Properties of γ-FeOOH, α-FeOOH and α-Fe 2O 3 particles precipitated by hydrolysis of Fe 3+ ions in perchlorate containing aqueous solutions

Abstract

The properties of γ-FeOOH, α-FeOOH and α-Fe 2O 3 particles formed by hydrolysis of Fe 3+ ions in perchlorate containing aqueous solutions were investigated using FT-IR and Mössbauer spectroscopies, TEM and FE SEM. At room temperature, slow hydrolysis of 5 × 10 −3 M Fe(ClO 4) 3 solution yielded γ-FeOOH as a single phase, whereas 1 × 10 −2 M Fe(ClO 4) 3 solution yielded γ-FeOOH as dominant phase and α-FeOOH as associated phase. Specific porous microstructures of laterally assembled lath-type γ-FeOOH particles were observed. Hydrolysis of 0.1 M Fe(ClO 4) 3 + 0.1 M HClO 4 solution at 90 °C for 21 days yielded monodisperse α-Fe 2O 3 particles with a layered substructure, whereas hydrolysis at 160 °C yielded layered and hollow substructures of α-Fe 2O 3 particles, and also showed intercrystal growth. In the absence of HClO 4, upon hydrolysis of 0.1 M Fe(ClO 4) 3 solution at 90 °C nanosize α-Fe 2O 3 particles were obtained with the maximum fraction of their sizes in the range of ∼15–60 nm. The observed substructure of α-Fe 2O 3 particles caused a decrease in the hyperfine magnetic field (HMF). The hydrolysis of Fe(ClO 4) 3 solution containing 1 wt.% sodium dodecyl sulphate (SDS) at 90 °C yielded α-FeOOH particles as a single phase. An important role of the specific adsorption of sulphate head groups in the formation of α-FeOOH particles in the presence of SDS was suggested. FE SEM has shown that these particles are made up of much smaller α-FeOOH units.