A three-dimensional (3D) nanocomposite of reduced graphene oxide (RGO) and zinc oxide (ZnO) was synthesized by a mild solution-process and a freeze-dried process effectively to keep the whole system fluffy. The BaFe12O19 nanocrystals were synthesized by nitrate citric acid sol–gel auto-ignition method. The electromagnetic and microwave absorption properties of 3D-RGO-ZnO/BaFe12O19 nanocomposites were investigated and this new type 3D material exhibited an efficient reflection loss value and a wide absorption bandwidth. The minimum reflection loss arrives −43.45 dB at 11.52 GHz for 7 wt% of 3D-RGO-ZnO in the nanocomposite with a thickness of 2.0 mm, and the effective absorption bandwidth is larger than 5.8 GHz (the reflection loss below −10 dB). Therefore, the 3D-RGO-ZnO/BaFe12O19 nanocomposites can be considered as an excellent material candidate for microwave absorbers.

•NiO/carbon shell/single-walled carbon nanotube composites were prepared.•The morphology of the composites was affected by heat treating temperature.•The unique nanostructure of the composites was investigated.•Electrochemical measurements show good cyclic stability and rate performance.In this study, NiO/carbon shell/single-walled carbon nanotube composites are prepared by heat treating the single-walled carbon nanotube samples synthesized by direct current arc discharge method. The morphology and nanostructure of the composites are affected by the heat treatment temperature according to the X-ray diffraction, Raman spectra and high-resolution transmission electron microscopy results. The electrochemical measurements are evaluated in coin-type cells versus metallic lithium. After heat treatment in H2 at 600 °C for 1 h and in air at 300 °C for 10 h, the NiO nanoparticles encapsulated by carbon shells are evenly distributed on the surface of web-like single-walled carbon nanotubes and a perfect NiO/carbon shell/single-walled carbon nanotube nanostructure is formed. This NiO/carbon shell/single-walled carbon nanotube composite shows a high reversible specific capacity of 758 mA h g−1 after 60 cycles at a current density of 100 mA g−1 and an excellent rate capacity of about 594 mA h g−1 even at a high current density of 1600 mA g−1. Therefore, the NiO/carbon shell/single-walled carbon nanotube composites have significant potential for applications in energy storage devices.

•LPA-SWCNTs have been abundantly fabricated by a facile, time-saving, economical and non-hazardous method using DC arc discharge technique in low-pressure air.•The electromagnetic and microwave absorption properties of LPA-SWCNTs, CoFe2O4 nanocrystals and LPA-SWCNT/CoFe2O4 nanocomposites were investigated and the LPA-SWCNT/CoFe2O4 nanocomposites exhibited excellent microwave absorption properties.•The Debye theory and impedance matching were used to analyze the electromagnetic parameters and microwave absorption properties.Single-walled carbon nanotubes were facilely and abundantly synthesized by low-pressure air arc discharge method (LPA-SWCNTs), and CoFe2O4 nanocrystals were synthesized by a nitrate citric acid sol–gel auto-ignition method. The electromagnetic and microwave absorption properties of LPA-SWCNTs, CoFe2O4 nanocrystals and their nanocomposites were investigated. The LPA-SWCNT/CoFe2O4 nanocomposites showed excellent microwave absorption properties. The minimum efficient reflection loss is −30.7 dB at 12.9 GHz for 10 wt% of LPA-SWCNTs in the nanocomposites, and an effective absorption bandwidth with a reflection loss below −10 dB is 7.2 GHz. The Debye equation and impedance matching were introduced to explain the microwave absorption properties. Compared with the single-component materials, the LPA-SWCNT/CoFe2O4 nanocomposites are an excellent candidate for microwave absorbers.