CN109607509B - Preparation method of full-biomass-based carbon aerogel with high electromagnetic shielding efficiency - Google Patents
Preparation method of full-biomass-based carbon aerogel with high electromagnetic shielding efficiency Download PDFInfo
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Abstract
The invention discloses a preparation method of a full biomass-based carbon aerogel with high electromagnetic shielding efficiency, which comprises the following raw materials: cellulose; comprises the following steps: (1) drying the raw materials; (2) and (3) preparing a cellulose solution. (3) Preparing cellulose aerogel; (4) preparation of carbon aerogel. The invention takes cellulose as a precursor, and a stable and excellent conductive network (592.3S/m) is constructed by dissolving regeneration, cosolvent treatment and freeze drying regulation and control of a three-dimensional continuous open pore lamellar network structure of the cellulose aerogel and high-temperature carbonization, so that the high-efficiency electromagnetic shielding performance (106.3dB) of the carbon aerogel is realized. The precursor of the invention has wide source, environmental protection, nontoxic solvent system, low price, simple material preparation process, easy control of process, low production cost and huge potential of large-scale production.
Description
Technical Field
The invention relates to the technical field of preparation of full-biomass-based carbon aerogel, and particularly relates to a preparation method of cellulose-based carbon aerogel with high electromagnetic shielding effectiveness.
Background
With the rapid development of electronic science and technology, electronic devices are increasingly used in military, industrial and civil fields, and the problems of electromagnetic pollution, electromagnetic interference, secret disclosure and the like are caused, so that the normal operation of precision electronic devices is interfered, and organs, tissues and systems of human bodies are damaged to different degrees (D.Chung et al. carbon,2001,39, 279). Therefore, it is of great significance to develop an efficient electromagnetic shielding material to inhibit the interference of electromagnetic radiation to electronic equipment and protect human beings from being damaged by electromagnetic wave radiation.
Polymer conductionThe composite materials (CPCs) have the advantages of light weight, low cost, easy processing and the like, and are novel electromagnetic shielding materials (J.M. Thomasin, et al.materials Science and Engineering: R: Reports,2013,74,211.) which have great application prospects and are expected to replace metal materials. However, the traditional physical CPCs electromagnetic shielding material and the air transmission medium have obvious impedance mismatching, and the electromagnetic shielding mechanism mainly takes electromagnetic wave reflection to generate a large amount of electromagnetic wave reflection, so that secondary electromagnetic pollution is caused. Aiming at the problems, a great deal of research is carried out on chemical foaming and supercritical CO2Foaming, freeze-drying, particle leaching, 3D printing, etc., to build a porous structure in CPCs to reduce impedance mismatch while greatly reducing material density and cost. Such as Gupta et al (Gupta M, et al advanced Materials,2005,17(16),1999), carbon nanotube/polystyrene porous CPCs with electromagnetic shielding effectiveness of 20dB were prepared by chemical foaming. Although the porous structure alleviates reflection of electromagnetic waves to some extent, it is due to its closed cell structure and greater density (0.56g cm)-3) The electromagnetic shielding mechanism of the material still takes reflection as the main factor. Yan et al (D. -X. Yan, et al. journal of Materials Chemistry,2012,22,18772.) prepare continuous vias by particle leaching with low density (0.45g cm)-3) The electromagnetic shielding effectiveness of the graphene/polystyrene porous composite material reaches 29dB, and the shielding mechanism mainly takes electromagnetic wave absorption as a main factor. The conductive path of the porous CPCs material strongly depends on the addition of high-content carbon nano-fillers, and the risk of agglomeration and deterioration of mechanical properties exists. And the density of the material is still large, so that the application of the material in the fields of aerospace and microelectronic devices is severely limited.
In recent years, a carbon aerogel prepared by high-temperature carbonization of an organic aerogel or self-assembly of a carbon nano material (such as a carbon nano tube, graphene and the like) is considered to be a highly effective electromagnetic shielding material with great potential due to a unique three-dimensional porous structure, extremely low density, high electrical conductivity and good chemical stability. For example, Li et al (Q.Li, et al. carbon,2016,104,90.) uses a sol-gel method to prepare an organic aerogel of phenolic resin, in the process, 2.0 wt% of carbon nano-tube and 7.0 wt% of ferroferric oxide are introduced in situ, and after carbonization treatment, the density of the organic aerogel is 0.126g cm-3And the electromagnetic shielding effectiveness is 62dB of the composite carbon aerogel. Song et al (Q.Song, et al. advanced Materials,2017,29,1701583.) produced carbon nanotubes and multilayer graphene in situ on the surface of a silica nanowire foam template by chemical vapor deposition and plasma enhanced chemical vapor deposition in sequence, and the prepared density was only 0.009g cm-3And composite carbon aerogel having an electromagnetic shielding effectiveness of 47.5 dB. Gao et al (C.Gao, et al. Carbon,2018,135,44.) produced a density of 0.41g cm using solution casting, chemical reduction, high temperature thermal expansion treatment-3And the electromagnetic shielding performance is 70-105 dB of graphene carbon aerogel. Although the above carbon aerogels all exhibit excellent electromagnetic shielding effectiveness, the following problems still remain: (1) the source of organic aerogel materials is highly dependent on petroleum resources; (2) the precursor for preparing the carbon aerogel in situ by the chemical vapor deposition method has high cost, toxicity and complex process; (3) the carbon aerogel directly constructed by the carbon nano material has poor mechanical stability and high forming processing difficulty; (4) the methods all rarely relate to the effective regulation and control of the pore structure of the carbon aerogel. Therefore, developing a carbon aerogel with high electromagnetic shielding effectiveness, which is environment-friendly in source, controllable in structure and easy to master in process, is very important in the field of electromagnetic shielding.
Disclosure of Invention
The method takes the green and environment-friendly cellulose with wide sources as a precursor, prepares the cellulose aerogel with controllable structure, stable performance and three-dimensional porous structure by simple methods of dissolution regeneration, cosolvent soaking treatment and freeze drying, and then constructs a carbon aerogel three-dimensional network structure by high-temperature carbonization treatment to prepare the carbon aerogel with low density, high conductivity and excellent electromagnetic shielding performance and the multilayer three-dimensional sheet network structure. The preparation process of the material is green and environment-friendly, and the process is easy to master. From the patent and published literature applied at present, the preparation of the three-dimensional porous carbon aerogel with high-efficiency electromagnetic shielding performance by using the holocellulose material as the precursor is not reported.
The invention is realized by the following means:
a preparation method of full biomass-based carbon aerogel with high electromagnetic shielding efficiency comprises the following raw materials and reagents:
raw materials: cellulose;
reagent: lithium hydroxide, urea, tert-butanol and water;
the preparation method comprises the following steps:
(1) and (3) drying the cellulose: fully drying the cellulose;
(2) preparation of cellulose solution: adding the cellulose dried in the step (1) into a mixed solvent of lithium hydroxide, urea and water at room temperature, and stirring until a stable and transparent cellulose solution is obtained;
(3) preparation of cellulose aerogel: gelling the cellulose solution obtained in the step (2) at room temperature to form a cellulose hydrogel; then soaking the cellulose hydrogel in water, and washing to be neutral to remove lithium hydroxide and urea, thereby forming a neutral cellulose hydrogel; soaking the neutral cellulose hydrogel in an aqueous solution of tert-butyl alcohol, freezing to obtain a gel-state sample low-temperature frozen solid phase, sufficiently sublimating and drying, and recovering to room temperature to obtain cellulose aerogel;
(4) preparation of carbon aerogel: carbonizing the cellulose aerogel obtained in the step (3) at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature to obtain the carbon aerogel.
In the step (2), the mass ratio of lithium hydroxide, urea and water is (5-10): (10-20): (70-85).
In the step (2), the temperature of the mixed solvent of lithium hydroxide, urea and water is-20.0-0 ℃.
In the step (2), the mass fraction of the cellulose in the cellulose solution is 0.1-10 wt%.
In the step (3), the gelation temperature for forming the cellulose hydrogel by the gelation of the cellulose solution is less than or equal to 80 ℃.
In the step (3), the gelation temperature in the step (3) is 20 to 80 ℃.
In the step (3), the freezing is slow freezing or quick freezing.
In the step (3), the mass fraction of the tertiary butanol in the tertiary butanol aqueous solution is 0-100 wt%.
In the step (4), the protective gas is one or more of helium, neon, argon or nitrogen.
In the step (4), the carbonization temperature is 500-2500 ℃.
The method takes cellulose as a precursor, and prepares the carbon aerogel with the three-dimensional flaky network structure by the methods of dissolution regeneration, cosolvent treatment, freeze drying and high-temperature carbonization. The prepared carbon aerogel has low density (0.158g cm)-3) High porosity (97.0%), good conductivity (592.3S/m), and high electromagnetic shielding effectiveness (106.3 dB). In addition, the advantages of the invention are also shown in the following aspects:
(1) the cellulose aerogel is prepared by adopting a method combining dissolution regeneration, cosolvent treatment and freeze drying, water molecule crystal grains can be refined through the cosolvent treatment, and a network structure is stabilized; the three-dimensional skeleton structure of the cellulose aerogel is regulated and controlled by utilizing the freezing rate to change from fibrous to flaky, and a foundation is laid for the preparation of the functional carbon aerogel.
(2) According to the invention, the carbon aerogel with a flaky skeleton structure is obtained through high-temperature carbonization, and while high conductivity is obtained, the multilevel and multilayer flaky network structure can increase the transmission path of incident electromagnetic waves in the material, so that the absorption loss is improved, and the electromagnetic shielding performance mainly based on absorption is obtained.
(3) The invention takes cellulose as a precursor, and the source of the cellulose is wide and environment-friendly; the alkaline urea solvent system is non-toxic, environment-friendly and low in cost; the preparation process of the material is simple, the process is easy to master, the production cost is low, and the material has great potential for large-scale production.
Drawings
FIG. 1 is a scanning electron microscope image of the microstructure of the sample before carbonization (a) and after carbonization (b).
Fig. 2 is a scanning electron microscope image of the microstructure after carbonization in comparative example 1.
Fig. 3 is a scanning electron microscope image of the microstructure after carbonization of comparative example 2.
FIG. 4 is an electrical property diagram of the cellulose solution of the example (mass fraction of cellulose in the cellulose solution is 2.0-4.0 wt%).
FIG. 5 is a graph showing electromagnetic shielding performance of examples (mass fraction of cellulose in cellulose solution: 4.0 wt%).
Detailed Description
The following examples are given to illustrate the present invention and it should be noted that the following examples are given only for the purpose of further illustrating the present invention and should not be construed as limiting the scope of the present invention. The preparation process mainly comprises three parts of raw material drying, cellulose aerogel preparation and carbon aerogel preparation, and the invention is described by taking cellulose with the polymerization degree of 500 as an example.
Examples 1 to 36 (see Table 1)
The invention discloses a preparation method of a full biomass-based carbon aerogel with high electromagnetic shielding efficiency, which comprises the following raw materials and reagents:
raw materials: cellulose;
reagent: lithium hydroxide, urea, tert-butanol and water;
the preparation method comprises the following steps:
(1) drying raw materials: the cellulose is thoroughly dried.
(2) Preparation of cellulose solution: adding the cellulose dried in the step (1) into a mixed solvent of lithium hydroxide, urea and water at room temperature, and stirring until a stable and transparent cellulose solution is obtained; step (ii) of
(2) For example, lithium hydroxide: urea: the water mass ratio can be 8:15: 77; the temperature of the mixed solvent is preferably low, for example, the temperature can be selected from-20.0 ℃, 10.0 ℃ or 0 ℃, and the like, as shown in Table 1; the stirring can be vigorous, for example, at 3000 r/min.
(3) Preparation of cellulose aerogel: gelling the cellulose solution obtained in the step (2) at room temperature to form a cellulose hydrogel; then soaking the cellulose hydrogel in water, repeatedly washing to be neutral to remove lithium hydroxide and urea so as to form neutral cellulose hydrogel; soaking the neutral cellulose hydrogel in an aqueous solution of tert-butyl alcohol, freezing to obtain a gel-state sample low-temperature frozen solid phase, sufficiently sublimating and drying, and recovering to room temperature to obtain the cellulose aerogel. In the step (3), the gelation temperature for forming the cellulose hydrogel by the gelation of the cellulose solution is less than or equal to 80 ℃, specifically, the temperature can be selected from 0 ℃,10 ℃,20 ℃, 50 ℃ or 80 ℃ and the like, as shown in table 1, for example, the gelation can be carried out for more than 1h at the temperature of below 50 ℃; the mass fraction of the tertiary butanol aqueous solution is shown in table 1; the sublimation drying can be carried out at a temperature of less than-20 deg.C and a pressure of less than 100Pa, and preferably for more than 30 h.
(4) Preparation of carbon aerogel: carbonizing the cellulose aerogel obtained in the step (3) at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature to obtain the carbon aerogel. And (3) performing high-temperature carbonization treatment, and converting the cellulose aerogel into carbon aerogel to obtain a stable and excellent conductive network and high-efficiency electromagnetic shielding efficiency. In the step (4), the high-temperature carbonization temperature is shown in table 1, and the high-temperature carbonization time is preferably within 2 h.
And (4) jointly regulating and controlling the size of ice crystals of the water phase in the cellulose hydrogel by using the aqueous solution treatment and freezing modes of the tert-butyl alcohol in the step (3) to obtain a highly continuous open-pore three-dimensional sheet or fibrous network structure.
Comparative example 1 (see Table 1)
The process comprises the following steps:
(1) drying raw materials: fully drying the cellulose;
(2) preparation of cellulose solution: adding the cellulose obtained after drying in the step (1) into lithium hydroxide with the temperature of-12.0 ℃ at room temperature: urea: stirring (such as stirring vigorously at 3000 r/min) in a mixed solvent of water (such as water with a mass ratio of 8:15:77) until a stable and transparent cellulose solution is obtained;
(3) preparation of cellulose aerogel: at room temperature, gelatinizing the cellulose transparent mixed solution obtained in the step (2) at the temperature of less than or equal to 80 ℃ (for example, the cellulose transparent mixed solution can be gelatinized at the temperature of less than 50 ℃ for more than 1 h) to form cellulose hydrogel, then soaking the cellulose hydrogel in water, repeatedly washing, washing to be neutral to remove lithium hydroxide and urea so as to form neutral cellulose hydrogel, freezing the neutral cellulose hydrogel to obtain a gel-state sample low-temperature frozen solid phase, then sufficiently sublimating and drying (for example, sublimating and drying at the temperature of less than-20 ℃ and the air pressure of less than 100Pa for more than 30 h), and returning to the room temperature to obtain cellulose aerogel;
(4) preparation of carbon aerogel: carbonizing the cellulose aerogel obtained in the step (3) at a high temperature of 1200 ℃ in a protective gas and vacuum atmosphere, and then cooling to room temperature to obtain the carbon aerogel.
Comparative example 2 (see Table 1)
The process comprises the following steps:
(1) drying raw materials: the cellulose is thoroughly dried.
(2) Preparation of cellulose solution: adding the cellulose obtained after drying in the step (1) into lithium hydroxide with the temperature of-12.0 ℃ at room temperature: urea: stirring (such as stirring vigorously at 3000 r/min) in a mixed solvent of water (such as water with a mass ratio of 8:15:77) until a stable and transparent cellulose solution is obtained;
(3) preparation of cellulose aerogel: at room temperature, the cellulose solution in the step (2) is gelatinized at the temperature of less than or equal to 80 ℃ (for example, the gelation can be carried out at the temperature of less than or equal to 50 ℃ for more than 1 h) to form cellulose hydrogel, then the cellulose hydrogel is soaked in water, and is repeatedly washed and washed to be neutral so as to remove lithium hydroxide and urea, thereby forming neutral cellulose hydrogel; soaking the neutral cellulose hydrogel in tert-butanol aqueous solution (mass fraction shown in Table 1), freezing to obtain gel-state sample low-temperature frozen solid phase, sufficiently sublimating and drying (for example, sublimating and drying at a temperature lower than-20 deg.C and a pressure lower than 100Pa for more than 30 h), and returning to room temperature to obtain cellulose aerogel;
(4) preparation of carbon aerogel: and (4) carbonizing the cellulose aerogel obtained in the step (3) at high temperature of 1200 ℃ in a nitrogen atmosphere, and naturally cooling to room temperature to obtain the carbon aerogel.
TABLE 1 examples 1-36 and comparative examples 1-2 formulations
TABLE 2 Density, conductivity and electromagnetic shielding effectiveness of examples 1-36 and comparative examples 1-2
The cellulose may be, but is not limited to, cellulose cotton linters. In the step (2), the mass ratio of lithium hydroxide, urea and water is (5-10): (10-20): (70-85). In the step (2), the temperature of the low-temperature mixed solvent of lithium hydroxide, urea and water is preferably-20.0-0 ℃, and the cellulose can be effectively dissolved in the temperature range. In the step (3), the freezing is slow freezing or quick freezing, for example, slow freezing such as a refrigerator can be adopted, and quick freezing such as liquid nitrogen can also be adopted. In the step (3), the gelation temperature is preferably 20 to 80 ℃, and the cellulose solution can be sufficiently gelled in the temperature range. In the step (3), the mass fraction of the tertiary butanol aqueous solution can be selected within the range of 0-100 wt%.
In the step (4), the carbonization temperature is preferably 500-2500 ℃, so that the sample can be fully graphitized in the temperature range, and the stability of the morphological structure of the sample is maintained. The protective gas may be one or more of helium, neon, argon or nitrogen.
And (3) appearance observation: in order to evaluate the feasibility of the preparation of the holocellulose-based carbon aerogel with high electromagnetic shielding performance and the evolution law of the three-dimensional porous microstructure of the material, a field emission scanning electron microscope (model insert-F, FEI) was used to observe the microstructure of the brittle fracture surface of the sample. As shown in FIG. 1a, the cellulose carbon aerogel prepared by the method of dissolution regeneration-co-solvent treatment-slow freezing-drying in the example has a three-dimensional sheet-like open-cell network structure with stable structure, high integrity and high continuity. After high temperature carbonization at 1200 ℃, the pore diameter is obviously reduced, the pore wall is thinned, but the continuous sheet layered highly porous structure of the sample is well maintained (fig. 1 b). Therefore, the method is developed to be low in density (0.068g cm) through dissolution regeneration, cosolvent treatment, freeze drying and high-temperature carbonization-3See table 2), a simple, efficient method for highly continuous open-cell lamellar network structure holocellulose-based carbon aerogels. Wherein, the cosolvent treatment and the freezing method effectively regulate and control the microscopic morphology of the material. As shown in fig. 2, the cellulose carbon aerogel treated with water co-solvent without t-butanol exhibited a large pore size, non-uniform size porous sheet layered network structure, and this structural integrity was poor and the process molding difficulty was large. This is mainly due to the fact that during the slow freezing process, the ice crystals of the aqueous phase in the cellulose hydrogel are large in size, and the cellulose phase is repelled and enriched to form a structure with a thick lamellar layer and a large pore size network (density of 0.097g cm)-3See table 2). The cosolvent treatment can induce the water phase to form acicular crystals in the freezing process, so that the size of the ice crystals is effectively regulated and controlled, the size of the ice crystals is matched with the three-dimensional network structure of the cellulose phase, and the integrity of the aerogel structure is maintained to the maximum extent. In addition, the method for controlling the cooling rate can also effectively regulate and control the micro-morphology of the carbon aerogel sample. As shown in FIG. 3, comparative example 2 exhibited a continuous open-cell fibrous network structure (density of 0.082g cm) having a small pore size and a relatively uniform size distribution-3See table 2). The rapid freezing method of liquid nitrogen cooling is adopted, so that the cellulose hydrogel has more water phase nucleation sites and limited crystal growth rate, thereby obtaining crystal with smaller size, and the cellulose phase can only be aggregated into fiber cluster-shaped knots in limited timeAnd (5) forming. The results show that the method of 'dissolving regeneration-cosolvent treatment-freeze drying-high temperature carbonization' can effectively regulate and control the micro-morphology of the cellulose-based carbon aerogel, and lays a foundation for researching the influence of the pore structure (diameter, framework and the like) on the electromagnetic shielding effect of the carbon aerogel material.
Electrical and electromagnetic shielding properties: in order to examine the electrical and electromagnetic shielding properties of the cellulose-based carbon aerogel electromagnetic shielding material, electrical and electromagnetic shielding property tests were performed on examples and comparative examples using RTS-8 type four probes (four probe technologies, ltd, guangzhou, china) and Agilent vector network analyzer, N5274A type Agilent, usa, respectively, and the results are shown in fig. 4 and 5 and table 2. When the mass fraction of the cellulose in the cellulose solution is only 2.0 wt%, the electrical property of the sample in the example reaches 47.3S/m, so that oxygen-containing functional groups on the surfaces of cellulose molecules can be removed in a high-temperature carbonization process, carbon chain skeletons of the cellulose molecules are exposed, and the regularity of molecular chains is improved; and at high temperature, the molecular chain of the cellulose is excessive from a six-carbon glucosyl structure to a four-carbon intermediate state, and finally an aromatic ring-like graphitized structure is formed. Such a structure will facilitate the migration of free electrons inside the molecular chain, giving the material excellent electrical conductivity. With the increase of the mass fraction of the cellulose in the cellulose solution, more cellulose molecular chains are gathered together under the extrusion effect of the growth of ice crystals, so that the porous network in the sample is more compact, a more complete conductive network is formed, and more excellent electrical property is represented. When the mass fraction of cellulose in the cellulose solution was 4.0 wt%, the conductivity of the example sample increased to 276.3S/m. While comparative example 1 shows a more dense lamellar packing structure, a more compact conductive network and higher conductivity (310.9S/m) due to excessive growth of ice crystals without co-solvent treatment. Comparative example 2 also exhibited excellent conductivity (416.6S/m) due to the formation of a dense, continuous fibrous network structure upon rapid freezing.
As shown in Table 2, the carbon aerogel has an electromagnetic shielding effectiveness of 32.5dB at a solution concentration of 2.0 wt%, and has satisfied the requirement (20.0dB) of the commercial electromagnetic shielding material. With the increase of the mass fraction of the cellulose in the cellulose solution, the electromagnetic shielding performance of the carbon aerogel sample of the embodiment shows the same change rule as the electrical performance, and the electromagnetic shielding performance of the sample is increased from 32.5dB to 106.3 dB. The excellent electromagnetic shielding effectiveness of the cellulose-based carbon aerogel is attributed to the excellent electrical performance of the material due to high-temperature carbonization, and is attributed to the dense lamellar porous network (fig. 1b) of the sample, which can greatly increase the movement path of the electromagnetic wave after the electromagnetic wave is incident on the sample, thereby increasing the absorption loss and improving the electromagnetic shielding effectiveness. However, the loose macroporous structure of the sample of comparative example 1 is not favorable for the multiple reflection loss of the electromagnetic wave, and the electromagnetic shielding effectiveness is only 15.3 dB. Comparative example 2 also can only obtain 40.6dB of electromagnetic shielding effectiveness because the fibrous skeleton structure inside cannot form effective absorption loss for the electromagnetic wave inside the incident material. By analyzing the shielding mechanism of the material (fig. 5), it was found that the cellulose-based carbon aerogel of the example obtained by slow freezing exhibited an electromagnetic shielding mechanism mainly based on absorption. This is mainly due to the low density, high porosity and unique highly continuous open-celled lamellar network structure of the material. The high porosity of the carbon aerogel can obviously reduce the impedance mismatching phenomenon when electromagnetic waves enter the surface of the material and reduce the reflection loss; the electromagnetic wave in the multiple reflection material with the continuous perforated lamellar network structure obviously increases the absorption loss. In conclusion, the cellulose-based carbon aerogel with high electromagnetic shielding performance has the characteristics of low density, high porosity, good conductivity and the like, is simple in material preparation process, easy to master in process, low in production cost and has great potential for large-scale production.
Claims (8)
1. A preparation method of full biomass-based carbon aerogel with high electromagnetic shielding efficiency comprises the following raw materials and reagents:
raw materials: cellulose;
reagent: lithium hydroxide, urea, tert-butanol and water;
the preparation method comprises the following steps:
(1) drying raw materials: fully drying the cellulose;
(2) preparation of cellulose solution: adding the cellulose dried in the step (1) into a mixed solvent of lithium hydroxide, urea and water at room temperature, and stirring until a stable and transparent cellulose solution is obtained;
(3) preparation of cellulose aerogel: gelling the cellulose solution obtained in the step (2) at room temperature to form a cellulose hydrogel; then soaking the cellulose hydrogel in water, and washing to be neutral to remove lithium hydroxide and urea, thereby forming a neutral cellulose hydrogel; soaking the neutral cellulose hydrogel in an aqueous solution of tert-butyl alcohol, freezing to obtain a gel-state sample low-temperature frozen solid phase, sufficiently sublimating and drying, and recovering to room temperature to obtain cellulose aerogel;
(4) preparation of carbon aerogel: carbonizing the cellulose aerogel obtained in the step (3) at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature to obtain carbon aerogel;
in the step (3), the freezing is slow freezing, and the mass fraction of the tertiary butanol in the tertiary butanol aqueous solution is more than 0 wt% and less than or equal to 100 wt%.
2. The preparation method according to claim 1, wherein in the step (2), the mass ratio of the lithium hydroxide to the urea to the water is (5-10): (10-20): (70-85).
3. The method according to claim 1, wherein in the step (2), the temperature of the mixed solvent of lithium hydroxide, urea and water is-20.0 to 0 ℃.
4. The method according to claim 1, wherein in the step (2), the mass fraction of the cellulose in the cellulose solution is 0.1 to 10 wt%.
5. The method according to claim 1, wherein the gelation temperature for gelling the cellulose solution to form the cellulose hydrogel in the step (3) is 80 ℃ or less.
6. The method according to claim 5, wherein the gelation temperature is 20 to 80 ℃.
7. The method according to claim 1, wherein in the step (4), the protective gas is one or more of helium, neon, argon or nitrogen.
8. The method according to claim 1, wherein in the step (4), the carbonization temperature is 500 to 2500 ℃.
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