A Nanoconfinement Strategy to Construct Co@CNTs for Lightweight and Ultra-Broadband Microwave Absorption.

The construction of stable and efficient nanocomposites with low addition and light weight has always been the goal pursued in the field of electromagnetic wave (EMW) absorption. In this study, the Co@CNTs nanocomposites with Co nanoparticles (13 nm) nanoconfined in the carbon nanotube (CNT) are successfully synthesized by a simple hydrothermal method and phenolic assisted pyrolysis method. The degree of graphitization of CNTs and the microstructure of Co nanoparticles can be effectively regulated by controlling the calcination temperature. The sample calcined at 700 °C can obtain excellent absorption performance at a low filling capacity of 10 wt.%: the minimum reflection loss (RL) is -41.2 dB and the effective absorption bandwidth (EAB) reaches a maximum width of 14.2 GHz. When the sample thickness is only 2.2 mm, the EAB of <-20 dB reaches 8.3 GHz, which is the maximum EAB of most current Co-based absorbers. In particular, the polarization and ferromagnetic coupling behaviors are elucidated in depth with the aid of electromagnetic field simulations using the High-Frequency Structure Simulator (HFSS). This work provides a new nanoconfinement strategy for constructing the Co@CNTs nanocomposites as lightweight and ultra-broadband absorbing materials for EMW protection and EMW pollution control.