Photocatalytic Degradation of Mecoprop and Clopyralid in Aqueous Suspensions of Nanostructured N-doped TiO₂

Abstract: The work describes a study of the oxidation power of N-doped and undoped anatase TiO₂, as well as TiO₂ Degussa P25 suspensions for photocatalytic degradation of the herbicides RS-2-(4-chloro-o-tolyloxy)propionic acid (mecoprop) and 3,6-dichloro-pyridine-2-carboxylic acid (clopyralid) using visible and UV light. Undoped nanostructured TiO₂ powder in the form of anatase was prepared by a sol-gel route. The synthesized TiO₂, as well as TiO₂ Degussa P25 powder, were modified with urea to introduce nitrogen into the structure. N-doped TiO₂ appeared to be somewhat more efficient than the starting TiO₂ (anatase) powder when visible light was used for mecoprop degradation. N-doped TiO₂ Degussa P25 was also slightly more efficient than TiO₂ Degussa P25. However, under the same experimental conditions, no degradation of clopyralid was observed in the presence of any of the mentioned catalysts. When the kinetics of mecoprop degradation was studied using UV light, more efficient were the undoped powders, while in the case of clopyralid, N-doped TiO₂ Degussa P25 powder was most efficient, which is probably a consequence of the difference in the molecular structure of the two herbicides.