Nanocrystalline iron-doped mesoporous titania and its phase transition

Abstract

Nanocrystalline mesoporous iron-doped TiO₂ was prepared as a single-phase product by a novel sol–gel technique. By transmission, scanning and analytical electron microscopy as well as by complementary techniques it has been found that the as-prepared solids exhibit a narrow size distribution and that the iron is homogeneously distributed in the TiO₂ matrix. The influence of the iron concentration on the phase transformations of the doped TiO₂ was investigated by X-ray diffractometry. The formation of the iron titanium oxide pseudobrookite, Fe₂Ti₂O₅, was observed above 670 °C, but only for an iron content of more than 3 atom%. UV-spectroscopic measurements reveal that the absorption spectrum of the iron doped titania is sensitively related to both the iron concentration and the calcination temperature. Whereas pure nanocrystalline TiO₂ undergoes grain growth (sintering) when the calcination temperature is increased, iron doped TiO₂ proves to be inert to grain growth. N₂ adsorption–desorption analysis indicated that the products calcined between 390 and 600 °C for 1 h in air have mesoporous structure and the distribution of mesopores is very narrow, centered at 3.7 nm.