Controlled synthesis of MnxFe1−xO concave nanocubes and highly branched cubic mesocrystals

Abstract

In this work, we reported the synthesis of concave nanocubes of iron-manganese oxide (Mn_xFe_1−xO) via a thermolysis process in a mixture of oleic acid (OA) and oleylamine (OAm). The shape and size of the iron-manganese oxide can be tuned by changing the experimental conditions such as the solvent composition (volume ratio of OA and OAm), heating rate, precursor concentration, thermolysis temperature and reaction time. The Mn_xFe_1−xO nanocrystals with different morphologies such as nanospheres, nanocubes, concave nanocubes, and octapods were synthesized under appropriate reaction conditions. The favorable reaction conditions and growth mechanism for concave Mn_xFe_1−xO cubes were investigated in detail. Moreover, monodisperse Mn_xFe_1−xO nanocrystals with anisotropic shapes and compositions tunable in the entire range (0 ≤ x ≤ 1) were obtained by changing the Mn/Fe ratio in the precursor solutions. The morphology of the Mn_xFe_1−xO nanocrystals varied from concave nanocubes, nanospindles, nanorods, T-shaped nanorods to nanoflowers with increasing Mn content x from 0 to 1. Furthermore, superparamagnetic, highly branched cubic Mn_xFe_1−xO mesocrystals with sizes more than 100 nm were synthesized for the first time by using 1-octadecene as a co-solvent in the reaction solutions. It was proposed that the highly branched cubic mesocrystals were formed via self-aggregation of concave nanocubes, accompanied by Ostwald ripening and crystal fusion and growth.