Enhanced Radical Generation in an Ultraviolet/Chlorine System through the Addition of TiO2

Ultraviolet (UV)/chlorine draws increasing attention for the abatement of recalcitrant organic pollutants. Herein, it was found that TiO 2 would significantly promote the degradation of dimethyl phthalate (DMP) in the UV/chlorine system (from 19 to 84%). Hydroxyl radicals (HO • ) and chlorine radicals (Cl • ) were the dominant reactive species for DMP degradation in the UV/chlorine/TiO 2 system. Chlorine decayed much faster in UV/chlorine/TiO 2 compared with UV/chlorine, which is possibly because photogenerated electrons (e cb – ) and superoxide radicals (O 2 •– ) have high reactivity with chlorine. As a result, the recombination of photogenerated holes (h vb + ) and e cb – was inhibited and the accumulation of HO • and Cl • was facilitated. A kinetic model was established to simulate the reaction process, and it was found that the concentrations of HO • and Cl • were several times to dozens of times higher in UV/chlorine/TiO 2 than that in UV/chlorine. The contributions of HO • and Cl • to DMP degradation were 70.3 and 29.7% by model simulation, respectively, and were close to the probe experiment result. In the UV/chlorine/TiO 2 system, the degradation of DMP did not follow pseudo-first-order kinetics but the degradation of benzoate fitted well with pseudo-first-order kinetics. This phenomenon was elucidated by the structure of the pollutant and TiO 2 and further tested by calculating the adsorption energy ( E ads )/binding energy ( E b ) with density functional theory. Due to faster decay of chlorine, lower amounts of disinfection byproducts formed in UV/chlorine/TiO 2 compared with UV/chlorine. Adding TiO 2 into the UV/chlorine system can promote the degradation of recalcitrant organic pollutants in an aqueous environment.