Direct Formation of Iron(III)‐Doped Titanium Oxide (Anatase) by Thermal Hydrolysis and Its Structural Property

Anatase‐type TiO 2 (titania) doped with iron up to 19.8 mol% was directly formed as nanometer‐sized particles from acidic precursor solutions of TiOSO 4 and Fe(NO 3 ) 3 by simultaneous hydrolysis, under mild hydrothermal conditions at 180°3C. Iron content in the anatase‐type TiO 2 was much less than that of the starting composition of the precursor solutions because of slower hydrolysis rate of Fe(NO 3 ) 3 than that of TiOSO 4 at 180°3C. The XRD data, TEM selected‐area diffraction patterns, and Mössbauer effect measurement showed that iron(III) formed a solid solution in the anatase‐type TiO 2 precipitates and that there was no iron oxide precipitated as secondary phase without making a solid solution with TiO 2 present in the precipitates. Doping of Fe 2 O 3 into TiO 2 shifted the phase transformation from anatase‐type to rutile‐type structure to a low temperature. On the phase transformation from anatase to rutile, iron oxide was precipitated as Fe 2 TiO 5 (pseudobrookite) phase. When the iron content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV‐light region and in the visible‐light region over 400–600 nm clearly appeared in the diffuse reflectance spectra of the as‐prepared Fe(III)‐doped TiO 2 .