Insight into the Performance of the Uv/Chlorine/Tio2 System: 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 the UV/chlorine/TiO2 (UCT) system, 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. 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. Both simulation and experimental results suggested that ClO• majorly contributed to carbamazepine degradation by the UCT system, and its concentration is less affected under varied conditions (solution pH, chlorine, bicarbonate, and chloride concentration) to keep an efficient carbamazepine degradation. In addition to the promotion of degradation efficiency, less disinfection byproducts and lower energy requirement were found in UCT compared with UC. 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.

Keywords: UV/chlorine/TiO2, chlorine oxide radical, model simulation, advanced oxidation process, water treatment