Constructing and optimizing core–shell structured Co@TiO₂ as highly efficient electromagnetic wave absorber

To achieve highly efficient electromagnetic wave absorber, elaborately designing magnetic–dielectric Co@TiO₂ microspheres with core–shell configuration are successfully constructed through a facile sequential process of liquid phase reduction–sol–gel–annealing. Owing to the core–shell configuration and the synergistic effect among magnetic and dielectric components, the annealed sample shows outstanding electromagnetic wave absorption (EMA) in X and K_u band. Impressively, a maximum reflection loss (RL_max) is reached –56.6 dB at a coating thickness of 2.3 mm with corresponding effective absorption bandwidth (EAB₁₀) of 7.2 GHz (including 65% of K_u band and 82.5% of X band), much stronger than those of as-prepared Co (EAB₁₀ of 1.6 GHz, RL_max of 14.6 dB) and pristine Co@TiO₂ (EAB₁₀ of 2.9 GHz, RL_max of 16.3 dB). An EAB₁₀ covering completely the whole X and K_u band could be obtained by controlling the thickness only from 2.0 mm to 2.5 mm. The composites have both outstanding RL and wide EAB₁₀ with the thin coating thickness, reinforcing that fabricating core–shell configuration composites is an efficient strategy to boost the EMA efficiency.