CN115449119B - Freeze-drying preparation method of chitosan-silicon dioxide hybrid aerogel - Google Patents
Freeze-drying preparation method of chitosan-silicon dioxide hybrid aerogel Download PDFInfo
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- 239000004964 aerogel Substances 0.000 title claims abstract description 61
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 58
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 55
- 238000004108 freeze drying Methods 0.000 title claims abstract description 20
- 238000002360 preparation method Methods 0.000 title abstract description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 86
- 239000002904 solvent Substances 0.000 claims abstract description 80
- 230000032683 aging Effects 0.000 claims abstract description 54
- 239000002243 precursor Substances 0.000 claims abstract description 53
- 229920001661 Chitosan Polymers 0.000 claims abstract description 48
- 239000007788 liquid Substances 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 46
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 claims abstract description 44
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 25
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 25
- 239000010703 silicon Substances 0.000 claims abstract description 25
- 238000009777 vacuum freeze-drying Methods 0.000 claims abstract description 18
- 239000000243 solution Substances 0.000 claims description 92
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 57
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 42
- 238000002156 mixing Methods 0.000 claims description 42
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 36
- 239000012153 distilled water Substances 0.000 claims description 33
- 239000012046 mixed solvent Substances 0.000 claims description 31
- 238000003756 stirring Methods 0.000 claims description 30
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 27
- SXRSQZLOMIGNAQ-UHFFFAOYSA-N Glutaraldehyde Chemical compound O=CCCCC=O SXRSQZLOMIGNAQ-UHFFFAOYSA-N 0.000 claims description 25
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 claims description 19
- 238000002791 soaking Methods 0.000 claims description 16
- LFQCEHFDDXELDD-UHFFFAOYSA-N tetramethyl orthosilicate Chemical compound CO[Si](OC)(OC)OC LFQCEHFDDXELDD-UHFFFAOYSA-N 0.000 claims description 16
- 239000004033 plastic Substances 0.000 claims description 15
- 239000003054 catalyst Substances 0.000 claims description 11
- 239000006185 dispersion Substances 0.000 claims description 10
- 239000011259 mixed solution Substances 0.000 claims description 10
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 9
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 9
- 239000003377 acid catalyst Substances 0.000 claims description 9
- 239000003513 alkali Substances 0.000 claims description 9
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 9
- 230000003301 hydrolyzing effect Effects 0.000 claims description 9
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 9
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 claims description 8
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 8
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 7
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 7
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 7
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 6
- 229910000030 sodium bicarbonate Inorganic materials 0.000 claims description 4
- 235000017557 sodium bicarbonate Nutrition 0.000 claims description 4
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 4
- 230000002431 foraging effect Effects 0.000 claims description 3
- 230000007062 hydrolysis Effects 0.000 claims description 3
- 238000006460 hydrolysis reaction Methods 0.000 claims description 3
- 235000006408 oxalic acid Nutrition 0.000 claims description 3
- 235000011118 potassium hydroxide Nutrition 0.000 claims description 3
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 3
- 235000017550 sodium carbonate Nutrition 0.000 claims description 3
- 239000002585 base Substances 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims 1
- 239000000499 gel Substances 0.000 abstract description 96
- 238000001035 drying Methods 0.000 abstract description 11
- 239000006184 cosolvent Substances 0.000 abstract description 7
- 239000000463 material Substances 0.000 abstract description 6
- 238000003980 solgel method Methods 0.000 abstract description 4
- 239000011240 wet gel Substances 0.000 abstract description 4
- 239000011159 matrix material Substances 0.000 abstract description 3
- 238000005728 strengthening Methods 0.000 abstract description 2
- 229960000583 acetic acid Drugs 0.000 description 13
- 238000001879 gelation Methods 0.000 description 10
- 239000002131 composite material Substances 0.000 description 7
- 238000007710 freezing Methods 0.000 description 7
- 238000000352 supercritical drying Methods 0.000 description 7
- 230000006835 compression Effects 0.000 description 6
- 238000007906 compression Methods 0.000 description 6
- 230000008014 freezing Effects 0.000 description 6
- 238000009413 insulation Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000006073 displacement reaction Methods 0.000 description 5
- -1 amino, hydroxyl Chemical group 0.000 description 3
- 239000012362 glacial acetic acid Substances 0.000 description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 239000004965 Silica aerogel Substances 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 230000000844 anti-bacterial effect Effects 0.000 description 1
- KTUQUZJOVNIKNZ-UHFFFAOYSA-N butan-1-ol;hydrate Chemical compound O.CCCCO KTUQUZJOVNIKNZ-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 150000004676 glycans Chemical class 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- 238000009396 hybridization Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000003607 modifier Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 239000000741 silica gel Substances 0.000 description 1
- 229910002027 silica gel Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000004753 textile Substances 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/157—After-treatment of gels
- C01B33/158—Purification; Drying; Dehydrating
- C01B33/1585—Dehydration into aerogels
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2305/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2301/00 or C08J2303/00
- C08J2305/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K7/00—Use of ingredients characterised by shape
- C08K7/22—Expanded, porous or hollow particles
- C08K7/24—Expanded, porous or hollow particles inorganic
- C08K7/26—Silicon- containing compounds
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Dispersion Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Inorganic Chemistry (AREA)
- Silicon Compounds (AREA)
Abstract
The application provides a freeze-drying preparation method of chitosan-silicon dioxide hybrid aerogel, which comprises the following steps: step 1, preparing chitosan precursor liquid; step 2, preparing a silicon source precursor liquid; step 3, preparing hybrid gel; step 4, solvent replacement; and 5, freeze drying. The method comprises the steps of preparing chitosan-silicon dioxide hybrid wet gel by a sol-gel method, strengthening a hybrid gel matrix by an aging process, replacing an internal solvent of the hybrid gel with a cosolvent of tertiary butanol and water in a specific range ratio by a solvent replacement process, and finally preparing high-quality chitosan-silicon dioxide hybrid aerogel by a vacuum freeze drying method. The chitosan-silicon dioxide hybrid aerogel is prepared by adopting a method of vacuum freeze drying in a cosolvent of tertiary butanol and water in a specific proportion, is safe, environment-friendly and low in cost, and the obtained chitosan-silicon dioxide hybrid aerogel material has good strength, large specific surface area and thorough drying.
Description
Technical Field
The specification relates to the technical field of aerogel preparation, in particular to a freeze-drying preparation method of chitosan-silicon dioxide hybrid aerogel.
Background
The nano porous three-dimensional network skeleton structure of the silica aerogel has the excellent characteristics of low density, high porosity, high specific surface area, super heat insulation and the like, and has wide application prospect in the fields of heat insulation and preservation, biomedicine, chemical industry, new energy materials, microelectronic material manufacturing and the like. However, the preparation process of the pure silica gel is complicated, the process requirement is high, the cost is high, the mechanical property is extremely poor, and the aerogel fiber composite felt and the aerogel fiber composite board which are prepared by the compression molding process or the integral molding process are mainly used for large-scale industrialized application at present.
The chitosan is used as a renewable biological alkaline polysaccharide polymer, is rich in amino, hydroxyl and other active groups, has the characteristics of wide sources, degradability, good biocompatibility, antibacterial property and the like, and is widely applied to the fields of textile industry, environmental protection, medicine and the like. The chitosan aerogel prepared from chitosan is one of organic aerogel, and can be applied to the environmental protection fields of dye degradation, heavy metal ion adsorption and the like as an adsorption catalytic material. However, chitosan aerogel still has limited mechanical strength and poor thermal stability, and cannot further expand the mass production of aerogel blocks.
Through hybridization of the silicon dioxide aerogel and the chitosan aerogel, the aerogel composite material with high mechanical strength, good toughness, strong heat insulation performance, excellent heat stability and functionality is expected to be prepared. However, the existing preparation method of chitosan-silica hybrid aerogel generally adopts a preparation method of supercritical drying and normal-pressure drying, and the mechanical properties of the prepared hybrid aerogel are poor. The Chinese patent publication No. CN109369975B, application No. CN201811337232.0 and publication No. 2019, 02 and 22 discloses a preparation method of magnetic chitosan-silicon dioxide composite aerogel, which is prepared by supercritical drying process to obtain magnetic SiO 2 The prepared composite aerogel has the characteristics of high porosity, low density and the like.
The existing scheme generally adopts a supercritical drying method or an atmospheric drying method to prepare the chitosan-silicon dioxide hybrid aerogel, wherein supercritical drying is generally carried out under the conditions of high temperature and high pressure by using an autoclave, has high energy consumption, high risk, expensive equipment and incapability of continuous large-scale output, and severely limits the industrialized application of the chitosan-silicon dioxide hybrid aerogel. The normal pressure drying method avoids a series of defects of a supercritical drying process, but has the defects of long period, complex operation, large use amount of an organic replacement solvent, toxicity of a modified solvent and the like, and the volume shrinkage rate of the dried aerogel is larger, the integrity is not high, and the heat insulation performance is poor.
Disclosure of Invention
In view of this, the embodiments of the present disclosure provide a freeze-drying preparation method of a chitosan-silica hybrid aerogel, which prepares a chitosan-silica hybrid wet gel by a sol-gel method, strengthens the hybrid gel matrix by an aging process, then replaces the internal solvent of the hybrid gel with a mixed solvent of tert-butanol and water in a specific range ratio by a solvent replacement process, and finally achieves the purposes of preparing a high-quality chitosan-silica hybrid aerogel with excellent mechanical properties and heat insulation properties, and simple, safe and environment-friendly production process by a vacuum freeze-drying method.
The embodiment of the specification provides the following technical scheme:
a method for preparing chitosan-silica hybrid aerogel by freeze drying, comprising:
step 1, preparing a chitosan precursor liquid, mixing chitosan, acetic acid and distilled water, and continuously stirring under a heating condition to obtain the chitosan precursor liquid;
step 2, preparing a silicon source precursor liquid, mixing a silicon source, an alcohol solvent and distilled water, and regulating the pH to 2-4.5 by using an acid catalyst; hydrolyzing at 30-60 ℃, adding dimethylformamide and distilled water into the hydrolyzed sol, and uniformly mixing to obtain silica sol to be polycondensed;
step 3, preparing hybrid gel, namely slowly adding glutaraldehyde solution into the chitosan precursor solution obtained in the step 1, magnetically stirring until uniformity, slowly adding an alkali catalyst into the silicon source precursor solution obtained in the step 2 until the pH of the dispersion solution is increased to about 6-8, magnetically stirring until uniformity, then mixing the ungelatinized chitosan precursor solution and the silicon source precursor solution according to a ratio (1:0.2-5) and fully magnetically stirring uniformly, pouring the mixed solution into a mould before gel, and obtaining the chitosan-silicon dioxide hybrid gel after gel;
step 4, solvent replacement, namely placing the hybrid gel obtained in the step 3 into a plastic tank, sealing the plastic tank, placing the plastic tank into a constant temperature box, completely reacting the inside of the gel under an aging condition, and then soaking the hybrid gel into an aging solution for aging under the aging condition; then removing the aging liquid to finish solvent replacement, and obtaining the replaced hybrid gel, wherein after the replacement is finished, the solvent in the hybrid gel is replaced by a mixed solvent in a specific proportion range;
and 5, freeze-drying, and performing vacuum freeze-drying on the hybrid gel obtained in the step 4 to obtain the chitosan-silicon dioxide hybrid aerogel.
Further, in the step 1, the mass concentration of chitosan in the precursor solution is controlled to be about 0.5% -5%, and the pH value of the precursor solution is controlled to be 1-4.
In the step 2, the silicon source is one or two of TEOS and TMOS, the alcohol solvent is one or more of ethanol, methanol, isopropanol and tertiary butanol, the acid catalyst is one or more of acetic acid, oxalic acid, hydrochloric acid and citric acid, the use mode of the acid catalyst is that the acid catalyst is prepared into a dilute solution with the concentration of 0.5mol/L to 4mol/L, the mole ratio of the silicon source, the alcohol solvent and distilled water is 1 (6 to 14) (2 to 4), and the hydrolysis time range is 4 hours to 24 hours.
Further, in the step 2, the molar addition ratio of the dimethylformamide to the distilled water is (0.05-0.2): 1-4.
Further, in step 3, the mold is a plastic container or a polytetrafluoroethylene container, and the mold is sized to be placed in a plastic tank used in a subsequent aging and replacement process and to be placed in a lyophilization chamber of a lyophilization machine.
Further, in the step 3, glutaraldehyde is added to 0.5-1% of the mass concentration of the solution; the alkali catalyst is one or more of ammonia water, potassium hydroxide, sodium bicarbonate and sodium carbonate, and the use mode of the alkali catalyst is that the alkali catalyst is prepared into a dilute solution of 0.5 mol/L-4 mol/L.
In step 4, the aging liquid is an alcohol solvent or a mixed liquid of one or two of alcohol solvent and TEOS/TMOS, the alcohol solvent is one or more of ethanol and methanol, and the mixed solvent is a mixed solvent of tertiary butanol and water.
Further, when a mixed solution of one or two of an alcohol solvent and TEOS/TMOS is used, the mass fraction of the alcohol solvent is 90% -95%; the mixed solvent of the tertiary butanol with water with the water content of 4wt.% to 25wt.% is used for the mixed solvent, and the mixed solvent of the tertiary butanol with the water content of 75wt.% to 85wt.% is used for the mixed solvent with the water content of high water content and is matched with the proportion of the solvent components in the gel after target replacement.
Further, in the step 4, the aging condition is that the aging is carried out for 6 to 12 hours at 20 to 60 ℃, the aging condition is that the aging is carried out for 6 to 48 hours at 40 to 60 ℃, the solvent replacement is carried out by immersing the hybrid gel in a replacement solvent with the volume of 2 to 5 times of the gel volume at about 35 to 60 ℃, replacing the replacement solvent once every about 8 to 24 hours, and carrying out 2 to 6 times of replacement.
Further, in the vacuum freeze-drying of step 5, the hybrid gel is pre-frozen for 1 to 2 hours at about-30 ℃ to-55 ℃, and then vacuum dried for 36 to 72 hours at a pressure lower than 100 Pa in a freeze-drying chamber of a vacuum freeze-dryer, wherein the hybrid gel is dried for 24 hours at least at a temperature platform lower than-20 ℃.
Compared with the prior art, the beneficial effects that above-mentioned at least one technical scheme that this description embodiment adopted can reach include at least:
the preparation method comprises the steps of preparing chitosan-silicon dioxide hybrid wet gel by a sol-gel method, strengthening a hybrid gel matrix by an aging process, replacing an internal solvent of the hybrid gel with a cosolvent of tertiary butanol and water in a specific range ratio by a solvent replacement process, and finally preparing high-quality chitosan-silicon dioxide hybrid aerogel with excellent mechanical properties and heat insulation performance, simple, convenient, safe and environment-friendly production process by a vacuum freeze drying method. The chitosan-silica hybrid aerogel is prepared by adopting a method of vacuum freeze drying in a cosolvent of tertiary butanol and water in a specific proportion, compared with a supercritical drying method commonly adopted in the prior art, the process for preparing the chitosan-silica hybrid aerogel is safer and beneficial to increasing the yield, and simultaneously compared with a normal pressure drying method commonly adopted in the prior art, the process for preparing the chitosan-silica hybrid aerogel avoids the tedious and large amount of organic reagent consumption and the replacement-modification process using a toxic modifier, thereby being more environment-friendly and capable of saving the cost. In addition, compared with the normal pressure drying method commonly adopted in the prior art, the obtained chitosan-silicon dioxide hybrid aerogel material has higher strength, low shrinkage rate in the drying process, large specific surface area of the product and thorough drying.
Detailed Description
Embodiments of the present application are described in detail below.
Other advantages and effects of the present application will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present application with reference to specific examples. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. The application may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present application. It should be noted that the following embodiments and features in the embodiments may be combined with each other without conflict. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It is noted that various aspects of the embodiments are described below within the scope of the following claims. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is merely illustrative. Based on the present disclosure, one skilled in the art will appreciate that one aspect described herein may be implemented independently of any other aspect, and that two or more of these aspects may be combined in various ways. For example, apparatus may be implemented and/or methods practiced using any number and aspects set forth herein. In addition, such apparatus may be implemented and/or such methods practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.
It should be further noted that the following embodiments merely schematically illustrate the basic concept of the present application, and only the components related to the present application are shown and not drawn according to the number, shape and size of the components in actual implementation, and the shape, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
In addition, in the following description, specific details are provided in order to provide a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects may be practiced without these specific details.
The application mainly comprises the following steps:
and 1, preparing a chitosan precursor liquid.
Mixing chitosan, acetic acid and distilled water, and continuously stirring under the heating condition to obtain the chitosan precursor liquid. The mass concentration of chitosan in the precursor solution is controlled to be about 0.5-5%, and the pH value of the precursor solution is controlled to be 1-4.
And 2, preparing a silicon source precursor liquid.
Mixing a silicon source, an alcohol solvent and distilled water, and regulating the pH value to 2-4.5 by using an acid catalyst; hydrolyzing at 30-60 ℃; and adding dimethylformamide and distilled water into the hydrolyzed sol, and uniformly mixing to obtain the silica sol to be polycondensed.
Specifically, the silicon source can be one or two of TEOS (tetraethyl orthosilicate) and TMOS (tetramethoxysilane); the alcohol solvent can be one or more of ethanol, methanol, isopropanol and tert-butanol; the acid catalyst can be one or more of acetic acid, oxalic acid, hydrochloric acid and citric acid, and is used in a manner of being configured into a dilute solution of 0.5mol/L to 4 mol/L;
the molar ratio of the silicon source to the alcohol solvent to the distilled water is 1 (6-14) (2-4), and the hydrolysis time ranges from 4h to 24h (the specific time can be determined according to the actual situation); the molar addition ratio of the dimethylformamide to the distilled water is (0.05-0.2) to (1-4).
And 3, preparing the hybrid gel.
Slowly adding glutaraldehyde solution into the chitosan precursor solution obtained in the step 1, and magnetically stirring until the solution is uniform; slowly adding a base catalyst into the silicon source precursor liquid obtained in the step 2 until the pH of the dispersion liquid is increased to about 6-8, and magnetically stirring until the dispersion liquid is uniform; then mixing the ungelled chitosan precursor liquid and the silicon source precursor liquid according to the proportion (1:0.2-5) and fully and magnetically stirring uniformly; pouring the mixed solution into a mould before the gel, and obtaining the chitosan-silicon dioxide hybrid gel after the gel.
The mould is a plastic container or polytetrafluoroethylene container which is not easy to adhere to gel, and the size of the mould can be placed in a plastic groove used in the subsequent ageing and replacement processes and can be placed in a freeze-drying chamber of a freeze dryer; glutaraldehyde is added to 0.5-1% of the mass concentration of the solution; the alkali catalyst is one or more of ammonia water, potassium hydroxide, sodium bicarbonate and sodium carbonate, and the use mode is that the alkali catalyst is prepared into a dilute solution of 0.5mol/L to 4 mol/L.
And 4, solvent replacement.
Placing the hybridized gel band die obtained in the step 3 into a plastic tank, sealing the plastic tank, placing the plastic tank into a constant temperature box, aging for 6-12 hours at 20-60 ℃ to enable the internal reaction of the gel to be complete, and then soaking the hybridized gel into aging liquid to age for 6-48 hours at 40-60 ℃; and then removing the aging liquid, soaking the hybrid gel in a replacement solvent with the volume of 2-5 times of that of the gel at the temperature of about 35-60 ℃, replacing the replacement solvent every about 8-24 hours, and completing the solvent replacement after 2-6 times of replacement to obtain the replaced hybrid gel. After the completion of the displacement, the solvent in the hybrid gel will be displaced to a target ratio of mixed solvent of t-butanol and water, i.e., a mixed solvent of t-butanol and water at a low water content of 4wt.% to 25wt.% and a mixed solvent of t-butanol and water at a high water content of 75wt.% to 85 wt.%.
The aging liquid is an alcohol solvent or a mixed liquid of one or two of the alcohol solvent and TEOS/TMOS, and the alcohol solvent is one or more of ethanol and methanol;
when the mixed solution of one or two of the alcohol solvent and TEOS/TMOS is selected, preferably, the mass fraction of the alcohol solvent is 90% -95%;
the replacement solvent is a mixed solvent of tertiary butanol and water, preferably, the water content of the mixed solvent is selected to be 4-25 wt.% at low water content and 75 wt-85 wt.% at high water content for the convenience of replacement operation, and the water content is matched with the proportion of solvent components in the gel after target replacement.
And 5, freeze drying.
And (3) performing vacuum freeze drying on the hybrid gel obtained in the step (4) to obtain the chitosan-silicon dioxide hybrid aerogel. Pre-freezing at about-30 ℃ to-55 ℃ for 1h to 2h, and then vacuum drying at a pressure lower than 100 Pa in a freeze-drying chamber of a vacuum freeze dryer for 36h to 72h, wherein the drying is performed at least at a temperature platform lower than-20 ℃ for 24h.
The tertiary butanol aqueous cosolvent displacement process described in step 4, if other various displacement modes including the ratio of displacement liquid, volume, number of displacement times and time are adopted, should all be included in the protection scope of the present patent if the solvent component in the composite gel is the mixed solvent of water and tertiary butanol in the preferred ratio when the freeze-drying step is finally carried out.
The method for preparing the complete block-shaped pure alumina aerogel by freeze drying is described below by way of specific examples, and the performance of the prepared composite gel is tested.
Example 1:
step 101, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor liquid with the mass fraction of chitosan of 0.5% and the pH=2. Uniformly mixing TMOS, ethanol and distilled water according to a molar ratio of 1:14:3, adding glacial acetic acid until the pH value of the solution is reduced to 2.0, and hydrolyzing for 12 hours at 45 ℃;
step 102, adding 0.1 mol ratio (TMOS is 1mol ratio) of dimethylformamide and 1mol ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 2mol/L of sodium bicarbonate solution into the silica sol to increase the pH to about 7.0. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the glutaraldehyde solution accounts for 0.5% of the mass concentration of the solution, and magnetically stirring until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:0.2, mixing and fully and magnetically stirring uniformly;
and 103, pouring the dispersion liquid into a mould during fast gelation, and obtaining the chitosan-silicon dioxide hybrid gel after gelation. Aging the hybrid gel at normal temperature for 12 hours to enable the gel to completely react, then soaking the hybrid gel in a mixed aging solution of TMOS and ethanol containing 5wt.% of TMOS, wherein the volume of the mixed aging solution is 2 times that of the gel, and aging the mixed aging solution at 40 ℃ for 48 hours;
step 104, removing the aging liquid, soaking the gel in a replacement solvent which is 5 times of gel volume and contains a mixed solvent of water with the water content of 4wt.% and tertiary butanol at the temperature of about 35 ℃, replacing the replacement solvent once every 24 hours, and completing solvent replacement after 2 times of replacement to obtain replaced gel, wherein the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 4wt.% and tertiary butanol;
and 105, transferring the gel after replacement into a freeze dryer, pre-freezing for 2 hours at the temperature of minus 30 ℃, and performing vacuum freeze drying for 36 hours to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.07g/cm 3 The specific surface area reaches 651m 2 And/g, the thermal conductivity is as low as 0.029W/(m.K), the compressive strength is up to 0.81MPa, the Young's modulus is up to 0.44MPa, and the compressive strength is up to 1.93MPa.
Example 2:
step 201, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor solution with the mass fraction of chitosan of 2% and the pH=1. Uniformly mixing TEOS, methanol and distilled water according to a molar ratio of 1:6:3, adding glacial acetic acid until the pH value of the solution is reduced to 3.0, and hydrolyzing for 8 hours at 60 ℃;
step 202, adding 0.1 mol ratio (calculated by TEOS as 1mol ratio) of dimethylformamide and 1mol ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 2mol/L of ammonia water solution into the silica sol to increase the pH to about 7.5. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the glutaraldehyde solution accounts for 1% of the mass concentration of the solution, and magnetically stirring until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:5, mixing and fully and magnetically stirring uniformly;
and 203, pouring the dispersion liquid into a mould during fast gelation, and obtaining the chitosan-silicon dioxide hybrid gel after gelation. Aging the hybrid gel at 60 ℃ for 12 hours to enable the gel to completely react, then soaking the hybrid gel in a mixed aging solution of 5wt.% TEOS and ethanol, wherein the mixed aging solution is 2 times of the gel volume and is used for aging 6h at 60 ℃;
step 204, removing the aging liquid, soaking the gel in a replacement solvent of a mixed solution of water with the water content of 10wt.% and tertiary butanol, wherein the replacement solvent is replaced every 8 hours, and the replacement of the solvent is completed after 6 times of replacement, so as to obtain a replaced gel, and the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 10wt.% and tertiary butanol;
step 205, transferring the gel after replacement into a freeze dryer, pre-freezing for 1h at the temperature of minus 55 ℃, and then performing vacuum freeze drying for 72h to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.15g/cm 3 The specific surface area reaches 891m 2 And/g, the thermal conductivity is as low as 0.031W/(m.K), the compressive strength is up to 1.51MPa, the Young's modulus is up to 2.21MPa, and the compressive strength is up to 5.89MPa.
Example 3:
step 301, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor solution with the mass fraction of chitosan of 1% and the pH=4. Uniformly mixing TEOS, ethanol and distilled water according to a molar ratio of 1:10:4, adding glacial acetic acid until the pH value of the solution is reduced to 4.0, and hydrolyzing for 10 hours at 50 ℃;
step 302, adding 0.2 mole ratio (calculated by TEOS as 1 mole ratio) of dimethylformamide and 1 mole ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 1 mole/L of ammonia water solution into the silica sol to increase the pH to about 7.1. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the glutaraldehyde solution accounts for 1.5% of the mass concentration of the solution, and magnetically stirring until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:1, mixing and fully and magnetically stirring uniformly;
and 303, pouring the dispersion liquid into a mould during fast gelation, and obtaining the chitosan-silicon dioxide hybrid gel after gelation. Aging the hybrid gel at 55 ℃ for 10 hours to enable the internal reaction of the gel to be complete, then soaking the hybrid gel in ethanol aging liquid with the volume being 2 times of that of the gel, and aging for 10 hours at 55 ℃;
step 304, removing aging liquid, soaking gel in a replacement solvent of a mixed solution of water with the water content of 20wt.% and tertiary butanol, wherein the replacement solvent is replaced every 12 hours, and the replacement of the solvent is completed after 4 times of replacement, so as to obtain replaced gel, and the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 20wt.% and tertiary butanol;
and 305, transferring the gel after replacement into a freeze dryer, pre-freezing for 2 hours at the temperature of minus 50 ℃, and performing vacuum freeze drying for 68 hours to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.09g/cm 3 Specific surface area up to 793m 2 And/g, the thermal conductivity is as low as 0.027W/(m.K), the compression strength is up to 1.91MPa, the Young's modulus is up to 1.25MPa, and the compression strength is up to 4.57MPa.
Example 4:
step 401, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor liquid with the mass fraction of chitosan of 1.5% and the pH=3. Uniformly mixing TMOS, methanol and distilled water according to a molar ratio of 1:12:4, adding 2mol/L dilute hydrochloric acid until the pH value of the solution is reduced to 2.0, and hydrolyzing for 12 hours at 45 ℃;
step 402, adding 0.09 mol ratio (TMOS is 1mol ratio) of dimethylformamide and 1mol ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 1mol/L of sodium carbonate solution into the silica sol to increase the pH to about 6.8. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the mass concentration of the glutaraldehyde solution is 1.2%, and magnetically stirring the glutaraldehyde solution until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:0.5, mixing and fully and magnetically stirring uniformly;
and 403, pouring the dispersion liquid into a mould during fast gelation, and obtaining the chitosan-silicon dioxide hybrid gel after gelation. Aging the hybrid gel at 45 ℃ for 12 hours to enable the internal reaction of the gel to be complete, then soaking the hybrid gel in methanol aging liquid with the volume being 2 times of that of the gel, and aging for 12 hours at 45 ℃;
step 404, removing the aging liquid, soaking the gel in a replacement solvent of a mixed solution of water with the water content of 80wt.% and tertiary butanol, wherein the replacement solvent is replaced every 16 hours, and the replacement of the solvent is completed after 3 times of replacement, so as to obtain a replaced gel, and the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 80wt.% and tertiary butanol;
and 405, transferring the gel after replacement into a freeze dryer, pre-freezing for 2 hours at the temperature of minus 45 ℃, and performing vacuum freeze drying for 66 hours to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.08g/cm 3 The specific surface area reaches 687m 2 And/g, the thermal conductivity is as low as 0.031W/(m.K), the compressive strength is up to 1.76MPa, the Young's modulus is up to 0.75MPa, and the compressive strength is up to 3.41MPa.
Example 5:
step 501, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor liquid with the mass fraction of chitosan of 1.2% and the pH=3.5. Uniformly mixing TEOS, ethanol and distilled water according to a molar ratio of 1:11:3, adding 1mol/L dilute nitric acid until the pH value of the solution is reduced to 2.5, and hydrolyzing for 8 hours at 50 ℃;
step 502, adding 0.2 mol ratio (TEOS is 1mol ratio, the same applies hereinafter) of dimethylformamide and 1mol ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 1mol/L of ammonia water solution into the silica sol to increase the pH to about 7.2. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the glutaraldehyde solution accounts for 0.9% of the mass concentration of the solution, and magnetically stirring until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:2, mixing and fully and magnetically stirring uniformly;
and 503, pouring the dispersion liquid into a mould during fast gelation, and obtaining the chitosan-silicon dioxide hybrid gel after gelation. Aging the hybrid gel at 55 ℃ for 10 hours to enable the internal reaction of the gel to be complete, then soaking the hybrid gel in ethanol aging liquid with the volume being 2 times of that of the gel, and aging for 10 hours at 55 ℃;
step 504, removing aging liquid, soaking gel in a replacement solvent of a mixed solution of water with the water content of 85wt.% and tert-butanol, wherein the replacement solvent is replaced every 20 hours for 3 times at the temperature of about 55 ℃ to obtain replaced gel, and the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 85wt.% and tert-butanol;
and 505, transferring the gel after replacement into a freeze dryer, pre-freezing for 2 hours at the temperature of minus 55 ℃, and performing vacuum freeze drying for 70 hours to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.08g/cm 3 The specific surface area reaches 811m 2 And/g, the thermal conductivity is as low as 0.033W/(m.K), the compression strength is up to 1.34MPa, the Young's modulus is up to 0.54MPa, and the compression strength is up to 1.95MPa.
Example 6:
step 601, mixing chitosan, acetic acid and distilled water, heating and continuously stirring to obtain a precursor liquid with the mass fraction of chitosan of 5% and the pH=4. Uniformly mixing TEOS, ethanol and distilled water according to a molar ratio of 1:10:3, adding 1.5mol/L dilute nitric acid until the pH value of the solution is reduced to 3, and hydrolyzing for 6 hours at 55 ℃;
step 602, adding 0.1 mol ratio (calculated by TEOS as 1mol ratio) of dimethylformamide and 1mol ratio of distilled water into the hydrolyzed sol, uniformly mixing, and continuously adding 2mol/L of ammonia water solution into the silica sol to increase the pH to about 7. And slowly adding glutaraldehyde solution into the chitosan precursor solution until the glutaraldehyde solution accounts for 0.6% of the mass concentration of the solution, and magnetically stirring until the glutaraldehyde solution is uniform. The method comprises the following steps of (1) mixing an ungelled chitosan precursor solution with a silicon source precursor solution according to a mass ratio of 1:3, mixing and fully and magnetically stirring uniformly;
and 603, pouring the dispersion liquid into a mould during the gel, and obtaining the chitosan-silicon dioxide hybrid gel after the gel. Aging the hybrid gel at 55 ℃ for 8 hours to enable the internal reaction of the gel to be complete, then soaking the hybrid gel in ethanol aging liquid with the volume being 2 times of that of the gel, and aging for 12 hours at 55 ℃;
step 604, removing the aging liquid, soaking the gel in a replacement solvent of a mixed solution of water with the water content of 11wt.% and tert-butanol, wherein the replacement solvent is replaced every 12 hours, and the replacement of the solvent is completed after 4 times of replacement, so as to obtain a replaced gel, and the internal solvent of the replaced hybrid gel is the mixed solvent of water with the water content of 11wt.% and tert-butanol;
step 605, transferring the gel after replacement into a freeze dryer, pre-freezing for 2 hours at the temperature of minus 50 ℃, and then performing vacuum freeze drying for 62 hours to obtain the freeze-dried chitosan-silicon dioxide hybrid aerogel.
The density of the hybrid aerogel was tested to be 0.13g/cm 3 The specific surface area reaches 845m 2 And/g, the thermal conductivity is as low as 0.035W/(m.K), the compression strength is up to 3.19MPa, the Young's modulus is up to 2.05MPa, and the compression strength is up to 5.83MPa.
According to the embodiment of the application, the chitosan-silicon dioxide hybrid wet gel is prepared by a sol-gel method, the internal solvent of the hybrid gel is replaced by a cosolvent of tertiary butanol and water in a specific range proportion by a solvent replacement process, and finally the chitosan-silicon dioxide hybrid aerogel is prepared by a vacuum freeze drying method. Compared with the traditional supercritical drying method and normal pressure drying method, the chitosan-silicon dioxide hybrid aerogel prepared by adopting the method of vacuum freeze drying under the cosolvent of tertiary butanol and water in a specific proportion in the embodiment of the application is safe, environment-friendly and low in cost, and the obtained chitosan-silicon dioxide hybrid aerogel material is good in quality, low in shrinkage rate, large in specific surface area and thorough in drying, and is an ideal method for preparing the chitosan-silicon dioxide hybrid aerogel.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment focuses on differences from other embodiments. In particular, for the method embodiments described later, since they correspond to the system, the description is relatively simple, and reference should be made to the description of some of the system embodiments.
The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present application should be included in the present application. Therefore, the protection scope of the application is subject to the protection scope of the claims.
Claims (9)
1. A method for preparing chitosan-silica hybrid aerogel by freeze drying, which is characterized by comprising the following steps:
step 1, preparing a chitosan precursor liquid, mixing chitosan, acetic acid and distilled water, and continuously stirring under a heating condition to obtain the chitosan precursor liquid;
step 2, preparing a silicon source precursor liquid, mixing a silicon source, an alcohol solvent and distilled water, and regulating the pH to 2-4.5 by using an acid catalyst; hydrolyzing at 30-60 ℃, adding dimethylformamide and distilled water into the hydrolyzed sol, and uniformly mixing to obtain silica sol to be polycondensed;
step 3, preparing hybrid gel, namely slowly adding glutaraldehyde solution into the chitosan precursor solution obtained in the step 1, magnetically stirring until uniformity, slowly adding a base catalyst into the silicon source precursor solution obtained in the step 2 until the pH of a dispersion liquid is increased to 6-8, magnetically stirring until uniformity, then mixing the ungelled chitosan precursor solution and the silicon source precursor solution according to a ratio (1:0.2-5) and fully magnetically stirring uniformly, pouring the mixed solution into a mould before gel, and obtaining the chitosan-silicon dioxide hybrid gel after gel;
step 4, replacing the solvent, namely placing the hybrid gel obtained in the step 3 into a plastic groove, sealing the plastic groove, placing the plastic groove into a constant temperature box, completely reacting the inside of the gel under an aging condition, and then soaking the hybrid gel into an aging solution for aging under the aging condition; removing the aging liquid to finish solvent replacement, and obtaining replaced hybrid gel, wherein after the replacement is finished, the solvent in the hybrid gel is replaced by a mixed solvent in a specific proportion range, the mixed solvent is a mixed solvent of tertiary butanol and water, the mixed solvent is a mixed solvent of tertiary butanol with water content of 4-25 wt.% when the water content of the mixed solvent is low, and the mixed solvent is a mixed solvent of tertiary butanol with water content of 75-85 wt.% when the water content of the mixed solvent is high, and the mixed solvent is matched with the proportion of solvent components in the gel after target replacement;
and 5, freeze drying, namely performing vacuum freeze drying on the hybrid gel obtained in the step 4 to obtain chitosan-silicon dioxide hybrid aerogel, wherein in the vacuum freeze drying, the hybrid gel is pre-frozen for 1-2 h at the temperature of minus 30 ℃ to minus 55 ℃, and then is dried for 36-72 h under the pressure of lower than 100 Pa in a freeze drying chamber of a vacuum freeze dryer, wherein the hybrid gel is dried for 24h at least at a temperature platform lower than minus 20 ℃.
2. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 1, the mass concentration of the chitosan in the precursor solution is controlled to be 0.5% -5%, and the pH value of the precursor solution is controlled to be 1-4.
3. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 2, the silicon source is one or two of TEOS and TMOS, the alcohol solvent is one or more of ethanol, methanol, isopropanol and tert-butanol, the acid catalyst is one or more of acetic acid, oxalic acid, hydrochloric acid and citric acid, the acid catalyst is a dilute solution prepared by 0.5mol/L to 4mol/L, the molar ratio of the silicon source to the alcohol solvent to the distilled water is 1 (6 to 14): (2 to 4), and the hydrolysis time range is 4h to 24h.
4. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 2, the molar addition ratio of dimethylformamide to distilled water is (0.05-0.2): 1-4.
5. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 3, the mold is a plastic container, and the mold is sized to be placed in a plastic tank used in the subsequent aging and replacement processes and placed in a lyophilization chamber of a freeze dryer.
6. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 3, glutaraldehyde is added to 0.5% -1% of the solution mass concentration; the alkali catalyst is one or more of ammonia water, potassium hydroxide, sodium bicarbonate and sodium carbonate, and the use mode of the alkali catalyst is that the alkali catalyst is prepared into a dilute solution of 0.5 mol/L-4 mol/L.
7. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 4, the aging liquid is an alcohol solvent or a mixture of one or two of alcohol solvent and TEOS/TMOS, and the alcohol solvent is one or more of ethanol and methanol.
8. The method for preparing a chitosan-silica hybrid aerogel according to claim 7, wherein when the mixed liquid of one or both of the alcohol solvent and TEOS/TMOS is used, the mass fraction of the alcohol solvent is 90% to 95%.
9. The method for preparing chitosan-silica hybrid aerogel according to claim 1, wherein in the step 4, the aging condition is aging for 6-12 hours at 20-60 ℃, the aging condition is aging for 6-48 hours at 40-60 ℃, the solvent replacement is completed by immersing the hybrid gel in a replacement solvent with a volume of 2-5 times of gel at 35-60 ℃ and replacing the replacement solvent every 8-24 hours for 2-6 times.
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