Photocatalytic decomposition of crotamiton over aqueous TiO(2) suspensions: determination of intermediates and the reaction pathway

The photocatalytic degradation of crotamiton in aqueous solution using TiO₂ was investigated. To investigate the effect of initial pH, the photodegradation behaviors of three types of pharmaceuticals were compared (crotamiton, clofibric acid, sulfamethoxazole). The degradation rates of crotamiton in the pH range 3-9 were nearly equal, but those of clofibric acid and sulfamethoxazole were affected by pH. At pH > 6.5, TiO₂ particles, clofibric acid and sulfamethoxazole had negative charge, therefore, the repulsive force between TiO₂ particles and anionic pharmaceuticals occurred and a low reaction rate at high pH was observed. The effect of UV intensity and TiO₂ concentration on photodegradation efficiency was also investigated. Linear and logarithmical relationships between UV intensity, TiO₂ concentration and the reaction rate constant were confirmed. Furthermore, the structures of photodegradation intermediates formed concomitantly with the disappearance of crotamiton were estimated. Seven intermediates were characterized by LC/MS/MS analyses, and it was assumed that the photocatalytic degradation of crotamiton was initiated by the attack of electrophilic hydroxyl radicals on aromatic rings and alkyl chains.