title: Comparison of the reactivity of ibuprofen with sulfate and hydroxyl radicals: An experimental and theoretical study.
abstract: Hydroxyl radical (•OH) and sulfate radical anion (SO4•-) based advanced oxidation technologies (AOTs) are effective methods to treat trace organic contaminants (TrOCs) in engineered waters. Although both technologies result in the same overall removal of TrOCs, the mechanistic differences between these two radicals involved in the oxidation of TrOCs remain unclear. In this study, we experimentally examined the degradation kinetics of neutral ibuprofen (IBU), a representative TrOC, by•OH and SO4•-at pH3 in UV/H2O2and UV/persulfate systems, respectively. The second-order rate constants (k) of IBU with•OH and SO4•-were determined to be 3.43±0.06×109and 1.66±0.12×109M-1s-1, respectively. We also theoretically calculated the thermodynamic and kinetic behaviors for reactions of IBU with•OH and SO4•-using the density functional theory (DFT) M06-2X method with 6-311++G** basis set. The results revealed that H-atom abstraction is the most favorable pathway for both•OH and SO4•-, but due to the steric hindrance SO4•-exhibits significantly higher energy barriers than•OH. The theoretical calculations corroborate our experimental observation that SO4•-has a smaller k value than•OH in reacting with IBU. These comparative results are of fundamental and practical importance in understanding the electrophilic interactions between radicals and IBU molecules, and to help select preferred radical oxidation processes for optimal TrOCs removal in engineered waters.
authors.affiliation: Institute of Environmental Engineering, School of Metallurgy and Environment, Central South University, Changsha 410083, China; Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, Changsha 410083, China.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Institute of Environmental Engineering, School of Metallurgy and Environment, Central South University, Changsha 410083, China; Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, Changsha 410083, China.
authors.forename: Rongkui
authors.initials: R
authors.lastname: Su
authors.affiliation: Institute of Environmental Engineering, School of Metallurgy and Environment, Central South University, Changsha 410083, China; Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, Changsha 410083, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Luo
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Spinney
authors.affiliation: School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou 310018, China.
authors.forename: Meiqiang
authors.initials: M
authors.lastname: Cai
authors.affiliation: Institute of Environmental Engineering, School of Metallurgy and Environment, Central South University, Changsha 410083, China; Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, Changsha 410083, China. Electronic address: xiao.53@csu.edu.cn.
authors.forename: Ruiyang
authors.initials: R
authors.lastname: Xiao
authors.affiliation: Grand Water Research Institute - Rabin Desalination Laboratory, The Wolfson Faculty of Chemical Engineering, Technion - Israel Institute of Technology, Technion City, Haifa 32000, Israel. Electronic address: zongsuw@technion.ac.il.
authors.forename: Zongsu
authors.initials: Z
authors.lastname: Wei
keywords: DFT; Hydroxyl radical; Ibuprofen; Sulfate radical anion; Trace organic contaminants