Surface structure of magnetite (111) under hydrated conditions by crystal truncation rod diffraction

X-ray crystal truncation rod (CTR) diffraction under hydrated conditions at circum-neutral pH was used to determine the surface structure of Fe3O4(111) following a wet chemical mechanical polishing (CMP) preparation method. The best-fit model to the CTR data shows the presence of two oxygen terminated domains that are chemically inequivalent and symmetrically distinct in the surface contribution ratio of 75% oxygen octahedraliron (OOI) termination (O-a(2.61)-O-a(1.00)-Fe-oh1(2.55)-O-b(1.00)-O-b(3.00)-Fe-td1(1.00)-Fe-oh2(1.00)-Fe-td2(1.00)-R) to 25% oxygen mixed-iron (OMI) termination (O-b(1.00)-O-b(3.00)-Fe-td1(0)-Fe-oh2(1.00)-Fe-td2(1.00)-O-a(3.00)-O-a(1.00)-Fe-oh1(3.00)-R). An adsorbed water layer could not be constrained in the best-fit model. However, bond-valence analyses suggest that both of the surfaces are hydro-oxo terminated. Furthermore, the topmost iron layers of both domains are inferred to be occupied with the redox active Fe2+ and Fe3+ cations indicating that these irons are the principle irons involved in controlling the surface reactivity of magnetite in industrial and environmentally relevant conditions. (C) 2010 Elsevier BM. All rights reserved.