Solid-state reaction induced defects in multi-walled carbon nanotubes for improving microwave absorption properties

• Defect structures and contents of MWCNTs have been optimized. • MA property of MWCNTs could be optimized by the defect engineering. • Dipole polarization can effectively improve MA performance. • Permeability-to-permittivity transformation is another MA mechanism. Dielectric polarization performance induced by defect engineering approach has been proved to be an effective way for improving the microwave absorption property of carbon-based materials. Assisting by the solid-state reaction, the structural integrity of multi-walled carbon nanotubes (MWCNTs) would be broken along with the volume expansion and etching process of cobalt oxides. Therefore, the defects could be obtained and result in the enhancement of microwave absorption property. Ascribing to the broken wall structures, the defect-distances ( L D ) and concentrations ( n D ) have been optimized to be 9.80 nm and 3.37 × 10 11 cm −2 . The minimum reflection loss ( RL ) had reached -54.6 dB at 4.5 GHz with a thickness of 4.13 mm and the corresponding effective absorption bandwidth (EAB <-10 dB ) was analyzed to be 14.6 GHz. Such enhancement is correlated to the dielectric polarization and the permeability-to-permittivity transformation raised from the defect structures and concentrations. The present work demonstrates an effective strategy for tailoring the microwave absorption property of MWCNTs by engineering defect concentrations, and could be further extended to other carbon-based absorbents.