CN114950287B - Chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with spiral structure, preparation method and application - Google Patents
Chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with spiral structure, preparation method and application Download PDFInfo
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Abstract
The invention discloses a chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure, a preparation method and application thereof, and the method comprises the following steps: step 1: dissolving calcium chloride and ammonium persulfate in a solvent, and uniformly mixing to obtain a coagulating bath solution; step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; step 3: adding camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain spinning solution; step 4: taking the coagulating bath solution obtained in the step 1 as a collector of microdroplets, and obtaining graphene hydrogel microspheres through wet spinning; step 5: standing the graphene hydrogel microspheres obtained in the step 4, and reducing; step 6: after cleaning, freeze-drying to obtain chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure; the preparation method is simple and convenient to operate, and the obtained aerogel wave-absorbing microsphere has excellent microwave absorption performance.
Description
Technical Field
The invention relates to the technical field of graphene aerogel microspheres, in particular to a chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure, a preparation method and application.
Background
In recent years, graphene aerogel has received a great deal of attention as the most representative light-weight, high-efficiency wave-absorbing material. The three-dimensional 3D network structure of graphene aerogel can be used as a skeleton structure to load other dielectric/magnetic loss media so as to further improve microwave absorption. However, in the face of complex application environments and use requirements, due to the lack of space structural design, the traditional massive graphene aerogel is difficult to regulate and control the loss capacity of the traditional massive graphene aerogel in a wide frequency band, and meanwhile, the traditional massive graphene aerogel is also unfavorable for realizing development and integration of multiple functions through the physical characteristics of the traditional massive graphene aerogel. Therefore, the design of the macroscopic shape and the microstructure of the aerogel is a necessary way for breaking the limitation and realizing the targets of broadband efficient microwave absorption, multifunctional integration and the like.
Compared with the traditional bulk integral graphene material, the spherical graphene aerogel retains the low density, high specific surface area, strong electricity loss capability and electromagnetic wave reflection loss capability of the graphene aerogel. Meanwhile, the customizable internal structure of the microsphere is beneficial to improving impedance matching of the graphene aerogel microsphere and enhancing dielectric loss or introducing magnetic loss by introducing different heterostructures, so that broadband efficient microwave absorption is realized.
In recent years, chirality has been considered as one of the most interesting properties of functional materials, as it provides the most advanced strategy for designing new chiral functional materials with electrical, magnetic and optical properties. The helical structure of the chiral material may exhibit good microwave absorption. This makes chiral materials the most potential high performance microwave absorbing materials because of their additional chiral parameters and structural chirality induced cross polarization, resulting in electromagnetic losses. Chiral conductive polymers are receiving much attention for their good conductive properties. However, the existing chiral material has the problems of unsatisfactory electromagnetic performance, complex preparation method and the like.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a chiral polyaniline@reduced graphene oxide aerogel microsphere with a spiral structure, which is simple in preparation method and excellent in electromagnetic absorption performance, and a preparation method and application thereof.
The technical scheme adopted by the invention is as follows:
the preparation method of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure comprises the following steps:
step 1: dissolving calcium chloride and ammonium persulfate in a solvent, and uniformly mixing to obtain a coagulating bath solution;
step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of graphene oxide to aniline is 0.5-3:1; the molar ratio of ammonium persulfate to aniline is 1-1.5:1;
step 3: adding camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain spinning solution; wherein the concentration of camphorsulfonic acid in the spinning solution is: 0.8mol/L to 1.2mol/L;
step 4: taking the coagulating bath solution obtained in the step 1 as a collector of microdroplets, and obtaining graphene hydrogel microspheres through wet spinning;
step 5: standing the graphene hydrogel microspheres obtained in the step 4, and reducing;
step 6: after cleaning, the polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a chiral structure can be obtained through freeze drying.
Further, in the wet spinning process in the step 4, the distance from the needle tip to the surface of the coagulating bath solution is 2cm, and the spinning solution speed is 0.1mL/min.
Further, the standing time in the step 5 is 5 hours, and the standing is performed in an ice-water bath.
Further, the reduction process in the step 5 is as follows: adopting sodium ascorbate for reduction, wherein the reduction is carried out at the temperature of 80 ℃ for 50min; wherein the molar ratio of sodium ascorbate to graphene oxide is 1.5:1.
Further, the freeze drying in the step 6 is 48 hours.
Further, the solvent in the step 1 is a mixed solution formed by deionized water and ethanol, and the volume ratio of the ethanol in the solvent is 30%; the concentration of calcium chloride in the mixed solution is as follows: 4wt.% to 6wt.%.
Further, the concentration of the graphene oxide dispersion liquid in the step 2 is 5mg/mL; the dispersion was completed in an ice-water bath.
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure is prepared by the preparation method, wherein the inside of the aerogel wave-absorbing microsphere is provided with a micro-channel structure which is orderly and divergently, and graphene sheets are orderly arranged in a regular manner to form a regular three-dimensional porous network structure.
The application of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure is that the polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere is used as a microwave absorbent.
The beneficial effects of the invention are as follows:
(1) According to the preparation method, the polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral chiral structure is prepared by a wet spinning-chemical reduction-freeze drying method, so that the preparation method is simple and convenient to operate;
(2) According to the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure, the chiral structure is built by chiral self-assembly of the graphene sheet layer under the induction of camphorsulfonic acid, so that the original conductive network of the graphene is destroyed, the conductivity is reduced, and meanwhile, the impedance matching performance is obviously improved due to the regular chiral structure; under the action of incident microwaves, cross polarization and self polarization are simultaneously and cooperatively generated in the chiral microspheres, so that the attenuation of electromagnetic waves is facilitated.
(3) According to the invention, the polyaniline is introduced into the graphene microsphere to bring a new heterogeneous interface and multiple reflection channels for the graphene microsphere, so that the interface polarization is further enhanced, and the synergistic effect of multiple loss mechanisms is realized;
(4) The sample obtained by taking the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure as a microwave absorber is tested, the minimum reflection loss reaches-48 dB at the frequency of 14.4GHz under the thickness of 2.8mm, and the corresponding effective absorption bandwidth is kept at 6.88GHz.
Drawings
Fig. 1 is an SEM image of a chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere having a spiral structure obtained in example 1 of the present invention, a-c are SEM images of reduced graphene oxide aerogel microspheres (RGO AMs and RGO in the following figures refer to the aerogel microspheres), and d-f are SEM images of aerogel wave-absorbing microspheres obtained in example 1 ([email protected] AMs in the following figures).
Fig. 2 is an SEM image of chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure obtained in the embodiment of the invention. a-c are SEM images of aerogel microspheres obtained in example 2 (each indicated by PANi@RGO-1AMs in the following figures), d-f are SEM images of aerogel absorbent microspheres obtained in example 3 (each indicated by PANi@RGO-2AMs in the following figures), and g-i are SEM images of aerogel absorbent microspheres obtained in example 4 (each indicated by [email protected] in the following figures).
FIG. 3 is a FT-IR spectrum (a) and a Raman spectrum (b) of a chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure obtained in an embodiment of the invention.
Fig. 4 is a three-dimensional reflection loss diagram of samples with different thicknesses obtained by using chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure as a microwave absorbent. a is RGO, b is the aerogel wave-absorbing microsphere obtained in example 1, c is the aerogel wave-absorbing microsphere obtained in example 2, d is the aerogel wave-absorbing microsphere obtained in example 3, and e is the aerogel wave-absorbing microsphere obtained in example 4.
Fig. 5 shows electromagnetic parameters of samples with different thicknesses obtained by using chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure as a microwave absorbent. a is the real part of dielectric constant, b is the imaginary part of dielectric constant, c is the real part of magnetic permeability, d is the imaginary part of magnetic permeability, e is the corresponding tan delta epsilon value, f is the corresponding tan delta mu value, and g is the cole-cole curve of the aerogel wave-absorbing microsphere obtained in example 1.
Fig. 6 is a two-dimensional impedance matching chart of samples with different thicknesses obtained by using chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure as a microwave absorbent. a is example 1, b is example 2, c is example 3, d is example 4, and e is the decay constant.
Detailed Description
The invention will be further described with reference to the drawings and specific examples.
The preparation method of the chiral polyaniline@reduced graphene oxide aerogel microsphere with the spiral structure comprises the following steps:
step 1: dissolving calcium chloride and ammonium persulfate in a solvent, and uniformly mixing to obtain a coagulating bath solution; the volume ratio of ethanol in the solvent is 30 percent; the concentration of calcium chloride in the mixed solution is as follows: 4wt.% to 6wt.%; preferably 5wt.%.
Step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of graphene oxide to aniline is 0.5-3:1; the concentration of the graphene oxide dispersion liquid is 5mg/mL; the dispersion process is completed in an ice water bath; the molar ratio of ammonium persulfate to aniline is 1-1.5:1.
Step 3: adding camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain spinning solution; wherein the concentration of camphorsulfonic acid in the spinning solution is: 0.8mol/L to 1.2mol/L;
step 4: taking the coagulating bath solution obtained in the step 1 as a collector of microdroplets, and obtaining graphene hydrogel microspheres through wet spinning; in the wet spinning process, the distance from the needle point to the surface of the coagulating bath solution is 2cm, and the spinning solution speed is 0.1mL/min.
Step 5: standing the graphene hydrogel microsphere obtained in the step 4 in an ice-water bath for 5 hours, and then reducing; adopting sodium ascorbate for reduction, wherein the reduction is carried out at the temperature of 80 ℃ for 50min; wherein the molar ratio of sodium ascorbate to graphene oxide is 1.5:1.
Step 6: after cleaning, freeze-drying for 48 hours, the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure can be obtained.
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure is characterized in that the interior of the aerogel wave-absorbing microsphere is provided with a micro-channel structure which is orderly dispersed, graphene sheets are orderly arranged in a regular manner, and a regular three-dimensional porous network structure is shown.
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure is used as a microwave absorbent.
Example 1
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is prepared according to the following steps:
step 1: 10g of calcium chloride and ammonium persulfate are added into 200mL of mixed solution of water and ethanol to be uniformly mixed to obtain a coagulating bath solution, wherein the volume ratio of ethanol in the solvent is 30%.
Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion liquid in ice water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion solution is 5mg/mL; the molar ratio of graphene oxide to aniline was 0.5:1. The molar ratio of ammonium persulfate to aniline was 1.5:1.
Step 3: and 5.05mL of deionized water is used for dissolving camphorsulfonic acid, the uniform solution is added into the mixed solution obtained in the step 2, and the spinning solution is obtained after full and uniform mixing.
Step 4: hydrogel microspheres were obtained by wet spinning, in which the coagulation bath solution was used as a collector for droplets, the distance from the tip of the needle to the coagulation bath liquid surface was about 2cm, and the spinning solution rate was 0.1mL/min.
Step 5: and (3) standing the graphene hydrogel microspheres obtained in the step (4) in an ice water bath for 5 hours to polymerize aniline. The aerogel microspheres were then washed and reduced with sodium ascorbate at 80 ℃ for 50min. Wherein the molar ratio of sodium ascorbate to graphene is 1.5:1.
step 6: and after the reduction is finished, cleaning the aerogel microspheres again, and freeze-drying for 48 hours to obtain the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres (recorded as [email protected]) with a spiral structure.
Example 2
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is prepared according to the following steps:
step 1: 10g of calcium chloride and ammonium persulfate are added into 200mL of mixed solution of water and ethanol to be uniformly mixed to obtain a coagulating bath solution, wherein the volume ratio of ethanol in the solvent is 30%.
Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion liquid in ice water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion solution is 5mg/mL; the molar ratio of graphene oxide to aniline is 1:1. The molar ratio of ammonium persulfate to aniline was 1.5:1.
Step 3: and 5.05mL of deionized water is used for dissolving camphorsulfonic acid, the uniform solution is added into the mixed solution obtained in the step 2, and the spinning solution is obtained after full and uniform mixing.
Step 4: hydrogel microspheres were obtained by wet spinning, in which the coagulation bath solution was used as a collector for droplets, the distance from the tip of the needle to the coagulation bath liquid surface was about 2cm, and the spinning solution rate was 0.1mL/min.
Step 5: and (3) standing the graphene hydrogel microspheres obtained in the step (4) in an ice water bath for 5 hours to polymerize aniline. The aerogel microspheres were then washed and reduced with sodium ascorbate at 80 ℃ for 50min. Wherein the molar ratio of sodium ascorbate to graphene is 1.5:1.
step 6: and after the reduction is finished, cleaning the aerogel microspheres again, and freeze-drying for 48 hours to obtain the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres (denoted as PANi@RGO-1) with a spiral structure.
Example 3
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is prepared according to the following steps:
step 1: 10g of calcium chloride and ammonium persulfate are added into 200mL of mixed solution of water and ethanol to be uniformly mixed to obtain a coagulating bath solution, wherein the volume ratio of ethanol in the solvent is 30%.
Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion liquid in ice water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion solution is 5mg/mL; the molar ratio of graphene oxide to aniline was 2:1. The molar ratio of ammonium persulfate to aniline was 1.5:1.
Step 3: and 5.05mL of deionized water is used for dissolving camphorsulfonic acid, the uniform solution is added into the mixed solution obtained in the step 2, and the spinning solution is obtained after full and uniform mixing.
Step 4: hydrogel microspheres were obtained by wet spinning, in which the coagulation bath solution was used as a collector for droplets, the distance from the tip of the needle to the coagulation bath liquid surface was about 2cm, and the spinning solution rate was 0.1mL/min.
Step 5: and (3) standing the graphene hydrogel microspheres obtained in the step (4) in an ice water bath for 5 hours to polymerize aniline. The aerogel microspheres were then washed and reduced with sodium ascorbate at 80 ℃ for 50min. Wherein the molar ratio of sodium ascorbate to graphene is 1.5:1.
step 6: and after the reduction is finished, cleaning the aerogel microspheres again, and freeze-drying for 48 hours to obtain the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres (denoted as PANi@RGO-2) with a spiral structure.
Example 4
The chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is prepared according to the following steps:
step 1: 10g of calcium chloride and ammonium persulfate are added into 200mL of mixed solution of water and ethanol to be uniformly mixed to obtain a coagulating bath solution, wherein the volume ratio of ethanol in the solvent is 30%.
Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion liquid in ice water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion solution is 5mg/mL; the molar ratio of graphene oxide to aniline was 3:1. The molar ratio of ammonium persulfate to aniline was 1.5:1.
Step 3: and 5.05mL of deionized water is used for dissolving camphorsulfonic acid, the uniform solution is added into the mixed solution obtained in the step 2, and the spinning solution is obtained after full and uniform mixing.
Step 4: hydrogel microspheres were obtained by wet spinning, in which the coagulation bath solution was used as a collector for droplets, the distance from the tip of the needle to the coagulation bath liquid surface was about 2cm, and the spinning solution rate was 0.1mL/min.
Step 5: and (3) standing the graphene hydrogel microspheres obtained in the step (4) in an ice water bath for 5 hours to polymerize aniline. The aerogel microspheres were then washed and reduced with sodium ascorbate at 80 ℃ for 50min. Wherein the molar ratio of sodium ascorbate to graphene is 1.5:1.
step 6: and after the reduction is finished, cleaning the aerogel microspheres again, and freeze-drying for 48 hours to obtain the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres (denoted as PANi@RGO-3) with a spiral structure.
The morphology and structure of the aerogel microspheres were observed using a field emission scanning electron microscope (FE-SEM, JEOL, JSM-7800F) as shown in fig. 1. The structure of the characterization material (FTIR Spectrometer; bruker, TENSOR II) is shown in FIG. 2a using Fourier infrared spectroscopy. The structural differences of the graphene microspheres were analyzed using 532nm argon ion laser raman spectroscopy (insia Renishaw). The complex permeability and dielectric constant of aerogel microspheres were measured with a vector network analyzer (AV 3618, CETC) over a frequency range of 2 to 18 GHz. The electromagnetic constants were measured by uniformly mixing 4.0wt.% of the sample with paraffin wax to prepare a ring-shaped sample having an outer diameter of 7.0mm and an inner diameter of 3.04 mm.
The internal structure of the prepared graphene-based aerogel wave-absorbing microsphere was observed by SEM, as shown in fig. 1 and 2. In order to explain the aerogel wave-absorbing microsphere structure obtained in this example, reduced graphene oxide aerogel microspheres RGO AMs (RGO in the following figures refers to the microsphere (preparation method such as chiral polyaniline@reduced graphene oxide aerogel microsphere with a spiral structure, except that no aniline is added in step 2, step 3 is not included, and other steps are the same)) are used as a comparison (fig. 1a to 1 c). Fig. 1d to 1f show chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres (pani@rgo AMs) having a helical structure obtained in example 1. It can be seen from the figure that the chiral structure is always formed centered on the edges of the microspheres, since the outer graphene sheets solidify first when solidifying in the coagulation bath. Further observing the local microscopic morphology as shown in fig. 1e and 1f, the regular ordered arrangement of graphene sheets can be found, a regular three-dimensional porous network structure is presented, the graphene sheets are very compact in arrangement, and the pore diameter is small. This is because the formation of chiral polyaniline consumes a part of camphorsulfonic acid, decreases its concentration, and reduces the induction effect on graphene sheets. ANi under the doping of camphorsulfonic acid + Intercalation occurs, and polymerization is carried out in graphene sheets and becomes a chiral center, which influences chiral arrangement of subsequent graphene sheets under the induction of camphorsulfonic acid.
To investigate the effect of aniline addition on the graphene-based aerogel wave-absorbing micropellet structure. The amounts of graphene oxide and aniline added in examples 1 to 4 were different; fig. 2 is an SEM image of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres having a spiral structure obtained in examples 2 to 4. FIGS. 2a to 2c are SEM images of aerogel microwave absorbing microspheres obtained in example 2, wherein the molar ratio of graphene oxide to aniline is 1:1; FIGS. 2d to 2f are SEM images of aerogel microwave absorbing microspheres obtained in example 3, the molar ratio of graphene oxide to aniline being 2:1; FIGS. 2g to 2i are SEM images of aerogel microwave absorbing microspheres obtained in example 4, and the molar ratio of graphene oxide to aniline is 3:1. As can be seen from the figure, all have chiral structures, but as the amount of aniline added decreases, chiral polyaniline as a chiral center decreases, resulting in a gradual decrease in the degree of order of subsequent chiral alignment. The arrangement of graphene sheets becomes disordered (as shown in fig. 2e, 2f, 2 i). The content of polyaniline mainly influences the conductive loss capacity and the impedance matching performance of the aerogel wave-absorbing microsphere.
The structure of RGO AMs and PANi@RGO AMs is shown in FIG. 3 by infrared spectroscopy analysis. As can be seen from FIG. 3a, 1639cm for RGO AMs -1 The characteristic peak at which is attributed to the c=c bond of the aromatic ring, while 1387cm -1 The peak at which is associated with C-OH. In PANi@RGO AMs, S-O stretching vibration (1046 cm -1 ) And C-S stretching vibration (671 cm) -1 ). The main characteristic peak of PANi includes quinone ring (Q) (1564 cm -1 ) And benzene ring (B) (1460 cm) -1 ) C=c stretching vibration, C-N stretching vibration (1257 cm -1 ) Vibration modes of-nh+=and n=q=n in PANi chain (-1122 cm) -1 ) And C-H in a substituted benzene ring (802 cm -1 ) Is mixed with the other surface of the substrate. As the aniline content increases, both the c=c stretching vibrations of the quinone ring and the benzene ring undergo a blue shift due to the enhancement of pi-pi interactions between graphene and PANi. Symmetrical telescopic vibration s=o bond (1238 cm) can be found in pani@rgo AMs -1 ) The result shows that the CSA is successfully introduced into a polyaniline molecular chain to form chiral CSA doped polyaniline. Raman spectroscopy (fig. 3 b) was used to study the structural differences between RGO AMs and pani@rgo AMs. Two strong peaks can be clearly observed, corresponding to the D and G bands of graphene, respectively. Compared to RGO AMs, the D band of pani@ams appears blue shifted, and the degree of blue shift of PANi AMs increases with increasing ANi usage, due to pi-pi interactions between PANi and GO. Raman I D /I G The ratio is widely used to evaluate the degree of disorder of the carbon material. The higher the ratio, the greater the degree of disorderThe more defects. In PANi@RGO AMs, with increasing aniline amount, I D /I G The ratio increases from 0.85 to 1.10 due to the more heterogeneous interface between GO and PANi. The increase of polyaniline causes an increase in defects, which is advantageous for a gradual increase in the impedance matching degree and the attenuation of electromagnetic waves.
Compared with RGO aerogel microspheres, the heterogeneous interface generated by polyaniline and RGO enhances the interface polarization, and the performance of PANi@RGO is further improved. The minimum reflection loss of the aerogel microspheres was calculated based on the transmission line theory. The relationship between the microstructure change of the aerogel microspheres and the electromagnetic wave absorption performance is studied.
Wherein Z is in Z is the input impedance of the microwave absorber 0 Is free space impedance, f is microwave frequency, c is speed of light, and d is thickness of the microwave absorber.
FIG. 4 is a graph showing three-dimensional reflection loss of samples obtained by using aerogel microwave absorbing microspheres obtained in the example of the present invention as microwave absorbers at different thicknesses. a is RGO, b is the aerogel wave-absorbing microsphere obtained in example 1, c is the aerogel wave-absorbing microsphere obtained in example 2, d is the aerogel wave-absorbing microsphere obtained in example 3, and e is the aerogel wave-absorbing microsphere obtained in example 4. It can be seen from the graph that RGO has poor MA characteristics, with RL min at 17.76GHz being-13.4 dB, as shown in FIG. 4 a. This is due to impedance mismatch caused by the high conductivity of the 3D graphene network. After PANi grows in situ on the graphene sheet, the difference in dielectric constant between graphene and PANi can lead to heterogeneous interface charge distortion, and interface polarization is enhanced. RLmin of [email protected] shows-48 dB at 14.4GHz at a thickness of 2.8mm, corresponding to f E At 6.88GHz, as shown in fig. 4 b. As the polyaniline content is reduced, the MA performance of PANi@RGO-1 is reduced to-18 dB at 14.32GHz,but f at 2.8mm E More preferably 7.52GHz (fig. 4 c). Similarly, PANi@RGO-2 exhibits a weak RLmin value of-17 dB at 13.63GHz, but still has an f of 7.60GHz at 2.8mm E (FIG. 4 d). For PANi@RGO-3, it shows a worst RLmin value of-15 dB at 16.65GHz and a worse f of 4.4GHz E (FIG. 4 e). From the above graph, it can be seen that adjusting the aniline addition is a key means for improving MA performance under CSA induction and doping, and the most suitable ratio exists between graphene and aniline, so that the graphene-based aerogel microsphere exhibits MA performance.
To further reveal the MA characteristics of these aerogel wave-absorbing microspheres, the relative complex dielectric constant (. Epsilon.) is in the frequency range of 2-18GHz r =ε '-j ε') and relative complex permeability (μ) r =μ' -j epsilon ") as shown in fig. 5. The real part (epsilon ') and the imaginary part (epsilon') of the dielectric constants of all samples show a decreasing trend with increasing frequency (FIGS. 5 a-b). The RGO has the highest ε' and ε ", as shown in FIG. 5 a. Epsilon' and epsilon "rise with polymerization of polyaniline, but the extent of influence varies with the proportion of aniline. As the aniline usage was reduced, ε' and ε "of PANi@RGO increased and then decreased, [email protected] exhibited a medium equivalence in these PANi@RGOs, probably due to better binding of graphene to polyaniline.
the tan delta epsilon value is an important parameter for evaluating the dielectric loss capability of a microwave absorbing material to an incident electromagnetic wave. A high dielectric loss tangent tan delta epsilon may be effective to absorb microwaves and convert them to thermal or other types of energy, but too high tan delta epsilon may result in impedance mismatch with free space. Thus, a moderate tan delta epsilon is critical to the MA performance of the absorbent material. [email protected] has a moderate tan delta epsilon, which means that the impedance matching of the system is improved and electromagnetic waves enter more easily (FIG. 5 e). FIGS. 5 c-5 e test the real part μ', imaginary part μ″ and tan δμ of the permeability of aerogel wave-absorbing microspheres. A distinct formant (multi-resonance behavior) can be found in fig. 5d, indicating that the material has this loss to the electromagnetic wave, which is due to the cross-polarization of the chiral structure. And the dielectric loss tangent tan delta epsilon is much larger than the magnetic conductivity tangent tan delta mu, which indicates that the magnetic loss of cross polarization caused by chiral structures is very weak, so that the PANi@RGO AMs realizes attenuation of electromagnetic waves mainly through dielectric loss.
Dielectric losses of the absorber mainly include conduction losses and polarization relaxation. According to debye relaxation theory, the polarization relaxation mechanism of composite materials can be described by Cole-Cole semicircle:
wherein ε s Is static dielectric constant epsilon ∞ Is the dielectric constant at infinite frequency. When the epsilon ' curve of epsilon ' and epsilon ' is a single semicircle (Cole-Cole semicircle), it corresponds to a dielectric polarization relaxation process. As shown in fig. 5 g. Debye semicircle can be obviously observed in the Cole-Cole curves of the graphene-based aerogel microspheres, which indicates that a certain polarization relaxation process exists in the graphene-based aerogel microspheres. For pani@rgo, the polarization relaxation is mainly dipole polarization caused by defects or residual polar groups of the graphene sheet and interfacial polarization caused by chiral alignment of the graphene sheet layers. In addition to the two polarization relaxations described above, the introduction of polyaniline creates a new hetero-interface, and the difference in dielectric constant between graphene sheets and polyaniline can lead to charge distortion of the hetero-interface, thereby creating a new interface polarization. In addition, all Cole-Cole curves present long tails, indicating that the conduction loss caused by the applied alternating electromagnetic field is the main loss mechanism of the aerogel wave-absorbing microspheres to electromagnetic waves.
Impedance matching is a key factor in evaluating absorber MA performance, representing the ability of microwaves to enter the absorbing material and convert to thermal energy or dissipate by interference. To better explore the MA performance of these aerogel wave-absorbing microspheres, the characteristic impedance z= |z was normalized in /Z 0 Evaluation of impedance matching. When the Z ratio approaches 1, almost all incident electromagnetic waves can penetrate the material integrity without microwave reflectivity, exhibiting optimal impedance matching. Typically, an absorber is considered to have a good impedance match when its Z is in the range of 0.8-1.2. The two-dimensional map of the Z values of PANi@RGO AMs is shown in FIG. 6. Wave absorbing in these aerogelsIn the microsphere, as the addition amount of aniline is reduced, the impedance matching performance of PANi@RGO gradually decreases, which means that the conductive loss and impedance matching of the microsphere can be effectively improved by adjusting the use amount of aniline.
Furthermore, the attenuation constant α is another important factor affecting the performance of the material MA, and is obtained by the following equation for explaining the attenuation capability of the wave-absorbing material to the incident microwaves:
proper impedance matching performance and high attenuation capability give the absorber excellent MA performance. As shown in fig. 6 e. Aerogel wave-absorbing microspheres have a higher alpha value and a damping constant value exceeding 100 at medium and high frequencies. The [email protected] has excellent absorption efficiency on electromagnetic waves by combining attenuation constant and impedance matching.
The chiral PANi@RGO AMs is prepared by a wet spinning-chemical reduction-freeze drying method. By utilizing the aggregation and segregation phenomena of graphene oxide, graphene oxide sheets contain a large amount of oxygen-containing groups, and thus are negatively charged when dispersed in water. The introduction of positively charged species into the graphene oxide aqueous dispersion causes aggregation and separation of the graphene oxide, resulting in self-assembly of the graphene oxide at the interface. When the microdroplets contact the coagulation bath, the outer graphene oxide sheets are first coagulated to form a graphene oxide film, while the graphene oxide dispersion is still within the film. During the long-term standing solidification process, ca 2+ Gradually penetrating into the interior of graphene oxide microdroplets under high osmotic pressure, causing self-assembly of graphene oxide sheets. Polyaniline polymerizes faster than graphene oxide platelets, so chiral polyaniline forms first and serves as a chiral center. In the subsequent polymerization process, chiral self-assembly is continuously generated by taking chiral polyaniline as chirality under the steric hindrance effect of CSA. After chemical reduction and freeze drying, oxygen-containing groups on the GO sheet layers are reduced to form Reduced Graphene Oxide (RGO), and finally the graphene-based aerogel wave-absorbing microspheres are obtained.
The chiral graphene-based aerogel wave-absorbing microsphere with light weight, wide frequency band and high microwave efficiency is successfully prepared by a wet spinning technology. From experimental test results, the chiral structure is constructed to be favorable for coordinating the conduction loss and the impedance matching, and the system interface polarization is enhanced along with the polymerization of chiral polyaniline. The [email protected] aerogel wave-absorbing microsphere has a minimum reflection loss RLmin value of-48 dB with a load of only 4wt% and a thickness of 2.8mm, and the effective absorption bandwidth can reach 6.88GHz. By changing the addition amount of aniline, the effective absorption bandwidth of the microsphere can be increased to 7.60GHz.
The invention provides new insight for designing and synthesizing the wave-absorbing material with a special structure, and the graphene-based aerogel wave-absorbing microsphere has stronger absorption efficiency and wider absorption bandwidth. The chiral structure is constructed by utilizing the interaction between the small molecules and the graphene, so that a new thought and foundation are provided for the design of the graphene-based aerogel wave-absorbing microsphere.
Claims (6)
1. The preparation method of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure is characterized by comprising the following steps of:
step 1: dissolving calcium chloride and ammonium persulfate in a solvent, and uniformly mixing to obtain a coagulating bath solution;
step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of graphene oxide to aniline is 0.5-3:1; the molar ratio of ammonium persulfate to aniline is 1-1.5:1;
step 3: adding camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain spinning solution; wherein the concentration of camphorsulfonic acid in the spinning solution is: 0.8mol/L to 1.2mol/L;
step 4: taking the coagulating bath solution obtained in the step 1 as a collector of microdroplets, and obtaining graphene hydrogel microspheres through wet spinning; in the wet spinning process, the distance from the needle point to the surface of the coagulating bath solution is 2cm, and the spinning solution speed is 0.1mL/min;
step 5: standing the graphene hydrogel microspheres obtained in the step 4, and reducing; standing for 5h, and standing in ice water bath;
step 6: after cleaning, freeze-drying to obtain polyaniline@reduced graphene oxide aerogel wave-absorbing microspheres with chiral structures;
the aerogel wave-absorbing microsphere is internally provided with a micro-channel structure which is orderly dispersed, and graphene sheets are orderly arranged in a regular manner to form a regular three-dimensional porous network structure.
2. The method for preparing the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure according to claim 1, wherein the reduction process in the step 5 is as follows: adopting sodium ascorbate for reduction, wherein the reduction is carried out at the temperature of 80 ℃ for 50min; wherein the molar ratio of sodium ascorbate to graphene oxide is 1.5:1.
3. The method for preparing the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure according to claim 1, wherein the freeze drying in the step 6 is 48h.
4. The preparation method of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure according to claim 1, wherein the solvent in the step 1 is a mixed solution formed by deionized water and ethanol, and the volume ratio of the ethanol in the solvent is 30%; the concentration of calcium chloride in the mixed solution is as follows: 4wt.% to 6wt.%.
5. The method for preparing the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure according to claim 1, wherein the concentration of the graphene oxide dispersion liquid in the step 2 is 5mg/mL; the dispersion was completed in an ice-water bath.
6. The application of the chiral polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure obtained by the preparation method according to any one of claims 1 to 5, wherein the polyaniline@reduced graphene oxide aerogel wave-absorbing microsphere is used as a microwave absorbent.
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