Liquid foam as a template for the synthesis of iron oxyhydroxide nanoparticles

Liquid foams have been used as a template to prepare iron oxyhydroxide nanoparticles. This is achieved by a process of electrostatic entrapment of Fe^2-/Fe³+ ions in the foam stabilized by the surfactant sodium dodecyl sulfate followed by the in situ hydrolysis of the metal ions. Infrared and selected area electron diffraction measurements suggest the formation of a mixture of β-FeO(OH) and γ-FeO(OH) crystallographic phases after the in situ hydrolysis of the metal ions in the foam template. Transmission electron microscopy analysis of the powders obtained from the foam indicates that the particles are fairly monodisperse with an average size of around 50 nm. Scanning electron microscopy pictures reveal that the particles form loosely bound aggregates of around 300 nm. After the powders obtained in the foam are annealed at 400 °C, X-ray diffraction measurements show that the FeO(OH) particles are converted to α-Fe₂O₃. The mechanistic aspects of metal ion hydrolysis in a foam are discussed, and some of the advantages of this method vis-à-vis the normal solution-based methods are outlined.