Tunable design of yolk-shell ZnFe2O4@RGO@TiO2 microspheres for enhanced high-frequency microwave absorption

A series of yolk-shell ZnFe2O4@reduced graphite oxide@TiO2 ( ZFO@RGO@TiO2) microspheres with different void sizes and TiO2 shell thicknesses has been successfully synthesized by combining a layer-by-layer coating process and chemical etching route. Compared to pure ZFO and hierarchical ZFO@SiO2@RGO@TiO2, the as-synthesized yolk-shell microspheres exhibited significantly enhanced microwave absorption properties in terms of effective bandwidth and reflection loss. Among these, the minimum reflection loss of the as-synthesized yolk-shell microspheres with a thickness of 2.6 mm could reach up to -44.3 dB at 15.92 GHz, and their effective absorption bandwidth at less than -10 dB was 4.1 GHz. In addition, as the shell thickness of the yolk-shell microspheres decreased, the frequency corresponding to the minimum reflection loss shifted to the high-frequency range. Hence, these obtained yolk-shell microspheres are potential new candidates for high-frequency shielding and lightweight microwave absorbing materials.