Striking effect of the iron stearate purity on the shape and size of maghemite nanoparticles

In general, the synthesis of maghemite nanoparticles (NPs) by thermal decomposition of commercially available iron stearate precursors, in the presence of oleic acid, yields spherical nanoparticles. However, we show in this article that the synthesis of NPs from commercially available precursors (Commercial grade and washed) results in the formation of uniformly monodisperse triangular or cubic NPs. Spherical NPs result only from the precursors synthesized in the laboratory. The detailed Energy Dispersive X-ray spectrometry (EDS) and X-ray diffraction analysis performed on the commercial precursors (Commercial grade and washed) reveal the presence of impurities: sodium stearate and/or sodium chloride (NaCl). This result highlights the importance of iron stearate precursor origin (commercial grade or washed or home-made) in terms of reproducibility and growth of iron oxide NPs, giving rise to either monodisperse spherical, cubic, or triangular NPs. We emphasize that this finding majorly affects the development of NPs and also our understanding of the NP growth mechanisms, which can be biased if we do not account for this additional key parameter among all the ones involved in the colloidal synthesis. The formation of the triangular nanoparticles in the conditions we use has never been reported. Further, the formation of both cubic and triangular NPs has been discussed in terms of selective adsorption on the growing NP of sodium stearate, sodium, and chloride salts.

Automated summary

This article demonstrates the significance of the origin of iron stearate precursors in the synthesis of iron oxide nanoparticles. Commercial grade and washed precursors result in triangular or cubic nanoparticles formation, while spherical nanoparticles are obtained from the laboratory-synthesized precursors. The presence of impurities, such as sodium stearate and/or sodium chloride, in the commercial precursors affects the reproducibility and growth of iron oxide nanoparticles. This finding has a major impact on the development and understanding of nanoparticle growth mechanisms.