Abstract:

Novel 3D-ultrathin CoS₂ nanoflakes wrapped by reduced graphene oxide (CoS₂/RGO) were successfully prepared via a facile method. The morphology and structure of the materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The microwave absorption properties of the CoS₂/RGO composites were also investigated. The composites exhibited optimal microwave absorption properties at a CoS₂/RGO loading of 20 wt.% in paraffin matrix, with a reflection loss (RL) value of −36.5 dB at 12.1 GHz and a thickness of 2.0 mm. Furthermore, CoS₂/RGO composites have an excellent absorption bandwidth (reflection loss below −10 dB) of 6.5 GHz. The results indicate that the RGO-wrapped 3D-ultrathin CoS₂ nanoflakes have a broad microwave absorption bandwidth, strong absorption, and are the candidates for the application as the advanced microwave absorbers.

Background Introduction:

Electronic devices have become indispensable with increasing demand for more intelligent devices of modern life. Nevertheless, electronic devices can disturb other electronic equipment by emitting electromagnetic waves (EW), as well as having hazards on human beings. Therefore, it needs urgently to develop EW absorption materials for protecting against the dangers of EW. The main factors affecting the EW absorption performance of materials are its electromagnetic parameters and material microstructures. Nanostructures will be helpful in raising performance of absorption materials.

In recent years, transition metal sulfides have been used in the EW absorption materials with better performance. It shows the best EW absorption of −47dB at X band with a loading of 6 wt.% mixed with paraffin. Similar to many other metal sulfides, CoS₂ is a semiconducting material that has drawn much attention regarding its application in electronic devices, lithium ion batteries, and solar cells . However, CoS₂ materials with 3D nanostructure have not been exploited for their EM absorption properties. On the other hand, graphene, as a new single-layer or multi-layer carbon material, has a special application in EW absorption materials. Graphene has high surface area, low thermal expansion coefficient, and appropriate conductivity, thus having a wide range of applications in solar cells, lithium ion batteries, and EM absorption materials. Furthermore, its high specific surface area, low density, abundant defects, hydroxyl, epoxy, and carboxyl groups, making it a promising light weight and highly efficient EW absorber material. A number of studies have shown that graphene sheets are a good carrier for the growth of transition metal sulfides, and the composites can show an excellent EW absorption performance. Similarly, hybrid composites of MnS hollow spheres grown in reduced graphene oxide (RGO) were fabricated and their EW properties were investigated. The above studies showed that graphene can cover the shortage of metal sulfides and enhance their EW absorption properties. However, the EM absorption properties of CoS₂/graphene composites are not yet to be assessed. This work reported the synthesis of particular 3D-ultrathin nanoflakes CoS₂ of hierarchical structure, and cladding with reduce graphene oxide via a simple and effective solvothermal method. And their EW properties were investigated in the frequency range of 2–18 GHz.

Article Highlights:

Novel 3D-ultrathin CoS₂ nanoflakes wrapped by reduced graphene oxide (CoS₂/RGO) were prepared via a facile method.

CoS₂/RGO composites have an integral type self-supporting metal sulfide framework, and high specific surface area. These open porous networks enable multiple scattering and the wrapping of graphene is beneficial to conducting electricity.

The heterogeneous interface polarization is also enhanced, the composites exhibited optimal microwave absorption performances and have an excellent absorption bandwidth of 6.5 GHz.

Summary and Outlook:

The novel CoS₂/RGO composites with a 3D-ultrathin nanosheet structure have been synthesized by a two-step solvothermal method. Furthermore, the CoS₂/RGO composites have been prepared by changing GO concentrations. The results shows that CoS₂ of special nanostructure greatly contributed to the permittivity of CoS₂/RGO. When the loading capacity of CoS₂/RGO composites in paraffin wax was 20 ​wt.%, the ε′ and ε" were higher than the individual RGO or CoS2. Thus, due to the stronger ability of dielectric loss, CoS₂/RGO showed excellent microwave absorption properties. Additionally, the values of the minimum reflection loss and the absorption bandwidth were both maintained up the high level. At a GO solution concentration of 0.8 mg/mL the optimal RL reached −36.5 dB at 12.1 GHz with the thickness of 2 mm, and a bandwidth of 6.5 GHz. Therefore, CoS₂/RGO composites with a 3D-ultrathin nanoflake structure are promising candidates for advanced microwave absorbers with a strong absorption, broad bandwidth, and light weight.

Article Details:

Reduced graphene oxide wrapped 3D-ultrathin CoS₂ nanoflakes as an absorbing material with enhanced microwave absorption

Danfeng Zhang, Chengjie Yan, Yun Zheng, Congai Han, Yunfei Deng, Jiale Yu, Guoxun Zeng, Haiyan Zhang

Article Link: https://doi.org/10.1016/j.pnsc.2022.01.006

Author introduction

Professor Zhang Haiyan is a member of the Academic Committee of the 2019 and 2021 China Materials Conference, serving as the Vice Chairman of the Guangdong Materials Research Society and the Director of the Energy Storage Materials and Devices Engineering Laboratory of the Guangdong Development and Reform Commission. The team has been engaged in the research and application of energy storage and absorbing materials and devices for a long time, and has presided over and undertaken more than 60 projects including the National Natural Science Foundation Guangdong Joint Fund Key Project, the National Natural Science Foundation General Project, the National Science and Technology Support Program Sub Project, the Guangdong Natural Science Foundation Key Project, the Guangdong Province Applied Research and Development Major Special Project, and the Guangdong Province Science and Technology Plan Key Project, achieving excellent results. They have won 5 Guangdong Science and Technology Awards and 3 Guangzhou Science and Technology Awards, and have been authorized with 24 national invention patents. They have published 331 papers and received 4540 citations. The H-index is 36. Selected for Stanford University's 2023 Global Top 2% Scientists List.