Construction of hydrangea-like core–shell SiO ₂@Ti ₃C ₂T x @CoNi microspheres for tunable electromagnetic wave absorbers

Ti₃C₂Tx MXene shows great potential in the application as microwave absorbers due to its high attenuation ability. However, excessively high permittivity and self-stacking are the main obstacles that constrain its wide range of applications. To tackle these problems, herein, the microspheres of SiO₂@Ti₃C₂Tx@CoNi with the hydrangea-like core–shell structure were designed and prepared by a combinatorial electrostatic assembly and hydrothermal reaction method. These microspheres are constructed by an outside layer of CoNi nanosheets and intermediate Ti₃C₂Tx MXene nanosheets wrapping on the core of modified SiO₂, engendering both homogenous and heterogeneous interfaces. Such trilayer SiO₂@Ti₃C₂Tx@CoNi microspheres are "magnetic microsize supercapacitors" that can not only induce dielectric loss and magnetic loss but also provide multilayer interfaces to enhance the interfacial polarization. The optimized impedance matching and core–shell structure could boost the reflection loss (RL) by electromagnetic synergy. The synthesized SiO₂@Ti₃C₂Tx@CoNi microspheres demonstrate outstanding microwave absorption (MA) performance benefited from these advantages. The obtained RL value was −63.95 dB at an ultra-thin thickness of 1.2 mm, corresponding to an effective absorption bandwidth (EAB) of 4.56 GHz. This work demonstrates that the trilayer core–shell structure designing strategy is highly efficient for tuning the MA performance of MXene-based microspheres.