CN116315732A - Nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material and preparation method thereof - Google Patents
Nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material and preparation method thereof Download PDFInfo
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Abstract
The invention provides a nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material and a preparation method thereof, which belong to the technical field of electromagnetic wave absorbing materials, wherein the ZIF-67 polyhedron is etched and protected by tannic acid to obtain a hollow ZIF-67 polyhedron; carrying out high-temperature annealing treatment on the hollow ZIF-67 polyhedron, wherein the annealing temperature is 700-900 ℃, and obtaining the magnetic Co/NC with a hollow structure; mnO with hierarchical structure is coated on the surface of the magnetic Co/NC with the hollow structure in situ by adopting a hydrothermal method 2 A nano-sheet. ZIF-67 surface coated with MnO with hierarchical structure after high-temperature annealing based on hydrothermal method 2 The nano sheet ensures that the material prepared by the invention has larger specific surface area and pore volume, is beneficial to improving the electromagnetic wave absorption performance of the nano hollow heterogeneous double-shell structure electromagnetic wave absorption material, and meets the light weight requirement in practical application.
Description
Technical Field
The invention belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material and a preparation method thereof.
Background
The rapid development of radar detection technology and the widespread use of electronic communication equipment pose serious threats to both the stealth characteristics of the weapon equipment and to the proper functioning of the instrument equipment. The electromagnetic wave absorbing material can effectively absorb electromagnetic waves and convert the electromagnetic waves into heat energy or other forms of energy to be dissipated, and is an effective means for solving electromagnetic pollution. Therefore, how to design and prepare a light and efficient electromagnetic wave absorbing material has urgent practical need for solving the above problems.
In recent years, derived materials prepared using high-temperature carbonized metal organic frameworks have been attracting attention in the field of electromagnetic wave absorption. Through the coordination design of the organic ligand and the metal ion, the derivative material has good impedance matching, is favorable for the electromagnetic wave to be incident into the material and be dissipated, and can realize the efficient electromagnetic wave absorption characteristic through the electromagnetic synergistic effect. However, there is a problem that the filling amount of the derivative material in the paraffin matrix tends to be large when the derivative material is used as an electromagnetic wave absorber (ACS appl. Mat. Interfaces, 2015, 7, 13604-13611; j. Mat. Chem. C, 2021, 9, 13860-13868; j. Mat. Chem. A, 2021, 9, 5086-5096.) and it is difficult to satisfy the light weight and high efficiency requirements of the ideal electromagnetic wave absorbing material.
Therefore, it is necessary to research a method for preparing the metal-organic frame derived electromagnetic wave absorbing material with strong absorption, wide frequency band and low filling amount by structural design, so as to meet the requirement of light weight in practical application.
Disclosure of Invention
In order to solve the problems, the invention aims to provide the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure and the preparation method thereof, and the etching-protection of tannic acid to the ZIF-67 is controlled so that the pore structure of the hollow ZIF-67 polyhedral structure meets the corresponding requirements, and meanwhile, the surface of the ZIF-67 subjected to high-temperature annealing is coated with MnO with a hierarchical structure in situ based on a hydrothermal method 2 The nano-sheet can make the prepared material have specific surface area not less than 140 and 140 m 2 /g, and pore volume of not less than 0.55. 0.55 cm 3 And/g, the electromagnetic wave absorption performance of the electromagnetic wave absorption material with the nano hollow heterogeneous double-shell structure is improved, and the light weight requirement in practical application is met.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
an electromagnetic wave absorbing material with a nano hollow heterogeneous double-shell structure, wherein the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure is Co/NC@MnO 2 The Co/NC@MnO 2 Is not less than 140 m 2 /g, and pore volume of not less than 0.55. 0.55 cm 3 /g。
Further, the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material has mesoporous-macroporous pore size distribution, wherein the mesoporous pore size distribution is 2-50 nm, and the macroporous pore size distribution is 50-nm-1000 nm.
Further, the ratio of the mesopores to the macropores is 1:20-30.
The preparation method of the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure comprises the following steps:
preparing a ZIF-67 polyhedron;
etching and protecting the ZIF-67 polyhedron through tannic acid to obtain a hollow ZIF-67 polyhedron;
carrying out high-temperature annealing treatment on the hollow ZIF-67 polyhedron, wherein the annealing temperature is 700-900 ℃, and obtaining the magnetic Co/NC with a hollow structure;
MnO with hierarchical structure is coated on the surface of the magnetic Co/NC with the hollow structure in situ by adopting a hydrothermal method 2 And (3) nano sheets to obtain the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material.
Further, the preparation method of the ZIF-67 polyhedron comprises the following steps: dissolving cobalt nitrate in methanol, and uniformly stirring to obtain a mixed solution A; dissolving 2-methylimidazole in methanol, and uniformly stirring to obtain a mixed solution B; pouring the mixed solution B into the mixed solution A, stirring, centrifuging and drying to obtain the ZIF-67 polyhedron.
Further, the nitrate of cobalt is Co (NO 3 ) 2 ·6H 2 O, the Co (NO) 3 ) 2 ·6H 2 The molar ratio of O to 2-methylimidazole was 1:4.
Further, the specific etching-protecting process is as follows: dissolving the ZIF-67 polyhedron in methanol, adding a tannic acid aqueous solution, and stirring for 8-12 min, wherein the mass ratio of tannic acid to the ZIF-67 polyhedron is 1:0.6 to 3.
Further, the volume ratio of the methanol to the tannic acid aqueous solution in the specific etching-protecting process is 20-25: 180-200, wherein the concentration of the tannic acid aqueous solution is 0.5-2mg/mL.
Further, the high-temperature annealing treatment is performed under the protection of Ar gas, the temperature is raised from room temperature to 700-900 ℃ at a heating rate of 1-5 ℃/min, and the annealing time is 1-3 h.
Further, the hydrothermal method specifically comprises the following steps: dissolving the magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 0.5-3.0 mg/mL, and then adding KMnO 4 Stirring allAfter homogenization, carrying out hydrothermal reaction, wherein the magnetism Co/NC and KMnO of the hollow structure 4 The mass ratio of (2) is 1:1.7-5.4; the hydrothermal reaction temperature is 140-180 ℃ and the reaction time is 10-14 h.
Compared with the prior art, the invention has the following beneficial effects:
the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material has larger specific surface area and pore volume, can improve the electromagnetic wave absorbing performance of the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material, and meets the light weight requirement in practical application.
Further, the hollow heterogeneous double-shell structured Co/NC@MnO prepared by the invention 2 The electromagnetic wave absorbing material has the pore diameter distribution of mesopores and macropores, wherein the pore diameter distribution of mesopores is 2-50 nm, the pore diameter distribution of macropores is 50-nm-1000 nm, and the ratio of mesopores to macropores is 1:20-30 by integral calculation based on the detection result, so that the filling amount of the material in paraffin can be greatly reduced, magnetic Co particles are generated in situ to provide magnetic loss, NC doping phase and MnO are provided 2 Providing dielectric loss, mnO 2 The hierarchical structure of the nano-sheets is also beneficial to electromagnetic wave multiple scattering, and the above factors are beneficial to realizing light and efficient electromagnetic wave absorption characteristics: the filling amount of paraffin wax is 10 wt% -20 wt%, the maximum absorption strength is-40 to-60 dB, and the effective absorption frequency bandwidth is 5.8-9.0 GHz.
The preparation method of the invention utilizes the unstable characteristic of the ZIF-67 polyhedron under the acidic condition and the slightly acidic tannic acid aqueous solution with larger component, and simultaneously etches and protects the ZIF-67 polyhedron and the H dissociated by tannic acid + Enters into the ZIF-67 polyhedron through the pore canal to destroy 2-methylimidazole and metal Co 2+ Coordination bonds among ions play a role in etching, tannic acid with larger molecular weight is attached to the surface of the ZIF-67 polyhedron, so that the coordination bonds play a role in protecting, and a metal organic framework precursor with a hollow structure can be obtained; carrying out high-temperature annealing treatment on the metal organic frame precursor with the hollow structure to obtain a magnetic Co/NC material with the hollow structure; carbon source in the hollow magnetic Co/NC material is used as a reducing agent, mnO can be obtained through hydrothermal reaction 4 - Reduction to MnO 2 The nano sheet is attached to the surface of the hollow-structure magnetic Co/NC material, and the reaction formula is as follows:
finally obtaining the Co/NC@MnO with the hollow heterogeneous double-shell structure 2 Electromagnetic wave absorbing material, and it is pointed out that the hierarchical structure MnO of cladding 2 The nano sheet provides mesoporous-macroporous pore size distribution for the material, the pore size distribution is closely related to the etching-protecting degree of tannic acid on the ZIF-67 polyhedron, the ZIF-67 polyhedron is broken due to the excessively high etching degree, the ZIF-67 polyhedron with a hollow structure cannot be prepared due to the excessively low etching degree, the protecting effect of the tannic acid is to ensure that hydrogen ions entering the interior of the ZIF-67 polyhedron through micropores are firstly etched on the inner structure of the ZIF-67 polyhedron in the etching process, and the tannic acid coated on the surface inhibits the etching of the ZIF-67 polyhedron by the hydrogen ions.
Further, the hydrothermal reaction conditions are different for the MnO 2 The shape of the nano material has great influence, such as needle shape and flake shape, and the invention controls MnO by controlling the hydrothermal reaction condition 2 The nano material is in a sheet shape, can greatly improve the reflection and absorption properties of electromagnetic waves on the surface of the material, and is due to the MnO 2 The shape of the nano material is sheet-shaped, and certain requirements are imposed on the degree of tannic acid etching ZIF-67, so that the size of the hollow ZIF-67 hole after high-temperature annealing meets the requirements.
Furthermore, the heating and annealing process of high-temperature annealing has great influence on the performance of the material, the stress exists in the material due to the fact that the heating temperature is too high, and when the stress is large, defects can occur in the material, so that the performance of a final product is affected.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an X-ray diffraction pattern of the samples prepared in example 1, comparative examples 1-3 of the present invention;
FIG. 2 is an SEM image of samples prepared in example 1, comparative examples 1-3 of the present invention, a: example 1; b: comparative example 1; c: comparative example 2; d: comparative example 3;
FIG. 3 is N of samples prepared in example 1, comparative examples 1-3 according to the present invention 2 Adsorption and desorption isotherms and pore size distribution profile, a: n (N) 2 Adsorption and desorption isotherms; b: a pore size distribution curve;
FIG. 4 is a graph showing the absorption reflection loss of the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material prepared in example 1 of the present invention when the filling amount of the electromagnetic wave absorbing material in the paraffin matrix is 20wt% and the thickness is 1 mm-4 mm.
Detailed Description
The present invention will be described in further detail with reference to the drawings and the embodiments, in order to make the objects, technical solutions and advantages of the present invention more apparent.
The embodiment of the invention provides a preparation method of a nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material, which improves the electromagnetic wave absorbing performance of the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material and meets the light weight requirement in practical application.
The general idea of the invention is as follows:
in a first aspect, the invention provides a nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material, wherein the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material is Co/NC@MnO 2 The Co/NC@MnO 2 Is not less than 140 m 2 /g, and pore volume of not less than 0.55. 0.55 cm 3 /g; the ratio of the mesopores to the macropores is 1:20-30; adopting tannic acid to etch and protect the ZIF-67 to form a hollow ZIF-67 polyhedron; hierarchical MnO 2 The coating layer of the nano sheet is prepared by a hydrothermal method and is prepared by KMnO 4 The aqueous solution reacts with carbon in the hollow ZIF-67 polyhedron after high-temperature annealing to generate MnO with hierarchical structure in situ 2 A nano-sheet.
It should be noted that the ratio of mesopores to macropores in the present invention is obtained by integrating the pore size distribution curve.
On the other hand, the invention provides a preparation method of the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material, which comprises the following steps:
preparing a ZIF-67 polyhedron;
the preparation method of the ZIF-67 polyhedron comprises the following steps: dissolving cobalt nitrate in methanol, and magnetically stirring uniformly to obtain a mixed solution A; dissolving 2-methylimidazole in methanol, and magnetically stirring uniformly to obtain a mixed solution B; and (3) rapidly pouring the mixed solution B into the mixed solution A, stirring at room temperature, and obtaining the ZIF-67 polyhedron through centrifugal drying. The nitrate of cobalt is Co (NO) 3 ) 2 ·6H 2 O, the Co (NO) 3 ) 2 ·6H 2 The molar ratio of O to 2-methylimidazole was 1:4, in order to obtain Co (NO 3 ) 2 ·6H 2 O and 2-methylimidazole are thoroughly reacted, and the two are mixed and stirred for not less than 24 hours in the embodiment of the invention.
Etching and protecting the ZIF-67 polyhedron through tannic acid to obtain a hollow ZIF-67 polyhedron;
etching-protecting process of tannic acid on ZIF-67 polyhedron and subsequent MnO 2 The nano lamellar hierarchical structure coating layer has great influence on the performance of subsequent materials, and the nano lamellar hierarchical structure coating layer are mutually coordinated though two working procedures, so that the etching-protection process of tannic acid on ZIF-67 reaches the required degree, and the etching-protection process comprises the following steps: dissolving a certain amount of ZIF-67 polyhedron into methanol, wherein the methanol is 20-25 mL; adding a certain amount of tannic acid aqueous solution, and stirring for 8-12 min at room temperature, wherein the mass ratio of tannic acid to ZIF-67 polyhedron is 1: 0.6-3, wherein the concentration of the tannic acid aqueous solution is 0.5-2mg/mL, and the volume of the tannic acid aqueous solution is 180-200 mL.
Carrying out high-temperature annealing treatment on the hollow ZIF-67 polyhedron, wherein the annealing temperature is 700-900 ℃, and obtaining the magnetic Co/NC with a hollow structure;
the high-temperature annealing treatment process comprises the following steps: under the protection of inert gas Ar, the temperature rising rate is 1-5 ℃/min, the temperature is raised to 700-900 ℃ from the room temperature, and the heat preservation time is 1-3 h. The heating and annealing process has great influence on the performance of the material, the temperature is too high, so that stress exists in the material, and when the stress is large, defects can occur in the material, and the performance of a final product is influenced.
In-situ generation of hierarchical MnO on the magnetic Co/NC by hydrothermal method 2 And a nanosheet cladding layer.
The hydrothermal method comprises the following steps: dissolving a certain amount of magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 0.5-3.0 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein the magnetic Co/NC and KMnO with hollow structures 4 The mass ratio of (2) is 1:1.7-5.4; the hydrothermal reaction temperature is 140-180 ℃ and the reaction time is 10-14 h.
According to the invention, ZIF-67 polyhedron is etched and protected by tannic acid and combined with hydrothermal reaction, and MnO with hierarchical structure is coated on the surface of the ZIF-67 polyhedron in situ 2 The nano sheet ensures that the filling amount of the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material in paraffin is 10 wt-20 wt percent, the maximum absorption intensity is-40 to-60 dB, and the effective absorption frequency band width is 5.8-9.0 GHz.
In order to better illustrate the embodiments of the present invention, the present invention will be described in further detail by way of specific examples.
Example 1
The embodiment provides a preparation method of a nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material, which comprises the following steps:
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; and rapidly pouring the mixed solution B into the mixed solution A, stirring at room temperature for 24h, and centrifugally drying to obtain a single ZIF-67 polyhedral product.
Taking 0.1 g of the single ZIF-67 polyhedron prepared by the method, fully dissolving the single ZIF-67 polyhedron in 20 mL of methanol, adding 200mL of tannic acid aqueous solution, wherein the tannic acid is 0.18g, namely the mass ratio of tannic acid to the single ZIF-67 polyhedron product is 1:1.8, wherein the concentration of the tannic acid aqueous solution is 0.54mg/mL; stirring the solution at room temperature for 10min, and then centrifugally drying to obtain the hollow ZIF-67 polyhedral product.
And (3) annealing the hollow ZIF-67 polyhedral product in a tube furnace at 800 ℃ for 2 h at a heating rate of 2 ℃/min under the protection of inert gas Ar to obtain the magnetic Co/NC with a hollow structure.
Dissolving 0.028 g hollow magnetic Co/NC in 35 mL deionized water to give a concentration of 0.8mg/mL, adding 0.1 KMnO 0.1 g 4 After magnetic stirring, namely the hollow-structure magnetic Co/NC and KMnO 4 Transferring the mixed solution into a polytetrafluoroethylene-lined high-pressure reaction kettle with the mass ratio of 1:3.57, performing hydrothermal reaction at 160 ℃ for 12 h, and centrifugally drying to obtain a hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
As shown in FIG. 1, the electromagnetic wave absorbing material with nano hollow heterogeneous double-shell structure prepared in the embodiment has obvious diffraction peaks at 44.4 degrees, 51.4 degrees and 75.8 degrees, and diffraction peaks at 12.5 degrees and 25.4 degrees respectively, which shows MnO 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface.
As can be seen from FIG. 2 a, the material prepared in this example not only has a distinct hollow structure, but also has a surface that is structured in a hierarchical manner as MnO 2 The nano sheet is completely coated to form a hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
It can be seen from fig. 3 a and b that the electromagnetic wave absorbing material with nano hollow heterogeneous double shell structure prepared in this embodiment has the most optimal mesoporous distribution, and also has macroporous pore diameter distribution, mainly due to hierarchical structure MnO 2 The design of the gaps between the nano sheets and the hollow structure leads to the pore diameter of the nano sheets to be enlarged, and the ratio of the mesopores to the macropores is 1:21.
as can be seen from FIG. 4, the electromagnetic wave absorbing material with nano hollow heterogeneous double-shell structure prepared by the embodiment of the invention has wave absorption and reflection loss when the filling amount of the electromagnetic wave absorbing material in the paraffin matrix is 20wt%, and the thickness of the electromagnetic wave absorbing material is 2.1mm, the electromagnetic wave absorbing material with nano hollow heterogeneous double-shell structure has Co/NC@MnO 2 The maximum reflection loss of the electromagnetic wave absorbing material can reach-54.7 dB and less than-10 dBThe effective frequency band width is 6.1GHz, and the requirements of the electromagnetic wave absorbing material on light weight and high efficiency are met.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was calculated to be 140.7. 140.7 m 2 Per gram, pore volume is 0.5612 cm 3 /g。
Example 2
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; and rapidly pouring the mixed solution B into the mixed solution A, stirring at room temperature for 24h, and centrifugally drying to obtain a single ZIF-67 polyhedral product.
Dissolving a certain amount of single ZIF-67 polyhedron in methanol which is fully dissolved in 25mL, adding a certain amount of tannic acid aqueous solution, and stirring for 8min at room temperature, wherein the mass ratio of tannic acid to single ZIF-67 polyhedron product is 1:0.6, wherein the concentration of the tannic acid aqueous solution is 0.5mg/mL, the volume of the tannic acid aqueous solution is 180mL, and the tannic acid aqueous solution is centrifugally dried to obtain a hollow ZIF-67 polyhedral product.
Annealing for 1 h at 700 ℃ in a tube furnace at a heating rate of 1 ℃/min under the protection of inert gas Ar to obtain the magnetic Co/NC with a hollow structure.
Dissolving a certain amount of magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 0.5 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein the magnetic Co/NC and KMnO with hollow structures 4 The mass ratio of (2) is 1:1.7; the hydrothermal reaction temperature is 140 ℃, and the reaction time is 10 hours; centrifugal drying to obtain hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
MnO in the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure prepared in the embodiment 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface; the ratio of mesopores to macropores is 1:20, a step of; the filling amount was 20wt%, and when the thickness was 1.5mm, the hollow heterogeneous double shell structure Co/NC@MnO was obtained 2 Of electromagnetic wave absorbing materialThe maximum reflection loss can reach-48.7 dB, the effective frequency bandwidth below-10 dB is 5.81GHz, and the requirements of light weight and high efficiency of the electromagnetic wave absorbing material are met.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was calculated to be 140.1. 140.1 m 2 Per gram, pore volume of 0.55 cm 3 /g。
Example 3
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; and rapidly pouring the mixed solution B into the mixed solution A, stirring at room temperature for 24h, and centrifugally drying to obtain a single ZIF-67 polyhedral product.
Dissolving a certain amount of single ZIF-67 polyhedral product into methanol which is fully dissolved in 23 mL, adding a certain amount of tannic acid aqueous solution, and stirring for 11min at room temperature, wherein the mass ratio of tannic acid to the single ZIF-67 polyhedral product is 1:2.5, the concentration of the tannic acid aqueous solution is 1.0mg/mL, the volume of the tannic acid aqueous solution is 190mL, and the tannic acid aqueous solution is centrifugally dried to obtain a hollow ZIF-67 polyhedral product.
Annealing for 3 h at 900 ℃ in a tube furnace at a heating rate of 5 ℃/min under the protection of inert gas Ar to obtain the magnetic Co/NC with a hollow structure.
Dissolving a certain amount of magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 1.5 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein Co/NC and KMnO with magnetic hollow structures 4 The mass ratio of (2) is 1:4.5; the hydrothermal reaction temperature is 170 ℃, and the reaction time is 14h; centrifugal drying to obtain hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
MnO in the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure prepared in the embodiment 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface; the ratio of mesopores to macropores is 1:25, a step of selecting a specific type of material; the loading was 20wt%, when the thickness was 2.1mm, the hollow hetero wasCo/NC@MnO with double-shell structure 2 The maximum reflection loss of the electromagnetic wave absorbing material can reach-52.7 dB, the effective frequency bandwidth below-10 dB is 8.1GHz, and the requirements of light weight and high efficiency of the electromagnetic wave absorbing material are met.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was calculated to be 146.5. 146.5 m 2 Per g, pore volume of 0.57cm 3 /g。
Example 4
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; and rapidly pouring the mixed solution B into the mixed solution A, stirring at room temperature for 24h, and centrifugally drying to obtain a single ZIF-67 polyhedral product.
Dissolving a certain amount of single ZIF-67 polyhedron into methanol which is fully dissolved in 24 mL, adding a certain amount of tannic acid aqueous solution, and stirring for 12min at room temperature, wherein the mass ratio of tannic acid to single ZIF-67 polyhedron product is 1:3, the concentration of the tannic acid aqueous solution is 2.0mg/mL, the volume of the tannic acid aqueous solution is 200mL, and the tannic acid aqueous solution is centrifugally dried to obtain a hollow ZIF-67 polyhedral product.
Annealing for 3 h at 900 ℃ in a tube furnace at a heating rate of 5 ℃/min under the protection of inert gas Ar to obtain the magnetic Co/NC with a hollow structure.
Dissolving a certain amount of magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 3.0 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein the magnetic Co/NC and KMnO with hollow structures 4 The mass ratio of (2) is 1:5.4; the hydrothermal reaction temperature is 180 ℃, and the reaction time is 14h; centrifugal drying to obtain hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
MnO in the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure prepared in the embodiment 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface; the ratio of mesopores to macropores is 1:30; the filling amount is 20wt% of hollow heterogeneous double-shell structure Co/NC@MnO when the thickness is 2.0mm 2 The maximum reflection loss of the electromagnetic wave absorbing material can reach-52.3 dB, the effective frequency bandwidth below-10 dB is 9.0GHz, and the requirements of the electromagnetic wave absorbing material for light weight and high efficiency are met.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was 145.1. 145.1 m 2 Per gram, pore volume of 0.57cm 3 /g。
Comparative example 1
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; pouring the mixed solution B into the mixed solution A rapidly, stirring at room temperature for 24h, and obtaining a single ZIF-67 polyhedral product by centrifugal drying; annealing 2 h at 800 ℃ in a tube furnace at a heating rate of 2 ℃/min under the protection of inert gas Ar, and collecting to obtain the solid Co/NC polyhedral electromagnetic wave absorbing material.
The filling amount is 20wt%, and when the thickness is 4.0mm, the maximum reflection loss of the prepared electromagnetic wave absorbing material can reach-28.5 dB, and the effective frequency bandwidth below-10 dB is 3.1GHz.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was 88.7. 88.7 m 2 Per gram, pore volume is 0.1139 cm 3 /g。
Comparative example 2
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; pouring the mixed solution B into the mixed solution A rapidly, stirring at room temperature for 24h, and obtaining a single ZIF-67 polyhedral product by centrifugal drying; taking 0.1 g of the single ZIF-67 polyhedron prepared by the method, fully dissolving the single ZIF-67 polyhedron in 20 mL of methanol, adding 200mL of tannic acid (tannic acid with the mass of 0.18 g) solution, stirring for 20min at room temperature, and centrifuging and drying to obtain a hollow ZIF-67 polyhedron product; under the protection of inert gas Ar, the temperature is increased at a rate of 2 ℃/min in a tubular typeAnnealing at 800 ℃ in a furnace for 2 h, and collecting to obtain the hollow Co/NC polyhedral electromagnetic wave absorbing material.
The filling amount is 20wt%, and when the thickness is 3.0mm, the maximum reflection loss of the prepared electromagnetic wave absorbing material can reach-30.3 dB, and the effective frequency bandwidth below-10 dB is 3.5GHz.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was calculated to be 101.2. 101.2 m 2 Per gram, pore volume is 0.1371 cm 3 /g。
Comparative example 3
6 mmol of Co (NO) 3 ) 2 ·6H 2 O is dissolved in 60 mL methanol, and after magnetic stirring is carried out for 30 min, a uniform mixed solution A is obtained; dissolving 24 mmol of 2-methylimidazole in 20 mL methanol, and magnetically stirring for 30 min to obtain a uniform mixed solution B; pouring the mixed solution B into the mixed solution A rapidly, stirring at room temperature for 24h, and obtaining a single ZIF-67 polyhedral product by centrifugal drying; annealing the hollow ZIF-67 polyhedral product in a tube furnace at 800 ℃ for 2 h under the protection of inert gas Ar at a heating rate of 2 ℃/min; dissolving 0.028. 0.028 g in 35 mL deionized water, and adding 0.1. 0.1 g KMnO 4 After magnetic stirring is uniform, transferring the mixed solution into a polytetrafluoroethylene-lined high-pressure reaction kettle, performing hydrothermal reaction at 160 ℃ for 12 h, and centrifugally drying to obtain a solid heterostructure Co/NC@MnO 2 An electromagnetic composite material.
The ratio of mesopores to macropores is 1:32; the filling amount is 20wt%, and when the thickness is 2.0mm, the maximum reflection loss of the prepared electromagnetic wave absorbing material can reach-42.2 dB, and the effective frequency bandwidth below-10 dB is 4.5GHz.
The specific surface area of the electromagnetic wave absorbing material prepared by this example was 139.8. 139.8 m 2 Per g, pore volume of 0.5061cm 3 /g。
Wherein, as can be seen from FIG. 1, the materials prepared in comparative examples 1 and 2 show obvious diffraction peaks at 44.4 degrees, 51.4 degrees and 75.8 degrees respectively, which are completely matched with the standard card (PDF#15-0806) of the body-centered cubic metal Co, and respectively correspond to the (111), (200) and (220) crystal faces thereof; the material prepared in comparative example 3 appeared at 12.5℃and 25.4℃in addition to the diffraction peak of metallic Co, respectivelyDiffraction peak, with MnO 2 The standard cards (PDF # 80-1098) completely coincide with their (001) and (002) crystal planes, respectively, indicating MnO 2 Successful loading of the nanoplatelets on the surface.
In fig. 2 b, the material prepared in comparative example 1 has no obvious hollow structure, and a large number of in-situ reduced metal Co particles are distributed in the framework of the carbon material. In fig. 2 c, the material prepared in comparative example 2 has a distinct hollow structure, and distinct metallic Co particles are observed on its surface, indicating that the hollow structure remains after the high temperature annealing treatment. In FIG. 2d, the material prepared in comparative example 3 has no obvious hollow structure, but its surface is classified by MnO of hierarchical structure 2 The nano sheet is completely coated to form Co/NC@MnO with a solid heterostructure 2 An electromagnetic composite material.
As can be seen from fig. 3 a, the samples prepared in comparative examples 1 to 3 all have mesoporous structure characteristics, and the adsorption and desorption isotherms of the material prepared in comparative example 3 have a significant rising trend in a high pressure region, indicating that the samples have macroporous structure characteristics. As can be seen from FIG. 3 b, the materials prepared in comparative examples 1 and 2 had an optimal pore size distribution at 3.4 nm and 3.7 nm, respectively, whereas the material prepared in comparative example 3 also had a macroporous pore size distribution in addition to the optimal mesoporous distribution, mainly due to the hierarchical structure MnO 2 The voids between the nanoplatelets cause their pore size to become large.
Comparative example 4
Unlike example 1, in this comparative example: dissolving a certain amount of ZIF-67 polyhedron in methanol which is fully dissolved in 24 mL, adding a certain amount of tannic acid aqueous solution, and stirring for 10min at room temperature, wherein the mass ratio of tannic acid to ZIF-67 is 1:0.5, wherein the concentration of the tannic acid aqueous solution is 0.4mg/mL. Stirring the solution at room temperature for 20min, and then centrifugally drying to obtain the hollow ZIF-67 polyhedral product.
MnO in the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material prepared in the comparative example 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface; the ratio of mesopores to macropores is 1:31; the filling amount was 20wt%, when the thickness was 2.3mm, the hollow heterogeneous double shell structure Co/NC@MnO 2 Electromagnetic waveThe maximum reflection loss of the absorbing material can reach-48.3 dB, and the effective frequency bandwidth below-10 dB is 5.3GHz.
The specific surface area of the electromagnetic wave absorbing material prepared by calculating this comparative example was 139.1m 2 Per gram, pore volume of 0.53 cm 3 /g。
Comparative example 5
Unlike example 1, in this comparative example: dissolving a certain amount of ZIF-67 polyhedron in methanol which is fully dissolved in 24 mL, adding a certain amount of tannic acid aqueous solution, and stirring for 10min at room temperature, wherein the mass ratio of tannic acid to ZIF-67 is 1:3.2, the concentration of the tannic acid aqueous solution is 2.1mg/mL. Stirring the solution at room temperature for 20min, and then centrifugally drying to obtain the hollow ZIF-67 polyhedral product.
MnO in the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material prepared in the comparative example 2 The nano lamellar hierarchical structure coating layer is successfully loaded on the surface; the ratio of mesopores to macropores is 1:25, a step of selecting a specific type of material; the filling amount was 20wt%, when the thickness was 2.0mm, the hollow heterogeneous double shell structure Co/NC@MnO 2 The maximum reflection loss of the electromagnetic wave absorbing material can reach-43.9 dB, and the effective frequency bandwidth below-10 dB is 5.6GHz.
The specific surface area of the electromagnetic wave absorbing material prepared by calculating this comparative example was 138.2 m 2 Per gram, pore volume of 0.54. 0.54 cm 3 /g。
Comparative example 6
Unlike example 1, in this comparative example: dissolving a certain amount of magnetic Co/NC in deionized water to form a solution with the concentration of 1.5 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein the magnetic Co/NC and KMnO are prepared by the following steps of 4 The mass ratio of (2) is 1:5.6; the hydrothermal reaction temperature is 130 ℃, and the reaction time is 14h; centrifugal drying to obtain hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
MnO prepared in this comparative example 2 The structure appearance is needle-shaped, the filling amount is 20wt%, and when the thickness is 2.0mm, the hollow heterogeneous double-shell structure Co/NC@MnO 2 The maximum reflection loss of the electromagnetic wave absorbing material can be reachedThe effective frequency bandwidth below-44.3 dB and-10 dB is 5.2GHz, so that the requirement of light weight and high efficiency of the electromagnetic wave absorbing material is met.
The specific surface area of the electromagnetic wave absorbing material prepared by this comparative example was calculated to be 146 m 2 Per gram, pore volume of 0.52. 0.52 cm 3 /g。
Comparative example 7
Unlike example 1, in this comparative example: dissolving a certain amount of magnetic Co/NC in deionized water to form a solution with the concentration of 1.5 mg/mL; adding KMnO 4 After magnetic stirring evenly, transferring the mixed solution into a high-pressure reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, wherein the magnetic Co/NC and KMnO are prepared by the following steps of 4 The mass ratio of (2) is 1:1.5; the hydrothermal reaction temperature is 190 ℃, and the reaction time is 14h; centrifugal drying to obtain hollow heterogeneous double-shell structure Co/NC@MnO 2 An electromagnetic wave absorbing material.
MnO prepared in this comparative example 2 The morphology of the nano lamellar hierarchical structure coating layer is lamellar with larger thickness, and the ratio of mesopores to macropores is 1:35; the filling amount was 20wt%, when the thickness was 2.0mm, the hollow heterogeneous double shell structure Co/NC@MnO 2 The maximum reflection loss of the electromagnetic wave absorbing material can reach-45.6 dB, the effective frequency bandwidth below-10 dB is 5.7GHz, and the requirements of the electromagnetic wave absorbing material on light weight and high efficiency are met.
The specific surface area of the electromagnetic wave absorbing material prepared by this comparative example was 138 m 2 Per gram, pore volume of 0.51 cm 3 /g。
Comparative example 4-comparative example 7 in which the data in the present invention were not used, the material obtained did not reach a specific surface area of not less than 140 m 2 /g, and pore volume of not less than 0.55. 0.55 cm 3 The performance of the material per gram is less than-40 to-60 dB, and the effective absorption bandwidth is 5.8 to 9.0GHz.
Compared with the prior art, as in the patent with publication number CN115633499A, the mechanism of preparing the hollow carbon/Co composite material with the hierarchical pore structure shell layer by removing Zn metal through a simple inert atmosphere in-situ carbonization process by utilizing the difference of thermal stability between ZIF-8 and ZIF-67 and combining the volatility of Zn metal is different.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (10)
1. The electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure is characterized in that the electromagnetic wave absorbing material with the nano hollow heterogeneous double-shell structure is Co/NC@MnO 2 The Co/NC@MnO 2 Is not less than 140 m 2 /g, and pore volume of not less than 0.55. 0.55 cm 3 /g。
2. The electromagnetic wave absorbing material of nano hollow heterogeneous double-shell structure according to claim 1, wherein the electromagnetic wave absorbing material of nano hollow heterogeneous double-shell structure has a mesoporous-macroporous pore size distribution, the mesoporous pore size distribution is 2-50 nm, and the macroporous pore size distribution is 50-nm-1000 nm.
3. The electromagnetic wave absorbing material of nano hollow heterogeneous double shell structure according to claim 2, wherein the ratio of mesopores to macropores is 1:20-30.
4. A method for preparing the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material according to any one of claims 1 to 3, comprising the steps of:
preparing a ZIF-67 polyhedron;
etching and protecting the ZIF-67 polyhedron through tannic acid to obtain a hollow ZIF-67 polyhedron;
carrying out high-temperature annealing treatment on the hollow ZIF-67 polyhedron, wherein the annealing temperature is 700-900 ℃, and obtaining the magnetic Co/NC with a hollow structure;
MnO with hierarchical structure is coated on the surface of the magnetic Co/NC with the hollow structure in situ by adopting a hydrothermal method 2 And (3) nano sheets to obtain the nano hollow heterogeneous double-shell structure electromagnetic wave absorbing material.
5. The preparation method of the ZIF-67 polyhedron according to claim 4, wherein the preparation method comprises the following steps: dissolving cobalt nitrate in methanol, and uniformly stirring to obtain a mixed solution A; dissolving 2-methylimidazole in methanol, and uniformly stirring to obtain a mixed solution B; pouring the mixed solution B into the mixed solution A, stirring, centrifuging and drying to obtain the ZIF-67 polyhedron.
6. The method according to claim 5, wherein the nitrate of cobalt is Co (NO 3 ) 2 ·6H 2 O, the Co (NO) 3 ) 2 ·6H 2 The molar ratio of O to 2-methylimidazole was 1:4.
7. The method according to claim 4, wherein the etching-protecting process is as follows: dissolving the ZIF-67 polyhedron in methanol, adding a tannic acid aqueous solution, and stirring for 8-12 min, wherein the mass ratio of tannic acid to the ZIF-67 polyhedron is 1:0.6 to 3.
8. The method according to claim 7, wherein the volume ratio of the methanol to the aqueous tannic acid solution in the specific etching-protecting process is 20-25: 180-200, wherein the concentration of the tannic acid aqueous solution is 0.5-2mg/mL.
9. The method according to claim 4, wherein the high-temperature annealing treatment is performed under Ar gas protection, and the temperature is raised from room temperature to 700 to 900 ℃ at a heating rate of 1 to 5 ℃/min, and the annealing time is 1 to 3 h.
10. The preparation method according to claim 4, wherein the hydrothermal method specifically comprises: dissolving the magnetic Co/NC with a hollow structure in deionized water to form a solution with the concentration of 0.5-3.0 mg/mL, and then adding KMnO 4 After being stirred uniformly, the mixture is subjected to hydrothermal reaction, and the magnetic Co/NC and KMnO with the hollow structure 4 The mass ratio of (2) is 1:1.7-5.4; the hydrothermal reaction temperature is 140-180 ℃, and the reaction is carried outThe reaction time is 10-14 h.
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