CN111117265A - Core-shell structure composite microwave absorbing material - Google Patents
Core-shell structure composite microwave absorbing material Download PDFInfo
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Abstract
The invention discloses a preparation method of a MOF-derived core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material, and relates to a preparation method of a composite wave absorbing material. The invention provides a method for preparing a core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite wave-absorbing material by taking HKUST-1 as a template, aiming at solving the problems of complex preparation method, severe preparation conditions, high cost, large material density and poor low-frequency-band absorption performance of the existing composite wave-absorbing material. The microwave absorbing material prepared by the invention has the advantages of small density, light weight, good low-frequency absorption effect, wide effective absorption bandwidth, good physical and chemical properties and machining performance, simple preparation process and low cost, and is suitable for large-scale batch production.
Description
Technical Field
The invention relates to a microwave absorption material technology, in particular to a MOF-derived core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorption material.
Background
The wide use of electromagnetic waves has greatly promoted the development of the human society and also brought about various problems. The electromagnetic wave pollution not only causes adverse effects on the health of human bodies but also interferes with the normal work of electronic equipment, and meanwhile, in the field of military industry, the electromagnetic stealth capability of weapon equipment can greatly improve the fighting capability of the weapon equipment, so that the weapon equipment becomes the development trend of the equipment. Therefore, the microwave absorbing material has wide application prospect, and the existing wave absorbing material is developing towards the direction of thin coating thickness, light weight, wide absorption bandwidth and strong low-frequency-band absorption. The carbon-based material has excellent physicochemical properties such as light weight, good stability and the like, and is expected to become an excellent wave-absorbing material.
Chinese patent 'La-Ce binary doped barium ferrite wave-absorbing material and preparation method' (publication number: CN 110511013A) provides a preparation method of rare earth doped barium ferrite wave-absorbing material, a sol is prepared by adopting a sol-gel method and taking iron salt, barium salt, rare earth salt and citric acid as raw materials, and the La-Ce binary doped barium ferrite wave-absorbing material is obtained by drying wet sol and then pyrolyzing the dried wet sol at high temperature in a muffle furnace. The maximum reflection loss of the wave-absorbing material prepared by the method is only about-8 dB, and the material has high density and is difficult to be practically applied. Chinese patent 'a porous carbon-based electromagnetic wave absorber and a preparation method thereof' (publication number: CN 108521754A) provides a preparation method of a carbon material with a two-dimensional sheet structure, and a solvothermal method is adopted to synthesize a bimetallic MOF precursor Fe by taking iron salt and nickel salt as metal ions and terephthalic acid as an organic ligand2And carrying out acid cleaning treatment on the precursor after pyrolysis in an inert gas atmosphere to obtain the material with the two-dimensional sheet structure, wherein the carbon material obtained by the method has light weight, wide absorption band and weak absorption capacity, and particularly has poor microwave absorption performance in a low frequency band. The institute of aerospace and aviation, Nanjing, was bred and studied to teach the subject group to use waterA thermal solvothermal method is characterized in that titanium-based MOF MIL-125(Ti) is synthesized by taking isopropyl titanate and terephthalic acid as raw materials, and then the titanium-based MOF MIL-125(Ti) is subjected to high-temperature pyrolysis by taking the isopropyl titanate and the terephthalic acid as precursors to obtain a Ti/C composite wave-absorbing material which is good in microwave absorption capacity and wide in absorption bandwidth, but poor in low-frequency-band absorption performance (J.N. Ma, W.Liu, X.H. Liang, et. al. Nanoporus TiO)2C compositions synthesized from directed gasification of Ti-based MOFs MIL-125(Ti) for impact microwave absorption Journal of Alloys and Compounds 728 (2017) 138- "144). The existing wave-absorbing material has improvements in absorption strength, effective wave-absorbing frequency bandwidth, density, thickness, performance stability and the like, but still has some problems to be solved: 1. the absorption strength and the effective absorption bandwidth still need to be improved; 2. the low frequency band (2-6 GHz) has poor wave-absorbing performance; 3. the relationship between the wave-absorbing properties and the microstructure of the material is still unclear.
The preparation method comprises the steps of preparing HKUST-1 by a solvothermal method, pyrolyzing the prepared HKUST-1 in nitrogen by using the HKUST-1 as a template to obtain a carbon-based material, removing metal in the carbon-based material, and carrying out in-situ polymerization on the carbon-based material and chiral poly-Schiff base ferric salt to obtain the core-shell structure nano porous carbon @ chiral poly-Schiff base ferric salt composite microwave absorbing material. The optimal mass ratio of the nano porous carbon to the chiral poly-Schiff base ferric salt is regulated and controlled by changing the preparation conditions of the nano porous carbon and the chiral poly-Schiff base ferric salt, so that the nano porous carbon @ chiral poly-Schiff base ferric salt microwave absorbing material with excellent wave absorbing performance is obtained. Compared with the granted patent, the process is simple, the cost is low, the stability and the processability of the material are excellent, the weight is light, and the absorption strength, the absorption bandwidth and the absorption effect of a low frequency band are obviously improved. When the thickness is 1.65mm and the mass ratio of the nano porous carbon to the chiral poly Schiff base ferric salt is 4-20:1, excellent wave-absorbing performance is shown, and the effective absorption bandwidth is more than 4 GHz. When the mass ratio of the nano porous carbon to the chiral poly Schiff base ferric salt is 10:1, the strongest reflection loss RL can reach-46.9 dB and the maximum effective absorption bandwidth can reach 5.6GHz when the thickness is 1.9 mm. When the mass ratio of the nano porous carbon to the chiral poly-Schiff base ferric salt is 15:1, the absorption performance at a low frequency band is excellent when the thickness is 5.49mm, the maximum reflection loss of-60.8 dB is obtained at 3.89GHz, and the performance is more excellent than that of the existing nano porous carbon and Schiff base wave-absorbing material.
Disclosure of Invention
The invention discloses a synthesis method of a core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material derived from MOF (metal organic framework), aiming at the problems of high density, narrow effective absorption band width, poor low-frequency-band absorption and the like of the existing wave absorbing material, and further tests the microwave absorption performance of the composite material, so that the defects of high density, narrow effective absorption band width, poor processing performance, easiness in oxidation and the like of the traditional wave absorbing material are overcome.
The object of the invention is thus achieved. A core-shell structure composite microwave absorbing material is prepared by the following steps:
1) preparation of HKUST-1:
1.8mmol of Cu (NO)3)2·3H2Dissolving O and 1.0mmol of trimesic acid in 12ml of mixed solution of ethanol/water, wherein the volume ratio of ethanol to water in the mixed solution is 1:1, transferring the mixed solution into a reaction kettle, reacting for 15-20h at the temperature of 120-130 ℃, centrifuging the obtained product, washing for 3 times by using deionized water and ethanol, and drying at the temperature of 40-80 ℃ to obtain HKUST-1;
2) preparing nano porous carbon:
pre-prepared HKUST-1 was added to N2Pyrolyzing at the heating rate of 2 ℃/min for 2h at 700 ℃ to obtain copper/nano porous carbon, stirring the copper/nano porous carbon in HF with the concentration of 15-30% for 8-12h, and washing away copper in the copper to obtain the nano porous carbon;
3) preparation of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly schiff base:
taking a 100ml flask, adding 10mmol of ferrocenecarboxaldehyde, 5mmol of (R, R) -1, 2-cyclohexanediamine and 30ml of ethanol, stirring for dissolving, heating to 50-70 ℃, refluxing for 6-8h, filtering, and drying at 40-60 ℃ to obtain yellow (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene-reduced Schiff base;
5mmol of anhydrous AlCl32mmol of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene Schiff base and 2mmol of adipoyl chloride are respectively dissolved in 45ml of chloroform, and 100ml of calcined potassium chloride is added after the dissolutionHeating to 60-70 deg.C in a bottle, stirring and refluxing for 15-20h, filtering after reaction, washing the obtained product with water and ethanol, and drying at 40-60 deg.C to obtain black (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base;
4) preparing a nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material:
0.1g of pre-prepared nanoporous carbon is dispersed in DMF, 0.05-0.1g of PVP is added as a surfactant, magnetic stirring is carried out at 60 ℃ for 0.5-1h, then a corresponding amount of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base is added, and stirring is continued for 1-2h, wherein the mass ratio of the nanoporous carbon to the (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base is 4-20: 1. Then adding the corresponding amount of FeSO4·7H2O aqueous solution of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base and FeSO4·7H2The mass ratio of O is 2-3: 1; stirring all mixed solutions at 100 ℃ to react for 6-8h, filtering after the reaction is finished, washing the obtained solid with water and ethanol for several times, and drying at 50 ℃ to obtain the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material; mixing the prepared nano porous carbon @ chiral poly Schiff base iron salt with a paraffin base according to the mass ratio of 1: 1-1.5.
Further, the thickness of the core-shell structure nanoporous carbon @ chiral poly-schiff base ferric salt composite microwave absorbing material in the step 4) is 1.5-5.5 mm.
Further, in the step 4), the mass ratio of the nano porous carbon in the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material to the chiral poly Schiff base ferric salt is 4-20: 1.
Further, the mass ratio of the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material to the paraffin base in the step 4) is 1: 1-1.5.
The microwave absorbing material with excellent performance is prepared by in-situ polymerization of the chiral poly-Schiff base on the surface of the nano porous carbon, has the advantages of simple process, low cost, excellent stability and processability of the material, light weight, excellent absorption strength, effective absorption bandwidth, low-frequency-band absorption effect and the like, and has strong practical value in the aspects of electromagnetic shielding, stealth materials and the like.
Drawings
FIG. 1 is a diffraction pattern of X-rays of powders of chiral poly-Schiff base ferric salt, nanoporous carbon and examples 1,2, 3, 4 and 5 in the present invention;
FIG. 2 is a scanning electron microscope photograph of a sample of example 2 of the present invention;
FIG. 3 is a scanning electron microscope photograph of a sample of example 3 of the present invention;
FIG. 4 is a transmission electron microscope image of the core-shell structure nanoporous carbon @ chiral poly-Schiff base ferric salt composite wave-absorbing material prepared in example 4 of the invention;
FIG. 5 is a transmission electron microscope image of the core-shell structure nanoporous carbon @ chiral poly-Schiff base ferric salt composite wave-absorbing material prepared in example 5 of the invention;
FIG. 6 is a reflection loss map of core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating simulation calculation prepared in example 1 of the present invention;
FIG. 7 is a reflection loss map of core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating simulation calculation prepared in example 2 of the present invention;
FIG. 8 is a reflection loss map of core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating simulation calculation prepared in example 3 of the present invention;
FIG. 9 is a reflection loss map of core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating simulation calculation prepared in example 4 of the present invention;
fig. 10 is a reflection loss spectrum of core-shell structure nanoporous carbon @ chiral poly-schiff base iron salt coating simulation calculation prepared in example 5 of the present invention.
Detailed Description
The invention is further illustrated by the following figures and examples.
Example 1: the invention has the following specific implementation steps:
the method comprises the following steps: preparation of HKUST-1:
adding 1.8mmol Cu (NO)3)2·3H2Dissolving O and 1.0mmol of trimesic acid in 12ml of mixed solution of ethanol and water (the volume of the ethanol and the water is 1: 1), transferring the mixed solution into a reaction kettle, reacting for 15h at 120 ℃, centrifuging the obtained product, washing with deionized water and ethanol for several times, and drying at 40 ℃ to obtain HKUST-1;
step two: preparing nano porous carbon:
pre-prepared HKUST-1 was added to N2Pyrolyzing at the heating rate of 2 ℃/min for 2h at 700 ℃ to obtain copper/nano porous carbon, stirring the copper/nano porous carbon in HF with the concentration of 15% for 8h, and washing away copper in the copper to obtain the nano porous carbon;
step three: preparation of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly schiff base:
taking a 100ml flask, adding 10mmol of ferrocenecarboxaldehyde, 5mmol of (R, R) -1, 2-cyclohexanediamine and 30ml of ethanol, stirring for dissolving, heating to 50 ℃, refluxing for 6h, filtering, and drying at 40 ℃ to obtain yellow (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene-reduced Schiff base.
5mmol of anhydrous AlCl3Respectively dissolving 2mmol of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene Schiff base and 2mmol of adipoyl chloride in 45ml of chloroform, adding the obtained solution into a 100ml flask after dissolving, heating to 60 ℃, stirring and refluxing for 15h, filtering after the reaction is finished, washing the obtained product with water and ethanol for several times, and drying at 40-60 ℃ to obtain black (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base.
Step four: preparing a nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material:
0.1g of pre-prepared nano porous carbon is dispersed in DMF, 0.05g of PVP is added to be used as a surfactant, magnetic stirring is carried out at 60 ℃ for 0.5h, then a corresponding amount of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base is added, and stirring is continued for 1h, wherein the mass ratio of the nano porous carbon to the (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base is 20: 1. Then adding the corresponding amount of FeSO4·7H2O aqueous solution of (1R,2R)) - (-) -1, 2-cyclohexanediamineferrocarbaldehyde poly-schiff base and FeSO4·7H2The mass ratio of O is 3: 1. All the mixed solutions are stirred and reacted for 6 hours at the temperature of 100 ℃, after the reaction is finished, the mixed solutions are filtered, the obtained solid is washed for a plurality of times by water and ethanol, and then the solid is dried at the temperature of 50 ℃ to obtain the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material. And fully mixing the prepared nano porous carbon @ chiral poly Schiff base iron salt and a paraffin base according to the mass ratio of 1:1.
The electromagnetic parameters of the material are measured by a vector network analyzer, and according to the transmission line theory, the reflection loss of the material to electromagnetic waves is calculated by the complex dielectric constant and the complex permeability under given frequency and the thickness of the wave-absorbing material through the following equation.
Example 2: the present embodiment differs from embodiment 1 in that: the reaction temperature for preparing the HKUST-1 in the step one is 125 ℃, the reaction time is 16h, and the drying temperature is 50 ℃. In the second step, the concentration of HF is 20%, and the stirring time is 9 h. The reaction temperature for preparing the Schiff base in the third step is 55 ℃, the reaction time is 6.5h, the drying temperature is 45 ℃, the addition amount of PVP in the fourth step is 0.06g, the stirring time is 0.6h, the stirring time is 1.5h after the poly-Schiff base is added, the mass ratio of the nano porous carbon to the chiral poly-Schiff base ferric salt is 15:1, and the poly-Schiff base and FeSO are mixed4·7H2The mass ratio of O is 2.5:1, the reaction time is 6.5h, and the mass ratio of the composite material to the paraffin base is 1: 1.1. The rest is the same as in embodiment 1.
Example 3: the present embodiment differs from embodiment 1 in that: the reaction temperature for preparing the HKUST-1 in the step one is 125 ℃, the reaction time is 17h, and the drying temperature is 60 ℃. In the second step, the concentration of HF is 25%, and the stirring time is 10 h. The reaction temperature for preparing the Schiff base in the third step is 60 ℃, the reaction time is 7h, the drying temperature is 50 ℃, the addition amount of PVP in the fourth step is 0.07g, the stirring time is 0.7h, the stirring time is 1.5h after the poly-Schiff base is added, and the nano porous carbon and the chiral poly-Schiff base iron are mixedThe mass ratio of the salt is 10:1, and the poly Schiff base to the FeSO4·7H2The mass ratio of O is 2.5:1, the reaction time is 7h, and the mass ratio of the composite material to the paraffin base is 1: 1.2. The rest is the same as in embodiment 1.
Example 4: the present embodiment differs from embodiment 1 in that: the reaction temperature for preparing the HKUST-1 in the step one is 125 ℃, the reaction time is 18h, and the drying temperature is 70 ℃. In the second step, the concentration of HF is 25%, and the stirring time is 11 h. The reaction temperature for preparing the Schiff base in the third step is 65 ℃, the reaction time is 7.5h, the drying temperature is 55 ℃, the addition amount of PVP in the fourth step is 0.08g, the stirring time is 0.8h, the stirring time is 1.5h after the poly-Schiff base is added, the mass ratio of the nano porous carbon to the chiral poly-Schiff base ferric salt is 5:1, and the poly-Schiff base and FeSO are added4·7H2The mass ratio of O is 2.5:1, the reaction time is 7.5h, and the mass ratio of the composite material to the paraffin base is 1: 1.3. The rest is the same as in embodiment 1.
Example 5: the present embodiment differs from embodiment 1 in that: the reaction temperature for preparing the HKUST-1 in the step one is 130 ℃, the reaction time is 20h, and the drying temperature is 80 ℃. In the second step, the concentration of HF is 30%, and the stirring time is 12 h. The reaction temperature for preparing the Schiff base in the third step is 70 ℃, the reaction time is 8 hours, the drying temperature is 60 ℃, the addition amount of PVP in the fourth step is 0.1g, the stirring time is 1 hour, the stirring time is 2 hours after the poly-Schiff base is added, the mass ratio of the nano porous carbon to the chiral poly-Schiff base ferric salt is 4:1, and the poly-Schiff base and FeSO are added4·7H2The mass ratio of O is 2:1, the reaction time is 8h, and the mass ratio of the composite material to the paraffin base is 1: 1.5. The rest is the same as in embodiment 1.
Fig. 1 is a diffraction pattern of X-ray powder of chiral poly-schiff base iron salt, nano porous carbon and the powder of example 1, example 2, example 3, example 4 and example 5, and it can be seen from the figure that the purity of the sample is high in five examples, the diffraction peak is mainly from the residual copper in the nano porous carbon, and the diffraction peak is weak in five examples because the content of the chiral poly-schiff base iron salt is small.
Fig. 2 is a scanning electron microscope image of the sample of example 2, from which it can be seen that the surface of the nanoporous carbon is roughened and the chiral poly-schiff base iron salt is coated on the surface.
FIG. 3 is a scanning electron microscope image of the sample of example 3, from which it can be seen that the surface of the nanoporous carbon is roughened and the chiral poly-Schiff base iron salt is coated on the surface.
Fig. 4 is a transmission electron microscope image of the core-shell structure nanoporous carbon @ chiral poly-schiff base iron salt composite wave-absorbing material prepared in example 4, from which it can be seen that the surface of the nanoporous carbon is uniformly coated with semitransparent chiral poly-schiff base iron salt, and the core-shell structure of the material is clear and visible.
Fig. 5 is a transmission electron microscope image of the core-shell structure nanoporous carbon @ chiral poly-schiff base iron salt composite wave-absorbing material prepared in example 5, from which it can be seen that the surface of the nanoporous carbon is uniformly coated with semitransparent chiral poly-schiff base iron salt, and the core-shell structure of the material is clear and visible.
FIG. 6 is a graph of reflection loss calculated by simulation of the core-shell structure nanoporous carbon @ chiral poly-Schiff base ferric salt coating prepared in example 1, and different reflection losses of the simulated thickness from 1.5mm to 5.5mm are calculated. It can be seen from the figure that the material has certain wave absorbing capability under different thicknesses, wherein the effective absorption bandwidth can reach 4.6GHz when the thickness is 1.5mm, and the maximum reflection loss of-34.8 dB can reach 11.54GHz when the thickness is 1.9 mm.
Fig. 7 is a graph of reflection loss calculated by simulation of the core-shell structure nanoporous carbon @ chiral poly-schiff base ferric salt coating prepared in example 2, and different reflection losses of the simulated thickness from 1.5mm to 5.5mm are calculated. It can be seen from the figure that the material has excellent wave absorbing capability under different thicknesses, and the reflection loss is less than-20 dB under all thicknesses, wherein the effective absorption bandwidth can reach 5.6GHz when the thickness is 1.65mm, and the maximum reflection loss reaches-60.9 dB at a low frequency band of 3.89GHz when the thickness is 5.49 mm.
Fig. 8 is a graph of reflection loss calculated by simulation of the core-shell structure nanoporous carbon @ chiral poly-schiff base ferric salt coating prepared in example 3, and different reflection losses of the simulated thickness from 1.5mm to 5.5mm are calculated. It can be seen from the figure that the material has excellent wave absorbing capability under different thicknesses, wherein the effective absorption bandwidth can reach 4.01GHz when the thickness is 1.9mm, and the maximum reflection loss reaches-46.9 dB at 11.37 GHz.
FIG. 9 is a graph of the simulated reflection loss of the core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating prepared in example 4, and the different reflection losses of the simulated thickness from 1.5mm to 5.5mm are calculated. It can be seen from the figure that the material has excellent wave absorbing capability under different thicknesses, wherein the effective absorption bandwidth can reach 4.08GHz when the thickness is 1.65mm, and the maximum reflection loss reaches-36.5 dB at the low frequency band of 11.2GHz when the thickness is 2.0 mm.
FIG. 10 is a graph of the simulated reflection loss of the core-shell structure nanoporous carbon @ chiral poly-Schiff base iron salt coating prepared in example 5, and the different reflection losses of the simulated thickness from 1.5mm to 5.5mm are calculated. It can be seen from the figure that the material has excellent wave absorbing capability under different thicknesses, wherein the maximum reflection loss can reach-24.02 GHz when the thickness is 2.0mm, and the maximum reflection loss reaches-28.11 dB at the low frequency band of 4.06GHz when the thickness is 5.5 mm.
According to the invention, the MOF derivative nano porous carbon @ chiral poly-Schiff base iron salt composite wave-absorbing material with a core-shell structure is obtained by designing chemical components and controlling the mass ratio of the nano porous carbon to the chiral poly-Schiff base iron salt. The large specific surface area of the nano porous carbon is utilized to increase the reflection inside the electromagnetic wave and enhance the absorption of the electromagnetic wave, a large number of core-shell interfaces of the porous carbon and the chiral poly Schiff base ferric salt enhance the interface polarization loss, the cross polarization generated by the chiral characteristics enhances the dielectric loss, and the wave absorbing performance of the 2-18GHz frequency band is enhanced under the combined action of the multi-loss mechanisms. When the thickness of the MOF derivative nanoporous carbon/chiral poly Schiff base ferric salt composite material is 1.9mm, the strongest reflection loss RL can reach-46.9 dB, and the maximum effective absorption bandwidth can reach 5.6 GHz. The thickness of 5.49mm is excellent in the absorption performance at a low frequency band, and the maximum reflection loss of-60.8 dB is obtained at 3.89 GHz. The absorption bandwidth of the MOF derivative nanoporous carbon/chiral poly Schiff base ferric salt composite material is superior to that of most of the existing carbon-based composite materials, and the MOF derivative nanoporous carbon/chiral poly Schiff base ferric salt composite material is expected to have a good application background in the field of electromagnetic wave absorption of a 1-18GHz frequency band.
The composite microwave absorbing material with the core-shell structure is a novel light wave absorbing material. The material is prepared by in-situ polymerization of chiral poly-Schiff base on the surface of nano porous carbon, has the advantages of simple process, low cost, excellent stability and processability of the material, light weight, excellent absorption strength, effective absorption bandwidth, low-frequency-band absorption effect and the like, and has strong practical value in the aspects of electromagnetic shielding, stealth materials and the like. The poly Schiff base salt belongs to chiral high molecular polymer, has small density, is easy to be hot-pressed and formed, and can widen the effective absorption bandwidth due to the chiral characteristic. The nano porous carbon has the advantages of low density, stable performance and strong loss capability to electromagnetic waves. The composite wave-absorbing material can realize electromagnetic impedance matching by adjusting the proportion, and obtains excellent wave-absorbing effect through the synergistic interaction of the chiral poly-Schiff base ferric salt and the nano porous carbon and the polarization of the core-shell interface.
Claims (4)
1. The core-shell structure composite microwave absorbing material is characterized by comprising the following preparation steps:
1) preparation of HKUST-1:
1.8mmol of Cu (NO)3)2·3H2Dissolving O and 1.0mmol of trimesic acid in 12ml of mixed solution of ethanol/water, wherein the volume ratio of ethanol to water in the mixed solution is 1:1, transferring the mixed solution into a reaction kettle, reacting for 15-20h at the temperature of 120-130 ℃, centrifuging the obtained product, washing for 3 times by using deionized water and ethanol, and drying at the temperature of 40-80 ℃ to obtain HKUST-1;
2) preparing nano porous carbon:
pre-prepared HKUST-1 was added to N2Pyrolyzing at the heating rate of 2 ℃/m for 2h at 700 ℃ to obtain copper/nano porous carbon, stirring the copper/nano porous carbon in HF with the concentration of 15-30% for 8-12h, and washing away copper in the copper to obtain the nano porous carbon;
3) preparation of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly schiff base:
taking a 100ml flask, adding 10mmol of ferrocenecarboxaldehyde, 5mmol of (R, R) -1, 2-cyclohexanediamine and 30ml of ethanol, stirring for dissolving, heating to 50-70 ℃, refluxing for 6-8h, filtering, and drying at 40-60 ℃ to obtain yellow (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene-reduced Schiff base;
5mmol of anhydrous AlCl3Respectively dissolving 2mmol of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene Schiff base and 2mmol of adipoyl chloride in 45ml of chloroform, adding the obtained solution into a 100ml flask after dissolving, heating to 60-70 ℃, stirring and refluxing for 15-20h, filtering after the reaction is finished, washing the obtained product with water and ethanol, and drying at 40-60 ℃ to obtain black (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base;
4) preparing a nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material:
dispersing 0.1g of pre-prepared nano porous carbon into DMF, adding 0.05-0.1g of PVP as a surfactant, magnetically stirring at 60 ℃ for 0.5-1h, adding a corresponding amount of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly-Schiff base, and continuously stirring for 1-2h, wherein the mass ratio of the nano porous carbon to the (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly-Schiff base is 4-20: 1; then adding the corresponding amount of FeSO4·7H2O aqueous solution of (1R,2R) - (-) -1, 2-cyclohexanediamine ferrocene carboxaldehyde poly Schiff base and FeSO4·7H2The mass ratio of O is 2-3: 1; stirring all mixed solutions at 100 ℃ to react for 6-8h, filtering after the reaction is finished, washing the obtained solid with water and ethanol for several times, and drying at 50 ℃ to obtain the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material; mixing the prepared nano porous carbon @ chiral poly Schiff base iron salt with a paraffin base according to the mass ratio of 1: 1-1.5.
2. The core-shell structure composite microwave absorbing material according to claim 1, characterized in that: the thickness of the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material in the step 4) is 1.5-5.5 mm.
3. The core-shell structure composite microwave absorbing material according to claim 1, characterized in that: the mass ratio of the nano porous carbon in the core-shell structure nano porous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material in the step 4) to the chiral poly Schiff base ferric salt is 4-20: 1.
4. The core-shell structure composite microwave absorbing material according to claim 1, characterized in that: the mass ratio of the core-shell structure nanoporous carbon @ chiral poly Schiff base ferric salt composite microwave absorbing material to the paraffin base in the step 4) is 1: 1-1.5.
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