CN112430451A - Nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material and preparation method thereof - Google Patents
Nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material and a preparation method thereof. Firstly, ferric chloride hexahydrate, zinc chloride and cobalt chloride hexahydrate are used as metal sources, ethylene glycol is used as a solvent, cobalt-zinc ferrite particles are prepared through a solvothermal method, and then Graphene Oxide (GO) is used as a template, ethylenediamine is used as a nitrogen doping reagent, and the nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel material is prepared through a hydrothermal method. The method is simple to operate, green and environment-friendly, and has no generation of any toxic and harmful substances. The prepared composite aerogel material has strong electromagnetic wave absorption capacity, wide absorption frequency band, low filling ratio and thin matching thickness; can realize the effective absorption of electromagnetic waves of different wave bands by adjusting the nitrogen doping amount of the composite aerogel and the thickness of the wave absorbent, and has important application value in the fields of electromagnetic absorption and electromagnetic shielding.
Description
Technical Field
The invention belongs to the technical field of electromagnetic composite materials, and relates to a nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material and a preparation method thereof.
Background
Since electronic devices are widely used, electromagnetic wave pollution causes serious environmental problems, so that electromagnetic wave absorbing materials become a research hotspot in the field of functional materials. Electromagnetic wave absorbing materials are materials that absorb, attenuate, and convert electromagnetic energy into heat or other forms of energy that are dissipated or that cause the electromagnetic waves to disappear by interference. Conventional electromagnetic wave absorbing materials, such as ferrite, metal powder, silicon carbide, etc., generally have the disadvantages of narrow absorption bandwidth and high density, thus limiting their application in the field of electromagnetic wave absorption. The ideal electromagnetic wave absorbing material generally needs to meet the requirements of thin thickness, light weight, wide absorption frequency band, strong absorption performance and the like.
Graphene (RGO) is a novel two-dimensional carbon nanomaterial, which is generally prepared from natural graphite by a chemical oxidation-reduction method. RGO has good application prospect in the field of electromagnetic wave absorption materials due to the characteristics of unique two-dimensional layered structure, good chemical stability, excellent dielectric loss capacity, ultralow density and the like. However, the single RGO has impedance mismatch and poor electromagnetic wave absorption capability, so that the application of RGO material in the field of electromagnetic wave absorption is limited and it is difficult to meet the requirement of commercial application (reflection loss value is lower than-10 dB). By substituting carbon atoms in the RGO lattice with nitrogen atoms using a nitrogen-doping agent (ethylenediamine), nitrogen atoms as well as defects are introduced, dipole polarization and defect polarization are generated, thereby enhancing electromagnetic wave absorption capability.
The three-dimensional (3D) RGO aerogel is used as a potential high-performance light electromagnetic wave absorption material due to the advantages of a unique three-dimensional network structure, extremely high specific surface area, ultralow density and the like.
Cobalt zinc ferrite (Co)0.5Zn0.5Fe2O4) The ferrite is a magnetic metal oxide with excellent performance, has the characteristics of good chemical stability, thermal stability, ferromagnetism and the like, but has the defects of unmatched single ferrite impedance, weak electromagnetic wave absorption capacity and high density, and limits Co to a certain extent0.5Zn0.5Fe2O4The application in the wave absorbing field.
According to electromagnetic theory, a material with excellent microwave absorption properties generally needs to satisfy two conditions: good impedance matching and strong electromagnetic attenuation. Therefore, the combination of dielectric loss RGO and magnetic materials (ferrite, magnetic metal, magnetic alloy, etc.) is expected to provide an electromagnetic wave absorbing material with light weight, high efficiency, thin thickness, and low filling ratio. By mixing Co0.5Zn0.5Fe2O4The composite aerogel material is expected to have dielectric loss and magnetic loss after being compounded with RGO, so that the impedance matching of the composite aerogel material is favorably adjusted, and the attenuation of incident electromagnetic waves is enhanced.
The invention is achieved by doping nitrogen with RGO and Co0.5Zn0.5Fe2O4Compounding, and preparing the nitrogen-doped graphene/cobalt zinc ferrite (NRGO/Co) by adopting a simple solvothermal-hydrothermal two-step method0.5Zn0.5Fe2O4) The composite aerogel wave-absorbing material changes the nitrogen content in RGO crystal lattices by controlling the adding volume of ethylenediamine in reactants, and regulates the matching thickness and the filling ratio of a sample to regulate and control the electromagnetic wave absorption capacity of the composite material.
Disclosure of Invention
Based on the problems of the background art, the invention provides NRGO/Co0.5Zn0.5Fe2O4The composite aerogel wave-absorbing material and the preparation method thereof have the advantages of strong absorption, controllable electromagnetic wave absorption frequency band, wide frequency and the like, and the preparation method is simple and environment-friendly.
In order to solve the technical problems, the technical scheme of the invention is as follows: the preparation method of the nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material comprises the steps of (1) preparing a three-dimensional porous network structure by winding cobalt-zinc ferrite microspheres with folded graphene; the preparation method comprises the following steps:
(1) taking 1 200mL beaker, adding 60mL ethylene glycol, then adding 1.08g ferric chloride hexahydrate, 0.24g cobalt chloride hexahydrate and 0.14g zinc chloride, and vigorously stirring to completely dissolve the materials;
(2) continuously adding a certain amount of 1.5g of polyethylene glycol into a200 mL beaker to obtain a first mixed dispersion liquid;
(3) transferring the first mixed dispersion liquid into a reaction kettle with the volume of 100mL, and carrying out thermal reaction for 8h at the temperature of 200 ℃ to obtain a product containing cobalt-zinc ferrite;
(4) after the reaction is finished, cooling to room temperature, carrying out magnetic separation on the product to obtain the hydrous cobalt-zinc ferrite, and washing the hydrous cobalt-zinc ferrite with deionized water for multiple times to enable the pH value of the hydrous cobalt-zinc ferrite to be neutral;
(5) pre-freezing the hydrous cobalt-zinc ferrite for 12h, transferring the hydrous cobalt-zinc ferrite into a freeze dryer, drying the hydrous cobalt-zinc ferrite at a low temperature for 24h, and grinding the hydrous cobalt-zinc ferrite to obtain pure cobalt-zinc ferrite;
(6) taking 3 100mL beakers, respectively adding 30mL deionized water into each beaker, and adding 90mg of graphite oxide while stirring to prepare graphene oxide aqueous dispersion;
(7) continuously adding 30mg of the cobalt-zinc ferrite obtained in the step (5) into each 100mL beaker, performing ultrasonic treatment for 30min, and stirring for 30min until the cobalt-zinc ferrite is uniformly dispersed;
(8) adding ethylenediamine with different volumes into each 100mL beaker, and stirring for 30min to obtain a second mixed dispersion, wherein the adding volumes of the ethylenediamine are 0, 250 and 350 μ L respectively;
(9) transferring the second mixed dispersion liquid into a reaction kettle with the volume of 50mL for hydrothermal reaction to obtain hydrogel;
(10) after the reaction is finished, cooling to room temperature, and dialyzing the obtained hydrogel to obtain an aerogel product;
(11) and pre-freezing the aerogel product for 12h, transferring to a freeze dryer, and drying at a low temperature for 48h to obtain the final aerogel product.
Further, the molar ratio of zinc ions, cobalt ions and iron ions in the step (1) is 1: 1: 4, adding a certain amount of 5.4g of sodium acetate, and stirring for 15min until the sodium acetate is completely dissolved.
Further, in the step (2), the polyethylene glycol must be stirred at 50 ℃ for 2 hours to dissolve the polyethylene glycol to obtain a first mixed dispersion.
Further, in the step (4), the lining of the reaction kettle of 100mL is taken out, and the upper layer liquid is removed, so that black precipitate at the bottom, namely the product containing the cobalt-zinc ferrite, is obtained.
Further, after graphite oxide is added in the step (6), ultrasonic treatment is carried out for 1 hour, stirring is carried out for 30min, and the graphite oxide sheet layer is peeled and dispersed in deionized water to form a uniform graphene oxide aqueous dispersion liquid with the concentration of 3 mg/mL.
Furthermore, in the step (7), magnetons need to be removed, and a mechanical stirring method is adopted, so that the cobalt-zinc ferrite is prevented from being adsorbed on the magnetons.
Furthermore, in the step (8), ethylenediamine is used as a nitrogen doping reagent, a reducing agent and alkali, and the nitrogen doping amount of the graphene is adjusted by adding ethylenediamine with different volumes, so that the electromagnetic parameters of the composite aerogel wave-absorbing material are regulated and controlled, and the wave-absorbing capacity of the composite aerogel wave-absorbing material is changed.
Further, the hydrothermal reaction in step (9) must be maintained at 120 ℃ for 12 hours.
Further, the dialysis in step (10) is performed for 36h using ethanol-water solution with volume fraction of 10 wt.%.
In order to solve the technical problems, the second technical scheme of the invention is as follows: the nitrogen-doped graphene/cobalt-zinc ferrite composite aerogel wave-absorbing material is prepared by the method.
For NRGO/Co0.5Zn0.5Fe2O4The composite aerogel is characterized by structure, appearance and performance by the following means:
x-ray diffraction (XRD) test: the crystal structure of the sample is characterized by adopting a LabX XRD-6000 type X-ray diffractometer, wherein X-rays are Cu-Ka rays,wavelength of 0.154nm, step size of 0.02 deg., light tube current of 36kV, current of 30mA, scanning angle of 10-80 deg., and scanning speed of 2 deg./min-1。
Scanning Electron Microscope (SEM) testing: the microstructure of the sample was characterized using a Hitachi-Su8020 scanning electron microscope. Adhering a small amount of sample on a sample seat by using conductive adhesive, blowing off redundant sample on the surface by using an ear washing ball, spraying gold, sampling and testing.
X-ray photoelectron spectroscopy (XPS) test: uniformly coating a small amount of sample on the surface of the aluminum foil stuck with the conductive adhesive, pressing into a thin sheet, shearing the thin sheet into a sample with a certain shape and size by using scissors, sticking the sample on a sample injection platform, and testing by adopting ESCALAB 250XI model XPS.
And (3) testing microwave absorption performance: the powder product and paraffin are pressed into coaxial samples with the outer diameter of 7.00mm, the inner diameter of 3.04mm and the thickness of about 2mm in a special die according to the mass ratio of 15 wt.%, an AV3629D vector network analyzer is used for testing the electromagnetic parameters of the coaxial samples, the wave absorbing performance is obtained through calculation, and the testing frequency is 2-18 GHz.
The wave absorbing action mechanism is as follows: NRGO/Co prepared by the application0.5Zn0.5Fe2O4The composite aerogel material has a unique three-dimensional porous network structure, not only can optimize impedance matching characteristics, but also can prolong a transmission path of electromagnetic waves entering the wave absorber, and enhance the attenuation loss of the electromagnetic waves. Oxygen-containing functional groups such as-COOH and-OH carried on the surface of RGO act as polarization centers, producing dipole polarization; in addition, structural defects on the RGO surface can further attenuate incident electromagnetic waves under the alternating electric field, and a large number of nitrogen atoms doped in RGO crystal lattices can destroy sp2Hybridization to generate disordered sites and sp3The defects are that because the electronegativity of C and N atoms is different, polarity is generated between C-N bonds, dipole polarization is generated under an alternating electric field, and the attenuation capability of the electromagnetic wave is enhanced. Introduction of Co0.5Zn0.5Fe2O4The impedance matching of the composite material can be regulated and controlled, and the magnetic loss capacity of the composite material is enhanced; furthermore, the homogeneous loading of Co on the wrinkled RGO surface0.5Zn0.5Fe2O4The microspheres can generate rich heterogeneous interfaces to form a capacitance-shaped junctionThe structure can convert incident electromagnetic waves into other forms of energy dissipation through electric charges generated by polar bonds or alternating electric fields. According to a micro current network and an electron transition model, electrons can absorb electromagnetic wave energy, can migrate and transition in an aerogel three-dimensional network structure in an alternating electric field, generate conductance loss, and convert the electromagnetic wave energy into heat energy.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention adopts a two-step method to prepare NRGO/Co0.5Zn0.5Fe2O4The composite aerogel wave-absorbing material is simple in preparation method, easily available in raw materials, free of any toxic and harmful substance, green and environment-friendly, free of any inert gas protection, and capable of controlling the nitrogen doping amount of the composite aerogel by changing the adding volume of ethylenediamine in the preparation process by taking ethylenediamine as a nitrogen doping reagent, so that the electromagnetic parameters of the composite aerogel wave-absorbing material are regulated and controlled, and the electromagnetic wave absorption performance is optimized.
2. NRGO/Co prepared by the invention0.5Zn0.5Fe2O4The composite aerogel wave-absorbing material has a unique three-dimensional porous network structure and ultralow density (respectively 0.0146, 0.0131 and 0.0121g cm)3About 11.3 to 9.3 times the air density).
3. NRGO/Co prepared by the invention0.5Zn0.5Fe2O4The composite aerogel material has excellent wave-absorbing performance, has the characteristics of strong absorption, wide frequency band, low filling ratio, low matching thickness and the like, has the effective wave-absorbing width of 5.0GHz (the reflection loss is less than-10 dB and the effective absorption is more than 90%) when the thickness is 1.6mm, and has the minimum reflection loss of-66.8 dB (the effective absorption is more than 99.9999%) when the thickness is 2.6 mm; the effective absorption of electromagnetic waves of different wave bands can be realized by adjusting the nitrogen doping amount of the composite aerogel and the thickness of the wave absorbent.
4. NRGO/Co prepared by the invention0.5Zn0.5Fe2O4The composite aerogel material can realize multiband compatible absorption: when the thickness is more than 4.5mm, the composite aerogel can be absorbed in the S and Ku wave bands; when the thickness is between 3.5 mm and 4.5mm, the composite aerogel has C andku band double absorption characteristic.
5. NRGO/Co prepared by the invention0.5Zn0.5Fe2O4The composite aerogel wave-absorbing material can effectively enhance the absorption capacity of the composite aerogel on electromagnetic waves by combining the synergistic effect of dielectric loss, conductance loss and magnetic loss through a multiple polarization mechanism (interface polarization, defect polarization, dipole polarization and the like).
In order to make the aforementioned and other objects, features and advantages of the invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
FIG. 1 is an XRD spectrum of the product of examples 1, 2 and 3 of the present invention.
FIG. 2 is an SEM photograph of product S1 of example 1 of the present invention.
FIG. 3 is a histogram of the particle size distribution of the product S1 in example 1 of the present invention.
FIG. 4 is an SEM photograph of product S2 of example 2 of the present invention.
FIG. 5 is a histogram of the particle size distribution of the product S2 in example 2 of the present invention.
FIG. 6 is an SEM photograph of product S3 of example 3 of the present invention.
FIG. 7 is a histogram of the particle size distribution of product S3 in example 3 of the present invention.
FIG. 8 is a plot of reflection loss versus frequency for a product S1 fill ratio of 15 wt.% in example 1 of the present invention.
FIG. 9 is a plot of reflection loss versus frequency for a product S2 fill ratio of 15 wt.% in example 2 of the present invention.
FIG. 10 is a plot of reflection loss versus frequency for a product S3 fill ratio of 15 wt.% in example 3 of the invention.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, structures, features and effects according to the present invention will be made with reference to the accompanying drawings and preferred embodiments.
The raw material sources are as follows: graphite oxide purchasing deviceObtained from Suzhou carbon rich graphene science and technology Co., Ltd, ferric chloride hexahydrate, zinc chloride, anhydrous sodium acetate, ethylene glycol, polyethylene glycol (PEG, Mw 6000 g. mol.)-1) Ethylenediamine, ammonia water and absolute ethyl alcohol were purchased from hadamard, all reagents were analytically pure and no further purification was required.
The instrument equipment comprises: JA2003N electronic balance, shanghai precision scientific instruments ltd; XD-1800D ultrasonic cleaner, Inc., of the firm International (hong Kong) group.
Example 1
(1) 1 200mL beaker was taken, 60mL ethylene glycol was added, followed by 1.08g (4mmol) of ferric chloride hexahydrate (FeCl)3·6H2O), 0.24g (1mmol) of cobalt chloride hexahydrate (CoCl)2·6H2O) and 0.14g (1mmol) of zinc chloride (ZnCl)2) Stirring vigorously to dissolve completely, wherein zinc ion (Zn) is added2+) Cobalt ion (Co)2+) And iron ion (Fe)3+) In a molar ratio of 1: 1: 4, then adding a certain amount of 5.4g of sodium acetate, stirring for 15min until the sodium acetate is completely dissolved, and adding the sodium acetate as an electrostatic stabilizer;
(2) adding a certain amount of polyethylene glycol (PEG) of 1.5g, and stirring for 2h at 50 ℃ to dissolve the PEG to obtain a first mixed dispersion liquid; PEG as a high molecular stabilizer must be stirred for 2 hours for dissolution under the condition of 50 ℃ water bath, otherwise, the PEG is difficult to dissolve to form uniform dispersion liquid;
(3) transferring the first mixed dispersion liquid into a reaction kettle with the volume of 100mL, carrying out solvothermal reaction for 8h at 200 ℃ to obtain a product containing cobalt-zinc ferrite, taking out the inner liner of the reaction kettle, and removing supernatant to obtain a black precipitate at the bottom, namely the product containing cobalt-zinc ferrite;
(4) after the reaction is finished, cooling to room temperature, carrying out magnetic separation on the product to obtain the hydrous cobalt-zinc ferrite, and washing the hydrous cobalt-zinc ferrite with deionized water for multiple times to enable the pH value of the hydrous cobalt-zinc ferrite to be neutral;
(5) pre-freezing the hydrous cobalt-zinc ferrite for 12h, transferring the hydrous cobalt-zinc ferrite into a freeze dryer, drying the hydrous cobalt-zinc ferrite at a low temperature for 24h, and grinding the hydrous cobalt-zinc ferrite to obtain pure cobalt-zinc ferrite, wherein the pure cobalt-zinc ferrite is required to be obtained by freeze drying, otherwise the pure cobalt-zinc ferrite is difficult to disperse uniformly in the subsequent reaction process;
(6) adding 30mL of deionized water into 1 100mL beaker, adding 90mg of graphite oxide while stirring, performing ultrasonic treatment for 1h, stirring for 30min to prepare graphene oxide aqueous dispersion with the concentration of 3mg/mL, and peeling and dispersing the graphite oxide sheet in the deionized water to form uniform graphene oxide aqueous dispersion;
(7) continuously adding 30mg of the cobalt-zinc ferrite obtained in the step (5) into a 100mL beaker, performing ultrasonic treatment for 30min, and stirring for 30min until the cobalt-zinc ferrite is uniformly dispersed to obtain a second mixed dispersion liquid, wherein magnetons need to be removed in the step, and a mechanical stirring method is adopted to prevent the cobalt-zinc ferrite from being adsorbed on the magnetons;
(8) transferring the second mixed dispersion liquid into a reaction kettle with the volume of 50mL, and carrying out hydrothermal reaction for 12h at the temperature of 120 ℃ to obtain hydrogel;
(9) after the reaction is finished, cooling to room temperature, dialyzing the obtained hydrogel for 36 hours by using an ethanol-water solution with the volume fraction of 10 wt.% to obtain an aerogel product, and removing unreacted ions;
(10) after the product was pre-frozen for 12h, it was transferred to a freeze dryer and cryodried for 48h to give the final aerogel product, denoted S1.
The XRD pattern of sample S1 is shown in fig. 1, where 2 θ is 30.0 °, 34.5 °, 42.2 °, 56.9 ° and 62.3 ° with CoFe2O4And ZnFe2O4The positions of the (220), (311), (400), (511) and (440) crystal faces of the standard cards (JCPDS No.22-1086, JCPDS No.22-1012) are consistent, and no other characteristic peaks are seen in the figure, which indicates that Co is prepared under the experimental condition0.5Zn0.5Fe2O4Particles.
FIG. 2 is an SEM photograph of sample S1, from which Co can be seen0.5Zn0.5Fe2O4The particles exhibit a uniform spherical configuration, are supported on the surface of the corrugated RGO, and in addition, adjacent sheets of RGO are stacked on top of each other to form a three-dimensional network structure. FIG. 3 is a histogram of the particle size distribution of sample S1, from which it can be seen that the average particle size of sample S1 was 218.3 nm.
Mixing NRGO/Co0.5Zn0.5Fe2O4Composite aerogel product and paraffin waxAccording to the mass ratio of 15 wt.%, coaxial samples with the outer diameter of 7.00mm, the inner diameter of 3.04mm and the thickness of about 2mm are pressed in a special die, electromagnetic parameters of the coaxial samples are tested by an AV3629D vector network analyzer, the wave absorbing performance is obtained through calculation, and the test frequency is 2-18 GHz. When the matching thickness is 6.0mm, the maximum absorption intensity reaches-16.3 dB at 15.68 GHz; the reflection loss versus frequency curve of sample S1 is shown in fig. 8.
Example 2
(1) 1 200mL beaker was taken, 60mL ethylene glycol was added, followed by 1.08g (4mmol) FeCl3·6H2O，0.24g(1mmol)CoCl2·6H2O and 0.14g (1mmol) ZnCl2Stirring vigorously to dissolve it completely, wherein Zn2+、Co2+And Fe3+In a molar ratio of 1: 1: 4, then adding a certain amount of 5.4g of sodium acetate, and stirring for 15min until the sodium acetate is completely dissolved;
(2) adding a certain amount of 1.5g PEG, stirring at 50 ℃ for 2h to dissolve the PEG to obtain a first mixed dispersion liquid;
(3) transferring the first mixed dispersion liquid into a reaction kettle with the volume of 100mL, and carrying out solvothermal reaction for 8h at the temperature of 200 ℃ to obtain a product containing cobalt-zinc ferrite;
(4) after the reaction is finished, cooling to room temperature, carrying out magnetic separation on the product to obtain the hydrous cobalt-zinc ferrite, and washing the hydrous cobalt-zinc ferrite with deionized water for multiple times to enable the pH value of the hydrous cobalt-zinc ferrite to be neutral;
(5) pre-freezing the hydrous cobalt-zinc ferrite for 12h, transferring the hydrous cobalt-zinc ferrite into a freeze dryer, drying the hydrous cobalt-zinc ferrite at a low temperature for 24h, and grinding the hydrous cobalt-zinc ferrite to obtain pure cobalt-zinc ferrite;
(6) and adding 30mL of deionized water into 1 100mL beaker, adding 90mg of graphite oxide while stirring, performing ultrasonic treatment for 1h, and stirring for 30min to prepare the graphene oxide aqueous dispersion with the concentration of 3 mg/mL.
(7) Adding a certain amount of Co obtained in the step (5) into a 100mL beaker0.5Zn0.5Fe2O4Performing ultrasonic treatment for 30min and stirring for 30min until the dispersion is uniform;
(8) adding a certain volume of EDA into a 100mL beaker, and stirring for 30min to obtain a second mixed dispersion liquid, wherein the adding volume of the ethylenediamine is 250 mu L;
(9) transferring the second mixed dispersion liquid into a reaction kettle with the volume of 50mL, and carrying out hydrothermal reaction for 12h at the temperature of 120 ℃ to obtain hydrogel;
(10) after the reaction is finished, cooling to room temperature, and dialyzing the obtained hydrogel for 36 hours by using an ethanol-water solution with the volume fraction of 10 wt.% to obtain an aerogel product;
(11) the aerogel product was pre-frozen for 12h, transferred to a freeze dryer and cryodried for 48h to give the final aerogel product, S2.
The aerogels of example 2 were tested.
The XRD pattern of sample S2 is shown in fig. 1, where 2 θ is 30.0 °, 34.5 °, 42.2 °, 56.9 ° and 62.3 ° with CoFe2O4And ZnFe2O4The positions of the (220), (311), (400), (511) and (440) crystal faces of the standard cards (JCPDS No.22-1086, JCPDS No.22-1012) are consistent, and no other characteristic peaks are seen in the figure, which indicates that Co is prepared under the experimental condition0.5Zn0.5Fe2O4Particles.
FIG. 4 is an SEM photograph of sample S2, from which Co can be seen0.5Zn0.5Fe2O4The particles exhibit a uniform spherical configuration, are supported on the surface of the corrugated RGO, and in addition, adjacent sheets of RGO are stacked on top of each other to form a three-dimensional network structure. FIG. 5 is a histogram of the particle size distribution of each of samples S2, and it can be seen that the average particle size of sample S2 was 228.4 nm.
Mixing NRGO/Co0.5Zn0.5Fe2O4The composite aerogel product and paraffin are pressed into a coaxial sample with the outer diameter of 7.00mm, the inner diameter of 3.04mm and the thickness of about 2mm in a special die according to the mass ratio of 15 wt.%, an AV3629D vector network analyzer is used for testing the electromagnetic parameters of the sample, and the wave-absorbing performance is obtained through calculation, wherein the testing frequency is 2-18 GHz. When the matching thickness is 6.0mm, the maximum absorption intensity reaches-42.0 dB at 3.52 GHz; the reflection loss versus frequency curve of sample S2 is shown in fig. 9.
Example 3
(1) 1 200mL beaker was taken and 60mL ethylene glycol was addedThen 1.08g (4mmol) FeCl was added3·6H2O，0.24g(1mmol)CoCl2·6H2O and 0.14g (1mmol) ZnCl2Stirring vigorously to dissolve it completely, wherein Zn2+、Co2+And Fe3+In a molar ratio of 1: 1: 4, then adding a certain amount of 5.4g of sodium acetate, and stirring for 15min until the sodium acetate is completely dissolved;
(2) adding a certain amount of 1.5g PEG, stirring at 50 ℃ for 2h to dissolve the PEG to obtain a first mixed dispersion liquid;
(3) transferring the first mixed dispersion liquid into a reaction kettle with the volume of 100mL, and carrying out solvothermal reaction for 8h at the temperature of 200 ℃ to obtain a product containing cobalt-zinc ferrite;
(4) after the reaction is finished, cooling to room temperature, carrying out magnetic separation on the product to obtain the hydrous cobalt-zinc ferrite, and washing the hydrous cobalt-zinc ferrite with deionized water for multiple times to enable the pH value of the hydrous cobalt-zinc ferrite to be neutral;
(5) pre-freezing the hydrous cobalt-zinc ferrite for 12h, transferring the hydrous cobalt-zinc ferrite into a freeze dryer, drying the hydrous cobalt-zinc ferrite at a low temperature for 24h, and grinding the hydrous cobalt-zinc ferrite to obtain pure cobalt-zinc ferrite;
(6) and adding 30mL of deionized water into 1 100mL beaker, adding 90mg of graphite oxide while stirring, performing ultrasonic treatment for 1h, and stirring for 30min to prepare the graphene oxide aqueous dispersion with the concentration of 3 mg/mL.
(7) Continuing to add a certain amount of Co obtained in the step (5) into the 100mL beaker0.5Zn0.5Fe2O4Performing ultrasonic treatment for 30min and stirring for 30min until the dispersion is uniform;
(8) continuously adding a certain volume of ethylenediamine into the 100mL beaker, and stirring for 30min to obtain a second mixed dispersion liquid, wherein the adding volume of the ethylenediamine is 250 mu L;
(9) transferring the second mixed dispersion liquid into a reaction kettle with the volume of 50mL, and carrying out hydrothermal reaction for 12h at the temperature of 120 ℃;
(10) after the reaction is finished, cooling to room temperature, and dialyzing the obtained hydrogel for 36 hours by using an ethanol-water solution with the volume fraction of 10 wt.% to obtain an aerogel product;
(11) the aerogel product was pre-frozen for 12h, transferred to a freeze dryer and cryodried for 48h to give the final aerogel product, S3.
The XRD pattern of sample S3 is shown in fig. 1, where 2 θ is 30.0 °, 34.5 °, 42.2 °, 56.9 ° and 62.3 ° with CoFe2O4And ZnFe2O4The positions of the (220), (311), (400), (511) and (440) crystal faces of the standard cards (JCPDS No.22-1086, JCPDS No.22-1012) are consistent, and no other characteristic peaks are seen in the figure, which indicates that Co is prepared under the experimental condition0.5Zn0.5Fe2O4Particles.
FIG. 6 is an SEM photograph of samples S1-S3, from which Co can be seen0.5Zn0.5Fe2O4The particles present uniform spherical morphology, are loaded on the surface of the corrugated RGO, and in addition, adjacent RGO sheets are mutually stacked to form a three-dimensional network structure. FIG. 7 is a histogram of the particle size distribution of sample S3, from which it can be seen that the average particle size of sample S3 was 219.7 nm.
Mixing NRGO/Co0.5Zn0.5Fe2O4The composite aerogel product and paraffin are pressed into a coaxial sample with the outer diameter of 7.00mm, the inner diameter of 3.04mm and the thickness of about 2mm in a special die according to the mass ratio of 15 wt.%, an AV3629D vector network analyzer is used for testing the electromagnetic parameters of the sample, and the wave-absorbing performance is obtained through calculation, wherein the testing frequency is 2-18 GHz. The reflection loss versus frequency curve of sample S3 is shown in FIG. 10, where the maximum absorption intensity reached-66.7 dB at 8.6GHz and the maximum absorption bandwidth 5.0GHz at 1.6mm matching thickness was 2.6 mm.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A preparation method of a nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite composite aerogel wave-absorbing material is characterized by comprising the following steps of: the composite aerogel wave-absorbing material is formed by assembling folded reduced graphene oxide tangled cobalt-zinc ferrite microspheres into a three-dimensional porous network structure; the preparation method comprises the following steps:
(1) taking 1 200mL beaker, adding 60mL ethylene glycol, then adding 1.08g ferric chloride hexahydrate, 0.24g cobalt chloride hexahydrate and 0.14g zinc chloride, and vigorously stirring to completely dissolve the materials;
(2) continuously adding a certain amount of 1.5g of polyethylene glycol into a200 mL beaker to obtain a first mixed dispersion liquid;
(3) transferring the first mixed dispersion liquid into a reaction kettle with the volume of 100mL, and carrying out thermal reaction for 8h at the temperature of 200 ℃ to obtain a product containing cobalt-zinc ferrite;
(4) after the reaction is finished, cooling to room temperature, carrying out magnetic separation on the product to obtain the hydrous cobalt-zinc ferrite, and washing the hydrous cobalt-zinc ferrite with deionized water for multiple times to enable the pH value of the hydrous cobalt-zinc ferrite to be neutral;
(5) pre-freezing the hydrous cobalt-zinc ferrite for 12h, transferring the hydrous cobalt-zinc ferrite into a freeze dryer, drying the hydrous cobalt-zinc ferrite at a low temperature for 24h, and grinding the hydrous cobalt-zinc ferrite to obtain pure cobalt-zinc ferrite;
(6) taking 3 100mL beakers, respectively adding 30mL deionized water into each beaker, and adding 90mg of graphite oxide while stirring to prepare graphene oxide aqueous dispersion;
(7) continuously adding 30mg of the cobalt-zinc ferrite obtained in the step (5) into each 100mL beaker, performing ultrasonic treatment for 30min, and stirring for 30min until the cobalt-zinc ferrite is uniformly dispersed;
(8) adding ethylenediamine with different volumes into each 100mL beaker, and stirring for 30min to obtain a second mixed dispersion, wherein the adding volumes of the ethylenediamine are 0, 250 and 350 μ L respectively;
(9) transferring the second mixed dispersion liquid into a reaction kettle with the volume of 50mL for hydrothermal reaction to obtain hydrogel;
(10) after the reaction is finished, cooling to room temperature, and dialyzing the obtained hydrogel to obtain an aerogel product;
(11) and pre-freezing the aerogel product for 12h, transferring to a freeze dryer, and drying at a low temperature for 48h to obtain the final aerogel product.
2. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: in the step (1), the molar ratio of zinc ions to cobalt ions to iron ions is 1: 1: 4, adding a certain amount of 5.4g of sodium acetate, and stirring for 15min until the sodium acetate is completely dissolved.
3. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: in the step (2), the polyethylene glycol must be stirred at 50 ℃ for 2 hours to dissolve the polyethylene glycol to obtain a first mixed dispersion.
4. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: and (4) taking out the 100mL inner liner of the reaction kettle in the step (4) and removing the upper layer liquid to obtain a black precipitate at the bottom, namely a product containing the cobalt-zinc ferrite.
5. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: and (4) after adding the graphite oxide in the step (6), carrying out ultrasonic treatment for 1h, stirring for 30min, and stripping and dispersing the graphite oxide sheet layer in deionized water to form a uniform graphene oxide aqueous dispersion solution with the concentration of 3 mg/mL.
6. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: in the step (7), magnetons need to be removed, and a mechanical stirring method is adopted to avoid the cobalt-zinc ferrite from being adsorbed on the magnetons.
7. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: and (4) in the step (8), ethylenediamine is used as a nitrogen doping reagent, a reducing agent and alkali, the nitrogen doping amount of the graphene is adjusted by adding ethylenediamine with different volumes, so that the electromagnetic parameters of the composite aerogel wave-absorbing material are regulated and controlled, and the wave-absorbing capacity of the composite aerogel wave-absorbing material is changed.
8. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: the hydrothermal reaction in step (9) must be maintained at 120 ℃ for 12 hours.
9. The preparation method of the nitrogen-doped reduced graphene oxide/cobalt zinc ferrite composite aerogel wave-absorbing material according to claim 1, which is characterized by comprising the following steps of: the dialysis in step (10) was performed for 36h using a volume fraction of 10 wt.% ethanol-water solution.
10. The nitrogen-doped reduced graphene oxide/cobalt-zinc ferrite composite aerogel wave-absorbing material is characterized in that: the composite aerogel wave-absorbing material is prepared by the method of any one of claims 1 to 9.
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