Synthesis and microwave absorption enhancement of graphene@Fe3O4@SiO2@NiO nanosheet hierarchical structures

Hierarchical structures of graphene@Fe₃O₄@SiO₂@NiO nanosheets were prepared by combining the versatile sol-gel process with a hydrothermal reaction. Graphene@Fe₃O₄ composites were first synthesized by the reduction reaction between FeCl₃ and diethylene glycol (DEG) in the presence of GO. Then, graphene@Fe₃O₄ was coated with SiO₂ to obtain graphene@Fe₃O₄@SiO₂. Finally, NiO nanosheets were grown perpendicularly on the surface of graphene@Fe₃O₄@SiO₂ and graphene@Fe₃O₄@SiO₂@NiO nanosheet hierarchical structures were formed. Moreover, the microwave absorption properties of both graphene@Fe₃O₄ and graphene@Fe₃O₄@SiO₂@NiO nanosheets were investigated between 2 and 18 GHz microwave frequency bands. The electromagnetic data demonstrate that graphene@Fe₃O₄@SiO₂@NiO nanosheet hierarchical structures exhibit significantly enhanced microwave absorption properties compared with graphene@Fe₃O₄, which probably originate from the unique hierarchical structure with a large surface area and high porosity.