Improved high temperature stability of Anatase TiO2 Photocatalysts by N, F, P co-doping

Among the three commonly occurring phases (anatase, rutile, and brookite) of TiO2, the anatase form is reported\ud to be the best photocatalyst due to the improved charge-carrier mobility and the greater number of surface\ud hydroxyl groups. The anatase to rutile transition in titania photocatalysts usually occurs at a temperature between\ud 500 °C to 700 °C. Development of a high temperature stable (above 1000 °C) anatase phase is important\ud for various environmental applications (e.g. self-cleaning ceramic tiles, anti-microbial sanitary wares, etc.). In\ud this study, the use of ammonium hexafluorophosphate as a single source dopant (method A) and urea,\ud trifluoroacetic acid and phosphoric acid as multiple sources (method B) was undertaken to improving its high\ud temperature stability. Method A was seen to produce a more stable anatase phase, with 68% anatase present at\ud 1100 °C, compared to method B which showed 100% rutile at 900 °C. Kinetic analysis shows a marked increase\ud in the photocatalytic degradation of a model dye using materials calcined at 1100 °C for method A\ud (0.042 min−1) compared to that for method B (0.005 min−1) and the commercial photocatalyst Evonik-\ud Degussa AEROXIDE® (0.031 min−1) at 1100 °C. XPS results showed that, the only dopant detected at high temperatures\ud is phosphorus in its P5+ form. The incorporation of phosphorus has proved to be an effective method in\ud stabilising the anatase phase at high temperature. The current investigation also showed that a single source precursor\ud is more favourable to obtain high temperature stable anatase phase photocatalysts