CN117463292A - Activated carbon fiber-based MOFs block moisture absorbent and mixed solvent thermal in-situ synthesis method and application thereof - Google Patents
Activated carbon fiber-based MOFs block moisture absorbent and mixed solvent thermal in-situ synthesis method and application thereof Download PDFInfo
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Abstract
The invention discloses an activated carbon fiber-based MOFs block moisture absorbent and a mixed solvent thermal in-situ synthesis method and application thereof. The method comprises the following steps: immersing activated carbon fibers into an aqueous solution containing a hydrophilic modified film-forming material to obtain hydrophilic modified activated carbon fibers; mixing DMF solution of organic dicarboxylic acid and aluminum salt water solution to obtain uniform reaction solution; immersing the modified activated carbon fiber in the reaction liquid for reaction, taking out the activated carbon fiber loaded with the MOFs coating, washing, drying and activating to obtain the MOFs block moisture absorbent. The active carbon fiber-based MOFs block moisture absorbent prepared by the invention has the advantages that MOFs grains are tightly combined with a base material, and powder is not dropped; MOFs load rate is high; the MOFs block moisture absorbent has the characteristics of high water vapor adsorption capacity, low desorption temperature, good circulation stability, strong photothermal conversion capability and the like under low humidity (30% RH), and can be applied to the field of solar-assisted driving atmospheric water collection in arid areas.
Description
Technical Field
The invention relates to the field of atmospheric water collection, in particular to an active carbon fiber-based MOFs block moisture absorber, a mixed solvent thermal in-situ synthesis method and application thereof.
Background
Although various water purification technologies such as filtration, reverse osmosis, multistage flash evaporation, etc. are currently developed to utilize seawater or wastewater, these water purification technologies are only applicable to coastal areas and are generally not available in inland areas due to the reliance on natural water sources. About 12900km in the atmosphere is reported 3 In the form of steam or droplets, which if utilized, would effectively alleviate the global water resource shortage pressure. While direct extraction is readily accomplished by mist collection or condensation by cooling the air below the dew point in humid climates, it is not desirable in arid environments. Thus, establishing atmospheric water collection (AWH) in arid areas is a promising strategy for the decentralized production of water.
Compared to traditional water vapor adsorbents such as silica gel, molecular sieves, metal Organic Frameworks (MOFs) with a large number of uniform micropores have been identified as promising next generation new water vapor adsorbents due to their abundant chemical variability and tunability. MOFs can exhibit excellent water vapor capture capacity and hydrothermal stability over a wide range of Relative Humidity (RH), with low regeneration energy consumption. As with the traditional powder adsorbent, the powder MOF has the problem of low mass and heat transfer efficiency, and if MOF grains are uniformly loaded on a substrate to prepare a so-called block adsorbent (Monolithic adsorbent), the key for improving the mass and heat transfer efficiency is that; and the moisture absorption of the bulk adsorbent can be adjusted by adjusting the coating thickness (MOF loading). In addition, in order to save operation energy consumption, particularly desorption energy consumption, the selection of solar energy to drive the adsorbent to desorb water is an important strategy for collecting water from the atmosphere. The base materials of the prior block adsorbent mainly comprise inorganic fiber paper such as asbestos fiber paper, glass fiber paper, ceramic fiber paper and the like; inorganic ceramic porous materials such as sepiolite, cordierite, etc.; and metal-based sheets such as aluminum foil, copper foil, and the like. The inorganic fiber paper has high porosity but large brittleness, is difficult to process or needs to be added with inorganic glue for shaping, thereby reducing the loading rate of the adsorbent; the inorganic ceramic porous material has high density, low porosity and quite low adsorbent loading rate; the metal base sheet has weak acting force with the adsorbent, small surface area and low adsorbent loading rate; and, besides metal foils, they have low thermal conductivity and low photo-thermal conversion efficiency. On the other hand, most MOFs are white or light-colored powders, and have poor light absorption ability and low photothermal conversion properties, and therefore, it is necessary to strengthen the photothermal properties thereof. A method of adding a photo-thermal agent is generally adopted to achieve photo-thermal enhancement. The photo-thermal agents reported at present are four types, namely noble metal nano-particles, metal semiconductor nano-particles, carbon-based nano-materials, polymers and the like. Among them, metal semiconductor nanoparticles and carbon-based nanomaterials are commonly used. However, the addition of these photothermal agents can reduce the moisture uptake of the MOF to some extent (including reduced loading of the MOF or partial blocking of the MOF microporous pores). Therefore, a substrate with high specific surface area (porosity), high thermal conductivity and high photo-thermal conversion performance is selected as a carrier of the adsorbent, so that the loading rate of the MOF adsorbent is improved, and meanwhile, the rapid dehydration of the adsorbent is realized through photo-thermal conversion under the assistance of solar energy, so that the desorption energy consumption of the adsorbent is reduced. Furthermore, how to uniformly disperse high loading rate MOF grains in a substrate is closely related to MOF loading process. There are generally two methods to support MOFs, namely direct dip coating and in situ synthesis. The dip coating method requires that the adsorbent is adhered to the substrate by the external addition of a binder, and common binders include sodium silicate solution, silicon solution, organopolysiloxane resin, etc. The binder of the method is easy to block the pores of the MOF adsorbent, thereby affecting the adsorption effect. The in-situ synthesis method is to make MOF grow in-situ on the base material, and through the method, adsorption coatings with different thickness, compactness and uniformity can be obtained, and the method has the advantages of one-step synthesis simplicity 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, which has more excellent photothermal conversion capability than glass fiber and the like, and solar energy is used to drive desorption of water without adding photothermal agent. The rich pore structure of the activated carbon fiber also endows MOF growth sites, has dual functions of improving mass transfer efficiency and photo-thermal reinforcement, and has wide application background in the field of solar-assisted dehydration atmospheric water collection.
Disclosure of Invention
In order to overcome the defects of low mass and heat transfer efficiency, low photo-thermal conversion efficiency and the like of the powder MOFs in the use process, the invention aims to provide the MOFs block moisture absorbent and the mixed solvent thermal in-situ synthesis method thereof. The active carbon fiber-based MOFs block moisture absorber synthesized in situ by mixed solvent heat provided by the invention has the characteristics of high water adsorption quantity, high adsorption rate, strong binding force (no powder falling) between MOFs and a substrate, strong photo-thermal conversion capability and the like, and can be used in the field of solar-driven desorption of water in the atmosphere water collection, and low energy consumption is realized.
The aim of the invention is achieved by the following technical scheme.
The invention provides a mixed solvent thermal in-situ synthesis method of an activated carbon fiber-based MOFs block moisture absorbent, which comprises the following steps:
(1) Hydrophilic modification treatment of the activated carbon fiber: immersing activated carbon fiber into an oxidant for activation, immersing the activated carbon fiber into an aqueous solution containing a hydrophilic modified film-forming material, and cleaning and drying the activated carbon fiber after the activated carbon fiber is fully immersed into the aqueous solution to obtain the hydrophilic modified activated carbon fiber;
(2) Preparing a reaction solution: mixing an N, N-dimethylformamide solution of organic dicarboxylic acid and an aluminum salt aqueous solution under the stirring condition to obtain a uniform reaction solution;
(3) MOFs block moisture absorbent mixed solvent thermal in-situ synthesis: immersing the modified activated carbon fiber into a reaction liquid for crystallization reaction, taking out, washing and drying the activated carbon fiber loaded with the MOFs coating after the reaction is finished, and obtaining the activated carbon fiber-based MOFs block moisture absorbent.
Preferably, the oxidizing agent in the step (1) comprises one of concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide, potassium permanganate, and a mixture of concentrated sulfuric acid and concentrated nitric acid (v/v: 1/1).
Further preferably, consider the oxidation of the activated carbon fibers with the above oxidizing agent, which is concentrated sulfuric acid.
Preferably, the hydrophilic modified film-forming material in the step (1) comprises one of chitosan quaternary ammonium salt, chitosan hydrochloride, carboxymethyl chitosan and chitosan oligosaccharide.
Further preferably, the hydrophilic modified film-forming material is chitosan hydrochloride in consideration of factors such as binding force between the substrate and the hydrophilic modified film-forming material, price and the like.
Preferably, the organic dicarboxylic acid in step (2) comprises one or two of 3, 5-pyrazoledicarboxylic acid, fumaric acid, 2, 5-furandicarboxylic acid, and isophthalic acid.
Preferably, the aluminum salt in the step (2) is one of aluminum nitrate nonahydrate, aluminum sulfate octadecanoate, aluminum chloride hexahydrate and aluminum acetate.
The MOF in the step (2) comprises one MOF or two mixed MOFs of MOF-303, al-fumarate (A520), MIL-160 (Al) and CAU-10-H respectively formed by the coordination of the organic dicarboxylic acid, 3, 5-pyrazoledicarboxylic acid, fumaric acid, 2, 5-furandicarboxylic acid and isophthalic acid and aluminum salt.
It is further preferred that the organic dicarboxylic acid is 3, 5-pyrazole dicarboxylic acid and fumaric acid, and the aluminum salt is aluminum nitrate nonahydrate, and the resulting products are MOF-303 and MOF-303/Al-Fum mixed MOFs, in view of the price of the organic dicarboxylic acid and aluminum salt, the ease of reaction, and the application background of the atmospheric water collection in arid regions, which requires that it should have a high moisture absorption under low humidity conditions.
Preferably, the molar ratio of the organic dicarboxylic acid in the step (2) to aluminum ions in the aluminum salt aqueous solution is 1:0.8-1.25.
Further preferably, the molar ratio of the organic dicarboxylic acid to aluminum ions in the aluminum salt aqueous solution is 1:0.9-1.2.
Preferably, the volume ratio of DMF in the step (2) to water in the aqueous solution of aluminum salt is 1:5-10.
Further preferably, the organic dicarboxylic acid has low solubility in water, and the addition of DMF can effectively dissolve the organic dicarboxylic acid. Due to DMF and H 2 O is mutually dissolved, so that the organic dicarboxylic acid is uniformly dispersed in the reaction liquid; increasing or decreasing H by fixing the amount of DMF added 2 The amount of O is used for regulating DMF and H in the reaction liquid 2 O volume ratio; h 2 The large amount of O, namely the small concentration of DMF, the poor solubility of the organic dicarboxylic acid in the reaction solution and the poor system dispersibility are unfavorable for the organic dicarboxylic acid and the peripheral Al of the substrate 3+ And MOF growth on the substrate; h 2 The O amount is small, namely the DMF concentration is large, the migration rate of aluminum ions to the substrate is high, and the aluminum ions can be matched with Al 3+ And the volume ratio of DMF to water in the aqueous solution of aluminum salt is 1:6-8.
Preferably, the crystallization reaction temperature in the step (3) is 80-120 ℃.
Further preferably, the reaction temperature is low, the crystallization rate is slow, the formed MOFs coating is thin, and the water absorption capacity of the block moisture absorbent is low; the reaction temperature is high, the crystallization rate is too fast, the formed MOFs coating is thick, the acting force between the MOFs coating and the substrate is weak, MOFs grains are easy to fall off, and the crystallization reaction temperature is 90-110 ℃.
Preferably, the crystallization reaction time in the step (3) is 10-14 h.
Preferably, the washing in the step (3) is to alternately wash 3 times respectively with ethanol and deionized water.
Preferably, the activation temperature in the step (3) is 100-150 ℃; the activation time is 6-10 h.
The invention provides an activated carbon fiber-based MOFs block moisture absorbent prepared by the preparation method.
According to the mixed solvent thermal in-situ synthesis method provided by the invention, the activated carbon fiber is used as a base material, the activated carbon fiber is treated by using an oxidant to increase oxygen-containing groups on the base material, and the activated carbon fiber is further subjected to hydrophilic modification by using a hydrophilic modification film-forming material to increase hydrophilic groups such as amino groups, carboxyl groups, hydroxyl groups and the like on the base material, so that the acting force between MOFs and the base material is enhanced.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the in-situ synthesis method provided by the invention, the prepared activated carbon fiber-based MOFs block moisture absorbent has strong binding force with a base material, is not easy to fall off, solves the problem of poor mass and heat transfer effects of powder MOFs, and improves the MOFs loading rate by the in-situ synthesis process.
2. The in-situ synthesis method provided by the invention does not use an adhesive, so that the problem that the adhesive blocks the pores of the MOFs adsorbent is avoided, and the moisture absorption capacity of the MOFs block moisture absorbent is improved.
3. Compared with MOFs powder, the MOFs block moisture absorbent prepared by the in-situ synthesis method provided by the invention has lower desorption temperature, so that the running energy consumption of a water collecting system is reduced.
4. The active carbon fiber substrate used by the invention not only has rich pore structures, but also has excellent photo-thermal conversion performance, overcomes the defect of poor photo-thermal conversion efficiency of the conventional substrate and MOFs, and can utilize solar energy to drive and desorb moisture adsorbed by the MOFs adsorbent.
5. According to the invention, MOF-303/Al-Fum mixed MOFs block adsorbents are synthesized in situ on an activated carbon fiber substrate by MOF-303 and Al-Fum monomers, a series of double-ligand mixed MOFs block adsorbents with different contents are prepared by changing the proportion of the two ligands, and the MOF water adsorption isothermal curve can be adjusted to adapt to different application occasions.
6. The block moisture absorbent prepared by the invention has high water vapor adsorption capacity under the condition of low humidity (less than or equal to 30% RH).
Drawings
Fig. 1 shows XRD spectra of the moisture absorbent prepared in examples 1 and 8 and comparative examples 1 and 2.
FIG. 2 is an SEM image of the activated carbon fiber-based MOF-303 block absorbent, activated carbon fiber before modification, and activated carbon fiber after modification, which were obtained in example 1.
FIG. 3 is a graph showing the dynamic water adsorption curves of the moisture absorbents prepared in example 1 and comparative example 1.
FIG. 4 is a graph showing the dynamic water adsorption profile of the hybrid MOFs block sorbents prepared in examples 6-10.
FIG. 5 shows the static water adsorption curves of the moisture absorbents prepared in examples 1, 8 and comparative example 1.
FIG. 6 is a UV-vis-NIR absorption spectrum of the moisture absorbent and unmodified activated carbon fiber prepared in examples 1, 8 and comparative example 1.
Fig. 7 is a graph showing the change of the surface temperature of the sample with time under simulated sunlight of the moisture absorbent prepared in example 1 and comparative example 1.
Detailed Description
Specific implementations of the invention are further described below with reference to the drawings and examples, but the implementations and protection of the invention are not limited thereto. It should be noted that the following processes, if not specifically described in detail, can be realized or understood by those skilled in the art with reference to the prior art. The reagents or apparatus used were not manufacturer-specific and were considered conventional products commercially available.
Pretreatment of activated carbon fiber: cutting activated carbon fiber into pieces of 3×3×0.5cm 3 Is a thin cloth. Firstly, immersing the cut activated carbon fibers in concentrated sulfuric acid for 2 hours, then cleaning the cut activated carbon fibers by using deionized water until the cut activated carbon fibers are neutral, and placing the cut activated carbon fibers in an oven for drying. Then, the activated carbon fiber is immersed in a solution of chitosan hydrochloride of 25mg/mL to be fully wetted, and the excessive solution on the substrate is taken out and washed by deionized water and then dried at 70 ℃.
Chitosan hydrochloride may also be replaced by chitosan quaternary ammonium salt, carboxymethyl chitosan or chitosan oligosaccharide.
Comparative example 1
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ Molar ratio of DMF to H1:1 2 O volume ratio 1:7, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was dissolved in 5mL of DMF to form a DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.52g (4 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 35mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 In an aqueous solution of (2)Stirring is continued for 20min to obtain a uniform reaction solution.
(2) And (3) adding the reaction solution prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, sealing, placing in a muffle furnace, reacting for 12h at 100 ℃, and cooling to room temperature after the reaction is finished. And (3) filtering the mixed solution by using a G4 funnel, respectively and alternately washing the obtained solid wet material by using absolute ethyl alcohol and deionized water for three times, and drying and activating the solid wet material for 6 hours at 120 ℃ in a blast drying oven to obtain MOF-303 absorbent powder.
Comparative example 2
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ Molar ratio of DMF to H1:1 2 O volume ratio 1:8, 0.269g (1.5 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.175g (1.5 mmol) of fumaric acid were taken and dissolved in 5mL of DMF to form a dual ligand DMF solution; 1.14g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 40mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction solution prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, sealing, placing in a muffle furnace for reaction at 110 ℃ for 12 hours, and cooling to room temperature after the reaction is finished. And (3) filtering the mixed solution by using a G4 funnel, alternately washing the obtained solid wet material with absolute ethyl alcohol and deionized water for three times, and drying and activating for 6 hours at 120 ℃ in a blast drying oven to obtain MOF-303/Al-Fum mixed absorbent powder.
Example 1
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ Molar ratio of DMF to H1:1 2 O volume ratio 1:6, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was dissolved in 5mL of DMF to form a DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.52g (4 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 30mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 100 ℃ for 12h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 6 hours at 120 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303 block absorbent.
Example 2
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ The molar ratio of DMF to H is 1:0.8 2 O volume ratio 1:5, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was taken and dissolved in 5mL of DMF to form a DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.22g (3.2 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 25mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 110 ℃ for 10 hours, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 8 hours at the temperature of 110 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303 block absorbent.
Example 3
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ The molar ratio of DMF to H is 1:0.9 2 O volume ratio 1:7, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was dissolved in 5mL of DMF to form a DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.37g (3.6 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 35mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 120 ℃ for 11h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 10 hours at 120 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303 block absorbent.
Example 4
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ The molar ratio of DMF to H is 1:1.1 2 O volume ratio 1:8, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was dissolved in 5mL of DMF to form DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.67g (4.4 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 40mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 80 ℃ for 13h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 10 hours at the temperature of 100 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303 block absorbent.
Example 5
(1) Under magnetic stirring at room temperature, 50mL beaker was taken and the mixture was stirred with Al according to 3, 5-pyrazoledicarboxylic acid 3+ 1:1.25, DMF and H 2 O volume ratio 1:10, 0.72g (4 mmol) of 3, 5-pyrazole dicarboxylic acid was dissolved in 5mL of DMF to form DMF solution of 3, 5-pyrazole dicarboxylic acid; 1.9g (5 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 50mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a DMF solution of 3, 5-pyrazoledicarboxylic acid to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 90 ℃ for 14h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 6 hours at 150 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303 block absorbent.
Example 6
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ The molar ratio of DMF to H is 1:0.8 2 O volume ratio 1:6, 0.43g (2.4 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.07g (0.6 mmol) of fumaric acid were taken and dissolved in 5mL of DMF to form a dual ligand DMF solution; 0.912g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 30mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 110 ℃ for 14h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 8 hours at the temperature of 120 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303/Al-Fum (8/2) mixed MOFs block moisture absorbent.
Example 7
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ The molar ratio of DMF to H is 1:0.9 2 O volume ratio 1:7, 0.377g (2.1 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.105g (0.9 mmol) of fumaric acid were dissolved in 5mL of DMF to form a dual ligand DMF solution; 1.026g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 30mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 110 ℃ for 13h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 6 hours at 130 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303/Al-Fum (7/3) mixed MOFs block moisture absorbent.
Example 8
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ Molar ratio of DMF to H1:1 2 O volume ratio 1:8, 0.269g (1.5 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.175g (1.5 mmol) of fumaric acid were taken and dissolved in 5mL of DMF to form a dual ligand DMF solution; 1.14g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 40mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 120 ℃ for 12h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 6 hours at 150 ℃ in a blast drying box to obtain the active carbon fiber-based MOF-303/Al-Fum (5/5) mixed MOFs block moisture absorbent.
Example 9
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ The molar ratio of DMF to H is 1:1.1 2 O volume ratio 1:9, 0.162g (0.9 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.245g (2.1 mmol) of fumaric acid were taken and dissolved in 5mL of DMF to form a dual ligand DMF solution; 1.254g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 50mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Is continuously stirred in the aqueous solution of (2)And obtaining uniform reaction liquid after 20 min.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 130 ℃ for 11h, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 10 hours at the temperature of 100 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303/Al-Fum (3/7) mixed MOFs block moisture absorbent.
Example 10
(1) Under magnetic stirring at room temperature, 50mL beaker is taken, and according to ligand and Al 3+ 1:1.25, DMF and H 2 O volume ratio 1:10, 0.108g (0.6 mmol) of 3, 5-pyrazole dicarboxylic acid and 0.28g (2.4 mmol) of fumaric acid were taken and dissolved in 5mL of DMF to form a dual ligand DMF solution; 1.425g (3 mmol) of Al (NO) 3 ) 3 ·9H 2 O was dissolved in 30mL deionized water to form Al (NO) 3 ) 3 Is an aqueous solution of (a); dropwise addition of a solution of the bis-ligand in DMF to Al (NO) 3 ) 3 Continuously stirring for 20min to obtain uniform reaction liquid.
(2) And (3) adding the reaction liquid prepared in the step (1) into a 100mL polytetrafluoroethylene lining reaction kettle, obliquely immersing the pretreated activated carbon fibers in the reaction liquid, sealing, placing in a muffle furnace for reaction at 140 ℃ for 10 hours, and cooling to room temperature after the reaction is finished. Taking out the block, alternately washing the block with absolute ethyl alcohol and deionized water for three times respectively, and drying and activating the block for 8 hours at the temperature of 110 ℃ in a forced air drying oven to obtain the active carbon fiber-based MOF-303/Al-Fum (2/8) mixed MOFs block moisture absorbent.
Test conditions and methods
Load calculation of bulk moisture absorbent (example):
the mass of the pretreated activated carbon fiber is set to be m 1 After the reaction is finished, the mass of the activated carbon fiber-based MOFs block moisture absorbent obtained after cleaning and drying is m 2 The loading w of the activated carbon fiber based MOFs bulk moisture absorber 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 absorbent (example 1) and activated carbon fiber-based MOF-303/Al-Fum mixed MOFs bulk moisture absorbent (example 8) were ground to powder, and a sample was subjected to phase analysis using a fully automatic X-ray powder diffractometer (XRD) model D8 advanced from Bruker, germany; the test conditions were Cu targets, diffraction angles in the range 5-60, scan rates of 0.1 seconds/step, and step sizes of 0.02.
Scanning Electron Microscope (SEM):
the surface morphology of the activated carbon fiber and activated carbon fiber-based MOF-303 block moisture absorbent before and after pretreatment was observed by using a Scanning Electron Microscope (SEM) SU8220 (Hitachi, japan), and the samples were subjected to a metal spraying treatment before the test, and a scanning voltage of 5kV was applied.
Dynamic and static isothermal water vapor adsorption curves:
the test uses a programmable constant temperature and humidity test box and an electronic balance to analyze the dynamic and static isothermal water vapor adsorption curves of MOF-303 powder (comparative example 1), MOF-303/Al-Fum mixed MOFs powder (comparative example 2), activated carbon fiber-based MOF-303 bulk moisture absorbent (example 1), and activated carbon fiber-based MOF-303/Al-Fum mixed MOFs bulk moisture absorbent (example 8). For dynamic adsorption, the temperature is set at 25 ℃, the sample is placed in a constant temperature and humidity box to be adsorbed to saturation within the range of 30-90% of relative humidity, and then the sample mass is taken out and recorded. For static adsorption, the samples were placed in a constant temperature and humidity cabinet (25 ℃,30% rh), and the mass change of the samples was recorded every 2min until the sample water adsorption was saturated (sample mass was not changing and stabilized for a period of time). The samples were placed in an oven at 120 ℃ to dry completely before testing.
The mass of the dried sample before the test was recorded as M 1 The mass of the sample at a certain time is recorded as M 2 The mass of the sample after adsorption saturation is recorded as M 3 . The adsorption rate R and the saturation adsorption rate R of the moisture absorbent s Can be expressed as
Differential thermogravimetric analysis (DTG):
the desorption activation energies of comparative example 1 and example 1 were analyzed using a TG 209F3 thermogravimetric analyzer (TG) from Netzsch, germany. The temperature rising rates were set to 4 ℃/min, 6 ℃/min, 8 ℃/min, 10 ℃/min, 12 ℃/min, respectively, and the temperature was raised from room temperature to 150 ℃. Before measurement, the sample was placed in a constant temperature and humidity box under test conditions of 25 ℃ and 90% rh to be adsorbed to saturation. Calculation of the desorption activation energy according to the Kectger equation (E d )。
Wherein E is d For desorption activation energy, the unit is kJ.mol -1 The method comprises the steps of carrying out a first treatment on the surface of the R is a gas constant, 8.314J/(mol.K); t represents the desorption temperature (K); beta is the rate of temperature rise (DEG C/min) and K is a constant.
UV-vis-NIR light absorption:
the light absorption properties of the activated carbon fibers, MOF-303 powder (comparative example 1) and bulk moisture absorbent (example) were analyzed by recording the reflectance spectra in the range of 200-2500nm using a UV-vis-NIR diffuse reflectometer (Lambda 750S, perkinelmer, USA).
Thermal imaging analysis:
the change in surface temperature of the MOF-303 powder (comparative example 1) and the bulk moisture absorbent (example) under simulated solar irradiation was recorded with time using a thermal imaging camera.
FIG. 1 shows XRD spectra of the moisture absorbent prepared in comparative examples (1, 2) and examples (1, 8). As can be seen from fig. 1, the XRD diffraction peak positions of the activated carbon fiber-based MOFs bulk hygroscopicity agents (examples 1 and 8) prepared by the mixed solvothermal method in situ synthesis are respectively consistent with those of the MOFs powder (comparative examples 1 and 2), which proves that the mixed solvothermal method can successfully load the MOF-303 on the activated carbon fiber substrate without changing the crystal structure.
FIG. 2 is an SEM image of activated carbon fiber before and after modification (magnification of 1k and 5k, respectively) and activated carbon fiber-based MOF-303 block moisture absorbent prepared in example 1 (magnification of 2k and 5k, respectively). As can be seen from fig. 2, the unmodified activated carbon fiber is in the shape of a smooth fiber rod, and a plurality of pore channels exist in the unmodified activated carbon fiber, so that sites are provided for MOF-303 particles; chitosan particles are loaded on the pretreated activated carbon fiber rod, so that the hydrophilicity of the activated carbon fiber and the acting force between the activated carbon fiber and MOF-303 particles are enhanced; MOF-303 crystals are loaded on an activated carbon fiber rod and are in a cube shape, which shows that the MOF-303 block moisture absorbent is successfully prepared.
FIG. 3 is a graph showing the dynamic water adsorption curves of the moisture absorbent prepared in comparative example 1 and example 1. The results show that the activated carbon fiber based MOF-303 bulk moisture absorbent (example 1) maintains consistent adsorption behavior with MOF-303 powder (comparative example), and has higher water adsorption capacity under low humidity conditions (30% RH) of 0.23g/g and 0.32g/g, respectively.
FIG. 4 is a graph showing the dynamic water adsorption curves of the moisture absorbents prepared in examples 6-10. The result shows that the MOFs water adsorption isotherm can be regulated and controlled by changing the content of the ligand, so that the MOFs water adsorption isotherm can be applied to more occasions. The examples all had a higher water adsorption capacity, the best ligand being 5/5 i.e. example 8, with moisture adsorption capacity at 30%, 60% and 90% RH of 0.16g/g, 0.23g/g and 0.28g/g respectively.
FIG. 5 shows the static water adsorption curves (25 ℃ C., 30% RH) of the moisture absorbent prepared in comparative example 1 and examples 1 and 8. The results show that the prepared moisture absorbent reaches adsorption saturation within 30min and has a rapid water adsorption rate.
FIG. 6 is a graph showing the light absorption curves of unmodified activated carbon fiber substrates, comparative examples, and examples in the wavelength range of 200-2500 nm. The results show that the examples exhibit better light absorption capacity than the comparative examples in the ultraviolet, visible and near infrared wavelength ranges, demonstrating that the vectorization of MOFs enhances the light absorption capacity of bulk hygroscopicity.
Fig. 7 is a graph simulating the change of the surface temperature of comparative example 1 and example 1 with time under irradiation of one sunlight. The results show that the surface temperature of comparative example 1 rises relatively slowly, with a peak temperature of 41.2 ℃; example 1 the temperature was rapidly increased from room temperature to 55 ℃ over 1min, followed by a constant rate of increase, and the temperature tended to stabilize over 30min with a peak temperature of 87.6 ℃ and a peak temperature of 2 times that of comparative example 1. This means that the activated carbon fiber endows the block moisture absorbent with strong photo-thermal conversion capability, and can realize solar-driven desorption of water, thereby reducing energy consumption.
TABLE 1
Table 1 shows the loading of the activated carbon fiber-based MOFs block sorbents prepared in examples 1-10. It can be seen that the activated carbon fiber based MOFs bulk hygroscopicity agent synthesized in situ by mixed solvothermal method all had a higher loading and was up to 70.49% as in example 1.
TABLE 2
Table 2 shows the desorption peak temperature (T) and the corresponding desorption activation energy (E) of the hygroscopic agent prepared in example 1 and comparative example 1 at different heating rates d ). As can be seen by comparison, under the same heating rate, the desorption peak temperature of the active carbon fiber-based MOF-303 block moisture absorbent (example 1) is far lower than that of MOF-303 powder (comparative example 1), which indicates that the active carbon fiber substrate can effectively improve the heat and mass transfer rate of the moisture absorbent. Meanwhile, the desorption peak temperature of the block moisture absorbent under different heating rates is lower than the peak temperature under the irradiation of simulated sunlight (figure 5), and the feasibility of solar-driven water desorption is verified. Calculated by the Kissinger equation, activated carbon fiber-based MOF-303 block moisture absorbent (solidThe desorption activation energies of example 1) and MOF-303 powder hygroscopicity agent (comparative example 1) were 56.99kJ/mol and 67.11kJ/mol, respectively, indicating that the former desorption requires lower energy consumption, further indicating that vectorizing the MOF is an effective way to achieve energy-efficient desorption.
The above examples are only preferred embodiments of the present invention, and are merely for illustrating the present invention, not for limiting the present invention, and those skilled in the art should not be able to make any changes, substitutions, modifications and the like without departing from the spirit of the present invention.
Claims (10)
1. An activated carbon fiber-based MOFs block moisture absorbent and a mixed solvent thermal in-situ synthesis method thereof are characterized by comprising the following specific steps:
(1) Hydrophilic modification treatment of the activated carbon fiber: immersing activated carbon fiber into an oxidant for activation, immersing the activated carbon fiber into an aqueous solution containing a hydrophilic modified film-forming material, and cleaning and drying the activated carbon fiber after the activated carbon fiber is fully immersed into the aqueous solution to obtain the hydrophilic modified activated carbon fiber;
(2) Preparing a reaction solution: mixing an N, N-dimethylformamide solution of organic dicarboxylic acid and an aluminum salt aqueous solution under the stirring condition to obtain a uniform reaction solution;
(3) MOFs block moisture absorbent mixed solvent thermal in-situ synthesis: immersing the modified activated carbon fiber into a reaction liquid for crystallization reaction, taking out, washing and drying the activated carbon fiber loaded with the MOFs coating after the reaction is finished, and obtaining the activated carbon fiber-based MOFs block moisture absorbent.
2. The method of claim 1, wherein the oxidizing agent in step (1) comprises one of concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide, potassium permanganate, and a mixture of concentrated sulfuric acid and concentrated nitric acid (v/v: 1/1).
3. The method for the mixed solvent thermal in-situ synthesis of the activated carbon fiber-based MOFs block hygroscopicity agent, according to claim 1, wherein the hydrophilic modified film-forming material in the step (1) comprises one of chitosan quaternary ammonium salt, chitosan hydrochloride, carboxymethyl chitosan and chitosan oligosaccharide.
4. The method for the mixed solvent thermal in situ synthesis of activated carbon fiber-based MOFs bulk hygroscopicity according to claim 1, wherein the organic dicarboxylic acid in step (2) comprises one or two of 3, 5-pyrazole dicarboxylic acid, fumaric acid, 2, 5-furan dicarboxylic acid and isophthalic acid.
5. The method for the mixed solvothermal in-situ synthesis of activated carbon fiber-based MOFs bulk hygroscopicity according to claim 1, wherein the aluminum salt in step (2) is one of aluminum nitrate nonahydrate, aluminum sulfate octadecanoate hydrate, aluminum chloride hexahydrate, and aluminum acetate.
6. The method for the mixed solvent thermal in-situ synthesis of the activated carbon fiber-based MOFs block moisture absorbent, which is characterized in that the molar ratio of the organic dicarboxylic acid to aluminum ions in the aqueous solution of aluminum salt in the step (2) is 1:0.8-1.25.
7. The method for the mixed solvent thermal in-situ synthesis of the activated carbon fiber-based MOFs body moisture absorbent, which is characterized in that the volume ratio of the N, N-dimethylformamide to water in the aluminum salt aqueous solution in the step (2) is 1:5-10.
8. The method for the mixed solvent thermal in-situ synthesis of the active carbon fiber-based MOFs body moisture absorbent, which is characterized in that the temperature of the crystallization reaction in the step (3) is 80-120 ℃; the crystallization reaction time in the step (3) is 10-14 h; the washing in the step (3) is to alternately and respectively wash 3 times by using ethanol and deionized water; the activation temperature in the step (3) is 100-150 ℃; the activation time is 6-10 h.
9. An activated carbon fiber based MOFs bulk moisture absorber synthesized by the method of thermal in situ synthesis of activated carbon fiber based MOFs bulk moisture absorbers and mixed solvents thereof as defined in any one of claims 1-8.
10. The use of an activated carbon fiber based MOFs bulk moisture absorber of claim 9 in the field of solar-assisted driven atmospheric water collection in arid areas.
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