CN107235744B - Preparation method of graphene-silicon dioxide aerogel - Google Patents
Preparation method of graphene-silicon dioxide aerogel Download PDFInfo
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 63
- 239000004964 aerogel Substances 0.000 title claims abstract description 42
- 238000002360 preparation method Methods 0.000 title claims abstract description 40
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 40
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 78
- 229910021389 graphene Inorganic materials 0.000 claims abstract description 56
- 229920001661 Chitosan Polymers 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 15
- 238000004108 freeze drying Methods 0.000 claims abstract description 3
- 239000000243 solution Substances 0.000 claims description 68
- 238000003756 stirring Methods 0.000 claims description 56
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 56
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 54
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 36
- 229910002804 graphite Inorganic materials 0.000 claims description 24
- 239000010439 graphite Substances 0.000 claims description 24
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 23
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 22
- 239000012153 distilled water Substances 0.000 claims description 22
- 238000001035 drying Methods 0.000 claims description 22
- 239000004965 Silica aerogel Substances 0.000 claims description 20
- 239000008367 deionised water Substances 0.000 claims description 20
- 229910021641 deionized water Inorganic materials 0.000 claims description 20
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 claims description 16
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 14
- 239000000047 product Substances 0.000 claims description 14
- 229910052710 silicon Inorganic materials 0.000 claims description 14
- 239000010703 silicon Substances 0.000 claims description 14
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 13
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 12
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims description 12
- 239000000084 colloidal system Substances 0.000 claims description 10
- 239000011259 mixed solution Substances 0.000 claims description 10
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 9
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 9
- 238000006243 chemical reaction Methods 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 9
- 238000003760 magnetic stirring Methods 0.000 claims description 8
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 8
- 239000012467 final product Substances 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
- 239000005457 ice water Substances 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 229910021382 natural graphite Inorganic materials 0.000 claims description 6
- 239000003921 oil Substances 0.000 claims description 6
- 239000012286 potassium permanganate Substances 0.000 claims description 6
- 238000007789 sealing Methods 0.000 claims description 6
- 239000004317 sodium nitrate Substances 0.000 claims description 6
- 235000010344 sodium nitrate Nutrition 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 6
- 238000001291 vacuum drying Methods 0.000 claims description 6
- 238000001879 gelation Methods 0.000 claims description 5
- 238000000926 separation method Methods 0.000 claims description 5
- 230000007935 neutral effect Effects 0.000 claims description 3
- 238000001816 cooling Methods 0.000 claims 1
- 235000012239 silicon dioxide Nutrition 0.000 abstract description 10
- 239000002131 composite material Substances 0.000 abstract description 6
- 238000009413 insulation Methods 0.000 abstract description 5
- 229910052681 coesite Inorganic materials 0.000 abstract description 3
- 229910052906 cristobalite Inorganic materials 0.000 abstract description 3
- 239000000463 material Substances 0.000 abstract description 3
- 229910052682 stishovite Inorganic materials 0.000 abstract description 3
- 229910052905 tridymite Inorganic materials 0.000 abstract description 3
- 238000004321 preservation Methods 0.000 abstract 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 10
- 238000007710 freezing Methods 0.000 description 7
- 230000008014 freezing Effects 0.000 description 7
- 239000007788 liquid Substances 0.000 description 7
- 239000000499 gel Substances 0.000 description 6
- 238000005303 weighing Methods 0.000 description 6
- 229910021529 ammonia Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000000227 grinding Methods 0.000 description 4
- 239000000017 hydrogel Substances 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- 238000002604 ultrasonography Methods 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000005119 centrifugation Methods 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 239000003638 chemical reducing agent Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000013329 compounding Methods 0.000 description 2
- -1 graphite alkene Chemical class 0.000 description 2
- 239000011810 insulating material Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- LZZYPRNAOMGNLH-UHFFFAOYSA-M Cetrimonium bromide Chemical compound [Br-].CCCCCCCCCCCCCCCC[N+](C)(C)C LZZYPRNAOMGNLH-UHFFFAOYSA-M 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 239000012774 insulation material Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
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Abstract
The invention provides a preparation method of graphene-silicon dioxide aerogelThe method is characterized in that the composite aerogel mainly comprises silicon dioxide aerogel, graphene aerogel and chitosan. The method disclosed by the invention utilizes the characteristic of low thermal conductivity of the silicon dioxide aerogel, the low density and high strength of the graphene aerogel and the bonding effect characteristic of chitosan, and adopts a freeze drying mode to prepare the graphene-reinforced silicon dioxide aerogel material. The composite material prepared by the method keeps good heat preservation and insulation performance and mechanical property under the condition of medium and low temperature, and greatly improves single SiO2The brittleness of the aerogel has the problem of poor mechanical performance; the density is low and can reach 96mg/cm3(ii) a Simple process, strong operability, lower cost and SiO2Aerogel and graphene aerogel.
Description
Technical Field
The invention relates to a novel composite aerogel heat-insulating material and a preparation method thereof, and particularly relates to a preparation method of graphene-silicon dioxide aerogel.
Background
The silica aerogel is an ultra-light porous condensed substance which takes gas as a dispersion medium and has a three-dimensional network structure. The silica aerogel has the advantages of stable chemical property, large specific surface area, low density, high porosity and the like, so that the aerogel is always active in the fields of heat insulation, sound insulation, adsorption catalysis and the like. In the field of thermal insulation, silica aerogel is currently the most studied. However, the silica aerogel has poor mechanical properties and high brittleness, and is a key problem that the aerogel is difficult to spread and apply. One mainly solves this problem in two ways: (1) adding the polymer into the skeleton of the SiO2 aerogel through in-situ reaction or soaking; (2) the reinforcement is carried out by compounding silica sol and fiber or adding nano filler into the nano structure of aerogel.
The graphene aerogel has the microstructure of aerogel, has lower density, higher mechanical strength and opacity simultaneously, and the opacity of graphite alkene can reduce the radiation conduction moreover, and consequently graphite alkene aerogel is expected to become a neotype thermal-insulated insulation material. In order to obtain graphene aerogel, a graphene oxide solution is generally used as a raw material, and a chemical reduction method is the simplest and most efficient method.
Patent CN104826582A utilizes the compounding of graphene and silica to obtain a composite material with adsorption capacity. The preparation method comprises the steps of mixing a graphene oxide solution, a NaOH aqueous solution and a silicon source, then sequentially dropwise adding the mixture into a hexadecyl trimethyl ammonium bromide aqueous solution, aging at room temperature, adding a reducing agent, putting the mixture into an oven at 70-100 ℃ for gathering for 1-10 hours to obtain hydrogel, washing the obtained reaction product, drying the reaction product for 12-24 hours at-70 to-90 ℃ in a vacuum drier to obtain the graphene-silica aerogel without removing the template agent, and removing the template agent to obtain the graphene-mesoporous silica aerogel.
Patent CN105217640A proposes a preparation method of graphene oxide/silicon dioxide hybrid aerogel, which comprises the following steps: firstly, respectively preparing silicon dioxide sol and graphene oxide dispersion liquid, mixing the silicon dioxide sol and the graphene oxide dispersion liquid to obtain hybrid hydrogel, and then freezing the hybrid hydrogel by using liquid nitrogen and freezing the hybrid hydrogel by using a freeze dryer to obtain the graphene oxide/silicon dioxide hybrid aerogel. The method skillfully controls the freezing process, and converts the liquid/gas interface into a gas/solid interface under the liquid nitrogen environment, thereby avoiding the curved liquid level in the hole and eliminating the influence of capillary force as much as possible.
Patent CN104860304A discloses a silica hybrid graphene aerogel with high specific surface area and a preparation method thereof. Mixing silica sol and graphene oxide dispersion liquid, reacting to generate silicon oxide nanoparticles with extremely small particle size, and drying to obtain the silicon oxide hybrid graphene aerogel with high specific surface area.
Disclosure of Invention
The technical problem is as follows: the invention solves the problem of poor brittleness and mechanical property of silicon dioxide aerogel, and prepares the composite aerogel heat-insulating material by utilizing the low density and good blocking performance of the graphene aerogel.
The technical scheme is as follows: the preparation method of the graphene-silicon dioxide aerogel comprises the following steps:
step 4, preparation of silica sol: respectively and sequentially taking a silicon source, water and ethanol in a container, keeping magnetic stirring, dropwise adding hydrochloric acid to adjust the pH value to 2-5, stirring and standing; then, dropwise adding N, N-dimethylformamide and ammonia water to adjust the pH value to 6-7, wherein the solution becomes a viscous silica sol;
step 6, preparing the graphene-silicon dioxide mixed sol: mixing the rGO, the silica sol and the chitosan solution respectively obtained in the steps 3, 4 and 5, magnetically stirring to obtain a mixed sol, keeping stirring, dropwise adding N, N-dimethylformamide and ammonia water, standing, and waiting for gelation;
step 7, preparing the graphene-silicon dioxide aerogel: and (3) placing the gel obtained in the step (6) in a low-temperature refrigerator for precooling, then carrying out freeze drying for 24-48h by using a freeze dryer, and finally placing in a vacuum oven for drying to obtain the graphene-silicon dioxide aerogel.
Wherein:
in the step 2, the ultrasonic dispersion frequency is 20-60KHZ, the ultrasonic power is 100W, and the rotational speed of the centrifugal separation is 1000-3000 r/min.
In the step 3, the dosage of the ethylenediamine is related to the volume of the graphene oxide solution, and the volume ratio of the ethylenediamine to the graphene oxide solution is 1: (300-800).
The silicon source, the water and the ethanol in the step 4 have the molar ratio of the silicon source to the ethanol: deionized water: the ethanol is 1, (2-6) to (4-9), and the stirring speed is controlled to be 500r/min to 2500 r/min.
The mole ratio of the silicon source and the ammonia water added dropwise in the step 4 is 1: (10-3-1.5×10-3)。
In the step 5, the mass ratio of the chitosan to the graphene oxide is (1-8): 1.
in step 6, the magnetic stirring speed is controlled to be 500r/min-1500 r/min.
In step 7, the precooling time is 1-3h, and the drying temperature is 60-100 ℃.
Has the advantages that: the invention and other preparation methods have the following beneficial effects:
1. different raw materials are used as silicon sources, the cost is low, the complex operations such as surface modification and solvent replacement in the normal-pressure drying process are omitted in the preparation process, the time is saved, and the efficiency is improved.
2. The graphene-silicon dioxide aerogel prepared by the method has good blocking property, good mechanical property and lower heat conductivity coefficient which can be as low as 0.037W/(m.K) and has the density as low as 96mg/cm3。
3. The composite aerogel material has a good framework structure and micron-sized pores, and is expected to be widely applied to the fields of catalyst carriers, adsorption and separation, high-temperature heat insulation and the like.
Drawings
Fig. 1 is an SEM image of graphene-silica aerogel.
Fig. 2 is a stress-strain curve of graphene-silica aerogel.
Fig. 3 is a graph of graphene-silica aerogel thermal conductivity as a function of graphene content.
Detailed Description
Specific embodiments of graphene-silica aerogel materials are provided below as further details of the invention.
Example 1
a. Synthesis of graphite oxide
In an ice-water bath, 21ml of 98% concentrated sulfuric acid is poured into a flask, and then 1g of natural graphite and 0.5g of sodium nitrate are poured into a 250ml round-bottom flask and stirred for 45min by ultrasound; stirring by magnetic force for 30min, weighing 3g of potassium permanganate, slowly adding into the flask, and continuing stirring for 45 min. Transferring the flask to another water bath, heating to 35 ℃, continuing to stir for 30min, measuring 23mL of distilled water, slowly adding the distilled water into the flask, transferring the flask into an oil bath at 98 ℃, continuing to stir for 15min, and finally adding 140mL of distilled water and 20mL of 30% hydrogen peroxide. The final mixture was bright yellow. The product was washed by centrifugation with 500mL of 5% hydrochloric acid and distilled water to near neutrality. And (3) drying the final product in a vacuum drying oven at 60 ℃ for 24h to obtain a tan sheet product, namely graphite oxide GO.
b preparation of graphene oxide solution
And grinding 60mg of graphite oxide, dissolving the graphite oxide in 10ml of deionized water, performing ultrasonic dispersion for 30min, and performing centrifugal treatment to remove impurities to obtain a homogeneous tawny graphene oxide solution.
c. Preparation of graphene
Dissolving 40 mu L of ethylenediamine in deionized water in a beaker, stirring for 10min by magnetic force, dropwise adding the prepared graphene oxide solution into the ethylenediamine solution, and keeping stirring for 30 min. And sealing the mixed solution, and then placing the mixed solution in an oven at the temperature of 75 ℃ for 6h to obtain a black colloid rGO.
d. Preparation of silica sols
Respectively weighing 20.8g of silicon source, 7.2g of water and 32.2g of ethanol in a beaker in sequence, keeping magnetic stirring for 30min, dropwise adding a proper amount of hydrochloric acid to adjust the pH value to 3, keeping stirring for 30min, and standing for 8 h; then, 1ml of N, N-dimethylformamide and 0.5ml of ammonia (0.3mol/L) were added dropwise to adjust the pH to 6, thereby obtaining a sol.
Preparation of e Chitosan solution
2ml of acetic acid solution is weighed by a using cylinder and is prepared into 100ml of 2% acetic acid solution with deionized water, and then 2g of chitosan is weighed and stirred to be dissolved in the 2% acetic acid solution, so as to obtain 100ml of chitosan solution.
f. Preparation of graphene-silica hybrid sol
And mixing the obtained graphene colloid, silica sol and 10ml of chitosan solution, and magnetically stirring for 20min to obtain mixed sol. Stirring for 20min, adding 1ml N, N-dimethylformamide and 1ml ammonia water dropwise, standing for 10min, and waiting for gel.
g. Preparation of graphene-silica aerogel
And (3) placing the gel obtained in the last step in a low-temperature refrigerator for precooling for 2h, wherein the precooling temperature is-40 ℃, then freezing and drying for 48h by using a freeze dryer, and finally placing in a vacuum oven at 60 ℃ for drying for 2h to obtain the graphene-silicon dioxide aerogel.
Example 2
a. Synthesis of graphite oxide
In an ice-water bath, 22ml of 98% concentrated sulfuric acid is poured into a flask, and then 1g of natural graphite and 0.5g of sodium nitrate are poured into a 250ml round-bottom flask and stirred for 50min by ultrasound; stirring for 45min by magnetic force, weighing 3g of potassium permanganate, slowly adding into the flask, and continuing stirring for 60 min. Transferring the flask to another water bath, heating to 35 ℃, continuing to stir for 35min, measuring 25mL of distilled water, slowly adding the distilled water into the flask, transferring the flask into an oil bath at 98 ℃, continuing to stir for 15min, finally adding 140mL of distilled water and 20mL of 30% hydrogen peroxide, and centrifugally washing the product to be close to neutral by using 500mL of 3% dilute hydrochloric acid and distilled water. And (3) drying the final product in a vacuum drying oven at 60 ℃ for 24h to obtain a tan sheet product, namely graphite oxide GO.
b preparation of graphene oxide solution
And grinding 120mg of graphite oxide, dissolving in 12ml of deionized water, performing ultrasonic dispersion for 45min, and performing centrifugal treatment to remove impurities to obtain a homogeneous tawny graphene oxide solution.
c. Preparation of graphene
Dissolving 25 mu L of ethylenediamine in deionized water in a beaker, stirring for 10min by magnetic force, dropwise adding the prepared graphene oxide solution into the ethylenediamine solution, and keeping stirring for 45 min. And sealing the mixed solution, and placing the sealed mixed solution in an oven at the temperature of 85 ℃ for 4 hours to obtain a black colloid rGO.
d. Preparation of silica sols
Respectively weighing 20.8g of silicon source, 7.2g of water and 32.2g of ethanol in a beaker in sequence, keeping magnetic stirring for 40min, dropwise adding a proper amount of hydrochloric acid to adjust the pH value to 3.5, keeping stirring for 40min, and standing for 9 h; subsequently, 1ml of N, N-dimethylformamide and 0.5ml of ammonia (0.3mol/L) were added dropwise to adjust the pH to 6.5, to obtain a sol.
Preparation of e Chitosan solution
2ml of acetic acid solution is weighed by a using cylinder and is prepared into 100ml of 2% acetic acid solution with deionized water, and then 2g of chitosan is weighed and stirred to be dissolved in the 2% acetic acid solution, so as to obtain 100ml of chitosan solution.
f. Preparation of graphene-silica hybrid sol
And mixing the obtained graphene colloid, silica sol and 10ml of chitosan solution, and magnetically stirring for 20min to obtain mixed sol. Stirring was maintained for 30min, 0.5ml of N, N-dimethylformamide and 0.5ml of ammonia water were added dropwise thereto, and the mixture was allowed to stand for 10min to wait for gelation.
g. Preparation of graphene-silica aerogel
And (3) placing the gel obtained in the last step in a low-temperature refrigerator for precooling for 3h, wherein the precooling temperature is-35 ℃, then freezing and drying for 48h by using a freeze dryer, and finally placing in a vacuum oven at 70 ℃ for drying for 2h to obtain the graphene-silicon dioxide aerogel.
Example 3
a. Synthesis of graphite oxide
In an ice-water bath, 21ml of 98% concentrated sulfuric acid is poured into a flask, and then 1g of natural graphite and 0.5g of sodium nitrate are poured into a 250ml round-bottom flask and stirred for 45min by ultrasound; magnetically stirring for 30min, slowly adding 3g potassium permanganate into the flask, and stirring for 45-60 min. Transferring the flask to another water bath, heating to 35 ℃, continuing to stir for 30min, measuring 23mL of distilled water, slowly adding the distilled water into the flask, transferring the flask into an oil bath at 98 ℃, continuing to stir for 15min, and finally adding 140mL of distilled water and 20mL of 30% hydrogen peroxide. The final mixture was bright yellow. The product was washed by centrifugation with 500mL of 5% hydrochloric acid and distilled water to near neutrality. And (3) drying the final product in a vacuum drying oven at 60 ℃ for 24h to obtain a tan sheet product, namely graphite oxide GO.
b preparation of graphene oxide solution
And grinding 180mg of graphite oxide, dissolving in 15ml of deionized water, performing ultrasonic dispersion for 40min, and performing centrifugal treatment to remove impurities to obtain a homogeneous tawny graphene oxide solution.
c. Preparation of graphene
Dissolving a small amount of ethylenediamine in deionized water in a beaker, stirring for 10min by magnetic force, dropwise adding the prepared graphene oxide solution into the ethylenediamine solution, and keeping stirring for 30 min. And sealing the mixed solution, and then placing the mixed solution in an oven at the temperature of 85 ℃ for 5 hours to obtain black graphene colloid.
d. Preparation of silica sols
Respectively weighing 20.8g of silicon source, 7.2g of water and 32.2g of ethanol in a beaker in sequence, keeping magnetic stirring for 30min, dropwise adding a proper amount of hydrochloric acid to adjust the pH value to 3.5, keeping stirring for 50min, and standing for 10 h; then, 1ml of N, N-dimethylformamide and 0.6ml of ammonia water (0.3mol/L) were added dropwise to adjust the pH to 6, thereby obtaining a sol.
Preparation of e Chitosan solution
2ml of acetic acid solution is weighed by a using cylinder and is prepared into 100ml of 2% acetic acid solution with deionized water, and then 2g of chitosan is weighed and stirred to be dissolved in the 2% acetic acid solution, so as to obtain 100ml of chitosan solution.
f. Preparation of graphene-silica hybrid sol
And mixing the obtained graphene colloid, silica sol and 10ml of chitosan solution, and magnetically stirring for 30min to obtain mixed sol. Stirring was maintained for 30min, 1ml of N, N-dimethylformamide and 1.5ml of ammonia were added dropwise thereto, and the mixture was allowed to stand for a while to wait for gelation.
g. Preparation of graphene-silica aerogel
And (3) placing the gel obtained in the last step in a low-temperature refrigerator for precooling for 3h, wherein the precooling temperature is-40 ℃, then freezing and drying for 48h by using a freeze dryer, and finally placing in a vacuum oven at 90 ℃ for drying for 3h to obtain the graphene-silicon dioxide aerogel.
Example 4
a. Synthesis of graphite oxide
In an ice-water bath, 21ml of 98% concentrated sulfuric acid is poured into a flask, and then 1g of natural graphite and 0.5g of sodium nitrate are poured into a 250ml round-bottom flask and stirred for 45min by ultrasound; magnetically stirring for 30min, slowly adding 3g potassium permanganate into the flask, and stirring for 45-60 min. Transferring the flask to another water bath, heating to 35 ℃, continuing to stir for 30min, measuring 23mL of distilled water, slowly adding the distilled water into the flask, transferring the flask into an oil bath at 98 ℃, continuing to stir for 15min, and finally adding 140mL of distilled water and 20mL of 30% hydrogen peroxide. The final mixture was bright yellow. The product was washed by centrifugation with 500mL of 5% hydrochloric acid and distilled water to near neutrality. And (3) drying the final product in a vacuum drying oven at 60 ℃ for 24h to obtain a tan sheet product, namely graphite oxide GO.
b preparation of graphene oxide solution
And grinding 240mg of graphite oxide, dissolving the graphite oxide in 20ml of deionized water, performing ultrasonic dispersion for 45min, and performing centrifugal treatment to remove impurities to obtain a homogeneous tawny graphene oxide solution.
c. Preparation of graphene
Dissolving a small amount of ethylenediamine in deionized water in a beaker, stirring for 20min by magnetic force, dropwise adding the prepared graphene oxide solution into the ethylenediamine solution, and keeping stirring for 45 min. And sealing the mixed solution, and placing the mixed solution in an oven at the temperature of 95 ℃ for 3h to obtain black graphene colloid.
d. Preparation of silica sols
Respectively weighing 20.8g of silicon source, 7.2g of water and 32.2g of ethanol in a beaker in sequence, keeping magnetic stirring for 35min, dropwise adding a proper amount of hydrochloric acid to adjust the pH value to 3, keeping stirring for 30min, and standing for 8 h; subsequently, 1ml of N, N-dimethylformamide and 0.7ml of ammonia (0.3mol/L) were added dropwise to adjust the pH to 6.5, to obtain a sol.
Preparation of e Chitosan solution
2ml of acetic acid solution is weighed by a using cylinder and is prepared into 100ml of 2% acetic acid solution with deionized water, and then 2g of chitosan is weighed and stirred to be dissolved in the 2% acetic acid solution, so as to obtain 100ml of chitosan solution.
f. Preparation of graphene-silica hybrid sol
And mixing the obtained graphene colloid, silica sol and 10ml of chitosan solution, and magnetically stirring for 30min to obtain mixed sol. Stirring was maintained for 30min, 1ml of N, N-dimethylformamide and 1.5ml of ammonia were added dropwise thereto, and the mixture was allowed to stand for a while to wait for gelation.
g. Preparation of graphene-silica aerogel
And (3) placing the gel obtained in the last step in a low-temperature refrigerator for precooling for 3h, wherein the precooling temperature is-35 ℃, then freezing and drying for 48h by using a freeze dryer, and finally placing in a vacuum oven at 80 ℃ for drying for 2h to obtain the graphene-silicon dioxide aerogel. When the doping amount of the graphene oxide is 120mg, the thermal conductivity coefficient of the graphene-silicon dioxide aerogel is measured to be 0.037W/(m.K), and the compressive strength is measured to be 0.45MPa and is far higher than that of the silicon dioxide aerogel.
Claims (7)
1. A preparation method of graphene-silicon dioxide aerogel is characterized by comprising the following steps:
step 1, preparation of graphite oxide: pouring concentrated sulfuric acid into a reaction container in an ice-water bath, and then pouring natural graphite and sodium nitrate into a reactor for ultrasonic stirring; slowly adding potassium permanganate into the reaction vessel, and continuously stirring; transferring the reaction vessel to another water bath, heating to 25-45 deg.C, slowly adding distilled water into the reaction vessel, transferring into high temperature oil bath, stirring, and adding distilled water and 10% -40% hydrogen peroxide H2O2The final mixture is bright yellow, the product is centrifugally washed by 1 to 10 percent hydrochloric acid and distilled water to be nearly neutral, the final product is dried in a vacuum drying oven at the temperature of between 50 and 100 ℃ for 12 to 24 hours, and the obtained tan sheet product is the graphite oxide GO;
step 2, preparing a graphene oxide solution: dissolving the graphite oxide GO obtained in the step 1 in deionized water, performing ultrasonic dispersion for more than 30min, and performing centrifugal separation to remove the graphite oxide which is not peeled off and impurities to obtain a tawny uniform graphene oxide solution;
step 3, preparing graphene: dissolving ethylenediamine in deionized water in a beaker, stirring for a period of time by magnetic force, dropwise adding the graphene oxide solution into the ethylenediamine solution, keeping stirring, sealing the mixed solution, and placing in a drying oven to obtain a black colloid, namely reduced graphene oxide (rGO);
step 4, preparation of silica sol: respectively and sequentially taking a silicon source, water and ethanol in a container, keeping magnetic stirring, dropwise adding hydrochloric acid to adjust the pH value to 2-5, stirring and standing; then, dropwise adding N, N-dimethylformamide and ammonia water to adjust the pH value to 6-7, wherein the solution becomes a viscous silica sol;
step 5, preparing a chitosan solution: measuring an acetic acid solution by using a measuring cylinder, preparing the acetic acid solution with deionized water, and then stirring and dissolving chitosan in the acetic acid solution to obtain a chitosan solution;
step 6, preparing the graphene-silicon dioxide mixed sol: mixing the rGO, the silica sol and the chitosan solution respectively obtained in the steps 3, 4 and 5, magnetically stirring to obtain a mixed sol, keeping stirring, dropwise adding N, N-dimethylformamide and ammonia water, standing, and waiting for gelation;
step 7, preparing the graphene-silicon dioxide aerogel: placing the gel obtained in the step 6 in a low-temperature refrigerator for precooling, then freeze-drying for 24-48h by using a freeze dryer, and finally placing in a vacuum oven for drying to obtain graphene-silicon dioxide aerogel;
the mass ratio of the chitosan to the graphene oxide is (1-8): 1.
2. the method for preparing graphene-silica aerogel according to claim 1, wherein the ultrasonic dispersion frequency in step 2 is 20-60KHZ, the ultrasonic power is 100W, and the rotational speed of the centrifugal separation is 1000-3000 r/min.
3. The method for preparing graphene-silica aerogel according to claim 1, wherein the amount of ethylenediamine used in step 3 is related to the volume of the graphene oxide solution, and the volume ratio of ethylenediamine to graphene oxide solution is 1: (300-800).
4. The method for preparing graphene-silica aerogel according to claim 1, wherein the silicon source, water and ethanol in the molar ratio of silicon source: deionized water: the ethanol is 1, (2-6) to (4-9), and the stirring speed is controlled to be 500r/min to 2500 r/min.
5. The method for preparing graphene-silica aerogel according to claim 1, wherein the molar ratio of the silicon source to the ammonia water added dropwise in step 4 is 1: (10-3-1.5×10-3)。
6. The method for preparing graphene-silica aerogel according to claim 1, wherein in step 6, the magnetic stirring speed is controlled to be 500r/min to 1500 r/min.
7. The method for preparing graphene-silica aerogel according to claim 1, wherein in step 7, the pre-cooling time is 1-3h, and the drying temperature is 60-100 ℃.
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