Near-Ultraviolet Light-Driven Photocatalytic Chlorine Activation Process with Novel Chlorine Activation Mechanisms

In this study, the near-ultraviolet (near-UV) light-driven TiO 2 photocatalytic chlorine activation process, termed as the UV 365 /TiO 2 /chlorine process, degrades a representative recalcitrant micropollutant, carbamazepine (CBZ), at an apparent first-order rate constant ( k CBZ ′) that is 34.2 and 3.9 times higher than those without TiO 2 and chlorine, respectively. In this process, chlorine serves a more important role as a catalyst to enhance the yield of hydroxyl radicals (HO·) without being consumed, in addition to its role as a radical precursor to produce HO· and reactive chlorine species. k CBZ ′ increased with increasing TiO 2 dosages from 1.0 to 20.0 mg/L and light intensities from 0.1 to 0.33 mW/cm 2 and with decreasing chlorine dosages from 5.0 to 1.0 mgCl 2 /L. Increasing pH increased the overall radical concentrations but transformed HO· and Cl· to less reactive ClO·, leading to a decreasing k CBZ ′ from pH 6.0 to 9.0. The dual roles of chlorine in the process enabled the rapid CBZ degradation at a chlorine dosage about 1/20 to that of the conventional UVC/chlorine process, at a TiO 2 dosage about 1/200 to that of the UVC/TiO 2 process and at an electrical energy per order of CBZ degradation at least 2-order of magnitude lower than those of the existing UVC-based processes.