Bifunctionalized chitosan / nanosilica composite aerogels, methods and uses thereof

Abstract

The application discloses a kind of bifunctional chitosan / nano-silica composite aerogel and method and application, belong to wastewater treatment technical field.The preparation method disclosed in the application comprises the following steps: carboxymethylation modification is carried out to chitosan to obtain carboxymethyl chitosan;Carboxymethyl chitosan is modified by amination to obtain bifunctional chitosan;Bifunctional chitosan is mixed with deionized water to obtain a bifunctional chitosan solution;Nano-SiO2 dispersion liquid is added dropwise to the bifunctional chitosan solution, and a composite sol is obtained after stirring and adding a crosslinking agent;The composite sol is sequentially subjected to gelation and aging treatment, followed by solvent replacement and drying treatment, to obtain a bifunctional chitosan / nano-silica composite aerogel.The method solves the technical problem that existing aerogels cannot simultaneously and efficiently remove organic matter and heavy metal ions in wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a bifunctionalized chitosan / nano silica composite aerogel, its method, and its application. Background Technology

[0002] Wastewater generated during the dyeing and printing industry is characterized by high color intensity (typically >1000 times), high chemical oxygen demand, and the presence of toxic and harmful substances such as azo dyes and hexavalent chromium. Traditional wastewater treatment methods mainly include physical adsorption, chemical oxidation, and biological treatment, but these methods all have limitations. Physical adsorption methods, such as using activated carbon as an adsorbent, are simple to operate, but have limited adsorption capacity (usually not exceeding 200 mg / g) and are difficult to regenerate, resulting in high operating costs. Chemical oxidation methods, such as Fenton's reagent treatment, can effectively degrade organic matter, but the treatment cost is high (approximately 50 yuan / ton of wastewater) and easily produces secondary pollutants such as iron sludge, increasing the complexity and cost of subsequent treatment. Biological treatment methods are environmentally friendly and economical, but their treatment efficiency drops significantly (more than 50%) when treating high-salinity wastewater (e.g., salinity exceeding 3%), limiting their application. Chitosan (CS), as a natural high-molecular-weight polysaccharide, shows great potential in the field of wastewater treatment due to its good biocompatibility and adsorption properties. However, pure chitosan aerogel suffers from poor mechanical properties (compressive strength typically below 0.1 MPa) and easy solubility (swelling rate exceeding 200% at pH values ​​greater than 6.5), which greatly limits its application in practical wastewater treatment. Nano-silica (SiO2) particles, due to their high specific surface area (200-400 m²), offer a more suitable alternative. 2 With its excellent physicochemical stability (g / g), chitosan is considered an ideal additive for enhancing the performance of composite materials. Although there has been some progress in the research on the composite of chitosan and nanomaterials, most studies have focused on the introduction of single functional groups or simple physical mixing, lacking in-depth research on the multifunctional modification of chitosan and its synergistic effect with nanomaterials.

[0003] Specifically, current chitosan modification techniques are mostly limited to single functionalization treatments such as carboxymethylation or amination. While these methods can improve the adsorption performance of chitosan to some extent, they cannot simultaneously and efficiently remove multiple pollutants from wastewater, such as organic matter and heavy metal ions. Furthermore, existing research has not fully explored the synergistic effects between chitosan and nanomaterials to further enhance the overall performance of composite materials. Currently, research on chitosan-nanomaterial composites focuses primarily on the introduction of single functional groups (such as carboxymethylation alone) or simple physical mixing, lacking in-depth research on the multifunctional modification of chitosan and its synergistic effects with nanomaterials. Summary of the Invention

[0004] The purpose of this invention is to provide a bifunctionalized chitosan / nano silica composite aerogel, its method, and its application, in order to solve the technical problem that existing aerogel materials are unable to simultaneously and efficiently remove organic matter and heavy metal ions from wastewater due to the single functional groups and lack of synergistic effects of nanomaterials.

[0005] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a bifunctionalized chitosan / nano-silica composite aerogel, comprising the following steps: Chitosan was modified by carboxymethylation to obtain carboxymethyl chitosan; Aminolation modification of carboxymethyl chitosan yields bifunctionalized chitosan; Bifunctionalized chitosan was mixed with deionized water to obtain a bifunctionalized chitosan solution. Nano-SiO2 dispersion was added dropwise to a bifunctionalized chitosan solution, stirred, and then a crosslinking agent was added to obtain a composite sol. The composite sol was subjected to gelation and aging treatments in sequence, followed by solvent replacement and drying treatments to obtain a bifunctional chitosan / nano silica composite aerogel.

[0006] Furthermore, the specific steps for carboxymethylation modification of chitosan are as follows: Chitosan was dissolved in acetic acid solution, followed by the addition of chloroacetic acid and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain carboxymethyl chitosan.

[0007] Furthermore, the ratio of chitosan, acetic acid solution, and chloroacetic acid used is 4~6 g: 80~120 mL: 2~4 g; The acetic acid solution is obtained by mixing acetic acid and deionized water; the volume concentration of the acetic acid solution is 1%~2%; Chloroacetic acid was then added, and the reaction was carried out at a temperature of 55-65 °C for 3-5 h with stirring. The pH value during the reaction was 4.5.

[0008] Furthermore, the degree of carboxymethylation of the carboxymethyl chitosan is 30%~50%; The degree of amination of the bifunctionalized chitosan is 20% to 40%.

[0009] Furthermore, the specific steps for amylating carboxymethyl chitosan are as follows: Carboxymethyl chitosan was dissolved in deionized water, followed by the addition of ethylenediamine and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain bifunctionalized chitosan.

[0010] Furthermore, the ratio of carboxymethyl chitosan, deionized water, and ethylenediamine is 1-3 g: 40-60 mL: 1-3 mL; The ethylenediamine was then added, and the reaction was carried out at a temperature of 45-55 °C for 5-7 h with stirring. The pH value during the reaction was 7.0-8.0.

[0011] Furthermore, the concentration of the bifunctionalized chitosan solution is 1~5 g / 100mL; The volume ratio of the nano-SiO2 dispersion, the bifunctionalized chitosan solution, and the crosslinking agent is 5~40:40~60:0.1~1; The preparation process of the nano-SiO2 dispersion is as follows: Nano-SiO2 particles are added to deionized water and then uniformly dispersed by ultrasonic treatment and mechanical stirring to obtain a nano-SiO2 dispersion; the ratio of nano-SiO2 particles to deionized water is 1~4 g: 40~60 mL. The crosslinking agent is an aqueous solution of glutaraldehyde, and the volume concentration of the aqueous solution of glutaraldehyde is 25%.

[0012] Furthermore, the gelation involves placing the composite sol in a mold and allowing it to stand for 24–48 hours; the aging treatment is carried out at 40–50 °C. The solvent replacement is performed using an organic solvent; the drying process is supercritical CO2 drying or freeze drying.

[0013] The present invention also discloses a bifunctional chitosan / nano silica composite aerogel, characterized in that the bifunctional chitosan / nano silica composite aerogel is prepared by the above preparation method and has a compressive strength of 0.5 MPa or higher.

[0014] This invention also discloses the application of the above-mentioned bifunctionalized chitosan / nano-silica composite aerogel in the adsorption of organic matter and heavy metal ions in dyeing and printing industrial wastewater. The bifunctionalized chitosan / nano-silica composite aerogel is effective in adsorbing Cu in dyeing and printing industrial wastewater. 2+ The removal rate reached 96.8%, and the removal rate of methylene blue from organic matter was 98.2%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a bifunctional chitosan / nano silica composite aerogel. The method involves carboxymethylation and amylation modification of chitosan to obtain bifunctional chitosan. Subsequently, nano-SiO2 particles from a nano-SiO2 dispersion are introduced into the bifunctional chitosan, and a crosslinking agent is used in conjunction to synergistically obtain a bifunctional chitosan / nano silica composite aerogel with a stable three-dimensional network structure. This method utilizes the carboxymethylation modification to introduce carboxymethyl (-COOH) groups, the amylation modification to introduce amino (-NH2) groups, and the synergistic effect of nano-SiO2 particles to form… This method employs a multi-mechanism adsorption approach. Carboxymethyl groups efficiently enrich positively charged pollutants through electrostatic attraction, while amino groups further enhance the binding capacity of heavy metal ions through coordination. Simultaneously, bifunctional modification significantly strengthens intermolecular hydrogen bonding, constructing a hydrogen bond network within the composite aerogel to specifically capture organic molecules. The introduction of nano-SiO2 particles not only provides additional adsorption sites with a high specific surface area but also forms a stable three-dimensional network structure through chemical bonding with chitosan chains (Si-OC crosslinking). This allows for precise control of the nanoparticle mass ratio and particle size, effectively preventing aggregation and achieving a balance between adsorption performance and mechanical strength. Through the synergistic effect of bifunctional groups and nanomaterials, this method effectively solves the technical challenge of existing aerogels simultaneously and efficiently removing organic matter and heavy metal ions from wastewater, achieving highly efficient and deep adsorption of high-color and toxic substances in dyeing and printing wastewater.

[0016] Furthermore, this invention specifies the specific steps and materials used for carboxymethylation modification of chitosan. These precisely controlled conditions ensure the efficient synthesis of carboxymethyl chitosan (CM-CS) and maintain the carboxymethylation degree at a stable level of 30% to 50%, providing a good foundation for subsequent amination modification.

[0017] Furthermore, this invention further specifies the ratio of chitosan, acetic acid solution, and chloroacetic acid, as well as the concentration range of the acetic acid solution. This ratio can optimize reaction efficiency, reduce the generation of by-products, and specify pH control during the reaction process, further ensuring the success rate of carboxymethylation modification and the purity of the product, and reducing subsequent purification costs.

[0018] Furthermore, the present invention defines the range of carboxymethylation degree of carboxymethyl chitosan. The degree of carboxymethylation is crucial for enhancing the adsorption and mechanical properties of the material, ensuring that the material surface has sufficient negative charge density, thereby effectively adsorbing organic pollutants while maintaining the structural stability of the material.

[0019] Furthermore, this invention specifies the specific steps for amylating carboxymethyl chitosan. By introducing ethylenediamine for amylation modification, the material is endowed with new functional amino groups (-NH2). These amino groups can not only bind heavy metal ions through coordination, but also enhance intramolecular and intermolecular hydrogen bonding, providing the possibility for the formation of a stable three-dimensional network structure and significantly improving the adsorption selectivity and mechanical strength of the material.

[0020] Furthermore, the present invention specifically defines the ratio of carboxymethyl chitosan, deionized water and ethylenediamine, as well as the stirring reaction temperature, time and pH value after the addition of ethylenediamine. Precise control of these conditions is crucial for obtaining bifunctionalized chitosan with a suitable degree of amination (20%~40%), which directly affects the material's adsorption capacity for heavy metal ions and organic matter, as well as the material's regeneration and recycling performance.

[0021] Furthermore, the present invention defines the range of amination degree of bifunctionalized chitosan. A suitable amination degree can maximize the adsorption capacity and selectivity of the material while maintaining high mechanical strength to meet the needs of practical applications.

[0022] Furthermore, this invention specifies the dosage ratio of each component and the selection of the crosslinking agent in the preparation process of bifunctional chitosan / nano silica composite aerogel. By precisely controlling the dosage of nano SiO2 dispersion, bifunctional chitosan solution and crosslinking agent, and selecting a suitable crosslinking agent (such as glutaraldehyde aqueous solution), the crosslinking reaction between each component is effectively promoted, forming a stable three-dimensional network structure, which significantly improves the specific surface area and adsorption performance of the material.

[0023] Furthermore, the present invention specifically defines the specific conditions for gelation, solvent replacement, aging treatment, and drying treatment; by precisely controlling the gelation time and temperature, aging treatment conditions, and using supercritical CO2 drying or freeze-drying technology, shrinkage and cracking of the material during the drying process are effectively avoided, maintaining the material's high specific surface area and three-dimensional network structure, thereby ensuring the material's high adsorption performance and mechanical strength.

[0024] The present invention also discloses a bifunctionalized chitosan / nano silica composite aerogel prepared by the above preparation method. This composite aerogel has the advantages of high specific surface area and stable three-dimensional network structure, exhibits efficient and selective adsorption capacity for organic matter and heavy metal ions in wastewater, and has high mechanical strength and excellent regeneration and recycling performance.

[0025] This invention also discloses the application of the above-mentioned bifunctionalized chitosan / nano-silica composite aerogel in the adsorption of organic matter and heavy metal ions in dyeing and printing industrial wastewater. According to relevant experimental results, this bifunctionalized chitosan / nano-silica composite aerogel exhibits good adsorption properties for Cu... 2+The removal rate reaches 96.8%, which is 13.1% higher than that of traditional activated carbon. It also has excellent regeneration performance (retention rate ≥85% after 3 cycles). The removal rate of methylene blue for organic matter is 98.2%. It enhances the adsorption selectivity and affinity of chitosan for organic matter and heavy metal ions. At the same time, combined with the high specific surface area advantage of nano-SiO2 particles in the nano-SiO2 dispersion, it can achieve efficient and deep purification of wastewater. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation process of the bifunctionalized chitosan / nano silica composite aerogel of the present invention. Figure 2 The macroscopic morphology of the bifunctionalized chitosan / nano silica composite aerogel prepared in Example 1 of this invention; Figure 3 This is a scanning electron microscope image of the bifunctionalized chitosan / nano silica composite aerogel prepared in Example 1 of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0029] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0030] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0031] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0032] This invention provides a method for preparing bifunctionalized chitosan / nano-silica composite aerogel, such as... Figure 1 As shown, it includes the following steps: S1: Chitosan was dissolved in acetic acid solution, followed by the addition of chloroacetic acid and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain carboxymethyl chitosan (CM-CS, carboxymethylation degree 30%~50%). The dialyzing time was 72 h, with water changed every 6 h during the dialyzing process. The freeze-drying temperature was -50 ℃ and the time was 48 h. S2: Carboxymethyl chitosan was dissolved in deionized water, followed by the addition of ethylenediamine and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain bifunctionalized chitosan (FC-CS, amination degree of 20%~40%). The dialyzing time was 72 h, with water changed every 6 h during the dialyzing process. The freeze-drying temperature was -50 ℃ and the time was 48 h. The above process can be achieved by using carboxymethyl (-COOH) groups to electrostatically attract and enrich positively charged pollutants, and amino groups (-NH2) to bind heavy metal ions through coordination. Simultaneously, a hydrogen bonding network traps organic molecules (such as azo dyes). The synergistic effect of the bifunctional groups enhances the material's resistance to Cu. 2+ The adsorption selectivity is improved compared to monofunctional materials; S3: Add bifunctionalized chitosan to deionized water to obtain a bifunctionalized chitosan solution; Nano-SiO2 particles were added to deionized water and dispersed uniformly by ultrasonic treatment and mechanical stirring to obtain a nano-SiO2 dispersion. Under stirring conditions, the nano-SiO2 dispersion was slowly added dropwise to the bifunctionalized chitosan solution, and stirring was continued until the mixture was uniform. Then, an appropriate amount of crosslinking agent was added to enhance the structural stability of the aerogel and obtain the composite sol. S4: Transfer the composite sol into a mold and let it stand for a period of time to allow it to gel, forming a wet gel; then, age the wet gel at a specific temperature to further improve the three-dimensional network structure of the aerogel. The wet gel is solvent-displaced using organic solvents such as ethanol to remove moisture and unreacted solvent. Then, the wet gel is converted into a composite aerogel material using supercritical CO2 drying or freeze-drying technology, thus obtaining a bifunctional chitosan / nano silica composite aerogel.

[0033] The components and related terms involved in this invention are defined as follows: CM-CS: Carboxymethyl chitosan; CS: Chitosan; FC-CS: Bifunctionalized chitosan; SiO2: Silicon dioxide.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0036] Example 1 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 5 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 100 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25 ℃) until completely dissolved. Next, slowly add 3.0 g of chloroacetic acid (molecular weight 94.50 g / mol, molar ratio to chitosan units approximately 3:1) and stir. The reaction is carried out in a 60 ℃ water bath with mechanical stirring (150 rpm) for 4 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000~14000 Da) and dialyzed with deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50 ℃, 48°C). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Weigh 2 g of CM-CS (carboxymethylation degree 40%) and place it in a 100 mL beaker. Add 50 mL of deionized water and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add 2 mL of ethylenediamine (density 0.90 g / mL, purity ≥99%, molar ratio of CM-CS carboxyl groups 2:1) and stir the reaction. The reaction is carried out under the conditions of heating in a 50 ℃ water bath and mechanical stirring (200 rpm) for 6 h. During the stirring reaction, the pH value is adjusted dropwise to 7.0~8.0 with 1 mol / L HCl (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (every 6 hours). The water was changed once every h to remove unreacted ethylenediamine and byproducts. The resulting dialysate was then freeze-dried (-50 °C, 48 h) to obtain bifunctionalized chitosan (FC-CS). The degree of amination was determined to be 40% by elemental analysis. Step 3: Dissolve 2 g of bifunctionalized chitosan in 100 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 20 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 10 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 2 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.5 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0037] Figure 2 The image shows the macroscopic morphology of the bifunctionalized chitosan / nano silica composite aerogel prepared in Example 1. It can be seen that the material has a uniform structure and uniform pore size distribution. Figure 3 The image shows a scanning electron microscope (SEM) image of the bifunctionalized chitosan / nano silica composite aerogel obtained in Example 1. The image reveals a clear three-dimensional network structure, with nano-SiO2 particles uniformly distributed within the chitosan matrix, forming a well-developed composite structure. This structure helps increase the specific surface area of ​​the material and improves its adsorption performance. Furthermore, the uniform dispersion of nano-SiO2 particles within the three-dimensional network structure formed by the chitosan matrix provides more adsorption sites. The synergistic effect of carboxymethyl (-COOH) and amino (-NH2) groups enhances the adsorption of positively charged pollutants (Cu). 2+ ) and specific adsorption of organic matter (MB).

[0038] The specific surface area (Brunauer-Emmett-Teller, BET) of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 1 was measured. The results showed that the average pore size of the bifunctionalized chitosan / nano-silica composite aerogel was 15-25 nm, and the specific surface area reached 420 m². 2 / g, the specific results are shown in Table 1. From the data in Table 1, it can be seen that 76.3% of the pore volume distribution is in the range of 5~20 nm, indicating that the bifunctionalized chitosan / nano silica composite aerogel is mainly mesoporous, suitable for adsorbing organic dyes with larger molecular sizes (such as methylene blue, with a molecular diameter of about 1.5 nm) and heavy metal ions (such as Cu). 2+ (Hydration radius approximately 0.4 nm).

[0039] Table 1. BET test data of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 1

[0040] Example 2 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 4 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 80 mL of 1% (v / v) acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Then slowly add 2.0 g of chloroacetic acid (molecular weight 94.50 g / mol) and stir. The reaction is carried out in a 55℃ water bath with mechanical stirring (150 rpm) for 5 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000~14000 Da) and dialyzed with deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50℃, 48℃). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Take 1 g of CM-CS (carboxymethylation degree 40%), place it in a 100 mL beaker, add 40 mL of deionized water, and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add ethylenediamine (1 mL, density 0.90 g / mL, purity ≥99%) dropwise, and carry out the reaction under the conditions of heating in a 45 ℃ water bath and mechanical stirring (200 rpm) for 7 h. During the reaction, the pH value is adjusted dropwise to 7.0~8.0 with 1 mol / L HCl (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube, centrifuge at 8000 rpm for 10 min to remove insoluble matter, and dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (changing the water every 6 h) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50 ℃, 48 h). h), a bifunctionalized chitosan (FC-CS) was obtained, with an amylation degree of 30% as determined by elemental analysis; Step 3: Dissolve 1 g of bifunctionalized chitosan in 40 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 10 nm) and add them to 40 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 5 mL of nano-SiO2 dispersion was slowly added dropwise to 40 mL of bifunctionalized chitosan solution (concentration 2.5 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.1 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40℃ and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0041] Example 3 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 5 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 100 mL of 1.5% acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Next, slowly add 2.5 g of chloroacetic acid (molecular weight 94.50 g / mol) and stir. The reaction is carried out in a 60℃ water bath with mechanical stirring (150 rpm) for 4 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000~14000 Da) and dialyzed with deionized water for 72 h (changing the water every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50℃, 48℃). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Take 2 g of CM-CS (carboxymethylation degree 40%), place it in a 100 mL beaker, add 50 mL of deionized water, and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add ethylenediamine (2 mL, density 0.90 g / mL, purity ≥99%) dropwise, and carry out the reaction under the conditions of heating in a 50 ℃ water bath and mechanical stirring (200 rpm) for 6 h. During the reaction, the pH value is adjusted dropwise with 1 mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube, centrifuge at 8000 rpm for 10 min to remove insoluble matter, and dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (changing the water every 6 h) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50 ℃, 48 h). h), a bifunctionalized chitosan (FC-CS) was obtained, with an amylation degree of 30% as determined by elemental analysis; Step 3: Dissolve 2 g of bifunctionalized chitosan in 50 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 2.5 g of nano-SiO2 particles (average particle size 10 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 25 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 4 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.5 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0042] Example 4 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 6 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 120 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Next, slowly add 4 g of chloroacetic acid (molecular weight 94.50 g / mol) and stir. The reaction is carried out in a 65℃ water bath with mechanical stirring (150 rpm) for 3 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000~14000 Da) and dialyzed with deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50℃, 48℃). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Take 3 g of CM-CS (carboxymethylation degree 40%), place it in a 100 mL beaker, add 60 mL of deionized water, and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add 3 mL of ethylenediamine (density 0.90 g / mL, purity ≥99%), and stir the reaction. The reaction is carried out under the conditions of heating in a 55 ℃ water bath and mechanical stirring (200 rpm) for 6 h. During the stirring reaction, the pH value is adjusted dropwise with 1 mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube, centrifuge at 8000 rpm for 10 min to remove insoluble matter, and dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (changing the water every 6 h) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50 ℃, 48 h). h), a bifunctionalized chitosan (FC-CS) was obtained, with an amylation degree of 40% determined by elemental analysis; Step 3: Dissolve 3 g of bifunctionalized chitosan in 60 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 4 g of nano-SiO2 particles (average particle size 10 nm) and add them to 60 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 40 mL of nano-SiO2 dispersion was slowly added dropwise to 60 mL of bifunctionalized chitosan solution (concentration 5 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 1 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0043] Example 5 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 4 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 80 mL of 1% (v / v) acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Then slowly add 2 g of chloroacetic acid and stir the reaction mixture. The reaction is carried out under the conditions of heating in a 55 ℃ water bath and mechanical stirring (150 rpm) for 5 h. During the stirring reaction, the pH value is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the reaction product to a dialysis bag (molecular weight cutoff 8000-14000 Da) and dialyze with deionized water for 72 h (changing the water every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. Then freeze-dry the obtained dialysate (-50 ℃, 48 h) to obtain carboxymethyl chitosan (CM-CS). The degree of carboxymethylation was determined to be 38% by titration. Step 2: Weigh 1 g of CM-CS (carboxymethylation degree 38%) and place it in a 100 mL beaker. Add 40 mL of deionized water and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add 1 mL of ethylenediamine (density 0.90 g / mL, purity ≥99%) while stirring. The reaction is carried out under the conditions of heating in a 45 ℃ water bath and mechanical stirring (200 rpm) for 7 h. During the reaction, the pH value is adjusted dropwise with 1 mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (changing the water every 6 h) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50 ℃, 48 h). h), a bifunctionalized chitosan (FC-CS) was obtained, with an amylation degree of 30% as determined by elemental analysis; Step 3: Dissolve 1 g of bifunctionalized chitosan in 100 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 10 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 5 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 1 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.1 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 48 h to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 50 ℃ for 24 h to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0044] Example 6 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 6 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 120 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25 ℃) until completely dissolved. Then slowly add 4 g of chloroacetic acid and stir the reaction mixture. The reaction is carried out under the conditions of heating in a 65 ℃ water bath and mechanical stirring (150 rpm) for 3 h. During the stirring reaction, the pH value is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the reaction product to a dialysis bag (molecular weight cutoff 8000~14000 Da) and dialyze with deionized water for 72 h (changing the water every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. Then freeze-dry the obtained dialysate (-50 ℃, 48 h) to obtain carboxymethyl chitosan (CM-CS). The degree of carboxymethylation was determined to be 42% by titration. Step 2: Weigh 3 g of CM-CS (carboxymethylation degree 42%) and place it in a 100 mL beaker. Add 60 mL of deionized water and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add ethylenediamine (3.0 mL, density 0.90 g / mL, purity ≥99%) dropwise while stirring. The reaction is carried out under the conditions of heating in a water bath at 55℃±1℃ and mechanical stirring (200 rpm) for 5 h. During the reaction, the pH value is adjusted dropwise with 1 mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (changing the water every 6 h) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50℃). Bifunctionalized chitosan (FC-CS) was obtained by 48 h at ℃, and the degree of amination was determined to be 30% by elemental analysis. Step 3: Dissolve 3.0 g of bifunctionalized chitosan in 100 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 50 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 40 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 3 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 1 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0045] Example 7 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 4 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 80 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Then slowly add 2.0 g of chloroacetic acid (molecular weight 94.50 g / mol) and stir. The reaction is carried out under the conditions of heating in a 55℃ water bath and mechanical stirring (150 rpm) for 5 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000-14000 Da) and dialyzed with deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50℃, 48℃). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Weigh 2 g of CM-CS (carboxymethylation degree 40%) and place it in a 100 mL beaker. Add 50 mL of deionized water and stir magnetically (400 rpm, 25 ℃) until completely dissolved. Then, slowly add 2 mL of ethylenediamine (density 0.90 g / mL, purity ≥99%, molar ratio of CM-CS carboxyl groups 2:1) and stir the reaction. The reaction is carried out under the conditions of heating in a 50 ℃ water bath and mechanical stirring (200 rpm) for 6 h. During the stirring reaction, the pH value is adjusted dropwise to 7.0~8.0 with 1 mol / L HCl (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (every 6 hours). The water was changed once every h to remove unreacted ethylenediamine and byproducts. The resulting dialysate was then freeze-dried (-50 °C, 48 h) to obtain bifunctionalized chitosan (FC-CS). The degree of amination was determined to be 40% by elemental analysis. Step 3: Dissolve 2 g of bifunctionalized chitosan in 100 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 20 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 10 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 2 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.5 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0046] Example 8 A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel includes the following steps: Step 1: Weigh 5 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100~300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 100 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25℃) until completely dissolved. Next, slowly add 2.0 g of chloroacetic acid (molecular weight 94.50 g / mol) and stir. The reaction is carried out in a 55℃ water bath with mechanical stirring (150 rpm) for 5 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000-14000 Da) and dialyzed with deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50℃, 48℃). h), obtained carboxymethyl chitosan (CM-CS), the degree of carboxymethylation was determined to be 40% by titration; Step 2: Weigh 3g of CM-CS (carboxymethylation degree 40%) and place it in a 100mL beaker. Add 60mL of deionized water and stir magnetically (400 rpm, 25℃) until completely dissolved. Then, slowly add 3mL of ethylenediamine (density 0.90 g / mL, purity ≥99%) while stirring. The reaction is carried out under the conditions of heating in a water bath at 50℃±1℃ and mechanical stirring (200rpm) for 5 hours. During the stirring reaction, the pH value is adjusted dropwise with 1mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 hours (changing the water every 6 hours) to remove unreacted ethylenediamine and byproducts. Then, freeze-dry the obtained dialysate (-50℃, 48 hours). h), a bifunctionalized chitosan (FC-CS) was obtained, with an amylation degree of 30% as determined by elemental analysis; Step 3: Dissolve 2 g of bifunctionalized chitosan in 100 mL of deionized water to obtain a bifunctionalized chitosan solution; Weigh 1 g of nano-SiO2 particles (average particle size 20 nm) and add them to 50 mL of deionized water; ultrasonically disperse for 30 min (power 200 W, frequency 40 kHz) to uniformly disperse the nano-SiO2 particles in the deionized water and form a stable nano-SiO2 dispersion. Under magnetic stirring, 10 mL of nano-SiO2 dispersion was slowly added dropwise to 50 mL of bifunctionalized chitosan solution (concentration 2 g / 100 mL), and stirring was continued for 2 h to fully mix the nano-SiO2 particles in the nano-SiO2 dispersion with FC-CS molecules. Then, 0.5 mL of glutaraldehyde solution (volume concentration 25%) was added, and stirring was continued for 30 min to allow the glutaraldehyde in the glutaraldehyde solution to undergo a cross-linking reaction with the amino groups on the FC-CS molecular chains, thereby enhancing the structural stability of the aerogel and obtaining a composite sol. Step 4: Transfer the composite sol to a polytetrafluoroethylene mold and let it stand for 24 hours to allow it to gel naturally at room temperature, forming a wet gel; then, place the wet gel in a constant temperature drying oven at 40 ℃ for 48 hours to further improve the three-dimensional network structure of the aerogel and enhance its mechanical strength. The aged wet gel was soaked in anhydrous ethanol, and the ethanol was replaced every 6 hours for a total of 3 times to remove water and unreacted solvent from the gel. Supercritical CO2 drying was used to dry the gel at 40 °C and 15 MPa for 6 hours to obtain bifunctionalized chitosan / nano silica composite aerogel (FC-CS / SiO2).

[0047] Comparative Example 1 A method for preparing an aerogel includes the following steps: Step 1: Weigh 5.0 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100-300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 100 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25 °C) until completely dissolved. Next, slowly add 3.0 g of chloroacetic acid (molecular weight 94.50 g / mol, molar ratio to chitosan units approximately 3:1) and stir. The reaction is carried out in a 60 °C water bath with mechanical stirring (150 rpm) for 4 h. During the reaction, the pH is adjusted dropwise with 1 mol / L NaOH solution to 4.5 ± 0.2 (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000-14000 Da) and dialyzed against deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (at -50 °C). Carboxymethyl chitosan (CM-CS) was obtained by titration at ℃ for 48 h, and the degree of carboxymethylation was determined to be 40%. Step 2: Weigh 2.0 g of CM-CS (carboxymethylation degree 40%) and place it in a 100 mL beaker. Add 50 mL of deionized water and stir magnetically (400 rpm, 25℃) until completely dissolved. Then, slowly add 2 mL of ethylenediamine (density 0.90 g / mL, purity ≥99%, molar ratio of CM-CS carboxyl groups 2:1) and stir. The reaction is carried out under the conditions of heating in a water bath at 50℃±1℃ and mechanical stirring (200 rpm) for 6 h. During the stirring reaction, the pH value is adjusted dropwise with 1 mol / L HCl to 7.0~8.0 (to maintain the stability of the reaction system) to obtain the reaction product. Transfer the obtained reaction product to a centrifuge tube and centrifuge at 8000 rpm for 10 min to remove insoluble matter. Dialyze the obtained supernatant through a dialysis bag (molecular weight cutoff 8000~14000 Da) for 48 h (every 6 hours). The water was changed once every h to remove unreacted ethylenediamine and byproducts. The resulting dialysate was then freeze-dried (-50 °C, 48 h) to obtain an aerogel (FC-CS). The degree of amination was determined to be 30% by elemental analysis.

[0048] Comparative Example 2 A method for preparing a monofunctional chitosan aerogel includes the following steps: Step 1: Weigh 5.0 g of chitosan (degree of deacetylation ≥90%, molecular weight approximately 100-300 kDa) and place it in a 250 mL Erlenmeyer flask. Then add 100 mL of 2% (v / v) acetic acid solution and stir magnetically (300 rpm, 25 °C) until completely dissolved. Next, slowly add 3.0 g of chloroacetic acid (molecular weight 94.50 g / mol, molar ratio to chitosan units approximately 3:1) and stir. The reaction is carried out in a 60 °C water bath with mechanical stirring (150 rpm) for 4 h. During the reaction, the pH is adjusted dropwise to 4.5 with 1 mol / L NaOH solution (to maintain the stability of the reaction system). The reaction product is then transferred to a dialysis bag (molecular weight cutoff 8000-14000 Da) and dialyzed against deionized water for 72 h (water changed every 6 h) to remove unreacted chloroacetic acid and low molecular weight byproducts. The resulting dialysate is then freeze-dried (-50 °C, 48 °C). h), carboxymethyl chitosan (CM-CS), i.e., monofunctionalized chitosan aerogel (CM-CS), was obtained, and the degree of carboxymethylation was determined to be 40% by titration.

[0049] The bifunctionalized chitosan / nano silica composite aerogels prepared in Examples 1 to 8, as well as the aerogels prepared in Comparative Examples 1 and 2, were tested for their adsorption performance on organic matter and heavy metal ions in dyeing and printing industrial wastewater, and their mechanical properties were also tested. The test methods are as follows: Adsorption performance test: First, 0.1 g of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Examples 1 to 8 was weighed and added to 100 mL of a solution containing methylene blue (MB, 50 mg / L) and Cu. 2+ The aerogel was placed in a constant-temperature shaker at 25 ℃ and 150 rpm for 24 hours in simulated dyeing and printing wastewater at a concentration of 20 mg / L. After shaking, the aerogel and wastewater were separated by centrifugation, and the supernatant was used to determine MB and Cu. 2+ The remaining concentration is used to calculate the adsorption capacity and removal rate; Mechanical property testing: The compressive strength of the bifunctional chitosan / nano silica composite aerogels prepared in Examples 1 to 8 was measured using a compressive strength tester (sample size was a cylinder with a diameter of 10 mm and a height of 10 mm, and the loading rate was 1 mm / min).

[0050] Table 2 shows the test data. As can be seen from the test data in Table 2, the bifunctionalized chitosan / nano silica composite aerogels prepared in Examples 1 to 8 exhibit excellent performance: their adsorption capacity for methylene blue reaches 105.2~125.6 mg / g (removal rate 92.3%~98.2%), and their adsorption capacity for Cu... 2+The adsorption capacity was 72.5~85.4 mg / g (removal rate 88.7%~96.8%), and the compressive strength remained in the range of 50.2~68.7 kPa; among them, Example 1 had the best overall performance (MB adsorption capacity 125.6 mg / g, Cu... 2+ The removal rate was 96.8% and the compressive strength was 68.7 kPa. The adsorption capacity and mechanical strength of Comparative Example 1 (FC-CS) and Comparative Example 2 (CM-CS) were significantly lower than those of the Example Group, indicating that bifunctional modification and nano-SiO2 composite can synergistically improve the adsorption efficiency of the material and the structural strength of the composite material.

[0051] Table 2. Aerogel performance test data for Examples 1-8 and Comparative Examples 1-2

[0052] The compressive strength (68.7 kPa) of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 1 was 114% higher than that of the aerogel prepared in Comparative Example 1 (32.1 kPa), and 31% higher than that of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 3 (52.3 kPa). This indicates that the introduction of nano-SiO2 significantly enhanced the material rigidity, which is attributed to the cross-linking effect between nanoparticles and chitosan chains and the densification of the three-dimensional network structure. The adsorption capacity and removal rate of the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 4 decreased by 12.4% and 4.9% respectively compared to the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 1, and the compressive strength decreased by 20%. This may be due to excessive nanoparticle aggregation blocking pores, leading to a decrease in specific surface area and weakened structural stability. In other words, the bifunctionalized chitosan / nano-silica composite aerogel prepared in Example 1 has the best overall performance, while maintaining high adsorption efficiency (MB 98.2%, Cu...). 2+ 96.8% and mechanical stability (68.7 kPa).

[0053] The bifunctional chitosan / nano silica composite aerogel prepared in Example 1 (experimental group 1), the aerogel prepared in Comparative Example 1 (control group 1), the monofunctional chitosan aerogel prepared in Comparative Example 2 (control group 3), and commercial activated carbon (control group 2) were used to conduct performance comparison tests between the experimental group and the control group.

[0054] Adsorption performance test: Weigh 0.1 g of the material from experimental group 1, control group 1, control group 2 and control group 3, and add them to 100 mL of simulated dyeing and printing wastewater (containing methylene blue MB 50 mg / L, Cu...). 2+ (20 mg / L), shaken at 25 ℃ for 24 h.

[0055] After shaking at 25 ℃ and 150 rpm for 24 h, the material and wastewater were separated by centrifugation, and the MB and Cu in the supernatant were determined. 2+ The remaining concentration was used to calculate the adsorption capacity and removal rate.

[0056] Regeneration performance test: The adsorbed material was desorbed with 0.1 mol / L HCl solution, washed with water until neutral, dried, and the adsorption was repeated 3 times. The adsorption capacity retention rate was calculated. The test results are shown in Table 3.

[0057] Table 3 Performance comparison test data between different experimental groups and control groups

[0058] As shown in Table 3, the adsorption capacity of FC-CS / SiO2 for MB in experimental group 1 reached 125.6 mg / g, which was 47.4% higher than that in control group 1 (85.2 mg / g) and 31.8% higher than that in control group 2 (95.3 mg / g); for Cu 2+ The adsorption capacity was 85.4 mg / g, which was 50.6% higher than that of control group 1 (56.7 mg / g) and 29.8% higher than that of control group 2 (65.8 mg / g).

[0059] The removal rate of MB in experimental group 1 was 98.2%, significantly higher than that in control group 1 (82.5%) and control group 2 (90.1%); for Cu... 2+ The removal rate was 96.8%, which was 23.6% higher than that of control group 1 (78.3%) and 13.1% higher than that of control group 2 (85.6%).

[0060] The overall adsorption performance of experimental group 1 was significantly better than that of control group 1 and control group 2, especially for heavy metal ions Cu. 2+ The adsorption effect is more prominent. This indicates that the introduction of nano-SiO2 dispersion not only enhances the mechanical strength of the aerogel, but also significantly improves its adsorption capacity for recalcitrant organic matter and heavy metal ions through a synergistic effect.

[0061] The adsorption performance of control group 3 (CM-CS) was significantly lower than that of experimental group 1 (FC-CS / SiO2), especially for Cu. 2+ The adsorption capacity (65.2 mg / g vs. 85.4 mg / g) indicates that amination modification plays a crucial role in the selective adsorption of heavy metal ions. The regeneration performance of control group 3 (72%) was also weaker than that of experimental group 1 (89%), indicating that the synergistic effect of bifunctional modification (carboxymethylation and amination) and nano-SiO2 particles in the nano-SiO2 dispersion can significantly improve the stability and recycling efficiency of the material.

[0062] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a bifunctionalized chitosan / nano-silica composite aerogel, characterized in that, Includes the following steps: Chitosan was modified by carboxymethylation to obtain carboxymethyl chitosan; Aminolation modification of carboxymethyl chitosan yields bifunctionalized chitosan; Bifunctionalized chitosan was mixed with deionized water to obtain a bifunctionalized chitosan solution. Nano-SiO2 dispersion was added dropwise to a bifunctionalized chitosan solution, stirred, and then a crosslinking agent was added to obtain a composite sol. The composite sol was subjected to gelation and aging treatments in sequence, followed by solvent replacement and drying treatments to obtain a bifunctional chitosan / nano silica composite aerogel.

2. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 1, characterized in that, The specific steps for carboxymethylation modification of chitosan are as follows: Chitosan was dissolved in acetic acid solution, followed by the addition of chloroacetic acid and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain carboxymethyl chitosan.

3. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 2, characterized in that, The ratio of chitosan, acetic acid solution, and chloroacetic acid used is 4~6 g: 80~120 mL: 2~4 g; The acetic acid solution is obtained by mixing acetic acid and deionized water; the volume concentration of the acetic acid solution is 1%~2%. Chloroacetic acid was then added, and the reaction was carried out at a temperature of 55-65 °C for 3-5 h with stirring. The pH value during the reaction was 4.

5.

4. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 1, characterized in that, The degree of carboxymethylation of the carboxymethyl chitosan is 30%~50%; The degree of amination of the bifunctionalized chitosan is 20% to 40%.

5. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 1, characterized in that, The specific steps for amylation modification of carboxymethyl chitosan are as follows: Carboxymethyl chitosan was dissolved in deionized water, followed by the addition of ethylenediamine and stirring. The resulting reaction product was then dialyzed and freeze-dried to obtain bifunctionalized chitosan.

6. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 5, characterized in that, The ratio of carboxymethyl chitosan, deionized water and ethylenediamine is 1~3 g: 40~60 mL: 1~3 mL; The ethylenediamine was then added, and the reaction was carried out at a temperature of 45-55 °C for 5-7 h with stirring. The pH value during the reaction was 7.0-8.

0.

7. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 1, characterized in that, The concentration of the bifunctionalized chitosan solution is 1~5g / 100mL; The volume ratio of the nano-SiO2 dispersion, the bifunctionalized chitosan solution, and the crosslinking agent is 5~40:40~60:0.1~1; The preparation process of the nano-SiO2 dispersion is as follows: Nano-SiO2 particles are added to deionized water and then uniformly dispersed by ultrasonic treatment and mechanical stirring to obtain a nano-SiO2 dispersion; the ratio of nano-SiO2 particles to deionized water is 1~4 g: 40~60 mL. The crosslinking agent is an aqueous solution of glutaraldehyde, and the volume concentration of the aqueous solution of glutaraldehyde is 25%.

8. The method for preparing a bifunctionalized chitosan / nano-silica composite aerogel according to claim 1, characterized in that, The gelation process involves placing the composite sol in a mold and allowing it to stand for 24–48 hours; the aging process is carried out at 40–50 °C. The solvent replacement is performed using an organic solvent; the drying process is supercritical CO2 drying or freeze drying.

9. A bifunctionalized chitosan / nano-silica composite aerogel, characterized in that, The bifunctionalized chitosan / nano silica composite aerogel prepared by any one of claims 1 to 8 has a compressive strength of 0.5 MPa or higher.

10. The application of the bifunctionalized chitosan / nano-silica composite aerogel according to claim 9 in the adsorption of organic matter and heavy metal ions in dyeing and printing industrial wastewater, characterized in that, The bifunctional chitosan / nano silica composite aerogel has a positive effect on Cu in dyeing and printing industrial wastewater. 2+ The removal rate reached 96.8%, and the removal rate of methylene blue from organic matter was 98.2%.

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