Influence of manganese ions on the anatase-rutile phase transition of TiO2 prepared by the sol-gel process

The anatase-rutile phase transformation of TiO2 containing various amounts of Mn2+ ions was studied by X-ray diffraction, electron spin resonance spectroscopy, and surface area measurements, The samples were prepared by the sol-gel process from titanium(IV) isopropoxide and manganese(II) acetate tetrahydrate. The amorphous powders were calcined for 2 h at different temperatures. Significant structural changes were observed during the various stages of the phase transformation. It was concluded that at low dopant concentrations, manganese ions are incorporated in the TiO2 structure, and the anatase phase is stabilized, but at larger amounts, part of the dopant is segregated on the surface of TiO2 and the rutile formation is accelerated. This was clearly confirmed by electron spin resonance. This experiment allowed the authors to follow the manganese oxidation and the phase transformation in detail. (C) 2002 Elsevier Science B.V All rights reserved.