CN106867019B - One-pot method for preparing SiO2Method for producing cellulose composite aerogel material - Google Patents
One-pot method for preparing SiO2Method for producing cellulose composite aerogel material Download PDFInfo
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Abstract
The invention relates to a one-pot method for preparing SiO2The method of the cellulose composite aerogel material takes cellulose as a raw material, and green alkaline urine solvent dissolves the cellulose; inorganic sodium silicate is used as a silicon source, cellulose and sodium silicate are uniformly mixed with an aqueous solution obtained by stirring and dispersing, and a sol-gel method is combined to obtain regenerated cellulose wet gel containing the silicon source; uses cellulose gel as a framework and inorganic acid as a reaction solvent to induce and generate SiO2Finally by CO2Drying by supercritical drying process to obtain SiO2-cellulosic organic-inorganic composite aerogels. The method has the advantages of simple and rapid process, high feasibility, environmental protection and effective overcoming of SiO in the in-situ impregnation method2The prepared inorganic-organic composite aerogel has the advantages of low heat conductivity coefficient, good heat insulation performance and good application prospect in the aspects of low-temperature cold insulation materials, medium and low-temperature heat 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.
Claims (8)
1. 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; the coagulating bath is methanol, ethanol or acetone;
(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 silica-cellulose wet gel with distilled water until the pH of the solution is 6-8; then transferring the silica-cellulose hydrogel to an organic solvent for solvent replacement and aging to obtain silica-cellulose alcohol gel; post-transfer to CO2Drying in a supercritical drying device to finally obtain the silicon dioxide-cellulose composite aerogel; wherein the drying treatment is carried out by taking 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.
2. The method according to claim 1, characterized in that the cellulose fiber in step (1) is one of cotton pulp, short staple 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.
3. The method as claimed in claim 1, wherein the rotation speed of the electric stirrer in 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.
4. The method according to claim 1, wherein the inorganic silicon source in step (2) is sodium silicate pentahydrate powder, sodium silicate nonahydrate powder, anhydrous sodium silicate or alkaline water glass.
5. The method according to claim 1, wherein the standing time in the step (3) is 5 to 360 min.
6. The method according to claim 1, wherein the dilute acid solution in step (4) is an aqueous solution of hydrochloric acid, nitric acid, sulfuric acid or acetic acid; the concentration of the diluted acid solution is 0.5-1 mol/L.
7. The method according to claim 1, wherein the organic solvent in step (5) is one of methanol and ethanol or a mixture thereof.
8. The method according to claim 1, wherein the apparent density of the silica-cellulose composite aerogel prepared in the step (5) is 0.092 to 0.143g/cm3Specific surface area of 227.41-264.93 m2The coefficient of thermal conductivity is 0.029-0.038W/m.K.
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| CN110975833A (en) * | 2019-12-18 | 2020-04-10 | 昆明理工大学 | Preparation method and application of silicon dioxide/cellulose composite porous material |
| CN113410450A (en) * | 2021-06-30 | 2021-09-17 | 华北水利水电大学 | Silicon-oxygen-carbon negative electrode material taking cellulose/silicon dioxide aerogel as precursor and preparation method thereof |
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| CN115849381A (en) * | 2022-11-18 | 2023-03-28 | 浙江新安化工集团股份有限公司 | Three-dimensional porous silicon-carbon composite material and preparation method and application thereof |
| CN115726192B (en) * | 2022-11-18 | 2023-08-25 | 浙江梅盛新材料有限公司 | Preparation method of sound-absorbing flame-retardant fiber-based microporous composite material |
| CN117511219B (en) * | 2024-01-05 | 2024-04-09 | 中铁建设集团有限公司 | Flexible fiber reinforced nano microporous aerogel and preparation method thereof |
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