CN104194066A - Silicon oxide-chitosan composite aerogel and preparation method thereof - Google Patents

Abstract

The invention relates to a silica-chitosan composite airgel and a preparation method thereof. The silica-chitosan composite airgel comprises chitosan, a chitosan cross-linking agent and silica, wherein the shell The mass fraction of polysaccharide is 9%-65%, the mass fraction of silicon oxide is 30%-90%, and the mass fraction of chitosan crosslinking agent is 1%-5%.

Description

Silica-chitosan composite airgel and preparation method thereof

technical field

The invention belongs to the field of composite new materials, and in particular relates to a silica-chitosan composite airgel and a preparation method thereof. The prepared composite airgel has good acid and alkali resistance, high specific surface area, and can be grafted with different functional groups as required , used in medicine, water treatment, chemical industry and other fields.

Background technique

Chitosan is derived from the natural polymer chitin, which is rich in nature, contains active functional groups such as amino and hydroxyl groups in the molecule, and has good biocompatibility and microbial degradability. It is widely used in medicine, food, chemical industry, cosmetics, Water treatment, metal extraction and recovery have important application prospects.

In aqueous solution, the amino groups of chitosan molecules are easily ionized. When the pH value is lower than 5, chitosan will dissolve, which greatly limits the application of chitosan in acidic solution. In order to improve the acid resistance of chitosan, chitosan is generally cross-linked with a cross-linking agent, but the prepared cross-linked chitosan resin has a small specific surface area. Chitosan is often used as a carrier or an adsorbent, and the specific surface area is an important parameter index. A smaller specific surface area will greatly affect the application effect of chitosan. In order to increase the specific surface area of chitosan, people try to prepare chitosan airgel. However, there are strong hydrogen bonds between chitosan molecules, which lead to severe deformation and shrinkage of the gel during drying, which increases the difficulty of preparing chitosan airgel. In order to increase the specific surface area of chitosan airgel, two methods are generally adopted: (1) supercritical drying is adopted, but the safety hazard is relatively large and the cost is high; (2) the shell is prepared by using inorganic gel as the skeleton support. Glycan composite aerogels.

Chen Dairong et al. (J. Phys. Chem. B 2008, 112, 7721-7725) disclosed a preparation method of chitosan airgel. Using formaldehyde, glyoxal or glutaraldehyde as the cross-linking agent to react with dilute acid solution of chitosan to form chitosan hydrogel, and prepare chitosan airgel by supercritical drying method, in which formaldehyde The specific surface area of chitosan airgel can reach 845m ² /g. However, this method adopts a supercritical drying method, which has great potential safety hazards and high cost, and is difficult to be applied on a large scale in industry.

Michael R. Ayers (Journal of Non-Crystalline Solids, 2001, 285, 123-127) discloses a preparation method of silica-chitosan airgel. In this method, tetraethyl orthosilicate is used as the silicon source, and the silica-chitosan wet gel is prepared first, and then the silica-chitosan composite airgel with high specific surface area is prepared by supercritical drying method, and the specific surface area is Up to 750m ² /g. However, this method does not react chitosan with a crosslinking agent, which limits its application in acidic environments. Simultaneously, this method adopts the supercritical drying method, which has great potential safety hazards and high cost.

Therefore, there is an urgent need for a simple and quick way to prepare chitosan aerogels in this field.

Contents of the invention

The invention aims to overcome the defects of the existing chitosan airgel performance and preparation method, and the invention provides a silicon oxide-chitosan composite airgel and a preparation method thereof.

The invention provides a silica-chitosan composite aerogel, the silica-chitosan composite aerogel comprises chitosan, a chitosan cross-linking agent and silica, wherein the mass of chitosan The fraction is 9%-65%, the mass fraction of silicon oxide is 30%-90%, and the mass fraction of chitosan crosslinking agent is 1%-5%. It should be understood that the chitosan cross-linking agent here includes the linking group formed by the chitosan cross-linking agent existing in the composite airgel due to the reaction with chitosan.

Preferably, the silica-chitosan composite airgel has a three-dimensional porous network structure, a BET specific surface area of 300-1000 m ² /g, and a tap density of 0.1-1.0 g/cm ³ .

Preferably, the chitosan crosslinking agent is at least one of formaldehyde, glyoxal, glutaraldehyde and succinaldehyde.

Again, the present invention also provides a kind of preparation method of above-mentioned silica-chitosan composite airgel, and described preparation method comprises:

1) mixing a silicic acid solution with a pH of 2-3 and a chitosan solution with a pH of 1-3 to obtain a silicic acid-chitosan mixed sol or solution;

2) adjusting the pH value of the silicic acid-chitosan mixed sol or solution prepared in step 1) to between 5-7, and adding a chitosan crosslinking agent to the silicic acid-chitosan mixed sol or solution , stirred evenly, and reacted at 40-80°C for 0.5-12 hours to obtain a silica-chitosan composite gel, wherein the mass ratio between chitosan, chitosan cross-linking agent and silicic acid complies with the The proportional relationship between the components in the silica-chitosan composite airgel;

3) First mash the silica-chitosan composite gel prepared in step 2) until the particle size is less than 1cm, then immerse the mashed silica-chitosan composite gel in a polar organic solvent, and stir Make the polar organic solvent replace the water in the silica-chitosan composite gel;

4) The silicon oxide-chitosan composite gel that has been replaced in step 3) is immersed in a non-polar organic solvent, and the non-polar organic solvent is replaced by the polar organic solvent in the silicon oxide-chitosan composite gel by stirring. Sexual organic solvents;

5) Drying the silica-chitosan composite gel replaced in step 4) under normal pressure.

Preferably, in step 1), the silicic acid solution is prepared by mixing water glass with a modulus of 1.0-3.5 with water to obtain a water glass solution, and then pouring the water glass solution into a strong acidic cation exchange resin , stirred for 5-30 minutes and then filtered to obtain the clear liquid to obtain the silicic acid solution with a pH value of 2-3.

Preferably, in step 1), the chitosan solution having a pH of 1-3 is prepared by dissolving chitosan powder in dilute acid of 0.01 to 0.1 mol/L, and the chitosan powder is The degree of deacetylation is 60%-95%.

Preferably, in step 3), the polar organic solvent is at least one of alcohol solvents, tetrahydrofuran, N,N-dimethylformamide, and acetone.

Preferably, in step 3), stirring at 25-80° C. for 1-24 hours is repeated for 2-5 times, so as to realize solvent replacement.

Preferably, in step 4), the surface tension of the non-polar organic solvent needs to be less than 25mN-m, preferably cyclohexane, n-hexane, n-heptane or a combination thereof.

Preferably, in step 4), stirring at 25-80° C. for 1-24 hours is repeated for 2-5 times, so as to realize solvent replacement.

Preferably, in step 4), when the silicon oxide-chitosan composite gel is immersed in a non-polar organic solvent for the first time, a silane coupling agent with a general formula of RSiX3 is added in the non-polar organic solvent, and R is Organic groups, preferably, vinyl, amino, epoxy, mercapto, isocyanate, X is an easily hydrolyzed group, preferably chlorine, methoxyl, ethoxyl, the addition of silane coupling agent is the volume of water glass used 0%-50%, depending on actual needs, sometimes even without surface chemical modification.

Preferably, in step 5), the drying treatment is: drying at 80-120° C. for 2-12 hours.

Beneficial effects of the present invention:

The present invention is characterized in that the prepared silica-chitosan composite airgel has a mass fraction of chitosan of 9%-65%, a mass fraction of chitosan cross-linking agent of 1%-5%, and a mass fraction of silica The score is 30%-90%. The present invention adopts sol-gel method to prepare silica-chitosan composite hydrogel by means of copolymerization, then implements multiple polar and non-polar solvent solvent replacement and surface chemical modification, and finally dries under normal pressure. Methods A silica-chitosan composite aerogel with high specific surface area and good acid and alkali resistance was prepared, which can be used in medicine, water treatment, chemical industry and other fields. The main raw materials used in the method are industrial water glass and chitosan, which are rich in sources, low in price, mild in production conditions, short in time, simple and easy to operate, high in production efficiency, and suitable for large-scale industrial production.

Description of drawings

Fig. 1 shows the SEM photo of the silica-chitosan composite airgel prepared in one embodiment of the present invention;

Fig. 2 shows the silicon oxide-chitosan airgel infrared absorption spectrum prepared in one embodiment of the present invention;

Fig. 3 shows the amino-modified silica-chitosan airgel infrared absorption spectrum prepared in one embodiment of the present invention;

Fig. 4 shows the infrared absorption spectrum of the silica-chitosan airgel prepared in one embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the drawings and the following embodiments. It should be understood that the drawings and the following embodiments are only used to illustrate the present invention rather than limit the present invention.

The invention relates to a silicon oxide-chitosan composite airgel and a preparation method thereof. The silica-chitosan composite airgel prepared by the present invention has a three-dimensional porous network structure, a BET specific surface area of 300-1000m ² /g, a tap density of 0.1-1.0g/cm ³ , and its components are: shell The polycan mass fraction is 9%-65%, the chitosan cross-linking agent mass fraction is 1%-5%, and the silicon oxide mass fraction is 30%-90%.

The method of the present invention comprises the following steps: (1) prepare silica-chitosan composite sol; (2) prepare silica-chitosan gel; (3) polar organic compound of silica-chitosan gel Solvent replacement; (4) non-polar solvent replacement and surface chemical modification of silica-chitosan gel; (5) normal pressure drying of silica-chitosan gel and silica-chitosan composite gas Obtaining the gel. The composite airgel prepared by the invention has good acid and alkali resistance and high specific surface area, and can be grafted with different functional groups according to needs, and can be used in the fields of medicine, water treatment, chemical industry and the like. The composite airgel preparation method provided by the invention has outstanding advantages such as low cost and short production time, and is suitable for large-scale industrial production.

The preparation method of described silica-chitosan airgel specifically comprises the steps:

1) Preparation of silica-chitosan composite sol. Select industrial water glass with different modulus as the silicon source, mix it with an appropriate amount of deionized water, and obtain a diluted water glass solution (A). Pour the diluted water glass solution (A) into a strong acidic cation exchange resin, stir for 5min-30min, and filter to obtain a clear solution, namely a silicic acid solution (B) with a pH value of 2-3. Chitosan powder is dissolved in dilute acid to prepare chitosan solution (C). Pour the silicic acid solution (B) into the chitosan solution (C), and stir evenly to obtain a mixed sol (D) of chitosan and silicic acid;

2) Preparation of silica-chitosan gel. Adjust the pH value of the mixed sol (D) of chitosan and silicic acid to 5-7 with an alkaline catalyst, add chitosan cross-linking agent, and stir evenly, and react at 40-80°C for 30min-12h to obtain oxidation Silicon-chitosan composite gel (E);

3) Polar organic solvent displacement of silica-chitosan gel. The silica-chitosan composite gel (E) prepared in step 2) is crushed until the particle size is less than 1 cm, immersed in a polar organic solvent, stirred at 25-80° C. for 1-24 h, and solvent replacement is performed. This step is repeated 2-5 times to obtain a composite gel (F);

4) Polar solvent replacement and surface chemical modification of silica-chitosan gel. Immerse the composite organogel (F) obtained in step 3) in a non-polar organic solvent, stir at 25-80°C for 1-24h, and perform solvent replacement. Repeat the solvent exchange step 2-5 times to obtain a composite gel (G). To chemically modify the composite organogel (F), a silane coupling agent can be added when the non-polar organic solvent is immersed for the first time, and then 2-5 solvent replacements are still required;

5) Atmospheric pressure drying of silica-chitosan gel and obtaining of silica-chitosan composite airgel. Put the composite gel (G) obtained in step 4) into an oven, and dry at 80-120° C. for 2-12 hours to obtain a silica-chitosan composite airgel.

The water glass modulus used in step 1) is 1.0-3.5.

The strongly acidic cation exchange resin used in step 1) can be styrene-based cation exchange resin and its modified resin or any other cation exchange resin.

The degree of deacetylation of the chitosan powder used in step 1) is 60%-95%.

The dilute acid used in step 1) is hydrochloric acid, sulfuric acid, nitric acid, acetic acid or any other inorganic or organic acid with a concentration of 0.01-0.1 mol/L.

The basic catalyst used in the step 2) is ammonia, sodium hydroxide, potassium hydroxide, hexamethylenetetramine, ethanolamine and the like that release hydroxide ions in water.

The chitosan cross-linking agent used in step 2) is formaldehyde, glyoxal, glutaraldehyde, succinaldehyde etc. or its composition.

Step 3) The polar organic solvent used is a polar organic solvent that can be freely mixed with water, and can be an alcohol solvent, tetrahydrofuran, N,N-dimethylformamide, acetone, etc., preferably a monohydric solvent that is miscible with water. Or polyols (such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol).

The surface tension of the non-polar organic solvent used in step 4) needs to be less than 25mN-m, preferably cyclohexane, n-hexane, n-heptane or a combination thereof.

The general formula of the silane coupling agent used in step five) is RSiX3, R is an organic group, such as vinyl, amino, epoxy, mercapto, isocyanate, etc., and X is some easily hydrolyzed groups, such as chlorine , methoxy, ethoxy, etc., specifically including trimethylchlorosilane, hexamethyldisilazane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-glycidyloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, etc. or a combination thereof, but not limited thereto.

In order to solve the defects in the current technology and prepare chitosan airgel with high specific surface area at the same time, the present invention uses silica gel as the supporting skeleton, adopts the method of copolymerization gel, and undergoes multiple solvent replacement processes and surface chemistry. Modified, the silica-chitosan composite aerogel with high specific surface area was prepared by normal pressure drying method. The present invention adopts sol-gel method to prepare silica-chitosan composite hydrogel by means of copolymerization, then implements multiple polar and non-polar solvent solvent replacement and surface chemical modification, and finally dries under normal pressure. Methods A silica-chitosan composite aerogel with high specific surface area and good acid and alkali resistance was prepared, which can be used in medicine, water treatment, chemical industry and other fields. The main raw materials used in the method are industrial water glass and chitosan, which are rich in sources, low in price, mild in production conditions, short in time, simple and easy to operate, high in production efficiency, and suitable for large-scale industrial production.

Some exemplary embodiments are further enumerated below to better illustrate the present invention. It should be understood that the above-mentioned embodiments described in detail in the present invention and the following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention, and those skilled in the art may make some non-essential improvements and improvements according to the above-mentioned contents of the present invention All adjustments belong to the protection scope of the present invention. In addition, the specific proportions, time, temperature, etc. in the following process parameters are only exemplary, and those skilled in the art can select appropriate values within the range defined above.

Example 1:

1) Select 10 milliliters of industrial water glass with a modulus of 3.0, mix it with 40 milliliters of deionized water, and stir evenly to obtain a diluted water glass solution (A). Mix strong acidic ion exchange resin with a volume ratio of 1:1 and dilute water glass, stir for 10 minutes, and filter to obtain the clear liquid, that is, the silicic acid solution (B) with a pH value of 2-3. Dissolve 0.5 g of chitosan powder in 50 ml of 0.1 mol/L acetic acid solution to prepare chitosan solution (C). Pour 50 milliliters of silicic acid solution (B) into 50 milliliters of chitosan solution (C), and stir for 20 min to obtain a mixed solution (D) of chitosan and silicic acid solution;

2) Use ammonia water to adjust the pH value of the mixed solution (D) to about 6, add 100 microliters of glutaraldehyde with a mass concentration of 25%, stir for 20 minutes, and react at 60°C for 1 hour to obtain silica-chitosan composite water Gel (E);

3) The silica-chitosan composite hydrogel (E) obtained in step 2) was mashed and immersed in 100 ml of ethanol, and stirred at 65° C. for 2 h to perform solvent replacement with ethanol. Repeat the solvent replacement step 2 times to obtain a composite gel (F);

4) The composite gel (F) obtained in step 3) was immersed in 100 ml of cyclohexane, and stirred at 65° C. for 2 hours to perform solvent replacement with cyclohexane. Repeat the solvent replacement step 3 times to obtain a composite gel (G);

5) Put the composite gel (G) obtained in step 4) into an oven, and dry at 120° C. for 3 hours to obtain a hydrophilic silica-chitosan composite airgel;

The silica-chitosan composite airgel prepared in this example has a three-dimensional porous network structure, and its SEM photo is shown in Figure 1; after BET isothermal adsorption test, the specific surface area is 514.4m ² /g, and the tap density is 0.64g /cm ³ ;

Fig. 2 shows the infrared absorption spectrum of the silica-chitosan composite airgel prepared in this embodiment, the absorption peaks near 1089, 800, 468 cm ^-1 are the vibration absorption peaks of Si-O-Si bond of silica skeleton , the peak around 969cm ^-1 corresponds to the absorption peak of silicon oxide skeleton Si-OH, and the peak around 1653cm ^-1 corresponds to the absorption peak of glutaraldehyde-crosslinked chitosan-C=N-bending vibration.

Example 2:

1) Select 10 milliliters of industrial water glass with a modulus of 3.0, mix it with 40 milliliters of deionized water, and stir evenly to obtain a diluted water glass solution (A). Mix strong acidic ion exchange resin with a volume ratio of 1:1 and dilute water glass, stir for 10 minutes, and filter to obtain the clear liquid, that is, the silicic acid solution (B) with a pH value of 2-3. Dissolve 1 g of chitosan powder in 50 milliliters of 0.1 mol/L acetic acid solution to prepare chitosan solution (C). Pour 50 milliliters of silicic acid solution (B) into 50 milliliters of chitosan solution (C), and stir for 20 min to obtain a mixed solution (D) of chitosan and silicic acid solution;

2) Use hexamethylenetetramine to adjust the pH value of the mixed solution (D) to about 6, add 200 microliters of glutaraldehyde with a mass concentration of 25%, stir for 20 minutes, and react at 60° C. for 1 hour to obtain silicon oxide- Chitosan composite hydrogel (E);

3) The silica-chitosan composite hydrogel (E) obtained in step 2) was mashed and immersed in 100 ml of ethanol, and stirred at 65° C. for 2 h to perform solvent replacement with ethanol. Repeat the solvent replacement step 2 times to obtain a composite gel (F);

4) The composite organogel (F) obtained in step 3) was immersed in 100 ml of cyclohexane, stirred at 65° C. for 2 h, and the solvent of cyclohexane was replaced. Repeat the solvent replacement step 3 times to obtain a composite gel (G);

5) Put the composite gel (G) obtained in step 4) into an oven, and dry at 100° C. for 3 hours to obtain a silica-chitosan composite airgel. After BET isothermal adsorption test, the specific surface area is 425.7m ² /g, and the tap density is 0.76g/cm ³ .

Example 3:

1) Select 10 milliliters of industrial water glass with a modulus of 3.0, mix it with 40 milliliters of deionized water, and stir evenly to obtain a diluted water glass solution (A). Mix strong acidic ion exchange resin with a volume ratio of 1:1 and dilute water glass, stir for 10 minutes, and filter to obtain the clear liquid, that is, the silicic acid solution (B) with a pH value of 2-3. Dissolve 1g of chitosan powder in 50 milliliters of 0.1mol-L acetic acid solution to prepare chitosan solution (C), pour 10ml of silicic acid solution (A) into chitosan solution (B), and stir 20min, obtain the mixed solution (D) of chitosan and silicic acid solution;

2) Use hexamethylenetetramine to adjust the pH value of the mixed solution (D) to about 6, add 200 microliters of glutaraldehyde with a mass concentration of 25%, stir for 10 minutes, and react at 60° C. for 2 hours to obtain silicon oxide- Chitosan composite hydrogel (E);

3) The silica-chitosan composite hydrogel (E) obtained in step 2) was mashed and immersed in 100 ml of ethanol, and stirred at 65° C. for 2 h to perform solvent replacement with ethanol. Repeat the solvent replacement step 2 times to obtain a composite gel (F);

4) Immerse the composite gel (F) obtained in step 3) in 100 ml of cyclohexane, then add 2 ml of 3-aminopropyltriethoxysilane (APTES), and stir at 65°C for 4 hours to obtain amino modified Sexual Complex Gel (G). Immerse the amino-modified gel (G) in 100 ml of cyclohexane again, stir at 65°C for 2 hours, perform solvent replacement, repeat the solvent replacement 3 times, and filter to obtain the amino-modified composite gel (H) after solvent replacement ;

5) Put the amino-modified composite gel (H) obtained in step 4) into an oven, and dry at 100° C. for 3 hours to obtain the amino-modified silica-chitosan composite airgel. After BET isothermal adsorption test, the specific surface area is 600.3m2/g, and the tap density is 0.5g/cm3;

Figure 3 shows the infrared absorption spectrum of the amino-modified silica-chitosan airgel prepared in this implementation, and the absorption peaks near 1071, 784, ^{and 461 cm} are the vibration absorption peaks of the Si-O-Si bond of the silica skeleton , compared with Fig. 2, for the unmodified silica-chitosan composite airgel sample, the absorption peak of silica Si-OH around 969cm ^-1 is significantly weaker, which indicates that APTES successfully modified the silica framework, while 1647cm The peak appearing around ^-1 is the superposition of _-NH2 and -C=N- absorption peaks.

Example 4:

1) Select 10 milliliters of industrial water glass with a modulus of 3.0, mix it with 40 milliliters of deionized water, and stir evenly to obtain a diluted water glass solution (A). Mix strong acidic ion exchange resin with a volume ratio of 1:1 and dilute water glass, stir for 10 minutes, and filter to obtain the clear liquid, that is, the silicic acid solution (B) with a pH value of 2-3. Dissolve 1 g of chitosan powder in 50 milliliters of 0.1 mol/L acetic acid solution to prepare chitosan solution (C). Pour 50 milliliters of silicic acid solution (B) into 50 milliliters of chitosan solution (C), and stir for 20 min to obtain a mixed solution (D) of chitosan and silicic acid solution;

2) Use hexamethylenetetramine to adjust the pH value of the mixed solution (D) to about 6, add 1.5 ml of formaldehyde solution with a mass fraction of 40%, stir for 20 minutes, and react at 60°C for 1 hour to obtain silica-chitopolymer Sugar complex hydrogel (E);

3) The silica-chitosan composite hydrogel (E) obtained in step 2) was mashed and immersed in 100 ml of ethanol, and stirred at 65° C. for 2 h to perform solvent replacement with ethanol. Repeat the solvent replacement step 2 times to obtain a composite gel (F);

4) The composite organogel (F) obtained in step 3) was immersed in 100 ml of cyclohexane, stirred at 65° C. for 2 h, and the solvent of cyclohexane was replaced. Repeat the solvent replacement step 3 times to obtain a composite gel (G);

5) Put the composite gel (G) obtained in step 4) into an oven, and dry at 100° C. for 3 hours to obtain a silica-chitosan composite airgel. After BET isothermal adsorption test, the specific surface area is 843.2m ² /g, and the tap density is 0.2g/cm ³ ;

Figure 4 shows the infrared absorption spectrum of the silica-chitosan airgel prepared in this implementation, the absorption peaks near 1087, 799, ^{and 466cm} are the vibration absorption peaks of the Si-O-Si bond of the silica skeleton, and the absorption peaks at ^970cm- The peak around ¹ corresponds to the absorption peak of silicon oxide skeleton Si-OH, and the peak around 1639 cm ^-1 corresponds to the absorption peak of formaldehyde-crosslinked chitosan-C=N-bending vibration.

Claims (12)

1. A silica-chitosan composite airgel, characterized in that, the silica-chitosan composite airgel comprises chitosan, chitosan cross-linking agent and silicon oxide, wherein chitosan The mass fraction of sugar is 9%-65%, the mass fraction of silicon oxide is 30%-90%, and the mass fraction of chitosan crosslinking agent is 1%-5%. 2. silica-chitosan composite airgel according to claim 1, is characterized in that, described silica-chitosan composite airgel has three-dimensional porous network structure, and BET specific surface area is ^300-1000m /g, the tap density is 0.1-1.0 g/cm ³ . 3. according to claim 1 and 2 described silica-chitosan composite aerogels, it is characterized in that, described chitosan cross-linking agent is formaldehyde, glyoxal, glutaraldehyde, succinaldehyde at least one. 4. a preparation method of silica-chitosan composite airgel described in any one of claims 1-3, is characterized in that, described preparation method comprises: 1) Mix a silicic acid solution with a pH of 2-3 and a chitosan solution with a pH of 1-3 to obtain a silicic acid-chitosan mixed sol or solution; 2) Adjust the pH value of the silicic acid-chitosan mixed sol or solution prepared in step 1) to between 5-7, and add a chitosan crosslinking agent to the silicic acid-chitosan mixed sol or solution , stirred evenly, and reacted at 40-80°C for 0.5-12 hours to obtain a silica-chitosan composite gel, wherein the mass ratio between chitosan, chitosan cross-linking agent and silicic acid complies with the The proportional relationship between the components in the silica-chitosan composite airgel; 3) First crush the silica-chitosan composite gel prepared in step 2) until the particle size is less than 1cm, then immerse the crushed silica-chitosan composite gel in a polar organic solvent, and stir to make The polar organic solvent displaces the water in the silica-chitosan composite gel; 4) Immerse the silica-chitosan composite gel replaced in step 3) in a non-polar organic solvent, and make the non-polar organic solvent replace the poles in the silica-chitosan composite gel by stirring. Sexual organic solvents; 5) Dry the silica-chitosan composite gel replaced in step 4) under normal pressure. 5. The preparation method according to claim 4, characterized in that, in step 1), the preparation method of the silicic acid solution is: first mix the water glass with a modulus of 1.0-3.5 with water to obtain the water glass solution, and then mix the The water glass solution is poured into a strongly acidic cation exchange resin, stirred for 5-30 minutes, and then filtered to obtain a clear solution to obtain a silicic acid solution with a pH value of 2-3. 6. The preparation method according to claim 4 or 5, characterized in that, in step 1), the chitosan solution with a pH of 1-3 has chitosan powder dissolved in 0.01-0.1mol/L dilute The deacetylation degree of the chitosan powder is 60%-95%. 7. The preparation method according to any one of claims 4-6, characterized in that, in step 3), the polar organic solvent is at least one of alcohol solvents, tetrahydrofuran, N,N-dimethylformamide and acetone A sort of. 8. The preparation method according to any one of claims 4-7, characterized in that, in step 3), repeated stirring at 25-80°C for 1-24 hours, the number of repetitions is 2-5 times, so that the solvent replacement. 9. The preparation method according to any one of claims 4-8, characterized in that, in step 4), the surface tension of the non-polar organic solvent needs to be less than 25mN-m, preferably cyclohexane, n-hexane, n-heptane or its combination. 10. The preparation method according to any one of claims 4-9, characterized in that, in step 4), repeated stirring at 25-80°C for 1-24 hours, the number of repetitions is 2-5 times, so that the solvent replacement. 11. The preparation method according to any one of claims 4-10, characterized in that, in step 4), when the silica-chitosan composite gel is immersed in a non-polar organic solvent for the first time, Add a silane coupling agent with the general formula RSiX ₃ in the organic solvent, R is an organic group, preferably vinyl, amino, epoxy, mercapto, isocyanate, X is an easily hydrolyzed group, preferably chloro, methoxy , Ethoxy, the volume ratio of the amount of silane coupling agent added to the water glass used is ≦50%. 12. The preparation method according to any one of claims 4-11, characterized in that, in step 5), the drying treatment is: drying at 80-120° C. for 2-12 hours.