CN111086979A - Compressible carbon black/wood derived carbon sponge and preparation method thereof - Google Patents
Compressible carbon black/wood derived carbon sponge and preparation method thereof Download PDFInfo
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- 239000002023 wood Substances 0.000 title claims abstract description 171
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 113
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 108
- 239000006229 carbon black Substances 0.000 title claims abstract description 85
- 238000002360 preparation method Methods 0.000 title abstract description 15
- 230000006835 compression Effects 0.000 claims abstract description 40
- 238000007906 compression Methods 0.000 claims abstract description 40
- 239000002245 particle Substances 0.000 claims abstract description 18
- 230000005540 biological transmission Effects 0.000 claims abstract description 10
- 238000006243 chemical reaction Methods 0.000 claims abstract description 9
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 51
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 claims description 30
- 238000001027 hydrothermal synthesis Methods 0.000 claims description 25
- 238000004108 freeze drying Methods 0.000 claims description 23
- 239000011259 mixed solution Substances 0.000 claims description 20
- 239000006185 dispersion Substances 0.000 claims description 19
- 239000007788 liquid Substances 0.000 claims description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 235000010265 sodium sulphite Nutrition 0.000 claims description 15
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 12
- 239000012300 argon atmosphere Substances 0.000 claims description 10
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 10
- 239000008367 deionised water Substances 0.000 claims description 9
- 229910021641 deionized water Inorganic materials 0.000 claims description 9
- 239000002244 precipitate Substances 0.000 claims description 8
- 239000012153 distilled water Substances 0.000 claims description 7
- 229920002678 cellulose Polymers 0.000 claims description 6
- 239000001913 cellulose Substances 0.000 claims description 6
- 229920005610 lignin Polymers 0.000 claims description 6
- 238000002791 soaking Methods 0.000 claims description 5
- 239000000243 solution Substances 0.000 claims description 5
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 4
- 229910017604 nitric acid Inorganic materials 0.000 claims description 4
- 238000010992 reflux Methods 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 238000011084 recovery Methods 0.000 claims description 3
- 238000003756 stirring Methods 0.000 claims description 3
- JVBXVOWTABLYPX-UHFFFAOYSA-L sodium dithionite Chemical compound [Na+].[Na+].[O-]S(=O)S([O-])=O JVBXVOWTABLYPX-UHFFFAOYSA-L 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 24
- 238000011065 in-situ storage Methods 0.000 abstract description 5
- 238000011031 large-scale manufacturing process Methods 0.000 abstract description 4
- 239000002994 raw material Substances 0.000 abstract description 4
- 238000010335 hydrothermal treatment Methods 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 230000005670 electromagnetic radiation Effects 0.000 description 2
- 230000008929 regeneration Effects 0.000 description 2
- 238000011069 regeneration method Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 239000004964 aerogel Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000012876 topography Methods 0.000 description 1
- 238000003911 water pollution Methods 0.000 description 1
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- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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Abstract
The invention discloses a compressible carbon black/wood derived carbon sponge and a preparation method thereof, wherein the carbon black/wood derived carbon sponge is a layered compressible carbon sponge, carbon black particles are arranged between layers and are compressed, gaps between the layers are narrowed, the contact area is increased, and the positions which cannot be contacted between the layers are contacted due to the carbon black particles, so that a conductive path is increased, more conductive networks are formed, the conductivity of the material is greatly improved, and the conversion from wave transmission before being uncompressed to electromagnetic shielding after being compressed is realized. The carbon black/wood derived carbon sponge is an all-carbon-based electromagnetic shielding material, has low density and good compressibility, can realize effective regulation of more than 75% permeation and more than 99% shielding of electromagnetic waves through compression, achieves in-situ regulation and control of electromagnetic shielding performance, realizes effective control of electromagnetic shielding function, and well meets the requirements of novel electromagnetic shielding materials. The preparation process is simple and is convenient for large-scale production; the raw material is natural wood with reproducibility.
Description
Technical Field
The invention relates to the technical field of electromagnetic shielding, in particular to a compressible carbon black/wood derived carbon sponge and a preparation method thereof.
Background
With the progress of society and the overall popularization of electronic devices, the harm caused by electromagnetic radiation is increasingly serious. Electromagnetic pollution is another environmental pollution problem following atmospheric pollution, water pollution, and noise pollution, and thus, electromagnetic shielding materials capable of effectively reducing electromagnetic radiation need to be studied.
The electromagnetic shielding is widely applied in the fields of daily life and military affairs. Most of the traditional electromagnetic shielding materials are metal, conductive high polymers and carbon-based composite materials, are generally directly coated on the surface of an object in a spraying mode, or are prepared into high-conductivity foam and aerogel type electromagnetic shielding materials, and have good and stable shielding performance. Although the traditional electromagnetic shielding material has stable shielding performance, the components and the proportion of the material are determined in the preparation stage, and the change of the conductivity is difficult to be carried out by changing the components and the proportion in the later stage, so that the electromagnetic shielding efficiency cannot be regulated in real time, and the selection (permeation or shielding) of electromagnetic waves is difficult to be achieved by a shielding means, thereby limiting the application of the electromagnetic shielding material in special scenes and failing to meet the application requirements in the fields of aerospace and portable electronic products.
In recent years, the microstructure and the appearance of the compressible electromagnetic shielding material researched by people are porous structures, the content of a conductive medium in a unit volume can only be increased by compressing the compressible electromagnetic shielding material, the improvement effect of the conductivity is not particularly obvious, and the conversion from wave transmission to shielding cannot be realized.
Disclosure of Invention
In view of the above, the present invention provides a compressible carbon black/wood-derived carbon sponge and a preparation method thereof, which are used for realizing the switching adjustment of the electromagnetic shielding function.
Therefore, the invention provides a compressible carbon black/wood-derived carbon sponge, which comprises a plurality of stacked wood-derived carbon layers, wherein two adjacent wood-derived carbon layers are adhered to each other and have gaps, and carbon black particles are added between the two adjacent wood-derived carbon layers;
when the carbon black/wood derived carbon sponge is compressed along the direction perpendicular to each wood derived carbon layer, each wood derived carbon layer is elastically deformed, a gap between two adjacent wood derived carbon layers is narrowed, the contact area of the two adjacent wood derived carbon layers is increased, and the positions, which are not contacted, of the two adjacent wood derived carbon layers are contacted through carbon black particles, so that the electromagnetic shielding function is realized; when the pressure is removed, each layer of wood derived carbon layer returns to the initial state due to elastic recovery, the gap between two adjacent layers of wood derived carbon layers is widened, the contact area between two adjacent layers of wood derived carbon layers is reduced, and the wave-transmitting function is realized; the on-off regulation and control of wave transmission and electromagnetic shielding are realized through compression deformation.
The invention also provides a preparation method of the compressible carbon black/wood-derived carbon sponge, which comprises the following steps:
s1: performing hydrothermal reaction on the natural wood blocks by using a mixed solution of sodium hydroxide and sodium sulfite and a hydrogen peroxide solution in sequence, removing part of lignin and cellulose in the wood blocks, and performing freeze drying treatment on the wood blocks after the hydrothermal reaction to obtain wood sponge;
s2: dropwise adding the acidified conductive carbon black into the wood sponge, and sequentially carrying out freeze drying treatment and heat treatment under an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
In a possible implementation manner, in the preparation method of the compressible carbon black/wood-derived carbon sponge provided by the invention, in step S1, a mixed solution of sodium hydroxide and sodium sulfite and a hydrogen peroxide solution are sequentially used to perform hydrothermal reaction on a natural wood block, remove part of lignin and cellulose in the wood block, and perform freeze drying treatment on the wood block after the hydrothermal reaction to obtain the wood sponge, specifically including the following steps:
s11: dissolving sodium hydroxide and sodium sulfite into deionized water, and stirring for 5-20 min to obtain a mixed solution of the sodium hydroxide and the sodium sulfite;
s12: putting natural wood blocks into a mixed solution of sodium hydroxide and sodium sulfite, transferring the mixed solution into a reaction kettle, and carrying out hydrothermal reaction for 20-30 h at the temperature of 80-120 ℃;
s13: repeatedly soaking the wood blocks subjected to the hydrothermal reaction of the mixed solution by using distilled water, and removing redundant chemical substances on the surfaces of the wood blocks;
s14: immersing the wood blocks repeatedly soaked in distilled water into a hydrogen peroxide solution, and carrying out hydrothermal reaction for 3-6 h at the temperature of 80-120 ℃;
s15: and (3) carrying out freeze drying treatment on the wood blocks subjected to the hydro-thermal reaction of the hydrogen peroxide solution for 24-48 h to obtain the wood sponge.
In a possible implementation manner, in the preparation method of the compressible carbon black/wood-derived carbon sponge provided by the invention, in step S2, the acidified conductive carbon black is dropwise added into the wood sponge, and the freeze-drying treatment and the heat treatment under an argon atmosphere are sequentially performed to obtain the carbon black/wood-derived carbon sponge, which specifically includes the following steps:
s21: dispersing conductive carbon black into a concentrated nitric acid solution, heating the mixture to 80-120 ℃ in an oil bath in a refluxing manner, and preserving the heat for 4-14 h to obtain a first dispersion liquid;
s22: centrifugally collecting precipitates in the first dispersion liquid at a speed of 6000 r/min-10000 r/min, and ultrasonically dispersing the collected precipitates into deionized water again to obtain a second dispersion liquid;
s23: dropwise adding the second dispersion liquid into the wood sponge;
s24: and (3) carrying out freeze drying treatment on the wood sponge dropwise added with the second dispersion liquid for 24-48 h, and carrying out heat treatment at 800-1200 ℃ for 2-6 h in an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
The carbon black/wood derived carbon sponge is a layered compressible carbon sponge, carbon black particles are added between layers, when external force is applied to the carbon black/wood derived carbon sponge to compress, gaps among layers of wood derived carbon layers can be narrowed, the contact area can be increased, and due to the carbon black particles added between the layers, certain two layers which cannot be contacted can be contacted due to the existence of the carbon black particles, so that a conductive path is increased, more conductive networks are formed, the conductivity of the material is greatly increased, and the conversion from wave-transparent before compression to electromagnetic shielding after compression is realized. The carbon black/wood derived carbon sponge provided by the invention is an all-carbon-based electromagnetic shielding material, has low density and good compressibility, the compression degree is as high as 75%, and the effective regulation of the transmission rate of electromagnetic waves of more than 75% (namely, the shielding effectiveness is less than 1.25dB) and the shielding rate of more than 99% (namely, the shielding effectiveness is more than 20dB) can be realized through compression, so that the in-situ regulation and control of electromagnetic shielding performance can be realized, the effective control of the electromagnetic shielding function can be realized, and the requirements of novel electromagnetic shielding materials can be well met. The carbon black/wood derived carbon sponge can be obtained by carrying out hydrothermal treatment and freeze-drying on the natural wood block, and the preparation process is simple and is convenient for large-scale production; the raw materials are natural wood, so that the storage capacity is rich and the regeneration is realized.
Drawings
FIG. 1 is a schematic structural view of a compressible carbon black/wood-derived carbon sponge according to the present invention;
FIG. 2 is one of the flow charts of a method for making a compressible carbon black/wood-derived carbon sponge according to the present invention;
FIG. 3 is a second flow diagram of a method of making a compressible carbon black/wood-derived carbon sponge according to the present invention;
FIG. 4 is a third flow diagram of a method of making a compressible carbon black/wood-derived carbon sponge according to the present invention;
FIG. 5 is a schematic illustration of the preparation of a compressible carbon black/wood-derived carbon sponge according to example 1 of the present invention;
FIG. 6a is a graph of the stress-strain curves of a compressible carbon black/wood-derived carbon sponge under different pressures according to example 1 of the present invention;
FIG. 6b is a stress-strain plot of a compressible carbon black/wood-derived carbon sponge of example 1 of the present invention under 5 cycles of compression;
FIG. 6c is a graph of the conductivity of a compressible carbon black/wood-derived carbon sponge as a function of the degree of compression in example 1 of the present invention;
FIG. 7 is a micro-topography of a compressible carbon black/wood-derived carbon sponge according to example 1 of the present invention before and after compression;
FIG. 8a is a graph of electromagnetic shielding effectiveness at various degrees of compression within the X frequency range when a compressible carbon black/wood-derived carbon sponge of example 1 of the present invention is cut to 22.8mm by 10.0mm dimensions;
FIG. 8b is a graph of electromagnetic shielding effectiveness at various degrees of compression within the Ku frequency range for a compressible carbon black/wood-derived carbon sponge of example 1 of the present invention cut to dimensions 15.7mm by 7.8 mm;
FIG. 8c is a graph showing the average electromagnetic shielding effectiveness of the compressible carbon black/wood-derived carbon sponge of example 1 of the present invention at different degrees of compression in the frequency range of X, Ku;
fig. 9 is a graph showing the electromagnetic shielding effectiveness of the compressible carbon black/wood-derived carbon sponge of example 1 of the present invention under multiple cycles of compression.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only illustrative and are not intended to limit the present invention.
The invention provides a compressible carbon black/wood-derived carbon sponge, which comprises a plurality of stacked wood-derived carbon layers 1, wherein two adjacent wood-derived carbon layers 1 are adhered to each other and have gaps, and carbon black particles 2 are added between the two adjacent wood-derived carbon layers 1;
when the carbon black/wood-derived carbon sponge is compressed along a direction (shown by an arrow in fig. 1) perpendicular to each wood-derived carbon layer 1, each wood-derived carbon layer 1 is elastically deformed, a gap between two adjacent wood-derived carbon layers 1 is narrowed, the contact area between two adjacent wood-derived carbon layers 1 is increased, and the positions, which are not contacted with each other, of the two adjacent wood-derived carbon layers 1 are contacted with each other through the carbon black particles 2, so that an electromagnetic shielding function is realized; when pressure is removed, each layer of the wood derived carbon layer 1 returns to the initial state due to elastic recovery, the gap between two adjacent layers of the wood derived carbon layers 1 is widened, the contact area between two adjacent layers of the wood derived carbon layers 1 is reduced, and the wave-transmitting function is realized; the on-off regulation and control of wave transmission and electromagnetic shielding are realized through compression deformation.
The conductivity is the fundamental factor for determining the electromagnetic shielding performance of a material. The higher the conductivity, the better the electromagnetic shielding performance; the lower the conductivity, the worse the electromagnetic shielding performance. The carbon black/wood derived carbon sponge provided by the invention is a layered compressible carbon sponge, and carbon black particles are added between layers. When external force is applied to the carbon black/wood-derived carbon sponge provided by the invention for compression, gaps among the wood-derived carbon layers are narrowed, the contact area is increased, and because carbon black particles are added between the layers, certain two layers which cannot be contacted are contacted due to the existence of the carbon black particles, so that a conductive path is increased, more conductive networks are formed, the conductivity of the material is greatly increased, and the conversion from wave-transparent before being compressed to electromagnetic shielding after being compressed is realized. The carbon black/wood derived carbon sponge provided by the invention is an all-carbon-based electromagnetic shielding material, has low density and good compressibility, the compression degree is as high as 75%, and the effective regulation of the transmission rate of electromagnetic waves of more than 75% (namely, the shielding effectiveness is less than 1.25dB) and the shielding rate of more than 99% (namely, the shielding effectiveness is more than 20dB) can be realized through compression, so that the in-situ regulation and control of electromagnetic shielding performance can be realized, the effective control of the electromagnetic shielding function can be realized, and the requirements of novel electromagnetic shielding materials can be well met.
Based on the same inventive concept, the invention also provides a preparation method of the compressible carbon black/wood-derived carbon sponge, as shown in fig. 2, which comprises the following steps:
s1: performing hydrothermal reaction on the natural wood blocks by using a mixed solution of sodium hydroxide and sodium sulfite and a hydrogen peroxide solution in sequence, removing part of lignin and cellulose in the wood blocks, and performing freeze drying treatment on the wood blocks after the hydrothermal reaction to obtain wood sponge;
s2: dropwise adding the acidified conductive carbon black into the wood sponge, and sequentially carrying out freeze drying treatment and heat treatment under an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
According to the preparation method of the carbon black/wood derived carbon sponge, the carbon black/wood derived carbon sponge can be obtained by carrying out hydrothermal treatment and freeze-drying on the natural wood block, and the process is simple and is convenient for large-scale production; the raw material of the carbon black/wood derived carbon sponge is natural wood, so that the carbon black/wood derived carbon sponge is abundant in reserves and has reproducibility; the prepared carbon black/wood derived carbon sponge is an all-carbon-based electromagnetic shielding material, has low density and good compressibility, the compression degree is as high as 75%, and the effective regulation of the transmission rate of electromagnetic waves of more than 75% (namely, the shielding effectiveness is less than 1.25dB) and the shielding rate of more than 99% (namely, the shielding effectiveness is more than 20dB) can be realized through compression, so that the in-situ regulation and control of electromagnetic shielding performance can be realized, the effective control of the electromagnetic shielding function can be realized, and the requirements of novel electromagnetic shielding materials can be well met.
In specific implementation, in step S1 of the method for preparing a compressible carbon black/wood-derived carbon sponge according to the present invention, a mixed solution of sodium hydroxide and sodium sulfite and a hydrogen peroxide solution are sequentially used to perform a hydrothermal reaction on a natural wood block, remove a portion of lignin and cellulose in the wood block, and perform a freeze-drying treatment on the wood block after the hydrothermal reaction, so as to obtain the wood sponge, as shown in fig. 3, the method specifically includes the following steps:
s11: dissolving sodium hydroxide and sodium sulfite into deionized water, and stirring for 5-20 min to obtain a mixed solution of the sodium hydroxide and the sodium sulfite;
s12: putting natural wood blocks into a mixed solution of sodium hydroxide and sodium sulfite, transferring the mixed solution into a reaction kettle, and carrying out hydrothermal reaction for 20-30 h at the temperature of 80-120 ℃;
s13: repeatedly soaking the wood blocks subjected to the hydrothermal reaction of the mixed solution by using distilled water, and removing redundant chemical substances on the surfaces of the wood blocks;
s14: immersing the wood blocks repeatedly soaked in distilled water into a hydrogen peroxide solution, and carrying out hydrothermal reaction for 3-6 h at the temperature of 80-120 ℃;
s15: and (3) carrying out freeze drying treatment on the wood blocks subjected to the hydro-thermal reaction of the hydrogen peroxide solution for 24-48 h to obtain the wood sponge.
In specific implementation, when the step S2 in the method for preparing the compressible carbon black/wood-derived carbon sponge provided by the present invention is executed, the acidified conductive carbon black is dropwise added into the wood sponge, and the freeze-drying treatment and the heat treatment under argon atmosphere are sequentially performed to obtain the carbon black/wood-derived carbon sponge, as shown in fig. 4, the method may specifically include the following steps:
s21: dispersing conductive carbon black into a concentrated nitric acid solution, heating the mixture to 80-120 ℃ in an oil bath in a refluxing manner, and preserving the heat for 4-14 h to obtain a first dispersion liquid;
s22: centrifugally collecting precipitates in the first dispersion liquid at a speed of 6000 r/min-10000 r/min, and ultrasonically dispersing the collected precipitates into deionized water again to obtain a second dispersion liquid;
s23: dropwise adding the second dispersion liquid into the wood sponge;
s24: and (3) carrying out freeze drying treatment on the wood sponge dropwise added with the second dispersion liquid for 24-48 h, and carrying out heat treatment at 800-1200 ℃ for 2-6 h in an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
The following is a detailed description of the specific implementation of the method for making the compressible carbon black/wood-derived carbon sponge according to the present invention, as shown in fig. 5.
Example 1:
(1) 6.0g of sodium hydroxide and 3.0g of sodium sulfite were dissolved in deionized water and stirred for 10 min. Putting natural wood blocks with the side length of about 3.0cm into a mixed solution of sodium hydroxide and sodium hydrosulfite, transferring the natural wood blocks into a reaction kettle with the volume of 100ml, and preserving the heat for 24 hours at the temperature of 100 ℃. Repeatedly soaking the wood blocks by using distilled water to remove redundant chemical substances on the surfaces of the wood blocks, soaking the wood blocks into a mixed solution consisting of 30ml of deionized water and 30ml of 30% hydrogen peroxide, and carrying out hydrothermal reaction for 4 hours at the temperature of 100 ℃. And then carrying out freeze drying treatment for 48 hours to obtain the wood sponge.
(2) 1.0g of conductive carbon black was dispersed in 50ml of a concentrated nitric acid solution, heated to 120 ℃ under reflux in an oil bath and kept warm for 12 hours to obtain a first dispersion. And centrifuging at the speed of 10000r/min to collect the precipitate in the first dispersion liquid, and then ultrasonically dispersing the precipitate again into 50ml of deionized water to obtain a second dispersion liquid. Dropwise adding the second dispersion liquid into the wood sponge, and then carrying out freeze drying treatment for 48h, and carrying out heat treatment for 3h at 1000 ℃ in an argon atmosphere to obtain the carbon black/wood-derived carbon sponge.
The carbon black/wood-derived carbon sponge prepared by example 1 has good compressibility and repeatability. As shown in fig. 6a, the strain is stronger and the degree of compression is larger with increasing pressure, and the degree of compression is gradually increased from 0% to 75% (degree of compression (volume before compression-volume after compression)/volume before compression). As shown in fig. 6b, the maximum stress and the maximum strain did not change significantly for 5 compression cycles, and the stress-strain curves substantially coincided. As shown in FIG. 6c, from the compression-conductivity curve, the conductivity increased from 1.285S/m to 91S/m as the degree of compression increased.
The microscopic morphology of the carbon black/wood-derived carbon sponge before and after compression is observed by using SEM, as shown in FIG. 7, the prepared carbon black/wood-derived carbon sponge is loaded with nano-scale carbon black particles, when external force is applied to the carbon black/wood-derived carbon sponge for compression, gaps of about 100 μm between the original layers are reduced or even disappear, and the contact area between the layers is obviously increased.
In order to characterize the electromagnetic shielding effectiveness of the material, the carbon black/wood-derived carbon sponge sample of example 1 was cut into two sizes of 22.8mm × 10.0mm and 15.7mm × 7.8mm, and the electromagnetic shielding effectiveness of the sample with different degrees of compression in the X frequency range (8.2GHz-12.4GHz) was tested on the sample with the size of 22.8mm × 10.0mm by the waveguide method, and the result is shown in fig. 8 a; electromagnetic shielding effectiveness tests of samples of different degrees of compression in the Ku frequency range (11.9GHz-18.0GHz) were performed on samples of 15.7mm × 7.8mm dimensions using the waveguide method, and the results are shown in fig. 8 b. Referring to fig. 8a and 8b, the average shielding effectiveness under different compression degrees can be obtained, as shown in fig. 8c, it can be seen from fig. 8c that the shielding effectiveness in both frequency ranges increases with the increase of the compression degree, and the average shielding effectiveness in both frequency ranges increases from 1.08dB in the uncompressed state to 29.21dB in the state of 75% in the compression degree(s) ((s))The average shielding effectiveness is the average of the sum of the shielding effectiveness values of all test points within the X, Ku test frequency range divided by the number of test points). According to the calculation formula of shielding effectiveness SE-10 log10 (P)T/PI) When the shielding effectiveness is less than 1.25dB, the wave-transparent performance can be more than 75%, and when the shielding effectiveness is more than 20dB, the electromagnetic shielding performance can be more than 99%. The shielding effectiveness measured by multiple compression is shown in fig. 9, and the electromagnetic wave can be effectively switched between the transmission of more than 75% and the shielding of more than 99% by circulating multiple compression, so that the on-off control of the electromagnetic shielding function is realized.
The carbon black/wood derived carbon sponge is a layered compressible carbon sponge, carbon black particles are added between layers, when external force is applied to the carbon black/wood derived carbon sponge to compress, gaps among layers of wood derived carbon layers can be narrowed, the contact area can be increased, and due to the carbon black particles added between the layers, certain two layers which cannot be contacted can be contacted due to the existence of the carbon black particles, so that a conductive path is increased, more conductive networks are formed, the conductivity of the material is greatly increased, and the conversion from wave-transparent before compression to electromagnetic shielding after compression is realized. The carbon black/wood derived carbon sponge provided by the invention is an all-carbon-based electromagnetic shielding material, has low density and good compressibility, the compression degree is as high as 75%, and the effective regulation of the transmission rate of electromagnetic waves of more than 75% (namely, the shielding effectiveness is less than 1.25dB) and the shielding rate of more than 99% (namely, the shielding effectiveness is more than 20dB) can be realized through compression, so that the in-situ regulation and control of electromagnetic shielding performance can be realized, the effective control of the electromagnetic shielding function can be realized, and the requirements of novel electromagnetic shielding materials can be well met. The carbon black/wood derived carbon sponge can be obtained by carrying out hydrothermal treatment and freeze-drying on the natural wood block, and the preparation process is simple and is convenient for large-scale production; the raw materials are natural wood, so that the storage capacity is rich and the regeneration is realized.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (4)
1. A compressible carbon black/wood-derived carbon sponge is characterized by comprising a plurality of stacked wood-derived carbon layers, wherein two adjacent wood-derived carbon layers are adhered to each other and have gaps, and carbon black particles are added between the two adjacent wood-derived carbon layers;
when the carbon black/wood derived carbon sponge is compressed along the direction perpendicular to each wood derived carbon layer, each wood derived carbon layer is elastically deformed, a gap between two adjacent wood derived carbon layers is narrowed, the contact area of the two adjacent wood derived carbon layers is increased, and the positions, which are not contacted, of the two adjacent wood derived carbon layers are contacted through carbon black particles, so that the electromagnetic shielding function is realized; when the pressure is removed, each layer of wood derived carbon layer returns to the initial state due to elastic recovery, the gap between two adjacent layers of wood derived carbon layers is widened, the contact area between two adjacent layers of wood derived carbon layers is reduced, and the wave-transmitting function is realized; the on-off regulation and control of wave transmission and electromagnetic shielding are realized through compression deformation.
2. A method of making the compressible carbon black/wood-derived carbon sponge of claim 1, comprising the steps of:
s1: performing hydrothermal reaction on the natural wood blocks by using a mixed solution of sodium hydroxide and sodium sulfite and a hydrogen peroxide solution in sequence, removing part of lignin and cellulose in the wood blocks, and performing freeze drying treatment on the wood blocks after the hydrothermal reaction to obtain wood sponge;
s2: dropwise adding the acidified conductive carbon black into the wood sponge, and sequentially carrying out freeze drying treatment and heat treatment under an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
3. The method for preparing the compressible carbon black/wood-derived carbon sponge according to claim 2, wherein in step S1, the mixed solution of sodium hydroxide and sodium hydrosulfite and the hydrogen peroxide solution are sequentially utilized to perform hydrothermal reaction on the natural wood block, remove part of lignin and cellulose in the wood block, and perform freeze drying treatment on the wood block after the hydrothermal reaction to obtain the wood sponge, and the method specifically comprises the following steps:
s11: dissolving sodium hydroxide and sodium sulfite into deionized water, and stirring for 5-20 min to obtain a mixed solution of the sodium hydroxide and the sodium sulfite;
s12: putting natural wood blocks into a mixed solution of sodium hydroxide and sodium sulfite, transferring the mixed solution into a reaction kettle, and carrying out hydrothermal reaction for 20-30 h at the temperature of 80-120 ℃;
s13: repeatedly soaking the wood blocks subjected to the hydrothermal reaction of the mixed solution by using distilled water, and removing redundant chemical substances on the surfaces of the wood blocks;
s14: immersing the wood blocks repeatedly soaked in distilled water into a hydrogen peroxide solution, and carrying out hydrothermal reaction for 3-6 h at the temperature of 80-120 ℃;
s15: and (3) carrying out freeze drying treatment on the wood blocks subjected to the hydro-thermal reaction of the hydrogen peroxide solution for 24-48 h to obtain the wood sponge.
4. The method for preparing the compressible carbon black/wood-derived carbon sponge according to claim 2, wherein the step S2 is to drop the acidified conductive carbon black into the wood sponge drop by drop, and to perform the freeze-drying treatment and the heat treatment under argon atmosphere in sequence to obtain the carbon black/wood-derived carbon sponge, and specifically comprises the following steps:
s21: dispersing conductive carbon black into a concentrated nitric acid solution, heating the mixture to 80-120 ℃ in an oil bath in a refluxing manner, and preserving the heat for 4-14 h to obtain a first dispersion liquid;
s22: centrifugally collecting precipitates in the first dispersion liquid at a speed of 6000 r/min-10000 r/min, and ultrasonically dispersing the collected precipitates into deionized water again to obtain a second dispersion liquid;
s23: dropwise adding the second dispersion liquid into the wood sponge;
s24: and (3) carrying out freeze drying treatment on the wood sponge dropwise added with the second dispersion liquid for 24-48 h, and carrying out heat treatment at 800-1200 ℃ for 2-6 h in an argon atmosphere to obtain the carbon black/wood derived carbon sponge.
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