CN116355586A - Composite shielding material and preparation method thereof - Google Patents
Composite shielding material and preparation method thereof Download PDFInfo
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- CN116355586A CN116355586A CN202111633649.3A CN202111633649A CN116355586A CN 116355586 A CN116355586 A CN 116355586A CN 202111633649 A CN202111633649 A CN 202111633649A CN 116355586 A CN116355586 A CN 116355586A
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- 239000002131 composite material Substances 0.000 title claims abstract description 88
- 239000000463 material Substances 0.000 title claims abstract description 82
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
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- 239000002184 metal Substances 0.000 claims abstract description 168
- 229920001690 polydopamine Polymers 0.000 claims abstract description 69
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 51
- VYFYYTLLBUKUHU-UHFFFAOYSA-N dopamine Chemical compound NCCC1=CC=C(O)C(O)=C1 VYFYYTLLBUKUHU-UHFFFAOYSA-N 0.000 claims abstract description 50
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- 150000003839 salts Chemical class 0.000 claims abstract description 40
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- 238000006243 chemical reaction Methods 0.000 claims description 29
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- 101710134784 Agnoprotein Proteins 0.000 description 2
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- WTDRDQBEARUVNC-UHFFFAOYSA-N L-Dopa Natural products OC(=O)C(N)CC1=CC=C(O)C(O)=C1 WTDRDQBEARUVNC-UHFFFAOYSA-N 0.000 description 2
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Images
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K3/00—Materials not provided for elsewhere
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A30/00—Adapting or protecting infrastructure or their operation
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
Abstract
The invention provides a composite shielding material and a preparation method thereof. The preparation method comprises the following steps: reacting a first metal salt with a nitrogen-containing heterocyclic organic ligand in the presence of a first solvent to obtain a metal organic framework compound; the first metal element in the first metal salt is selected from one or more of the element species in group VIII; calcining the metal organic framework compound in an inert atmosphere to obtain a first metal/porous carbon composite material; reacting the first metal/porous carbon composite material with dopamine to obtain first metal/porous carbon@polydopamine; under the condition that the pH value is 8.0-8.5, reacting the first metal/porous carbon@polydopamine with a second metal salt in a second solvent to obtain a composite shielding material; the second metal element in the second metal salt is a metal element having electromagnetic shielding property. The reflection of the composite shielding material on electromagnetic waves can be greatly improved, so that the shielding effectiveness of the composite shielding material is greatly improved.
Description
Technical Field
The invention relates to the technical field of electromagnetic shielding, in particular to a composite shielding material and a preparation method thereof.
Background
Electronic devices radiate high-frequency electromagnetic waves, such as microwaves and radio-frequency electromagnetic waves, at high power and high speed operation, which not only interrupt or hinder the effective operation of neighboring devices, but also pollute the ecological environment and harm the health of living beings. In order to protect natural environments from electromagnetic pollution, equipment from electromagnetic interference, and surrounding organisms from electromagnetic hazards, electromagnetic shielding materials have been developed and become one of effective methods for solving the above problems.
Metal Organic Frameworks (MOFs) have a rich spatial topology. Through modification and modification, the design and improvement of the pore channel structure and the pore size distribution of MOFs can be realized, so that the specific surface area of the MOFs is larger than that of the traditional carbon material, and the specific surface area of the MOFs can reach 6200m at most 2 And/g. In addition, MOFs have the characteristics of large specific surface area, high porosity, multiple active sites and the like. In the preparation process of the single-metal MOFs or multi-metal MOFs, after the MOFs are subjected to high-temperature calcination treatment, high-permeability metals (such as iron and cobalt) are often embedded into MOFs matrix materials, so that the permeability of MOFs derivative materials is improved. This aspect increases the magnetic losses; on the other hand, the difference between the dielectric constant and the magnetic permeability of MOFs derivative materials is reduced, impedance matching is better realized, and the porous structure formed after high-temperature calcination and an interface polarization mechanism can provide more microwave reflection and scattering effects.
However, in the conventional preparation methods of MOFs and carbonized derivatives thereof, the introduction of carbon-based fillers (such as graphene, carbon nanotubes, carbon fibers, carbon black, etc.) limits the formation of microscopic current networks and electron relaxation polarization behavior (jumping conductance is dominant in MOFs materials, and larger lattice energy is required for charge-skipping interfaces, defects and functional groups) in carbonized derivatives, which leads to poor conductive properties of the materials and thus poor shielding effectiveness.
In view of the above problems, a method for preparing an electromagnetic shielding material, which is commonly used at present, includes: the high conductivity is obtained by introducing conductive particles, and the reflectivity of the material surface to electromagnetic waves is improved by means of impedance mismatch characteristics, so that higher shielding effectiveness is obtained. However, this approach is mostly filled with metal particles, which not only have a high percolation value (mass fraction > 50%) but also have an excessive density. Thus, constructing a highly conductive network structure is not the best solution for designing an ideal EMI shielding material. An excessively high conductivity generally represents a high reflection of electromagnetic waves, which may result in secondary pollution of the electromagnetic waves.
On the basis, in order to improve the conductivity and shielding effectiveness of the electromagnetic shielding material and avoid secondary pollution of electromagnetic waves, the preparation method of the electromagnetic shielding material and the structure of the electromagnetic shielding material need to be reasonably designed in an optimized way.
Disclosure of Invention
The invention mainly aims to provide a composite shielding material and a preparation method thereof, which are used for solving the problem that an electromagnetic shielding material in the prior art is difficult to simultaneously have good conductivity and good shielding effect.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method for preparing a composite shielding material, the method comprising: s1, reacting a first metal salt with a nitrogen-containing heterocyclic organic ligand in the presence of a first solvent to obtain a metal organic framework compound; the first metal element in the first metal salt is selected from one or more of the element species in group VIII; s2, calcining the metal organic framework compound in an inert atmosphere to obtain a first metal/porous carbon composite material; s3, reacting the first metal/porous carbon composite material with dopamine to obtain first metal/porous carbon@polydopamine; s4, under the condition that the pH is 8.0-8.5, enabling the first metal/porous carbon@polydopamine to react with a second metal salt in a second solvent to obtain a first metal/porous carbon@polydopamine@second metal, namely a composite shielding material; the second metal element in the second metal salt is a metal element having electromagnetic shielding property.
Further, the weight ratio of the first metal/porous carbon@polydopamine to the second metal salt is (1-2): 2-5; preferably, the second metal element is selected from Ag and/or Au.
Further, in the step S4, the pH of the reaction system is 8.0-8.5, and the reaction time is 30-60 min.
Further, the first metal element is selected from Co and/or Ni; the nitrogen-containing heterocyclic organic ligand is selected from one or more of the group consisting of 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole.
Further, the mass ratio of the first metal element, the nitrogen-containing heterocyclic organic ligand and the dopamine is (3.44-7.39): 12.18-24.36): 0.53-3.16.
Further, the temperature of the calcination treatment is 700-800 ℃, the temperature rising rate is 1-5 ℃/min, and the time is 5-8 h.
Further, step S3 further includes: adding a buffering agent into the reaction system to adjust the pH; preferably, the buffer is an aqueous solution of a first compound with an acid or a base, wherein the first compound is selected from one or more of the group consisting of tris, potassium dihydrogen phosphate, citric acid and sodium bicarbonate; the acid is selected from one or more of hydrochloric acid, nitric acid and acetic acid, and the base is selected from ammonia water and/or sodium hydroxide.
Further, the reaction time in the step S3 is 6-12 h.
Further, step S4 further includes: reducing the second metal ions in the second metal salt by adding a reducing agent into the reaction system; preferably, the reducing agent is selected from the group of aldehyde group containing organic reducing agents, preferably one or more of the group consisting of glucose, tartaric acid and acetaldehyde; preferably, the first solvent is selected from one or more of the group consisting of methanol, isopropanol and ethanol; the second solvent is selected from distilled water and/or deionized water; more preferably, when the reducing agent is a combination of glucose and tartaric acid, the weight ratio of glucose to tartaric acid is (3-4): 1-2.
In order to achieve the above object, another aspect of the present invention further provides a composite shielding material, which is manufactured by the manufacturing method of the composite shielding material provided herein, or from inside to outside, and includes a first metal/porous carbon core, a polydopamine coating layer, and a second metal conductive layer in this order, wherein the first metal is selected from one or more of element types in group VIII, and the second metal is selected from Ag and/or Au; preferably, the first metal is selected from Co and/or Ni; preferably, the thickness of the polydopamine coating layer is 10-20 nm, and the thickness of the second metal conductive layer is 20-60 nm.
By applying the technical scheme of the invention, the following multiple loss mechanisms are simultaneously introduced into the composite shielding material by adopting the preparation method, wherein the multiple loss mechanisms comprise a magnetic loss mechanism of a first metal element (such as Co and Ni), a dielectric loss mechanism of a second metal element (metal element with electromagnetic shielding performance (such as Ag and Au)), an interface loss mechanism between the first metal and porous carbon, a porous carbon and polydopamine coating layer and between the polydopamine coating layer and a second metal conducting layer, and a dipole polarization loss mechanism. The reflection of the composite shielding material on electromagnetic waves can be greatly improved by utilizing the combined action of the diversified loss mechanisms, so that the shielding effectiveness of the composite shielding material is greatly improved. In addition, compared with the traditional electroless plating method, the preparation method provided by the application is simple, convenient, efficient, nontoxic, pollution-free and low in cost.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 shows a scanning electron micrograph (SEM image) of a metal-organic framework compound ZIF-67 prepared in example 1 of the present invention at 10000 times with a scale bar of 1. Mu.m;
FIG. 2 shows a scanning electron micrograph (SEM image) of Co/C@PDA prepared in example 1 of the present invention at 10000 times with a scale bar of 1. Mu.m.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present invention will be described in detail with reference to examples.
As described in the background art, the existing electromagnetic shielding material has the problem that it is difficult to have both good conductivity and good shielding effectiveness. In order to solve the technical problems, the application provides a preparation method of a composite shielding material, which comprises the following steps: s1, reacting a first metal salt with a nitrogen-containing heterocyclic organic ligand in the presence of a first solvent to obtain a metal organic framework compound; the first metal element in the first metal salt includes, but is not limited to, one or more of the group VIII element species; s2, calcining the metal organic framework compound in an inert atmosphere to obtain a first metal/porous carbon composite material; s3, reacting the first metal/porous carbon composite material with dopamine to obtain first metal/porous carbon@polydopamine; s4, under the condition that the pH is 8.0-8.5, enabling the first metal/porous carbon@polydopamine to react with a second metal salt in a second solvent to obtain a first metal/porous carbon@polydopamine@second metal, namely a composite shielding material; the second metal element in the second metal salt is a metal element having electromagnetic shielding property.
In the step S1, a first metal salt and a nitrogen-containing heterocyclic organic ligand undergo a coordination reaction and self-assembly to form a metal organic framework compound; in the step S2, the calcining treatment is performed to carbonize the nitrogen-containing heterocyclic organic ligand to form porous carbon, and meanwhile, the first metal element in the metal organic framework compound forms a first metal simple substance under an inert atmosphere, so as to finally form the first metal/porous carbon composite material.
In step S3, the Dopamine (DA) undergoes an oxidative self-polymerization reaction to form Polydopamine (PDA), and the phenolic hydroxyl groups and the nitrogen-containing functional groups (such as amino groups) contained in the polydopamine structure can form a strong physical adsorption effect with the surface of the first metal/porous carbon composite material. Through in-situ polymerization of dopamine and bridging action of polydopamine, a firm polydopamine coating layer is formed on the surface of the first metal/porous carbon composite material.
In step S4, under a specific pH condition, polydopamine is used as a reducing agent to reduce the second metal ions in the second metal salt into a second metal simple substance, and the second metal simple substance generated in this part can also continuously catalyze the oxidation-reduction reaction, so as to continuously generate more second metal simple substance particles, and the second metal simple substance particles are gradually deposited and coated on the surface of the first metal/porous carbon@polydopamine composite material, so as to obtain the composite shielding material. The in-situ synthesis and cladding of the second metal can obtain a second metal conductive layer with higher dielectric constant, thereby improving the conductivity of the composite shielding material.
The preparation method introduces the following multiple loss mechanisms into the composite shielding material, wherein the multiple loss mechanisms comprise a magnetic loss mechanism of a first metal element (such as Co and Ni), a dielectric loss mechanism of a second metal element (metal element with electromagnetic shielding performance such as Ag and Au), an interface loss mechanism between the first metal and porous carbon, a porous carbon and polydopamine coating layer and between the polydopamine coating layer and a second metal conducting layer, and a dipole polarization loss mechanism. The reflection of the composite shielding material on electromagnetic waves can be greatly improved by utilizing the combined action of the diversified loss mechanisms, so that the shielding effectiveness of the composite shielding material is greatly improved. In addition, compared with the traditional electroless plating method, the preparation method provided by the application is simple, convenient, efficient, nontoxic, pollution-free and low in cost.
In a preferred embodiment, the weight ratio of the first metal/porous carbon @ polydopamine to the second metal salt is (1-2): 2-5. The weight ratio of the first metal/porous carbon@polydopamine to the second metal salt comprises but is not limited to the above range, and the weight ratio is limited to the above range, so that the generation rate of the second metal simple substance is improved, and meanwhile, the thickness of the second metal conductive layer is controlled in a proper range, so that the conductivity of the composite shielding material is further improved.
In order to further exert the dielectric loss property of the second metal element, the dielectric loss of the composite shielding material is improved, thereby further improving the shielding effectiveness thereof, preferably the second metal element includes, but is not limited to, ag and/or Au.
In order to further control the reaction rate and the reaction degree of the oxidation-reduction reaction within a proper range, and further make the thickness of the second metal conductive layer within a proper range, it is advantageous to achieve that the conductive performance of the composite shielding material can be improved without increasing the weight of the composite shielding material, and in a preferred embodiment, in the step S4, the pH of the reaction system is 8.0 to 8.5, and the reaction time is 30 to 60 minutes.
In a preferred embodiment, the first metal element includes, but is not limited to, co and/or Ni. The first metal element of the above kind has a certain magnetism, and the use of the first metal element of the above kind is advantageous for further improving the magnetic loss performance. In an alternative embodiment, the nitrogen-containing heterocyclic organic ligands include, but are not limited to, one or more of the group consisting of 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole. The nitrogen-containing heterocyclic organic ligand and the first metal salt can undergo coordination reaction and self-assembly to form a metal organic framework compound with a specific structure, which is beneficial to improving the shielding effectiveness of the composite shielding material.
In a preferred embodiment, the ratio of the amounts of the first metal element, the nitrogen-containing heterocyclic organic ligand and the dopamine is (3.44-7.39): 12.18-24.36): 0.53-3.16. The mass ratio of the first metal element, the nitrogen-containing heterocyclic organic ligand and the dopamine comprises but is not limited to the above range, and the limitation of the mass ratio in the above range is beneficial to improving the generation rate of the metal organic framework compound with a specific structure on one hand, and improving the coating amount of polydopamine on the surface of the first metal/porous carbon composite material on the other hand, so as to improve the interfacial loss between the porous carbon and polydopamine coating layer and between the polydopamine coating layer and the second metal conductive layer.
In order to carbonize the nitrogen-containing heterocyclic organic ligand in the metal-organic framework compound to form porous carbon with specific porosity, and further introduce polarization loss generated by dipole polarization, and simultaneously, in order to improve the structural stability and the crystal form uniformity of the metal/porous carbon composite material, in a preferred embodiment, the calcination treatment temperature is 700-800 ℃, the heating rate is 1-5 ℃/min, and the time is 5-8 h.
Dopamine (DA) is capable of undergoing oxidative self-polymerization and forming Polydopamine (PDA). In a preferred embodiment, step S3 further comprises: a buffer is added into the reaction system to adjust the pH. The buffer is adopted to adjust the pH of the reaction system in the step S3 to create proper reaction conditions for the reaction, so that the oxidation self-polymerization reaction of the dopamine is more thorough, the generation rate of the polydopamine is improved, and the interface loss of the composite shielding material is further improved.
In an alternative embodiment, the buffer is an aqueous solution of a first compound with an acid or base, wherein the first compound includes, but is not limited to, one or more of the group consisting of tris, potassium dihydrogen phosphate, citric acid, and sodium bicarbonate; the acid includes, but is not limited to, one or more of the group consisting of hydrochloric acid, nitric acid, and acetic acid (acetic acid), and the base includes, but is not limited to, ammonia and/or sodium hydroxide. Compared with other types of buffering agents, the buffer agents can further improve the generation rate of polydopamine and further improve the interface loss of the composite shielding material.
In a preferred embodiment, the reaction time of step S3 is from 6 to 12 hours. The reaction time in the step S3 includes, but is not limited to, the above-mentioned range is limited to be favorable for making the reaction more thorough, and making the polydopamine coating layer formed by cladding the polydopamine generated by the reaction stronger, so that the interface loss of the polydopamine coating layer can be further developed, and the subsequent cladding treatment of the second metal conductive layer can be facilitated.
In a preferred embodiment, step S4 further comprises: and adding a reducing agent into the reaction system to reduce second metal ions in the second metal salt. The reaction efficiency of reducing the second metal ion into the second metal simple substance is improved under the synergistic reduction effect of polydopamine and a reducing agent (such as glucose, tartaric acid and the like).
In order to further increase the reaction efficiency of the reduction of the second metal ion to the second metal simple substance, preferably, the reducing agent includes, but is not limited to, an organic-based reducing agent containing an aldehyde group. Compared with an inorganic reducing agent, the organic reducing agent can be used for combining the second metal salt with the organic reducing agent and then adsorbing the second metal salt on the surface of the first metal/porous carbon@polydopamine, so that the in-situ synthesis and coating of the second metal are facilitated. In an alternative embodiment, the reducing agent includes, but is not limited to, one or more of the group consisting of glucose, tartaric acid, and acetaldehyde. More preferably, when the reducing agent is a combination of glucose and tartaric acid, the weight ratio of glucose to tartaric acid is (3-4): 1-2.
In a preferred embodiment, the first solvent includes, but is not limited to, one or more of the group consisting of methanol, ethanol, and propanol. Compared with other types of solvents, the first solvent of the type is favorable for improving the dispersion uniformity of the first metal salt and the nitrogen-containing heterocyclic organic ligand, and further improving the reaction degree of coordination reaction and self-assembly of the first metal salt and the nitrogen-containing heterocyclic organic ligand.
In a preferred embodiment, the second solvent includes, but is not limited to distilled and/or deionized water. Compared with other types of solvents, the second solvent of the type is favorable for improving the dispersion uniformity of the first metal/porous carbon@polydopamine and the second metal salt, further improving the thickness uniformity of a second metal simple substance layer generated in situ by the second metal salt, and inhibiting the condition of unstable shielding performance caused by nonuniform coating thickness of the second metal conductive layer.
The second aspect of the present application also provides a composite shielding material, which is prepared by the preparation method of the composite shielding material provided by the present application, or from inside to outside, and sequentially comprises a first metal/porous carbon core, a polydopamine coating layer and a second metal conductive layer, wherein the first metal comprises one or more of element types in group VIII, but not limited to Ag and/or Au.
The composite shielding material is simultaneously introduced with the following multiple loss mechanisms, including a magnetic loss mechanism of a first metal element (such as Co and Ni), a dielectric loss mechanism of a second metal element (such as Ag and Au), an interface loss mechanism between the first metal and porous carbon, a porous carbon and polydopamine coating layer and a second metal conductive layer, and a dipole polarization loss mechanism. The reflection of the composite shielding material on electromagnetic waves can be greatly improved by utilizing the combined action of the diversified loss mechanisms, so that the shielding effectiveness of the composite shielding material is greatly improved.
In a preferred embodiment, the first metal includes, but is not limited to, co and/or Ni. The first metal element of the above kind has a certain magnetism, and the use of the first metal element of the above kind is advantageous for further improving the magnetic loss performance.
In a preferred embodiment, the thickness of the polydopamine coating is 10 to 20nm and the thickness of the second metallic conductive layer is 20 to 60nm. The thickness of the polydopamine coating layer includes, but is not limited to, the above range, and the limitation of the thickness in the above range is beneficial to improving the conductivity of the composite shielding material without increasing the weight of the composite shielding material, and simultaneously inhibiting secondary pollution of electromagnetic waves.
The electromagnetic shielding performance of the composite shielding materials prepared in all examples and comparative examples in the present application was evaluated by the following test methods.
The composite shielding materials prepared in all examples and comparative examples in this application were mixed with paraffin wax in a weight ratio of 3:1 to prepare a coaxial ring having an inner diameter of 3.0mm, an outer diameter of 7.0mm and a thickness of 2.0 mm. Electromagnetic parameters and S parameters of the composite shielding material are tested by using a vector network analyzer E5071C, and shielding effectiveness of the composite shielding material in the 8.2-12.4 GHz frequency band is calculated, wherein the test standard is GB/T32596-2016.
Wherein, the index of the good or bad electromagnetic shielding material performance is called the shielding effectiveness of the composite shielding material. Total Shielding Effectiveness (SE) of the composite shielding material T ) Including reflection losses (SE) at the shield surface R ) Absorption loss of shielding body (SE A ) Multiple reflection losses (SE MR )。
The present application is described in further detail below in conjunction with specific embodiments, which should not be construed as limiting the scope of the claims.
Example 1
A method of preparing a composite shielding material, comprising:
s1, 1g of cobalt nitrate hexahydrate Co (NO) 3 ) 2 ·6H 2 O was dissolved in 100ml of methanol. 1g of 2-methylimidazole was weighed and added to 100ml of methanol, and the mixture was sufficiently dissolved to obtain a 2-methylimidazole dispersion. The methanol dispersion of 2-methylimidazole was poured into the methanol dispersion of cobalt nitrate hexahydrate, and magnetically stirred at room temperature for 24 hours, and the product was collected by centrifugation through methanol. Finally, drying the mixture in a vacuum drying oven at 60 ℃ for 18 hours to obtain the metal organic framework compound ZIF-67. As shown in FIG. 1, the micro-morphology of ZIF-67 was polyhedral particles with smooth surfaces.
And S2, calcining the metal organic framework compound sample in a nitrogen atmosphere, wherein the heating rate is 2 ℃/min, and continuously calcining for 6 hours at the calcining temperature of 700 ℃ to obtain the Co/C composite material sample.
S3, dissolving 0.5g of Tris (hydroxymethyl) aminomethane (Tris) in 500mL of distilled water, regulating the pH of a reaction system to 8.0 by using 1.0mol/L HCl, adding 1g of Co/C or Ni/C sample into Tris-HCl buffer solution, stirring for 45min, adding 0.3g of dopamine hydrochloride (DOPA. HCl) into the solution, stirring for about 8h, washing the sample by using deionized water, and vacuum drying at 60 ℃ to obtain Co/C@PDA. The mass ratio of cobalt nitrate hexahydrate, 2-methylimidazole and dopamine hydrochloride (or dopamine) is 3.44:12.18:1.58. As can be seen from the SEM image shown in FIG. 2, the surface roughness of the prepared Co/C@PDA indicates that the coated sample with dopamine was successfully prepared as compared with FIG. 1.
S4, using dropper to transfer silver nitrate (AgNO 3 ) Slowly dropwise adding ammonia water into the solution, changing the solution from transparent to turbid, continuously dropwise adding the ammonia water until the solution is just clarified to obtain 10g/L silver ammonia solution, adding 1g Co/C@PDA sample into the 500mL 10g/L silver ammonia solution (the weight ratio of the first metal/porous carbon@polydopamine to the second metal salt is 1:5), dissolving glucose and tartaric acid with the weight ratio of 3:1 into the reaction solution, reacting at normal temperature (25 ℃) for 45min, and obtaining the productAnd drying the mixture at room temperature to obtain Co/C@PDA@Ag.
Example 2
The difference from example 1 is that: the first metal salt is nickel nitrate hexahydrate Ni (NO) 3 ) 2 ·6H 2 O，Ni(NO 3 ) 2 ·6H 2 The mass ratio of O, 2-methylimidazole to dopamine hydrochloride (or dopamine) is 3.67:12.18:1.58.. The final Ni/C@PDA@Ag was prepared in this example.
Example 3
The difference from example 1 is that: in the step S4, 2g of Co/C@PDA sample is added into 200mL of 10g/L silver ammonia solution, namely the weight ratio of the first metal/porous carbon@polydopamine to the second metal salt is 1:1.
Example 4
The difference from example 1 is that: in step S4, 4g of the Co/C@PDA sample was added to 200mL of a 10g/L silver ammonia solution at a ratio of 2:1.
Example 5
The difference from example 1 is that: in step S4, the reaction time was 30min.
Example 6
The difference from example 1 is that: the pH of the reaction system in the step S4 was 8.5, and the reaction time was 60min.
Example 7
The difference from example 1 is that: in step S4, the reaction time was 120min.
Example 8
The difference from example 1 is that: the weight ratio of the weighed cobalt nitrate hexahydrate, 2-methylimidazole and dopamine hydrochloride is 1:1:0.1, namely Co (NO 3 ) 2 ·6H 2 The mass ratio of O, 2-methylimidazole to dopamine was 3.44:12.18:0.53.
Example 9
The difference from example 1 is that: the weight ratio of the weighed cobalt nitrate hexahydrate, 2-methylimidazole and dopamine hydrochloride is 2:2:0.6, namely Co (NO 3 ) 2 ·6H 2 The mass ratio of O, 2-methylimidazole to dopamine was 6.87:24.36:3.16.
Example 10
The difference from example 1 is that: the weight ratio of the weighed cobalt nitrate hexahydrate, 2-methylimidazole and dopamine hydrochloride is 1:0.5:0.6, namely Co (NO 3 ) 2 ·6H 2 The mass ratio of O, 2-methylimidazole to dopamine was 3.44:6.09:3.16.
Example 11
The difference from example 1 is that: in step S1, cobalt nitrate hexahydrate Co (NO 3 ) 2 ·6H 2 The dosage of O is 2g, the dosage of 2-methylimidazole is 2g, and the dosage of methanol in the cobalt nitrate hexahydrate dispersion liquid and the 2-methylimidazole dispersion liquid are respectively 200mL; in the step S3, the amount of Tris is 1g, and the amount of dopamine hydrochloride is 0.6g. I.e. the mass ratio of cobalt element, 2-methylimidazole and dopamine hydrochloride (or dopamine) is 6.87:24.36:3.16.
Example 12
The difference from example 1 is that: in step S1, 1g of Co (NO 3 ) 2 ·6H 2 O and 1g Ni (NO) 3 ) 2 ·6H 2 O was dissolved in 100ml of methanol; the amount of 2-methylimidazole used was 1.5g (18.27 mmol). I.e. cobalt and nickel salts, 2-methylimidazole to dopamine hydrochloride (or dopamine) in a mass ratio of 7.13:18.27:1.58. The final Co-Ni/C@PDA@Ag was prepared in this example.
Example 13
The difference from example 1 is that: in step S2, the calcination treatment time was 8 hours.
Example 14
The difference from example 1 is that: in step S2, the calcination treatment is carried out at 800 ℃ for 5 hours.
Example 15
The difference from example 1 is that: in step S2, the calcination treatment was carried out at 500℃for 3 hours.
Example 16
The difference from example 1 is that: in step S2, the temperature rising rate of the calcination treatment is 8 ℃/min.
Example 17
The difference from example 1 is that: in step S4, no reducing agent (glucose and tartaric acid) is added.
Comparative example 1
The difference from example 1 is that: 1g of Co (NO) was weighed out 3 ) 2 ·6H 2 O was dissolved in 200ml of methanol to obtain a cobalt salt dispersion, and 1.0g of 2-methylimidazole was weighed and dissolved in 200ml of methanol to obtain a 2-methylimidazole dispersion after complete dissolution. The 2-methylimidazole dispersion was poured into the cobalt salt dispersion to give solution A.
0.5g of Tris (hydroxymethyl) aminomethane (Tris) was dissolved in 500mL of distilled water, the pH was adjusted to 7.0 with 1.0mol/L HCl, and stirred for 30min, and 0.3g of DOPA HCl was added to the above solution and stirred for about 8 hours, to give solution B.
AgNO is moved to by a dropper 3 Slowly dropwise adding ammonia water into the solution, changing the solution from transparent to turbid, continuously dropwise adding the ammonia water until the solution is just clarified, obtaining 10g/L silver ammonia solution, and dissolving glucose and tartaric acid with the weight ratio of 3:1 into the 500mL, 10g/L silver ammonia solution to obtain solution C.
The above-prepared solution A, solution B and solution C were mixed and stirred at room temperature for 24 hours, and the product was collected by centrifugation through methanol. Finally, drying for 12 hours in a vacuum drying oven at 70 ℃ to obtain the ZIFs/PDA/Ag composite material.
And (3) calcining the ZIFs/PDA/Ag sample in a nitrogen atmosphere, wherein the heating rate is 2 ℃/min, and the calcination is continuously performed for 5 hours at the calcination temperature of 700 ℃ to finally obtain the Co/C/Ag composite material.
Comparative example 2
The difference from example 1 is that: the first metal salt is zinc nitrate hexahydrate Zn (NO) 3 ) 2 ·6H 2 O, namely the first metal element is zinc element, and the mass ratio of Zn element, 2-methylimidazole and dopamine hydrochloride (or dopamine) is 3.36:12.18:1.58. The final preparation of this comparative example is Zn/C@PDA@Ag nonmagnetic samples.
TABLE 1
| SE of composite shielding material T (dB) | |
| Example 1 | 57.7 |
| Example 2 | 50.5 |
| Example 3 | 57.9 |
| Example 4 | 52.2 |
| Example 5 | 55.0 |
| Example 6 | 55.9 |
| Example 7 | 39.2 |
| Example 8 | 57.2 |
| Example 9 | 56.8 |
| Example 10 | 42.0 |
| Example 11 | 54.0 |
| Example 12 | 62.0 |
| Example 13 | 57.8 |
| Example 14 | 58.2 |
| Example 15 | 49.5 |
| Example 16 | 56.7 |
| Example 17 | 50.2 |
| Comparative example 1 | 41.7 |
| Comparative example 2 | 43.5 |
From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:
in comparative example 1, a first metal salt, a nitrogen-containing heterocyclic organic ligand, dopamine and a second metal salt were prepared into respective dispersions, the dispersions were directly mixed, and finally, calcination was directly performed to obtain a product Co/C/Ag composite. In comparison with example 1, the preparation method in comparative example 1 cannot obtain the polydopamine coating layer because it is carbonized to form porous carbon during the calcination treatment; meanwhile, since the reduced product silver particles are incorporated into the ZIFs/C or ZIFs/PDA structures during the calcination process, a complete metallic silver conductive layer cannot be formed, and thus the composite shielding material obtained in comparative example 1 is completely different from that obtained in example 1. As can be seen from comparison of the results of the shielding performance test in Table 1, the Co/C@PDA@Ag composite shielding material prepared in example 1 of the present application has a shielding performance (57.7 dB) significantly better than that of the Co/C/Ag composite material of comparative example 1 (46.8 dB). This indicates that the following multiple loss mechanisms are simultaneously introduced into the composite shielding material provided by the application, including a magnetic loss mechanism of a first metal element (such as Co), a dielectric loss mechanism of a second metal element (such as Ag) per se, an interface loss mechanism between the first metal and porous carbon, porous carbon and polydopamine coating, and between the polydopamine coating and the second metal conductive layer, and a loss mechanism caused by dipole polarization. The reflection of the composite shielding material on electromagnetic waves can be greatly improved by utilizing the combined action of the diversified loss mechanisms, so that the shielding effectiveness of the composite shielding material is greatly improved.
The first metal element in example 1 is cobalt, and the first metal element in example 2 is nickel, both of which are elements in group VIII; whereas the first metal salt in comparative example 2 was zinc nitrate hexahydrate, i.e., the first metal element was zinc element of group IIB. From the test results in Table 1, the shielding effectiveness (57.7 dB) of example 1 is significantly better than 49.7dB of comparative example 2. This shows that the introduction of the element species in group VIII can improve the magnetic loss properties of the composite shielding material based on the reason of the magnetic properties of the first metal element itself, thereby improving the shielding effectiveness of the composite shielding material.
Comparing examples 1, 3 and 4, the shielding effectiveness of example 1 (57.7 dB) and example 3 (57.9 dB) was superior to example 4, as seen from the results of the shielding effectiveness test in table 1, indicating that the shielding effectiveness obtained was better when the weight ratio of Co/c@pda to silver salt was values within the preferred ranges of the present application. It is known that the weight ratio of the Co/C@PDA to the silver salt includes but is not limited to the preferred range of the application, and the weight ratio is limited to the preferred range of the application, so that the production rate of the second elemental silver metal is improved, and the thickness of the metallic silver conductive layer is controlled in a proper range, so that the conductivity of the composite shielding material is further improved.
Comparing examples 1, 5 to 7, the reaction time in step S4 of example 7 was too long, 120min, and the shielding effectiveness was only 39.2dB, which was significantly lower than 55.0dB in example 5. This means that the pH and the reaction time of the reaction system in step S4 include, but are not limited to, the preferred ranges of the present application, and limiting the reaction system to the preferred ranges of the present application is advantageous for making the thickness of the second metal conductive layer in a suitable range, and for improving the conductive performance of the composite shielding material without increasing the weight of the composite shielding material.
Comparing examples 1, 8 to 12, the amount of 2-methylimidazole used in example 10 is significantly smaller than that in examples 1, 8 and 9, and the shielding effectiveness test results in Table 1 show that example 10 achieves only 42.0dB, which is significantly lower than that in examples 1, 8 and 9. The first metal element in the first metal salt used in example 11 is the preferred species (cobalt element and nickel element) in the present application, and the use amount ratio is also within the preferred range in the present application, and the shielding effectiveness is better, which can reach 54.0dB. It is understood that the mass ratio of the first metal element, the 2-methylimidazole and the dopamine includes, but is not limited to, the preferred range of the application, and the limiting of the mass ratio to the preferred range of the application is beneficial to improving the interfacial loss between the porous carbon and the polydopamine coating layer and between the polydopamine coating layer and the second metal conductive layer.
Comparing examples 1, 13 to 15, the calcination treatment temperature in example 15 was lower than the preferred range of the present application, and the calcination treatment time was also shorter than the preferred range of the present application, and the shielding effectiveness in example 15 was only 49.5dB, which is significantly lower than that in examples 13 (57.8 dB) and 14 (58.2 dB) as shown in Table 1. It is understood that, compared with other ranges, the temperature and time of the calcination treatment are limited within the preferred ranges of the application, which is favorable for introducing the polarization loss generated by dipole polarization, thereby improving the shielding effectiveness of the composite shielding material.
Comparing examples 1 and 16, it is understood that limiting the rate of temperature rise of the calcination treatment to the preferred ranges of the present application is advantageous in improving the structural stability and the crystalline homogeneity of the Co/C composite material, and thus the shielding effectiveness of the composite shielding material, compared to other ranges.
As is clear from comparing examples 1 and 17, in example 17, the reduction agent was not added additionally, and in the reaction of step S4 in this example, only polydopamine actually had a reduction effect, and it was impossible to reduce all of the silver in the silver salt to elemental silver. The polydopamine in example 1 and the reducing agent (such as glucose, tartaric acid, etc.) have synergistic effect, and the reaction efficiency of reducing the second metal ion into the second metal simple substance is improved under the synergistic reduction effect.
It should be noted that the terms "first," "second," and the like in the description and in the claims of the present application are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the composite shielding material is characterized by comprising the following steps of:
s1, reacting a first metal salt with a nitrogen-containing heterocyclic organic ligand in the presence of a first solvent to obtain a metal organic framework compound; the first metal element in the first metal salt is selected from one or more of element types in a VIII group;
s2, calcining the metal-organic framework compound in an inert atmosphere to obtain a first metal/porous carbon composite material;
s3, enabling the first metal/porous carbon composite material to react with dopamine to obtain first metal/porous carbon@polydopamine;
s4, reacting the first metal/porous carbon@polydopamine with a second metal salt in a second solvent under the condition that the pH is 8.0-8.5 to obtain a first metal/porous carbon@polydopamine@second metal, namely the composite shielding material; the second metal element in the second metal salt is a metal element with electromagnetic shielding performance.
2. The method for preparing the composite shielding material according to claim 1, wherein the weight ratio of the first metal/porous carbon@polydopamine to the second metal salt is (1-2): (2-5);
preferably, the second metal element is selected from Ag and/or Au.
3. The method for preparing a composite shielding material according to claim 1, wherein in the step S4, the pH of the reaction system is 8.0-8.5, and the reaction time is 30-60 min.
4. The method for producing a composite shielding material according to claim 1, wherein the first metal element is selected from Co and/or Ni; the nitrogen-containing heterocyclic organic ligand is selected from one or more of the group consisting of 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole.
5. The method according to claim 4, wherein the ratio of the amounts of the first metal element, the nitrogen-containing heterocyclic organic ligand and the dopamine is (3.44 to 7.39): 12.18 to 24.36): 0.53 to 3.16.
6. The method for producing a composite shielding material according to claim 5, wherein the calcination treatment is performed at a temperature of 700 to 800 ℃, at a temperature rise rate of 1 to 5 ℃/min, and for a time of 5 to 8 hours.
7. The method for preparing a composite shielding material according to claim 5, wherein the step S3 further comprises:
adding a buffering agent into the reaction system to adjust the pH;
preferably, the buffer is an aqueous solution of a first compound with an acid or a base, wherein the first compound is selected from one or more of the group consisting of tris, potassium dihydrogen phosphate, citric acid and sodium bicarbonate; the acid is selected from one or more of the group consisting of hydrochloric acid, nitric acid and acetic acid, and the base is selected from ammonia water and/or sodium hydroxide.
8. The method for preparing a composite shielding material according to claim 5, wherein the reaction time of the step S3 is 6 to 12 hours.
9. The method for preparing a composite shielding material according to claim 8, wherein the step S4 further comprises:
reducing a second metal ion in the second metal salt by adding a reducing agent into the reaction system;
preferably, the reducing agent is selected from the group of aldehyde group-containing organic reducing agents, preferably one or more of the group consisting of glucose, tartaric acid and acetaldehyde;
preferably, the first solvent is selected from one or more of the group consisting of methanol, isopropanol and ethanol; the second solvent is selected from distilled water and/or deionized water;
more preferably, when the reducing agent is a combination of the glucose and the tartaric acid, the weight ratio of the glucose to the tartaric acid is (3-4): 1-2.
10. A composite shielding material, characterized in that the composite shielding material is prepared by the preparation method of the composite shielding material according to claim 1, or comprises a first metal/porous carbon core, a polydopamine coating layer and a second metal conductive layer from inside to outside in sequence, wherein the first metal is selected from one or more of element types in group VIII, and the second metal is selected from Ag and/or Au;
preferably, the first metal is selected from Co and/or Ni;
preferably, the thickness of the polydopamine coating layer is 10-20 nm, and the thickness of the second metal conductive layer is 20-60 nm.
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