Facile Design of Three-Dimensional Nitrogen-Doped Reduced Graphene Oxide/Multi-Walled Carbon Nanotubes Composite Foams as Lightweight and High-Efficient Microwave Absorbers.

Abstract

Graphene foams with three-dimensional (3D) network structure, high porosity and ultralow density have been regarded as lightweight microwave absorbing materials. Herein, nitrogen-doped reduced graphene oxide/multi-walled carbon nanotubes composite foams were prepared through a two-step strategy of hydrothermal self-assembly and subsequent high-temperature calcination. Morphology analysis indicated that the 3D networks were composed of overlapped flaky RGO. In addition, the influences of nitrogen doping, calcination temperature and filler ratios on microwave absorbing of composite foams were explored. Results manifested that the microwave absorbing of composite foams was remarkably improved with the calcination temperature increased. Dramatically, it was noteworthy that the composite foam obtained under 600 oC calcination (bulk density ~ 10.8 mg/cm3) with an 8 wt% mass filler ratio presented the strongest microwave absorbing of -69.6 dB at 12.5 GHz, and broadest absorption bandwidth achieved 4.3 GHz (13.2‒17.5 GHz) at an extremely low matching thickness equal to 1.5 mm. Moreover, the microwave absorbing performance could be conveniently adjusted through modifying the thicknesses, filler ratios and calcination temperature. The excellent microwave absorbing performance of as-prepared composite foams was greatly derived from a well-constructed 3D network structure, significant nitrogen doping, enhanced polarization relaxation and improved conduction loss. This work proposed a new strategy for fabricating graphene-based composites with a 3D network structure as high-efficiency microwave absorbers.