite precursor solution. The difference is that this composite precursor solution was formed using a non-directional freeze-drying method and then lyophilized to obtain a non-directional triazine-based COF@CNF composite aerogel.

[0043] Comparative Example 4: Preparation of Non-directional Heptaazine-based COF@CNF Composite Aerogel

[0044] In this comparative example, the heptaazine-based covalent organic framework material TpHt was prepared using the same method as in Example 2, and then introduced into a CNF / GPTMS / PEI crosslinking system to obtain a composite precursor solution. The difference is that this composite precursor solution was formed using a non-directional freeze-drying method and then lyophilized to obtain a non-directional heptaazine-based COF@CNF composite aerogel.

[0045] The aerogel samples prepared in Examples 1, 2 and the comparative samples were characterized by scanning electron microscopy (SEM) to analyze their microstructure and pore structure characteristics.

[0046] like Figure 2 As shown, cellulose aerogels prepared by non-directional freezing exhibit a randomly distributed fiber network structure with no obvious orientation of the pores; while COF@CNF composite aerogels formed by directional freezing develop a continuous pore structure with oriented channels along the freezing direction. Further, as... Figure 3 After introducing covalent organic framework materials, the resulting composite aerogel can still maintain a clear and continuous oriented pore structure, indicating that the introduction of COF did not destroy the macroscopic orientation structure of the aerogel.

[0047] The crystal structures of covalent organic framework materials and their composite aerogels were characterized by powder X-ray diffraction (PXRD), and the results are as follows: Figure 4 As shown, characteristic diffraction peaks consistent with the corresponding COF material can be detected in the COF@CNF composite aerogel, indicating that COF has been successfully introduced and stably exists in the aerogel framework.

[0048] Further analysis of the material's chemical structure and elemental chemical states was conducted using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), with results as follows: Figure 5 and Figure 6 As shown in the figure. The test results show that the COF@CNF composite aerogel retains the characteristic vibrational absorption peaks and characteristic nitrogen chemical states of covalent organic framework materials, indicating that its molecular structure is maintained during the composite process.

[0049] Mechanical properties were tested on the samples from Examples 1 and 2. Figure 7 As shown, after 20 consecutive loading cycles under 80% compressive strain conditions, it still maintains an excellent stress recovery rate, indicating that the directional composite aerogel still has good elastic recovery performance and cyclic stability under large strain and multiple cyclic loading conditions.

[0050] The photocatalytic hydrogen peroxide production performance of the aerogels prepared in Examples 1, 2, and the comparative samples was tested, and the results are as follows: Figure 8As shown. The tests were conducted under simulated standard sunlight conditions to evaluate the effects of different pore structures and covalent organic framework types on photocatalytic performance.

[0051] The test results show that, under the same COF loading conditions, the COF@CNF composite aerogel prepared by directional freezing exhibits a higher hydrogen peroxide generation rate, indicating that the oriented continuous pore structure is beneficial to reactant diffusion and interfacial reactions. With the increase of covalent organic framework doping, the photocatalytic performance of the samples shows a trend of first increasing and then decreasing.

[0052] Further comparison of different types of COFs reveals that the composite aerogel using heptaazine-based COFs exhibits superior photocatalytic hydrogen peroxide production performance under the same conditions, indicating that the nitrogen source configuration in the COF molecular structure has a significant impact on the photocatalytic reaction.

[0053] The photothermal evaporation performance of the aerogels prepared in the examples and comparative samples was tested. A carbon nanotube photothermal layer was constructed on the surface of the COF@CNF composite aerogel to form a photothermal evaporator, and the test was conducted under simulated standard sunlight conditions. The results are as follows: Figure 9 As shown.

[0054] Test results show that the COF@CNF photothermal evaporator prepared by directional freezing can achieve a stable and efficient water evaporation process, and its oriented continuous pore structure is conducive to continuous water transport and steam escape.

[0055] In the same illumination system, the photothermal evaporator obtained in Example 2 was used for synergistic operation testing of photothermal evaporation and photocatalytic reaction. Figure 10 As shown, while achieving water evaporation, the system can simultaneously generate hydrogen peroxide, and its performance remains stable during multiple cycles, indicating that the material system is suitable for photothermal-photocatalytic synergistic applications.

[0056] In summary, by constructing an oriented continuous pore structure using a directional freezing method and introducing covalent organic frameworks of different molecular structures as functional components, a COF@CNF composite aerogel material with both photothermal evaporation and photocatalytic hydrogen peroxide production functions was successfully prepared. This composite aerogel exhibits stable structure and a controllable preparation method, making it suitable for solar-driven interfacial evaporation and chemical conversion applications.

[0057] The above description is merely a preferred embodiment of the present invention, used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Any equivalent substitutions, equivalent improvements, or modifications made to the above embodiments within the spirit and principles of the present invention should be covered within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the content defined in the claims.

Claims

1. A covalent organic framework and cellulose composite aerogel, characterized in that: Using cellulose nanofibers as a three-dimensional porous framework, a cross-linked network is constructed by γ-glycidoxypropyltrimethoxysilane and polyethyleneimine, and covalent organic framework materials are introduced as functional components. After directional freeze-forming and freeze-drying, a composite aerogel material with a directional continuous pore structure is formed.

2. The composite aerogel according to claim 1, characterized in that: The covalent organic framework material is prepared by condensation reaction of 1,3,5-tricarboxyphenol (Tp) with melamine (Tt) and melamine (Ht) monomers to form triazine and heptaazine covalent organic framework structures.

3. A method for preparing a covalent organic framework and cellulose composite aerogel as described in claim 1 or 2, characterized in that, Includes the following steps: 1) The cellulose nanofiber dispersion was mixed with γ-glycidoxypropyltrimethoxysilane and reacted. 2) Add polyethyleneimine to the system obtained in step 1) to form a cellulose crosslinking system; 3) Add the covalent organic framework material to the crosslinking system and mix to obtain a composite precursor solution; 4) The composite precursor liquid is subjected to directional freeze-forming and freeze-drying to obtain a covalent organic framework and cellulose composite aerogel with a directional continuous pore structure.

4. The application of the covalent organic framework / cellulose composite aerogel according to claim 1 or 2 in photothermal-photocatalytic reactions, characterized in that: Under the same illumination conditions, it is used to simultaneously achieve photothermal evaporation of water and generation of hydrogen peroxide.

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