| It is well known that two-dimensional nanomaterials,such as graphene,hexagonal boron nitride,carbonitrides,and layered transition metal sulfides,have high specific surface area and polymorphism,giving them special electronic properties.Therefore,it has shown great application prospects in the fields of optoelectronics,catalysis,electromagnetic shielding and microwave absorption.As one of the most important semiconductor transition metal sulfides,copper sulfide has been widely studied in the fields of secondary batteries,photocatalysts,supercapacitors and optical sensors due to its excellent optical,electronic and other physicochemical properties.However,compared with other two-dimensional materials,microwave absorption and infrared stealth performance of metallic copper sulfide are rarely studied in detail.In this paper,a two-dimensional copper sulfide nanosheet with a diameter of 192 nm and a thickness of 3.2 nm was successfully prepared by wet chemical method.On this basis,CuS/RGO,CuS/ZnS and CuS/ZnS/RGO nanocomposites were prepared by combining copper sulfide with graphene and zinc sulfide.The absorbing properties and infrared stealth properties of nanocomposites were studied.(1)In this paper,hexagonal CuS nanosheets were successfully prepared by wet chemical method.The effects of reaction time,copper salt type and reactant ratio on the morphology of CuS nanosheets were studied.The results show that the hexagonal copper sulfide nanosheets with regular morphology are prepared by using cuprous chloride as the copper salt for 9 hours with a diameter of about 192 nm and a thickness of 3.2 nm.Then the electromagnetic parameters of the CuS nanosheets were tested,the microwave absorption properties were studied,and the mechanism of microwave absorption was explored.The results show that the absorbing properties of the material increase with the addition of CuS in the matrix.When the addition amount of CuS is 50% and the thickness is 3.0mm,CuS has the best absorbing effect.The reflection loss at 8.0 GHz is-27.5 dB,and the corresponding effective absorption bandwidth is 3.4 GHz.It is because CuS is a p-type semiconductor that easily forms a defect dipole,which produces polarization relaxation under the action of an alternating electromagnetic field.In addition,the charge accumulated at the interface between CuS and paraffin causes interfacial polarization relaxation in the alternating electromagnetic field.Defective dipoles and interfacial polarization relaxation enable CuS to effectively absorb and attenuate electromagnetic waves.(2)The problem of effective absorption is achieved when the CuO nanosheets are added in a large amount in the matrix.CuS is combined with graphene to improve the dielectric parameters of CuS,so that CuS also has good absorbing effect at low addition.The CuS/RGO nanocomposites were prepared by wet chemical method.The effects of the preparation process on the morphology and structure of CuS/RGO nanocomposites were investigated.The results show that the CuS nanosheets can be evenly distributed on the surface of graphene when the amount of graphene added in the nanocomposite is 20 wt%.The results of the absorbing test showed that the CuS/RGO nanocomposite with a graphene content of 20 wt% exhibited the best absorbing effect when the amount of CuS/RGO added in the matrix was 30% by weight.The optimum reflection loss of CuS/RGO composite is-34.5dB,and the corresponding effective absorption bandwidth is 3.3 GHz.Compared with pure CuS nanosheets,CuS/RGO nanocomposites can not only reduce the amount of absorbing filler in the matrix from 50 wt% to 30 wt% but also increase the maximum reflection loss from-27.5 dB to-34.5 dB.It is because the high dielectric graphene is added to the composite material,so that the composite material also has good dielectric properties under the underfill amount.Moreover,the interaction between graphene and CuS nanosheets in the composite material produces dielectric relaxation,interfacial relaxation,etc.,which can effectively attenuate electromagnetic waves.(3)The combination of graphene and CuS can improve the addition of pure CuS in the matrix,but the addition of graphene does not increase the absorption bandwidth.Therefore,long ZnS nanoparticles are grown on CuS nanosheets by simple wet chemical method.By precisely controlling the ratio of CuS to ZnS,the interfacial area between the two phases of CuS and ZnS can be well adjusted to achieve continuous bimodal absorption.When the molar ratio of CuS to ZnS is 8:2,only a small amount of ZnS nanoparticles adhere to the surface of the CuS nanosheet.When the molar ratio of CuS to ZnS is 7:3,the surface of CuS nanosheets is uniformly coated with ZnS particles,and the morphology of CuS/ZnS nanocomposites is the best.When the content of ZnS continues to increase,most of the CuS nanosheets are coated with ZnS and the CuS/ZnS nanosheets agglomerate.The nano-composite particles with CuS and ZnS molar ratio of 7:3 were selected to test their electromagnetic parameters,and their microwave absorption properties were studied.The results show that when the molar ratio of CuS to ZnS is 7:3,the amount of CuS/ZnS nanocomposite particles added in the matrix is 50wt%,and the thickness of the sample is 3.5 mm,the CuS/ZnS nanocomposite particles achieved bimodal absorption at 5.8 GHz and 7.3 GHz,respectively.Because copper vacancy defects in CuS can cause defects to form defect dipoles.The addition of ZnS causes the charge accumulated at the interface between CuS and ZnS to cause interfacial polarization relaxation in the alternating electromagnetic field.The combination of defect dipole polarization and interfacial polarization enables bimodal absorption of CuS/ZnS nanocomposite particles.Compared with copper sulfide,the CuS/ZnS nanosheets achieved double peak absorption at the same addition amount,but the absorbing strength was weakened.And the addition of zinc sulfide can reduce the infrared emissivity of the material,so that the composite material has a certain infrared stealth performance.(4)CuS/ZnS nanocomposite particles can achieve bimodal absorption by coating ZnS nanoparticles on CuS surface,but the increase of ZnS addition reduces the absorbing strength of CuS/ZnS nanocomposite particles.Therefore,CuS/ZnS/RGO composites were prepared by wet chemical method,and graphene was added to CuS/ZnS nanocomposite particles to improve the absorption strength of CuS/ZnS nanocomposites.The effects of preparation process on the morphology and structure of CuS/ZnS/RGO nanocomposites were investigated.It has shown that CuS/ZnS nanoparticles can be uniformly distributed on the surface of graphene when the addition amount of graphene in CuS/ZnS/RGO composite is 20 wt%.The synthesized CuS/ZnS/RGO nanocomposite particles were added to the matrix at 30% by weight to prepare a sample.When the sample thickness is 3.5 mm,the optimal reflection loss of CuS/ZnS/RGO nanocomposite particles is-39.1 dB,and the corresponding effective absorption bandwidth is 4.5 GHz.The absorption intensity and absorption bandwidth of CuS/ZnS/RGO nanocomposite particles are significantly improved.Defective polarization and interfacial polarization of CuS/ZnS/RGO nanocomposite particles and dielectric properties of graphene on CuS/ZnS nanocomposite particles improve the absorbing properties of nanocomposite particles.In addition,the effect of the amount of zinc sulfide coating on the absorbing properties and infrared emissivity was also studied.As the content of the zinc sulfide increases,the emissivity of the nanocomposite decreases,and the coating of the zinc sulfide is beneficial to reduce the infrared emissivity of the nanocomposite. |
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