Towards efficient microwave absorption: intrinsic heterostructure of fluorinated SWCNTs

The construction of heterostructures is always effective to achieve efficient microwave absorption (MA) properties. Herein, different from conventional hybrid techniques, a novel microwave absorber with an intrinsic heterostructure is fabricated via direct heating fluorination of SWCNTs (F-SWCNTs) utilizing F-2/N-2. The as-prepared inhomogeneous F-SWCNTs are confirmed to contain both fluorinated domains and aromatic domains at the nanoscale. The evolution of the fluorinated domains is closely related to the development of the C-F groups, whereas the -CF2 groups have no effect. For MA, it is proposed that the aromatic domains function as attenuation regions, whereas the fluorinated domains serve as microwave transparent regions. When the area of aromatic domains is almost equal to that of fluorinated domains, the complementarity between attenuation ability and impedance match endows F-SWCNTs (fluorine content equals of 6.8%) with a good MA performance. Specifically, with only 4.8 wt% Loading, the minimum reflection Loss (RL) reaches -64.3 dB at the thickness of 1.61 mm, and the effective absorption region (RL < 10 dB) covers a range of 14.1-18 GHz at the thickness of 1.15 mm. The MA performances rely on the evolution of the physical heterostructure, instead of the introduced chemical bonds or fluorine-containing functional groups. The simplicity and feasibility of our design concept indicate the potential application of F-SWCNTs industrially.