Hollow core-shell CoNi@C and CoNi@NC composites as high-performance microwave absorbers

Magnetic nanoparticles are readily oxidized in air, resulting in a poor electromagnetic wave (EMW) absorption performance. In this study, hollow CoNi alloy was used as the core, and two kinds of carbon shells were explored to protect it from oxidation and improve its complex permittivity. The hollow core-shell shaped [email protected] and [email protected] absorbers were synthesized by in-situ polymerization of phenolic resin (PR) and polydopamine (PDA) on the surface of CoNi alloy, respectively, which was followed by high-temperature pyrolysis. The EMW absorption performance of the absorbers was tuned by varying the calcination temperature. Compared to the pristine CoNi alloy, the [email protected] and [email protected] composites displayed significantly enhanced microwave absorption (MA) performance. The [email protected] microspheres exhibited a maximum reflection loss (RL) of −47.1 dB at a thickness of 2 mm. Further, [email protected] and [email protected] displayed effective bandwidths (RL ≤ −10 dB) of 5.1 GHz at 1.7 mm-thickness and 4.97 GHz at 1.5 mm-thickness, respectively. Overall, this study establishes a facile and effective approach for the preparation of high-performance absorbers with tunable properties.