Structural characterization of Fe/Ti oxide photocatalysts by X-ray,ESR, and Mössbauer methods

The polycrystalline solids TiO₂Fe₂O₃, with iron contents in the range 0–10 at.%, prepared by coprecipitation and by impregnation, and treated in air at temperatures in the range 500–1000°C, have been studied by X-ray, ESR, and Mössbauer methods. The TiO₂ in the samples treated at 800 and 1000°C always forms the rutile phase and the Fe³⁺ has a rather low solubility in it (～0.1 at.%). The Fe³⁺ in excess forms the antiferromagnetic pseudobrookite phase (Fe₂TiO₅). The samples treated at 500 and 650°C show a dependence on the preparation method. Those prepared by coprecipitation give at 500°C the pure anatase phase in which the Fe³⁺ has a higher solubility (≥ 1%); those prepared by impregnation give the anatase phase accompanied by a variable amount of rutile. The treatment at 650°C provokes the partial transformation of anatase to rutile and the complete development of the Fe₂TiO₅ phase. The relevance of these results to the photocatalytic properties shown by these solids for the photoreduction of dinitrogen to ammonia is discussed.