Size- and Shape-Controlled Magnetic (Cr, Mn, Fe, Co, Ni) Oxide Nanocrystals via a Simple and General Approach

TLDR

The authors present a general, reproducible, and simple strategy using generic chemicals to control the size, shape, and size distribution of oxide nanocrystals. The method employs metal fatty acid salts and fatty acids in a hydrocarbon solvent, pyrolyzes them, and tunes nanocrystal size and shape by varying precursor reactivity, ligand chain length, concentration, and optional activation reagents such as alcohols or amines. Using this approach, nearly monodisperse Fe₃O₄ nanocrystals ranging from 3 to 50 nm were synthesized, and the technique was successfully extended to Cr₂O₃, MnO, Co₃O₄, and NiO, demonstrating precise size and shape control across fourth‑row magnetic oxides.

Abstract

A general, reproducible, and simple strategy using generic chemicals is introduced for controlling the size, shape, and size distribution of oxide nanocrystals. The reaction system was generally composed of the metal fatty acid salts, the corresponding fatty acids, and a hydrocarbon solvent. The method is based on the pyrolysis of metal fatty acid salts, the most common metal compounds compatible with nonaqueous solutions. Synthesis of nearly monodisperse Fe3O4 nanocrystals in a large size range (3−50 nm) was developed as the model system. The method was further applied for the growth of oxide nanocrystals of the other magnetic metals in the fourth rowCr2O3, MnO, Co3O4, and NiO nanocrystals. The size and shape control of the nanocrystals were achieved by varying the reactivity and concentration of the precursors. The reactivity was tuned by changing the chain length and concentration of the ligands, the fatty acids. Alcohols or primary amines could be used as the activation reagents when a given metal fatty acid salt was not sufficiently active under selected reaction conditions.