Papaya seeds-derived CoNi/C magnetic biochar nanocomposites for strong microwave absorption and ultra-wide bandwidth

Biomass-derived carbon materials preserve the distinctive physicochemical architecture of their biological precursors, offering the benefits of ready availability and eco-friendliness, which renders them favored candidates in the realm of microwave absorption. Herein, a continuous cryodesiccation, soaking and thermal treatment was employed to produce papaya seeds-derived CoNi/C magnetic biochar nanocomposites (MBNCs) consisting of CoNi nanoparticles and carbon layers. By increasing the concentration of Co and Ni sources, progressively large size and enhanced content of CoNi nanoparticles could be produced in the obtained CoNi/C MBNCs. Additionally, the increased degree of graphitization for CoNi/C MBNCs were also acquired by raising the calcination temperature from 700 to 900 °C. Owing to excellent magnetic-dielectric synergies, all the acquired CoNi/C MBNCs presented very extraordinary microwave absorption properties. Especially, the optimized CoNi/C MBNCs presented an effective absorption band of 7.40 GHz and a minimum reflection loss of −59.90 dB, corresponding to thin matching thicknesses of 1.84 mm and 1.76 mm, respectively. To sum up, a straightforward, economical and reproducible biomass-derived strategy was proposed to synthesize CoNi/C MBNCs, which could be acted as a desirable lightweight efficient microwave absorber.