CN112919445A - Lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material and preparation method and application thereof - Google Patents
Lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material and preparation method and application thereof Download PDFInfo
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
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Abstract
The invention discloses a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material and a preparation method and application thereof. According to the invention, carbonized lignin is used as a conductive framework, polarization loss and conductivity loss are improved, graphene oxide is introduced as a conductive filler, and the composite carbon aerogel with volume shrinkage resistance and a directional pore network structure is constructed by ultrasonic cavitation, redox, freeze drying and high-temperature carbonization treatment, so that the preparation of the hydrophobic electromagnetic shielding material with high electromagnetic shielding efficiency, low density and high conductivity is realized. The invention has the advantages of wide raw material source, environmental protection, nontoxic solvent system, low price, simple material preparation process and low production cost. The electromagnetic shielding material with wide frequency and high efficiency obtained by the invention has very wide application in the aspects of military equipment, aerospace, microwave darkroom, electromagnetic information leakage protection, portable mobile equipment and the like.
Description
Technical Field
The invention belongs to the field of electromagnetic shielding materials, and particularly relates to a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material as well as a preparation method and application thereof.
Background
With the development of science and technology, the wide application of various electromagnetic radiation systems such as mobile phones, computers, televisions and the like brings about an increasingly serious electromagnetic pollution problem. Electromagnetic radiation poses a significant challenge to the application and design of various electronic systems, as well as an increasing number of disasters and accidents to people's lives. Electromagnetic radiation refers to the phenomenon of electromagnetic waves emitted or leaked into the air due to the interaction of electric and magnetic fields. In recent years, the use of electromagnetic equipment has increased due to the rapid development of the telecommunications and electronics industries, and electromagnetic wave radiation has become an increasingly serious problem. Shielding electromagnetic waves that are conducted or radiated to sensitive areas by shielding materials is called electromagnetic interference shielding, thereby reducing or even completely eliminating the harm of electromagnetic radiation to human bodies and other electronic devices. Electromagnetic shielding materials have a wide range of applications including commercial and scientific electronics, antenna systems, space exploration and medical devices. Electromagnetic shielding materials also have a wide range of military applications, such as stealth, where Radar Absorbing Materials (RAMs) (Micheli D, Vricella a, palatore R, et al. carbon,2014: 756-.
The traditional electromagnetic shielding material is mainly made of metal materials, and the metal materials are limited in application and high in cost due to the defects of high density, high corrosion tendency, high filling amount of ferrite materials, high mechanical property and the like. The carbon material has many excellent properties, such as large conductivity, high surface area, light weight, environmental friendliness, excellent flexibility, low density, chemical stability and excellent mechanical properties, makes up for the disadvantages, can be applied to the field of electromagnetic interference shielding materials, and gradually becomes a very promising substitute for the traditional metal electromagnetic shielding material. In addition, the rapid development of portable, smart wearable electronic devices has increased the demand for lighter, thinner, more flexible and even foldable high performance shielding Materials (Lin S, Ju S, Shi G, et al. journal of Materials Science,2019,54(9): 7165-. Therefore, the development of light and efficient electromagnetic interference shielding materials is of great significance and is the key research direction in the current application field.
Graphene is of great interest because of its superior electrical conductivity, large specific surface area and ultra-light weight. Particularly, when two-dimensional graphene is connected to form a three-dimensional (3D) network structure with a large internal free space, the porous structure can significantly improve random multiple reflections of electromagnetic waves entering the internal interface of the wall of the closed cell, resulting in greatly enhanced absorption of the electromagnetic waves. Carbon aerogels are porous foam carbon materials prepared by self-assembling conductive carbon materials such as graphene through a template or a non-template, and sometimes some polymers are added into the aerogel materials to enhance the strength of the aerogel. However, in the preparation process of the reduced graphene oxide carbon aerogel, since the gelation of the graphene sheet causes volume shrinkage, it is difficult to control the density, so that the preparation efficiency is reduced, and the cost is increased. In addition, the uniform dispersion of graphene sheets and the formation of an interconnection network are crucial to endow the material with high conductivity and shielding effectiveness, and a single graphene aerogel is very easy to agglomerate in the preparation process, so that the dispersion is not uniform, the shielding performance of a material main body is poor, and the fluctuation is generated.
Lignin is a natural polymer compound which is second to cellulose in total biomass in nature, is an uneven amorphous natural polymer, and is the most abundant renewable aromatic compound source on earth except petroleum. The preparation of the polymer material by using the lignin is one of the ways for the high-value utilization of the abundant renewable resources, and the application of the lignin to the aerogel is rarely reported. The lignin has three basic phenylpropyl structural units, the carbon content is over 55 percent, and the carbonized lignin has a high-conductivity carbon skeleton, can be used as a carbon source of a carbon material, has a three-dimensional network structure, a large number of benzene rings and conjugated structures, has rich active sites, and is very favorable for preparing various functional carbon materials, such as electrode materials of a supercapacitor. The lignin is used as a matrix material, which is beneficial to preparing the carbon material with a firm space structure and a multi-level special pore channel.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention mainly aims to provide a preparation method of a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material.
The carbon aerogel electromagnetic shielding material has wide raw material sources, uses industrial lignin as a supplementary carbon source, and can be prepared with the same quality by adopting a smaller amount of graphene oxide compared with the existing carbon aerogel shielding material. The lignin has a large number of benzene rings and hydrogen bonds, and can have a good synergistic effect with the graphene oxide; in addition, the amphipathy and the macromolecular skeleton of the lignin can well disperse the conductive filler in the solution, so that the volume shrinkage in the preparation process of the reduced graphene oxide carbon aerogel can be resisted, and the internal structure of the material is improved.
The invention also aims to provide the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material prepared by the method.
The invention further aims to provide application of the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material in the field of electromagnetic shielding.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material comprises the following steps:
(1) dissolving graphene oxide and a reducing agent in water, adding a lignin alkali solution, uniformly mixing, and performing ultrasonic cavitation for 3-8 minutes;
(2) carrying out reduction reaction on the solution obtained by ultrasonic cavitation in the step (1) at 70-80 ℃ for 3-4h, cleaning to obtain hydrogel, and freeze-drying the hydrogel after directional freezing to obtain aerogel;
(3) and carbonizing the aerogel in inert gas or nitrogen atmosphere to obtain the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material.
Preferably, the mass ratio of the graphene oxide to the reducing agent in the step (1) is 6-10: 3-15, more preferably 1: 0.5-1.5; the lignin in the lignin alkali solution accounts for 5-30% of the total mass of the graphene oxide, the reducing agent and the lignin; more preferably 10 to 30%.
Preferably, the mass concentration of the lignin in the lignin alkali solution in the step (1) is 10-30 wt%, and the pH value is 11-12; the mass concentration is more preferably 15 to 20%.
Preferably, the graphene oxide and the reducing agent in the step (1) are dissolved in water, and the mass ratio of the graphene oxide to the water is 6-10: 1000.
preferably, the lignin in the lignin alkali solution in the step (1) is at least one of alkali lignin, enzymatic lignin, hydrolyzed lignin and organic solvent lignin.
Preferably, the lignin base solution of step (1) is prepared by the following method: preparing a certain amount of lignin into 10-30 wt% aqueous solution, adjusting pH to 10-12, stirring for 12-48 hr to dissolve lignin, centrifuging, and collecting supernatant to obtain lignin alkali solution.
More preferably, the adjusting agent for adjusting the pH to 10 to 12 is at least one of sodium hydroxide and potassium hydroxide.
More preferably, the rotating speed of the centrifugation is 8000-10000r/min, and the time is 8-15 min.
Preferably, the reducing agent in step (1) is at least one of L-ascorbic acid, hydrazine hydrate and sodium thiosulfate.
Preferably, the ultrasonic cavitation in the step (1) refers to cavitation for 2-3s and 2-4s, and the accumulation time is 3-8 minutes; the power of the ultrasonic cavitation is 200-300W.
Preferably, the ultrasonic cavitation in the step (1) is performed by using an ultrasonic cell crusher.
Preferably, the washing in step (2) is to alternately wash the hydrogel with deionized water and absolute ethyl alcohol to remove unreacted raw materials.
Preferably, the directional freezing in step (2) is directional freezing with liquid nitrogen from the bottom of the hydrogel for 25-45min to form an ice crystal growing upwards. The ice crystal nuclei in the interior of hydrogels frozen directionally using liquid nitrogen form rapidly at the bottom and the high temperature gradient causes unidirectional growth of the ice crystals towards the top of the hydrogel.
Preferably, the temperature of the freeze drying in the step (2) is-60 to-80 ℃, the pressure is 10-20Pa, and the time is 2-3 days.
Preferably, the inert gas in step (3) is at least one of helium, neon and argon.
Preferably, the carbonization temperature in the step (3) is 500-600 ℃, and the time is 1.5-2 h.
Preferably, the carbonization in step (3) is performed in a tube furnace; the procedure of the carbonization is as follows: the temperature is raised to 200 ℃ at the speed of 2 ℃/min, then raised to 600 ℃ at the speed of 5 ℃/min, and then the temperature is kept for 1.5-2 h.
According to the invention, carbonized lignin is used as a conductive framework, polarization loss and conductivity loss are improved, and graphene oxide is introduced as a conductive filler; the composite carbon aerogel with the directional pore canal network structure is prepared by ultrasonic cavitation, oxidation reduction, freeze drying and high-temperature carbonization.
The lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material prepared by the method. The density of the obtained lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material is 5.25-12.35mg/cm3。
The lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material is applied to the field of electromagnetic shielding.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the method, a conductive network is constructed by using carbonized lignin, and polarization loss is introduced by using the conductivity difference between the conductive network and the reduced graphene oxide lamella; the lignin with amphipathy can well disperse the graphene oxide filler, increase the propagation direction of electromagnetic waves in the material to a certain extent, prolong the propagation path, improve the interface polarization effect of the composite material and generate different electromagnetic response properties.
(2) By changing the freezing mode, the aerogel prepared by using the directional freezing-ice template method has an ordered directional pore channel structure (directional ordered vertical pore channels are left in the aerogel after ice crystals growing unidirectionally sublimate), so that multiple reflection and attenuation of electromagnetic waves in the material are increased; meanwhile, due to the weak amphipathy of the lignin and the synergistic effect of the macromolecular skeleton, the volume shrinkage phenomenon of the aerogel in the preparation process can be weakened to a great extent, the preparation efficiency and the raw material utilization rate are improved, and the cost is reduced.
(3) The invention takes the industrial lignin as the conductive framework and the supplementary carbon source of the material, and the source is wide and environment-friendly; the graphene oxide is a conductive filler, so that the reduced graphene oxide has excellent electrical property and lower cost; the solvent system is green and environment-friendly; the preparation process of the material is easy to master.
Drawings
Fig. 1a is a physical diagram of the lignin-based carbon aerogel electromagnetic shielding material prepared in example 1, where it can be observed that the aerogel has a lower density, fig. 1b is a volume comparison graph of example 3 (left) and comparative example 1 (right), and fig. 1c is a volume retention rate (volume ratio of carbon aerogel to volume of solution obtained by ultrasonic cavitation) of carbon aerogels with different lignin contents, it can be known that the increase of the lignin mass fraction can effectively resist the aerogel volume shrinkage.
Fig. 2 is an internal scanning electron microscope image of the lignin-based carbon aerogel prepared by the directional freezing-ice template method in example 1, and an internal honeycomb directional pore structure and a lamellar structure of aerogel cell walls can be observed.
Fig. 3 shows the electrical conductivity of the carbon aerogel electromagnetic shielding materials obtained in examples 1 to 4 and comparative example 1, and it can be observed that the lignin-based carbon aerogel has excellent electrical conductivity.
Fig. 4 is static contact angles of the carbon aerogel electromagnetic shielding materials obtained in examples 1 to 4 and comparative example 1, (a) is comparative example 1, (b) is example 1, (c) is example 2, (d) is example 3, and (e) is example 4, excellent hydrophobic properties of the aerogel can be observed.
Fig. 5a is a graph comparing the shielding effectiveness of examples 1 to 4 with that of comparative example 1 in the X band and the Ku band, and fig. 5b is a graph comparing the shielding effectiveness of Ku band of examples 3 and comparative examples 1 to 3 (D-prefix indicates directional freezing), and it can be observed that the lignin-based carbon aerogel has excellent electromagnetic shielding performance.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.
Those who do not specify specific conditions in the examples of the present invention follow conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents and the like which are not indicated for manufacturers are all conventional products which can be obtained by commercial purchase.
Example 1
Preparing a certain amount of lignin into a 20 wt% aqueous solution, dissolving with sodium hydroxide, adjusting the pH to about 11, and stirring for 24 hours to fully dissolve the lignin; centrifuging the solution with a centrifuge at 10000r/min for 10min, and collecting the supernatant as lignin alkali solution; the solid content of the lignin solution was measured 3 times using a rapid moisture evaporator, and the average value was taken as the mass fraction of lignin in the lignin solution (16.94 wt%). 0.12g of each of graphene oxide and L-ascorbic acid is taken and dissolved in 20mL of deionized water, 0.0745g of lignin alkali solution is added, after uniform mixing, ultrasonic cavitation is carried out by using an ultrasonic cell crusher, the cavitation time is 5 minutes, the power is 200W, and the cavitation interval is 3s and stops for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel on a copper plate, placing the copper plate on liquid nitrogen for directional freezing for 30min (gradually freezing upwards from the bottom of the hydrogel), and then carrying out freeze drying for 3 days by using a freeze dryer at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to carbonize in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2h to obtain the lignin-based carbon aerogel electromagnetic shielding material, namely D-L5RGA (the mass fraction of lignin is 5%).
For the carbon aerogel prepared in this example (5.25 mg/cm)3) The electromagnetic shielding material (thickness 6mm) was subjected to a shielding effect test, which was total in X-bandThe shielding effect is 34.21dB, and the total shielding effect of the Ku wave band is 80.93 dB.
Example 2
Preparing a certain amount of lignin into a 20 wt% aqueous solution, dissolving with sodium hydroxide, adjusting the pH to about 11, and stirring for 24 hours to fully dissolve the lignin; centrifuging the solution with a centrifuge at 10000r/min for 10min, and collecting the supernatant as lignin alkali solution; the solid content of the lignin solution was measured 3 times using a rapid moisture evaporator, and the average value was taken as the mass fraction of lignin in the lignin solution (16.94 wt%). 0.12g of each of graphene oxide and L-ascorbic acid is taken and dissolved in 20mL of deionized water, 0.1574g of lignin alkali solution is added, after uniform mixing, ultrasonic cavitation is carried out by using an ultrasonic cell crusher, the cavitation time is 5 minutes, the power is 200W, and the cavitation interval is 3s and stops for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel on a copper plate, placing the copper plate on liquid nitrogen for directional freezing for 30min (gradually freezing upwards from the bottom of the hydrogel), and then carrying out freeze drying for 3 days by using a freeze dryer at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to carbonize in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2 hours to obtain the lignin-based carbon aerogel electromagnetic shielding material, namely D-L10RGA (the mass fraction of lignin is 10%).
For the carbon aerogel prepared in this example (7.89 mg/cm)3) The electromagnetic shielding material (thickness 6mm) is subjected to a shielding effect test, and the total shielding effect of the electromagnetic shielding material in an X wave band is 39.73dB, and the total shielding effect of a Ku wave band is 80.84 dB.
Example 3
Preparing a certain amount of lignin into a 20 wt% aqueous solution, dissolving with sodium hydroxide, adjusting the pH to about 11, and stirring for 24 hours to fully dissolve the lignin; centrifuging the solution with a centrifuge at 10000r/min for 10min, and collecting the supernatant as lignin alkali solution; the solid content of the lignin solution was measured 3 times using a rapid moisture evaporator, and the average value was taken as the mass fraction of lignin in the lignin solution (16.94 wt%). 0.12g of each of graphene oxide and L-ascorbic acid is taken and dissolved in 20mL of deionized water, 0.3549g of lignin alkali solution is added, after uniform mixing, ultrasonic cavitation is carried out by using an ultrasonic cell crusher, the cavitation time is 5 minutes, the power is 200W, and the cavitation interval is 3s and stops for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel on a copper disc, placing the copper disc on liquid nitrogen, qualitatively freezing for 30min (gradually freezing upwards from the bottom of the hydrogel), and then carrying out freeze drying for 3 days by using a freeze dryer at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to carbonize in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2h to obtain the lignin-based carbon aerogel electromagnetic shielding material, namely D-L20RGA (the mass fraction of lignin is 20%).
For the carbon aerogel prepared in this example (9.74 mg/cm)3) The electromagnetic shielding material (thickness 6mm) is subjected to a shielding effect test, and the total shielding effect of the electromagnetic shielding material in an X wave band is 42.69dB, and the total shielding effect of a Ku wave band is 80.06 dB.
Example 4
Preparing a certain amount of lignin into a 20 wt% aqueous solution, dissolving with sodium hydroxide, adjusting the pH to about 11, and stirring for 24 hours to fully dissolve the lignin; centrifuging the solution with a centrifuge at 10000r/min for 10min, and collecting the supernatant as lignin alkali solution; the solid content of the lignin solution was measured 3 times using a rapid moisture evaporator, and the average value was taken as the mass fraction of lignin in the lignin solution (16.94 wt%). 0.12g of each of graphene oxide and L-ascorbic acid is taken and dissolved in 20mL of deionized water, 0.6072g of lignin alkali solution is added, after uniform mixing, ultrasonic cavitation is carried out by using an ultrasonic cell crusher, the cavitation time is 5 minutes, the power is 200W, and the cavitation interval is 3s and stops for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel on a copper plate, placing the copper plate on liquid nitrogen for directional freezing for 30min (gradually freezing upwards from the bottom of the hydrogel), and then carrying out freeze drying for 3 days by using a freeze dryer at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to carbonize in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2 hours to obtain the lignin-based carbon aerogel electromagnetic shielding material, namely D-L30RGA (the mass fraction of lignin is 30%).
For the carbon aerogel prepared in this example (12.35 mg/cm)3) The electromagnetic shielding material (thickness 6mm) is subjected to a shielding effect test, and the total shielding effect of the electromagnetic shielding material in the X wave band is 52.83dB, and the total shielding effect of the Ku wave band is 77.44 dB.
Comparative example 1
Dissolving 0.12g of each graphene oxide and L-ascorbic acid in 20mL of deionized water, uniformly mixing, and performing ultrasonic cavitation by using an ultrasonic cell crusher for 5 minutes at a power of 200W at a cavitation interval of 3s and stopping for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel on a copper plate, placing the copper plate on liquid nitrogen for directional freezing for 30min (gradually freezing upwards from the bottom of the hydrogel), and then carrying out freeze drying for 3 days by using a freeze dryer at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to be carbonized in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2 hours to obtain the lignin-based carbon aerogel electromagnetic shielding material, which is marked as D-RGA.
For the carbon aerogel prepared in this comparative example (4.22 mg/cm)3) The electromagnetic shielding material (thickness 6mm) is subjected to a shielding effect test, and the total shielding effect of the electromagnetic shielding material in an X wave band is 30.97dB, and the total shielding effect of a Ku wave band is 80.94 dB.
Comparative example 2
Dissolving 0.12g of each graphene oxide and L-ascorbic acid in 20mL of deionized water, uniformly mixing, and performing ultrasonic cavitation by using an ultrasonic cell crusher for 5 minutes at a power of 200W at a cavitation interval of 3s and stopping for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel into a refrigerator for freezing overnight, and then using a freeze dryer for freeze drying for 3 days at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to be carbonized in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2 hours to obtain the lignin-based carbon aerogel electromagnetic shielding material, which is marked as RGA.
For the carbon aerogel prepared in this comparative example (4.31 mg/cm)3) The electromagnetic shielding material (thickness 6mm) was subjected to a shielding effect test, and the total shielding effect in the Ku band was 74.94 dB.
Comparative example 3
Preparing a certain amount of lignin into a 20 wt% aqueous solution, dissolving with sodium hydroxide, adjusting the pH to about 11, and stirring for 24 hours to fully dissolve the lignin; centrifuging the solution with a centrifuge at 10000r/min for 10min, and collecting the supernatant as lignin alkali solution; the solid content of the lignin solution was measured 3 times using a rapid moisture evaporator, and the average value was taken as the mass fraction of lignin in the lignin solution (16.94 wt%). 0.12g of each of graphene oxide and L-ascorbic acid is taken and dissolved in 20mL of deionized water, 0.3549g of lignin alkali solution is added, after uniform mixing, ultrasonic cavitation is carried out by using an ultrasonic cell crusher, the cavitation time is 5 minutes, the power is 200W, and the cavitation interval is 3s and stops for 2 s. And putting the solution subjected to ultrasonic cavitation into a 70 ℃ oven for reaction and reduction of graphene oxide for 3h, taking out, alternately cleaning the hydrogel by using deionized water and absolute ethyl alcohol, removing unreacted raw materials, putting the hydrogel into a refrigerator for freezing overnight, and then using a freeze dryer for freeze drying for 3 days at-60 ℃ and 10Pa to obtain the aerogel. And putting the aerogel into a tubular furnace to carbonize in an inert gas atmosphere, heating to 200 ℃ at the speed of 2 ℃/min, heating to 600 ℃ at the speed of 5 ℃/min, and keeping for 2h to obtain the lignin-based carbon aerogel electromagnetic shielding material, wherein the lignin-based carbon aerogel electromagnetic shielding material is marked as L20RGA (the mass fraction of lignin is 20%).
Comparison of the bookExample prepared carbon aerogel (9.69 mg/cm)3) The electromagnetic shielding material (thickness 6mm) was subjected to a shielding effect test, and the total shielding effect in the Ku band was 68.75 dB.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A preparation method of a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material is characterized by comprising the following steps:
(1) dissolving graphene oxide and a reducing agent in water, adding a lignin alkali solution, uniformly mixing, and performing ultrasonic cavitation for 3-8 minutes;
(2) carrying out reduction reaction on the solution obtained by ultrasonic cavitation in the step (1) at 70-80 ℃ for 3-4h, cleaning to obtain hydrogel, and freeze-drying the hydrogel after directional freezing to obtain aerogel;
(3) and carbonizing the aerogel in inert gas or nitrogen atmosphere to obtain the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material.
2. The preparation method of the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the mass ratio of the graphene oxide to the reducing agent in the step (1) is 6-10: 3-15; the lignin in the lignin alkali solution accounts for 5-30% of the total mass of the graphene oxide, the reducing agent and the lignin.
3. The method for preparing the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the lignin alkali solution in the step (1) has a mass concentration of lignin of 10-30 wt% and a pH of 11-12; the graphene oxide and the reducing agent are dissolved in water, and the mass ratio of the graphene oxide to the water is 6-10: 1000.
4. the method for preparing a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material as claimed in claim 1, wherein the directional freezing in step (2) is performed by directional freezing with liquid nitrogen from the bottom of the hydrogel for 25-45min to form an ice crystal growing upward.
5. The method for preparing the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the ultrasonic cavitation in the step (1) refers to cavitation for 2-3s and 2-4s, and the ultrasonic cavitation is accumulated for 3-8 minutes; the power of the ultrasonic cavitation is 200-300W; the carbonization temperature in the step (3) is 500-600 ℃, and the time is 1.5-2 h.
6. The method for preparing the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the lignin in the lignin alkali solution of step (1) is at least one of alkali lignin, enzymatic lignin, hydrolysis lignin and organic solvent lignin; the reducing agent is at least one of L-ascorbic acid, hydrazine hydrate and sodium thiosulfate; and (3) the inert gas in the step (3) is at least one of helium, neon and argon.
7. The method for preparing a lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the lignin alkali solution in step (1) is prepared by the following steps: preparing a certain amount of lignin into a 10-30 wt% aqueous solution, adjusting the pH to 10-12, stirring for 12-48 hours to fully dissolve the lignin, centrifuging, and taking supernatant, namely the lignin alkali solution;
the rotating speed of the centrifugation is 8000-10000r/min, and the time is 8-15 min; the regulator for regulating the pH value to 10-12 is at least one of sodium hydroxide and potassium hydroxide.
8. The method for preparing the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material according to claim 1, wherein the freeze-drying temperature in the step (2) is-60 to-80 ℃, the pressure is 10 to 20Pa, and the time is 2 to 3 days; the carbonization in the step (3) is carried out in a tube furnace; the procedure of the carbonization is as follows: the temperature is raised to 200 ℃ at the speed of 2 ℃/min, then raised to 600 ℃ at the speed of 5 ℃/min, and then the temperature is kept for 1.5-2 h.
9. A lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material made by the method of any one of claims 1-8.
10. The application of the lignin/reduced graphene oxide carbon aerogel electromagnetic shielding material of claim 9 in the field of electromagnetic shielding.
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| CN113501976A (en) * | 2021-08-11 | 2021-10-15 | 电子科技大学 | Preparation method of electromagnetic shielding self-repairing skin-friendly hydrogel |
| WO2023180971A1 (en) * | 2022-03-25 | 2023-09-28 | Aspen Aerogels, Inc. | Apparatus and method for heating at pyrolytic temperatures using microwave radiation |
| CN117482918A (en) * | 2023-12-29 | 2024-02-02 | 内蒙古农业大学 | Preparation method and application of hydrophobic graphene oxide/polyvinyl alcohol@wood carbon aerogel |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113501976A (en) * | 2021-08-11 | 2021-10-15 | 电子科技大学 | Preparation method of electromagnetic shielding self-repairing skin-friendly hydrogel |
| WO2023180971A1 (en) * | 2022-03-25 | 2023-09-28 | Aspen Aerogels, Inc. | Apparatus and method for heating at pyrolytic temperatures using microwave radiation |
| CN117482918A (en) * | 2023-12-29 | 2024-02-02 | 内蒙古农业大学 | Preparation method and application of hydrophobic graphene oxide/polyvinyl alcohol@wood carbon aerogel |
| CN117482918B (en) * | 2023-12-29 | 2024-03-26 | 内蒙古农业大学 | Preparation method and application of hydrophobic graphene oxide/polyvinyl alcohol@wood carbon aerogel |
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