Predominance role of the superoxide radical over the hydroxyl radical in the dechlorination of trichloroethene in aqueous phase using Cu doped TiO₂

Trichloroethylene (TCE), a frequently used chlorinated solvent has been completely degraded in aqueous solution over the as-synthesised Cu-TiO₂ irradiated with UV light. The effect of pH and the role played by specific generated reactive oxygen species in the mineralisation process were evaluated. Cu-TiO₂ was synthesised and characterised according to our previous study. The photodegradation results, which followed the pseudo-first-order kinetic model, revealed that pH had a negligible effect on the degradation as the complete dechlorination occurred in all adjusted pH solutions. In addition, probe compound tests using nitrobenzene and tetrachloromethane suggested that the hydroxyl radical (^•OH) is mainly generated when coupling UV with Cu-TiO₂, and the superoxide radical anion (O₂^•−) is highly generated when UV is applied alone. Free radical quenching studies demonstrated that O₂^•− is the major radical responsible for the degradation of TCE compared to ^•OH. The results obtained in the present study can serve as a support for further studies on the removal of TCE using UV coupling catalyst.