Radical chemistry of diethyl phthalate oxidation via UV/peroxymonosulfate process: Roles of primary and secondary radicals
Authors: Lei, Yu; Lu, Jun; Zhu, M; Xie, J; Peng, S; Zhu, C
HERO ID: 5933500
The UV/peroxymonosulfate (PMS) process forms hydroxyl radicals ((OH)-O-center dot) and sulfate radicals . . .
The UV/peroxymonosulfate (PMS) process forms hydroxyl radicals ((OH)-O-center dot) and sulfate radicals (SO4 center dot-) to degrade micro-pollutants. Both these two radicals can be converted to secondary radicals (e.g. Cl-2(center dot-), CO3 center dot- and Cl-center dot) by effects of water matrix components. By using laser flash photolysis, the second-order rate constants for reactions of three PAEs with (OH)-O-center dot, SO4 center dot-, Cl-2(center dot-), Cl-center dot and CO3 center dot- were determined as (3.5-4.4) x 10(9), (4.9-5.6) x 10(8), (1.1-1.3) x 10(7), (1.8-2.0) x 10(10) and < 1 x 10(6) M-1 s(-1), respectively. Then diethyl phthalate (DEP) was selected as the target compound to investigate the radical chemistry of its degradation during the 254 nm UV/PMS process. Multiple effects of water matrix components in DEP degradation were investigated. Alkaline condition, chloride, bicarbonate and natural organic matter (NOM) inhibited DEP degradation while their effects were radical specific. SO4 center dot- could better withstand the negative effect of alkaline condition, bi- carbonate and NOM than (OH)-O-center dot, while (OH)-O-center dot was less affected by chloride than SO4 center dot-. Cl-center dot accounted for 12% of DEP degradation in the presence of 1 mM chloride. Cl-2(center dot-), CO3 center dot- and O-1(2) hardly contributed to DEP oxidation but they might be involved in the further oxidation of transformation intermediates. Transient-state intermediates and steady-state products were identified by time-resolved spectroscopy and GC-MS, respectively, from which the degradation pathways of DEP in different water matrices were proposed.