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 Fe-0/iron oxides mixtures, i.e. Fe3O4 (magnetite), gamma-Fe2O3 (maghemite) or alpha-Fe2O3 (hematite) prepared by mechanical grinding and thermal treatment at 200, 400, 600 or 800 degrees C under argon atmosphere. Mossbauer 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 degrees 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 degrees C leads to an extensive solid state reaction of Fe-0 with Fe3O4 to produce the phase wustite, 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 H2O2. The mixtures Fe-0/Fe3O4 treated at 200 and 400 degrees C showed a remarkable increase in activity for the H2O2 decomposition. The high reactivity of these samples is discussed in terms of Fe-surf(2+) species formed by electron transfer from Fe-0 to Fe3+ at the interface metal/oxide which are active to initiate the H2O2 decomposition via a Haber-Weiss mechanism. The mixtures Fe-0/gamma-Fe2O3 and Fe-0/alpha-Fe2O3 ground and thermally treated were also studied, however much lower activities for the H2O2 decomposition were observed. (c) 2006 Elsevier B.V. All rights reserved.