Effect of halide contaminant ions in the hydrothermal treatment of amorphous titania on the phase change from anatase to rutile during calcination

Hydrothermal treatment in salt solutions has been used to crystallise and s tabilise the anatase phase of titania. Halide contaminants have been shown to accelerate crystallisation of anatase when compared to reactions in pure water, but as anion size increases, the crystallisation improvement is les s, The crystallised anatase has then been calcined to form rutile. The impu rity ions appear to adsorb to the titania surface and have been shown to ha ve a strong influence on the anatase/rutile transition, reducing the rutile formation during calcination due to the steric hindrance of the rutile nuc leation sites on the titania surface. The adsorption sites for the anions a ffecting anatase crystallisation and rutile formation are different.