Fe@CN_x Nanocapsules for Microwave Absorption at Gigahertz Frequency

In order to solve growing electromagnetic wave pollution issues, development of high-performance microwave absorption materials composed of dielectric loss and magnetic loss characteristics has been attracting considerable attention. Herein, we demonstrate an effective approach for the transformation of Fe@C into Fe@CN_x nanocapsules by in situ microwave-assisted heating effect. Ascribed to the high effective microwave absorption capacity, the microwave energy could be localized around the nanoscale environment of Fe@C nanocapsules, resulting in the in situ chemical decomposition of urea precursor and the transformation of the initial graphitic shells to CN_x shells. Microstructure characterizations coupled with complex permittivity spectra further reveal that the intrinsic dielectric enhancement for the Fe@CN_x nanocapsules originates from the atomic-scale C-N complexes that induce the space charge separation and form the electric dipoles. The present study indicates a novel approach for in situ synthesizing Fe@CN_x nanoparticles and has promising potentials to extend to other carbon-based materials and diverse applications.