Green carbonization of waste coffee grounds into porous C/Fe hybrids for broadband and high-efficiency microwave absorption

Recently great efforts have been focused on designing high-performance microwave absorbers using sustainable biomass resources, but there remains a lack of green and efficient fabrication methods. Herein, inspired by natural porous character of biomass waste, we demonstrated a green one-step route to convert waste coffee grounds into porous C/Fe hybrids, and further explored their potential applications for broadband and high-efficiency microwave absorption. In this design, the WCG-20-750 (incorporated 20 wt% Fe(C₅H₇O₂)₃ catalyst and carbonized at 750 °C) exhibited porous microstructure with the highest char yield of 55.45 wt%. Furthermore, the as-prepared C/Fe hybrids from WCG-20-750 displayed excellent microwave absorption performances. Typically, the minimum reflection loss (RLmin) reached to -52.86 dB and the widest effective absorption bandwidth (EAB) was 6.40 GHz at the thickness of 3.0 mm. This work provides an economically viable and environmentally friendly strategy to convert biomass wastes into value-added microwave absorbers, ultimately making contributions to the upcycling of renewable biomass resources and the fostering of sustainable environment.