CN106867019B - Method for preparing SiO2-cellulose composite aerogel material by one-pot method - Google Patents
Method for preparing SiO2-cellulose composite aerogel material by one-pot method Download PDFInfo
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- 239000001913 cellulose Substances 0.000 title claims abstract description 161
- 229920002678 cellulose Polymers 0.000 title claims abstract description 159
- 239000004964 aerogel Substances 0.000 title claims abstract description 49
- 239000002131 composite material Substances 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 35
- 239000000463 material Substances 0.000 title claims abstract description 19
- 238000005580 one pot reaction Methods 0.000 title claims abstract description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 42
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 40
- 239000010703 silicon Substances 0.000 claims abstract description 40
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000004115 Sodium Silicate Substances 0.000 claims abstract description 34
- 229910052911 sodium silicate Inorganic materials 0.000 claims abstract description 34
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 27
- 238000003756 stirring Methods 0.000 claims abstract description 25
- 239000011240 wet gel Substances 0.000 claims abstract description 25
- 239000007864 aqueous solution Substances 0.000 claims abstract description 24
- 239000002904 solvent Substances 0.000 claims abstract description 15
- 239000000499 gel Substances 0.000 claims abstract description 13
- PTHCMJGKKRQCBF-UHFFFAOYSA-N Cellulose, microcrystalline Chemical compound OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC)C(CO)O1 PTHCMJGKKRQCBF-UHFFFAOYSA-N 0.000 claims abstract description 12
- 238000000352 supercritical drying Methods 0.000 claims abstract description 9
- 229910004298 SiO 2 Inorganic materials 0.000 claims abstract 3
- 235000010980 cellulose Nutrition 0.000 claims description 109
- 239000000243 solution Substances 0.000 claims description 63
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 35
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 26
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 18
- 239000004202 carbamide Substances 0.000 claims description 18
- 239000011259 mixed solution Substances 0.000 claims description 16
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 15
- 238000002156 mixing Methods 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- 239000002253 acid Substances 0.000 claims description 13
- 239000011148 porous material Substances 0.000 claims description 13
- 238000002360 preparation method Methods 0.000 claims description 13
- 238000001035 drying Methods 0.000 claims description 12
- 239000003513 alkali Substances 0.000 claims description 11
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 10
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
- 230000032683 aging Effects 0.000 claims description 10
- 239000012153 distilled water Substances 0.000 claims description 10
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 9
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 9
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 8
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 6
- 229920000742 Cotton Polymers 0.000 claims description 6
- 239000000017 hydrogel Substances 0.000 claims description 6
- 238000006386 neutralization reaction Methods 0.000 claims description 6
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 claims description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 5
- 235000019353 potassium silicate Nutrition 0.000 claims description 5
- 239000000843 powder Substances 0.000 claims description 5
- 230000008929 regeneration Effects 0.000 claims description 5
- 238000011069 regeneration method Methods 0.000 claims description 5
- 229920003043 Cellulose fiber Polymers 0.000 claims description 4
- 239000003960 organic solvent Substances 0.000 claims description 4
- 229920000168 Microcrystalline cellulose Polymers 0.000 claims description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 3
- 239000001569 carbon dioxide Substances 0.000 claims description 3
- 238000005345 coagulation Methods 0.000 claims description 3
- 230000015271 coagulation Effects 0.000 claims description 3
- 235000019813 microcrystalline cellulose Nutrition 0.000 claims description 3
- 239000008108 microcrystalline cellulose Substances 0.000 claims description 3
- 229940016286 microcrystalline cellulose Drugs 0.000 claims description 3
- 229910017604 nitric acid Inorganic materials 0.000 claims description 3
- 238000005119 centrifugation Methods 0.000 claims description 2
- 239000008367 deionised water Substances 0.000 claims description 2
- 229910021641 deionized water Inorganic materials 0.000 claims description 2
- 238000007789 sealing Methods 0.000 claims description 2
- PHIQPXBZDGYJOG-UHFFFAOYSA-N sodium silicate nonahydrate Chemical compound O.O.O.O.O.O.O.O.O.[Na+].[Na+].[O-][Si]([O-])=O PHIQPXBZDGYJOG-UHFFFAOYSA-N 0.000 claims description 2
- -1 sodium silicate pentahydrate Chemical class 0.000 claims description 2
- 230000000284 resting effect Effects 0.000 claims 1
- 229910052681 coesite Inorganic materials 0.000 abstract description 16
- 229910052906 cristobalite Inorganic materials 0.000 abstract description 16
- 229910052682 stishovite Inorganic materials 0.000 abstract description 16
- 229910052905 tridymite Inorganic materials 0.000 abstract description 16
- 235000012239 silicon dioxide Nutrition 0.000 abstract description 8
- 239000012774 insulation material Substances 0.000 abstract description 3
- 239000002994 raw material Substances 0.000 abstract description 3
- 238000005470 impregnation Methods 0.000 abstract description 2
- 238000009413 insulation Methods 0.000 abstract description 2
- 239000007810 chemical reaction solvent Substances 0.000 abstract 1
- 239000006185 dispersion Substances 0.000 abstract 1
- 239000000835 fiber Substances 0.000 abstract 1
- 238000011065 in-situ storage Methods 0.000 abstract 1
- 150000007522 mineralic acids Chemical class 0.000 abstract 1
- 239000004627 regenerated cellulose Substances 0.000 abstract 1
- 238000003980 solgel method Methods 0.000 abstract 1
- 238000001179 sorption measurement Methods 0.000 abstract 1
- 210000002700 urine Anatomy 0.000 abstract 1
- 239000011734 sodium Substances 0.000 description 13
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 9
- 229910052708 sodium Inorganic materials 0.000 description 9
- 230000001112 coagulating effect Effects 0.000 description 5
- 239000011159 matrix material Substances 0.000 description 5
- 230000001939 inductive effect Effects 0.000 description 4
- 238000005191 phase separation Methods 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- 238000002210 supercritical carbon dioxide drying Methods 0.000 description 4
- 229910020489 SiO3 Inorganic materials 0.000 description 3
- 238000003760 magnetic stirring Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001879 gelation Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000010355 oscillation Effects 0.000 description 2
- 238000004626 scanning electron microscopy Methods 0.000 description 2
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 2
- 238000002336 sorption--desorption measurement Methods 0.000 description 2
- 239000012798 spherical particle Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 241000218691 Cupressaceae Species 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 239000004965 Silica aerogel Substances 0.000 description 1
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical class [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 238000005904 alkaline hydrolysis reaction Methods 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 229940079593 drug Drugs 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 150000004676 glycans Chemical class 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000000413 hydrolysate Substances 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 239000008204 material by function Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 239000012047 saturated solution Substances 0.000 description 1
- 229910000077 silane Inorganic materials 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000010183 spectrum analysis Methods 0.000 description 1
- LFQCEHFDDXELDD-UHFFFAOYSA-N tetramethyl orthosilicate Chemical compound CO[Si](OC)(OC)OC LFQCEHFDDXELDD-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
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- 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
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
-
- 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
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
- C08J3/075—Macromolecular gels
-
- 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
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/34—Silicon-containing compounds
- C08K3/36—Silica
-
- 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
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/05—Elimination by evaporation or heat degradation of a liquid phase
- C08J2201/0502—Elimination by evaporation or heat degradation of a liquid phase the liquid phase being organic
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- 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
- C08J2205/00—Foams characterised by their properties
- C08J2205/02—Foams characterised by their properties the finished foam itself being a gel or a gel being temporarily formed when processing the foamable composition
- C08J2205/026—Aerogel, i.e. a supercritically dried gel
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- 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
- C08J2301/00—Characterised by the use of cellulose, modified cellulose or cellulose derivatives
- C08J2301/02—Cellulose; Modified cellulose
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- Dispersion Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Silicon Compounds (AREA)
Abstract
本发明涉及一种一锅法制备SiO2‑纤维素复合气凝胶材料的方法，以纤维素为原料，绿色碱尿溶剂溶解纤维素；以无机硅酸钠为硅源，通过搅拌分散获得纤维素和硅酸钠均匀混合水性溶液，结合溶胶‑凝胶法得到含硅源的再生纤维素湿凝胶；以纤维素凝胶为骨架，以无机酸为反应溶剂诱导生成SiO2，最后通过CO2超临界干燥工艺制干燥得到SiO2‑纤维素有机‑无机复合气凝胶。本发明工艺简易快速、可行性高且绿色环保，有效克服原位浸渍法中SiO2在纤维素多孔网络结构中分散性差、复合含量低和复合稳定性差等问题，所制备的无机‑有机复合气凝胶具有较低的导热系数、良好的隔热性能，在低温保冷材料、中低温隔热保温材料以及吸附材料方面具有良好的应用前景。
The invention relates to a one-pot method for preparing a SiO 2 -cellulose composite aerogel material. The cellulose is used as a raw material, and the green alkaline urine solvent dissolves the cellulose; the inorganic sodium silicate is used as the silicon source, and fibers are obtained by stirring and dispersing Silica and sodium silicate are uniformly mixed with an aqueous solution, and combined with the sol-gel method to obtain a regenerated cellulose wet gel containing silicon source; the cellulose gel is used as the skeleton, and the inorganic acid is used as the reaction solvent to induce SiO 2 , and finally pass through CO 2. The supercritical drying process is dried to obtain the SiO2 -cellulose organic-inorganic composite aerogel. The process of the invention is simple, fast, highly feasible and environmentally friendly, and effectively overcomes the problems of poor dispersion, low composite content and poor composite stability of SiO2 in the cellulose porous network structure in the in-situ impregnation method. The prepared inorganic-organic composite gas The gel has low thermal conductivity and good thermal insulation performance, and has good application prospects in low temperature cold insulation materials, medium and low temperature thermal insulation materials and adsorption materials.
Description
Technical Field
The invention belongs to the field of preparation of high-molecular nano functional materials, and relates to a one-pot method for preparing SiO2-a method of cellulose composite aerogel material.
Background
Cellulose aerogels are a new class of natural biomass novel materials that have been developed in recent years. Cellulose is a green renewable resource with the largest reserve on the earth, and cellulose aerogel has the characteristics of renewable natural high molecular weight and a plurality of advantages of the traditional high-porosity nano inorganic porous material, and has the characteristics of good toughness, easy processing and the like compared with silicon aerogel with poor strength and fragility, so that the cellulose aerogel becomes a new material with wide application prospect and high development value, and has great potential in controlling drug release of a bracket, a gas absorbent, a heat insulation material, a carbon battery during pyrolysis and an electrode material of the fuel battery.
Cellulose aerogel has many excellent characteristics, but the limitations of polysaccharide aerogel, such as poor stability and poor flame retardancy, limit the development of cellulose aerogel to some extent. Conventional SiO2Aerogels, while excellent in performance, are difficult to overcome for friability. And cellulose-SiO2The composite aerogel not only has the characteristics of two kinds of aerogels, but also shows a plurality of new excellent performances.
Conventional SiO2Cellulose composite aerogels are generally obtained by impregnating a wet cellulose film into tetraethylorthosilicate/methylsilicate, forming a silica aerogel in the micropores of a cellulose matrix and then subjecting the cellulose matrix to supercritical CO2Medium drying, etc., however, this method causes the silica to rapidly gel on the outer surface of the cellulose, thereby blocking the pore openings and preventing the silica from penetrating into the cellulose matrix, and the porosity is urgently decreased. However, the method of directly mixing the cellulose solution with the tetraethoxysilane is not preferable, and the alkali-soluble cellulose solution is a metastable system, and the direct mixing with the silane hydrolysate can cause the cellulose to be immediately solidified and the silica sol to be phase-separated.
Aqueous sodium silicate is a basic silicate, the saturated solution having a pH of about 14; the same pH value of 14 alkali solution cellulose aqueous solution sodium silicate solution is used as initial solution, and is directly mixed by adopting one-pot method to form uniform and stable mixed solution, the cellulose self-association in alcohol bath can lead to gelation to generate type II cellulose gel, the sodium silicate solution is dispersed in cellulose network structure, and when the solidified cellulose is placed in acid water bath, the sodium silicate can be converted into SiO2。
Disclosure of Invention
The invention aims at the prior SiO2The limitation in the preparation process of the cellulose composite aerogel provides a pot method for preparing SiO2Method for producing cellulose composite aerogels, which is simple and feasibleThe method has the advantages that the inorganic silicon source is directly and uniformly dispersed into the three-dimensional network structure of the cellulose gel by adopting a one-pot method, the phenomena of pore channel blockage and phase separation are avoided, and simultaneously the SiO can be improved to a certain degree2Mechanical properties and thermal insulation effect of cellulose aerogels.
The technical scheme of the invention is as follows: one-pot method for preparing SiO2-a method for cellulose composite aerogel material, comprising the following specific steps:
(1) preparation of cellulose solution
Dispersing cellulose fibers into an alkali-urea mixed aqueous solution under the stirring action, sealing, precooling to-20 to-5 ℃, taking out, stirring and dissolving the cellulose by using an electric stirrer to obtain a viscous solution, and centrifuging to remove bubbles to obtain a clear and transparent cellulose solution; wherein the mass fractions of cellulose, alkali, urea and deionized water in the cellulose solution are respectively (2% -6%), (4% -20%), (10% -20%), (54% -84%);
(2) preparation of inorganic silicon source-cellulose mixed solution
Dissolving an inorganic silicon source under the stirring action to obtain an inorganic silicon source aqueous solution with the mass fraction of 1-7%; according to the volume ratio of the cellulose aqueous solution to the inorganic silicon source aqueous solution of 1: (0.1-1), adding an inorganic silicon source aqueous solution into a cellulose aqueous solution, stirring and mixing, and then removing bubbles by ultrasonic oscillation to form a uniformly mixed inorganic silicon source-cellulose mixed solution;
(3) preparation of wet gel containing inorganic silicon source-cellulose
Pouring the uniformly mixed inorganic silicon source-cellulose mixed solution into a mould, placing the mould in a coagulating bath for regeneration, and standing to obtain cellulose wet gel containing an inorganic silicon source;
(4) preparation of silica-cellulose Wet gels
Transferring the cellulose wet gel containing the inorganic silicon source into a dilute acid solution, and inducing the inorganic silicon source to form silicon dioxide in cellulose gel pores after a neutralization reaction;
(5) preparation of composite aerogels
Rinsing the wet silica-cellulose gel with distilled water to form a solutionThe pH is 6-8; then transferring the silica-cellulose hydrogel to an organic solvent for solvent placement and aging to obtain silica-cellulose alcohol gel; post-transfer to CO2And (4) drying in a supercritical drying device to finally obtain the silicon dioxide-cellulose composite aerogel.
Preferably, the cellulose fiber in the step (1) is one of cotton pulp, short stapled cotton or microcrystalline cellulose; the alkali in the alkali-urea mixed aqueous solution is one of sodium hydroxide or lithium hydroxide; the urea is urea or thiourea.
Preferably, the rotation speed of the electric stirrer in the step (1) is 1000-2000rpm, and the stirring time is 4-12 min; the rotation speed of the centrifuge is 8000-10000rpm, and the centrifugation time is 5-10 min.
Preferably, the inorganic silicon source in step (2) is sodium silicate pentahydrate powder, sodium silicate nonahydrate powder, anhydrous sodium silicate or alkaline water glass.
Preferably, the coagulating bath in the step (3) is methanol, ethanol, acetone or dilute sulfuric acid. Preferably, the standing time in the step (3) is 5-360 min.
Preferably, the dilute acid solution in the step (4) is hydrochloric acid, nitric acid, sulfuric acid or acetic acid aqueous solution; the concentration of the diluted acid solution is 0.5-1 mol/L.
Preferably, the organic solvent in step (5) is one or a mixture of methanol, ethanol and acetone.
Preferably, the carbon dioxide supercritical drying method in the step (5) takes carbon dioxide as a drying medium, the reaction temperature is 40-70 ℃, the pressure in the high-pressure reaction kettle is 8-12 MPa, and the drying time is 10-20 h.
Preferably, the apparent density of the silicon dioxide-cellulose composite aerogel prepared in the step (5) is 0.092-0.143 g/cm3Specific surface area of 227.41-264.93 m2The coefficient of thermal conductivity is between 0.029 and 0.038W/m.K.
Has the advantages that:
the method of the invention and the organic-inorganic composite SiO prepared by the one-pot method2The cellulose aerogel materials have the following characteristics:
(1) the process is simple and effective. The preparation method overcomesSiO in dipping method preparation method2The problem of pore channel blockage in the case of cellulose aerogel materials and the problem of phase separation of the organic silicon source from the alkali-soluble cellulose solution. In the dipping method, the silica sol is penetrated into the three-dimensional cellulose matrix to fill the space of the porous cellulose gel. This process has certain limitations because it is a diffusion process, the silica distribution in the cellulose matrix is not uniform, it is susceptible to the preparation of cellulose gel, and the time required for the impregnation process is long. The organic silicon source and the alkali-soluble cellulose aqueous solution are directly mixed, because the alkali-soluble cellulose aqueous solution is not really dissolved but is in a metastable state dissolving system, after the organic silicon source is added, the organic silicon source is strongly hydrolyzed, and competes for water with cellulose, so that hydrogen bonds among and in cellulose molecules are exposed, and rapid gelation and phase separation of the cellulose occur. And sodium silicate which is alkaline at the same time is selected as a silicon source, and a metastable state dissolving system cannot be damaged when the sodium silicate is directly mixed into an alkaline hydrolysis cellulose solution after being dissolved, and meanwhile, the occurrence of phase separation is also inhibited, and a stable solution which is uniformly mixed can be formed. After the gel is washed by alcohol, sodium silicate is converted to the direction of producing silicon dioxide and sodium salt under the action of acid, and finally, SiO is obtained by supercritical drying2-a cellulose composite aerogel.
(2) The raw materials are low in price and wide in source, and the mainly selected cellulose and sodium silicate (water glass) are cheap and easily available industrial raw materials, so that the production and manufacturing cost is greatly reduced, and the large-scale production is easy to realize. And has good green environmental protection effect. Meanwhile, all selected cellulose dissolving systems are green, and only sodium hydroxide, urea and other materials are needed to dissolve cellulose in a low-temperature environment, so that the method is simple and effective.
(3) Compared with other aerogel heat-insulating materials, the SiO is prepared by adopting a one-pot mixing method2Cellulose composite aerogel, which takes a three-dimensional network structure of the cellulose aerogel as a generation template, sodium silicate is filled in holes of cellulose, and SiO is generated under the catalysis of an acid solution2Particles of SiO2Agglomeration into larger spherical particles to form agglomerates attached to the nanofibrils of cellulose, avoiding free SiO2The particles appear, the prepared material has smooth surface, controllable thickness and better formability, and the prepared SiO has2The microstructure of the cellulose composite aerogel is shown by a scanning electron microscope image. And the prepared SiO2The cellulose composite aerogel still has extremely high porosity and relatively uniform pore structure.
Drawings
FIG. 1 is SiO as prepared in example 12-a sample plot of a cellulose composite aerogel material;
FIG. 2 is SiO as prepared in example 22-an X-ray diffraction pattern of a cellulose composite aerogel material;
FIG. 3 is SiO as prepared in example 22-scanning electron microscopy of cellulose composite aerogel material;
FIG. 4 is SiO as prepared in example 32-nitrogen adsorption-desorption curve of cellulose composite aerogel.
Detailed Description
Example 1
1. 2g of microcrystalline cellulose were dispersed with stirring in an alkali urea solution (4.0g LiOH/10g Urea/84g H)2O), transferring the dispersed cellulose into a refrigerator to pre-cool the cellulose at-5 ℃, immediately stirring the cellulose for 4min by using a motor under the condition of 2000rpm after taking out the cellulose to obtain a viscous solution, and immediately centrifuging the cellulose for 10min under the condition of 8000rpm to remove air bubbles to obtain a clear and transparent cellulose solution, wherein the mass fraction of the solvent is 2%; 16.3g of Na were weighed2SiO3·9H2Dissolving O into 83.7g of distilled water by magnetic stirring to obtain a sodium silicate aqueous solution with the mass fraction of 7%, and mixing the cellulose solution and the sodium silicate solution according to the volume ratio of 10: 1, mechanically stirring and mixing, and then ultrasonically oscillating to remove bubbles to form a uniformly mixed sodium silicate-cellulose mixed solution. And pouring the uniformly mixed sodium silicate-cellulose mixed solution into a mould, putting the mould into a methanol coagulating bath for regeneration, and standing for 360min to obtain the cellulose wet gel containing sodium silicate. After aging, demoulding the cellulose wet gel containing sodium silicate, transferring the cellulose wet gel into dilute sulfuric acid solution with the volume of 200ML and the concentration of 0.5mol/L, inducing sodium silicate to generate silicon dioxide in cellulose gel pores after neutralization reaction, and thenThe silica-cellulose composite wet gel was rinsed with distilled water to remove excess acid and salt formed, at which time the solution had a pH of 7. Then transferring the silica-cellulose hydrogel to ethanol solvent for solvent replacement and aging, replacing for 8 times in total to obtain silica-cellulose alcohol gel, and placing the silica-cellulose alcohol gel in CO2Drying in a supercritical drying device at 40 deg.C under 8MPa for 20 hr. Passing through supercritical CO2Drying to form organic-inorganic SiO2-a cellulose aerogel. The density was 0.092/cm3Specific surface area of 227.41m2The coefficient of thermal conductivity is 0.032W/m.K. FIG. 1 is the SiO prepared in example 12-a sample plot of a cellulose composite aerogel material. As can be seen in the figure, the composite aerogel and the pure cellulose aerogel have the same milky white color, the surface of the material is flat, the powder falling condition is avoided, and the mechanical strength is good.
Example 2
6g of cotton pulp cypress cellulose are dispersed with stirring in an alkali urea solution (4g of LiOH/10g of Thiourea/80g of H)2O), transferring the dispersed cellulose into a refrigerator to pre-cool the cellulose at-20 ℃, taking out the cellulose, immediately stirring the cellulose for 4min by using a motor under the condition of 2000rpm to obtain a viscous solution, and immediately centrifuging the cellulose for 5min under the condition that the rotation speed is 10000rpm to remove air bubbles to obtain a clear and transparent cellulose solution, wherein the mass fraction of the solvent is 6%; 1.74g of Na were weighed2SiO3·5H2Dissolving O into 98.3g of distilled water by magnetic stirring to obtain a sodium silicate aqueous solution with the mass fraction of 1%, and mixing the cellulose solution and the sodium silicate solution according to the volume ratio of 1: 1, mechanically stirring and mixing, and ultrasonically oscillating to remove bubbles to form a uniformly mixed sodium silicate-cellulose mixed solution. And pouring the uniformly mixed sodium silicate-cellulose mixed solution into a mould, putting the mould into an ethanol coagulating bath for regeneration, and standing for 60min to obtain the cellulose wet gel containing sodium silicate. After aging, demoulding the cellulose wet gel containing sodium silicate, transferring the cellulose wet gel into dilute hydrochloric acid solution with the volume of 100ML and the concentration of 1mol/L, inducing sodium silicate to generate silicon dioxide in cellulose gel pores after neutralization reaction, and thenThe silica-cellulose composite wet gel was rinsed with distilled water to remove excess acid and salt formed, at which time the pH of the wash solution was 7. Then transferring the silica-cellulose hydrogel to a methanol solvent for solvent replacement and aging, replacing for 5 times in total to finally obtain the silica-cellulose alcohol gel, and placing the silica-cellulose alcohol gel in CO2Drying in a supercritical drying device at 40 deg.C under 8MPa for 20 hr. Passing through supercritical CO2Drying to form organic-inorganic SiO2-a cellulose aerogel. The density was 0.143/cm3Specific surface area of 243.46m2The coefficient of thermal conductivity is 0.032W/m.K. FIG. 2 is SiO2-scanning electron microscopy of cellulose composite aerogel materials, SiO2Agglomerated into agglomerates of larger spherical particles, adhering to the three-dimensional network structure of the cellulose gel (as indicated by the reference symbols in the figure), SiO2Formed in the pore structure of cellulose and has no free SiO2Particles appear. FIG. 3 is SiO2Cross-sectional energy spectrum of cellulose composite aerogel, EDS energy spectrum analysis shows that Si peak is approximately located at 1.73KeV, Na peak is 1.04KeV, mainly because of SiO2Sodium salts are formed as a result of the conversion process.
Example 3
3g of linters cotton cellulose was dispersed with stirring in an alkali urea solution (4.6 g NaOH/15g Urea/77.4g H therein)2O), transferring the dispersed solution to a refrigerator for precooling at-15 ℃, immediately stirring the solution for 12min by using a motor under the condition of 1000rpm after taking out the solution to obtain a viscous solution, and immediately centrifuging the solution for 10min under the condition of 8000rpm to remove air bubbles to obtain a clear and transparent cellulose solution, wherein the mass fraction of the solvent is about 3%; 3g of anhydrous Na was weighed2SiO3Dissolving the mixture into 97ml of distilled water by magnetic stirring to obtain a sodium silicate aqueous solution with the mass fraction of 3%, and mixing the cellulose solution and the sodium silicate solution according to the volume ratio of 2: 1, mechanically stirring, mixing, mechanically stirring and mixing, and removing bubbles by ultrasonic oscillation to form a uniformly mixed sodium silicate-cellulose mixed solution. Then pouring the uniformly mixed sodium silicate-cellulose mixed solution into a mould and placing the mould in acetoneRegenerating in coagulating bath, standing for 5min to obtain cellulose wet gel containing sodium silicate. After aging, demoulding the cellulose wet gel containing sodium silicate, transferring the cellulose wet gel into dilute nitric acid solution with the volume of 200ML concentration, inducing sodium silicate to generate silicon dioxide in cellulose gel pores after neutralization reaction, rinsing the silicon dioxide-cellulose composite wet gel by using distilled water to remove excessive acid and generated salt, wherein the pH value of the washing solution is 6. Then transferring the silicon dioxide-cellulose hydrogel to an acetone solvent for solvent replacement and aging, replacing for 10 times in total to finally obtain silicon dioxide-cellulose alcohol gel, and placing the silicon dioxide-cellulose alcohol gel in CO2Drying in a supercritical drying device at 70 deg.C under 12MPa for 10 hr. Passing through supercritical CO2Drying to form organic-inorganic SiO2-a cellulose aerogel. The density was 0.109g/cm3Specific surface area of 264.93m2The coefficient of thermal conductivity is 0.029W/m.K. FIG. 4 is the SiO solution thus prepared2The nitrogen adsorption-desorption curve of the cellulose composite aerogel belongs to IV type in IUPAC classification, and meets the inherent essential characteristics of the porous material.
Example 4
6g of linters cotton cellulose was dispersed with stirring in an alkali urea solution (20 g of NaOH/20g of Urea/54g of H)2O), transferring the dispersed solution to a refrigerator for precooling at-15 ℃, taking out the solution, immediately stirring the solution by using a motor for 5min at 1000rpm to dissolve cellulose to obtain a viscous solution, immediately centrifuging the solution for 5min at 8000rpm to remove bubbles to obtain a clear and transparent cellulose solution, wherein the mass fraction of the solvent is about 3%; weighing 3g of alkaline water glass, magnetically stirring and dissolving the alkaline water glass into 97g of distilled water to obtain a sodium silicate aqueous solution with the mass fraction of about 3%, and mixing a cellulose solution and the sodium silicate solution according to the volume ratio of 1: 1, mechanically stirring and mixing, and ultrasonically oscillating to remove bubbles to form a uniformly mixed sodium silicate-cellulose mixed solution. And pouring the uniformly mixed sodium silicate-cellulose mixed solution into a mould, placing the mould in a dilute sulfuric acid coagulation bath for regeneration, and standing for 5min to obtain the cellulose wet gel containing sodium silicate. After aging, the mixture containing sodium silicateThe cellulose wet gel is transferred to dilute acetic acid solution with the volume of 200ML concentration of lmol/L after being demoulded, sodium silicate is induced to generate silicon dioxide in cellulose gel pores after neutralization reaction, then the silicon dioxide-cellulose composite wet gel is rinsed by distilled water to remove excessive acid and generated salt, and the pH value of the washing solution is 8. Then transferring the silica-cellulose hydrogel to ethanol solvent for solvent replacement and aging, replacing for 7 times in total to obtain silica-cellulose alcohol gel, and placing the silica-cellulose alcohol gel in CO2Drying in a supercritical drying device at 40 deg.C under 8MPa for 20 hr. Passing through supercritical CO2Drying to form organic-inorganic SiO2-a cellulose aerogel. The density was 0.128/cm3The specific surface area is 238.56m2The coefficient of thermal conductivity is 0.033W/m.K.
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