Constructing magnetic metal doping carbon micro-particles with columnar structure via carbonization of waste masks for microwave absorption

The recycling of waste masks (melt-blown polypropylene nonwoven fabrics) generated during the COVID-19 outbreak has now become a social issue of high priority. Converting these waste masks into electromagnetic wave (EMW) absorbers is one of the most cost-effective and high-value-added methods. In this study, we successfully converted household masks into magnetic metal doping carbon micro-particles with columnar structure to achieve excellent microwave absorption properties through sulfuric acid modification and doping magnetic metal. Specifically, the cobalt-doped carbon columnar micro-particles have a minimum reflection loss (RL min ) of −52.8 dB at 7.0 GHz (d = 3 mm) and an effective absorption bandwidth (EAB) of 4.6 GHz (d = 1.4 mm). The nickel/carbon hybrid materials have an RL min of −26.2 dB at 8.8 GHz (d = 3 mm) and an EAB of 5.3 GHz (d = 2.4 mm). The multiple reflection or scattering of EMWs, conduction and magnetic losses, dipolar polarization, and interfacial polarization effects can be enhanced in those magnetic metal doping carbon micro-particles with columnar structure, which leads to the excellent microwave absorption performance.