Mechanistic Features of the TiO 2 Heterogeneous Photocatalysis of Arsenic and Uranyl Nitrate in Aqueous Suspensions Studied by the Stopped‐Flow Technique

The dynamics of the transfer of electrons stored in TiO 2 nanoparticles to As III , As V , and uranyl nitrate in water was investigated by using the stopped‐flow technique. Suspensions of TiO 2 nanoparticles with stored trapped electrons (e trap − ) were mixed with solutions of acceptor species to evaluate the reactivity by following the temporal evolution of e trap − by the decrease in the absorbance at λ =600 nm. The results indicate that As V and As III cannot be reduced by e trap − under the reaction conditions. In addition, it was observed that the presence of As V and As III strongly modified the reaction rate between O 2 and e trap − : an increase in the rate was observed if As V was present and a decrease in the rate was observed in the presence of As III . In contrast with the As system, U VI was observed to react easily with e trap − and U IV formation was observed spectroscopically at λ =650 nm. The possible competence of U VI and NO 3 − for their reduction by e trap − was analyzed. The inhibition of the U VI photocatalytic reduction by O 2 could be attributed to the fast oxidation of U V and/or U IV .