Controllable synthesis of pine leaf-like CoO/3D carbon foam composites as efficient microwave absorbers

The development of high-performance microwave absorbing materials (MAMs) is an effective and sustainable solution for mitigating electromagnetic pollution. Inspired by the radiation-resistant structure of pine leaves, CoO/Carbon foam composites (COCF) with 3D network structures were constructed using alkali treatment and in situ hydrothermal and carbothermal reduction strategies. The 3D-structured carbon foam effectively prevents the agglomeration of CoO in COCF composites, improves the electron transfer efficiency, and enriches the heterogeneous interfaces; in this way, a superb microwave attenuation capability is realized. The optimum reflection loss (RLmin) reaches -90.67 dB, and the effective absorption bandwidth (EAB, RL<-10 dB) is 4.18 GHz at a thickness of 1.34 mm. The total EAB included almost all four bands, namely S, C, X, and Ku. Moreover, the present study offers new ideas for optimizing transition metal oxides (TMOs) and carbon materials combinations and for the structural design of MAMs with multiscale fine micro-nanostructures.