CN114950287A

CN114950287A - Chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with spiral structure, preparation method and application

Info

Publication number: CN114950287A
Application number: CN202210591560.3A
Authority: CN
Inventors: 孟凡彬; 田颖睿; 李天�; 邓文婷; 徐正康
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2022-05-27
Filing date: 2022-05-27
Publication date: 2022-08-30
Anticipated expiration: 2042-05-27
Also published as: CN114950287B

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 preparation 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; and step 3: adding a camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain a spinning solution; and 4, 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; and 5: standing the graphene hydrogel microspheres obtained in the step 4, and reducing; step 6: after cleaning, freezing and drying to obtain the 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 microspheres have excellent microwave absorption performance.

Description

Chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with spiral structure, preparation method and application

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 much attention as the most representative light-weight and efficient wave-absorbing material. The three-dimensional 3D network structure of the graphene aerogel can be used as a framework structure to load other dielectric/magnetic loss media, so that microwave absorption is further improved. However, in the face of complex application environments and use requirements, the traditional bulk graphene aerogel is difficult to regulate and control the loss capacity in a wide frequency range due to the lack of a spatial structure design, and meanwhile, the traditional bulk graphene aerogel is also not beneficial to realizing development and integration of multiple functions through the physical characteristics of the traditional bulk graphene aerogel. Therefore, by designing the macroscopic shape and the microstructure of the aerogel, obtaining a specific spatial arrangement structure is a necessary way to break the above limitations and achieve the goals of broadband efficient microwave absorption, multifunctional integration, and the like.

Compared with the traditional blocky whole graphene material, the spherical graphene aerogel keeps the low density, the high specific surface area, the strong current loss capacity and the reflection loss capacity to electromagnetic waves of the graphene aerogel. Meanwhile, the customizable internal structure of the microsphere is beneficial to improving the impedance matching of the graphene aerogel microsphere and enhancing the dielectric loss or introducing the magnetic loss by introducing different heterostructures, so that the broadband high-efficiency 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. Because of the additional chiral parameters and cross polarization induced by structural chirality, electromagnetic loss is caused, which makes chiral materials the most potential high-performance microwave absorbing materials. Chiral conductive polymers have received much attention because of their good electrical conductivity. However, the existing chiral material has the problems of unsatisfactory electromagnetic performance, complex preparation method and the like.

Disclosure of Invention

The invention provides a chiral polyaniline @ reduced graphene oxide aerogel microsphere with a spiral structure, a preparation method and application, which are simple and have excellent electromagnetic absorption performance, aiming at the problems in the prior art.

The technical scheme adopted by the invention is as follows:

a preparation method of chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a 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;

and 2, step: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of the graphene oxide to the aniline is 0.5-3: 1; the molar ratio of ammonium persulfate to aniline is 1-1.5: 1;

and 3, step 3: adding a camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain a spinning solution; wherein the concentration of camphorsulfonic acid in the spinning solution is: 0.8mol/L-1.2 mol/L;

and 4, 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;

and 5: standing the graphene hydrogel microspheres obtained in the step 4, and reducing;

step 6: after cleaning, freeze drying is carried out, and the polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with chiral structures can be obtained.

Further, in the wet spinning process in the step 4, the distance from the needle tip to the surface of the coagulation bath solution is 2cm, and the speed of the spinning solution is 0.1 mL/min.

Further, the standing time in the step 5 is 5 hours, and the standing is carried out in an ice water bath.

Further, the reduction process in the step 5 is as follows: reducing with sodium ascorbate at 80 deg.C for 50 min; 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 composed of deionized water and ethanol, and the volume ratio of ethanol in the solvent is 30%; the concentration of calcium chloride in the mixed solution is as follows: 4 wt.% to 6 wt.%.

Further, the concentration of the graphene oxide dispersion liquid in the step 2 is 5 mg/mL; the dispersion was done in an ice-water bath.

The chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure, which is obtained by the preparation method, has a sequentially-dispersed micro-channel structure inside the aerogel wave-absorbing microsphere, and graphene sheets are regularly and sequentially arranged to present a regular three-dimensional porous network structure.

An application of chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure is disclosed, wherein the polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres are used as a microwave absorbent.

The invention has the beneficial effects that:

(1) the polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with the spiral chiral structures are prepared by a wet spinning-chemical reduction-freeze drying method, and 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, under the induction of camphorsulfonic acid, the graphene sheet layers form a chiral structure through chiral self-assembly, so that the original conductive network of graphene is damaged, the conductivity is reduced, and meanwhile, the impedance matching performance is obviously improved due to the regular chiral structure; under the action of incident microwave, cross polarization and self polarization are generated in the chiral microsphere simultaneously and synergistically, so that electromagnetic wave attenuation is facilitated.

(3) According to the invention, polyaniline is introduced into the graphene microspheres, so that a new heterogeneous interface and a multi-reflection channel are brought to the graphene microspheres, 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 absorbent is tested, the minimum reflection loss reaches-48 dB at the thickness of 2.8mm and the frequency of 14.4GHz, and the corresponding effective absorption bandwidth is kept at 6.88 GHz.

Drawings

Fig. 1 is an SEM image of chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres having a helical structure obtained in example 1 of the present invention, a-c are SEM images of the reduced graphene oxide aerogel microspheres (RGO AMs and RGO in the following figures both refer to the aerogel microspheres), and d-f are SEM images of the aerogel wave-absorbing microspheres obtained in example 1 (PANi @ RGO-0.5AMs in the following figures).

Fig. 2 is an SEM image of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with a helical structure obtained in the embodiment of the present invention. a-c are SEM pictures of the aerogel microspheres obtained in example 2 (all shown as PANI @ RGO-1AMs in the following figures), d-f are SEM pictures of the aerogel wave-absorbing microspheres obtained in example 3 (all shown as PANI @ RGO-2AMs in the following figures), and g-i are SEM pictures of the aerogel wave-absorbing microspheres obtained in example 4 (all shown as PANI @ RGO-0.5AMs in the following figures).

Fig. 3 is an FT-IR spectrum (a) and a raman spectrum (b) of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with a helical structure obtained in the embodiment of the present invention.

Fig. 4 is a three-dimensional reflection loss diagram of samples with different thicknesses, which is obtained by using chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a helical structure as a microwave absorbent according to an embodiment of the present invention. 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 helical structure as a microwave absorbent in an embodiment of the present invention. a is a real part of dielectric constant, b is an imaginary part of dielectric constant, c is a real part of magnetic permeability, d is an imaginary part of magnetic permeability, e is a corresponding tan delta epsilon value, f is a corresponding tan delta mu value, and g is a cole-cole curve of the aerogel wave-absorbing microspheres obtained in example 1.

Fig. 6 is a two-dimensional impedance matching graph of samples with different thicknesses, which is obtained by using the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure as a microwave absorbent according to the embodiment of the present invention. 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 is further described with reference to the following figures and specific embodiments.

A preparation method of chiral polyaniline @ reduced graphene oxide aerogel microspheres with a 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 mixed solution is composed of deionized water and ethanol, and the volume ratio of ethanol in the solvent is 30%; the concentration of calcium chloride in the mixed solution is as follows: 4 wt.% to 6 wt.%; preferably 5 wt.%.

Step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of the graphene oxide to the aniline is 0.5-3: 1; the concentration of the graphene oxide dispersion liquid is 5 mg/mL; the dispersion process was completed in an ice-water bath; the molar ratio of ammonium persulfate to aniline is 1-1.5: 1.

And step 3: adding a camphorsulfonic acid solution into the mixed solution obtained in the step 2, and fully mixing to obtain a spinning solution; wherein the concentration of camphorsulfonic acid in the spinning solution is: 0.8mol/L-1.2 mol/L;

and 4, 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 tip to the surface of the coagulation bath solution was 2cm, and the spinning solution rate was 0.1 mL/min.

And 5: standing the graphene hydrogel microspheres obtained in the step 4 in an ice-water bath for 5 hours, and reducing; reducing with sodium ascorbate at 80 deg.C for 50 min; wherein the molar ratio of sodium ascorbate to graphene oxide is 1.5: 1.

Step 6: after cleaning, freeze-drying for 48 hours to obtain the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with the spiral structure.

A chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is characterized in that a micro-channel structure which is orderly dispersed is arranged in the aerogel wave-absorbing microsphere, graphene layers are regularly and orderly arranged, and a regular three-dimensional porous network structure is presented.

A chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with a spiral structure is used as a microwave absorbent.

Example 1

Preparing chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure according to the following steps:

step 1: adding 10g of calcium chloride and ammonium persulfate into 200mL of mixed solution of water and ethanol, and uniformly mixing 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 in an ice-water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion is 5 mg/mL; the molar ratio of graphene oxide to aniline is 0.5: 1. The molar ratio of ammonium persulfate to aniline was 1.5: 1.

And step 3: dissolving camphorsulfonic acid in 5.05mL of deionized water, adding the uniform solution into the mixed solution obtained in the step 2, and fully and uniformly mixing to obtain a spinning solution.

And 4, step 4: the hydrogel microspheres are obtained by wet spinning, in the spinning process, a coagulating bath solution is used as a collector of microdroplets, the distance from a needle point to the liquid surface of the coagulating bath is about 2cm, and the speed of the spinning solution is 0.1 mL/min.

And 5: and (4) 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 50 min. Wherein the molar ratio of sodium ascorbate to graphene is 1.5: 1.

step 6: after the reduction is finished, the aerogel microspheres are washed again, and are frozen and dried for 48 hours to obtain the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres (marked as PANI @ RGO-0.5) with the spiral structure.

Example 2

Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion in an ice-water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion is 5 mg/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 6: after the reduction is finished, the aerogel microspheres are washed again, and are frozen and dried for 48 hours to obtain the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres (marked as PANI @ RGO-1) with the spiral structure.

Example 3

Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion in an ice-water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion is 5 mg/mL; the molar ratio of graphene oxide to aniline is 2: 1. The molar ratio of ammonium persulfate to aniline was 1.5: 1.

and 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 (marked as PANI @ RGO-2) with the spiral structures.

Example 4

Step 2: adding aniline into 10mL of graphene oxide aqueous dispersion in an ice-water bath, and fully stirring and uniformly mixing; the concentration of the graphene oxide aqueous dispersion is 5 mg/mL; the molar ratio of graphene oxide to aniline is 3: 1. The molar ratio of ammonium persulfate to aniline was 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 (marked as PANI @ RGO-3) with the 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 material (FTIR Spectrometer; Bruker, TENSOR II) was characterized using Fourier Infrared spectroscopy as shown in FIG. 2 a. The structural difference of the graphene microspheres is analyzed by using 532nm argon ion laser Raman spectroscopy (InVia Renishaw). And measuring the complex permeability and the dielectric constant of the aerogel microspheres in a frequency range of 2-18GHz by using a vector network analyzer (AV3618, CETC). Measurement of electromagnetic constant a sample of 4.0 wt.% was uniformly mixed 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 microspheres is observed through SEM, as shown in fig. 1 and 2. To illustrate the structure of the aerogel wave-absorbing microspheres obtained in this example, reduced graphene oxide aerogel microspheres RGO AMs (RGO in the following drawings refers to the microspheres (the preparation method is, for example, chiral polyaniline @ reduced graphene oxide aerogel microspheres with a helical structure, except that aniline is not added in step 2, step 3 is not included, and other steps are the same)) are used for comparison (fig. 1a to fig. 1 c). Fig. 1d to fig. 1f are chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a helical structure obtained in this embodiment 1(PANI @ RGO AMs). It can be seen from the figure that the formation of chiral structures is always centered at the edges of the microsphere, 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 fig. 1f, the graphene sheets are regularly and orderly arranged, a regular three-dimensional porous network structure is presented, and the graphene sheets are very compact in arrangement and have small pore size. This is because the formation of chiral polyaniline consumes a part of camphorsulfonic acid, which lowers its concentration and reduces the induction effect on graphene sheets. ANi with doping of camphorsulfonic acid ⁺ Intercalation occurs, polymerization is carried out in graphene sheet layers and becomes a chiral center, and the chiral arrangement of subsequent graphene sheet layers under the induction of camphorsulfonic acid is influenced.

In order to research the influence of the addition of aniline on the chiral structure of the graphene-based aerogel wave-absorbing microsphere. The addition amounts of graphene oxide and aniline 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 helical structure obtained in examples 2 to 4. Wherein, fig. 2a to fig. 2c are SEM images of the aerogel wave-absorbing microspheres obtained in example 2, and the molar ratio of graphene oxide to aniline is 1: 1; FIGS. 2d to 2f are SEM images of the aerogel wave-absorbing microspheres obtained in example 3, wherein the molar ratio of graphene oxide to aniline is 2: 1; fig. 2g to fig. 2i are SEM images of the aerogel wave-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 addition amount of aniline is reduced, chiral polyaniline as a chiral center is reduced, resulting in gradually reduced order of subsequent chiral arrangements. The arrangement of the graphene sheets becomes disordered (as shown in fig. 2e, 2f, 2 i). The content of polyaniline mainly influences the conductive loss capability and the impedance matching performance of the aerogel wave-absorbing microspheres.

The structures of RGO AMs and PANI @ RGO AMs are shown in FIG. 3 by infrared spectroscopy. From FIG. 3a it can be seen that 1639cm for RGO AMs ^-1 The characteristic peak at (A) is attributed to the C ═ C bond of the aromatic ring, and 1387cm ^-1 The peak at (a) is associated with C-OH. S-O stretching vibration (1046 cm) can be clearly observed in PANI @ RGO AMs ^-1 ) And C-S stretching vibration(671cm ^-1 ). The main characteristic peak of PANI comprises quinone ring (Q) (1564 cm) ^-1 ) And a benzene ring (B) (1460 cm) ^-1 ) C ═ C stretching vibration, C — N stretching vibration (1257 cm) ^-1 ) Vibration modes (-1122 cm), protonated-NH + and N-Q-N in PANi chain ^-1 ) And C-H in a substituted phenyl ring (802 cm) ^-1 ) Out-of-plane mixing of (1). With increasing aniline content, both the C ═ C stretching vibrations of the quinone ring and the benzene ring undergo a blue shift due to the enhanced pi to pi interactions between graphene and PANi. Symmetric stretching vibration S ═ O bond (1238 cm) can be found in PANI @ RGO AMs ^-1 ) The results show that the CSA is successfully introduced into the polyaniline molecular chain to form the polyaniline doped with the chiral CSA. Raman spectroscopy (FIG. 3b) 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. The D-band of PANI @ AMs exhibited a blue shift compared to RGO AMs, and the degree of blue shift of PANI AMs increased with increasing amounts of ANi due to the π - π interaction 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 disorder and the more defects. In PANI @ RGO AMs, I is the amount of aniline increased _D /I _G The ratio increased from 0.85 to 1.10 due to the more heterogeneous interface that occurred between GO and PANi. The increase in polyaniline results in an increase in defects, which is advantageous for a gradual increase in impedance matching degree and attenuation of electromagnetic waves.

Compared with the RGO aerogel microspheres, the interface polarization is enhanced by virtue of a heterogeneous interface generated by polyaniline and RGO, and the performance of PANI @ RGO is further improved. The minimum reflection loss of the aerogel microspheres was calculated according to transmission line theory. The relation between the microstructure change of the aerogel microspheres and the electromagnetic wave absorption performance is researched.

Wherein Z is _in Is the input impedance of the microwave absorber, Z ₀ For free space impedance, f is the microwave frequency, c is the speed of light, and d is the thickness of the microwave absorber.

Fig. 4 is a three-dimensional reflection loss diagram of samples with different thicknesses, obtained by using aerogel wave-absorbing microspheres obtained in the embodiment of the present invention 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. 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 the impedance mismatch caused by the high conductivity of the 3D graphene network. After PANi grows in situ on a graphene sheet layer, the charge distortion of a heterogeneous interface can be caused by the dielectric constant difference between the graphene and the PANi, and the interface polarization is enhanced. RLmin for PANI @ RGO-0.5 shows-48 dB at 14.4GHz at a thickness of 2.8mm, corresponding to f _E And maintains 6.88GHz as shown in fig. 4 b. As the polyaniline content decreased, the MA performance of PANI @ RGO-1 decreased 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 showed a worst RLmin value of-15 dB and a poor f of 4.4GHz at 16.65GHz _E (FIG. 4 e). From the above figure, it can be seen that under CSA induction and doping, adjusting the addition amount of aniline is a key means for improving MA performance, and the graphene and aniline have the most appropriate ratio, so that the graphene-based aerogel microspheres exhibit MA performance.

To further reveal the MA characteristics of these aerogel wave-absorbing microspheres, the relative complex dielectric constant (. epsilon.) in the frequency range of 2-18GHz _r ═ epsilon' -j epsilon ") and relative complex permeability (mu) _r μ' -j ∈ ") as shown in fig. 5. The real (epsilon ') and imaginary (epsilon') parts of the dielectric constants of all the samples showed a decreasing trend with increasing frequency (FIGS. 5 a-b). The ε' and ε "of RGO are the highest, as shown in FIG. 5 a. ε 'and ε' increase with polymerization of polyaniline, but the degree of influence increases with the ratio of anilineBut may vary. As the amount of aniline used was reduced, the ε' and ε "of the PANI @ RGO increased and then decreased, and the value of PANI @ RGO-0.5 was found to be of moderate value in these PANI @ RGOs, probably due to better binding of graphene to polyaniline.

the value of tan δ ∈ is an important parameter for evaluating the dielectric loss capability of microwave absorbing materials for incident electromagnetic waves. High dielectric loss tangent tan δ ε can effectively absorb microwaves and convert them to heat or other types of energy, but too high a tan δ ε can result in impedance mismatch with free space. Therefore, a moderate tan δ ∈ is crucial for the MA performance of the absorbent material. PANI @ RGO-0.5 has a moderate tan δ ε, which means that the impedance matching of the system is improved and electromagnetic waves are more easily entered (FIG. 5 e). 5 c-5 e, the real part of magnetic permeability mu ', the imaginary part of magnetic permeability mu' and the tangent value tan delta mu of the aerogel wave-absorbing microspheres are tested. A distinct resonance peak (multi-resonance behavior) can be found in fig. 5d, indicating that there is this loss of material to the electromagnetic wave due to cross-polarization of the chiral structure. Furthermore, the dielectric loss tangent value tan δ ∈ is much larger than the permeability tangent value tan δ μ, indicating that the magnetic loss of cross polarization due to the chiral structure is weak, and thus PANi @ RGO AMs achieve attenuation of electromagnetic waves mainly by dielectric loss.

The dielectric loss of the absorber mainly includes conduction loss and polarization relaxation. According to debye relaxation theory, the polarization relaxation mechanism of the composite material can be described by Cole-Cole semi-circles:

wherein epsilon _s Is the static dielectric constant,. epsilon _∞ Is the dielectric constant at infinite frequency. When the curve of ε 'versus ε' is a single semicircle (Cole-Cole semicircle), it corresponds to a dielectric polarization relaxation process. As shown in fig. 5 g. Debye semi-circles can be obviously observed in 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, polarization relaxation is mainly caused by defects or residual polar groups of graphene sheetsDipole polarization and interfacial polarization caused by the chiral arrangement of the graphene lamellae. In addition to the two polarization relaxations, the introduction of polyaniline generates a new heterogeneous interface, and the difference in dielectric constant between the graphene sheet layer and the polyaniline can cause the distortion of charges on the heterogeneous interface, thereby generating new interface polarization. In addition, all Cole-Cole curves show long tail strips, which indicates that the conductive 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 and represents the ability of microwaves to enter the absorbing material and be converted to thermal energy or dissipated by interference. In order to better explore the MA performance of the aerogel wave-absorbing microspheres, the characteristic impedance Z ═ Z is normalized _in /Z ₀ The impedance matching is evaluated. When the Z ratio is close to 1, almost all incident electromagnetic waves can penetrate the material integrity without microwave reflectivity, exhibiting the most ideal impedance matching. Generally, an absorber is considered to have a good impedance match when its Z is in the range of 0.8-1.2. A two-dimensional mapping of the Z values of PANi @ RGO AMs is shown in FIG. 6. In the aerogel wave-absorbing microspheres, with the reduction of the addition amount of aniline, the impedance matching performance of the PANI @ RGO shows a gradual reduction trend, which means that the conduction loss and impedance matching of the microspheres can be effectively improved by adjusting the use amount of the aniline.

In addition, the attenuation constant α is another important factor influencing the MA performance of the material, and is obtained by the following formula, which is used to explain the attenuation ability of the wave-absorbing material to incident microwaves:

proper impedance matching performance and high attenuation capability provide the absorber with excellent MA performance. As shown in fig. 6 e. The aerogel wave-absorbing microspheres have a high alpha value, and the attenuation constant value of the aerogel wave-absorbing microspheres is over 100 at medium-high frequency. In combination with the attenuation constant and the impedance matching, PANI @ RGO-0.5 has excellent absorption efficiency for electromagnetic waves.

The invention adopts wet spinning, chemical reduction and freezingChiral PANi @ RGO AMs were prepared by drying. By utilizing the aggregation and segregation phenomena of graphene oxide, graphene oxide sheets contain a large number of oxygen-containing groups and thus are negatively charged when dispersed in water. The introduction of positively charged species into aqueous graphene oxide dispersions causes the aggregation and separation of graphene oxide, resulting in the self-assembly of graphene oxide at the interface. When the droplets contact the coagulation bath, the outer graphene oxide lamellae first solidify to form a graphene oxide film, while the graphene oxide dispersion remains within the film. During long-term standing solidification, Ca ²⁺ Gradually penetrate into the interior of the graphene oxide microdroplets under high osmotic pressure, causing self-assembly of graphene oxide sheets. The polymerization speed of polyaniline is faster than the arrangement of graphene oxide lamella, so that chiral polyaniline is formed first and serves as a chiral center. In the subsequent polymerization process, the graphene sheet layer continues to perform chiral self-assembly by taking chiral polyaniline as chirality under the steric hindrance effect of CSA. After chemical reduction and freeze drying, oxygen-containing groups on GO sheets 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 microspheres with light weight, wide frequency band and high microwave efficiency are successfully prepared by a wet spinning technology. From experimental test results, the construction of the chiral structure is beneficial to coordinating the conduction loss and the impedance matching, and the interface polarization of the system is enhanced along with the polymerization of the chiral polyaniline. The load of the PANI @ RGO-0.5 aerogel wave-absorbing microspheres is only 4 wt%, the minimum reflection loss RLmin value of the thickness of 2.8mm is-48 dB, and the effective absorption bandwidth can reach 6.88 GHz. By changing the addition amount of aniline, the effective wave-absorbing bandwidth of the microspheres can be increased to 7.60 GHz.

The invention provides new insight for designing and synthesizing the wave-absorbing material with a special structure, and the graphene-based aerogel wave-absorbing microspheres have stronger absorption efficiency and wider absorption bandwidth. The chiral structure is constructed by utilizing the interaction between the micromolecules and the graphene, so that a new thought and a new basis are provided for the design of the graphene-based aerogel wave-absorbing microspheres.

Claims

1. A preparation method of chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with a spiral structure is characterized by comprising the following steps:

step 2: adding aniline into the graphene oxide dispersion liquid, and fully stirring and uniformly mixing; wherein the molar ratio of the graphene oxide to the aniline is 0.5-3: 1; the molar ratio of ammonium persulfate to aniline is 1-1.5: 1;

2. The preparation method of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the helical structure as claimed in claim 1, wherein in the wet spinning process in step 4, the distance from the needle tip to the surface of the coagulation bath solution is 2cm, and the speed of the spinning solution is 0.1 mL/min.

3. The preparation method of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the helical structure as claimed in claim 1, wherein the standing time in step 5 is 5 hours, and the standing is performed in an ice water bath.

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 reduction process in the step 5 is as follows: reducing with sodium ascorbate at 80 deg.C for 50 min; wherein the molar ratio of sodium ascorbate to graphene oxide is 1.5: 1.

5. The preparation method of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microspheres with the spiral structure according to claim 1, wherein the freeze-drying time in the step 6 is 48 hours.

6. The preparation method of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the helical structure according to claim 1, wherein the solvent in the step 1 is a mixed solution composed of deionized water and ethanol, and the volume ratio of ethanol in the solvent is 30%; the concentration of calcium chloride in the mixed solution is as follows: 4 wt.% to 6 wt.%.

7. The preparation method of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the helical structure according to claim 1, wherein the concentration of the graphene oxide dispersion liquid in the step 2 is 5 mg/mL; the dispersion was done in an ice-water bath.

8. The chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure obtained by any one of the preparation methods of claims 1 to 7, which is characterized in that the aerogel wave-absorbing microsphere has a sequentially dispersed micro-channel structure, graphene layers are regularly and sequentially arranged, and a regular three-dimensional porous network structure is presented.

9. The application of the chiral polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere with the spiral structure as claimed in claim 8, wherein the polyaniline @ reduced graphene oxide aerogel wave-absorbing microsphere is used as a microwave absorbent.