CN113015422B - Cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves, and preparation method and application thereof - Google Patents
Cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves, and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding, and a preparation method and application thereof. Firstly, preparing hydrogel by using soluble cobalt salt, soluble nickel salt, an additive and graphene oxide aqueous dispersion as raw materials through a hydrothermal reaction; after being washed, the obtained hydrogel is soaked in a solution for preventing nano particles from agglomerating, and then a xerogel-shaped precursor is obtained after drying; and finally, calcining under the protection of inert atmosphere to obtain the cobalt-nickel alloy/reduced graphene oxide nanocomposite. The preparation method has reasonable design, simple process, low cost and easy realization; the cobalt-nickel alloy nanoparticles in the obtained composite material have uniform particle size, are uniformly distributed on the surface of graphene, and have good dispersibility; the obtained composite material has excellent electromagnetic shielding performance.
Description
Technical Field
The invention relates to a cobalt-nickel alloy/reduced graphene oxide nano composite material for high-frequency electromagnetic wave shielding, and a preparation method and application thereof, and belongs to the fields of preparation of nano materials and electromagnetic shielding application.
Background
Since nearly two hundred years when faraday has discovered the phenomenon of electromagnetic induction, electromagnetic technology has been widely used in many fields, such as communications, manufacturing, medicine, scientific research, military, etc., and its application range has been expanding. As a new technology and a new resource, the electromagnetic technology not only greatly promotes the innovation and the development of the society, but also brings great convenience to the aspects of work, communication, entertainment and the like of human beings. However, with the wide application of electronic devices and wireless communication devices, the electromagnetic radiation and electromagnetic interference caused thereby make the space electromagnetic environment increasingly complex; in addition, electromagnetic radiation pollution has been juxtaposed to noise pollution, water pollution, and air pollution as a fourth environmental pollution source. On one hand, the operation of communication signals, precision instruments and electronic equipment can be interfered by electromagnetic pollution, so that serious problems such as leakage of electromagnetic signals and the like are caused; on the other hand, if the human body is radiated by excessive electromagnetic waves for a long time, the reproductive system, the immune system and the nervous system are damaged, and the serious threat to the human health is caused. Therefore, research on new electromagnetic shielding materials to overcome electromagnetic radiation and electromagnetic interference is urgent and is receiving wide attention.
In the face of diverse application fields and complex electromagnetic environments, although the metal electromagnetic shielding material has excellent electromagnetic shielding performance, the shielding mechanism is single, mainly takes reflection as the main, and the further application of the metal electromagnetic shielding material is limited by the defects of high metal density, easy corrosion and the like. Therefore, the development of light, corrosion-resistant and efficient electromagnetic shielding materials is urgent, and the search for novel electromagnetic shielding materials has become a research hotspot in all countries of the world.
Graphene, a novel carbon material, has unique two-dimensional structure and excellent physicochemical properties, and this makes graphene-based material have characteristics such as flexibility is good, the quality is light, corrosion resistance is strong. Particularly, the graphene-based material has an ultrathin structure and effective microwave attenuation capability, and has a remarkable position in the field of electromagnetic shielding. Patent document CN110040724A discloses a preparation method of folded graphene; by utilizing the synergistic effect of the ascorbic acid and the hydroiodic acid, the reduced graphene oxide with a good fold structure can be obtained while the graphene oxide is reduced. The aggregation and stacking of the graphene nanosheet layer can be effectively inhibited by the fold structure, so that fluffer graphene powder is obtained, and the electromagnetic wave shielding effect is enhanced. However, the graphene material prepared by the method is limited by the characteristics of single structure, low magnetic permeability and the like, so that the excellent performance requirement of the electromagnetic shielding material cannot be met.
In order to obtain better electromagnetic shielding effectiveness, graphene is compounded with other materials (magnetic nanoparticles, ceramics, metals, polymers and the like), so that the defects of single structure and low magnetic permeability of graphene can be obviously improved. Among the effective electromagnetic shielding materials, magnetic nanoparticles (Fe, Co, Ni, Fe) are loaded3O4Etc.) are becoming increasingly interesting for research. Jianming Wu et al (J.colloid Interface Sci.,2017,506,217-226.) use of carbon fibers (rGO-CF, GCF) coated with reduced graphene oxide and deposited Fe3O4The electromagnetic shielding performance of epoxy resins (EP) is enhanced by the reduced graphene oxide material (magnetic graphene, MG) of nanoparticles. The results showed that good electromagnetic shielding effectiveness was exhibited with only 0.5 wt% GCF and 9 wt% MG (8.2-26.5GHz,>30 dB). However, the synthesis of the composite material has high requirements on equipment, the synthesis steps are complex, and large-scale preparation is not easy. Chinese patent document CN108439376A discloses a preparation method of a magnetic nanoparticle-loaded graphene aerogel composite material, which comprises the steps of taking graphene oxide, polyvinyl alcohol, a reducing agent and metal salt as raw materials, and preparing a three-dimensional porous cross-linked network graphene oxide hydrogel loaded with the metal salt by a hydrothermal method; and (3) carrying out freeze drying and roasting reduction in a protective atmosphere to obtain the magnetic nanoparticle-loaded graphene aerogel composite material in situ. According to the invention, the electromagnetic performance of the composite material can be adjusted by adjusting the ratio of graphene to metal salt, and the prepared graphene aerogel composite material can be used as an electromagnetic wave absorption material; however, the freeze-drying method is used in the invention, the energy consumption is severe, the requirement on equipment is high, the large-scale preparation is not easy to realize, the obtained aerogel composite material nano particles are easy to agglomerate, and the electromagnetic wave absorption performance needs to be improved.
Therefore, there is a need to develop an electromagnetic shielding material with small density, uniform particle size, good dispersibility, excellent electromagnetic shielding effect, low cost, simple synthesis process, and easy realization.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves, and a preparation method and application thereof. The invention adopts a method combining solvent heating, leaching drying and high-temperature thermal reduction; the preparation method has reasonable design, simple process, low cost and easy realization; the cobalt-nickel alloy nanoparticles in the obtained composite material have uniform particle size, are uniformly distributed on the surface of graphene, and have good dispersibility; the obtained composite material has excellent electromagnetic shielding performance.
The technical scheme of the invention is as follows:
a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding, the composite having a micro-morphology of: the cobalt-nickel alloy nanoparticles with uniform particle size are uniformly distributed on the surface of the reduced graphene oxide sheet.
The preparation method of the cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves comprises the following steps:
(1) dissolving soluble cobalt salt, soluble nickel salt and an additive in water to obtain a mixed solution; uniformly mixing the obtained mixed solution with graphene oxide aqueous dispersion, and then carrying out hydrothermal reaction to obtain hydrogel;
(2) washing the hydrogel obtained in the step (1), soaking the hydrogel in a solution for preventing nano particles from agglomerating, and drying to obtain a xerogel-shaped precursor;
(3) and (3) calcining the xerogel-shaped precursor obtained in the step (2) under the protection of inert atmosphere to obtain the cobalt-nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO).
Preferably, in step (1), the soluble cobalt salt is cobalt chloride, cobalt sulfate, cobalt nitrate or cobalt acetate; the soluble nickel salt is nickel chloride, nickel sulfate, nickel nitrate or nickel acetate; the mass ratio of the soluble cobalt salt to the soluble nickel salt is 10: 1-1: 10; preferably, the mass ratio of the soluble cobalt salt to the soluble nickel salt is 1: 3-3: 1.
Preferably, in step (1), the additive is one or a combination of more than two of glucose, fructose, sucrose, citric acid monohydrate, ascorbic acid or soluble starch; the mass of the additive is 1-3 times of that of the soluble cobalt salt.
According to the invention, the concentration of the soluble cobalt salt in the mixed solution in the step (1) is preferably 0.02-0.1 mol/L.
According to the invention, in the step (1), the graphene oxide aqueous dispersion is prepared according to the existing modified Hummers method (refer to the literature, "j.am. chem.soc.,2008,130, 5856-.
According to the invention, in the step (1), the mass concentration of the graphene oxide aqueous dispersion is preferably 1-10 mg mL-1(ii) a The ratio of the D band to the G band of the graphene oxide is 0.6-1.4.
According to the invention, in the step (1), the mass ratio of the mixed solution to the graphene oxide aqueous dispersion is 5: 1-1: 5; preferably, the mass ratio of the mixed solution to the graphene oxide aqueous dispersion is 1:1-1: 3.
According to the invention, in the step (1), the temperature of the hydrothermal reaction is 120-200 ℃, and the reaction time is 5-30 h; preferably, the temperature of the hydrothermal reaction is 160-200 ℃, and the reaction time is 12-18 h.
Preferably, in step (2), the washing method comprises: and washing the water gel for 3-5 times by using distilled water and ethanol respectively.
Preferably, in step (2), the solution for preventing the nanoparticles from agglomerating is prepared by dissolving an additive for preventing the nanoparticles from agglomerating in a solvent; the additive is two or three of thiourea, urea or melamine; the solvent is one or the combination of more than two of ethanol, acetone, isopropanol, tetrahydrofuran, deionized water, N-methyl pyrrolidone, glycol or N, N-dimethylformamide; in the solution for preventing the nano particles from agglomerating, the concentration of the additive is 0.1-20 mol/L; preferably, the additive is a combination of urea and melamine, and the mass ratio of the urea to the melamine is 1:1-1: 3; and in the solution for preventing the nano particles from agglomerating, the concentration of the additive is 2-10 mol/L. The solution for preventing the nano-particles from agglomerating is used in an amount capable of immersing the hydrogel.
Preferably, in the step (2), the soaking temperature is 25-60 ℃, and the soaking time is 6-56 hours; preferably, the soaking temperature is 25-40 ℃, and the soaking time is 10-14 h.
According to the invention, in the step (2), the drying is carried out in the air, the drying temperature is 60-100 ℃, and the drying time is 12-48 h.
Preferably, in step (3), the inert atmosphere is nitrogen, argon or helium.
According to the invention, in the step (3), the calcination temperature is 300-1000 ℃, and the calcination time is 1-12 h; preferably, the calcination temperature is 500-700 ℃, and the calcination time is 1-3 h.
The cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves is applied to high-frequency electromagnetic wave shielding materials.
According to the optimization of the invention, the cobalt-nickel alloy/reduced graphene oxide nanocomposite can be directly used as an active substance to be added into a coating to prepare an electromagnetic shielding coating, and the preparation method specifically comprises the following steps:
dispersing the cobalt-nickel alloy/reduced graphene oxide nano composite material into a polymer monomer or a polymer prepolymer, adding a curing agent, and uniformly mixing to obtain an electromagnetic shielding coating;
or dispersing the cobalt-nickel alloy/reduced graphene oxide nano composite material in a polymer melt, and performing melt blending to obtain the electromagnetic shielding coating;
or dispersing the cobalt-nickel alloy/reduced graphene oxide nano composite material in a polymer solution, uniformly mixing, and removing the solvent to obtain the electromagnetic shielding coating.
According to the invention, the polymer is preferably one or the combination of more than two of polyvinyl alcohol, epoxy resin, certain polystyrene, polyethylene, polypropylene, polyimide, certain ethylene propylene rubber, polyurethane, certain polycarbonate, polymethyl methacrylate or polyamide; epoxy resins are preferred.
According to the invention, the prepolymer is commercially available or prepared according to the prior art; the curing agent is a conventional known curing agent; the polymer solution is prepared by dissolving a polymer in a solvent according to the prior art.
According to the invention, the content of the cobalt-nickel alloy/reduced graphene oxide nanocomposite in the electromagnetic shielding coating is preferably 1-20 wt%.
According to the invention, the thickness of the film obtained by coating the electromagnetic shielding coating is 0.1-3 mm.
According to the present invention, the preparation method of the electromagnetic shielding paint is preferably as follows:
and uniformly mixing the solvent, the epoxy resin prepolymer and the cobalt-nickel alloy/reduced graphene oxide nanocomposite, and adding an epoxy resin curing agent to obtain the electromagnetic shielding coating. The types of the solvent and the epoxy resin curing agent can be selected according to the prior art, and the dosage of the solvent, the epoxy resin prepolymer and the epoxy resin curing agent can be selected according to the prior art.
The invention has the following technical characteristics and beneficial effects:
(1) according to the invention, the cobalt and nickel ions can be better bonded with the oxygen-containing functional group of the graphene oxide by adopting the solvothermal reaction under a specific condition; and the particles containing cobalt and nickel are uniformly distributed on the surface of the graphene oxide sheet. The subsequent soaking-drying method of hydrogel replaces the freeze-drying method, so that the defects of high energy consumption and high equipment requirement of the freeze-drying method are overcome, the agglomeration of cobalt-nickel alloy nanoparticles in the subsequent calcining process can be better inhibited, the dispersibility of the nano composite material is improved, and the nano composite material is easy to prepare in a large scale and disperse in a coating.
(2) The thermal reduction of the xerogel-shaped precursor in the preparation method can ensure that nickel and cobalt ions are reduced into cobalt-nickel alloy particles, and the magnetic permeability of the material is increased; and the partially reduced graphene oxide GO can be completely converted into the high-conductivity reduced graphene oxide rGO, so that a cobalt-nickel alloy/reduced graphene oxide NiCo/rGO nano composite material with more fluffiness and lower density can be obtained.
(3) The type and amount of the materials, hydrothermal reaction conditions, soaking conditions, calcining conditions and the like of the invention all affect the performance of the obtained material. The preparation method of the invention is taken as a whole, all steps and conditions act together to ensure that cobalt-nickel alloy nano particles with uniform particle size in the cobalt-nickel alloy/reduced graphene oxide nano composite material obtained by the invention are uniformly distributed on the surface of a reduced graphene oxide sheet, and simultaneously, the composite material has better dispersibility and shows excellent electromagnetic wave shielding performance when being applied to preparation of electromagnetic shielding paint. The prepared electromagnetic shielding coating is used for coating, and under the conditions of low thickness and low active substance consumption, the electromagnetic shielding effectiveness can be maintained above 26dB at a frequency band of 2-18GHz, and particularly the electromagnetic shielding effectiveness at a frequency band of 8-12GHz can be maintained above 41dB overall; this means that: due to the proper addition of the cobalt-nickel alloy/reduced graphene oxide (NiCo/rGO) nano composite material, more than 99.88% of incident electromagnetic waves can be shielded, and the commercial requirement (more than or equal to 20dB) of the electromagnetic shielding material is far greater.
Drawings
Fig. 1 is an XRD pattern of cobalt nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO) prepared in example 1.
Fig. 2 is an SEM image of cobalt nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO) prepared in example 1.
Fig. 3 is a graph showing the electromagnetic shielding effectiveness of the nanocomposites prepared in example 1 and comparative examples 1, 2, 3 as active materials applied to paints.
Detailed Description
The present invention will be further described with reference to the following examples, but is not limited thereto.
Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
Example 1
A preparation method of a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding comprises the following steps:
(1) dissolving 1.5mmol of cobalt chloride, 1.5mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) a modified Hummers method was used to prepare a concentrated aqueous dispersion of graphene oxide GO (see J.Am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 180 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; soaking the mixture in 100mL of 5mol/L melamine and urea solution (the molar ratio of melamine to urea is 1:1, the solvent is a mixed solution of ethanol and acetone, and the volume ratio of ethanol to acetone is 1:1) at 30 ℃ for 12h, and then drying the soaked mixture in air at 80 ℃ for 48h to obtain a black and xerogel-shaped precursor.
(5) And (3) placing the xerogel-shaped precursor prepared in the step (4) into a tubular furnace, and calcining for 2 hours in a nitrogen atmosphere at 600 ℃ to obtain the cobalt-nickel alloy/reduced graphene oxide (CoNi/rGO) nanocomposite.
Fig. 1 is an XRD pattern of the cobalt-nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO) prepared in this example, from which it can be known that all diffraction peaks of the material are located between metal cobalt and metal nickel, confirming the existence of the cobalt-nickel alloy, and combining the diffraction peaks of the reduced graphene oxide, determining the successful preparation of the cobalt-nickel alloy/reduced graphene oxide (CoNi/rGO) nanocomposite.
Fig. 2 is an SEM image of the cobalt-nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO) prepared in this example, which shows that cobalt-nickel alloy particles are uniformly distributed on the graphene nanosheets, and no agglomeration of the particles occurs.
Example 2
A preparation method of a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding comprises the following steps:
(1) dissolving 1.0mmol of cobalt chloride, 1.5mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) a modified Hummers method was used to prepare a concentrated aqueous dispersion of graphene oxide GO (see J.Am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 180 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; soaking the mixture in 100mL of 5mol/L melamine and urea solution (the molar ratio of melamine to urea is 1:1, the solvent is a mixed solution of ethanol and acetone, and the volume ratio of ethanol to acetone is 1:1) at 30 ℃ for 12h, and then drying the soaked mixture in air at 80 ℃ for 48h to obtain a black and xerogel-shaped precursor.
(5) And (3) placing the xerogel-shaped precursor prepared in the step (4) into a tubular furnace, and calcining for 2 hours in a nitrogen atmosphere at 600 ℃ to obtain the cobalt-nickel alloy/reduced graphene oxide (CoNi/rGO) nanocomposite.
Example 3
A preparation method of a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding comprises the following steps:
(1) dissolving 1.5mmol of cobalt chloride, 1.0mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) a modified Hummers method was used to prepare a concentrated aqueous dispersion of graphene oxide GO (see J.Am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 180 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; the precursor is placed in 100mL of 5mol/L melamine and urea (the molar ratio of the melamine to the urea is 1:1, the solvent is a mixed solution of ethanol and acetone, and the volume ratio of the ethanol to the acetone is 1:1), soaked for 12h at 30 ℃, and then dried for 48h at 80 ℃ in the air to obtain a black and xerogel-shaped precursor.
(5) And (3) placing the dry gel-like precursor prepared in the step (4) into a tube furnace, and calcining for 2 hours in a nitrogen atmosphere at 600 ℃ to obtain the cobalt-nickel alloy/reduced graphene oxide (CoNi/rGO) nano composite material.
Comparative example 1
A method of preparing a nanocomposite comprising the steps of:
(1) dissolving 1.5mmol of cobalt chloride, 1.5mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) a modified Hummers method was used to prepare a concentrated aqueous dispersion of graphene oxide GO (see J.Am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 180 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; freezing in liquid nitrogen, and drying in a freeze dryer to obtain precursor.
(5) And (4) placing the precursor prepared in the step (4) into a tubular furnace, and calcining for 2 hours in a nitrogen atmosphere at 600 ℃ to obtain the nano composite material.
Comparative example 2
A method of preparing a nanocomposite comprising the steps of:
(1) dissolving 1.5mmol of cobalt chloride, 1.5mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) preparation of concentrated aqueous dispersions of graphene oxide GO by a modified Hummers method (ref.) "J.am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 100 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; soaking the mixture in 100mL of 5mol/L melamine and urea solution (the molar ratio of melamine to urea is 1:1, the solvent is a mixed solution of ethanol and acetone, and the volume ratio of ethanol to acetone is 1:1) at 30 ℃ for 12h, and then drying the soaked mixture in air at 80 ℃ for 48h to obtain a black and xerogel-shaped precursor.
(5) And (4) placing the xerogel-shaped precursor prepared in the step (4) into a tubular furnace, and calcining for 2 hours at 600 ℃ in a nitrogen atmosphere to obtain the nanocomposite.
Comparative example 3
A method of preparing a nanocomposite comprising the steps of:
(1) dissolving 1.5mmol of cobalt chloride, 1.5mmol of nickel chloride and 0.3g of glucose in 20mL of water, and stirring for 30min to obtain a mixed solution;
(2) a modified Hummers method was used to prepare a concentrated aqueous dispersion of graphene oxide GO (see J.Am.chem.Soc.,2008,130,5856--1A graphene oxide aqueous dispersion;
(3) mixing the mixed solution obtained in the step (1) and the graphene oxide aqueous dispersion obtained in the step (2) according to a mass ratio of 1:2, transferring the mixture into a hydrothermal reaction kettle, and reacting the mixture for 16 hours in an environment at 180 ℃ to obtain hydrogel;
(4) taking out the hydrogel, and washing the hydrogel for 3-5 times by using distilled water and ethanol respectively; soaking the mixture in 100mL of 5mol/L melamine and urea solution (the molar ratio of melamine to urea is 1:1, the solvent is a mixed solution of ethanol and acetone, and the volume ratio of ethanol to acetone is 1:1) at 30 ℃ for 12h, and then drying the soaked mixture in air at 80 ℃ for 48h to obtain a black and xerogel-shaped precursor.
(5) And (4) placing the xerogel-shaped precursor prepared in the step (4) into a tubular furnace, and calcining for 2 hours at the temperature of 250 ℃ in a nitrogen atmosphere to obtain the nanocomposite.
Application example
Preparing the electromagnetic shielding coating:
adding an acetone solvent, an epoxy resin prepolymer (Meclin reagent) and the nano composite material (the mass ratio of the epoxy resin to the nano composite material is 9:1) prepared in the embodiment or the comparative example into a reaction bottle, uniformly mixing, and adding an epoxy resin curing agent ethylenediamine, wherein the mass ratio of the epoxy resin prepolymer to the curing agent is 5:1, so as to obtain the electromagnetic shielding coating.
Pouring the electromagnetic shielding coating into a PVC film forming die for thermosetting treatment to obtain an electromagnetic shielding coating with the thickness of 1.0 mm. The electromagnetic shielding effectiveness of the prepared electromagnetic shielding coating is tested in the frequency range of 2.0-18 GHz, and the result is shown in FIG. 3.
As can be seen from FIG. 3, under the conditions of low thickness and low active material usage, the electromagnetic shielding effectiveness of the composite material prepared by the present invention applied to the coating can be maintained above 26dB at the frequency band of 2-18GHz, and especially the electromagnetic shielding effectiveness of the composite material applied to the coating can be maintained above 41dB at the frequency band of 8-12 GHz; this means that: the proper amount of the cobalt-nickel alloy/reduced graphene oxide (NiCo/rGO) nano composite material can shield over 99.88% of incident electromagnetic waves, and is far greater than the commercial requirement (more than or equal to 20dB) of an electromagnetic shielding material. Compared with the comparative ratio, the invention has more excellent electromagnetic shielding performance, thereby proving that the preparation condition of the invention has important influence on the electrical measurement shielding performance.
Claims (6)
1. A preparation method of a cobalt-nickel alloy/reduced graphene oxide nano composite material for shielding high-frequency electromagnetic waves is characterized in that the micro-morphology of the composite material is as follows: cobalt-nickel alloy nanoparticles with uniform particle size are uniformly distributed on the surface of the reduced graphene oxide sheet;
the preparation method of the cobalt-nickel alloy/reduced graphene oxide nanocomposite for shielding high-frequency electromagnetic waves comprises the following steps:
(1) dissolving soluble cobalt salt, soluble nickel salt and an additive in water to obtain a mixed solution; uniformly mixing the obtained mixed solution with graphene oxide aqueous dispersion, and then carrying out hydrothermal reaction to obtain hydrogel;
the soluble cobalt salt is cobalt chloride, cobalt sulfate, cobalt nitrate or cobalt acetate; the soluble nickel salt is nickel chloride, nickel sulfate, nickel nitrate or nickel acetate; the mass ratio of the soluble cobalt salt to the soluble nickel salt is 10: 1-1: 10; the additive is one or the combination of more than two of glucose, fructose, sucrose, citric acid monohydrate, ascorbic acid or soluble starch; the mass of the additive is 1-3 times of that of the soluble cobalt salt; in the mixed solution, the concentration of the soluble cobalt salt is 0.02-0.1 mol/L; the mass concentration of the graphene oxide aqueous dispersion is 1-10 mg mL-1(ii) a The ratio of a D band to a G band of the graphene oxide is 0.6-1.4; the mass ratio of the mixed solution to the graphene oxide aqueous dispersion is 5: 1-1: 5; the temperature of the hydrothermal reaction is 120-200 ℃, and the reaction time is 5-30 h;
(2) washing the hydrogel obtained in the step (1), soaking the hydrogel in a solution for preventing nano particles from agglomerating, and drying to obtain a xerogel-shaped precursor;
(3) calcining the xerogel-shaped precursor obtained in the step (2) under the protection of inert atmosphere to obtain a cobalt-nickel alloy/reduced graphene oxide nanocomposite (CoNi/rGO);
the calcination temperature is 300-1000 ℃, and the calcination time is 1-12 h.
2. The method for preparing a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding according to claim 1, wherein the step (1) comprises one or more of the following conditions:
i. the mass ratio of the soluble cobalt salt to the soluble nickel salt is 1: 3-3: 1;
ii. The mass ratio of the mixed solution to the graphene oxide aqueous dispersion is 1:1-1: 3;
and iii, the temperature of the hydrothermal reaction is 160-200 ℃, and the reaction time is 12-18 h.
3. The method for preparing a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding according to claim 1, wherein the step (2) comprises one or more of the following conditions:
i. the washing method comprises the following steps: washing the hydrogel with distilled water and ethanol for 3-5 times respectively;
ii. The solution for preventing the nano particles from agglomerating is prepared by dissolving an additive for preventing the nano particles from agglomerating in a solvent; the additive is two or three of thiourea, urea or melamine; the solvent is one or the combination of more than two of ethanol, acetone, isopropanol, tetrahydrofuran, deionized water, N-methyl pyrrolidone, glycol or N, N-dimethylformamide; in the solution for preventing the nano particles from agglomerating, the concentration of the additive is 0.1-20 mol/L;
iii, the soaking temperature is 25-60 ℃, and the soaking time is 6-56 hours;
iv, drying in air at 60-100 ℃ for 12-48 h.
4. The method for preparing a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding according to claim 3, comprising one or more of the following conditions:
i. the additive is a combination of urea and melamine, and the mass ratio of the urea to the melamine is 1:1-1: 3; in the solution for preventing the nano particles from agglomerating, the concentration of the additive is 2-10 mol/L;
ii. The soaking temperature is 25-40 ℃, and the soaking time is 10-14 h.
5. The method for preparing a cobalt-nickel alloy/reduced graphene oxide nanocomposite for high-frequency electromagnetic wave shielding according to claim 1, wherein the step (3) comprises one or more of the following conditions:
i. the inert atmosphere is nitrogen, argon or helium;
ii. The calcination temperature is 500-700 ℃, and the calcination time is 1-3 h.
6. Use of the nanocomposite material of claim 1 in high frequency electromagnetic wave shielding materials; the specific application method is as follows: uniformly mixing a solvent, an epoxy resin prepolymer and a cobalt-nickel alloy/reduced graphene oxide nanocomposite material, and adding an epoxy resin curing agent to obtain an electromagnetic shielding coating; the solvent is acetone; the content of the cobalt-nickel alloy/reduced graphene oxide nanocomposite in the electromagnetic shielding coating is 1-20 wt%; the thickness of the film obtained by coating the electromagnetic shielding coating is 0.1-3 mm.
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