Bead-like flexible ZIF-67-derived Co@Carbon composite nanofibre mat for wideband microwave absorption in C-band

The lightweight and wideband microwave attenuation performance with low-frequency compatibility, has always been desired for advanced microwave absorbing materials. However, most of the current solutions for lowfrequency absorption rely on magnetic materials, which is limited by the high-density and narrow absorption bandwidth. Herein, we present a co-electrospinning synthesis strategy to fabricate lightweight and porous Co@C composite nanofibres (Co@CNFs) with bead-like (cubic Co particles embedded in carbon nanofibres) morphology. The continuous and fibrous carbon nanofibres template provides wideband microwave attenuation capacity. And the inserted MOF-derived Co additives further improve the low-frequency absorption performance by inducing magnetic losses, rich interfaces, and enhanced conductivity. The optimized Co@CNFs sample, with a filler loading of only 7.5 wt %, offers the effective absorption bandwidth (EAB) of 3.84 GHz (4.16-8.00 GHz) within C-band at 6.63 mm. At an alternative sample thickness of 2.90 mm, the EAB reaches 6.42 GHz. In addition, the nanofibre mat also demonstrates excellent flexibility according to a 500-time 180 degrees bending test. Furthermore, the broadband absorption matching formula based on the quarter wavelength (lambda/4) cancellation theory was also optimized by containing permeability part, which could be served as the guidance for designing lightweight and broadband microwave attenuation fibrous materials that are compatible with low frequency absorption.