Highly reactive species formed by interface reaction between Fe0–iron oxides particles: An efficient electron transfer system for environmental applications

This work studied the formation of highly reactive species in the interface of Fe0/iron oxides mixtures, i.e. Fe3O4 (magnetite), γ-Fe2O3 (maghemite) or α-Fe2O3 (hematite) prepared by mechanical grinding and thermal treatment at 200, 400, 600 or 800 °C under argon atmosphere. Mössbauer spectroscopy, powder X-ray diffraction, scanning electron microscopy, BET surface area and magnetization measurements suggest a strong interaction between the metal and the oxide surfaces at temperature as low as 200 °C, producing highly reactive surface species. These reactive species are readily oxidized when exposed to air at room temperature to form large quantities of Fe2O3. The treatment at 600 and 800 °C leads to an extensive solid state reaction of Fe0 with Fe3O4 to produce the phase wüstite, FeO, with a strong decrease in BET surface area and reactivity. These thermally treated mixtures Fe0/iron oxides were also studied as heterogeneous catalysts to promote the decomposition of H2O2. The mixtures Fe0/Fe3O4 treated at 200 and 400 °C showed a remarkable increase in activity for the H2O2 decomposition. The high reactivity of these samples is discussed in terms of Fesurf2+ species formed by electron transfer from Fe0 to Fe3+ at the interface metal/oxide which are active to initiate the H2O2 decomposition via a Haber–Weiss mechanism. The mixtures Fe0/γ-Fe2O3 and Fe0/α-Fe2O3 ground and thermally treated were also studied, however much lower activities for the H2O2 decomposition were observed.