CN115838585A - Preparation method of graphene-loaded iron hexagonal nanosheet composite wave-absorbing material - Google Patents
Preparation method of graphene-loaded iron hexagonal nanosheet composite wave-absorbing material Download PDFInfo
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Abstract
The invention discloses a preparation method of a graphene-loaded iron hexagonal nanosheet composite wave-absorbing material, and relates to the technical field of preparation of electromagnetic wave-absorbing materials. The invention aims to solve the technical problems of unobvious dielectric frequency dispersion characteristic, narrow wave-absorbing frequency band and weak absorption performance of graphene under low filling content. The method comprises the following steps: 1. preparing single-layer graphene; 2. preparing a graphene/iron two-dimensional heterogeneous interface field effect transistor device; 3. preparation of alpha-Fe 2 O 3 Hexagonal nanosheets; 4. alpha-Fe 2 O 3 Modifying the cationic surfactant of the hexagonal nanosheets; 5. preparing graphene oxide; 6. graphene oxide/alpha-Fe 2 O 3 And (3) carrying out low-temperature thermal reduction on the hexagonal nanosheets to obtain reduced graphene oxide/Fe hexagonal nanosheets. According to the invention, the abundant free electrons in the metal Fe nanosheet are utilized to realize graphene carrier injection, and the dielectric frequency dispersion characteristic of graphene is fully exerted. The material has simple preparation process and lower raw material cost, and can realize large-scale production. The composite wave-absorbing material is applied to the field of electromagnetic wave absorption.
Description
Technical Field
The invention relates to the technical field of preparation of electromagnetic wave absorbing materials, in particular to a preparation method of a graphene-loaded iron hexagonal nanosheet composite wave absorbing material.
Background
The idea of interconnection of everything becomes reality in the 5G era, and further becomes a supporting technical support for industrial transformation and upgrading. However, due to the rapid development of microwave communication technology and the widespread use of electronic devices, electromagnetic radiation pollution in the environment has become a considerable problem, which not only interferes with the operation of electronic devices, but also causes harm to human health. In recent years, carbon materials with thin thickness, low density and excellent electrical properties have been applied to the preparation of wave-absorbing materials, such as graphite, graphene, carbon black, carbon nanotubes and the like, and have a wide application prospect in the field of electromagnetic wave absorption.
As a novel carbon material, graphene (Graphene) is more likely to be a novel effective electromagnetic wave absorbing material. The main reasons include the following aspects: (1) the graphene is a hexagonal plane film consisting of carbon atoms, and is a two-dimensional material with the thickness of only one carbon atom; (2) graphene is the thinnest and hardest nanomaterial in the world; (3) the thermal conductivity coefficient is higher than that of the carbon nano tube and the diamond and reaches 5300W/(m.K); (4) the graphene is the material with the minimum resistivity in the world at present and is only 10 -6 Omega cm; (5) the electron mobility of the graphene is higher than that of a carbon nano-tube or a silicon crystal at normal temperature and exceeds 15000cm 2 ·V -1 S. Compared with the traditional material, the graphene can break through the original limitation, becomes an effective novel wave absorbing agent, and meets the requirements of the wave absorbing material on thinness, lightness, width and strength. Therefore, the wave-absorbing material with broadband excellent performance is developed by taking graphene as a direction, and has important economic benefits and values from military and civil use and consideration now and in the future.
At present, the wave-absorbing performance of graphene-based materials can be improved through component optimization and structural design, but the problems that how graphene exerts its own dielectric properties and the interaction mechanism of each component to graphene in the composite material are still uncertain are still faced. Therefore, how to fully exert the dielectric properties of graphene is a key challenge in realizing dielectric parameter regulation and absorption property optimization.
Disclosure of Invention
The invention provides a preparation method of a graphene loaded iron hexagonal nanosheet composite wave-absorbing material, which aims to solve the technical problems of unobvious dielectric frequency dispersion characteristic, narrow wave-absorbing frequency band and weak absorption performance of graphene under low filling content.
A preparation method of a graphene-supported iron hexagonal nanosheet composite wave-absorbing material specifically comprises the following steps:
1. placing a copper foil substrate in electrolyte, performing electrochemical polishing, then performing ultrasonic cleaning, drying by blowing argon, placing the copper foil substrate in a tube furnace for CVD, introducing argon, heating to 300-310 ℃, then introducing oxygen, oxidizing the copper foil substrate, then closing the oxygen, introducing hydrogen, controlling the temperature to rise to 1000-1005 ℃ in 35-40 min, then controlling the temperature to rise to 1035-1040 ℃ in 30-35 min, preserving the temperature for 30-90 min, and then cooling to 1000-1005 ℃; then heating to 1035-1040 ℃, introducing high-purity methane for nucleation growth of graphene to obtain single-layer graphene;
2. transferring the single-layer graphene obtained in the step one to Si/SiO 2 Placing the substrate in an evaporation sample chamber, taking high-purity iron particles as an evaporation source, and controlling the background vacuum degree to be 1.0x10 -3 Pa, cleaning an evaporation boat, accurately setting the thickness of an iron film to be evaporated by using a coating instrument, and performing Cr/Au evaporation on a metal electrode to obtain a graphene/iron field effect transistor device;
3. dissolving ferric trichloride hexahydrate in an ethanol solution, magnetically stirring until the ferric trichloride hexahydrate is completely dissolved, adding sodium acetate to adjust the pH value to 9-11, completely stirring and dissolving, then transferring to a Teflon hot-pressing kettle, controlling the temperature to be 180-220 ℃, and carrying out hydrothermal treatment for 18-24 hours; cooling to room temperature, centrifugally washing with deionized water and absolute ethyl alcohol, and drying to obtain alpha-Fe 2 O 3 Hexagonal nanosheet powder;
4. bromination of the cationic surfactant cetyl trimethylAmmonium and alpha-Fe obtained in step three 2 O 3 Hexagonal nano-sheet powder dispersed in deionized water, alpha-Fe 2 O 3 The mass-volume ratio of the total mass of the hexagonal nanosheet powder and the hexadecyl trimethyl ammonium bromide to the mass of the deionized water is (4-6) g (100-200) mL, the temperature of the constant-temperature water bath is controlled to be 60-80 ℃, the stirring is carried out for 2-3 h, the mixture is naturally cooled, then the mixture is washed by the deionized water and dried, and the surface modified alpha-Fe is obtained 2 O 3 Hexagonal nanosheet powder;
5. adding graphite powder, sodium nitrate and concentrated sulfuric acid into a three-neck flask, placing the three-neck flask in an ice bath for mechanical stirring, controlling the rotation speed of the mechanical stirring to be 200-400 r/min, adding potassium permanganate during the stirring process, then controlling the constant-temperature water bath to be 35-45 ℃, continuously stirring for 1.5-2.5 h, adding deionized water during the reaction process, transferring the three-neck flask to an oil bath condition of 98-105 ℃ after the reaction is finished, and continuously stirring for 15-20 min; then cooling to room temperature, adding deionized water and hydrogen peroxide solution, sealing, preserving and standing; hydrochloric acid with volume concentration of 10-15% and deionized water are adopted for centrifugal washing until the solution is neutral; adding ionized water after dialysis for one week, and performing ultrasonic dispersion to obtain a graphene oxide suspension;
6. the surface modified alpha-Fe obtained in the fourth step 2 O 3 Ultrasonically stirring and mixing the hexagonal nanosheet powder and the graphene oxide suspension obtained in the fifth step, and freeze-drying; and then putting the mixture into a tubular furnace for thermal reduction, wherein the reducing atmosphere is hydrogen atmosphere or hydrogen-argon mixed atmosphere, the heating rate is controlled to be 2-10 ℃/min, the temperature is controlled to be 350-600 ℃, and the heat preservation time is 1-3 h, so that the graphene-loaded iron hexagonal nanosheet composite wave-absorbing material is obtained, and the preparation is completed.
According to the theory of free electrons of metal, due to the difference of work functions, free electrons (serving as electron donors) in Fe can form directional transportation to RGO (serving as electron acceptors) in an external electric field. The carrier transport characteristic behavior of the graphene/iron field effect transistor proves that the carrier transport type is converted from hole transport to electron transport due to the introduction of iron. The ohmic contact form of the graphene/iron interface can better promote the electron transport of iron to graphene to realize carrier injection. Based on the theory, the inventionalpha-Fe surface modified by rich oxygen-containing functional groups and cations of graphene oxide 2 O 3 The hexagonal nanosheets are combined in an electrostatic adsorption mode, and then the reduced graphene oxide/iron nanosheet (RGO/Fe) composite material is obtained by a low-temperature thermal reduction method. Compared with a pure RGO absorbent, the introduction of the trace Fe nano-sheet improves the dielectric constant of the graphene and shows an obvious dielectric frequency dispersion characteristic. The electrical and dielectric properties of the graphene are improved, the conduction loss and relaxation polarization of the graphene are enhanced, more interface polarization is introduced in the surface-to-surface contact mode of the RGO and the Fe nanosheets, and the dielectric loss property is enhanced.
The invention has the beneficial effects that:
1. the composite material is synthesized by using commercial materials, complex equipment and harsh experimental environment are not needed in the synthesis process, the preparation process is low in cost and simple in process, and large-scale production can be realized.
2. Provides a preparation method of a novel graphene supported iron hexagonal nanosheet composite material.
3. The material prepared by the method is a broadband, strong-absorption and thin-matching-thickness wave-absorbing material, when the filling amount is 2wt%, the matching thickness is 2.5mm, the frequency is 14.39GHz, the maximum reflection loss is-46.71 dB, and the effective bandwidth is 6.73GHz (11.27-18 GHz). The invention provides a good theoretical basis for the development of the graphene-based material and provides a good design idea for the multi-component compounding aspect of the electromagnetic wave absorption material.
4. According to the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared by the method, the RGO is a novel carbon material, and the wave-absorbing performance of the material can be improved due to good conductivity and adjustability. By introducing a trace amount of Fe, the optimal impedance matching is provided by properly adjusting the complex dielectric constant of the RGO/Fe, and incident microwaves can enter the RGO/Fe composite material conveniently; second, the carrier injection mechanism (including electron transport and electron hopping) of RGO/Fe and the resulting charge rearrangement effectively enhance conduction loss and interface polarization. In addition, the polarization relaxation caused by the heterogeneous interface formed between RGO and Fe is advantageous for enhancing the interface polarization. In addition, dipole polarization caused by the edge and in-plane defects of RGO/Fe increases dielectric loss, thereby attenuating electromagnetic wave energy. In conclusion, through the introduction of the metal Fe nanosheet, RGO carrier injection can be realized, the dielectric frequency dispersion characteristic of graphene can be effectively exerted, the dielectric characteristic is enhanced, and meanwhile, good impedance matching is realized, so that the remarkable electromagnetic wave absorption performance is obtained.
The graphene iron-loaded hexagonal nanosheet composite wave-absorbing material prepared by the method is applied to the field of electromagnetic wave absorbing materials.
Drawings
FIG. 1 is a HRTEM image of single-layer graphene obtained in the first step of the example;
fig. 2 is a SAED diagram of single-layer graphene obtained in the first step of the embodiment, which shows that graphene prepared by the method is single crystal;
FIG. 3 is a Raman diagram of single-layer graphene obtained in a first step of the embodiment;
fig. 4 is a KPFM diagram of a graphene/iron field effect transistor device obtained in step two of the example;
FIG. 5 is a graph of transfer characteristics of a graphene effect transistor device;
FIG. 6 is a graph of the output of a graphene effect transistor device, curve 1 representing-60V, curve 2 representing-40V, curve 3 representing-20V, curve 4 representing 0V, curve 5 representing 20V, curve 6 representing 40V, curve 7 representing 60V;
FIG. 7 is a graph of transfer characteristics of a graphene/iron field effect transistor device obtained in step two of the example;
FIG. 8 is a graph of the output of a graphene/iron field effect transistor device obtained in step two of the example, where curve 1 represents 60V, curve 2 represents 40V, curve 3 represents 20V, curve 4 represents 0V, curve 5 represents-20V, curve 6 represents-40V, and curve 7 represents-60V;
FIG. 9 is an SEM image of an RGO control;
fig. 10 is an SEM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example;
fig. 11 is TEM, HRTEM and SAED images of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is a TEM image, b is a HRTEM image, and c is a SAED image;
fig. 12 is an XRD pattern of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example and a comparative sample of reduced graphene oxide;
fig. 13 is a Raman chart of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example and a comparative sample of reduced graphene oxide;
fig. 14 is an XPS spectrum (Fe 2p spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example;
fig. 15 is an XPS spectrum (C1 s spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example;
fig. 16 is an XPS spectrum (O1 s spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment;
fig. 17 is a room temperature hysteresis loop diagram of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example and a comparative sample of Fe, and compared with the saturation magnetization of metallic Fe of about 169.08emu/g, the magnetic property of the RGO/Fe composite material is very weak (the saturation magnetization is about 1.40 emu/g) due to the low content of Fe (0.68 wt%) in the RGO/Fe composite material, and the magnetic property is negligible.
FIG. 18 is an AFM topography and a C-AFM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is the AFM topography and b is the C-AFM image;
FIG. 19 is an AFM topography and a KPFM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example, wherein a is the AFM topography and b is the KPFM image;
fig. 20 is an AFM topography and an EFM map of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is the AFM topography, and b is the EFM map;
FIG. 21 is a graph of the electromagnetic parameter test for an RGO control;
FIG. 22 is a graph showing the wave absorption properties of an RGO control sample, curve 1 representing 1.0mm thickness, curve 2 representing 1.5mm thickness, curve 3 representing 2.0mm thickness, curve 4 representing 2.5mm thickness, curve 5 representing 3.0mm thickness, curve 6 representing 3.5mm thickness, curve 7 representing 4.0mm thickness, curve 8 representing 4.5mm thickness, curve 9 representing 5.0mm thickness, and curve 10 representing 5.5mm thickness;
fig. 23 is a graph of an electromagnetic parameter test curve of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment;
fig. 24 is a wave-absorbing performance test curve diagram of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, where a curve 1 represents a thickness of 1.0mm, a curve 2 represents a thickness of 1.5mm, a curve 3 represents a thickness of 2.0mm, a curve 4 represents a thickness of 2.5mm, a curve 5 represents a thickness of 3.0mm, a curve 6 represents a thickness of 3.5mm, a curve 7 represents a thickness of 4.0mm, a curve 8 represents a thickness of 4.5mm, a curve 9 represents a thickness of 5.0mm, and a curve 10 represents a thickness of 5.5 mm.
Detailed Description
The first embodiment is as follows: the preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material specifically comprises the following steps:
1. placing a copper foil substrate in electrolyte, performing electrochemical polishing, then performing ultrasonic cleaning, drying by blowing argon, placing the copper foil substrate in a tube furnace for CVD, introducing argon, heating to 300-310 ℃, then introducing oxygen, oxidizing the copper foil substrate, then closing the oxygen, introducing hydrogen, controlling the temperature to rise to 1000-1005 ℃ in 35-40 min, then controlling the temperature to rise to 1035-1040 ℃ in 30-35 min, preserving the temperature for 30-90 min, and then cooling to 1000-1005 ℃; then heating to 1035-1040 ℃, introducing high-purity methane for nucleation growth of graphene to obtain single-layer graphene;
2. transferring the single-layer graphene obtained in the step one to Si/SiO 2 Placing the substrate in an evaporation sample chamber, taking high-purity iron particles as an evaporation source, and controlling the background vacuum degree to be 1.0x10 -3 Pa, cleaning an evaporation boat, accurately setting the thickness of an iron film to be evaporated by using a film coating instrument, and performing evaporation of Cr/Au on a metal electrode to obtain a graphene/iron field effect transistor device;
3. dissolving ferric trichloride hexahydrate in ethanol solution, and magnetically dissolvingStirring until the mixture is completely dissolved, adding sodium acetate to adjust the pH value to 9-11, stirring and dissolving completely, then transferring the mixture into a Teflon autoclave, controlling the temperature to be 180-220 ℃, and carrying out hydrothermal treatment for 18-24 hours; cooling to room temperature, centrifugally washing with deionized water and absolute ethyl alcohol, and drying to obtain alpha-Fe 2 O 3 Hexagonal nanosheet powder;
4. the cationic surfactant cetyl trimethyl ammonium bromide and the alpha-Fe obtained in the third step 2 O 3 Hexagonal nano-sheet powder dispersed in deionized water, alpha-Fe 2 O 3 The mass-volume ratio of the total mass of the hexagonal nanosheet powder and the hexadecyl trimethyl ammonium bromide to the mass of the deionized water is (4-6) g (100-200) mL, the temperature of the constant-temperature water bath is controlled to be 60-80 ℃, the stirring is carried out for 2-3 h, the mixture is naturally cooled, then the mixture is washed by the deionized water and dried, and the surface modified alpha-Fe is obtained 2 O 3 Hexagonal nanosheet powder;
5. adding graphite powder, sodium nitrate and concentrated sulfuric acid into a three-neck flask, placing the three-neck flask in an ice bath for mechanical stirring, controlling the rotation speed of the mechanical stirring to be 200-400 r/min, adding potassium permanganate during the stirring process, then controlling the constant-temperature water bath to be 35-45 ℃, continuously stirring for 1.5-2.5 h, adding deionized water during the reaction process, transferring the three-neck flask to an oil bath condition of 98-105 ℃ after the reaction is finished, and continuously stirring for 15-20 min; then cooling to room temperature, adding deionized water and a hydrogen peroxide solution, sealing, storing and standing; hydrochloric acid with volume concentration of 10-15% and deionized water are adopted for centrifugal washing until the solution is neutral; adding ionized water after dialysis for one week, and performing ultrasonic dispersion to obtain a graphene oxide suspension;
6. the surface modified alpha-Fe obtained in the fourth step 2 O 3 Ultrasonically stirring and mixing the hexagonal nanosheet powder and the graphene oxide suspension obtained in the fifth step, and freeze-drying; and then putting the mixture into a tubular furnace for thermal reduction, wherein the reducing atmosphere is hydrogen atmosphere or hydrogen-argon mixed atmosphere, the heating rate is controlled to be 2-10 ℃/min, the temperature is controlled to be 350-600 ℃, and the heat preservation time is 1-3 h, so that the graphene-loaded iron hexagonal nanosheet composite wave-absorbing material is obtained, and the preparation is completed.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: step one, mixing the electrolyte with phosphoric acid and polyethylene glycol, wherein the volume ratio of phosphoric acid to polyethylene glycol is 3; the oxidation time of the copper foil substrate is controlled to be 30-40 min, and the introduction time of high-purity methane is controlled to be 10-20 min. The rest is the same as the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: and the thickness of the vapor plating iron film in the second step is 10-50 nm. The other is the same as in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment mode and one of the first to third embodiment modes is: and step three, the volume ratio of the absolute ethyl alcohol to the water in the ethyl alcohol solution is 14. The others are the same as in one of the first to third embodiments.
The fifth concrete implementation mode: the difference between this embodiment and one of the first to fourth embodiments is: and step three, controlling the centrifugal washing rotating speed to be 8000-10000 rpm/min, and controlling the time to be 30-50 min. The rest is the same as one of the first to fourth embodiments.
The sixth specific implementation mode: the difference between this embodiment and one of the first to fifth embodiments is: step three the obtained alpha-Fe 2 O 3 The hexagonal nano-sheet powder has a transverse size of 100-200 nm and a thickness of 10-20 nm. The other is the same as one of the first to fifth embodiments.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: step four said alpha-Fe 2 O 3 The mass ratio of the hexagonal nanosheet powder to the hexadecyl trimethyl ammonium bromide is 3-5. The other is the same as one of the first to sixth embodiments.
The specific implementation mode is eight: the present embodiment differs from one of the first to seventh embodiments in that: in the reaction process of the step five, the mass volume ratio of the graphite powder, the sodium nitrate, the concentrated sulfuric acid, the potassium permanganate, the deionized water and the hydrogen peroxide solution is 3g:1.5g:75mL of: 9g:150mL of: 15mL;
the mesh number of the graphite powder is 200-8000 meshes. The rest is the same as one of the first to seventh embodiments.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the concentration of the graphene pentoxide suspension liquid in the step is 2-10 mg/mL. The rest is the same as the first to eighth embodiments.
The detailed implementation mode is ten: the present embodiment differs from one of the first to ninth embodiments in that: sixthly, reducing graphene oxide and the surface modified alpha-Fe in the graphene oxide suspension 2 O 3 The mass ratio of the hexagonal nanosheet powder is 1g:2 to 8mg. The other is the same as one of the first to ninth embodiments.
The invention is not limited to the above embodiments, and one or a combination of several embodiments may also achieve the object of the invention.
The first embodiment is as follows:
the embodiment of the invention provides a preparation method of a graphene-supported iron hexagonal nanosheet composite wave-absorbing material, which comprises the following steps:
1. graphene growth was carried out on a commercial copper foil substrate with a thickness of 25 μm using a CVD method: placing a copper foil substrate in an electrolyte, performing electrochemical polishing for 30min under the voltage of 1.8V, wherein the electrolyte is a mixture of phosphoric acid and polyethylene glycol, the volume ratio of the phosphoric acid to the polyethylene glycol is 3; heating to 1035 ℃, introducing high-purity methane with the flow of 5sccm, keeping for 10min, performing nucleation growth of graphene, closing the introduced gas, filling argon, and cooling to room temperature to obtain single-layer graphene;
2. transferring the single-layer graphene obtained in the step one to Si/SiO 2 Placing the substrate in a vapor deposition sample chamber, and coating with high-purity ironThe particles (purity 99.99%) are used as evaporation source, the background vacuum degree is controlled to be 1.0x10 -3 Pa, cleaning the evaporation boat by using absolute ethyl alcohol, accurately setting the thickness of an iron film to be evaporated to be 20nm by using a coating instrument, and performing evaporation plating on a metal electrode Cr/Au (the thickness of Cr is 15 nm/the thickness of Au is 30 nm) to obtain a graphene/iron field effect transistor device;
3. 1.092g FeCl 3 ·6H 2 Dissolving O in an ethanol solution, mixing 70.0mL of absolute ethanol and 5mL of deionized water in the ethanol solution, magnetically stirring until the absolute ethanol and the deionized water are completely dissolved, controlling the rotating speed to be 600r/min, adding 5.6g of sodium acetate to adjust the pH value to be 9-11, completely stirring and dissolving, then transferring to a 100mL Teflon autoclave, controlling the temperature to be 180 ℃, and carrying out hydrothermal treatment for 18 hours; cooling to room temperature, sequentially centrifugally washing with deionized water and absolute ethyl alcohol for three times, and controlling the centrifugal rotation speed to be 8000r/min and the time to be 30min; then controlling the temperature to be 60 ℃ for vacuum drying for 10h to obtain alpha-Fe 2 O 3 Hexagonal nanosheet powder;
4. 0.2g of cetyltrimethylammonium bromide as a cationic surfactant and 0.6g of α -Fe obtained in the third step 2 O 3 Dispersing hexagonal nanosheet powder in 100mL of deionized water, controlling the temperature of a constant-temperature water bath to be 60 ℃, stirring for 2h, controlling the rotating speed to be 600600r/min, naturally cooling, sequentially cleaning for three times by using deionized water and absolute ethyl alcohol, and drying at the temperature of 60 ℃ to obtain surface-modified alpha-Fe 2 O 3 Hexagonal nanosheet powder;
5. adding 3g of graphite powder, 1.5g of sodium nitrate and 75mL of concentrated sulfuric acid into a three-neck flask, mechanically stirring in an ice bath, controlling the rotation speed of mechanical stirring to be 300r/min, adding 9g of potassium permanganate during stirring, controlling a constant-temperature water bath to be 35 ℃, continuously stirring for 2 hours, adding 150mL of deionized water during reaction, transferring to a 98 ℃ oil bath condition after the reaction is finished, and continuously stirring for 15 minutes; then cooling to room temperature, transferring into a 1000mL big beaker, adding 500mL deionized water and 15mL hydrogen peroxide solution, sealing, preserving and standing; sequentially adopting hydrochloric acid with the volume concentration of 10% and deionized water for centrifugal washing for three times, controlling the rotating speed to be 8000r/min and the time to be 5min, then dialyzing until the water is clear, collecting the product, and filling the product into a wide-mouth bottle; adding ionized water, and performing ultrasonic dispersion to obtain a graphene oxide suspension liquid with the concentration of 2 mg/mL;
6. 0.4mg of surface-modified alpha-Fe obtained in step four 2 O 3 Ultrasonically stirring and mixing hexagonal nanosheet powder and 500mL of graphene oxide suspension obtained in the fifth step for 2h, controlling the ultrasonic frequency to be 4040KHz, controlling the temperature to be 50 ℃ below zero and the pressure to be 0.1Pa, and carrying out freeze-drying treatment for 24h to obtain solid graphene oxide/Fe 2 O 3 Nanosheets; and then putting the graphene-supported iron hexagonal nanosheet composite wave-absorbing material into a tubular furnace for thermal reduction, wherein the reduction atmosphere is hydrogen atmosphere, the temperature rise rate is controlled to be 10 ℃/min, the temperature is controlled to be 350 ℃, and the heat preservation time is 2 hours, so that the graphene-supported iron hexagonal nanosheet composite wave-absorbing material is obtained, and the preparation is completed.
And step three, controlling the centrifugal washing rotating speed to be 8000-10000 r/min, and controlling the time to be 30-50 min.
Step three of obtaining alpha-Fe 2 O 3 The hexagonal nano-sheet powder has a transverse size of 100-200 nm and a thickness of 10-20 nm.
Preparation of test samples:
the graphene iron-loaded hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment is placed in paraffin according to the mass ratio of 2%, heated to 75 ℃, kept for 0.5h, and placed in a mold to finally obtain a coaxial ring with the size of 7mm in outer diameter, 3.04mm in inner diameter and 2mm in height.
Reduced Graphene Oxide (RGO) vs Fe control:
and (4) sealing 500mL of the graphene oxide suspension obtained in the fifth step of the embodiment, placing the sealed graphene oxide suspension into a refrigerator for refrigeration, and treating the graphene oxide suspension for 24h by adopting a freeze drying method (-50 ℃,0.1 Pa) to obtain solid graphene oxide. Mixing graphene oxide and Fe obtained in the third step 2 O 3 The nano sheets are respectively put into a tube furnace for thermal reduction, and are thermally treated for 2h at the temperature of 350 ℃, and the heating rate is controlled to be 10 ℃/min. The whole heat treatment process is carried out in reducing gas (H) 2 ) Under protection, RGO and Fe control samples are obtained respectively.
The RGO control was prepared as a test sample as in the examples.
And testing the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment and a reduced graphene oxide comparison sample.
FIG. 1 is a HRTEM image of single-layer graphene obtained in the first step of the example; fig. 2 is a SAED diagram of single-layer graphene obtained in the first step of the embodiment, which can be seen that graphene prepared by the method is a single crystal. FIG. 3 is a Raman diagram of single-layer graphene obtained in a first step of the embodiment; it can be seen that the graphene is a single layer. Fig. 4 is a KPFM of the graphene/iron field effect transistor device (graphene/iron two-dimensional heterogeneous material) obtained in the second step of the example, and it can be seen that there is a significant surface potential change between graphene and iron, which proves that there is a charge transfer phenomenon between the interfaces.
In the second step of the embodiment, evaporation is performed without adding an evaporation source, so as to obtain the graphene effect transistor device.
FIG. 5 is a graph of transfer characteristics of a graphene effect transistor device; the transistor exhibits typical P-type carrier dominated transfer characteristic behavior; FIG. 6 is a graph of the output of a graphene effect transistor device, curve 1 representing-60V, curve 2 representing-40V, curve 3 representing-20V, curve 4 representing 0V, curve 5 representing 20V, curve 6 representing 40V, curve 7 representing 60V; the output characteristic curve shows that the output current of the transistor is continuously increased along with the increase of the negative gate voltage, and the fact that the hole is smoothly transmitted between the graphene and the electrode is shown.
FIG. 7 is a graph of transfer characteristics of a graphene/iron field effect transistor device obtained in step two of the example; the transistor exhibits typical N-type carrier dominated transfer characteristic behavior. FIG. 8 is a graph of the output of a graphene/iron field effect transistor device obtained in step two of the example, where curve 1 represents 60V, curve 2 represents 40V, curve 3 represents 20V, curve 4 represents 0V, curve 5 represents-20V, curve 6 represents-40V, and curve 7 represents-60V; the output characteristic curve of the transistor shows that the output current of the transistor continuously increases along with the increase of the forward grid voltage, the main transmission current carrier of the device is electrons, and the graphene is in contact with iron to form good ohmic contact, so that the electron is smoothly transmitted between the graphene and the iron.
FIG. 9 is an SEM image of an RGO control; fig. 10 is an SEM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example; fig. 11 is TEM, HRTEM and SAED images of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is a TEM image, b is a HRTEM image, and c is a SAED image; it can be seen from the figure that the RGO sheet layer exhibits translucent and abundant wrinkles, and the Fe nanosheets are uniformly dispersed on the RGO sheet, exhibiting a surface-to-surface contact pattern with dimensions of about 100nm in width, about 10nm in thickness, and an aspect ratio of about 0.1.
Fig. 12 is an XRD pattern of a comparative sample of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material and reduced graphene oxide prepared in example one, and it can be seen from the XRD pattern that the crystallinity of RGO carbon is poor and exists in the form of amorphous carbon, since the content of metallic Fe is only 0.68wt%, the diffraction peak after loading Fe is not obvious, but can correspond to the strongest peak of standard PDF card 06-0696, which proves that Fe is successfully supported on the RGO lamella.
FIG. 13 is a Raman diagram of a comparative sample of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material and reduced graphene oxide prepared in the first example, and the D band peak (1351 cm) -1 ) And peak of G band (1590 cm) -1 ) Respectively representing defects and disorder of the graphitic carbon; intensity ratio of D and G band peaks (I) D /I G ) Reflecting the degree of in-plane defects and edge defects of the carbon skeleton. As shown, I of RGO and RGO/Fe D /I G The ratios are 0.82 and 0.91 respectively, which indicates that the introduction of Fe is not beneficial to the reconstruction of carbonization. But more defects will result in more dipole polarization, which is beneficial for dielectric losses.
Fig. 14 is an XPS spectrum (Fe 2p spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, fig. 15 is an XPS spectrum (C1 s spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, and fig. 16 is an XPS spectrum (O1 s spectrum) of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein the XPS spectra represent chemical components and elemental valence states of the RGO/Fe composite material. The curve fit of the Fe2p spectrum found that there were two typical peaks at 711.2 and 724.8eV, fe2p 3/2 And Fe2p 1/2 . From the Fe2p spectrum, the peaks at 724.5 and 710.9eV are Fe 2+ Fe2p of 1/2 And Fe2p 3/2 Peaks at 726.7 and 713.1eV are Fe 3+ Fe2p of 1/2 And Fe2p 3/2 . In addition, there is a Satellite peak (labeled "Satellite") near 719.2 eV. The C1s spectrum of RGO/Fe has three peaks at 284.8, 286.0 and 289.7eV, corresponding to C = C/C-C, C-O and C = O, respectively. In addition, the O1s spectrum of RGO/Fe peaks at 531.9, 532.8 and 534eV, corresponding to surface physical/chemical method adsorbed O = C, O-C and water.
Fig. 17 is a room temperature hysteresis loop diagram of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example and a comparative sample of Fe, and compared with the saturation magnetization of metallic Fe of about 169.08emu/g, the magnetic property of the RGO/Fe composite material is very weak (the saturation magnetization is about 1.40 emu/g) due to the low content of Fe (0.68 wt%) in the RGO/Fe composite material, and the magnetic property is negligible.
FIG. 18 is an AFM topography and a C-AFM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is the AFM topography and b is the C-AFM image; the current varies significantly in different regions, as indicated by the white lines. The current is lower in the RGO region (dark region) and higher in the near-contact region of the RGO/Fe interface (light region).
FIG. 19 is an AFM topography and a KPFM image of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first example, wherein a is the AFM topography and b is the KPFM image; the RGO layer exhibits a uniform surface potential at the same location, indicating that the electronic properties of the RGO are not significantly affected by air-doped charges and substrate defects. The surface potential of the RGO/Fe region increases with the convex position of Fe, indicating that the degree of charge transfer between Fe and RGO increases due to the continuity of the interface.
Fig. 20 is an AFM topography and an EFM map of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, wherein a is the AFM topography, and b is the EFM map; the phase difference increases with increasing surface charge density of the sample. The charge is mainly distributed on the convex part of the RGO surface, while the charge is less distributed on the flat part of the RGO surface, indicating that Fe improves the electrical properties of RGO by carrier injection.
FIG. 21 is a graph of an RGO control sample showing a low dielectric dispersion and a low energy storage and loss in electromagnetic field, as measured by electromagnetic parameters.
FIG. 22 is a graph showing the wave absorption properties of an RGO control sample, curve 1 representing 1.0mm thickness, curve 2 representing 1.5mm thickness, curve 3 representing 2.0mm thickness, curve 4 representing 2.5mm thickness, curve 5 representing 3.0mm thickness, curve 6 representing 3.5mm thickness, curve 7 representing 4.0mm thickness, curve 8 representing 4.5mm thickness, curve 9 representing 5.0mm thickness, and curve 10 representing 5.5mm thickness. The composite wave-absorbing material basically does not show obvious excellent wave-absorbing performance under the thickness of 2-18GHz and 1-5.5 mm. When the matching thickness is 3.5mm, the filling amount is 2wt%, and the frequency is 10.89GHz, the maximum reflection loss is-13.01 dB, and the effective bandwidth is 2.25GHz (9.82-12.07 GHz).
Fig. 23 is a graph of an electromagnetic parameter test of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, and from the aspect of electromagnetic parameters, the RGO/Fe material shows excellent dielectric loss capability and has an obvious dielectric frequency dispersion characteristic.
Fig. 24 is a wave-absorbing performance test curve diagram of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material prepared in the first embodiment, where a curve 1 represents a thickness of 1.0mm, a curve 2 represents a thickness of 1.5mm, a curve 3 represents a thickness of 2.0mm, a curve 4 represents a thickness of 2.5mm, a curve 5 represents a thickness of 3.0mm, a curve 6 represents a thickness of 3.5mm, a curve 7 represents a thickness of 4.0mm, a curve 8 represents a thickness of 4.5mm, a curve 9 represents a thickness of 5.0mm, and a curve 10 represents a thickness of 5.5 mm. It shows excellent wave absorbing performance under the thickness of 2-18GHz and 1-5.5 mm. When the matching thickness is 2.5mm, the maximum reflection loss is-46.71 dB and the effective bandwidth is 6.73GHz (11.27-18 GHz) at a frequency of 14.39GHz when the filling amount is 2 wt%.
Claims (10)
1. A preparation method of a graphene-supported iron hexagonal nanosheet composite wave-absorbing material is characterized by comprising the following steps:
1. placing a copper foil substrate in electrolyte, performing electrochemical polishing, then performing ultrasonic cleaning, drying by blowing argon, placing the copper foil substrate in a tube furnace for CVD, introducing argon, heating to 300-310 ℃, then introducing oxygen, oxidizing the copper foil substrate, then closing the oxygen, introducing hydrogen, controlling the temperature to rise to 1000-1005 ℃ in 35-40 min, then controlling the temperature to rise to 1035-1040 ℃ in 30-35 min, preserving the temperature for 30-90 min, and then cooling to 1000-1005 ℃; then heating to 1035-1040 ℃, introducing high-purity methane for nucleation growth of graphene to obtain single-layer graphene;
2. transferring the single-layer graphene obtained in the first step to Si/SiO 2 Placing the substrate in an evaporation sample chamber, taking high-purity iron particles as an evaporation source, and controlling the background vacuum degree to be 1.0x10 -3 Pa, cleaning an evaporation boat, accurately setting the thickness of an iron film to be evaporated by using a coating instrument, and performing Cr/Au evaporation on a metal electrode to obtain a graphene/iron field effect transistor device;
3. dissolving ferric trichloride hexahydrate in an ethanol solution, magnetically stirring until the ferric trichloride hexahydrate is completely dissolved, adding sodium acetate to adjust the pH value to 9-11, completely stirring and dissolving, then transferring to a Teflon hot-pressing kettle, controlling the temperature to be 180-220 ℃, and carrying out hydrothermal treatment for 18-24 hours; cooling to room temperature, centrifugally washing with deionized water and absolute ethyl alcohol, and drying to obtain alpha-Fe 2 O 3 Hexagonal nanosheet powder;
4. the cationic surfactant cetyl trimethyl ammonium bromide and the alpha-Fe obtained in the third step 2 O 3 Dispersing hexagonal nano-sheet powder in deionized water to obtain alpha-Fe 2 O 3 The mass-volume ratio of the total mass of the hexagonal nanosheet powder and the hexadecyl trimethyl ammonium bromide to the mass of the deionized water is (4-6) g (100-200) mL, the temperature of the constant-temperature water bath is controlled to be 60-80 ℃, the stirring is carried out for 2-3 h, the mixture is naturally cooled, then the mixture is washed by the deionized water and dried, and the surface modified alpha-Fe is obtained 2 O 3 Hexagonal nanosheet powder;
5. adding graphite powder, sodium nitrate and concentrated sulfuric acid into a three-neck flask, placing the three-neck flask in an ice bath for mechanical stirring, controlling the rotation speed of the mechanical stirring to be 200-400 r/min, adding potassium permanganate during the stirring process, then controlling the constant-temperature water bath to be 35-45 ℃, continuously stirring for 1.5-2.5 h, adding deionized water during the reaction process, transferring the three-neck flask to an oil bath condition of 98-105 ℃ after the reaction is finished, and continuously stirring for 15-20 min; then cooling to room temperature, adding deionized water and hydrogen peroxide solution, sealing, preserving and standing; hydrochloric acid with volume concentration of 10-15% and deionized water are adopted for centrifugal washing until the solution is neutral; adding ionized water after dialysis for one week, and performing ultrasonic dispersion to obtain a graphene oxide suspension;
6. the surface modified alpha-Fe obtained in the fourth step 2 O 3 Ultrasonically stirring and mixing the hexagonal nanosheet powder and the graphene oxide suspension obtained in the fifth step, and freeze-drying; and then putting the mixture into a tubular furnace for thermal reduction, wherein the reducing atmosphere is hydrogen atmosphere or hydrogen-argon mixed atmosphere, the heating rate is controlled to be 2-10 ℃/min, the temperature is controlled to be 350-600 ℃, and the heat preservation time is 1-3 h, so that the graphene-loaded iron hexagonal nanosheet composite wave-absorbing material is obtained, and the preparation is completed.
2. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the electrolyte in the first step is a mixture of phosphoric acid and polyethylene glycol, and the volume ratio of phosphoric acid to polyethylene glycol is 3; the oxidation time of the copper foil substrate is controlled to be 30-40 min, and the introduction time of high-purity methane is controlled to be 10-20 min.
3. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the thickness of the evaporated iron film in the second step is 10-50 nm.
4. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the volume ratio of anhydrous ethanol to water in the ethanol solution in step three is 14.
5. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the centrifugal washing speed is controlled to be 8000-10000 rpm/min in the third step, and the time is 30-50 min.
6. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the alpha-Fe obtained in step three 2 O 3 The hexagonal nano-sheet powder has a transverse size of 100-200 nm and a thickness of 10-20 nm.
7. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the step four of the alpha-Fe 2 O 3 The mass ratio of the hexagonal nanosheet powder to the hexadecyl trimethyl ammonium bromide is 3-5.
8. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein in the reaction process of step five, the mass-to-volume ratio of the graphite powder, sodium nitrate, concentrated sulfuric acid, potassium permanganate, deionized water and hydrogen peroxide solution is 3g:1.5g:75mL of: 9g:150mL of: 15mL;
the mesh number of the graphite powder is 200-8000 meshes.
9. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, wherein the concentration of the graphene pentoxide suspension in the step is 2-10 mg/mL.
10. The preparation method of the graphene-supported iron hexagonal nanosheet composite wave-absorbing material according to claim 1, characterized in that step six is to reduce graphene oxide and the surface-modified α -Fe in the graphene oxide suspension 2 O 3 The mass ratio of the hexagonal nanosheet powder is 1g:2 to 8mg.
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