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 CoNi@C and CoNi@NC 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 CoNi@C and CoNi@NC composites displayed significantly enhanced microwave absorption (MA) performance. The CoNi@NC-70 0 microspheres exhibited a maximum reflection loss (RL) of ?47.1 dB at a thickness of 2 mm. Further, CoNi@NC-70 0 and CoNi@C-700 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 highperformance absorbers with tunable properties. ? 2021 Elsevier B.V. All rights reserved.

Automated summary

This study utilized hollow CoNi alloy as the core and two types of carbon shells to protect it from oxidation and enhance its electromagnetic wave absorption performance. The CoNi@C and CoNi@NC absorbers were synthesized by in-situ polymerization on the surface of the alloy, with the absorption performance tuned by varying calcination temperature. The composites exhibited significantly improved microwave absorption performance compared to the pristine alloy, with effective bandwidths achieved at specific thicknesses.