阅读说明：本技术 一种超疏水、高吸收电磁屏蔽效能纤维素基复合碳气凝胶的制备方法 (Preparation method of super-hydrophobic and high-absorption electromagnetic shielding cellulose-based composite carbon aerogel ) 是由 黄华东 周子涵 李忠明 雷军 于 2019-11-01 设计创作，主要内容包括：本发明公开了一种超疏水、高吸收电磁屏蔽效能纤维素基复合碳气凝胶的制备方法,所需原料如下：纤维素、碳纳米管；经如下的步骤：(1)原料干燥；(2)碳纳米管/纤维素混合溶液的制备；(3)碳纳米管/纤维素复合气凝胶的制备；(4)复合碳气凝胶的制备。本发明以纤维素为基体,引入碳纳米管为异相导电网络,提供极化损耗；通过溶解再生、共溶剂处理、冷冻干燥、高温碳化以及氢氧化钾活化处理的方法构建了具有多级多层次开孔片层状网络结构的复合碳气凝胶,实现了同时具有高电磁屏蔽效能(109.3 dB)和高吸收性能(A=0.81)超疏水(160.1°)电磁屏蔽材料的制备。且本发明基体来源广泛、绿色环保,溶剂体系无毒、价廉,材料制备过程简单,工艺易于掌握,生产成本低,有大规模生产的巨大潜力。(The invention discloses a preparation method of a cellulose-based composite carbon aerogel with super-hydrophobic and high-absorption electromagnetic shielding effectiveness, which comprises the following raw materials: cellulose, carbon nanotubes; comprises the following steps: (1) drying the raw materials; (2) preparing a carbon nano tube/cellulose mixed solution; (3) preparing carbon nano tube/cellulose composite aerogel; (4) and (3) preparing the composite carbon aerogel. The invention takes cellulose as a matrix, introduces carbon nanotubes as a heterogeneous conductive network, and provides polarization loss; the composite carbon aerogel with a multi-level and multi-layer open pore sheet layered network structure is constructed by the methods of dissolution regeneration, cosolvent treatment, freeze drying, high-temperature carbonization and potassium hydroxide activation treatment, and the preparation of the super-hydrophobic (160.1 ℃) electromagnetic shielding material with high electromagnetic shielding effectiveness (109.3 dB) and high absorption performance (A = 0.81) is realized. The invention has wide substrate source, environmental protection, nontoxic solvent system, low price, simple material preparation process, easy mastering of process, low production cost and huge potential of large-scale production.)

1. The composite carbon aerogel is characterized in that the density is 0.009-0.068 g cm^-3The electromagnetic shielding effectiveness is 20.8-109.3dB, the absorption coefficient is 0.74-0.83, and the contact angle is 128-160 deg.

2. A preparation method of a cellulose-based composite carbon aerogel with super-hydrophobic and high-absorption electromagnetic shielding effectiveness is characterized by comprising the following steps:

step 1, dissolving carbon nano tubes in water solution containing a dispersing agent, adding lithium hydroxide and urea after ultrasonic dispersion, and freezing at low temperature; then adding cellulose, and stirring until a stable carbon nano tube/cellulose mixed solution is obtained;

step 2, gelatinizing the mixed solution obtained in the step 1 to generate composite hydrogel, then soaking the composite hydrogel in water, and washing to be neutral to remove lithium hydroxide and urea to form neutral composite hydrogel; soaking the neutral composite 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/carbon nanotube composite aerogel;

step 3, pre-carbonizing the composite aerogel obtained in the step 2 at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature to obtain carbon aerogel; fully soaking the carbon aerogel in an ethanol solution of potassium hydroxide, and drying in an oven; carbonizing at high temperature under protective gas or vacuum atmosphere, cooling to room temperature, soaking the obtained product in ethanol, and drying in an oven to obtain composite carbon aerogel; in one embodiment, the cellulose should be substantially dry prior to use.

3. The method for preparing the superhydrophobic and high-absorption electromagnetic shielding effectiveness cellulose-based composite carbon aerogel according to claim 2, wherein in step 1, the concentration of the carbon nanotubes in the aqueous solution containing the dispersing agent is 0.01 ~ 10 mg/ml, preferably 0.2 ~ 5 mg/ml, the mass fraction of the cellulose in the carbon nanotube/cellulose mixed solution is 0.1 ~ 10 wt%, in step 1, the mass ratio of the dispersing agent to the carbon nanotubes is 0.5 ~ 5, and the dispersing agent is preferably a surfactant such as polyvinylpyrrolidone, cetyl trimethyl ammonium bromide, sodium dodecyl sulfonate and the like.

4. The method for preparing the cellulose-based composite carbon aerogel with super-hydrophobic and high electromagnetic shielding effectiveness according to claim 2, wherein in step 1, the mass ratio of the lithium hydroxide, the urea and the water is (5 ~ 10): (10 ~ 20): (70 ~ 85).

5. The method for preparing the superhydrophobic cellulose-based composite carbon aerogel with high electromagnetic shielding effectiveness according to claim 2, wherein in step 1, the low-temperature freezing is performed at a temperature of-20.0 ~ 0 ℃.

6. The method for preparing the cellulose-based composite carbon aerogel with super-hydrophobic and high electromagnetic shielding effectiveness according to claim 2, wherein in step 2, the gelation temperature for gelling the cellulose solution to form the cellulose hydrogel is less than or equal to 80 ℃, preferably 20 ~ 80 ℃.

7. The method for preparing the superhydrophobic cellulose-based composite carbon aerogel with high electromagnetic shielding effectiveness according to claim 2, wherein in step 2, the mass fraction of the tert-butyl alcohol in the aqueous solution of tert-butyl alcohol is 0 ~ 100 wt%.

8. The method of claim 2, wherein the protective gas is one or more selected from helium, neon, argon, and nitrogen in step 3, the ethanol solution of potassium hydroxide is 1 ~ 50 wt% in step 3, the pre-carbonization temperature is 300 ~ 800 ℃ and the high temperature carbonization temperature is 500 ~ 2500 ℃ in step 3.

9. Use of carbon nanotubes for the preparation of carbon aerogels.

10. Use of lithium hydroxide for the preparation of carbon aerogels.

Technical Field

The invention relates to the technical field of preparation of biomass-based composite carbon aerogel, in particular to a preparation method of cellulose-based composite carbon aerogel with super-hydrophobic and high-absorption electromagnetic shielding effects.

Background

With the rapid development of the communication industry, the communication frequency band is increasing, and various electronic devices with high transmission speed and low delay are gradually popularized. Compared with low-frequency signal transmission, a large amount of high-frequency transmission causes more serious problems of electromagnetic pollution, electromagnetic interference, disclosure and the like, influences the normal operation of precision electronic equipment, and causes different degrees of harm to human organs, tissues and systems (d. Chung et al).Carbon, 2001, 39, 279.). Therefore, it is of great importance to develop an electromagnetic shielding material that can efficiently convert electromagnetic energy into heat energy and inhibit the transmission of harmful electromagnetic waves.

In recent years, organic aerogel carbonized at high temperature or carbon aerogel prepared by self-assembly of carbon nanomaterials (such as carbon nanotubes, graphene and the like) is considered to be a highly efficient electromagnetic shielding material with great potential due to its unique three-dimensional porous structure, extremely low density, high electrical conductivity, good chemical stability and large specific surface area. Such as Liao et al (w. Liao, ethanol.Carbon2017, 115, 629) by mixing cellulose nanofibers with a larger length-diameter ratio with sheet graphene oxide, and carbonizing at 1000 ℃ in a hydrogen/argon mixed atmosphere to obtain the graphene oxide with excellent elasticity and the density as low as 2.83 mg cm^-3The electromagnetic shielding performance reaches 47.8 dB. Similar procedure was used, Lu et al (X. Lu, et al.ACS Applied Materials & Interfaces2018, 10, 8205.) by using good hydrogen bond interaction between lignin and graphene oxide, carbonizing at 900 ℃ to obtain a conductive path formed by reduced graphene oxide, and constructing a conductive path with a density of 8.0 mg cm^-3And the electromagnetic shielding effectiveness is reduced graphene oxide/lignin derived carbon composite aerogel of 49.2 dB. Although, the high-temperature carbonization method can endow the material with better electromagnetic shielding performance and meet the requirements of partThe requirements of application scenes, however, due to the low graphitization degree and the low total shielding effectiveness, the application of the composite material in certain fields requiring high shielding performance, such as military, high integrated circuits and the like, is limited.

Ultra-high temperature carbonization and chemical vapor deposition are considered as effective means for producing high performance carbon materials. The ultrahigh-temperature carbonization method can repair the defect part in the carbon material to a great extent and induce the defect part to be converted into graphite carbon, so that the high-performance carbon material with few defects and high graphitization degree is obtained. Such as Yu, etc. (Z. Yu, et al.Carbon2018, 30, 95) discovered that the carbon aerogel material with the conductivity as high as 1000S/m and the electromagnetic shielding performance as high as 83.0 dB can be obtained by graphitizing the graphene oxide/polyimide composite aerogel at 2800 ℃, and is attributed to good interface interaction and ultrahigh-temperature thermal reduction. Gao, et al (C. Gao, et al.Carbon2018, 135, 44.) preparation of a density of 0.41 g cm using solution casting, chemical reduction, ultra high temperature (2800 deg.C.) thermal expansion^-3And the electromagnetic shielding performance is 70-105 dB of graphene carbon aerogel. Compared with the ultrahigh-temperature thermal reduction method, the chemical vapor deposition method consumes less energy and is widely applied to the preparation of high-quality carbon materials. Such as Yu, et al (J. Yu, et al.Advanced Materials2018, 1705380) growing high-quality graphene on polyacrylonitrile fibers in an ammonia atmosphere by using a chemical vapor deposition method, wherein the obtained porous film with a three-dimensional structure shows a thickness of 1.2 multiplied by 10 when the thickness is only 26.3 mu m⁵Electrical performance of S/m and electromagnetic shielding performance of 56.0 dB. Although the above carbon aerogels all exhibit excellent electromagnetic shielding effectiveness, the following problems still remain: (1) the ultrahigh-temperature carbonization method has complex process and huge energy consumption; (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 high shielding efficiency is highly dependent on the high electrical performance, and the high electrical performance can greatly reduce the absorption performance due to the impedance mismatching phenomenon, thereby generating a large amount of secondary pollution; therefore, the development of the high-absorption electromagnetic shielding effectiveness carbon aerogel with green and environment-friendly source, controllable structure and easily-mastered process is very important in the field of electromagnetic shielding.

Disclosure of Invention

The invention takes the environment-friendly cellulose with wide sources as a matrix, introduces the carbon nano tube as a heterogeneous conductive network and provides polarization loss; the method of dissolution regeneration, cosolvent treatment, freeze drying, high-temperature carbonization and potassium hydroxide activation treatment endows the material with a unique multi-stage multi-level perforated lamellar network structure, so that the structural absorption is further improved, and the super-hydrophobic shielding material which is ultra-light and has excellent high-absorption electromagnetic shielding effect is obtained. 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 superhydrophobic and high-absorption electromagnetic shielding performance three-dimensional porous carbon aerogel by using cellulose as a matrix, introducing carbon nanotubes as a heterogeneous conductive network and constructing a multilevel multi-level porous structure by using potassium hydroxide activation is not reported.

In a first aspect of the present invention, there is provided:

a composite carbon aerogel with density of 0.009-0.068 g cm^-3The electromagnetic shielding effectiveness is 20.8-109.3dB, the absorption coefficient is 0.74-0.83, and the contact angle is 128-160 deg.

In a second aspect of the present invention, there is provided:

a preparation method of a cellulose-based composite carbon aerogel with super-hydrophobic and high-absorption electromagnetic shielding effectiveness comprises the following steps:

step 1, dissolving carbon nano tubes in water solution containing a dispersing agent, adding lithium hydroxide and urea after ultrasonic dispersion, and freezing at low temperature; then adding cellulose, and stirring until a stable carbon nano tube/cellulose mixed solution is obtained;

step 2, gelatinizing the mixed solution obtained in the step 1 to generate composite hydrogel, then soaking the composite hydrogel in water, and washing to be neutral to remove lithium hydroxide and urea to form neutral composite hydrogel; soaking the neutral composite 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/carbon nanotube composite aerogel;

step 3, pre-carbonizing the composite aerogel obtained in the step 2 at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature to obtain carbon aerogel; fully soaking the carbon aerogel in an ethanol solution of potassium hydroxide, and drying in an oven; and carbonizing at high temperature under protective gas or vacuum atmosphere, cooling to room temperature, fully soaking the obtained product in ethanol, and drying in an oven to obtain the composite carbon aerogel.

In one embodiment, the cellulose should be substantially dry prior to use.

In one embodiment, in step 1, the concentration of the carbon nanotubes in the aqueous solution containing the dispersant is 0.01 ~ 10 mg/ml, preferably 0.2 ~ 5 mg/ml, and the mass fraction of the cellulose in the carbon nanotube/cellulose mixed solution is 0.1 ~ 10 wt%.

In one embodiment, in step 1, the mass ratio of the dispersing agent to the carbon nanotubes is 0.5 ~ 5, and the dispersing agent is preferably a surfactant such as polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecyl sulfate, and the like.

In one embodiment, the mass ratio of the lithium hydroxide, the urea and the water in the step 1 is (5 ~ 10): (10 ~ 20): (70 ~ 85).

In one embodiment, in step 1, cryo-freezing refers to a temperature of-20.0 ~ 0 ℃.

In one embodiment, the gelation temperature for the gelation of the cellulose solution to form the cellulose hydrogel in step 2 is 80 ℃ or less, preferably 20 ~ 80 ℃.

In one embodiment, in step 2, the mass fraction of t-butanol in said aqueous solution of t-butanol is 0 ~ 100 wt%.

In one embodiment, in step 3, the protective gas is one or more of helium, neon, argon or nitrogen.

In one embodiment, the ethanol solution of potassium hydroxide in step 3 has a mass fraction of 1 ~ 50 wt%.

In one embodiment, in step 3, the pre-carbonization temperature is 300 ~ 800 ℃ and the high-temperature carbonization temperature is 500 ~ 2500 ℃.

In a third aspect of the present invention, there is provided:

use of carbon nanotubes for the preparation of carbon aerogels.

In one embodiment, the carbon nanotubes are used to reduce the density of, improve the electromagnetic shielding effectiveness of, increase the electromagnetic absorption coefficient of, increase the conductivity of, or increase the contact angle of a carbon aerogel.

In a fourth aspect of the present invention, there is provided:

use of lithium hydroxide for the preparation of carbon aerogels.

In one embodiment, the carbon nanotubes are used to reduce the density of the carbon aerogel, increase the carbon aerogel electromagnetic shielding effectiveness, increase the aerogel conductivity, increase the carbon aerogel electromagnetic absorption coefficient, or increase the contact angle of the carbon aerogel.

Advantageous effects

The method takes cellulose as a matrix, introduces carbon nano tubes as a heterogeneous conductive network, and prepares the three-dimensional flaky network carbon aerogel with a multilevel and multilayer structure by the methods of dissolution regeneration, cosolvent treatment, freeze drying, high-temperature carbonization and potassium hydroxide activation. The prepared carbon aerogel has low density (0.041 g cm)^-3) High porosity (98.0%) and good conductivity (293.7S/m), electromagnetic shielding effectiveness as high as 109.3dB, and absorption coefficient as high as 0.83; water contact angles as high as 160.1 ° also reveal its potential application in superhydrophobic materials. In addition, the advantages of the invention are also shown in the following aspects:

(1) the invention adopts the carbon nano tube to construct the heterogeneous conductive network, and introduces the polarization loss by utilizing the conductivity difference between the heterogeneous conductive network and the cellulose derived carbon; the multilevel and multilayer porous skeleton network realized by the potassium hydroxide activation treatment can greatly increase the propagation direction of electromagnetic waves in the material and prolong the propagation path. The polarization loss and the structural absorption loss introduced by the invention enable the material to show the electromagnetic shielding performance mainly based on absorption, and lay a foundation for the preparation of the functional carbon aerogel.

(2) The surface energy of the cellulose material is greatly reduced by a high-temperature carbonization method, and a multistage multi-layer pore structure which is continuously distributed from micron level to nanometer level is constructed by introducing a carbon nano tube with a large length-diameter ratio and chemically activating, so that the composite carbon aerogel shows excellent super-hydrophobic performance.

(3) The invention takes cellulose as a matrix, and the source of the cellulose is wide and environment-friendly; the carbon nano tube is used as a filler, so that the carbon nano tube has excellent electrical property and lower cost; the alkaline urea solvent system is non-toxic, environment-friendly and low in cost; the preparation process of the material is easy to master and has great potential for large-scale production.

Drawings

FIG. 1 is a scanning electron micrograph (a) and a transmission electron micrograph (b) of the microstructure of the example.

Fig. 2 is a scanning electron microscope image of the microstructure of comparative example 1.

Fig. 3 is a scanning electron microscope image of the microstructure of comparative example 2.

FIG. 4 is an electrical property diagram of comparative examples 1 and 2 and examples (mass fraction of cellulose in cellulose solution 3.0 wt%, carbon nanotube concentration 2.0 mg/ml, ethanol solution of potassium hydroxide concentration 3.0 wt%).

FIG. 5 is a graph showing electromagnetic shielding performance and absorption, reflection and transmission coefficients of examples (mass fraction of cellulose in cellulose solution: 3.0 wt%, carbon nanotube concentration: 2.0 mg/ml) (a, b) and comparative examples 1 (c, d), 2 (e, f).

FIG. 6 is a graph showing the hydrophobic properties of comparative examples 1 and 2 and examples (mass fraction of cellulose in cellulose solution: 3.0 wt%, carbon nanotube concentration: 2.0 mg/ml, and ethanol solution of potassium hydroxide: 3.0 wt%).

Detailed Description

The invention discloses a preparation method of a cellulose-based composite carbon aerogel with super-hydrophobic and high-absorption electromagnetic shielding effectiveness, which comprises the following raw materials: cellulose, carbon nanotubes; comprises the following steps: (1) drying the raw materials; (2) preparing a carbon nano tube/cellulose mixed solution; (3) preparing carbon nano tube/cellulose composite aerogel; (4) and (3) preparing the composite carbon aerogel. The invention takes cellulose as a matrix, introduces carbon nanotubes as a heterogeneous conductive network, and provides polarization loss; the composite carbon aerogel with a multi-level and multi-layer open pore sheet layered network structure is constructed by the methods of dissolution regeneration, cosolvent treatment, freeze drying, high-temperature carbonization and potassium hydroxide activation treatment, and the preparation of the super-hydrophobic (160.1 ℃) electromagnetic shielding material with high electromagnetic shielding effectiveness (109.3 dB) and high absorption performance (A = 0.81) is realized. The invention has wide substrate source, environmental protection, nontoxic solvent system, low price, simple material preparation process, easy mastering of process, low production cost and huge potential of large-scale production.

In some typical embodiments, the preparation method of the cellulose-based composite carbon aerogel with super-hydrophobic and high electromagnetic shielding effectiveness comprises the following steps of:

raw materials: cellulose, carbon nanotubes;

reagent: surfactant, lithium hydroxide, urea, potassium hydroxide, tert-butyl alcohol, ethanol and water;

the preparation method comprises the following steps:

(1) drying raw materials: fully drying the cellulose;

(2) preparing a carbon nano tube/cellulose mixed solution: adding carbon nanotube into surfactant dispersion at room temperature, wherein the dispersion can be polyvinylpyrrolidone water solution, ultrasonically dispersing by probe, adding lithium hydroxide and urea, and freezing. In this step, the carbon nanotubes need to be dispersed in a solvent; adding lithium hydroxide and urea to serve as a dissolving system for subsequent cellulose, adding the cellulose dried in the step (1) into the frozen mixed solvent, and stirring until a stable carbon nano tube/cellulose mixed solution is obtained;

the dispersant is polyvinylpyrrolidone, cetyl trimethyl ammonium bromide, sodium dodecyl sulfate, etc. The mass ratio of the dispersing agent to the carbon nano tube is 0.5-5. The mass ratio of the lithium hydroxide, the urea and the water is (5-10): (10-20): (70-85). The temperature of the mixed solvent of lithium hydroxide, urea and water is-20.0-0 ℃. The concentration of the carbon nano tube is 0.01-20 mg/ml. The mass fraction of the cellulose in the cellulose solution is 0.1-10 wt%.

(3) Preparing the carbon nano tube/cellulose composite aerogel: gelatinizing the mixed solution in the step (2) at room temperature to form a composite hydrogel, wherein the solvent system forms the hydrogel in the mold under the conditions; then soaking the composite hydrogel in water, and washing to be neutral to remove lithium hydroxide and urea, thereby forming a neutral composite hydrogel; soaking the neutral composite hydrogel in an aqueous solution of tert-butyl alcohol, wherein the tert-butyl alcohol has higher freezing point and vapor pressure, so that the drying speed can be increased, the surface tension can be lower in the sublimation process, the space network structure in the gel can be better preserved, a gel-state sample is frozen to obtain a low-temperature frozen solid phase, and then the gel-state sample is fully sublimated and dried and is recovered to room temperature to obtain the carbon nanotube/cellulose composite aerogel; the gelation temperature for forming the cellulose hydrogel by the gelation of the cellulose solution is less than or equal to 80 ℃. The gelation temperature is 20-80 ℃. The mass fraction of the tertiary butanol in the tertiary butanol aqueous solution is 0-100 wt%.

(4) Preparing composite carbon aerogel: pre-carbonizing the composite 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; fully soaking the carbon aerogel in an ethanol solution of potassium hydroxide, and drying in an oven; and carbonizing the dried sample at high temperature in a protective gas or vacuum atmosphere, and then cooling to room temperature. And fully soaking the obtained product in ethanol, and drying in an oven to obtain the composite carbon aerogel. The protective gas is one or more of helium, neon, argon or nitrogen. The mass fraction of the ethanol solution of the potassium hydroxide is 0 to 50 wt percent. The pre-carbonization temperature is 300-800 ℃. The carbonization temperature is 500-2500 ℃.

The preparation process mainly comprises four parts of raw material drying, preparation of a carbon nanotube/cellulose mixed solution, preparation of a carbon nanotube/cellulose composite aerogel and preparation of a composite carbon aerogel, and the preparation process is described by taking cellulose with the polymerization degree of 500 and a carbon nanotube with the trademark of NC7000 as examples.