title: Kinetics and mechanisms of degradation of chloroacetonitriles by the UV/H2O2 process.
abstract: Haloacetonitriles (HANs) are emerging disinfection by-products (DBPs) that are more toxic than the regulated DBPs and widely found in the chlorinated/chloraminated water. This paper studied kinetics and mechanisms of the degradation of chloroacetonitriles (CANs) by the UV/H2O2 process at pH 6 and 7.5 and H2O2 concentrations of 1 × 10(-3) M, 5 × 10(-3) M and 1 × 10(-2) M. The degradation followed pseudo first-order degradation kinetics. The degradation rate of monochloroacetonitrile (MCAN) remained similar, while those of dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) increased with increasing pH and H2O2 concentrations. The different trends were attributed to the changing contributions of the two major mechanisms: the nucleophilic attack by hydroperoxide ions ( [Formula: see text] ) and the hydroxyl radical (•OH) oxidation. The second-order rate constants of [Formula: see text] towards MCAN, DCAN and TCAN were determined to be 11.8 (±0.62), 4.83 (±0.01) × 10(3), and 2.54 (±0.23) × 10(5) M(-1) s(-1), respectively, while that of •OH were 8.7 × 10(6), 4.4 × 10(6), and < 10(6) M(-1) s(-1), respectively. The degradation of TCAN was mainly attributed to the [Formula: see text] nucleophilic attack, while that of MCAN was dominated by the •OH oxidation. DCAN was degraded by both mechanisms. The nucleophilic attack increased linearly with increasing [Formula: see text] concentration as a result of increasing H2O2 concentration and/or pH, while the •OH oxidation was less dependent on H2O2 concentrations and/or pH. The nucleophilic attack mainly transformed HANs to haloacetamides, while the •OH oxidation dechlorinated HANs. This paper firstly illustrated the importance of the [Formula: see text] nucleophilic attack, in addition to the •OH oxidation, on the CAN degradation in the UV/H2O2 process.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Li
authors.initials: L
authors.lastname: Ling
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors.forename: Jianliang
authors.initials: J
authors.lastname: Sun
authors.affiliation: Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China. Electronic address: fangjy3@mail.sysu.edu.cn.
authors.forename: Jingyun
authors.initials: J
authors.lastname: Fang
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong; Hong Kong Branch of Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. Electronic address: cechii@ust.hk.
authors.forename: Chii
authors.initials: C
authors.lastname: Shang
mesh_terms: D006861:Hydrogen Peroxide; D017665:Hydroxyl Radical; D007700:Kinetics; D010084:Oxidation-Reduction; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical
chemical_list: D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide
keywords: Haloacetonitriles; Hydrogen peroxide; Hydroxyl radicals; Nucleophilic attack; UV; Water treatment