Preparation of a highly thermally stable titania anatase phase by addition of mixed zirconia and silica dopants

Sol-gel methods using a titanium isopropoxide precursor were employed in the synthesis of titania and the conversion of the amorphous product to anatase and then rutile by high temperature thermal treatment was followed by powder X-ray diffraction (PXRD), differential thermal analysis (DTA) and electron microscopy (EM). The thermal stability of the anatase phase was limited when pure materials were prepared. However, addition of 4+ dopants such as Zr ⁴⁺ and Si⁴⁺ showed higher transition temperatures for the anatase to rutile phase change. The highest stability of the anatase phase was found for tertiary materials containing both Zr⁴⁺ and Si ⁴⁺. The mechanism for the anatase to rutile phase transition in these materials appears to be largely related to the attainment of a critical particle size above which the phase change becomes energetically favourable. The role of silicon and zirconium ions appears to reduce mass transport in the system thereby preventing the materials reaching the critical particle size until higher temperatures compared to undoped materials.