Facile fabrication of 3D biochar absorbers dual-loaded with Fe3O4 nanoparticles for enhanced microwave absorption

Abstract

Biochar microwave absorption (MA) materials are attracting significant attention due to their sustainability and cost-effective features. To endow them with enhanced MA performance, surface loading of magnetic nanoparticles (NPs) based on biotemplates is becoming a valid strategy. However, realizing hybrid deposition of magnetic NPs onto surfaces and internal spaces of the biotemplates still remains a big challenge for effective absorption. Herein, we proposed a novel biochar absorber based on Spirulina (SP) cells dual-loaded with Fe3O4 NPs and demonstrated their enhanced performance for MA. In this approach, the SP cells were permeabilized and deposited with Fe3O4 NPs both extracellularly and intracellularly, to obtain the precursors (Fe3O4@SPs). Then, annealing treatment was conducted at various temperatures (X °C) to fabricate the biochar absorbers (Fe3O4@SP-BCs-X). The Fe3O4@SP-BCs-700 composites exhibited the best MA performance among the samples, and the minimum reflection loss (RLmin) could attain −45.54 dB at 14.68 GHz (thickness: 1.49 mm, mass ratio in paraffin: 18.6 wt%). Moreover, the biochar absorbers with hybrid deposition could achieve enhanced absorption compared to the samples with single deposition. Due to these superior features and facile fabrication, the Fe3O4@SP-BCs demonstrated great potential for MA applications.