title: Influence of pH on the formation of sulfate and hydroxyl radicals in the UV/peroxymonosulfate system.
abstract: The influence of pH on the degradation of refractory organics (benzoic acid, BA) in UV(254 nm)/Peroxymonosulfate (UV/PMS) system was investigated. The degradation of BA was significantly enhanced at the pH range of 8-11, which could not be explained only by the generally accepted theory that SO(4)(•-) was converted to HO(•) at higher pH. A hypothesis was proposed that the rate of PMS photolysis into HO(•) and SO(4)(•-) increased with pH. The hypothesis was evidenced by the measured increase of apparent-molar absorption coefficient of PMS (ε(PMS), 13.8-149.5 M(-1)·cm(-1)) and photolysis rate of PMS with pH, and further proved by the increased quasi-stationary concentrations of both HO(•) and SO(4)(•-) at the pH range of 8-10. The formation of HO(•) and SO(4)(•-) in the UV/PMS system was confirmed mainly from the cooperation of the photolysis of PMS, the decay of peroxomonosulfate radical (SO(5)(•-)) and the conversion of SO(4)(•-) to HO(•) by simulation and experimental results. Additionally, the apparent quantum yield for SO(4)(•-) in the UV/PMS system was calculated as 0.52 ± 0.01 at pH 7. The conclusions above as well as the general kinetic expressions given might provide some references for the UV/PMS applications.
authors: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, People's Republic of China.
authors: Ying-Hong
authors: YH
authors: Guan
authors: Jun
authors: J
authors: Ma
authors: Xu-Chun
authors: XC
authors: Li
authors: Jing-Yun
authors: JY
authors: Fang
authors: Li-Wei
authors: LW
authors: Chen
mesh_terms: D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D010545:Peroxides; D013431:Sulfates; C038288:peroxymonosulfate; D017665:Hydroxyl Radical