Insight into the performance of UV/chlorine/TiO2 on carbamazepine degradation: The crucial role of chlorine oxide radical (ClO•)

Abstract

The UV/chlorine (UC) system is a homogeneous advanced oxidation process with increasing attention in water decontamination. The addition of TiO2 is a newly found strategy to enhance the generation of hydroxyl radical (HO•) and chlorine radical (Cl•) in the UC system. However, the crucial role of chlorine oxide radical (ClO•, generated by the reactions of HO• and Cl• with chlorine) on pollutant degradation, has not been noticed in UV/chlorine/TiO2 (UCT), the heterogeneous photocatalytic system for chlorine activation. Herein, the role of ClO• in UCT was clarified through quenching experiments combined with model simulations during carbamazepine degradation. Tert-butyl alcohol completely inhibited while bicarbonate only partly suppressed carbamazepine degradation in UCT, indicating the important role of ClO•. The second-order reaction rate constant between ClO• and carbamazepine (kClO•,carbamazepine) was fitted to be (1.21 ± 0.08) × 107 M−1 s−1 by the kinetic model, which avoided the influence of carbonate radical (CO3•−), whose contribution couldn't be excluded during kClO•,carbamazepine determination in commonly used competitive kinetic methods with bicarbonate. With the obtained kClO•,carbamazepine, model simulation suggested that ClO• contributed about 50 % to carbamazepine degradation in UCT, and its concentration was less affected under varied conditions (solution pH, chlorine, bicarbonate, and chloride concentration) to keep an efficient carbamazepine degradation. On the contrary, pollutant degradation dominated by HO• in UCT was largely inhibited with the increase of pH, chlorine, and bicarbonate concentration. In addition to the promotion of degradation efficiency, less disinfection byproducts and lower energy requirement were found in UCT compared with UC. Furthermore, UCT could maintain satisfactory degradation efficiency and energy saving in ground water and surface water samples. Results of this study unraveled the crucial role of ClO• for pollutant degradation in UCT, and showed bright prospects and great potentials of the system in water treatment.