Overlooked Pathway of UV Filter Degradation in the UV/H<sub>2</sub>O<sub>2</sub>: The Important Role of Triplet State UV Filter
Qingqing Kong, Liaoliao Yao, Yangjian Zhou, Xin Yang
Abstract
The large production and usage of UV filters resulted in pervasive contamination in the aquatic environment. UV/H 2 O 2 is a widely used advanced oxidation process (AOP) to eliminate contaminants including UV filters relying on the generated HO • . In this study, the degradation of UV filters in the UV/H 2 O 2 AOP was investigated by using benzophenone (BP) as a representative. A previously overlooked pathway for BP degradation and HO • formation was newly identified. The triplet state species generated from BP photosensitization (i.e., 3 BP*) was found to react with H 2 O 2 to produce HO •, and this pathway contributed to 31% of BP degradation. The second-order rate constant of 3 BP* with H 2 O 2 was determined to be 8.7(±1.0) × 10 7 M –1 s –1 at pH 7.0 by using a laser flash photolysis system. 3 BP* acted as a reductant, and it was transformed into a radical cation (BP •+ ). The further hydrolysis of BP •+ produced hydroxylated BPs as products. This pathway can be barely influenced by pH and inorganic ions in the real water matrix. This work not only reported an unrecognized pathway for pollutant degradation in the UV/H 2 O 2 AOP but also inspired ideas to develop novel technologies to abate pollutants by taking advantage of their triplet states.