Photocatalytic degradation of a sulfonylurea herbicide over pure and tin-doped TiO2 photocatalysts

The heterogeneous photocatalytic degradation of chlorsulfuron (ChS), a sulfonylurea herbicide, has been studied using home-made Sn-doped TiO2 samples and TiO2 P25 from Degussa as photocatalysts. First-order kinetics were found for the disappearance of chlorsulfuron using both types of materials. Three synthesized photocatalysts were used, two of them containing 11 and 20 mass% of Sn, respectively, and one composed of pure anatase TiO2. The sample with the lower content of tin is formed by anatase and rutile crystallites, whereas the one with a higher doping level contains anatase, rutile and SnO2 phases. Comparison between their efficiency in the photocatalytic degradation of chlorsulfuron indicated a beneficial effect of the presence of Sn4+ in the TiO2 lattice, whereas segregated SnO2 phase induced a slower degradation of ChS when compared to pure TiO2. However, Degussa TiO2 P25 remains the most active material for this reaction. Based on DRIFTS and adsorption observations, an inverse dependence of the photocatalytic activity on the water adsorption capacity of the samples is proposed.