Two-dimensional confinement engineering of SiO₂ nanosheets supported nano-cobalt for high-efficiency microwave absorption

Advanced electromagnetic (EM) absorbers containing magnetic and dielectric components have garnered substantial attention due to rapid expansion of wireless communication equipment. However, the EM absorbing performance of magnetic materials is greatly hindered by the substantial decrease in permeability at gigahertz frequencies, commonly referred to the Snoek limit. Confinement engineering provides effective strategy for precisely modulating particle size in a confined region to enhance the surface anisotropy and thereby surpass the Snoek limit. Herein, a novel space-confined strategy is proposed to develop two-dimensional (2D) SiO₂ nanosheets that involves manipulating the topological exfoliation of CaSi₂ with CoCl₂ and thereafter high-temperature reduction. The resulting SiO₂ supported nano-Co (Co-2DSiO₂) heterostructure exhibits uniform dispersion and nearly single domain size. Contributing to the magnetic-dielectric synergistic effect, fascinating EM properties can be achieved by regulating the size of nano-Co at varied temperatures, and the Co-2DSiO₂ delivers the optimal reflection loss of –51.6 dB at 2.5 mm and the effective absorption bandwidth of 4.6 GHz. Electronic structures of Co-2DSiO₂ were simulated by theoretical calculation, further verifying the potential mechanism of enhanced dielectric loss and analyzing the formation of heterostructure. The proposed confinement strategy lays the groundwork for the development of advanced absorbers and provides a universal approach for other metal-based SiO₂ nanosheets with tunable structures.