Highly reactive species formed by interface reaction between Fe 0–iron oxides particles: An efficient electron transfer system for environmental applications

Abstract

This work studied the formation of highly reactive species in the interface of Fe 0/iron oxides mixtures, i.e. Fe 3O 4 (magnetite), γ-Fe 2O 3 (maghemite) or α-Fe 2O 3 (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 Fe 2O 3. The treatment at 600 and 800 °C leads to an extensive solid state reaction of Fe 0 with Fe 3O 4 to produce the phase wüstite, FeO, with a strong decrease in BET surface area and reactivity. These thermally treated mixtures Fe 0/iron oxides were also studied as heterogeneous catalysts to promote the decomposition of H 2O 2. The mixtures Fe 0/Fe 3O 4 treated at 200 and 400 °C showed a remarkable increase in activity for the H 2O 2 decomposition. The high reactivity of these samples is discussed in terms of Fe surf 2+ species formed by electron transfer from Fe 0 to Fe 3+ at the interface metal/oxide which are active to initiate the H 2O 2 decomposition via a Haber–Weiss mechanism. The mixtures Fe 0/γ-Fe 2O 3 and Fe 0/α-Fe 2O 3 ground and thermally treated were also studied, however much lower activities for the H 2O 2 decomposition were observed.