Hollow silicon dioxide nanofiber aerogel as well as preparation method and application thereof

Abstract

The invention provides hollow silicon dioxide nanofiber aerogel as well as a preparation method and application thereof, and belongs to the technical field of aerogel. The hollow silicon dioxide nanofiber is prepared by using a coaxial electrostatic spinning method, the cohesiveness of the hollow silicon dioxide nanofiber is improved by using an organosilane cross-linking agent, and the hollow silicon dioxide nanofiber aerogel is prepared by using a vacuum freeze-drying method. According to the method disclosed by the invention, the toughness of the silicon dioxide nanofiber aerogel is enhanced by 125%, the rebound resilience is good, and the prepared silicon dioxide nanofiber aerogel has low density (the density is as low as 0.018 g / cm < 3 >), low heat conductivity coefficient (0.031 W / (m.K)) and high-temperature heat insulation performance, and is expected to be widely applied to the fields of high-temperature heat insulation, liquid hydrogen heat insulation, noise prevention and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogels, and particularly to a hollow silica nanofiber aerogel, a preparation method thereof, and an application thereof. Background Art

[0002] Silica nanofiber aerogel is a lightweight nanoporous amorphous solid material with a spatial network structure, and has great application potential in thermics, acoustics, optics, electricity, etc. due to its unique properties such as high porosity, low density, and large specific surface area.

[0003] Currently, the prior art mostly adopts an electrospinning method with the addition of polymers to further improve the spinnability of silica nanofibers, but the addition of polymers increases the production cost. In addition, most aerogel materials are composed of solid-core fibers, which are heavier in mass, larger in density, and lower in flexibility, restricting their further development and application. Summary of the Invention

[0004] The object of the present invention is to provide a hollow silica nanofiber aerogel, a preparation method thereof, and an application thereof. This method does not involve a polymer template, and utilizes the advantages of lighter weight, higher flexibility, and lower thermal conductivity of hollow silica nanofibers to prepare a hollow silica nanofiber aerogel, effectively solving the problem that the composition structure of traditional silica nanofiber aerogels is solid-core silica nanofibers and has low toughness.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a hollow silica nanofiber aerogel, comprising the following steps:

[0007] 1) Mix a silicon source, an organic solvent, an acid, and water, and carry out a hydrolysis-polycondensation reaction to obtain a silica sol spinning solution;

[0008] 2) Electrospin the silica sol spinning solution through a coaxial electrospinning device to obtain a hollow silica nanofiber membrane;

[0009] 3) Mix the hollow silica nanofiber membrane with an organosilane crosslinking agent and water, and carry out vacuum freeze-drying to obtain a hollow silica nanofiber aerogel.

[0010] Preferably, in step 1), the silicon source includes one or more of tetraethyl orthosilicate, polysilicic acid ethyl ester, and methyl orthosilicate.

[0011] Preferably, in step 1), the acid includes one or more of hydrochloric acid, nitric acid, and boric acid, the mass fraction of the acid is 1-38%, the molar ratio of the silicon source to the organic solvent is 0.5-1.0:1.0-2.0, and the molar ratio of the silicon source, acid, and water is 0.5-1.0:0.005-0.01:1.8-2.5.

[0012] Preferably, in step 1), the temperature of the hydrolysis-polycondensation is 70-90 °C, and the time is 0.6-1.5 h.

[0013] Preferably, in step 2), the coaxial needle head of the coaxial electrospinning device is used, the outer layer is passed through with the silica sol spinning solution, and the inner layer is passed through with oil; the oil includes sesame oil, linseed oil, or peanut oil.

[0014] Preferably, the temperature of the electrospinning is 20-30 °C, the injection speed of the spinning solution is 2-8 mL / h, the distance between the nozzle and the collector is 6-20 cm, and the high-voltage static voltage is 15-25 kV.

[0015] Preferably, in step 3), the organosilane crosslinking agent includes one or more of methyltrimethoxysilane and 3-aminopropyltriethoxysilane; the mass ratio of the hollow silica nanofiber membrane, the organosilane crosslinking agent, and water is 0.8-1.5:0.3-1.5:70-90.

[0016] Preferably, the vacuum freeze-drying includes freezing and vacuum drying carried out in sequence; the freezing is carried out using liquid nitrogen, the time of the freezing is 30-60 min; the time of the vacuum drying is 36-48 h.

[0017] The present invention provides a hollow silica nanofiber aerogel prepared by the preparation method described in the above technical solution.

[0018] The present invention provides the application of the hollow silica nanofiber aerogel described in the above technical solution in the fields of high-temperature heat insulation, liquid hydrogen thermal insulation, or noise prevention.

[0019] The present invention provides a preparation method of a hollow silica nanofiber aerogel, which uses silica sol to prepare hollow silica nanofibers by a coaxial electrospinning method, then uses the hollow silica nanofibers as raw materials, uses an organosilane crosslinking agent to improve the adhesiveness of the hollow silica nanofibers, and prepares a hollow silica nanofiber aerogel by a vacuum freeze-drying method.

[0020] The present invention uses silica sol as a spinning solution. The fibers obtained after spinning this spinning solution do not contain polymers and can still maintain a stable structure at high temperatures. Moreover, the silica gel fibers formed by spinning contain a relatively large amount of SiOH and have high elasticity. A hollow silica nanofiber membrane is prepared by coaxial electrospinning without using polymers as a template agent. The size of the prepared hollow silica nanofibers is stable. The prepared hollow fibers have the advantages of being lighter, more flexible, and having a lower thermal conductivity compared to ordinary fibers, greatly improving the structural properties of the silica nanofiber aerogel and expanding its application fields.

[0021] In the present invention, the silica nanofiber membrane is mixed with a crosslinking agent. The covalent bonds of the crosslinking agent provide a permanent network, and physical crosslinking allows for dynamic reorganization, which can meet the toughness requirements. Using an organosilane crosslinking agent can limit the slippage of hollow fiber chains, enhance interfacial bonding, and prevent fiber-matrix debonding. The present invention improves the mechanical properties of the hollow silica nanofiber aerogel by constructing the characteristics of a hollow fiber network. The hollow silica nanofiber aerogel is prepared by vacuum freeze-drying, which improves the crosslinkability of the hollow silica nanofiber aerogel, increases the toughness of the silica nanofiber aerogel by 125%, shows good resilience, and improves its application value.

[0022] The present invention uses coaxial electrospinning to achieve the controllable preparation of the morphology and structure of the silica nanofiber aerogel. The prepared hollow-structured aerogel has heat insulation properties. This is because there are many nano micropores in the prepared aerogel, and each pore wall has the function of a heat shield, which can reduce thermal radiation to the lowest level. Moreover, an infinite number of pore walls form an infinitely long and loose path, reducing the heat conduction ability to the lowest level. The air molecules in the pores lose their ability to flow freely and are approximately in a vacuum state, unable to conduct heat convection, thereby improving the heat insulation performance. In addition, the prepared aerogel has a unique microporous structure as a thermal insulation material, effectively suppressing these heat transfer methods (heat conduction, heat convection, and thermal radiation). The lower the thermal conductivity, the better the heat insulation effect. Therefore, the silica nanofiber aerogel prepared by the present invention has a low density (as low as 0.018 g / cm 3 ), a low thermal conductivity (0.031 W / (m·K)), and high-temperature heat insulation performance. The low density of the aerogel makes it thinner under the same heat insulation effect and is suitable for use in spacesuits or aircraft heat insulation layers.

[0023] The method steps of the present invention are simple.

[0024] Currently, the composition units of silica nanofiber aerogels are all solid fibers, while the present invention uses a hollow-structured aerogel composed of hollow silica nanofiber units. Since the building units are hollow, it can provide a lower density, a higher porosity, and a lower thermal conductivity. Combining the good mechanical properties of the fiber aerogel, it is expected to be applied in industrial fields such as fire and heat insulation, liquid hydrogen thermal insulation, and noise prevention. Description of the Drawings

[0025] Figure 1 It is a flow chart of the preparation device for the coaxial electrospun hollow silica nanofiber membrane of the present invention;

[0026] Figure 2 It is a physical picture (a) and a flexible picture (b) of the hollow silica nanofiber membrane prepared in Example 1;

[0027] Figure 3 It is an SEM picture of the hollow silica nanofiber membrane prepared in Example 1;

[0028] Figure 4 It is a tensile property graph of the hollow silica nanofiber membrane prepared in Example 1 under different conditions;

[0029] Figure 5 It is a physical picture of the hollow silica nanofiber aerogel prepared in Example 1;

[0030] Figure 6 It is a graph of the compression resilience data of the mechanical property test of the hollow silica nanofiber aerogel prepared in Example 1 under the condition of 60% deformation;

[0031] Figure 7 It is a heat insulation property graph of the silica nanofiber aerogel prepared in Example 1 (a) and Comparative Example 1 (b);

[0032] Figure 8 It is a thermal conductivity graph of the hollow silica nanofiber aerogel prepared in Example 1;

[0033] Figure 9 It is a flow chart of the preparation of the silica nanofiber aerogel in Comparative Example 1;

[0034] Figure 10 It is a physical picture (a) and a graph of the compression resilience data of the mechanical property test (b) of the silica nanofiber aerogel in Comparative Example 1;

[0035] Figure 11 It is an SEM picture of the hollow silica nanofiber aerogel prepared in Example 1. Specific Embodiments

[0036] In the present invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well-known to those skilled in the art.

[0037] The present invention provides a method for preparing a hollow silica nanofiber aerogel, comprising the following steps:

[0038] 1) Mix a silicon source, an organic solvent, an acid and water, and carry out a hydrolysis-polycondensation reaction to obtain a silica sol spinning solution;

[0039] 2) Electrospin the silica sol spinning solution through a coaxial electrospinning device to obtain a hollow silica nanofiber membrane;

[0040] 3) Mix the hollow silica nanofiber membrane with an organosilane crosslinking agent and water, and perform vacuum freeze-drying to obtain a hollow silica nanofiber aerogel.

[0041] In the present invention, in step 1), the silicon source preferably includes one or more of tetraethyl orthosilicate, polysilicic acid ethyl ester, and methyl orthosilicate; the organic solvent preferably includes one or more of anhydrous ethanol, isopropanol, and methanol.

[0042] In the present invention, the molar ratio of the silicon source to the organic solvent is preferably 0.5 - 1.0:1.0 - 2.0, more preferably 0.6 - 0.8:1.2 - 1.8, and even more preferably 0.7 - 0.8:1.4 - 1.5.

[0043] In the present invention, in step 1), the acid preferably includes one or more of hydrochloric acid, nitric acid, and boric acid, and the mass fraction of the acid is 1 - 38%, more preferably 5 - 30%, and even more preferably 10 - 20%.

[0044] In the present invention, the molar ratio of the silicon source, the acid, and water is preferably 0.5 - 1.0:0.005 - 0.01:1.8 - 2.5, more preferably 0.6 - 0.9:0.005 - 0.009:2.0 - 2.4, and even more preferably 0.7 - 0.8:0.006 - 0.008:2.1 - 2.3.

[0045] In the present invention, it is preferred to mix the silicon source with the organic solvent, and perform a hydrolysis - polycondensation reaction on the obtained mixture with the acid and water under the conditions of water bath heating and stirring to obtain a silica sol spinning solution.

[0046] In the present invention, in step 1), the temperature of the hydrolysis - polycondensation is preferably 70 - 90°C, more preferably 80°C; the time is preferably 0.6 - 1.5 h, more preferably 0.7 - 1.2 h, and even more preferably 0.8 - 1 h.

[0047] In the present invention, in step 2), the coaxial electrospinning device uses a coaxial needle, with the outer layer passing through the silica sol spinning solution (shell layer spinning solution) and the inner layer passing through oil (core layer spinning solution); the oil preferably includes sesame oil, linseed oil, or peanut oil; the oil is a commercially available edible oil; the needle is a conventional conductive pure metal in the art.

[0048] In the present invention, the temperature of the electrospinning is preferably 20 to 30 °C, more preferably 20 to 28 °C, and even more preferably 22 to 25 °C; the injection rates of the spinning solutions for the outer layer and the inner layer are independently preferably 2 to 8 mL / h, more preferably 3 to 4 mL / h; the distance between the nozzle and the collector is preferably 6 to 20 cm, more preferably 8 to 15 cm, and even more preferably 10 to 13 cm, and the high-voltage static voltage is preferably 15 to 25 kV, more preferably 16 to 23 kV, and even more preferably 20 to 22 kV.

[0049] After completing the electrospinning, in the present invention, it is preferred to wash the obtained fiber membrane with an organic solvent and then dry it in an oven to obtain a hollow silica nanofiber membrane; the organic solvent preferably includes one or more of alcohol, acetone, petroleum ether, methanol, and n-hexane, and the number of washing times is preferably 3 to 10 times, more preferably 4 to 8 times, and even more preferably 5 to 6 times. The present invention has no special limitation on the drying, and it can be carried out according to the process well-known in the art.

[0050] In the present invention, in step 3), the organosilane crosslinking agent preferably includes one or more of methyltrimethoxysilane and 3-aminopropyltriethoxysilane; the viscosity of the organosilane crosslinking agent is preferably 38 to 86 mPa·s, more preferably 40 to 80 mPa·s, and even more preferably 42 to 56.9 mPa·s.

[0051] In the present invention, the mass ratio of the hollow silica nanofiber membrane, the organosilane crosslinking agent, and water is preferably 0.8 to 1.5:0.3 to 1.5:70 to 90, more preferably 0.9 to 1.3:0.5 to 1.5:70 to 80, and even more preferably 1.0 to 1.2:0.8 to 1.0:80.

[0052] The present invention preferably cuts the hollow silica nanofiber membrane into pieces, adds it to water and stirs for 1 h until a homogeneous mixture state is obtained, and then drops the organosilane crosslinking agent and stirs with a high-speed stirrer at a speed of 2000 rpm for 0.16 to 0.25 h until a homogeneous mixture state is obtained, and a hollow silica nanofiber aerogel is obtained by vacuum freeze-drying.

[0053] In the present invention, the vacuum freeze-drying preferably includes freezing and vacuum drying carried out in sequence; the freezing is preferably carried out using liquid nitrogen (the temperature of liquid nitrogen is -196 °C), and the freezing time is preferably 30 to 60 min; the vacuum drying time is preferably 36 to 48 h, more preferably 38 to 48 h, and even more preferably 45 to 48 h.

[0054] The present invention provides a hollow silica nanofiber aerogel prepared by the preparation method described in the above technical solution.

[0055] The present invention provides the application of the hollow silica nanofiber aerogel described in the above technical solution in the fields of high-temperature heat insulation, liquid hydrogen thermal insulation or noise prevention. The present invention has no special limitation on the method of the application, and it can be applied according to the methods well-known in the art.

[0056] The specific embodiments of the present invention will be described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0057] The following experimental methods and detection methods are all conventional methods unless otherwise specified; the following reagents and raw materials are all commercially available unless otherwise specified.

[0058] Example 1

[0059] 18.0 g of tetraethyl orthosilicate (0.086 mol) and 9.37 g of absolute ethanol (the concentration of absolute ethanol is 99.7%, ethanol 0.203 mol) were mixed. The obtained mixed solution was stirred and heated in a water bath environment at 80 °C for 1 h with 0.248 mL of hydrochloric acid (the mass fraction of hydrochloric acid is 10%, hydrochloric acid 0.00068 mol) and 3.39 g of deionized water (10.188 mol) to obtain a silica sol spinning solution;

[0060] As Figure 1 shown, the above silica sol spinning solution was electrospun using a coaxial electrospinning device. The temperature of electrospinning was 25 °C, the high-voltage static voltage was 20 kV, the distance between the nozzle and the drum collecting device was 10 cm, the silica sol spinning solution was used as the shell layer spinning solution, and sesame oil was used as the core layer spinning solution. The inner shaft was 4 mL / h and the outer shaft was 3 mL / h. The obtained fiber membrane was washed 6 times with alcohol and then dried in an oven for 1 h to obtain a hollow silica nanofiber membrane;

[0061] 0.8 g of the dried hollow silica nanofiber membrane was cut into pieces of 1×1 cm size and added to 80.0 g of deionized water and stirred for 1 h until a homogeneous mixture state was obtained. Then 0.5 g of methyltrimethoxysilane (viscosity 86 mPa·s) was added dropwise, and the high-speed stirrer was stirred at a speed of 2000 rpm for 10 min until a homogeneous mixture state was obtained. The obtained mixed solution was frozen with liquid nitrogen (the temperature of liquid nitrogen was -196 °C) for 30 min and then vacuum dried in a vacuum dryer for 48 h to obtain a hollow silica nanofiber aerogel.

[0062] Example 2

[0063] 20.0 g of tetraethyl orthosilicate (0.096 mol) and 10.37 g of absolute ethanol (the concentration of absolute ethanol is 99.7%, 0.224 mol) were mixed. The resulting mixture was stirred and heated in a water bath at 85 °C for 1 h with 0.251 mL of hydrochloric acid (the mass fraction of hydrochloric acid is 10%, 0.00069 mol) and 3.70 g (0.205 mol) of deionized water to obtain a silica sol spinning solution;

[0064] The above silica sol spinning solution was electrospun using a coaxial electrospinning device. The electrospinning temperature was 25 °C, the high-voltage static voltage was 20 kV, the distance between the nozzle and the drum collector was 10 cm, the silica sol spinning solution was used as the shell spinning solution, and sesame oil was used as the core spinning solution. The inner axis was 3 mL / h and the outer axis was 3 mL / h. The resulting fiber membrane was washed 5 times with alcohol and then dried in an oven for 1 h to obtain a hollow silica nanofiber membrane;

[0065] 1.0 g of the dried hollow silica nanofiber membrane was cut into pieces of 1×1 cm size and added to 80.0 g of deionized water and stirred for 1 h until a homogeneous mixture was obtained. Then 0.8 g of methyltrimethoxysilane (viscosity 56.9 mPa·s) was added dropwise, and the high-speed stirrer was stirred at a speed of 2000 rpm for 10 min until a homogeneous mixture was obtained. The resulting mixture was frozen with liquid nitrogen (the temperature of liquid nitrogen is -196 °C) for 30 min and then vacuum dried in a vacuum dryer for 48 h to obtain a hollow silica nanofiber aerogel.

[0066] Example 3

[0067] 25.0 g of tetraethyl orthosilicate (0.12 mol) and 12.37 g of absolute ethanol (the concentration of absolute ethanol is 99.7%, 0.268 mol) were mixed. The resulting mixture was stirred and heated in a water bath at 86 °C for 1 h with 0.335 mL of hydrochloric acid (the mass fraction of hydrochloric acid is 10%, 0.00092 mol) and 4.55 g (0.253 mol) of deionized water to obtain a silica sol spinning solution;

[0068] The above silica sol spinning solution was electrospun using a coaxial electrospinning device. The electrospinning temperature was 25 °C, the high-voltage static voltage was 20 kV, the distance between the nozzle and the drum collector was 10 cm, the silica sol spinning solution was used as the shell spinning solution, and sesame oil was used as the core spinning solution. The inner axis was 4 mL / h and the outer axis was 4 mL / h. The resulting fiber membrane was washed 7 times with alcohol and then dried in an oven for 1 h to obtain a hollow silica nanofiber membrane;

[0069] 1.2 g of the dried hollow silica nanofiber membrane was cut into pieces of 1×1 cm size, added to 80.0 g of deionized water, and stirred for 1 h until a homogeneous mixture was obtained. Then, 1.0 g of methyltrimethoxysilane (viscosity: 42 mPa·s) was added dropwise, and the mixture was stirred at a speed of 2000 rpm for 10 min until a homogeneous mixture was obtained. The resulting mixture was frozen with liquid nitrogen (liquid nitrogen temperature: -196 °C) for 30 min and then vacuum-dried in a vacuum dryer for 48 h to obtain a hollow silica nanofiber aerogel.

[0070] Comparative Example 1

[0071] As Figure 9 shown, the silica sol spinning solution in Example 1 was electrospun using a single-hole needle. Only the silica sol spinning solution was passed through, and no oil was passed through. After electrospinning, the fiber membrane was not washed with alcohol. 1.0 g of the obtained solid silica nanofiber membrane was mixed with 80 g of deionized water, and no cross-linking agent was added. The mixture was freeze-dried according to the method of Example 1 to obtain a silica nanofiber aerogel.

[0072] Characterization and Performance Testing

[0073] 1) Figure 2 Figures (a) and (b) are the physical and flexible images of the hollow silica nanofiber membrane prepared in Example 1. As Figure 2 shown, the thickness of the prepared hollow silica nanofiber membrane is 1022 μm, and the size is 22×22 cm. It has good flexibility and will not break after being bent 180°.

[0074] 2) Figure 3 Figure is the SEM image of the hollow silica nanofiber membrane prepared in Example 1; it can be observed that the silica nanofiber membrane is entirely a hollow structure.

[0075] 3) Figure 4 Figure is the tensile property diagram of the hollow silica nanofiber membrane prepared in Example 1 under different conditions; as Figure 4 can be seen, it breaks under the tensile force of 0.129 MPa.

[0076] 4) Figure 5 Figure is the physical image of the hollow silica nanofiber aerogel prepared in Example 1; tests found that its density is as low as 0.018 g / cm 3 , and it can still recover to its original state after being cyclically compressed 30 times under a compression of 60% deformation, indicating that the hollow silica nanofiber aerogel has good elasticity.

[0077] 5) The compression and rebound test method of a universal testing machine was adopted to test the mechanical properties of the hollow silica nanofiber aerogel prepared in Example 1. The compression and rebound performance data under the conditions of 60% deformation and 30 - cycle compression are as Figure 6 shown. The gauge length (i.e., the sample height) of the silica nanofiber aerogel is 8 mm, the rebound compression strain is set at 60%, the number of compression and rebound cycles is 30 times, the compression operation is carried out at a die rate of 100 mm / min, the maximum compression force is 16 N, and the maximum deformation is 5 mm. As Figure 6 shown, each curve almost coincides, indicating that after the first compression with a deformation of 5 mm, it returns to 8 mm, and when compressed with the same force for the second time with a deformation of 5 mm, it still returns to 8 mm. Repeating 30 times remains the same, indicating that the aerogel has perfect resilience and can completely return to its original state after compression.

[0078] When testing the ordinary silica nanofiber aerogel prepared in Comparative Example 1, the gauge length is 6 mm, the maximum compression force is 16 N, the maximum deformation is 3 mm, and it cannot return to its original state after compression (see Figure 10 (b) in it). Therefore, the resilience of the coaxial electrospun hollow silica nanofiber aerogel in Example 1 (the resilience is 5 / 8 = 0.625 (the variable of deformable amount that can be tolerated / the original height)) is 125% of the resilience performance of the ordinary silica nanofiber aerogel (3 / 6 = 0.5) in Comparative Example 1.

[0079] 6) Place the fresh petals on the hollow silica nanofiber aerogel prepared in Example 1. As Figure 7 shown in (a) in it, it can be observed that under the silica nanofiber aerogel, there is no obvious water - loss damage phenomenon when heated by a flame for one minute, the water - loss damage phenomenon appears only when heated for two minutes, and the obvious water - loss damage phenomenon appears only when heated for four minutes.

[0080] Place the fresh petals on the ordinary silica nanofiber aerogel prepared in Comparative Example 1. As Figure 7 shown in (b) in it, it can be observed that under this silica nanofiber aerogel, the obvious water - loss damage phenomenon appears after heating by a flame for 20 seconds, and the petals are completely withered when heated for one minute. Figure 7 The results show that the coaxial electrospun hollow silica nanofiber aerogel prepared by the present invention has better heat insulation performance.

[0081] 7) The thermal conductivity of the hollow silica nanofiber aerogel prepared in Example 1 was tested by the method of a thermal conductivity meter with a flat - plate heat - flow meter. The results are as Figure 8 shown. The silica nanofiber aerogel has a low thermal conductivity (0.03075 W / (m·K)), indicating that the coaxial electrospun hollow silica nanofiber aerogel prepared by the present invention has heat - preservation ability.

[0082] 8) Figure 10 The physical picture (a) of the silica nanofiber aerogel in Comparative Example 1 and the compression resilience data graph (b) of the mechanical property test; as Figure 10 shown in (b) therein, the highest points of each line are different and getting lower and lower. The curves of this sample cannot coincide after each compression, indicating that it cannot return to the original height after each compression. Therefore, the silica nanofiber aerogel prepared in Comparative Example 1 has extremely low elasticity and is extremely easy to crack after 30 cycles of compression at 60% deformation and cannot return to the original state. Moreover, there are multiple small holes at the bottom of the outer surface of the finished product, compared with Figure 6 which shows that the elasticity of the silica nanofiber aerogel in Comparative Example 1 is worse than that of the hollow silica nanofiber aerogel in Example 1.

[0083] 9) Figure 11 The SEM image of the hollow silica nanofiber aerogel prepared in Example 1; from Figure 11 which it can be seen that the prepared aerogel is in a hollow state.

[0084] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of hollow silica nanofiber aerogel, characterized in that, It includes the following steps: 1) Mix a silicon source, an organic solvent, an acid, and water, and carry out a hydrolysis-polycondensation reaction to obtain a silica sol spinning solution; 2) Electrospin the silica sol spinning solution through a coaxial electrospinning device to obtain a hollow silica nanofiber membrane; 3) Mix the hollow silica nanofiber membrane with an organosilane crosslinking agent and water, and carry out vacuum freeze-drying to obtain a hollow silica nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that In step 1), the silicon source includes one or more of tetraethyl orthosilicate, polysilicic acid ethyl ester, and methyl orthosilicate.

3. The preparation method according to claim 1 or 2, characterized in that, In step 1), the acid includes one or more of hydrochloric acid, nitric acid, and boric acid. The mass fraction of the acid is 1-38%. The molar ratio of the silicon source to the organic solvent is 0.5-1.0:1.0-2.

0. The molar ratio of the silicon source, the acid, and water is 0.5-1.0:0.005-0.01:1.8-2.

5.

4. The preparation method according to claim 3, characterized in that, In step 1), the temperature of the hydrolysis-polycondensation is 70-90°C, and the time is 0.6-1.5 h.

5. The preparation method according to claim 1, wherein In step 2), the coaxial electrospinning device uses a coaxial needle. The outer layer is fed with the silica sol spinning solution, and the inner layer is fed with oil. The oil includes sesame oil, linseed oil, or peanut oil.

6. The preparation method according to claim 5, characterized in that, The temperature of the electrospinning is 20-30°C, the injection speed of the spinning solution is 2-8 mL / h, the distance between the nozzle and the collector is 6-20 cm, and the high-voltage static voltage is 15-25 kV.

7. The preparation method according to claim 6, characterized in that, In step 3), the organosilane crosslinking agent includes one or more of methyltrimethoxysilane and 3-aminopropyltriethoxysilane. The mass ratio of the hollow silica nanofiber membrane, the organosilane crosslinking agent, and water is 0.8-1.5:0.3-1.5:70-90.

8. The preparation method according to claim 7, wherein The vacuum freeze-drying includes freezing and vacuum drying carried out in sequence. The freezing is carried out using liquid nitrogen, and the freezing time is 30-60 min. The vacuum drying time is 36-48 h.

9. A hollow silica nanofiber aerogel prepared by the preparation method according to any one of claims 1-8.

10. Application of the hollow silica nanofiber aerogel according to claim 9 in the fields of high-temperature heat insulation, liquid hydrogen thermal insulation, or noise prevention.

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