Near-Ultraviolet Light-Driven Photocatalytic Chlorine Activation Process with Novel Chlorine Activation Mechanisms
Zihang Cheng, Li Ling, Chii Shang
Abstract
In this study, the near-ultraviolet (near-UV) light-driven TiO2 photocatalytic chlorine activation process, termed as the UV365/TiO2/chlorine process, degrades a representative recalcitrant micropollutant, carbamazepine (CBZ), at an apparent first-order rate constant (kCBZ′) that is 34.2 and 3.9 times higher than those without TiO2 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. kCBZ′ increased with increasing TiO2 dosages from 1.0 to 20.0 mg/L and light intensities from 0.1 to 0.33 mW/cm2 and with decreasing chlorine dosages from 5.0 to 1.0 mgCl2/L. Increasing pH increased the overall radical concentrations but transformed HO· and Cl· to less reactive ClO·, leading to a decreasing kCBZ′ 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 TiO2 dosage about 1/200 to that of the UVC/TiO2 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.