Shape anisotropic Fe₃O₄ nanotubes for efficient microwave absorption

Although Fe₃O₄ particles have exhibited excellent microwave absorbing capacity and widely used in practical application due to the synergistic effect of magnetic loss and dielectric loss, their applications are still limited for the required high mass fraction in absorbers. To overcome this problem, the development of Fe₃O₄ materials with low dimensional structures is necessary. In this study, the shape anisotropic Fe₃O₄ nanotubes (NTs) with low mass ratios were applied to realize efficient microwave absorption. The NTs with different aspect ratios were prepared through facile electrospinning followed by two-step thermal treatments and mechanical shearing. The cross-linked nanotubular structure enabled the absorbers to have much higher electrical conductivity, multiple scattering, polarization relaxation and better anti-reflection surface, while the shape anisotropic NTs maintained significant multiple resonances with stronger coercivity. These all were beneficial to microwave absorption with enhanced dielectric loss, magnetic loss and sterling impedance matching. Results showed that the absorber with 33.3 wt.% of short Fe₃O₄ NTs had minimum reflection loss of -58.36 dB at 17.32 GHz with a thickness of 1.27 mm, and had the maximum effective absorbing bandwidth (EAB) of 5.27 GHz when the thickness was 1.53 mm. The absorber with 14.3 wt.% of long Fe₃O₄ NTs presented the widest EAB in certain radar band with attenuated 80.75% X band and 85% Ku band energy bellow -10 dB at the thickness of 2.65 and 1.53 mm, respectively. This study provided an approach for the development of shape anisotropic magnetic absorbing materials, and broadened their practical applications as magnetic absorbers.