It is well accepted that the microwave absorption performance (MAP) of carbon nanotubes (CNTs) can be enhanced via coating magnetic nanoparticles on their surfaces. However, it is still unclear if the magnetic coating structure has a significant influence on the microwave absorption behavior. In this work, nano-FeO compact-coated CNTs (FCCs) and FeO loose-coated CNTs (FLCs) are prepared using a simple solvothermal method. The MAP of the FeO-coated CNTs is shown to be adjustable via controlling the FeO nanocoating structure. The results reveal that the overall MAP of coated CNTs strongly depends on the magnetic coating structure. In addition, the FCCs show a much better MAP than the FLCs. It is shown that the microwave absorption difference between the FLCs and FCCs is due to the disparate complementarities between the dielectric loss and the magnetic loss, which are related to the coverage density of FeO nanoparticles on the surfaces of CNTs. For FCCs, the mass ratio of CNTs to Fe is then optimized to maximize the effective complementarities between the dielectric loss and the magnetic loss. Finally, a comparison is made with the literature on FeO-carbon-based composites. The FCCs at the optimized CNT to Fe ratio in the present work show the most effective specific RL (28.7 dB·mm) and the widest effective bandwidth (RL < -10 dB) (8.3 GHz). The excellent MAP of the as-prepared FCC sample is demonstrated to result from the consequent dielectric relaxation process and the improved magnetic loss. Consequently, the structure-property relationship revealed is significant for the design and preparation of CNT-based materials with effective microwave absorption.

Novel three-dimensional (3D) urchin-like a-Fe 2 O 3 superstructures were successfully prepared by a template-free hydrothermal synthetic route using FeSO 4 ?7H 2 O and NaClO 3 as reagents. The as-obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis and vibrating sample magnetometry. It is shown that the superstructures consisted of well-aligned a-Fe 2 O 3 nanorods growing radially from the cores of the superstructures. The a-Fe 2 O 3 nanorods have an average length of about 800 nm and a mean diameter of about 80 nm. Magnetic hysteresis measurement reveal that the urchin-like a-Fe 2 O 3 superstructures display weak ferromagnetic behavior with a remanence of 4.6783 6 10 23 emu g 21 and a coercivity of 92.235 Oe at room temperature. The formation mechanism of the 3D urchin-like a-Fe 2 O 3 superstructures was also discussed.