Nanoferric tetroxide decorated N-doped residual carbon from entrained-flow coal gasification fine slag for enhancing the electromagnetic wave absorption capacity

Highlights: : • Ferroferric oxide@N-doped residual carbon (Fe₃O₄@NRC) composites were successfully fabricated. • The widest absorption bandwidths can cover 4.32 GHz at 1.5 mm thickness. • Strong absorption, broad bandwidth and thin thickness were simultaneously achieved. • The reasons of high-performance microwave absorption are studied. -- Abstract: Residual carbon (RC) from entrained-flow coal gasification fine slag is formed with graphitized structure after high-temperature gasification of pulverized coal. Here, ferroferric oxide@N-doped residual carbon (Fe₃O₄@NRC) composites were successfully fabricated by decorating RC with Fe₃O₄ nanoparticles via a facile chemical coprecipitation method. The structure, morphologies, thermal stability, chemical compositions, and related electromagnetic (EM) parameters of the RC and as-prepared Fe₃O₄@NRC with different filler loadings were characterized by using various analytical techniques. The RC shows a certain EM wave (EMW) absorption ability. The Fe₃O₄@NRC composites exhibit excellent EMW absorption performance. When 40% mass was added, the minimal reflection loss (RL_min) value of Fe₃O₄@NRC is − 41.4 dB, and the effective absorption bandwidth (RL≤−10 dB) is up to 4.32 GHz (13.6818 GHz) at a thickness of 1.5 mm. The EMW absorption ability of Fe₃O₄@NRC can be tailored by controlling the filler loading composites. The well-matched dielectric loss and magnetic loss result in the enhancement of EMW absorption performance of Fe₃O₄@NRC composites. The magnetic carbon composites display an excellent EMW performance, thereby promoting the by-product utilization of coal gasification.