CN117463292A - An activated carbon fiber-based MOFs bulk hygroscopic agent and its mixed solvent thermal in-situ synthesis method and application - Google Patents

Abstract

The invention discloses an activated carbon fiber-based MOFs bulk hygroscopic agent and its mixed solvent thermal in-situ synthesis method and application. The method includes the following steps: immersing activated activated carbon fiber into an aqueous solution containing hydrophilic modified film-forming material to obtain hydrophilic modified activated carbon fiber; mixing a DMF solution of organic dicarboxylic acid and an aluminum aqueous solution to obtain a uniform reaction solution ; Immerse the modified activated carbon fiber in the reaction solution, take out the activated carbon fiber loaded with MOFs coating, wash, dry and activate it to obtain a MOFs bulk hygroscopic agent. The activated carbon fiber-based MOFs bulk hygroscopic agent prepared by the invention has a tight combination of MOFs crystal grains and the base material and does not lose powder; the MOFs loading rate is high; the MOFs bulk hygroscopic agent has a high water vapor adsorption capacity under low humidity (30% RH), It has the characteristics of low desorption temperature, good cycle stability, and strong photothermal conversion ability, and can be applied to the field of solar-assisted atmospheric water collection in arid areas.

Description

Thermal in-situ synthesis of an activated carbon fiber-based MOFs bulk hygroscopic agent and its mixed solvent Methods and applications

Technical field

The invention relates to the field of atmospheric water collection, and specifically relates to an activated carbon fiber-based MOFs bulk hygroscopic agent and its mixed solvent thermal in-situ synthesis method and application.

Background technique

Although various water purification technologies such as filtration, reverse osmosis, multi-stage flash evaporation, etc. have been developed to utilize seawater or wastewater, these water purification technologies are only applicable to coastal areas due to their dependence on natural water sources, and are generally not available in inland areas. get. According to reports, about ^12,900km3 of water exists in the form of steam or liquid droplets in the atmosphere. If it is utilized, it will effectively alleviate the pressure of global water shortages. While direct extraction is easily achieved in humid climates by fog collection or by condensation by cooling the air below the dew point, it is not advisable in arid environments. Therefore, establishing atmospheric water harvesting (AWH) in arid regions becomes a promising strategy for decentralized water production.

Compared with traditional water vapor adsorbents such as silica gel and molecular sieves, metal-organic frameworks (MOFs) with large amounts of uniform micropores have been identified as promising next-generation new water vapor adsorbents due to their rich chemical variability and tunability. . MOF can exhibit excellent water vapor capture capability and hydrothermal stability over a wide relative humidity (RH) range, and its regeneration energy consumption is also low. Like traditional powder adsorbents, powdered MOF has the problem of low mass and heat transfer efficiency. If the MOF grains are uniformly loaded on the substrate to prepare a so-called monolithic adsorbent, its mass and heat transfer can be improved. The key to efficiency; and the moisture absorption of the bulk adsorbent can be adjusted by adjusting the coating thickness (MOF loading rate). In addition, in order to save operating energy consumption, especially desorption energy consumption, the use of solar-driven adsorbents to desorb water is an important strategy for atmospheric water collection. At present, the base materials of bulk adsorbents mainly include inorganic fiber paper such as asbestos fiber paper, glass fiber paper, ceramic fiber paper, etc.; inorganic ceramic porous materials such as sepiolite, cordierite, etc.; and metal-based sheets such as aluminum foil, copper foil, etc. . Inorganic fiber paper has high porosity, but is brittle and difficult to process or requires the addition of inorganic glue for shaping, which reduces the adsorbent loading rate; inorganic ceramic porous materials have high density, low porosity, and very low adsorbent loading rate; metal-based sheets and The adsorbents have weak force, small surface area, and low adsorbent loading rate; and, except for metal foils, they have low thermal conductivity and low photothermal conversion efficiency. On the other hand, most MOFs are white or light-colored powders with poor light absorption capabilities and low photothermal conversion performance, so their photothermal properties need to be enhanced. The commonly used method is to add photothermal agents to achieve photothermal strengthening. There are currently four types of photothermal agents reported, namely precious metal nanoparticles, metal semiconductor nanoparticles, carbon-based nanomaterials and polymers. Among them, metal semiconductor nanoparticles and carbon-based nanomaterials are commonly used. However, the addition of these photothermal agents will reduce the moisture absorption of MOF to a certain extent (including reducing the MOF loading rate or partially blocking the MOF micropores). Therefore, it is necessary to choose a substrate with high specific surface area (porosity), high thermal conductivity and high photothermal conversion performance as the carrier of the adsorbent to increase the loading rate of the MOF adsorbent and at the same time, use photothermal energy with the assistance of solar energy. It is a reasonable design strategy to achieve rapid dehydration of the adsorbent by conversion, thereby reducing the desorption energy consumption of the adsorbent. In addition, how to uniformly disperse high loading MOF grains in the substrate is closely related to the MOF loading process. There are generally two methods to load MOFs, namely direct dip coating and in-situ synthesis. The dip coating method requires the addition of an external adhesive to adhere the adsorbent to the substrate. Commonly used adhesives include sodium silicate solution, silicon solution and organopolysiloxane resin. In this method, the adhesive easily blocks the pores of the MOF adsorbent, thereby affecting the adsorption effect. The in-situ synthesis method allows MOF to grow in situ on the substrate. This method can obtain different thicknesses, dense and uniform adsorption coatings, with the simplicity of one-step synthesis and excellent heat and mass transfer performance.

Based on the above discussion, in the present invention, activated carbon fiber is selected as the MOF-loaded substrate. Compared with glass fiber, it has better photothermal conversion capabilities and can use solar energy to drive desorption of water without adding photothermal agents. The rich pore structure of activated carbon fiber also gives MOF growth sites. It also has the dual functions of improving mass transfer efficiency and photothermal enhancement. It has a broad application background in the field of atmospheric water collection for solar-assisted dehydration.

Contents of the invention

In order to overcome the shortcomings of low mass and heat transfer efficiency and low photothermal conversion efficiency of powder MOFs during use, the purpose of the present invention is to provide a thermal in-situ synthesis method of MOFs bulk hygroscopic agent and its mixed solvent. The activated carbon fiber-based MOFs bulk hygroscopic agent synthesized thermally in situ by mixed solvents provided by the present invention has the characteristics of high water adsorption capacity, fast adsorption rate, strong binding force between MOFs and the substrate (no powder falling off), and strong photothermal conversion ability. It can be used in the field of atmospheric water collection for solar-driven desorption of water to achieve low energy consumption.

The object of the present invention is achieved through the following technical solutions.

The invention provides a mixed solvent thermal in-situ synthesis method of activated carbon fiber-based MOFs bulk hygroscopic agent, which includes the following steps:

(1) Hydrophilic modification treatment of activated carbon fiber: Dip the activated carbon fiber into an oxidant for activation, and then immerse it into an aqueous solution containing hydrophilic modified film-forming materials. After sufficient infiltration, clean and dry to obtain hydrophilic modification. activated carbon fiber;

(2) Preparation of the reaction solution: Under stirring conditions, mix the N,N-dimethylformamide solution of the organic dicarboxylic acid and the aluminum salt solution to obtain a uniform reaction solution;

(3) MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis: immerse the modified activated carbon fiber in the reaction solution for crystallization reaction. After the reaction, take out the activated carbon fiber loaded with MOFs coating, wash and dry to obtain the activity Carbon fiber-based MOFs bulk moisture absorber.

Preferably, the oxidizing agent in step (1) includes one of concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide, potassium permanganate, and a mixture (v/v: 1/1) of concentrated sulfuric acid and concentrated nitric acid.

It is further preferred to consider the oxidation of the activated carbon fiber in the above oxidant, and the oxidant is concentrated sulfuric acid.

Preferably, the hydrophilic modified film-forming material in step (1) includes one of chitosan quaternary ammonium salt, chitosan hydrochloride, carboxymethyl chitosan, and chitosan oligosaccharide.

Further preferably, considering factors such as the binding force between the substrate and the hydrophilic modified film-forming material, price, etc., the hydrophilic modified film-forming material is chitosan hydrochloride.

Preferably, the organic dicarboxylic acid in step (2) includes one or two of 3,5-pyrazoledicarboxylic acid, fumaric acid, 2,5-furandicarboxylic acid and isophthalic acid.

Preferably, the aluminum salt in step (2) is one of aluminum nitrate nonahydrate, aluminum sulfate octahydrate, aluminum chloride hexahydrate, and aluminum acetate.

The MOF in step (2) includes MOFs formed respectively from the above-mentioned organic dicarboxylic acids, 3,5-pyrazoledicarboxylic acid, fumaric acid, 2,5-furandicarboxylic acid and isophthalic acid combined with aluminum salts One MOF or two mixed MOFs among -303, Al-fumarate (A520), MIL-160 (Al), and CAU-10-H.

Further preferably, taking into account the price of organic dicarboxylic acids and aluminum salts, the ease of reaction, and the application background of atmospheric water collection in arid areas (requiring that they should have high moisture absorption under low humidity conditions), the organic dicarboxylic acid The carboxylic acids are 3,5-pyrazoledicarboxylic acid and fumaric acid, the aluminum salt is aluminum nitrate nonahydrate, and the products formed are MOF-303 and MOF-303/Al-Fum mixed MOFs.

Preferably, the molar ratio of aluminum ions in the organic dicarboxylic acid and aluminum salt solution described in step (2) is 1:0.8-1.25.

Further preferably, the molar ratio of aluminum ions in the organic dicarboxylic acid and aluminum salt solution is 1:0.9-1.2.

Preferably, the volume ratio of DMF to water in the aluminum salt solution in step (2) is 1:5-10.

Further preferably, the solubility of organic dicarboxylic acid in water is low, and the addition of DMF can effectively dissolve the organic dicarboxylic acid. Since DMF and H ₂ O are mutually soluble, the organic dicarboxylic acid is evenly dispersed in the reaction solution; by fixing the added amount of DMF and increasing or decreasing the amount of H ₂ O, the DMF and H ₂ in the reaction solution can be adjusted. The volume ratio of O; the large amount of H ₂ O, that is, the concentration of DMF is small, the solubility of organic dicarboxylic acid in the reaction solution is poor, and the dispersion of the system is poor, which is not conducive to the combination of organic dicarboxylic acid and Al ³⁺ around the substrate And the growth of MOF on the substrate; the amount of H ₂ O is small, that is, the concentration of DMF is large, the aluminum ions migrate to the substrate quickly, and can effectively combine with Al ³⁺ and load the substrate, the DMF and aluminum salt The volume ratio of water in the aqueous solution is 1:6~8.

Preferably, the temperature of the crystallization reaction in step (3) is 80-120°C.

It is further preferred that the reaction temperature is low, the crystallization rate is slow, the MOFs coating formed is thin, and the water absorption capacity of the bulk hygroscopic agent is low; the reaction temperature is high, the crystallization rate is too fast, the MOFs coating formed is thick, and the MOFs coating is The interaction force with the substrate is weak, and the MOFs crystal grains are easy to fall off. The temperature of the crystallization reaction is 90 to 110°C.

Preferably, the crystallization reaction time in step (3) is 10 to 14 hours.

Preferably, the washing in step (3) is to wash three times with ethanol and deionized water alternately.

Preferably, the activation temperature in step (3) is 100-150°C; the activation time is 6-10 hours.

The invention provides an activated carbon fiber-based MOFs bulk moisture absorbent prepared by the above preparation method.

The mixed solvent thermal in-situ synthesis method provided by the invention uses activated carbon fiber as the base material, uses oxidant to treat it to increase the oxygen-containing groups on the base material, and uses hydrophilic modified film-forming materials to further hydrophilize the activated carbon fiber. Water modification is used to increase hydrophilic groups such as amino groups, carboxyl groups, and hydroxyl groups on the substrate to strengthen the interaction between MOFs and the substrate.

Compared with the existing technology, the present invention has the following advantages and beneficial effects:

1. The in-situ synthesis method provided by the present invention produces an activated carbon fiber-based MOFs bulk hygroscopic agent. The MOFs have strong binding force with the substrate and are not prone to falling off, thus solving the problem of poor mass and heat transfer effects of powdered MOFs. , while the in-situ synthesis process improves the loading rate of MOFs.

2. The in-situ synthesis method provided by the present invention does not use adhesives, which avoids the problem of adhesives blocking the pores of MOFs adsorbents, thereby increasing the moisture absorption capacity of MOFs bulk hygroscopic agents.

3. According to the in-situ synthesis method provided by the present invention, the MOFs bulk hygroscopic agent produced has a lower desorption temperature than MOFs powder, thereby reducing the energy consumption of the water collection system.

4. The activated carbon fiber substrate used in the present invention not only has a rich pore structure, but also has excellent photothermal conversion performance, which makes up for the shortcomings of poor photothermal conversion efficiency of conventional substrates and MOFs, and can use solar energy to drive the desorption of MOFs adsorbents. Adsorbed moisture.

5. The present invention uses MOF-303 and Al-Fum monomers to in-situ synthesize MOF-303/Al-Fum mixed MOFs bulk adsorbents on activated carbon fiber substrates, and prepares a series of MOF-303/Al-Fum mixed MOFs bulk adsorbents by changing the ratio of the two ligands. Mixed MOFs bulk adsorbents with different contents of double ligands can adjust the MOF water adsorption isotherm curve to suit different applications.

6. The bulk hygroscopic agent prepared by the present invention has high water vapor adsorption capacity under low humidity conditions (≤30% RH).

Description of the drawings

Figure 1 is the XRD spectrum of the hygroscopic agents prepared in Examples 1 and 8 and Comparative Examples 1 and 2.

Figure 2 is a SEM image of the activated carbon fiber-based MOF-303 bulk moisture absorbent prepared in Example 1, the activated carbon fiber before modification, and the activated carbon fiber after modification.

Figure 3 is the dynamic water adsorption curve of the hygroscopic agent prepared in Example 1 and Comparative Example 1.

Figure 4 is the dynamic water adsorption curve of the mixed MOFs bulk hygroscopic agent prepared in Examples 6-10.

Figure 5 shows the static water adsorption curves of the hygroscopic agents prepared in Examples 1, 8 and Comparative Example 1.

Figure 6 shows the UV-vis-NIR absorption spectra of the hygroscopic agents and unmodified activated carbon fibers prepared in Examples 1, 8 and Comparative Example 1.

Figure 7 is a curve of the surface temperature of the sample prepared in Example 1 and Comparative Example 1 under simulated sunlight as a function of time.

Detailed ways

The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be pointed out that any process that is not specifically described in detail below can be implemented or understood by those skilled in the art with reference to the existing technology. If the manufacturer of the reagents or instruments used is not indicated, they are regarded as conventional products that can be purchased commercially.

Pretreatment of activated carbon fiber: Cut the activated carbon fiber into thin cloth of 3×3× ^0.5cm3 . First, the cut activated carbon fiber was immersed in concentrated sulfuric acid for 2 hours, washed with deionized water until neutral, and placed in an oven to dry. Then, the activated activated carbon fiber was immersed in 25 mg/mL chitosan hydrochloride solution to fully moisten it, and the excess solution on the substrate was washed with deionized water and dried at 70°C.

Chitosan hydrochloride can also be replaced by chitosan quaternary ammonium salt, carboxymethyl chitosan or chitosan oligosaccharide.

Comparative example 1

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:1, the volume ratio of DMF to H ₂ O 1:7, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.52g (4mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 35mL. An aqueous solution of Al(NO ₃ ) ₃ is formed in the ionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100 mL polytetrafluoroethylene-lined reactor, seal it and place it in a muffle furnace at 100°C for 12 hours. After the reaction is completed, cool to room temperature. After filtering the mixed solution using a G4 funnel, the obtained solid wet material was washed three times with absolute ethanol and deionized water alternately, and dried and activated in a blast drying oven at 120°C for 6 hours to obtain MOF-303 hygroscopic agent powder.

Comparative example 2

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:1, the volume ratio of DMF to H ₂ O 1:8, take 0.269g (1.5mmol) 3,5- Dissolve pyrazole dicarboxylic acid and 0.175g (1.5mmol) fumaric acid in 5mL DMF to form a double-ligand DMF solution; take 1.14g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 40mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100 mL polytetrafluoroethylene-lined reactor, seal it and place it in a muffle furnace at 110°C for 12 hours. After the reaction is completed, cool to room temperature. After filtering the mixed solution using a G4 funnel, the obtained solid wet material was washed three times with absolute ethanol and deionized water alternately, and dried and activated in a blast drying oven at 120°C for 6 hours to obtain MOF-303/Al-Fum mixed hygroscopic agent. powder.

Example 1

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:1, the volume ratio of DMF to H ₂ O 1:6, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.52g (4mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 30mL. An aqueous solution of Al(NO ₃ ) ₃ is formed in the ionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 100 The reaction was carried out for 12 hours at ℃. After the reaction was completed, the mixture was cooled to room temperature. Take out the block, wash it three times with absolute ethanol and deionized water alternately, dry and activate it in a blast drying oven at 120°C for 6 hours to obtain the activated carbon fiber-based MOF-303 block moisture absorbent.

Example 2

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:0.8, the volume ratio of DMF to H ₂ O 1:5, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.22g (3.2mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 25mL An aqueous solution of Al(NO ₃ ) ₃ is formed in deionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 110 The reaction was carried out for 10 hours at ℃, the reaction was completed, and the mixture was cooled to room temperature. Take out the block, wash it three times with absolute ethanol and deionized water alternately, dry and activate it in a blast drying oven at 110°C for 8 hours to obtain the activated carbon fiber-based MOF-303 block moisture absorbent.

Example 3

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:0.9, the volume ratio of DMF to H ₂ O 1:7, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.37g (3.6mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 35mL An aqueous solution of Al(NO ₃ ) ₃ is formed in deionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction liquid prepared in step (1) to a 100 mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction liquid obliquely, seal it and place it in a muffle furnace for 120 The reaction was carried out for 11 hours at ℃, the reaction was completed, and the mixture was cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 120°C for 10 hours to obtain an activated carbon fiber-based MOF-303 block moisture absorbent.

Example 4

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:1.1, the volume ratio of DMF to H ₂ O 1:8, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.67g (4.4mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 40mL An aqueous solution of Al(NO ₃ ) ₃ is formed in deionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 80 The reaction was carried out for 13 hours at ℃, and then the reaction was completed and cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 100°C for 10 hours to obtain an activated carbon fiber-based MOF-303 block moisture absorbent.

Example 5

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of 3,5-pyrazoledicarboxylic acid to Al ³⁺ 1:1.25, the volume ratio of DMF to H ₂ O 1:10, take 0.72g ( Dissolve 4mmol) 3,5-pyrazoledicarboxylic acid in 5mL DMF to form a DMF solution of 3,5-pyrazoledicarboxylic acid; take 1.9g (5mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 50mL. An aqueous solution of Al(NO ₃ ) ₃ is formed in the ionized water; add the DMF solution of 3,5-pyrazoledicarboxylic acid dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 90 The reaction was carried out for 14 hours at ℃, and then the reaction was completed and cooled to room temperature. Take out the block, wash it three times with absolute ethanol and deionized water alternately, dry and activate it in a blast drying oven at 150°C for 6 hours to obtain the activated carbon fiber-based MOF-303 block moisture absorbent.

Example 6

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:0.8, the volume ratio of DMF to H ₂ O 1:6, take 0.43g (2.4mmol) 3,5- Pyrazole dicarboxylic acid and 0.07g (0.6mmol) fumaric acid were dissolved in 5mL DMF to form a double-ligand DMF solution; 0.912g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O was dissolved in 30mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 110 The reaction was carried out for 14 hours at ℃, and then the reaction was completed and cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 120°C for 8 hours to obtain an activated carbon fiber-based MOF-303/Al-Fum (8/2) mixed MOFs block that absorbs moisture. agent.

Example 7

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:0.9, the volume ratio of DMF to H ₂ O 1:7, take 0.377g (2.1mmol) 3,5- Pyrazole dicarboxylic acid and 0.105g (0.9mmol) fumaric acid were dissolved in 5mL DMF to form a double-ligand DMF solution; 1.026g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O was dissolved in 30mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 110 The reaction was carried out for 13 hours at ℃, and then the reaction was completed and cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 130°C for 6 hours to obtain an activated carbon fiber-based MOF-303/Al-Fum (7/3) mixed MOFs block that absorbs moisture. agent.

Example 8

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:1, the volume ratio of DMF to H ₂ O 1:8, take 0.269g (1.5mmol) 3,5- Dissolve pyrazole dicarboxylic acid and 0.175g (1.5mmol) fumaric acid in 5mL DMF to form a double-ligand DMF solution; take 1.14g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 40mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction liquid prepared in step (1) to a 100 mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction liquid obliquely, seal it and place it in a muffle furnace for 120 The reaction was carried out for 12 hours at ℃. After the reaction was completed, the mixture was cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 150°C for 6 hours to obtain an activated carbon fiber-based MOF-303/Al-Fum (5/5) mixed MOFs block that absorbs moisture. agent.

Example 9

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:1.1, the volume ratio of DMF to H ₂ O 1:9, take 0.162g (0.9mmol) 3,5- Dissolve pyrazole dicarboxylic acid and 0.245g (2.1mmol) fumaric acid in 5mL DMF to form a double-ligand DMF solution; take 1.254g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 50mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 130 The reaction was carried out for 11 hours at ℃, the reaction was completed, and the mixture was cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 100°C for 10 hours to obtain an activated carbon fiber-based MOF-303/Al-Fum (3/7) mixed MOFs block that absorbs moisture. agent.

Example 10

(1) Under room temperature and magnetic stirring, take a 50mL beaker, according to the molar ratio of ligand to Al ³⁺ 1:1.25, the volume ratio of DMF to H ₂ O 1:10, take 0.108g (0.6mmol) 3,5- Dissolve pyrazole dicarboxylic acid and 0.28g (2.4mmol) fumaric acid in 5mL DMF to form a double-ligand DMF solution; take 1.425g (3mmol) Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in 30mL deionized water. An aqueous solution of Al(NO ₃ ) ₃ is formed; add the double-ligand DMF solution dropwise into the aqueous solution of Al(NO ₃ ) ₃ , and stir continuously for 20 minutes to obtain a uniform reaction solution.

(2) Add the reaction solution prepared in step (1) to a 100mL polytetrafluoroethylene-lined reactor, immerse the pretreated activated carbon fiber in the reaction solution obliquely, seal it and place it in a muffle furnace for 140 The reaction was carried out for 10 hours at ℃, the reaction was completed, and the mixture was cooled to room temperature. Take out the block, wash it three times alternately with absolute ethanol and deionized water, and dry and activate it in a blast drying oven at 110°C for 8 hours to obtain an activated carbon fiber-based MOF-303/Al-Fum (2/8) mixed MOFs block that absorbs moisture. agent.

Test conditions and methods

Loading capacity calculation of bulk moisture absorbent (example):

Assume that the mass of the activated carbon fiber after pretreatment is m ₁ and the mass of the activated carbon fiber-based MOFs bulk hygroscopic agent obtained after cleaning and drying after the reaction is m ₂ , then the loading w of the activated carbon fiber-based MOFs bulk hygroscopic agent is:

X-ray diffraction analysis (XRD):

The MOF-303 powder (Comparative Example 1), MOF-303/Al-Fum mixed MOFs powder (Comparative Example 2), activated carbon fiber-based MOF-303 bulk moisture absorber (Example 1) and activated carbon fiber-based MOF -303/Al-Fum mixed MOFs bulk hygroscopic agent (Example 8) was ground to powder, and a fully automatic X-ray powder diffractometer (XRD) model D8 Advance from Bruker Company of Germany was used to conduct phase analysis on the sample; test conditions It is a Cu target, the diffraction angle range is 5-60°, the scanning rate is 0.1 seconds/step, and the step size is 0.02°.

Scanning electron microscope (SEM):

The surface morphology of activated carbon fiber and activated carbon fiber-based MOF-303 bulk moisture absorbent before and after pretreatment was observed using the SU8220 scanning electron microscope (SEM) of Hitachi Company of Japan. The samples were sprayed with gold before testing, and the voltage was scanned. 5kV.

Dynamic and static isothermal water vapor adsorption curves:

This test uses a programmable constant temperature and humidity test chamber and an electronic balance to analyze the moisture absorption of MOF-303 powder (Comparative Example 1), MOF-303/Al-Fum mixed MOFs powder (Comparative Example 2), and activated carbon fiber-based MOF-303 blocks. Dynamic and static isothermal water vapor adsorption curves of the agent (Example 1) and activated carbon fiber-based MOF-303/Al-Fum mixed MOFs bulk moisture absorbent (Example 8). For dynamic adsorption, set the temperature to 25°C, place the sample in a constant temperature and humidity box, and adsorb to saturation in the relative humidity range of 30-90%, then take out and record the sample mass. For static adsorption, place the sample in a constant temperature and humidity chamber (25°C, 30% RH), take out the sample every 2 minutes and record the mass change until the sample water adsorption is saturated (the sample mass no longer changes and is stable for a period of time). The samples were placed in a 120°C oven to dry completely before testing.

The mass of the dried sample before the test is recorded as M ₁ , the mass of the sample at a certain time is recorded as M ₂ , and the mass of the sample after adsorption saturation is recorded as M ₃ . Then the adsorption rate R and saturation adsorption rate R _s of the hygroscopic agent can be expressed as

Differential Thermogravimetry (DTG):

The desorption activation energy of Comparative Example 1 and Example 1 was analyzed using a TG 209F3 thermogravimetric analyzer (TG) from Netzsch Company of Germany. Set the heating rate to 4°C/min, 6°C/min, 8°C/min, 10°C/min, and 12°C/min, respectively, from room temperature to 150°C. Before measurement, the sample was first placed in a constant temperature and humidity chamber with test conditions of 25°C and 90% RH to adsorb to saturation. The desorption activation energy (E _d ) was calculated according to the Kissinger equation.

Among them, E _d is the desorption activation energy, the unit is kJ·mol ^-1 ; R is the gas constant, 8.314J/(mol·K); T represents the desorption temperature (K); β is the heating rate (℃/min) , K is a constant.

UV-vis-NIR light absorption:

A UV-vis-NIR diffuse reflectometer (Lambda 750S, PerkinElmer, USA) was used to record the reflection spectra of activated carbon fiber, MOF-303 powder (Comparative Example 1) and bulk hygroscopic agent (Example) in the range of 200-2500nm, and analyze Its light absorption properties.

Thermal imaging analysis:

A thermal imaging camera was used to record the surface temperature changes with time of MOF-303 powder (Comparative Example 1) and bulk hygroscopic agent (Example) under simulated sunlight irradiation.

Figure 1 is the XRD spectrum of the hygroscopic agents prepared in Comparative Examples (1, 2) and Examples (1, 8). It can be concluded from Figure 1 that the XRD diffraction peak positions of the activated carbon fiber-based MOFs bulk hygroscopic agent (Examples 1 and 8) synthesized in situ by the mixed solvothermal method are consistent with those of the MOFs powder (Comparative Examples 1 and 2). It is proved that the mixed solvothermal method can be used to successfully load MOF-303 on the activated carbon fiber substrate without changing its crystal structure.

Figure 2 is an SEM image of the activated carbon fiber before and after modification (magnification: 1k and 5k, respectively) and the activated carbon fiber-based MOF-303 bulk moisture absorbent prepared in Example 1 (magnification: 2k and 5k, respectively) . As can be seen from Figure 2, the unmodified activated carbon fiber is in the shape of a smooth fiber rod with a large number of pores inside it, which provides attachment sites for MOF-303 particles; the pretreated activated carbon fiber rod is loaded with chitosan particles, which enhances the hydrophilicity of the activated carbon fiber and the interaction force with the MOF-303 particles; the MOF-303 crystals are loaded on the activated carbon fiber rods and appear in a cube shape, indicating that the MOF-303 bulk hygroscopic agent has been successfully prepared.

Figure 3 shows the dynamic water adsorption curves of the hygroscopic agents prepared in Comparative Example 1 and Example 1. The results show that the activated carbon fiber-based MOF-303 bulk hygroscopic agent (Example 1) maintains consistent adsorption behavior with MOF-303 powder (Comparative Example), and has higher water adsorption under low humidity conditions (30% RH) The amounts are 0.23g/g and 0.32g/g respectively.

Figure 4 is a dynamic water adsorption curve of the hygroscopic agent prepared in Examples 6-10. The results show that the water adsorption isotherm of MOFs can be adjusted by changing the ligand content, making it applicable to more applications. The examples all have higher water adsorption capacity. The best ligand is 5/5, that is, Example 8. Its moisture absorption capacity at 30% RH, 60% RH and 90% RH is 0.16g/g and 0.23g/g respectively. g and 0.28g/g.

Figure 5 is the static water adsorption curve (25°C, 30% RH) of the hygroscopic agents prepared in Comparative Example 1 and Examples 1 and 8. The results show that the prepared hygroscopic agent reaches adsorption saturation within 30 minutes and has a rapid water adsorption rate.

Figure 6 shows the light absorption curves of the unmodified activated carbon fiber substrate, comparative examples and examples in the wavelength range of 200-2500 nm. The results show that the examples show better light absorption capabilities than the comparative examples in the ultraviolet, visible and near-infrared wavelength ranges, indicating that carrier-based MOFs can enhance the light absorption capabilities of the bulk hygroscopic agent.

Figure 7 is a simulated surface temperature change curve with time of Comparative Example 1 and Example 1 under sunlight irradiation. The results show that the surface temperature of Comparative Example 1 rises relatively slowly, with the highest peak temperature being 41.2°C; in Example 1, the temperature rises rapidly from room temperature to 55°C within 1 minute, and then maintains a certain rate of increase, and the temperature stabilizes within 30 minutes. The highest peak temperature reached 87.6°C, which was twice that of Comparative Example 1. This means that the activated carbon fiber gives the bulk hygroscopic agent strong light-to-heat conversion ability, which can realize solar-driven desorption of water, thereby reducing energy consumption.

Table 1

Table 1 shows the loading capacity of the activated carbon fiber-based MOFs bulk moisture absorbent prepared in Examples 1-10. It can be seen that the activated carbon fiber-based MOFs bulk moisture absorbent synthesized by mixed solvothermal in situ all has a higher loading capacity, with the highest loading capacity of 70.49% in Example 1.

Table 2

Table 2 shows the desorption peak temperatures (T) and corresponding desorption activation energies (E _d ) of the hygroscopic agents prepared in Example 1 and Comparative Example 1 at different heating rates. By comparison, it can be seen that at the same heating rate, the desorption peak temperature of activated carbon fiber-based MOF-303 bulk moisture absorbent (Example 1) is much lower than that of MOF-303 powder (Comparative Example 1), indicating that The activated carbon fiber substrate can effectively improve the heat and mass transfer rate of the hygroscopic agent. At the same time, the desorption peak temperature of the bulk hygroscopic agent at different heating rates is lower than the peak temperature under simulated sunlight irradiation (Figure 5), which verifies the feasibility of sunlight-driven water desorption. Calculated by the Kissinger equation, the desorption activation energies of activated carbon fiber-based MOF-303 bulk moisture absorbent (Example 1) and MOF-303 powder moisture absorbent (Comparative Example 1) are 56.99kJ/mol and 67.11kJ/mol respectively, indicating The former requires lower energy consumption for desorption, further indicating that carrierizing MOF is an effective way to achieve energy-saving desorption.

The above embodiments are only preferred embodiments of the present invention and are only used to explain the present invention rather than limit the present invention. Changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit and essence of the present invention shall all belong to this invention. protection scope of the invention.

Claims (10)

1. An activated carbon fiber-based MOFs bulk hygroscopic agent and its mixed solvent thermal in-situ synthesis method, which is characterized in that the specific steps are as follows: (1) Hydrophilic modification treatment of activated carbon fiber: Dip the activated carbon fiber into an oxidant for activation, and then immerse it into an aqueous solution containing hydrophilic modified film-forming materials. After sufficient infiltration, clean and dry to obtain hydrophilic modification. activated carbon fiber; (2) Preparation of the reaction solution: Under stirring conditions, mix the N,N-dimethylformamide solution of the organic dicarboxylic acid and the aluminum salt solution to obtain a uniform reaction solution; (3) MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis: immerse the modified activated carbon fiber in the reaction solution for crystallization reaction. After the reaction, take out the activated carbon fiber loaded with MOFs coating, wash and dry to obtain the activity Carbon fiber-based MOFs bulk moisture absorber. 2. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that the oxidant in step (1) includes concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide, high One of the mixtures of potassium manganate, concentrated sulfuric acid and concentrated nitric acid (v/v: 1/1). 3. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that the hydrophilic modified film-forming material in step (1) includes chitosan quaternary ammonium One of salt, chitosan hydrochloride, carboxymethyl chitosan, and chitosan oligosaccharide. 4. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that the organic dicarboxylic acid in step (2) includes 3,5-pyrazole bis One or two of carboxylic acid, fumaric acid, 2,5-furandicarboxylic acid and isophthalic acid. 5. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that the aluminum salt in step (2) is aluminum nitrate nonahydrate, aluminum sulfate octahydrate , one of aluminum chloride hexahydrate and aluminum acetate. 6. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that the mole of aluminum ions in the organic dicarboxylic acid and aluminum salt solution in step (2) The ratio is 1:0.8~1.25. 7. A kind of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent thermal in-situ synthesis method according to claim 1, characterized in that, in the N, N-dimethylformamide and aluminum aqueous solution in step (2) The volume ratio of water is 1:5~10. 8. A thermal in-situ synthesis method of activated carbon fiber-based MOFs bulk hygroscopic agent mixed solvent according to claim 1, characterized in that the temperature of the crystallization reaction in step (3) is 80-120°C; step (3) ) The crystallization reaction time is 10 to 14 hours; the washing in step (3) is to wash 3 times with ethanol and deionized water alternately; the activation temperature in step (3) is 100 to 150°C; the activation time It is 6~10h. 9. An activated carbon fiber-based MOFs bulk hygroscopic agent according to any one of claims 1 to 8 and an activated carbon fiber-based MOFs bulk hygroscopic agent synthesized by a mixed solvent thermal in-situ synthesis method. 10. The application of an activated carbon fiber-based MOFs bulk hygroscopic agent according to claim 9 in the field of solar-assisted atmospheric water collection in arid areas.