Evaluating Intrinsic Photocatalytic Activities of Anatase and Rutile TiO₂ for Organic Degradation in Water

Various factors that influence the photocatalytic activity of TiO 2 for organic degradation in aerated aqueous solution have been reported. For instance, anatase is considered to be much more active than rutile. However, no attention has been paid to the difference in their sorption capacities toward O 2 in water, which might be critical to the activity determination. In this work, Ag + has been used as an electron scavenger, for the photocatalytic degradation of 4-chlorophenol in the N 2 -purged aqueous suspension of TiO 2 under UV light. Three different TiO 2 samples in the crystal forms of anatase and rutile, containing micro- and mesopores, were prepared, followed by sintering at different temperatures ( T s ). The initial rate of 4-chlorophenol photodegradation, per the initial amount of Ag + adsorbed, increased exponentially with T s . Such T s -dependent normalized rates were observed with three differently prepared TiO 2 samples, and three curves were almost overlapped. Comparatively, in the aerated aqueous suspension of TiO 2, the initial rate of 4-chlorophenol photodegradation, per surface area of the catalyst, first increased and then decreased with T s, the trend similar to those widely reported. Moreover, from the literature data of water photosplitting over TiO 2, the initial rate of O 2 evolution, per the initial amount of Ag + adsorbed, increased exponentially with T s . Evidence clearly shows that with the same amount of electron scavenger on the catalyst surfaces, anatase and rutile actually have a similar photocatalytic activity at a given T s, for organic degradation or water oxidation. It is recommended that to evaluate the photocatalytic activities of different TiO 2 samples in an aerated aqueous solution, the difference in O 2 adsorption needs to be taken into account.