Microporous Co@CoO nanoparticles with superior microwave absorption properties.

Nanoporous metal materials with many potential applications have been synthesized by a chemical dealloying approach. The fabrication of nanoporous metal nanoparticles (NPs), however, is still challenging due to the difficulties in producing suitable nanoscale precursors. Herein, nanoporous Co NPs of 31 nm have been successfully prepared by dealloying Co-Al NPs, and surprisingly they possess micropores in a range from 0.7 to 1.7 nm and a large surface area of 50 m(2) g(-1). The crystalline size of the microporous NPs is 2-5 nm. Through the passivation process, the microporous Co NPs covered with CoO (Co@CoO) are generated as a result of the surface oxidation of Co. They exhibit better microwave absorption properties than their nonporous counterpart. An enhanced reflection loss (RL) value of -90.2 dB is obtained for the microporous Co@CoO NPs with a thickness of merely 1.3 mm. The absorption bandwidth corresponding to the RL below -10 dB reaches 7.2 GHz. The microwave absorption mechanism is discussed in terms of micropore morphology, core@shell structure and nanostructure. This novel microporous material may open new routes for designing high performance microwave absorbers.