High-temperature growth of anatase on kaolinite substrate

When a fine fraction of kaolinite (less than 2 μm) is mixed with titanyl sulphate (weight ratio approx. 1:7), hydrolysed, washed, dried and heated to temperatures between 750 and 900 ° C, it transforms into metakaolin, and titania crystallizes as anatase with a small particle size (approx. 20–30 nm). In parallel experiments with plain titania (without kaolinite), rutile is the sole product phase at 850 and 900 ° C and the dominant phase in a mixture with anatase at 750 ° C. The particle sizes are much larger (approx. 400–1100 nm). It appears that kaolinite is instrumental in preserving titania in the anatase form and with a small particle size even at fairly high temperatures and hindering its transformation to rutile. However, this anatase exhibits poor photocatalytic activity.