Preparation of superparamagnetic Mn(x)Fe(1-x)O nanoparticles from low-index-facet cubes to high-index-facet concave structures and their catalytic performance in aqueous solution.

We report the synthesis of concave magnetic Mn(x)Fe(1-x)O nanoparticles with high-index facet structures by a thermal decomposition approach. The particle morphology varies from cubic shape under pure Ar, to star-like shapes with exposure to air during the reaction. The oxidative etching in the presence of air (O2) strongly affects the exposed facets on the surface. These concave nanoparticles are transferred from the organic phase to aqueous solution and show distinct catalytic activity toward the degradation of xylenol orange in aqueous solution.