Preparation method of nanocellulose composite aerogel for in-situ growth of ZIF-L with assistance of supercritical CO2

Abstract

The invention belongs to the field of nano-crystalline cellulose composite materials, and relates to a preparation method of nano-crystalline cellulose composite aerogel for in-situ growth of ZIF-L with assistance of supercritical CO.According to the preparation method, a supercritical COfluid technology is creatively applied to an in-situ growth reaction of ZIF-L and a drying process of aerogel at the same time; the beneficial effects are generated by the application of the supercritical COtechnology, the in-situ growth strategy and the synergistic reaction of the nanocellulose and the ZIF-L. Supercritical COs have the characteristics of low viscosity, high diffusivity and no surface tension. According to the present invention, the MOF is introduced into the nano-cellulose network, such that the MOF can efficiently penetrate into the micro-pores of the nano-cellulose network so as to promote the mass transfer and the contact between the zinc ions and the 2-methylimidazole ligand, such that the uniform and compact growth of the ZIF-L crystal in the cellulose three-dimensional network is achieved, and the common problems of MOF particle agglomeration, non-uniform distribution and the like in the traditional liquid phase method are effectively avoided; in-situ growth of ZIF-L and aerogel drying are integrated in the same supercritical COtreatment process, the technological process is simplified, and complex operation of a traditional multi-step method is avoided.

Description

Technical Field

[0001] This invention belongs to the field of nanocellulose composite materials, specifically relating to a method for in-situ growth of ZIF-L in nanocellulose aerogel using supercritical CO2 technology. Background Technology

[0002] Nanocellulose aerogels, as third-generation biomass polymer materials, not only possess the high porosity, large specific surface area, and low thermal conductivity of traditional inorganic aerogels, but also have advantages such as good biocompatibility and biodegradability. However, pure nanocellulose aerogels suffer from limited functionality, strong hydrophilicity, and insufficient mechanical properties, which restricts their application in high-value-added fields.

[0003] To endow cellulose nanogels with new functions, researchers often construct composite aerogels by introducing functional nanoparticles such as metal-organic frameworks (MOFs). Zeolite imidazole ester framework (ZIF) materials, especially ZIF-L, have outstanding performance in gas adsorption, molecular sieving, and catalysis due to their high specific surface area, tunable pore size, and excellent thermal and chemical stability. Combining them with cellulose nanogels can significantly enhance the functional properties of aerogels.

[0004] Currently, conventional methods for preparing ZIF-L / nanocellulose composite aerogels have many limitations: First, multiple steps are required to synthesize MOFs separately before combining them with cellulose, resulting in poor interfacial interactions, low mass transfer efficiency in the liquid-phase reaction system, and easy aggregation of ZIF-L crystals, leading to uneven distribution within the cellulose network and affecting the performance of the composite material. Second, the multi-step process is complex and time-consuming, and the subsequent drying process is prone to collapse of the gel network structure due to capillary forces, damaging the porous structure. In addition, traditional methods usually use a large amount of organic solvents, which not only increases costs but also contradicts the concept of green and environmentally friendly development. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a simple, low-energy-consumption, and environmentally friendly method for preparing ZIF-L nanocellulose composite aerogels using supercritical CO2-assisted in-situ growth. This method achieves in-situ growth and simultaneous drying of ZIF-L in a nanocellulose network through a one-pot process, solving problems such as uneven ZIF-L particle distribution, long process flow, high energy consumption, and easy structural collapse in traditional methods.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing ZIF-L nanocellulose composite aerogels grown in situ with supercritical CO2 assistance includes the following steps: Step 1: Prepare oxidized nanocellulose TOCN by treating cellulose raw materials with a TEMPO-NaClO-NaBr oxidation system; Step 2: Disperse the oxidized cellulose nanoparticles TOCN prepared in Step 1 in water to prepare an oxidized cellulose nanoparticles TOCN hydrogel; Step 3: Add anhydrous zinc nitrate to the TOCN hydrogel in Step 2, mix well, and form a zinc ion-containing TOCN hydrogel; Step 4: Add hydrochloric acid to induce the zinc ion-containing TOCN hydrogel described in Step 3 to self-support and form a rigid hydrogel block; Step 5: Perform solvent exchange on the rigid hydrogel block described in Step 4, replacing it with ethanol solvent to obtain an ethanol gel block containing zinc ions; Step 6: Place the zinc ion-containing TOCN hydrogel block that has undergone solvent exchange as described in Step 5 and 2-methylimidazole in a supercritical CO2 reactor, react under supercritical conditions and dry simultaneously to generate ZIF-L in situ, thus obtaining ZIF-L cellulose composite aerogel.

[0007] Furthermore, step 1 includes: Step 1.1: Disperse the lignocellulose wet pulp in distilled water, adjust the pH of the system to 2 with HCl solution, stir to remove mineral components; then filter and wash with water until neutral, and finally dry at 105℃ for 1 hour, and determine the cellulose content for later use; Step 1.2: Prepare a reaction solution by adding 0.016g TEMPO catalyst, 0.1g NaBr co-catalyst, and 100mL deionized water per gram of cellulose; add the pretreated cellulose raw material, stir evenly, and then add NaClO solution at a rate of 5mmol / g cellulose to start the oxidation reaction; Step 1.3: During the reaction, 0.5M NaOH solution is continuously added dropwise to maintain the pH of the system at 10.0–10.5 until the NaOH consumption rate decreases significantly, indicating that the oxidation reaction is complete; Step 1.4: Add sodium borohydride and ethanol to the system after the reaction is complete. The ratio of sodium borohydride to cellulose raw material is 0.1 g / g, and the ratio of ethanol to cellulose raw material is 1 mL / g. React for 3 hours to reduce potential aldehyde byproducts. Step 1.5: The reaction solution is washed with water, filtered, and the pH is adjusted to neutral to obtain transparent gel-like oxidized nanocellulose TOCN.

[0008] Furthermore, step 2 includes: Step 2.1: Disperse the oxidized nanocellulose obtained in Step 1 in deionized water at a solid content of 1 wt%, and form a uniform suspension by mechanical stirring; then use an AH-1500 high-pressure homogenizer to perform gradient pressure treatment of 100-300-500 bar, using high pressure shear force to destroy the fiber agglomeration structure, promote the dispersion of nanofibers in stages, and form oxidized nanocellulose TOCN hydrogel.

[0009] Furthermore, step 3 includes: Step 3.1: Add the metered anhydrous zinc nitrate to the TOCN hydrogel, wherein the mass ratio of anhydrous zinc nitrate to dry cellulose is 1:15. Use mechanical stirring to homogenize the mixture. Then, perform vacuum degassing on the mixture to eliminate air dissolved in the gel and ensure the integrity and uniformity of the cellulose three-dimensional network structure.

[0010] Furthermore, step 4 includes: Step 4.1: Cut the 0.22μm pore size hydrophilic filter membrane into 5*5cm size and gently cover it on the surface of the hydrogel; then apply 1M hydrochloric acid solution evenly to its surface and let it stand at room temperature for 1 hour to induce the hydrogel to undergo self-supporting cross-linking and hardening through acid penetration, and finally form a rigid hydrogel block with a specific shape and stable structure.

[0011] Furthermore, step 5 includes: Step 5.1: Immerse the gel in a mixed replacement solution consisting of 0.01 M hydrochloric acid solution and anhydrous ethanol at a volume ratio of 1:1, and allow it to stand at room temperature for 24 hours for replacement. Step 5.2: Transfer the primary displacement gel to a sufficient amount of anhydrous ethanol and perform displacement treatment at room temperature for a total time of 72 hours. During this period, replace the gel with fresh anhydrous ethanol every 12 hours to ensure that the solvent in the gel pores is fully replaced and residual moisture is removed.

[0012] Furthermore, step 6 includes: Step 6: The zinc ion-containing ethanol gel block obtained after solvent exchange is placed together with 2-methylimidazole in a supercritical CO2 reactor. The molar ratio of zinc ions to 2-methylimidazole is controlled at 1:18. The reaction is carried out at a reaction temperature of 40°C and a reaction pressure of 10 MPa for 24 hours to complete the in-situ growth and crystallization process of ZIF-L. At the same time, the supercritical carbon dioxide is used to dry the cellulose aerogel, and finally the in-situ grown ZIF-L / cellulose composite aerogel is obtained.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention innovatively applies supercritical CO2 fluid technology to both the in-situ growth reaction of ZIF-L and the drying process of aerogel. These beneficial effects are jointly generated by the application of supercritical CO2 technology, the in-situ growth strategy, and the synergistic reaction between nanocellulose and ZIF-L.

[0014] 1. Supercritical CO2 possesses characteristics of low viscosity, high diffusivity, and no surface tension. This allows it to efficiently penetrate into the micropores of the nanocellulose network, promoting mass transfer and contact between zinc ions and 2-methylimidazole ligands. This enables uniform and dense growth of ZIF-L crystals in the three-dimensional cellulose network, effectively avoiding problems such as MOF particle agglomeration and uneven distribution commonly found in traditional liquid-phase methods.

[0015] 2. Integrating the in-situ growth of ZIF-L with aerogel drying into the same supercritical CO2 treatment process simplifies the process flow and avoids the complex operation of traditional multi-step methods.

[0016] 3. Supercritical CO2 serves both as a reaction medium to promote the crystal growth of ZIF-L and as a drying medium to prevent the collapse of the aerogel structure, thus achieving the integration of reaction and drying.

[0017] 4. The entire preparation process uses renewable nanocellulose as a base and supercritical CO2 as a green reaction and drying medium. Furthermore, this method avoids the use of large amounts of organic solvents, making the process clean and environmentally friendly.

[0018] 5. The prepared composite aerogel combines the mechanical properties of nanocellulose with the functional characteristics of ZIF-L, and has broad application prospects in adsorption, catalysis and other fields. Attached Figure Description

[0019] Figure 1 Schematic diagram of X-ray diffraction analysis for different crystal structures; Figure 2 This is a schematic diagram of the cellulose composite aerogel prepared by the method of the present invention; Figure 3 This is a schematic diagram of the cellulose composite aerogel prepared by the comparative scheme in Example 2. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Example 1 Step 1: Prepare oxidized nanocellulose (TOCN) by treating cellulose raw materials with a TEMPO-NaClO-NaBr oxidation system. Step 1.1: Disperse the lignocellulose wet pulp in distilled water, adjust the pH of the system to 2 with HCl solution, stir to remove mineral components; then filter and wash with water until neutral, and finally dry at 105℃ for 1 hour, and determine the cellulose content for later use; Step 1.2: Prepare a reaction solution by adding 0.016g TEMPO catalyst, 0.1g NaBr co-catalyst, and 100mL deionized water per gram of cellulose; add the pretreated cellulose raw material, stir evenly, and then add NaClO solution at a rate of 5mmol / g cellulose to start the oxidation reaction; Step 1.3: During the reaction, 0.5M NaOH solution is continuously added dropwise to maintain the pH of the system at 10.0–10.5 until the NaOH consumption rate decreases significantly, indicating that the oxidation reaction is complete; Step 1.4: Add sodium borohydride (0.1 g / g cellulose) and ethanol (1 mL / g cellulose) to the system after the reaction is complete, and react for 3 hours to reduce potential aldehyde byproducts and improve product stability; Step 1.5: The reaction solution is washed with water, filtered, and the pH is adjusted to neutral to obtain transparent gel-like oxidized cellulose nanoparticles (TOCN).

[0022] Step 2: Disperse the oxidized cellulose nanoparticles TOCN prepared in Step 1 in water to prepare an oxidized cellulose nanoparticles TOCN hydrogel; Step 2.1: Disperse the oxidized nanocellulose obtained in Step 1 in deionized water at a solid content of 1 wt%, and form a uniform suspension by mechanical stirring; then use a high-pressure homogenizer to perform gradient pressure treatment on the suspension, using high-pressure shear force to break the fiber agglomeration structure, promote the dispersion of nanofibers, and form oxidized nanocellulose TOCN hydrogel.

[0023] Step 3: Add anhydrous zinc nitrate to the TOCN hydrogel in Step 2, mix well, and form a zinc ion-containing TOCN hydrogel; Step 3.1: Add the metered anhydrous zinc nitrate to the TOCN hydrogel, wherein the mass ratio of anhydrous zinc nitrate to dry cellulose is 1:15. Use mechanical stirring to homogenize the mixture, and then perform vacuum degassing treatment on the mixture to eliminate air dissolved in the gel and ensure the integrity and uniformity of the cellulose three-dimensional network structure.

[0024] Step 4: Add hydrochloric acid to induce the zinc ion-containing TOCN hydrogel described in Step 3 to self-support and form a rigid hydrogel block; Step 4.1: Cut the 0.22μm pore size hydrophilic filter membrane into 5*5cm size and gently cover it on the surface of the hydrogel; then apply 1M hydrochloric acid solution uniformly to its surface and let it stand for 1 hour at room temperature. The hydrogel undergoes self-supporting cross-linking and hardening through acid penetration, and finally forms a rigid hydrogel block with a specific shape and stable structure.

[0025] Step 5: Perform solvent exchange on the rigid hydrogel block described in Step 4, replacing it with ethanol solvent to obtain an ethanol gel block containing zinc ions; Step 5.1: Immerse the gel in a mixed replacement solution consisting of 0.01 M hydrochloric acid solution and anhydrous ethanol at a volume ratio of 1:1, and allow it to stand at room temperature for 24 hours for replacement. Step 5.2: Transfer the primary displacement gel to a sufficient amount of anhydrous ethanol and perform displacement treatment at room temperature for a total time of 72 hours. During this period, replace the gel with fresh anhydrous ethanol every 12 hours to ensure that the solvent in the gel pores is fully replaced and residual moisture is removed.

[0026] Step 6: The zinc ion / ethanol TOCN gel block obtained after solvent exchange is placed together with 2-methylimidazole in a supercritical CO2 reactor. The molar ratio of zinc ions to 2-methylimidazole is controlled at 1:18. The reaction is carried out at a reaction temperature of 40°C and a reaction pressure of 10 MPa for 24 hours to complete the in-situ growth and crystallization process of ZIF-L. At the same time, the supercritical carbon dioxide is used to dry the cellulose aerogel, and finally the in-situ grown ZIF-L / cellulose composite aerogel is obtained.

[0027] Example 2 Step 1: Prepare oxidized nanocellulose (TOCN) by treating cellulose raw materials with a TEMPO-NaClO-NaBr oxidation system. Step 1.1: Disperse the lignocellulose wet pulp in distilled water, adjust the pH of the system to 2 with HCl solution, stir to remove mineral components; then filter and wash with water until neutral, and finally dry at 105℃ for 1 hour, and determine the cellulose content for later use; Step 1.2: Prepare a reaction solution by adding 0.016g TEMPO catalyst, 0.1g NaBr co-catalyst, and 100mL deionized water per gram of cellulose; add the pretreated cellulose raw material, stir evenly, and then add NaClO solution at a rate of 5mmol / g cellulose to start the oxidation reaction; Step 1.3: During the reaction, 0.5M NaOH solution is continuously added dropwise to maintain the pH of the system at 10.0–10.5 until the NaOH consumption rate decreases significantly, indicating that the oxidation reaction is complete; Step 1.4: Add sodium borohydride (0.1 g / g cellulose) and ethanol (1 mL / g cellulose) to the system after the reaction is complete, and react for 3 hours to reduce potential aldehyde byproducts and improve product stability; Step 1.5: The reaction solution is washed with water, filtered, and the pH is adjusted to neutral to obtain transparent gel-like oxidized cellulose nanoparticles (TOCN).

[0028] Step 2: Disperse the oxidized cellulose nanoparticles TOCN prepared in Step 1 in water to prepare an oxidized cellulose nanoparticles TOCN hydrogel; Step 2.1: Disperse the oxidized nanocellulose obtained in Step 1 in deionized water at a solid content of 1 wt%, and form a uniform suspension by mechanical stirring; then use a high-pressure homogenizer to perform gradient pressure treatment on the suspension, using high-pressure shear force to break the fiber agglomeration structure, promote the dispersion of nanofibers, and form oxidized nanocellulose TOCN hydrogel.

[0029] Step 3: Add ZIF-8 to the TOCN hydrogel in Step 2, mix well, and form a TOCN composite hydrogel with mixed ZIF-8; Step 3.1: Add the metered ZIF-8 to the TOCN hydrogel, wherein the mass ratio of ZIF-8 to cellulose dry basis is 1:15. Use mechanical stirring to homogenize the mixture, and then perform vacuum degassing treatment on the mixture to eliminate air dissolved in the gel and ensure the integrity and uniformity of the cellulose three-dimensional network structure.

[0030] Step 4: Add hydrochloric acid to induce the TOCN composite hydrogel of mixed ZIF-8 described in Step 3 to self-support and form a rigid hydrogel block; Step 4.1: Cut the 0.22μm pore size hydrophilic filter membrane into 5*5cm size and gently cover it on the surface of the hydrogel; then apply 1M hydrochloric acid solution uniformly to its surface and let it stand for 1 hour at room temperature. The hydrogel undergoes self-supporting cross-linking and hardening through acid penetration, and finally forms a rigid hydrogel block with a specific shape and stable structure.

[0031] Step 5: Freeze-dry the rigid hydrogel block described in Step 4 to obtain ZIF-8 / cellulose composite aerogel.

[0032] Experimental results: 1. X-ray diffraction analysis Based on the appendix Figure 1The X-ray diffraction patterns shown reveal significant differences in crystal structure between the ZIF-L / nanocellulose composite aerogel (ZIF-L-AER) prepared in this invention and pure nanocellulose aerogel (TOCN-AER). TOCN-AER exhibits a broad, flat "bun peak" at approximately 22°, a typical characteristic of amorphous cellulose, indicating that pure nanocellulose aerogel lacks a regular crystal structure. The ZIF-L-AER curve shows multiple sharp and high-intensity diffraction peaks in the low-angle region at 8.5°, 10.4°, 11.6°, and 12.7°. In a supercritical CO2 environment, the cellulose network exerts stress constraints on crystal growth, leading to lattice shrinkage. The main peak of standard ZIF-L at 7.3° shifts to around 8.5°, coinciding with the characteristic peaks of the ZIF-L zeolite imidazole ester framework, demonstrating that ZIF-L crystals have been successfully grown in situ within the cellulose network.

[0033] 2. Microscopic morphology As attached Figure 2 As shown in the SEM images, this invention visually demonstrates that the preparation method described in this invention can successfully construct a three-dimensional porous material composed of ZIF-L and nanocellulose. ZIF-L crystals are uniformly loaded in irregular sheet-like forms on the surface and network nodes of the porous three-dimensional framework formed by the interwoven cellulose fibers. The supercritical CO2-assisted in-situ growth method effectively avoids the aggregation problem of MOF particles, achieving molecular-level composite formation. Simultaneously, the three-dimensional framework of cellulose is well preserved under supercritical drying. The uniform composite morphology observed in the images and the crystal structure results from XRD analysis corroborate each other, jointly confirming the innovation and reliability of the technical solution of this invention.

[0034] As attached Figure 3 As shown in the SEM image, this is the preparation method described in Specific Example 2. Compared with the method of in-situ growth combined with supercritical drying, the image shows obvious agglomeration, with ZIF particles scattered on the surface or in the pores of the TOCN network, resulting in uneven distribution. Furthermore, there is a clear physical boundary between the ZIF particles and the TOCN fibers, indicating that their interaction is merely a simple physical adsorption and mechanical intercalation. This weak interfacial bonding force will cause the ZIF particles to detach from the cellulose skeleton during use, leading to a degradation in material performance. Simultaneously, the freeze-drying method causes ice crystal growth, which can compress and damage the gel network formed by TOCN. This results in structural defects such as local collapse and pore fusion in the aerogel, failing to present a good cellulose skeleton and network structure, significantly reducing its application in adsorption, sensing, and other fields.

[0035] Therefore, traditional physical mixing and freeze-drying techniques are insufficient to prepare ZIF / cellulose composite aerogels with uniform structure and excellent performance. The "supercritical CO2-assisted in-situ growth" technology used in this invention aims to fundamentally solve these shortcomings. By promoting uniform nucleation and growth of ZIF at the molecular level and perfectly preserving the structure through supercritical drying, an advanced composite material with significantly improved overall performance is obtained.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nanocellulose composite aerogel grown in situ with ZIF-L assisted by supercritical CO2, characterized in that The method comprises the following steps: Step 1: preparing oxidized nanocellulose TOCN by treating the cellulose raw material through a TEMPO-NaClO-NaBr oxidation system; Step 2: dispersing the oxidized nanocellulose TOCN prepared in step 1 in water to prepare an oxidized nanocellulose TOCN hydrogel; Step 3: adding anhydrous zinc nitrate into the TOCN hydrogel in step 2 and uniformly mixing to form a TOCN hydrogel containing zinc ions; Step 4: adding hydrochloric acid to induce self-supporting of the TOCN hydrogel containing zinc ions in step 3 to form a rigid hydrogel block; Step 5: performing solvent exchange on the rigid hydrogel block in step 4 to replace it with an ethanol solvent to obtain an ethanol gel block containing zinc ions; Step 6: placing the TOCN hydrogel block containing zinc ions after the solvent exchange in step 5 and 2-methylimidazole in a supercritical CO2 reaction device to react and simultaneously dry under supercritical conditions to generate ZIF-L in situ, thereby obtaining a ZIF-L cellulose composite aerogel.

2. The method of claim 1, wherein the method of growing ZIF-L nanocellulose composite aerogels in situ with supercritical CO2 assistance is characterized by The step 1 comprises: Step 1.1: dispersing the lignocellulose wet paper pulp in distilled water, adjusting the pH of the system to 2 with an HCl solution, stirring to remove the mineral components, then filtering and washing with water until neutral, and finally drying at 105 DEG C for 1 hour to determine the cellulose content for standby; Step 1.2: preparing a reaction solution according to the proportion of 0.016 g TEMPO catalyst, 0.1 g NaBr catalyst and 100 mL deionized water per gram of cellulose; adding the pretreated cellulose raw material, uniformly stirring, and then adding a NaClO solution in an amount of 5 mmol / g of cellulose to start the oxidation reaction; Step 1.3: continuously adding 0.5 M NaOH solution during the reaction to maintain the pH of the system at 10.0-10.5 until the NaOH consumption rate significantly decreases; Step 1.4: adding sodium borohydride and ethanol to the system after the reaction is completed, the addition ratio of sodium borohydride to the cellulose raw material being 0.1 g / g, and the addition ratio of ethanol to the cellulose raw material being 1 mL / g, and reacting for 3 hours to reduce potential aldehyde by-products; Step 1.5: treating the reaction solution by water washing and filtering, adjusting the pH to neutral, and obtaining transparent gel-like oxidized nanocellulose TOCN.

3. The method of claim 1, wherein the method further comprises The step 2 comprises: Step 2.1: dispersing the oxidized nanocellulose prepared in step 1 in deionized water at a solid content of 1 wt%, forming a uniform suspension by mechanical stirring; then using an AH-1500 high-pressure homogenizer to perform pressure increasing treatment on the suspension at a gradient of 100-300-500 bar to form an oxidized nanocellulose TOCN hydrogel.

4. The method of claim 1, wherein the method of growing ZIF-L nanocellulose composite aerogels in situ with supercritical CO2 assistance is characterized by The step 3 comprises: Step 3.1: adding a metered amount of anhydrous zinc nitrate to the TOCN hydrogel, wherein the mass ratio of anhydrous zinc nitrate to cellulose dry basis is 1:15, and the mixed system is uniformly mixed by mechanical stirring; then the mixed system is subjected to vacuum degassing treatment to eliminate air dissolved in the gel.

5. The method of claim 1, wherein the method of growing ZIF-L nanocellulose composite aerogels in situ with supercritical CO2 assistance is characterized by The step 4 comprises: Step 4.1: Cut the hydrophilic filter membrane with a pore size of 0.22 μm into a size of 5*5 cm, cover it on the surface of the hydrogel; then uniformly apply 1 M hydrochloric acid solution on its surface, and stand for reaction at room temperature for 1 hour. The self-supporting cross-linking hardening of the hydrogel is induced by acid penetration, and finally a rigid hydrogel block is formed.

6. The method of claim 1, wherein the method of growing ZIF-L nanocellulose composite aerogels in situ with supercritical CO2 assistance is characterized by The step 5 comprises: Step 5.1: immerse the gel in a mixed displacement solution composed of 0.01 M hydrochloric acid solution and anhydrous ethanol at a volume ratio of 1:1, and stand for displacement at room temperature for 24 hours; Step 5.2: transfer the primary displacement gel to sufficient anhydrous ethanol, and perform displacement treatment at room temperature for a total time of 72 hours; during this period, fresh anhydrous ethanol is replaced every 12 hours.

7. The method of claim 1, wherein the method further comprises The step 6 comprises: Step 6: place the ethanol gel block of zinc ions obtained after solvent exchange together with 2-methylimidazole in a supercritical CO2 reaction device, control the molar ratio of zinc ions to 2-methylimidazole to be 1:18, and react at a reaction temperature of 40°C and a reaction pressure of 10 MPa for 24 hours to complete the in-situ growth and crystallization process of ZIF-L. At the same time, the supercritical carbon dioxide is used to dry the cellulose aerogel, and finally the in-situ growth ZIF-L / cellulose composite aerogel is obtained.

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