1D Electromagnetic-Gradient Hierarchical Carbon Microtube via Coaxial Electrospinning Design for Enhanced Microwave Absorption.

1D structures have been gaining traction in the microwave absorption (MA) field benefiting from their electromagnetic (EM) anisotropy. However, there remain considerable challenges in adjusting EM properties by structural design. Herein, using the coaxial electrospinning and solvothermal method, the EM gradient has been achieved in TiO2@Co/C@Co/Ni multilayered microtubes. From the outer layer to the inner one, the impedance matching is gradually worsened, while the EM loss capacity is continuously enhanced, facilitating both the incidence and attenuation of microwave. Besides, 1D structural anisotropy simultaneously realizes multilevel magnetic interaction and 3D conductive double network. Therefore, the 1D EM-gradient hierarchical TiO2@Co/C@Co/Ni carbon microtube composite exhibits excellent MA performance. Its maximum reflection loss (RL) value reaches -53.99 dB at 2.0 mm and effective absorption bandwidth (EAB, RL ≤ -10 dB) is as wide as 6.0 GHz, covering most of the Ku band with only 15% filling. The unique design of 1D EM-gradient hierarchical composites promises great potential in the construction of advanced MA materials.