Enhanced photocatalytic formation of hydroxyl radicals on fluorinated TiO2.

Direct experimental evidence of the higher concentration of hydroxyl radicals generated on fluorinated titanium dioxide (F-TiO2) under irradiation was obtained by spin-trapping EPR measurements. The faster photoinduced bleaching of the azo dye Acid Red 1 (AR1) observed in the presence of F-TiO2 was explained by the high affinity of the azo double bond towards *OH radicals. Moreover, the pronounced decrease of the AR1 bleaching rate by addition of 2-propanol, as hydroxyl radicals scavenger, on F-TiO2 and not on naked TiO2 demonstrated that on fluorinated titania AR1 is mainly degraded via *OH radical attack.