Preparation method of eutectic solvent-based nanocellulose composite aerogel

Abstract

The invention discloses a preparation method of deep-eutectic solvent-based nano lignocellulose composite aerogel, and belongs to the technical field of biomass nano cellulose aerogel preparation. Lignin and nanocellulose components are separated from peanut shells by utilizing a ternary eutectic solvent, the eutectic solvent is combined as a component of the aerogel, and chitosan and polyvinyl alcohol are added, so that the composite aerogel with excellent performance is prepared. The preparation method is simple, the mechanical performance and the structural performance of the composite aerogel are remarkably improved on the basis that the eutectic solvent is combined with the nanocellulose and / or the lignin to serve as components of the aerogel, and a basis is provided for application of the aerogel in various fields due to the excellent performance of the aerogel. Meanwhile, the used deep-eutectic solvent is green and environment-friendly, the nano lignocellulose also meets the standard of green chemical production, and a new thought is provided for high-value utilization of the deep-eutectic solvent nano lignocellulose and preparation of a multifunctional gel material.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass nanocellulose aerogel preparation, and particularly relates to a method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel. Background Art

[0002] Aerogel is an ultra-light solid material with a nanoporous structure. It is known as "solid smoke" or "frozen smoke" due to its unique physical and chemical properties. It is made by removing the liquid component of gel through special drying technology (such as supercritical drying). The three-dimensional network structure of the gel is retained, and it has extremely high porosity (80% to 99.8%) and extremely low density (as low as 0.001g / cm 3 As one of the most promising new materials of the 21st century, aerogels hold broad application prospects in thermal insulation, energy, environmental protection, and healthcare. With advances in manufacturing technology, further breakthroughs are possible in flexible electronics, smart wearables, and green buildings.

[0003] Nanocellulose, a class of nanoscale biomaterials derived from natural cellulose, exhibits high surface area, high crystallinity, excellent mechanical properties, and biodegradability. It is widely used in composite materials, biomedicine, energy storage, food packaging, and other fields. Lignin, a complex aromatic polymer found in the cell walls of many plants, is the second most abundant biopolymer after cellulose. It is a byproduct of the pulp and paper industry and is also present in agricultural waste streams. Lignin's highly aromatic structure holds great potential for a variety of applications, including as an adsorbent for pollutant removal from wastewater. Nanocellulose and lignin can be separated through pretreatment methods (physical, chemical, physicochemical, and biological). Conventional pretreatment solvents, such as acids, bases, and ionic liquids, have drawbacks for nanocellulose and lignin separation, including lignin coagulation, the generation of pseudolignin during pretreatment, and the formation of high molecular weight, low purity, which hinders lignin upgrading. Furthermore, environmental pollution hinders the recovery of pretreatment solvents.

[0004] Peanut shells are a major byproduct of peanut processing, accounting for 20% to 30% of the total peanut weight. Millions of tons of peanut shells are produced annually worldwide, and traditionally, they are disposed of by incineration or landfill, which wastes resources and pollutes the environment. However, the abundant cellulose and lignin in peanut shells represent a bioresource awaiting development and utilization. Developing a method for preparing peanut shell nano-lignocellulosic composites would not only achieve high-value utilization of crop waste resources, broaden the application areas of peanut shells, and enhance their performance in multiple fields, but also have significant theoretical and practical significance for promoting the innovative development of green preparation technologies and promoting interdisciplinary and industrial applications.

[0005] In addition, the new low eutectic solvent is a type of low-melting-point mixture formed by hydrogen bond donors and hydrogen bond acceptors through intermolecular interactions. It has adjustable physicochemical properties similar to ionic liquids, but with lower cost and simpler preparation. In recent years, low eutectic solvents have shown great potential in the fields of materials science, energy storage, and environmental governance. At present, the preparation of aerogels usually involves a sol-gel method and a drying process. The composite membrane materials prepared by the solution casting method have limitations such as poor permeability and difficulty in transporting nutrients and signal molecules. Therefore, it is very necessary to solve the current technical difficulties and provide a low eutectic solvent-based nano-lignocellulose composite aerogel with excellent performance through the deep combination of low eutectic solvents and aerogels. Summary of the Invention

[0006] In view of the problems that traditional nanocellulose and lignin separation methods generate a large amount of waste, are difficult to recycle chemicals, and have a relatively serious impact on the environment, and the composite membrane materials prepared by the solution casting method have limitations such as poor permeability and difficulty in transporting nutrients and signal molecules. The purpose of the present invention is to provide a method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel. The problem to be solved is how to separate nanocellulose and lignin from peanut shells in a green and efficient manner, so that the pretreatment system costs are reduced and is environmentally friendly; more importantly, nanocellulose and / or lignin and a green solvent - a deep eutectic solvent - are used as components of the aerogel for the preparation of the nano-lignocellulose aerogel, effectively enhancing the performance of the aerogel and improving the shortcomings of the aerogel prepared by the traditional method, such as irregular structure, low porosity, and easy deformation.

[0007] The purpose of the present invention and the solution to the technical problem are achieved by adopting the following technical solutions.

[0008] A method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel comprises the following steps:

[0009] (1) Synthesis of a ternary deep eutectic solvent: Choline chloride, lactic acid, and aluminum chloride are mixed in a certain molar ratio and stirred at a certain temperature until a uniform transparent liquid is formed to obtain a ternary deep eutectic solvent;

[0010] (2) Synthesis of a binary deep eutectic solvent: Glycerol and lactic acid are mixed in a certain molar ratio and stirred at a certain temperature until a uniform transparent liquid is formed to obtain a binary deep eutectic solvent;

[0011] (3) Preparation of peanut shell lignin: Weigh peanut shells and add them to the ternary low eutectic solvent of step (1), and heat them for reaction. After the reaction is completed, cool them to room temperature to obtain a reaction solution; centrifuge the reaction solution to obtain a supernatant, add an ethanol solution to the remaining precipitate, and use suction filtration to wash the precipitate with the ethanol solution, and collect the filtrate; then, combine the filtrate and the supernatant to obtain a mixed solution, collect the concentrated solution after rotary evaporation, add deionized water to the concentrated solution and let it settle, and finally centrifuge to obtain the precipitate, which is the peanut shell lignin;

[0012] (4) Preparation of peanut shell nanocellulose:

[0013] The peanut shell lignin obtained in step (3) is added to water and placed in a dialysis bag, and dialyzed in deionized water (to remove the low eutectic solvent) until the pH of the solution becomes neutral; then the solution is taken out, homogenized, and centrifuged to obtain a turbid supernatant (the turbid supernatant indicates the presence of nanocellulose), and water is added to the remaining precipitate again for homogenization and centrifugation to collect the turbid supernatant; the operation is repeated until the supernatant collected by centrifugation becomes clear and transparent; finally, all the turbid supernatants collected by centrifugation are mixed and freeze-dried to obtain peanut shell nanocellulose;

[0014] (5) Preparation of composite aerogel: Chitosan is dissolved in distilled water, and the binary low eutectic solvent in step (2) is added and stirred continuously until a uniform gel-like substance is formed, i.e., a low eutectic solution gel is obtained; then polyvinyl alcohol solution, nanocellulose and / or lignin are mixed with the low eutectic solution gel, and stirred continuously until the mixed solution becomes uniform and no precipitation is observed, thereby obtaining a gel solution; the gel solution is allowed to stand at room temperature for defoaming, and after defoaming, the gel is poured into a mold, and freeze-dried to obtain a composite aerogel.

[0015] Preferably, the molar ratio of choline chloride, lactic acid and aluminum chloride in step (1) is 1:1:0.1, the constant temperature is 70° C., and the stirring time to form a uniform transparent liquid is 2 hours.

[0016] Preferably, the molar ratio of glycerol to lactic acid in step (2) is 1:1.5, the constant temperature is 70° C., and the stirring time to form a uniform transparent liquid is 2 hours.

[0017] Preferably, the mass ratio of peanut shells to the ternary deep eutectic solvent in step (3) is 1:10, the heating reaction temperature is 100° C., and the reaction time is 3 h.

[0018] Preferably, the centrifugation condition in step (3) is 8000 rpm for 10 min; and the rotary evaporation condition is: temperature 60° C., and rotary evaporation to 1 / 3 of the volume of the mixed solution.

[0019] Preferably, the dosage of the precipitate and the ethanol solution in step (3) is 1-2 g:10 ml; the volume ratio of the concentrate to deionized water is 1:6, and the precipitation time is 12 h.

[0020] Preferably, the lignin in step (4) is added to water, and the dosage relationship of the two is 0.5-1g:10mL; the molecular weight cutoff of the dialysis bag is 8000-14000Da; water is added to the precipitate for homogenization, and the dosage relationship of the precipitate and water is 0.5-1g:10mL, and the homogenization conditions are all: homogenization at 10000rpm for 30min; the centrifugation conditions are all: 4000rpm for 5min.

[0021] Preferably, in step (5), the mass ratio of chitosan, distilled water, binary deep eutectic solvent, polyvinyl alcohol solution, nanocellulose and / or lignin is 1:30:2:5:0.1:0.1, wherein the mass fraction of the polyvinyl alcohol solution is 9%.

[0022] Preferably, the defoaming time at room temperature in step (5) is 12 hours.

[0023] Preferably, the mold in step (5) comprises a polyvinyl alcohol dish; and the freeze-drying conditions are: freeze-drying at -40°C for 48 hours.

[0024] Characterization of peanut shell wood nanocellulose composite aerogels: The chemical structure of the synthesized peanut shell wood nanocellulose composite aerogels was analyzed using Fourier transform infrared spectroscopy. The infrared spectra were recorded in transmission mode at 400–4000 cm -1 Thermogravimetric curves of the peanut shell wood nanocellulose composite aerogels were analyzed using a synchronous thermal analyzer with a temperature ramp of 10°C / min from 25 to 800°C under a nitrogen atmosphere. The microstructure and surface morphology of the aerogels were observed using a scanning electron microscope. The compressive properties of the peanut shell wood nanocellulose composite aerogels were tested using a universal testing machine. The surface contact angle of the aerogels was measured to characterize their surface wettability.

[0025] Beneficial effects of the present invention:

[0026] (1) The ternary low eutectic solvent pretreatment system used in the present invention is simple to operate and has a good pretreatment effect. It can efficiently separate nanocellulose and lignin and achieve efficient dissociation of peanut shell structure. At the same time, the low eutectic solvent prepared by the present invention is not only used as a green solution for the separation of nanocellulose and lignin, but also has achieved significant technical effects in the preparation and functionalization of aerogels. The present invention creatively combines the low eutectic solvent with the aerogel in depth. The introduction of the low eutectic solvent can optimize the gelation process, improve the material properties, can be used as a drying medium to replace supercritical drying, and can also be used as a phase change material carrier to construct smart aerogels and give the aerogels special functions (such as flame retardancy, conductivity, adsorption, etc.). In addition, its preparation conditions are mild, the operation is simple, the cost is low, and the pollution is small. The low eutectic solvent can also be recovered by methods such as rotary evaporation, so that it can be recycled. It is environmentally friendly, meets the production standards of green chemistry, has good practical application value, and is suitable for industrial production.

[0027] (2) The low eutectic solvent-based nano-lignocellulose composite aerogel prepared by the present invention has excellent mechanical properties. The addition of lignin significantly enhances the compressive strength of the composite aerogel, and its value can reach 1.95 MPa.

[0028] (3) The low eutectic solvent-based nano-lignocellulose composite aerogel prepared by the present invention presents a supramolecular skeleton-type 3D network porous structure with a smaller density and a larger porosity.

[0029] (4) The low eutectic solvent-based nano-lignocellulose composite aerogel prepared by the present invention is lightweight and has an extremely low density. The addition of wood nanocellulose improves the surface wettability of the aerogel, thereby expanding its application range.

[0030] (5) The low eutectic solvent-based nano-lignocellulose composite aerogel prepared by the present invention has good chemical structure and thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 1 is a microstructure diagram of the low eutectic solvent-based nano-lignocellulose composite aerogel in Comparative Example 1 (A) and Comparative Example 2 (B).

[0032] Figure 2 1 is a microstructure diagram of the low eutectic solvent-based nano-lignocellulose composite aerogel in Example 1 (A), Example 2 (B), and Example 3 (C).

[0033] Figure 3 These are the compression curves of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1-2 and Examples 1-3.

[0034] Figure 4This is the water contact angle test result of the low eutectic solvent-based nano-lignocellulose composite aerogel in Comparative Example 1.

[0035] Figure 5 This is the water contact angle test result of the low eutectic solvent-based nano-lignocellulose composite aerogel in Comparative Example 2.

[0036] Figure 6 These are the water contact angle test results of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Examples 1, 2, and 3.

[0037] Figure 7 These are the results of characterizing the lightweight properties of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1-2 and Examples 1-3.

[0038] Figure 8 It is a graph showing the infrared spectra of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1-2 and Examples 1-3.

[0039] Figure 9 Graph showing the thermal stability test results of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1-2 and Examples 1-3. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described in the present invention are only for describing particular embodiments and are not intended to limit the present invention. Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art in the art. Although the present invention has only described preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] Example 1:

[0045] (1) Synthesis of a ternary deep eutectic solvent: Choline chloride, lactic acid, and aluminum chloride (AlCl3·6H2O) were mixed in a molar ratio of 1:1:0.1 and stirred at 70°C until a homogeneous transparent liquid was formed (stirring time: 2 h) to obtain a ternary deep eutectic solvent;

[0046] (2) Synthesis of binary deep eutectic solvent: Glycerol and lactic acid were mixed in a molar ratio of 1:1.5 and stirred at 70°C until a homogeneous transparent liquid was formed (stirring time 2 h) to obtain a binary deep eutectic solvent;

[0047] (3) Preparation of peanut shell lignin: Weigh 1g of peanut shell and 10g of ternary low eutectic solvent, mix the two and place them in a glass reaction tube, react at 100°C for 3h and then cool to room temperature to obtain a reaction solution; centrifuge the reaction solution at 8000rpm for 10min in a high-speed centrifuge, pour out the supernatant, and add 90% ethanol solution to the remaining precipitate in a dosage relationship of 1g:10mL, wash the precipitate in the centrifuge tube by suction filtration, collect the filtrate after washing and combine the filtrate and the supernatant after centrifugation to obtain a mixed solution, remove the low eutectic solvent and ethanol by rotary evaporation at 60°C, collect the concentrated solution (1 / 3 of the volume of the mixed solution) after rotary evaporation, and add deionized water to the concentrated solution in a volume ratio of 1:6 and let it stand for 12h to obtain a precipitate, and finally centrifuge to separate the precipitate, which is lignin;

[0048] (4) Preparation of peanut shell nanocellulose: The peanut shell lignin in step (3) was added to water at a dosage of 1 g:10 mL, placed in a dialysis bag of 8000-14000 Da, and dialyzed in deionized water to remove the low eutectic solvent until the pH of the solution became neutral; then the solution was taken out and homogenized at 10000 rpm for 30 min using a high-speed homogenizer, and the turbid supernatant was collected by centrifugation (the turbid supernatant indicates the presence of nanocellulose); and water was added to the remaining precipitate again at a dosage of 1 g:10 mL, homogenized at 10000 rpm for 30 min, and the turbid supernatant was collected by centrifugation; this operation was repeated until the supernatant collected by centrifugation became clear and transparent, and the centrifugation conditions were all 4000 rpm for 5 min; finally, all the collected turbid supernatants were mixed and freeze-dried to obtain peanut shell nanocellulose;

[0049] (5) Preparation of peanut shell lignin composite aerogel: 1 g of chitosan was dissolved in 30 g of distilled water. Subsequently, 2 g of the binary eutectic solvent in step (2) was added and stirred until a uniform gel-like substance was formed to obtain a binary eutectic solution gel. A polyvinyl alcohol solution with a mass fraction of 9% was then prepared; then 5 g of the polyvinyl alcohol solution and 0.1 g of lignin were added to the binary eutectic solution gel and mixed. The mixture was stirred continuously until the mixed solution became uniform and no precipitation was observed to obtain a gel solution. The gel solution was placed at room temperature for 12 h to eliminate bubbles in the gel. The gel was poured into a polyvinyl alcohol plate (diameter 50 mm) and freeze-dried (-40°C, 48 h) to obtain a peanut shell lignin composite aerogel. The aerogel was placed in a desiccator for storage and recorded as CS-PVA-DES-LN.

[0050] Example 2:

[0051] (1) Synthesis of a ternary deep eutectic solvent: Choline chloride, lactic acid, and aluminum chloride (AlCl3·6H2O) were mixed in a molar ratio of 1:1:0.1 and stirred at 70°C to form a homogeneous transparent liquid (stirring time: 2 h) to obtain a ternary deep eutectic solvent;

[0052] (2) Synthesis of binary deep eutectic solvent: Glycerol and lactic acid were mixed in a molar ratio of 1:1.5 and stirred at 70°C to form a homogeneous transparent liquid (stirring time 2 h) to obtain a binary deep eutectic solvent;

[0053] (3) Preparation of peanut shell lignin: Weigh 1g of peanut shell and 10g of ternary low eutectic solvent, mix the two and place them in a glass reaction tube, react at 100°C for 3h and then cool to room temperature to obtain a reaction solution; centrifuge the reaction solution at 8000rpm for 10min in a high-speed centrifuge, pour out the supernatant, and add 90% ethanol solution to the remaining precipitate in a dosage relationship of 1g:10mL, wash the precipitate in the centrifuge tube by suction filtration, collect the filtrate after washing and combine the filtrate and the supernatant after centrifugation to obtain a mixed solution, remove the low eutectic solvent and ethanol by rotary evaporation at 60°C, collect the concentrated solution (1 / 3 of the volume of the mixed solution) after rotary evaporation, and add deionized water to the concentrated solution in a volume ratio of 1:6 and let it stand for 12h to obtain a precipitate, and finally centrifuge to separate the precipitate, which is lignin;

[0054] (4) Preparation of peanut shell nanocellulose: The lignin in step (3) was added to water at a dosage of 1 g:10 mL, placed in a dialysis bag of 8000-14000 Da, and dialyzed in deionized water to remove the low eutectic solvent until the pH of the solution became neutral; then the solution was taken out and homogenized at 10000 rpm for 30 min using a high-speed homogenizer, and the turbid supernatant was collected by centrifugation (the turbid supernatant indicates the presence of nanocellulose); and water was added to the remaining precipitate at a dosage of 1 g:10 mL again, homogenized at 10000 rpm for 30 min, and the turbid supernatant was collected by centrifugation; this operation was repeated until the supernatant collected by centrifugation became clear and transparent, and the centrifugation conditions were all 4000 rpm for 5 min; finally, all the collected turbid supernatants were mixed and freeze-dried to obtain peanut shell nanocellulose;

[0055] (5) Preparation of peanut shell nanocellulose aerogel: 1 g of chitosan was dissolved in 30 g of distilled water. Subsequently, 2 g of the binary eutectic solvent in step (2) was added and stirred until a uniform gel-like substance was formed to obtain a binary eutectic solution gel. A polyvinyl alcohol solution with a mass fraction of 9% was then prepared; 5 g of the polyvinyl alcohol solution and 0.1 g of nanocellulose were added to the binary eutectic solution gel and mixed. The mixture was stirred continuously until the mixed solution became uniform and no precipitation was observed to obtain a gel solution. The gel solution was placed at room temperature for 12 h to eliminate bubbles in the gel. The gel was poured into a polyvinyl alcohol plate (diameter 50 mm) and freeze-dried (-40°C, 48 h) to obtain peanut shell nanocellulose aerogel, which was placed in a desiccator for storage and recorded as CS-PVA-DES-NC.

[0056] Example 3:

[0057] (1) Synthesis of a ternary deep eutectic solvent: Choline chloride, lactic acid, and aluminum chloride (AlCl3·6H2O) were mixed in a molar ratio of 1:1:0.1 and stirred at 70°C to form a homogeneous transparent liquid (stirring time: 2 h) to obtain a ternary deep eutectic solvent;

[0058] (2) Synthesis of binary deep eutectic solvent: Glycerol and lactic acid were mixed in a molar ratio of 1:1.5 and stirred at 70°C to form a homogeneous transparent liquid (stirring time 2 h) to obtain a binary deep eutectic solvent;

[0059] (3) Preparation of peanut shell lignin: Weigh 1g of peanut shell and 10g of ternary low eutectic solvent, mix the two and place them in a glass reaction tube, react at 100°C for 3h and then cool to room temperature to obtain a reaction solution; centrifuge the reaction solution at 8000rpm for 10min in a high-speed centrifuge, pour out the supernatant, and add 90% ethanol solution to the remaining precipitate in a dosage relationship of 1g:10mL, wash the precipitate in the centrifuge tube by suction filtration, collect the filtrate after washing and combine the filtrate and the supernatant after centrifugation to obtain a mixed solution, remove the low eutectic solvent and ethanol by rotary evaporation at 60°C, collect the concentrated solution (1 / 3 of the volume of the mixed solution) after rotary evaporation, and add deionized water to the concentrated solution in a volume ratio of 1:6 and let it stand for 12h to obtain a precipitate, and finally centrifuge to separate the precipitate, which is lignin;

[0060] (4) Preparation of peanut shell nanocellulose: The lignin in step (3) was added to water at a dosage of 1 g:10 mL, placed in a dialysis bag of 8000-14000 Da, and dialyzed in deionized water to remove the low eutectic solvent until the pH of the solution became neutral; then the solution was taken out and homogenized at 10000 rpm for 30 min using a high-speed homogenizer, and the turbid supernatant was collected by centrifugation (the turbid supernatant indicates the presence of nanocellulose); and water was added to the remaining precipitate at a dosage of 1 g:10 mL again, homogenized at 10000 rpm for 30 min, and the turbid supernatant was collected by centrifugation; this operation was repeated until the supernatant collected by centrifugation became clear and transparent, and the centrifugation conditions were all 4000 rpm for 5 min; finally, all the collected turbid supernatants were mixed and freeze-dried to obtain peanut shell nanocellulose;

[0061] (5) Preparation of low eutectic solvent-based nano-lignocellulose composite aerogel: 1 g of chitosan was dissolved in 30 g of distilled water. Subsequently, 2 g of the binary low eutectic solvent in step (2) was added and stirred until a uniform gel-like substance was formed to obtain a binary low eutectic solution gel. A polyvinyl alcohol solution with a mass fraction of 9% was then prepared; then 5 g of the polyvinyl alcohol solution, 0.1 g of lignin, and 0.1 g of nanocellulose were added to the binary low eutectic solution gel and mixed. The mixture was stirred continuously until the mixed solution became uniform and no precipitation was observed to obtain a gel solution. The gel solution was placed at room temperature for 12 h to eliminate bubbles in the gel. The gel was poured into a polyvinyl alcohol plate (diameter 50 mm) and freeze-dried (-40°C, 48 h) to obtain a low eutectic solvent-based nano-lignocellulose composite aerogel. The aerogel was placed in a desiccator for storage and was recorded as CS-PVA-DES-LN-NC.

[0062] Comparative Example 1:

[0063] (1) Synthesis of a binary deep eutectic solvent: Glycerol and lactic acid were mixed in a molar ratio of 1:1.5 and stirred at 70°C until a homogeneous transparent liquid was formed (stirring time 2 h) to obtain a binary deep eutectic solvent;

[0064] (2) Preparation of chitosan-polyvinyl alcohol composite aerogel: 1 g of chitosan was dissolved in 30 g of distilled water. Subsequently, 2 g of the binary eutectic solvent in step (2) was added and stirred until a uniform gel-like substance was formed to obtain a binary eutectic solution gel. A polyvinyl alcohol solution with a mass fraction of 9% was then prepared; 5 g of the polyvinyl alcohol solution was then added to the binary eutectic solution gel and mixed. The mixture was stirred continuously until the mixed solution became uniform and no precipitation was observed to obtain a gel solution. The gel solution was placed at room temperature for 12 h to eliminate bubbles in the gel. The gel was poured into a polyvinyl alcohol plate (diameter 50 mm) and freeze-dried (-40°C, 48 h) to obtain a chitosan-polyvinyl alcohol composite aerogel, which was placed in a desiccator for storage and recorded as CS-PVA-DES.

[0065] Comparative Example 2:

[0066] (1) Synthesis of a binary deep eutectic solvent: Glycerol and lactic acid were mixed in a molar ratio of 1:1.5 and stirred at 70°C until a homogeneous transparent liquid was formed (stirring time 2 h) to obtain a binary deep eutectic solvent;

[0067] (2) Preparation of chitosan-deep eutectic solvent composite aerogel: 1 g of chitosan was dissolved in 30 g of distilled water. Subsequently, 2 g of the binary depleted eutectic solvent from step (1) was added and stirred until a uniform gel-like substance was obtained and no precipitation was observed, thereby obtaining a gel solution. The gel solution was placed at room temperature for 12 h to eliminate bubbles in the gel. The gel was poured into a polyvinyl alcohol plate (50 mm in diameter) and freeze-dried to obtain a chitosan-deep eutectic solvent composite aerogel, which was placed in a desiccator for storage and recorded as CS-DES.

[0068] S1. Test the microstructure of composite aerogel:

[0069] Figure 1 The SEM images of deep eutectic solvent-based nano-lignocellulose composite aerogels are shown. It can be observed that the CS-DES (Comparative Example 2) composite aerogel has essentially no porous structure, while the CS-PVA-DES (Comparative Example 1) composite aerogel exhibits a non-uniform pore structure and uneven pore size distribution. Figure 2The figure is a microscopic structure diagram of the low eutectic solvent-based nano-lignocellulose composite aerogel in Examples 1-3; it can be seen from the figure that the low eutectic solvent-based nano-lignocellulose composite aerogel in Examples 1-3 is composed of a multi-scale pore structure that is stacked and interwoven with each other. Among them, the porous structure in the CS-PVA-DES-LN-NC composite aerogel structure is more evenly distributed, the macropore defects are reduced, and the pore wall thickness is increased, indicating that under the action of the low eutectic solvent, the addition of nanocellulose enhances the aerogel's ability to resist collapse, the addition of lignin fills the gaps between cellulose fibers, and improves the fracture toughness of the aerogel. The synergistic effect of nanocellulose and lignin further enhances the aerogel's ability to resist collapse, allowing the aerogel to form a honeycomb pore skeleton structure. The porous structure presented by the low eutectic solvent-based nano-lignocellulose composite aerogel gives it unique physical and chemical properties, such as ultra-light characteristics, high specific surface area and adsorption performance, adjustable thermal properties, and biocompatibility and drug carrier capabilities. The porous structure is the "functional engine" of aerogel. The present invention effectively improves the pore characteristics (such as gradient pores and hierarchical pores) through the design of a low eutectic solvent base, which can realize cross-field applications from environmental governance to energy storage.

[0070] S2. Testing the mechanical properties of the composite aerogel:

[0071] Figure 3 Figure 2 shows the compressive stress-strain curves of the products in Comparative Examples 1-2 and Examples 1-3 at 80% strain. The composite aerogels all exhibit the three-stage deformation characteristics (elastic zone, yield zone, and densification zone) characteristic of porous materials. Compared with CS-PVA-DES (Comparative Example 1) and CS-DES (Comparative Example 2), the compression modulus of the composite aerogels in Examples 1-3 was improved. Compared with CS-PVA-DES (Comparative Example 1) and CS-DES (Comparative Example 2), the compressive strength of the composite aerogels in CS-PVA-DES-LN (Example 1) and CS-PVA-DES-LN-NC (Example 3) was particularly significant, increasing to 1.95 and 1.81 MPa, respectively. This increase in compressive strength may be due to a closer association between cellulose and lignin within the aerogels or a higher bulk density. Furthermore, the introduction of polyvinyl alcohol, a hydrogen bond enhancer, also enhances stress transfer between aerogel fibers, creating a synergistic effect that reduces deformation and thus strengthens the interfacial interactions of the aerogels.

[0072] S3. Testing the surface wettability of the composite aerogel:

[0073] Figure 4-6The water contact angle test results of the deep eutectic solvent-based nano-lignocellulose composite aerogels in the comparative examples and examples are shown; among them, the water contact angles of the CS-DES (Comparative Example 2) and CS-PVA-DES (Comparative Example 1) composite aerogels when just dropped with water droplets are 96.6° ( Figure 5 A) and 95.9°( Figure 4 A), after 5 seconds, the water droplets gradually penetrate into the aerogel, such as Figure 4 B and Figure 5 As shown in Figure B, it shows that the CS-DES (Comparative Example 2) and CS-PVA-DES (Comparative Example 1) composite aerogels are hydrophilic. This may be because chitosan (containing amino groups / -NH2 and hydroxyl groups / -OH) and polyvinyl alcohol (containing a large amount of -OH) contain strong polar groups that form hydrogen bonds with water molecules. When no hydrophobic modification is performed, the porous structure of the aerogel further enhances water absorption through capillary action. However, after the CS-PVA-DES-LN, CS-PVA-DES-NC and CS-PVA-DES-LN-NC composite aerogels come into contact with water droplets for 5 seconds, the water droplets still maintain a spherical shape and the contact angle remains unchanged, as shown in Figure 3. Figure 6 As shown in Figure 5, the hydrophilic properties of the composite aerogels are effectively improved based on the synergistic effect of the deep eutectic solvent base and nanocellulose and lignin.

[0074] S4. Testing the lightweight properties of composite aerogels:

[0075] Figure 7 The lightness characterization results of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1 (A), 2 (B) and Examples 1 (C), 2 (D), and 3 (E) are shown; Figure 7 As shown in Figure 4, the composite aerogels prepared based on the low eutectic solvent base can be stably placed on the stamens of peony flowers without any deformation (Figures AE), further demonstrating the ultra-light properties and excellent mechanical adaptability of the composite aerogels. The invention creatively introduces a low eutectic solvent base to achieve the effect of lightweight and extremely low-density composite aerogels; the low eutectic solvent also induces the nano-lignocellulose to form an elastic cross-linked network, realizing a multi-level pore structure of the composite aerogel (such as a macropore-micropore gradient distribution), further dispersing contact stress and avoiding stress concentration.

[0076] In addition, low eutectic solvents can also reduce the surface energy of nano-lignocellulose, making the interface interaction between the aerogel and the pistil weak (no adhesion or penetration), avoiding damage to the microstructure of the pistil; at the same time, the green synthesis process of low eutectic solvents (non-volatile toxicity) may retain the open-pore structure of the aerogel, avoid shrinkage and embrittlement, and thus maintain its soft properties.

[0077] S6. Test the chemical structure of the composite aerogel:

[0078] Figure 8 The infrared spectra of the deep eutectic solvent-based nano-lignocellulose composite aerogels in Comparative Examples 1 and 2 and Examples 1, 2, and 3 are shown; Figure 8 As shown, the deep eutectic solvent-based nano-lignocellulose composite aerogel is -1 The broad peak formed near the hydroxyl group (-OH) is mainly attributed to the presence of -OH. The composite aerogel in Comparative Example 1 is mainly attributed to the superposition of the hydroxyl group (-OH) and amino group (-NH2) of chitosan. The composite aerogel in Comparative Example 2 is attributed to the stretching vibration of the intermolecular / internal hydroxyl hydrogen bonds of polyvinyl alcohol in addition to chitosan. The composite aerogel in the embodiment, in addition to the above chemical structure, also includes the stretching vibration of the intermolecular / internal hydrogen bonds of cellulose and the stretching vibration of the free phenolic hydroxyl groups in lignin.

[0079] In addition, the composite aerogel in Comparative Example 1 has a -1 The absorption peak at 1582 cm is attributed to the stretching vibration of C—O in the deep eutectic solvent. -1 The peak at is caused by the shear vibration of -NH2 in chitosan. Example 1 The presence of lignin aromatic ring C=C stretching vibration peak (1600-1595cm -1 ) and CH3 asymmetric bending vibrations of methoxy and methylene (1460-1450cm -1 ) and other characteristic absorption peaks; while in Example 2, the composite aerogel contains cellulose CO stretching vibration (1050-1030cm -1 ) and β-glycosidic bond characteristic peaks (890–895 cm -1 ); The FT-IR absorption peaks of the composite aerogel in Example 3 are all superimposed by chitosan, deep eutectic solvent, polyvinyl alcohol and nano-lignocellulose, indicating that the composite aerogel is formed by hydrogen bonding of several substances rather than chemical reaction.

[0080] S7. Test the thermal stability of the composite aerogel:

[0081] Figure 9 1 and 2 and Examples 1, 2, 3 in which the deep eutectic solvent-based nano-lignocellulose composite aerogels were subjected to thermal stability tests; Figure 9As shown in Figure (a) and (b), the TG curves of the deep eutectic solvent-based nanocellulose composite aerogels are divided into three to five weight loss stages. The first stage, from room temperature to 150°C, is primarily due to the volatilization of water and residual solvent in the aerogel. The second stage, from 150°C to 300°C, is primarily due to the decomposition of unstable components in the aerogel, such as the deep eutectic solvent components. For the aerogel in Example 2, this stage saw the β-1,4 glycosidic bonds of the nanocellulose begin to break. For the aerogels with added polyvinyl alcohol, condensation of the polyvinyl alcohol side groups occurs during this stage. The third stage, from 300°C to 600°C, primarily involves the decomposition of the cellulose backbone and the combined decomposition of chitosan units. For the composite aerogels with added polyvinyl alcohol, polyvinyl alcohol chain scission also occurs during this stage. The composite aerogels in Examples 1 and 3 experienced less mass loss during this stage. The improved thermal stability of the aerogels with the addition of lignin is primarily due to the enhanced interaction and crosslinking between lignin and chitosan. First, hydrogen bonding and electrostatic interactions occur between chitosan and lignin, further stabilizing the aerogel structure. These interactions promote cross-linking between aerogel molecules, thereby increasing the aerogel's stability and high-temperature resistance. Second, the introduction of lignin molecules increases the number of aromatic structures in the aerogel, effectively preventing thermal decomposition and oxidation reactions, thereby improving the aerogel's thermal stability. Finally, the cross-linking of chitosan and lignin enhances the structural stability and thermal stability of the aerogel. This cross-linking forms a porous aerogel structure with a large specific surface area and pore size distribution, effectively preventing thermal decomposition and oxidation reactions. The fourth stage, 600-800°C, is primarily characterized by carbonization and ash residue. The curve at this stage tends to be flat, and the mass loss is essentially flat, indicating that the residual components in the sample are less decomposed and the weight loss tends to be stable.

[0082] Therefore, the interaction and cross-linking between chitosan and nano-lignocellulose can significantly improve the thermal stability and high temperature resistance of the aerogel, so that the composite aerogel in the embodiment has better thermal stability than the aerogel in the comparative example.

[0083] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification has described the present invention in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel, characterized in that: The specific steps are as follows: (1) Synthesis of a ternary deep eutectic solvent: Choline chloride, lactic acid, and aluminum chloride are mixed in a certain molar ratio and stirred at a certain temperature until a uniform transparent liquid is formed to obtain a ternary deep eutectic solvent; (2) Synthesis of a binary deep eutectic solvent: Glycerol and lactic acid are mixed in a certain molar ratio and stirred at a certain temperature until a uniform transparent liquid is formed to obtain a binary deep eutectic solvent; (3) Preparation of peanut shell lignin: Weigh peanut shells and add them to the ternary low eutectic solvent of step (1), and heat them for reaction. After the reaction is completed, cool them to room temperature to obtain a reaction solution; centrifuge the reaction solution to obtain a supernatant, add an ethanol solution to the remaining precipitate, and use suction filtration to wash the precipitate with the ethanol solution, and collect the filtrate; then, combine the filtrate and the supernatant to obtain a mixed solution, collect the concentrated solution after rotary evaporation, add deionized water to the concentrated solution and let it settle, and finally centrifuge to obtain the precipitate, which is the peanut shell lignin; (4) Preparation of peanut shell nanocellulose: The peanut shell lignin obtained in step (3) is added to water and placed in a dialysis bag, and dialyzed in deionized water (to remove the deep eutectic solvent) until the pH of the solution becomes neutral; Then, the solution is taken out, homogenized, and centrifuged to obtain a turbid supernatant, and water is added to the remaining precipitate again, homogenized, and centrifuged to collect the turbid supernatant; the operation is repeated until the supernatant collected by centrifugation becomes clear and transparent; finally, all the turbid supernatants collected by centrifugation are mixed and freeze-dried to obtain peanut shell nanocellulose; (5) Preparation of composite aerogel: Chitosan is dissolved in distilled water, and the binary low eutectic solvent in step (2) is added and stirred continuously until a uniform gel-like substance is formed, i.e., a low eutectic solution gel is obtained; then polyvinyl alcohol solution, nanocellulose and / or lignin are mixed with the low eutectic solution gel, and stirred continuously until the mixed solution becomes uniform and no precipitation is observed, thereby obtaining a gel solution; the gel solution is allowed to stand at room temperature for defoaming, and after defoaming, the gel is poured into a mold, and freeze-dried to obtain a composite aerogel.

2. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The molar ratio of choline chloride, lactic acid and aluminum chloride in step (1) is 1:1:0.1, the constant temperature is 70° C., and the stirring time to form a uniform transparent liquid is 2 hours.

3. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The molar ratio of glycerol to lactic acid in step (2) is 1:1.5, the constant temperature is 70° C., and the stirring time to form a uniform transparent liquid is 2 hours.

4. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The mass ratio of peanut shells to the ternary deep eutectic solvent in step (3) is 1:10, the heating reaction temperature is 100° C., and the reaction time is 3 h.

5. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The centrifugation condition in step (3) is 8000 rpm for 10 min; the rotary evaporation condition is: temperature 60° C., and rotary evaporation until the volume of the mixed solution is 1 / 3.

6. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The dosage of the precipitate and the ethanol solution in step (3) is 1-2 g:10 ml; the volume ratio of the concentrate to deionized water is 1:6, and the precipitation time is 12 h.

7. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The lignin described in step (4) is added to water, and the dosage relationship of the two is 0.5-1g:10mL; the molecular weight cutoff of the dialysis bag is 8000-14000Da; water is added to the precipitate for homogenization, and the dosage relationship of the precipitate and water is 0.5-1g:10mL, and the homogenization conditions are all: homogenization at 10000rpm for 30min; the centrifugation conditions are all: 4000rpm for 5min.

8. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The mass ratio of chitosan, distilled water, binary low eutectic solvent, polyvinyl alcohol solution, nanocellulose and / or lignin in step (5) is 1:30:2:5:0.1:0.1, wherein the mass fraction of the polyvinyl alcohol solution is 9%.

9. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The defoaming time at room temperature in step (5) is 12 hours.

10. The method for preparing a deep eutectic solvent-based nano-lignocellulose composite aerogel according to claim 1, characterized in that: The mold in step (5) includes a polyvinyl alcohol plate; the freeze-drying conditions are: freeze-drying at -40°C for 48 hours.

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