Synergistic influence of micropore architecture and TiO₂ coating on the microwave absorption properties of Co nanoparticles

Microporous Co@TiO₂ nanoparticles (NPs) have been synthesized by combining chemical de-alloying and sol–gel strategies. The NPs with a mean size of 30 nm display a TiO₂ shell of 5 nm in thickness and possess micropores in a range from 0.4 to 0.8 nm. The saturation magnetization (M_S) and coercivity (H_C) of the NPs are 18.6 emu/g and 337.4 Oe, respectively. The microwave absorption properties of the microporous Co@TiO₂ NPs mixed with paraffin were investigated in the range of 2–18 GHz. Due to the relatively high dielectric loss tangent value and low magnetic loss tangent value, the impedance matching of the composite is better than the nonporous counterpart. The composite shows a minimum reflection loss (RL) of − 16.6 dB at a thickness of merely 2.2 mm, and the absorption bandwidth for RL ≤ − 10 dB is as large as 5.0 GHz. At a thickness of 1.9 mm, the maximum absorption bandwidth for RL ≤ − 10 dB of 6.8 GHz can be obtained, which is much larger than that of its nonporous counterpart. Furthermore, the microwave absorption mechanism is discussed on the basis of the synergistic influence of micropores and TiO₂ shell. This study provides a good reference for designing novel materials for electromagnetic interference applications.