Solid-state water-mediated transport reduction of nanostructured iron oxides

摘要

The Fe~(2+)/Fe~(3+) ratio in two-dimensional iron oxide nanosructures (nanolayers with a thickness of 0.3-1.5 nm on silica surface) may be precisely controlled using the transport reduction (TR) technique. The species ≡Si-O-Fe(OH)_2 and (≡Si-O-)_2-FeOH forming the surface monolayer are not reduced at 400-600 ℃ because of their covalent bonding to the silica surface, as demonstrated by Mossbauer spectroscopy. Iron oxide microparticles (microstructures) obtained by the impregnation technique, being chemically unbound to silica, are subjected to reduction at T ≥ 500 ℃ with formation of metallic iron in the form of α-Fe. Transport reduction of supported nanostructures (consisting of 1 or 4 monolayers) at T ≥ 600 ℃ produces bulk iron(II) silicate and metallic iron phases. The structural-chemical transformations occurring in transport reduction of supported iron oxide nanolayers are proved to be governed by specific phase processes in the nanostructures themselves.