Preparation method of a flexible graphene composite aerogel

Abstract

The present invention discloses a method for preparing a flexible graphene composite aerogel based on gas template-assisted forming and high-temperature thermal reduction. The steps of the preparation method are as follows: 1) Prepare a silica fiber dispersion; 2) Prepare a graphene oxide aqueous solution; 3) Prepare a mixed solution; 4) Gas template-assisted forming; 5) Prepare an aerogel; 6) High-temperature treatment. The method introduces silica fibers into the graphene aerogel to improve the overall performance. The characteristics of this process are that the problem of difficult dispersion of silica fibers in aqueous solution is solved by physical and chemical modification methods, and a three-dimensional flexible network structure is constructed by gas template assistance, solving the problem that the application of graphene aerogel is limited due to poor flexibility. The aerogel has a hierarchical network structure, with some silica fibers distributed between the graphene nanosheets to form polygonal pore walls; the other part of the fibers is located on the polygonal pore walls, playing a supporting role for the porous structure. The gas template-assisted forming proposed in this paper can prepare a stable porous structure through a simple process, not only simplifying the process flow but also shortening the preparation time and improving the efficiency. Importantly, the composite aerogel prepared by the present invention has excellent electromagnetic-infrared stealth performance while also possessing flexibility, high elasticity, heat insulation, and ablation resistance properties, and is expected to be applied in various fields such as electromagnetic stealth, heat insulation, and sensors.

Description

Technical Field

[0001] The present invention relates to the field of functional materials, and particularly to a preparation method of a flexible graphene composite aerogel. Background Art

[0002] In recent years, with the development of radar detection technology, the frequency range of electromagnetic waves emitted by new radars has been broadened. Therefore, there is an urgent need to develop a wave-absorbing material with a wider absorption band. In order to be applied in the engineering field, it is necessary to prepare a thin, light, wide-band, and strong wave absorber with a convenient, green process and low cost. In addition, such a wave-absorbing material also needs to have excellent comprehensive properties such as compression resistance, flexibility, high temperature resistance, heat insulation, and infrared stealth to meet the actual application requirements. Graphene is a super-light material with a large specific surface area, excellent electrical conductivity, chemical stability, and mechanical properties, and has received extensive attention in the field of electromagnetic stealth. However, the high electrical conductivity of graphene results in poor impedance matching characteristics of the material. Therefore, electromagnetic waves will be directly reflected on the surface of the material before entering the material interior, and a good absorption effect cannot be achieved. Only by reasonably designing the material components and microstructure and balancing the impedance matching characteristics and dielectric loss ability of the material can the material obtain the best wave-absorbing performance.

[0003] In terms of structural design, researchers have obtained an ultra-low density and highly elastic aerogel by overlapping two-dimensional graphene nanosheets into a three-dimensional porous network structure. The preparation processes include chemical vapor deposition, hydrothermal reduction method, freeze-drying method, electrochemical method, and 3D printing, etc. However, these methods are restricted by experimental equipment, cost, and efficiency and are not suitable for industrial production. In addition, although the impedance matching characteristics of the material can be improved by constructing a three-dimensional structure with high porosity and the transmission path of electromagnetic waves in the material interior can be extended, which is beneficial to enhancing the electromagnetic wave absorption performance. However, the flexibility of pure graphene aerogel is poor, which has severely affected its development and application. In short, we need to design a new composite material that can introduce flexibility while improving the electromagnetic wave absorption ability of graphene aerogel and can be realized by a simple, environmentally friendly, and low-cost process. The present invention will provide new ideas for the development of wave-absorbing materials.

[0004] Silica fiber is a one-dimensional lightweight flexible material. When compounded with graphene aerogel, it can not only support the graphene porous framework to improve the elasticity of the material, but also may form a flexible framework composed of fibers to obtain a flexible composite aerogel. In addition, silica fiber hardly produces dielectric loss to electromagnetic waves. After being compounded with graphene, the graphene content is reduced, which can further improve the overall impedance matching characteristics of the material. By adjusting the ratio of the two, the impedance matching and attenuation ability can be adjusted to obtain the optimal wave-absorbing performance. Moreover, silica fiber is a material with high temperature resistance, heat insulation, and flame retardancy, which can endow the composite aerogel with more excellent thermal properties and enable it to be applied in complex environments.

[0005] First, the silica fibers are pretreated to obtain a silica fiber dispersion, which solves the problem that silica fibers are difficult to stably exist in water. Then, the graphene oxide slurry is uniformly mixed with the silica fiber dispersion, and a hierarchical network structure in which graphene nanosheets and silica fibers overlap is obtained by introducing a gas template. Finally, an ultra-light wave-absorbing aerogel is obtained through high-temperature heat treatment. The aerogel has a hierarchical network structure. Part of the silica fibers are distributed between the graphene nanosheet layers to form polygonal pore walls; the other part of the fibers are located on the polygonal pore walls, playing a supporting role for the porous structure. And it can be found that a three-dimensional network structure is also formed between the fibers after removing the graphene sheets, which is the key to the flexibility of the composite aerogel. The gas-template-assisted forming proposed in this paper can prepare a stable porous structure through a simple process, which not only simplifies the process flow but also shortens the preparation time and improves the efficiency. Importantly, the composite aerogel prepared by the present invention has excellent electromagnetic-infrared stealth performance, and at the same time has flexibility, high elasticity, heat insulation, and ablation resistance, and is expected to be applied in various fields such as electromagnetic stealth and heat insulation. Summary of the Invention

[0006] The object of the present invention is to prepare a flexible graphene composite aerogel, and a preparation method assisted by a gas template is provided.

[0007] In view of the above problems, the present invention provides a preparation method for a flexible graphene composite aerogel, which includes the following steps:

[0008] 1) Prepare a silica dispersion: Pretreat the silica fibers and disperse them in deionized water;

[0009] 2) Prepare an aqueous solution of graphene oxide: Oxidize graphite to prepare an aqueous solution of graphene oxide;

[0010] 3) Prepare a mixed solution: Uniformly mix the graphene oxide solution obtained in step 2) with the silica dispersion obtained in step 1);

[0011] 4) Gas-template-assisted forming: Introduce a gas template into the graphene oxide and silica mixed solution obtained in step 3) to make the graphene sheets surround the bubbles to form a porous structure, and obtain a composite hydrogel;

[0012] 5) Prepare an aerogel: Freeze the hydrogel obtained in step 4) and dry it in an air environment at 60 °C to obtain an aerogel block;

[0013] 6) High-temperature treatment: Perform high-temperature heat treatment on the aerogel block obtained in step 5) to obtain a graphene / silica fiber aerogel.

[0014] In the above step 1), first, the silica fibers are cut, and then dispersed in deionized water by high-speed stirring with a disperser. Then, Tween-20 is added and further dispersed in a cell crusher.

[0015] In the above step 2), a graphene oxide solution can be prepared by methods well-known in the art. For example, concentrated sulfuric acid and graphite are uniformly mixed, and a certain amount of potassium permanganate is added to the solution several times with stirring at a certain heating temperature. Then, the solution is cooled to room temperature and washed with deionized water to obtain a graphene oxide solution.

[0016] In the above step 3), the graphene oxide solution obtained in step 2) is blended with the silica dispersion obtained in step 1), and the water is evaporated to obtain a mixed solution with the required concentration.

[0017] In the above step 4), the mixed solution obtained in step 3) is stirred at high speed. Since air is introduced during the high-speed rotation of the stirring paddle, the interfacial tension is reduced under the action of Tween-20, and the graphene sheets and silica fibers together wrap the air to form pores, and the liquid level of the mixed solution rises to form a stable foam hydrogel.

[0018] 5) Preparation of aerogel: Pour the mixed solution in step 4) into a mold, freeze and shape it, and then dry it. Repeat the freezing and drying several times to obtain an aerogel block.

[0019] 6) High-temperature treatment: Heat the block obtained in step 5) in a high-temperature furnace to obtain a graphene / silica fiber composite aerogel block.

[0020] Preferably, in the above step 1), the silica fibers are placed in a shearer, and the fibers are cut into a certain length, for example, cut into short fibers of 0.5 mm to 10 mm. Deionized water is poured into a beaker, and the cut silica fibers are placed in the beaker filled with water and stirred at high speed with a disperser for 1 - 10 h. Then, the silica fibers are added in batches as needed. The maximum concentration of the dispersion is 20 mg / ml. The stirred dispersion is placed in a cell crusher, and the single-time setting is 90 s, and it is crushed several times. To increase the stability of the silica fiber dispersion, 0.1 - 1 ml of Tween-20 is taken with a 1 ml syringe and added to the dispersion during the crushing interval.

[0021] Preferably, the number of times of cell crushing described in the above step 1) is 1 - 100 times.

[0022] Preferably, the specific steps in step 2) are as follows: Measure 90 ml of concentrated sulfuric acid and pour it into a beaker. Weigh 0.5 g of graphite with a precision balance and pour it into the beaker containing concentrated sulfuric acid. Stir the solution evenly at room temperature by means of a magnetic stirrer. Ultrasonic it in an ultrasonic cleaner for 20 min, then add 10 ml of phosphoric acid, and transfer the solution to a water bath environment and stir for 1 h. Add 0.5 g of potassium permanganate to the solution, stir for 0.5 h and then add potassium permanganate again, 6 times in total, 3 g in total. After the reaction is completed, ice-bath the solution for 12 h, wash it many times and then centrifuge. Test the concentration of the centrifuged slurry and prepare a graphene solution with a concentration of 1 - 12 mg / ml.

[0023] Preferably, the power of the ultrasonic cleaner described in step 2) is 60 watts.

[0024] Preferably, the temperature of the water bath pot described in step 2) is set at 65 °C.

[0025] Preferably, the specific steps in step 3) are as follows: According to the volume ratio of graphene oxide solution to silica dispersion of 100:1 to 1:100, measure the graphene oxide solution obtained in step 2) and the silica fiber dispersion obtained in step 1), mechanically stir evenly, and evaporate the water of the mixed solution for 2 h - 6 h to obtain a solution with the required concentration.

[0026] Preferably, the concentration of the solution after evaporation in step 3) is about 18 - 36 mg / ml.

[0027] Preferably, the evaporation operation in step 3) is carried out in a drying oven, and the heating temperature is 50 °C.

[0028] Preferably, the specific steps in step 4) are as follows: Measure 100 ml of the mixed solution obtained in step 3) with a beaker, and stir it at high speed with a disperser. Since air is introduced during the high-speed rotation process, the graphene sheets are mixed with silica fibers to jointly wrap the air to form pores, and the liquid level of the mixed solution rises to 200 ml - 350 ml.

[0029] Preferably, the stirring speed during the high-speed stirring process of the disperser in step 4) is set at 1800 r / min - 3200 r / min, and the stirring time is 5 min - 30 min.

[0030] Preferably, the specific steps in step 5) are as follows: Pour the mixed solution in step 4) into a freezing mold, freeze and shape it at -18 °C, then place it in an environment of 40 °C and dry it for 12 h, freeze it again and dry it under normal pressure. The freeze-drying operation is repeated 2 - 6 times to obtain an aerogel block;

[0031] Preferably, the single freezing time in step 5) is at least 2 h.

[0032] Preferably, the heat treatment process described in step 6) above uses a high-temperature tube furnace or box furnace, the temperature is set at 200°C - 1800°C, and the heat treatment time is 2h - 24h.

[0033] Preferably, the heat treatment process described in step 6) above improves the reduction degree of graphene oxide through high-temperature treatment.

[0034] The beneficial effects of the present invention compared with the prior art are as follows:

[0035] 1. The present invention solves the problem that silica fibers are difficult to disperse in aqueous solutions and prepares a stable silica fiber dispersion.

[0036] 2. The present invention uses air as a template to assist in the co-construction of a three-dimensional porous structure by graphene sheets and silica fibers. Due to the supporting effect of silica fibers, the composite aerogel forms a stable three-dimensional structure, can still maintain the porous configuration after drying under normal pressure, and obtains excellent compressive resistance.

[0037] 3. The present invention prepares a flexible graphene composite aerogel, and for the first time proposes to introduce silica fibers as a reinforcing phase in the three-dimensional graphene structure to solve the problem of poor flexibility of graphene aerogels, providing new ideas for the development of wearable electromagnetic and infrared stealth materials and flexible wave-absorbing devices.

[0038] 4. The graphene / silica fiber composite aerogel prepared by the present invention has excellent mechanical, electromagnetic absorption, ablation resistance, heat insulation, high-temperature resistance and other characteristics, and is expected to be applied in various fields such as electromagnetic stealth, fireproof materials, and flexible sensors.

[0039] 5. The present invention proposes a method for preparing a flexible multifunctional aerogel by combining a gas template-assisted configuration with high-temperature thermal reduction, which reduces the production cost, has strong operability, and is very suitable for popularization and application in industrial production. Description of the Drawings

[0040] Figure 1 is a photograph of the prepared silica fiber dispersion.

[0041] Figure 2 is an SEM image of the prepared graphene oxide solution.

[0042] Figure 3 is a photograph of the product obtained in Example 1.

[0043] Figure 4 is an SEM image of the product obtained in Example 2.

[0044] Figure 5 is an SEM image of the product obtained in Example 3. Detailed Embodiments

[0045] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0046] Example 1

[0047] The method for preparing a flexible graphene composite aerogel described in this embodiment is specifically carried out according to the following steps:

[0048] 1) Prepare silica dispersion for use: First, cut the silica fibers, then disperse them in deionized water by high-speed stirring with a disperser, add Tween-20 and further disperse them in a cell disruptor.

[0049] Specifically: weigh 2g of silica fiber, lay it flat in the material shearing machine, set the cutting length to 0.5mm, the advancing speed to 0.1mm / s, and collect it in a clean sample box after cutting. Clean a 150ml measuring cylinder, dry it, and use it to measure 100ml of deionized water and pour it into a 200ml beaker. Use a precision balance to weigh 100mg of silica fiber cut to 0.5mm in the sample box and add it to the beaker containing water. Then place the beaker under the stirring paddle of the disperser, set the stirring speed to 5000r / min, and the stirring time to 1h. Then add the remaining silica fiber in 19 times, and set the speed to 5000r / min and stir for 2h after adding 100mg each time. In order to increase the stability of the silica fiber dispersion, use a 1ml syringe to measure 0.1ml Tween-20 and add it to the dispersion. Finally, place the solution in a cell crusher, set the single time to 90s, and crush it 100 times. Note that every 10 times, 0.1 ml of Tween-20 is added to the solution using a syringe. The purpose of adding in batches is to better disperse and prevent agglomeration when added all at once.

[0050] 2) preparing a graphene oxide aqueous solution for standby use: after evenly mixing concentrated sulfuric acid and graphite, adding a certain amount of potassium permanganate to the solution several times at a certain heating temperature and stirring, then cooling the solution to room temperature, and washing to obtain a graphene oxide aqueous solution.

[0051] Wash one 20 ml graduated cylinder, one 100 ml graduated cylinder and one 1 L beaker, and place them in a drying oven to dry. Measure 90 ml of concentrated sulfuric acid with the 100 ml graduated cylinder and pour it into the beaker. Weigh 0.5 g of graphite with a precision balance and pour it into the beaker containing concentrated sulfuric acid. The resulting solution is denoted as solution a. Place solution a on a magnetic stirrer, set the rotation speed to 100 r / min, and stir evenly at room temperature to obtain solution b. Select an ultrasonic cleaner with a power of 60 watts to ultrasonically disperse the stirred solution b for 20 min, denoted as solution c. Then measure 10 ml of phosphoric acid with the 20 ml graduated cylinder and pour it into solution c, and transfer it to a water bath for stirring. Set the heating temperature to 65 °C and stir for 1 h at this temperature to obtain solution d. Weigh 0.5 g of potassium permanganate with a precision balance, six portions in total, that is, 3 g of potassium permanganate in total. Add one portion of potassium permanganate to solution d every 0.5 h, for a total of 6 additions. The reacted solution is denoted as solution e. Immerse solution e in an ice bath at -18 °C for 12 h, wash it multiple times and then centrifuge (more than three times). Test the concentration of the centrifuged slurry and prepare a solution with a concentration of 12 mg / ml.

[0052] 3) Prepare the mixed solution: Prepare a cleaned 150 ml graduated cylinder, a 500 ml beaker and a 2 ml disposable dropper. Measure 100 ml of the graphene oxide solution obtained in step 2) with the graduated cylinder and pour it into the 500 ml beaker according to the volume ratio of 100:1. Then use the dropper to suck 1 ml of the silicon dioxide fiber dispersion and drop it into the beaker. Mechanically stir the resulting mixed solution, set the stirring speed of the disperser to 3500 r / min, and stir for 24 h. After mechanical stirring is uniform, place the mixed solution in a drying oven, set the temperature of the drying oven to 50 °C, and evaporate part of the water in the solution for 6 h to obtain a solution with a concentration of about 36 mg / ml.

[0053] 4) Gas template assisted forming: Measure 100 ml of the mixed solution obtained in step 3) with a clean 500 ml beaker, fix it under the stirring paddle of the disperser with a clamp, set the stirring speed to 1800 r / min, and stir for 30 min. It can be observed that the color of the solution changes from deep to light, and the height of the solution rises to 250 ml.

[0054] 5) Prepare the aerogel: Pour the mixed solution obtained in step 4) into a square mold, place it in an environment at -18 °C and freeze for 2 h. After shaping, place it in an environment at 40 °C and dry for 12 h. Repeat the process of freezing and drying under normal pressure 2 times to obtain an aerogel block.

[0055] 6) High temperature treatment: Perform thermal reduction treatment on the composite aerogel block obtained in step 5). Heat it in a box furnace with a heating rate of 5 °C / min, a maximum temperature of 1800 °C, and a heat treatment time of 2 h.

[0056] The photo of the prepared silicon dioxide fiber dispersion is as Figure 1As shown, the SEM image of the prepared graphene oxide solution is as Figure 2 shown. It can be seen that the silica fibers are evenly dispersed in the aqueous solution, which is attributed to the control of fiber size and the addition of the hydrophilic surface modifier Tween-20. From Figure 2 it can be seen that the graphene oxide sheets are relatively thin and maintain a large surface area, indicating that the graphite is well exfoliated during the preparation process. The photograph of the graphene / silica fiber composite aerogel prepared in this example is as Figure 3 shown. The density of the composite aerogel is 22.5 mg / cm 3 , which is a super-light material. Its conductivity is 3.2 S / m, the pore volume is 5 cm 3 / g. The electromagnetic wave absorption ability of the material is tested by the bow method, and the maximum reflection loss value can reach -50 dB, and the maximum absorption bandwidth (reflection loss less than -10 dB) covers 1 - 70 GHz. In addition, the graphene / silica fiber composite aerogel prepared by the present invention can be twisted 1000 times with excellent flexible performance. In summary, the graphene / silica fiber composite aerogel prepared by the present invention has flexibility, super-light weight, high porosity, and excellent electromagnetic absorption, thermal and mechanical properties, and is expected to be applied in various fields such as electromagnetic stealth, flexible sensors, adsorption, electrochemistry, etc.

[0057] Comparative Example

[0058] A pure graphene aerogel was prepared in the same manner as in Example 1, except that no silica fibers were added to obtain the aerogel. The aerogel cracked when folded at 1 degree in the bending test and brittle fractured at 10 degrees in the torsion test. It shows that the graphene aerogel is a brittle material, and its flexibility is greatly improved after adding silica fibers. And the electromagnetic wave absorption ability of the graphene aerogel was tested, and its maximum reflection loss was only -8 dB, and effective absorption could not be achieved.

[0059] Example 2

[0060] The preparation method of a flexible graphene composite aerogel described in this example is specifically carried out according to the following steps:

[0061] 1) Preparation of silica dispersion: Weigh 2 g of silica fibers, lay them flat in a material shearer, set the cutting length to 5.5 mm, the advancing speed to 0.5 mm / s. After cutting, collect them in a clean sample box for later use. Wash a 150-ml measuring cylinder, dry it, and use it to measure 100 ml of deionized water and pour it into a 200-ml beaker. Weigh 100 mg of the silica fibers cut to 5.5 mm in the sample box with a precision balance and add them to the beaker containing water. Then place the beaker under the stirring paddle of a disperser, set the stirring speed to 8000 r / min, and stir for 5 h. Then add the silica fibers in 19 portions, each time adding 100 mg and setting the rotation speed to 8000 r / min and stirring for 5 h. To increase the stability of the silica fiber dispersion, use a 0.5-ml syringe to measure 1 ml of Tween-20 and add it to the dispersion. Finally, place the solution in a cell disruptor, set the single-time duration to 90 s, and disrupt it 10 times. Note that every 10 times, use a syringe to measure 0.5 ml of Tween-20 and add it to the solution.

[0062] 2) Preparation of graphene oxide aqueous solution: Wash one 20-ml measuring cylinder, one 100-ml measuring cylinder, and one 1-L beaker, and place them in a drying oven to dry. Use the 100-ml measuring cylinder to measure 90 ml of concentrated sulfuric acid and pour it into the beaker. Weigh 0.5 g of graphite with a precision balance and pour it into the beaker containing concentrated sulfuric acid. The resulting solution is denoted as solution a. Place solution a on a magnetic stirrer, set the rotation speed to 100 r / min, and stir evenly at room temperature, denoted as solution b. Select an ultrasonic cleaner with a power of 60 watts to perform ultrasonic dispersion on the stirred solution b for 20 min, denoted as solution c. Then use the 20-ml measuring cylinder to measure 10 ml of phosphoric acid and add it to solution c, and transfer it to a water bath for stirring. Set the heating temperature to 65 °C and stir at this temperature for 1 h to obtain solution d. Weigh 0.5 g of potassium permanganate in six portions, and add one portion of potassium permanganate to solution d every 0.5 h, for a total of 6 additions. The reacted solution is denoted as solution e. Immerse solution e in an ice bath at -18 °C for 12 h, wash it multiple times, and then centrifuge. Test the concentration of the centrifuged slurry and prepare a 6-mg / ml solution.

[0063] 3) Preparation of the mixed solution: Prepare two washed 150-ml measuring cylinders and one 500-ml beaker. According to the volume ratio of 1:1, use the measuring cylinder to measure 100 ml of the graphene oxide solution obtained in step 2) and pour it into the 500-ml beaker. Then measure 100 ml of the silica fiber dispersion and pour it into this beaker. Mechanically stir the resulting mixed solution, set the stirring speed of the disperser to 3500 r / min, and stir for 24 h. After mechanical stirring is uniform, place the mixed solution in a drying oven, set the temperature of the drying oven to 50 °C, and evaporate some of the water in the solution for 4 h to obtain a solution with a concentration of approximately 27 mg / ml.

[0064] 4) Gas template-assisted forming: Measure 100 ml of the mixed solution obtained in step 3) with a clean 500 ml beaker, fix it under the stirring paddle of the disperser with a clamp, set the stirring speed to 2500 r / min, and the stirring time to 18 min. It can be observed that the color of the solution changes from dark to light, and the solution height rises to 200 ml.

[0065] 5) Preparation of aerogel: Pour the mixed solution obtained in step 4) into a square mold, place it in an environment of -18 °C and freeze for 4 h. After shaping, place it in an environment of 40 °C and dry for 12 h. Repeat the process of freezing and drying under normal pressure 4 times to obtain an aerogel block.

[0066] 6) High-temperature treatment: Perform thermal reduction treatment on the composite aerogel block obtained in step 5), heat it in a box furnace, with a heating rate of 5 °C / min, a maximum temperature of 1000 °C, and a heat treatment time of 13 h.

[0067] The photo of the prepared silica fiber dispersion is as Figure 1 shown, and the SEM image of the prepared graphene oxide solution is as Figure 2 shown. It can be seen that the silica fibers are uniformly dispersed in the aqueous solution, which is attributed to the control of fiber size and the addition of the hydrophilic surface modifier Tween-20. From Figure 2 it can be seen that the graphene oxide sheets are thinner and maintain a large surface area, indicating that the graphite is well exfoliated during the preparation process. Figure 4 This is the scanning photo of the sample prepared in this example. Some millimeter-sized large pores can be observed. The density of the graphene / silica fiber composite aerogel prepared in this example is 18.5 mg / cm 3 , which is a super-light material, its conductivity is 2.8 S / m, the pore volume is 6.2 cm 3 / g. The electromagnetic wave absorption ability of the material is tested by the bow-tie method, and its maximum reflection loss value can reach -43 dB, and the maximum absorption bandwidth (reflection loss less than -10 dB) covers 1 - 70 GHz. In addition, the graphene / silica fiber composite aerogel prepared by the present invention can be twisted 1000 times with excellent flexible properties. In summary, the graphene / silica fiber composite aerogel prepared by the present invention has flexibility, super-lightness, high porosity, and excellent electromagnetic absorption, thermal and mechanical properties, and is expected to be applied in various fields such as electromagnetic stealth, flexible sensors, adsorption, electrochemistry, etc.

[0068] Example 3

[0069] A preparation method of a flexible graphene composite aerogel described in this example is specifically carried out according to the following steps:

[0070] 1) Preparation of silica dispersion: Weigh 2 g of silica fibers, lay them flat in a material shearer, set the cutting length to 10 mm, the feeding speed to 1 mm / s. After cutting, collect them in a clean sample box for later use. Wash a 150-ml graduated cylinder, dry it, and use it to measure 100 ml of deionized water and pour it into a 200-ml beaker. Weigh 100 mg of the silica fibers cut to 10 mm in the sample box with a precision balance and add them to the beaker containing water. Then place the beaker under the stirring paddle of a disperser, set the stirring speed to 8000 r / min, and stir for 10 h. Then add the silica fibers in 19 portions, each time adding 100 mg and setting the rotation speed to 5000 r / min and stirring for 2 h. To increase the stability of the silica fiber dispersion, use a 1-ml syringe to measure 1 ml of Tween-20 and add it to the dispersion. Finally, place the solution in a cell crusher, set the single-time duration to 90 s, and crush it once.

[0071] 2) Preparation of graphene oxide aqueous solution: Wash one 20-ml graduated cylinder, one 100-ml graduated cylinder, and one 1-L beaker, and place them in a drying oven to dry. Use the 100-ml graduated cylinder to measure 90 ml of concentrated sulfuric acid and pour it into the beaker. Weigh 0.5 g of graphite with a precision balance and add it to the beaker containing concentrated sulfuric acid. The resulting solution is denoted as solution a. Place solution a on a magnetic stirrer, set the rotation speed to 100 r / min, and stir evenly at room temperature, denoted as solution b. Select an ultrasonic cleaner with a power of 60 watts to ultrasonically disperse the stirred solution b for 20 min, denoted as solution c. Then use the 20-ml graduated cylinder to measure 10 ml of phosphoric acid and add it to solution c, and transfer it to a water bath for stirring, set the heating temperature to 65 °C, and stir at this temperature for 1 h to obtain solution d. Weigh 0.5 g of potassium permanganate in six portions, add one portion of potassium permanganate to solution d every 0.5 h, add a total of 6 times, and the reacted solution is denoted as solution e. Place solution e in an ice bath at -18 °C for 12 h, wash it multiple times and then centrifuge. Test the concentration of the centrifuged slurry and prepare a 1-mg / ml solution.

[0072] 3) Preparation of the mixed solution: Prepare a washed 150-ml graduated cylinder, a 500-ml beaker, and a 2-ml disposable dropper. According to the volume ratio of 1:100, use the dropper to suck 1 ml of the graphene oxide solution obtained in step 2) and drop it into the 500-ml beaker. Then use the graduated cylinder to measure 100 ml of the silica fiber dispersion and pour it into the beaker. Mechanically stir the resulting mixed solution, set the stirring speed of the disperser to 3500 r / min, and stir for 24 h. After mechanical stirring is uniform, place the mixed solution in a drying oven, set the temperature of the drying oven to 50 °C, and evaporate part of the water in the solution for 2 h to obtain a solution with a concentration of approximately 18 mg / ml.

[0073] 4) Gas template-assisted forming: Measure 100 ml of the mixed solution obtained in step 3) with a clean 500 ml beaker, fix it under the stirring paddle of the disperser with a clamp, set the stirring speed to 3200 r / min, and the stirring time to 5 min. It can be observed that the color of the solution changes from deep to light, and the solution height rises to 350 ml.

[0074] 5) Preparation of aerogel: Pour the mixed solution obtained in step 4) into a square mold, place it in an environment of -18 °C and freeze for 2 h. After shaping, place it in an environment of 40 °C and dry for 12 h. Repeat the process of freezing and drying under normal pressure 6 times to obtain an aerogel block.

[0075] 6) High-temperature treatment: Perform thermal reduction treatment on the composite aerogel block obtained in step 5), heat it in a box furnace, with a heating rate of 5 °C / min, a maximum temperature of 200 °C, and a heat treatment time of 24 h.

[0076] The photo of the prepared silica fiber dispersion is as Figure 1 shown, and the SEM image of the prepared graphene oxide solution is as Figure 2 shown. It can be seen that the silica fibers are evenly dispersed in the aqueous solution, which is attributed to the control of fiber size and the addition of the hydrophilic surface modifier Tween-20. From Figure 2 it can be seen that the graphene oxide sheets are thin and maintain a large surface area, indicating that the graphite is well exfoliated during the preparation process. Figure 5 is the SEM image of the product obtained in this example. Due to the very small content of graphene oxide, it can be seen that the silica fibers crisscross to form a porous skeleton. The density of the graphene / silica fiber composite aerogel prepared in this example is 16.5 mg / cm 3 , which is a super-light material, with an electrical conductivity of 0.2 S / m and a pore volume of 5.4 cm 3 / g. In addition, the graphene / silica fiber composite aerogel prepared by the present invention can be twisted 10,000 times and has excellent flexible properties. In summary, the graphene / silica fiber composite aerogel prepared by the present invention has flexibility, super-light weight, high porosity, and excellent electromagnetic absorption, thermal and mechanical properties, and is expected to be applied in various fields such as electromagnetic stealth, flexible sensors, adsorption, electrochemistry, etc.

[0077] The above embodiments are only illustrative of the present invention and do not limit its protection scope. Those skilled in the art can also make partial changes to it. As long as it does not exceed the spirit of the present invention, it is regarded as an equivalent replacement of the present invention and is within the protection scope of the present invention.

Claims

1. A preparation method of a flexible graphene composite aerogel, characterized in that: It includes the following steps: 1) Prepare a silica dispersion: First, cut the silica fiber, then use a disperser to stir it at high speed to disperse it in deionized water, add Tween-20 and further disperse it in a cell disruptor; 2) Prepare an aqueous solution of graphene oxide: After uniformly mixing concentrated sulfuric acid and graphite, take a certain amount of potassium permanganate and add it to the solution in several portions while stirring at a certain heating temperature, then cool the solution to room temperature, and obtain an aqueous solution of graphene oxide after washing; 3) Prepare a mixed solution: Blend the aqueous solution of graphene oxide obtained in step 2) with the silica dispersion obtained in step 1), and evaporate the water to obtain a mixed solution with the required concentration; 4) Gas template-assisted forming: Stir the mixed solution obtained in step 3) at high speed. Since air is introduced during the high-speed rotation of the stirring paddle, to reduce the interfacial tension, under the action of Tween-20, the graphene sheets sandwich the silica fibers and jointly wrap the air to form pores, the liquid level of the mixed solution rises and stably exists, and a composite hydrogel is obtained; 5) Prepare an aerogel: Pour the composite hydrogel obtained in step 4) into a mold, freeze and shape it, and then dry it in an air environment at 40 °C for several times to obtain an aerogel block; 6) High-temperature treatment: Heat the aerogel block obtained in step 5) in a high-temperature furnace to obtain a graphene / silica fiber composite aerogel block.

2. The preparation method of the flexible graphene composite aerogel according to claim 1, characterized in that: In step 1), place the silica fiber in a shear machine, cut the fiber into different sizes of 0.5 mm to 10 mm for standby, measure 100 ml of deionized water with a measuring cylinder and pour it into a 200 ml beaker, take 100 mg of the cut silica fiber and place it in the beaker containing water, stir it at high speed with a disperser for 1 - 10 h, then add the silica fiber in batches as needed, place the stirring solution in a cell crusher, set the single time to 90 s, and crush it several times. To increase the stability of the silica dispersion, use a 1 ml syringe to take 0.1 - 1 ml of Tween-20 and add it to the dispersion during the crushing interval. The number of crushing times of the stirring solution placed in the cell crusher is selected from 1 - 100 times.

3. The preparation method of the flexible graphene composite aerogel according to claim 2, characterized in that: In step 2), measure 90 ml of concentrated sulfuric acid with a 100 ml measuring cylinder and pour it into a beaker, weigh 0.5 g of graphite with a precision balance and pour it into the beaker containing concentrated sulfuric acid. Stir the solution evenly at room temperature under the action of a magnetic stirrer, ultrasonicate it in an ultrasonic cleaner at a power of 60 watts for 20 min, then add 10 ml of phosphoric acid, transfer the solution to a water bath environment at 65 °C and stir for 1 h, add 0.5 g of potassium permanganate to the solution, stir for 0.5 h and then add another 0.5 g of potassium permanganate, add a total of 6 times. After the reaction is completed, ice-bath the solution for 12 h, wash it several times and centrifuge it, test the concentration of the centrifuged slurry, and prepare an aqueous solution of graphene oxide with a concentration of 1 - 12 mg / ml.

4. The preparation method of the flexible graphene composite aerogel according to claim 3, characterized in that: In step 3), according to the volume ratio of 100:1 to 1:100, measure the graphene oxide aqueous solution obtained in step 2) and the silica dispersion obtained in step 1). After mechanically stirring evenly, evaporate the water of the mixed solution for 2h - 6h to obtain a solution with the required concentration.

5. The preparation method of the flexible graphene composite aerogel according to claim 4, characterized in that: The concentration of the solution after evaporation in step 3) is 18 - 36 mg / ml, and the evaporation operation is carried out in a drying oven at a heating temperature of 50 °C.

6. The preparation method of the flexible graphene composite aerogel according to claim 1, characterized in that: The gas template-assisted forming in step 4) is specifically as follows: Measure 100 ml of the mixed solution obtained in step 3) with a beaker, and use a disperser to stir at a high speed. The stirring speed is set to 1800 r / min - 3200 r / min, and the stirring time is 5 min - 30 min. The liquid level of the mixed solution rises to 200 ml - 350 ml.

7. The preparation method of the flexible graphene composite aerogel according to claim 1, characterized in that: The preparation of the aerogel in step 5) is specifically as follows: Pour the composite hydrogel in step 4) into a freezing mold, freeze and shape it, then place it in an environment at 40 °C for drying for 12 h, freeze again and dry under normal pressure, repeating 2 - 6 times to obtain an aerogel block, where the single freezing time is at least 2 h.

8. The preparation method of the flexible graphene composite aerogel according to claim 1, characterized in that: In step 6), the high-temperature treatment uses a high-temperature tube furnace or a box furnace, the temperature is set to 200 °C - 1800 °C, and the heat treatment time is 2 h - 24 h.

9. A flexible graphene composite aerogel prepared by the method according to any one of claims 1 - 8.

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