Nanoholes in Carbon Sheets via Air-Controlled Annealing for Improved Microwave Absorption

Despite carbon materials normally exhibiting good absorption toward microwave radiation, there is still the need to develop facile strategies for further exploring the carbon matrix to achieve stronger and broadened absorbing performance. Here, we report a one-step air-controlled annealing approach to fabricate holey carbon sheets with significantly strengthened microwave-absorbing properties. The obtained metal-free product is barely synthesized from prawn crackers without any additive reagent addition. Both electric field simulations and experiments verify the improved absorbing capability achieved on the derived holey carbon absorbent. The performance measurements demonstrate that its reflection loss reaches −64.1 dB at a thickness of 1.45 mm, and the corresponding absorption bandwidth approaches 5.36 GHz at 1.65 mm, almost covering the whole Ku band from 12.64 to 18.00 GHz. These results overperform most biomass-derived absorbents. Benefiting from this air-modulated nanoscale holey structure, it endows the carbon matrix with higher surface areas associated with richer oxygen functional groups, which facilitates more incident microwaves to be consumed and regulates the dielectric loss of the final product. Meanwhile, the inherited Si components from raw prawn crackers supply more polarization centers, thereby enhancing the absorbing properties. We expect that these can represent a feasible addition to the family of sustainable carbon-based microwave absorbents.