Yolk-shell structure synergistic defect engineering for boosting electromagnetic wave absorption in Co9S8@Humins-derived carbon

Exploring new strategies to incorporate the concepts of green chemistry and defect engineering into new architectures to address the problem of severe electromagnetic wave (EMW) pollution is challenging. In this work, by using a by-product of catalytic conversion of biomass as a carbon source, we prepare two-dimensional (2D) Co 9 S 8 -coated humins-derived carbon nanomaterials with a yolk-shell structure. The EMW attenuation ability is finally optimized by controlling the morphology and defects of the composite material through the pyrolysis temperature. As expected, with the synergy of conductive loss/interfacial polarization and defects regulating, the composite material achieves a reflection loss (RL) value of −51.4 dB in Ku-band and the effective absorption bandwidth (EAB) can be as high as 5.92 GHz (12.08–18.00 GHz) at 1.8 mm ultra-thin coating thickness. A strong absorption capacity in the low-frequency C-band (6.4 GHz) reaches RL value of −49.9 dB and a thickness of 3.50 mm, which grants it the characteristic of convertible microwave absorption from high frequency to low frequency. Taking account of the facile synthesis and tunable absorption properties, the encouraging findings shed light on exploring waste-turned-microwave absorbents with promising practical applications.