Synthesis of iron oxide nanoparticles by decomposition of iron-oleate: influence of the heating rate on the particle size

Abstract

Nanoparticles from transition metal oxides can be synthesized in various ways. A common synthesis route uses metal-oleate complex precursors that can be thermally decomposed, leading to crystalline metal-oxide nanoparticles with a narrow size distribution. The morphology of nanoparticles synthesized in such a way is strongly influenced by the synthesis parameters. In this study, the influence of the heating profile during the decomposition of iron oleate precursor on the size of the resulting iron oxide nanoparticles in the presence of surfactants was investigated. As surfactants oleic acid and sodium oleate were utilized for nanoparticle synthesis allowing additionally for shape control. Most of the prepared nanoparticles reveal a characteristic core–shell structure. The dominant structure is the cubic spinel structure of maghemite (γ-(Fe3+)2O3) or magnetite (Fe2+(Fe3+)2O4), while in the core region of the nanoparticles, wustite (Fe2+O) is present. The heating rate applied for the nanoparticle synthesis was systematically varied from 1 to 30 °C/min, while all other parameters were kept constant. A strong increase of the particle size (> 20 nm) was observed for low heating rates, which could be explained qualitatively in the frame of the LaMer model and allows for fine-tuning and control of the particle size.