Influence of Anions and Cations on the Formation of Iron Oxide Nanoparticles in Aqueous Media

Recently, various types of functionalized metal oxide nanoparticles have been used for many applications because of their unique chemical and physical properties. To synthesize metal oxide nanoparticles, liquid-phase synthesis techniques have been developed. The production process of metal oxide nanoparticles in aqueous media is extremely complex because the formation, crystal structure, crystallinity, chemical composition, and morphology of the particles are considerably dependent on the preparation conditions (e.g., anion and cation concentrations and species, additives, solution pH, reaction temperature, and reaction time). Accordingly, clarifying these effects is fundamental to accurately understand the formation mechanism of metal oxide nanoparticles to further develop new functionalized nanoparticles. In this review, the influence of anions (Cl−, SO42−, and NO3−) and cations (Ni2+, Cu2+, and Cr3+) on the formation and structure of iron oxide nanoparticles in aqueous media is described.