Role of the Counteranions on the Formation of Different Crystal Structures of Iron Oxyhydroxides via Redox Reaction

Redox reactions have been employed for the conversion of various metal oxide nanocrystals, where several parameters were examined to understand the reaction mechanism. However, the role of the counteranions still has not yet been studied. Herein, we present the influence of the counteranions (sulfate, chloride, and acetate) on the formation of iron oxyhydroxide nanofiber structure (100 nm × few microns; diameter × length) via redox reaction using iron salt and manganese oxide as a template. We found that different structures of iron oxide/oxyhydroxide (goethite, hydrohematite, and maghemite) were obtained when different anions (sulfate, chloride, and acetate, respectively) were used. Moreover, we studied the effect of various parameters such as the concentration of iron precursor, the time, and the temperature of the reaction. Finally, we converted the iron oxyhydroxide film to hematite and examined its photoelectrochemical properties.