title: Photodegradation of malachite green under simulated and natural irradiation: kinetics, products, and pathways.
abstract: In this work photodegradation rates and pathways of malachite green were studied under simulated and solar irradiation with the goal of assessing the potential of photolysis as a removal mechanism in real aquatic environment. Factors influencing the photodegradation process were investigated, including pH, humic acid, Fe(2+), Ca(2+), HCO3(-), and NO3(-), of which favorable conditions were optimized by the orthogonal array design under simulated sunlight irradiation in the presence of dissolved oxygen. The degradation processes of malachite green conformed to pseudo first-order kinetics and their degradation rate constants were between 0.0062 and 0.4012 h(-1). Under solar irradiation, the decolorization efficiency of most tests can reach almost 100%, and relatively thorough mineralization could be observed. Forty degradation products were detected by liquid chromatography-mass spectrometry, and thirteen small molecular products were identified by gas chromatography-mass spectrometry. Based on the analyses of the degradation products and calculation of the frontier electron density, the pathways were proposed: decomposition of conjugated structure, N-demethylation reactions, hydroxyl addition reactions, the removal of benzene ring, and the ring-opening reaction. This study has provided a reference, both for photodegradation of malachite green and future safety applications and predictions of decontamination of related triphenylmethane dyes under real conditions.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Li
authors.initials: L
authors.lastname: Yong
authors.affiliation: State Environmental Protection Key Laboratory of Monitoring and Analysis for Organic Pollutants in Surface Water, Jiangsu Provincial Environmental Monitoring Center, Nanjing 210036, China.
authors.forename: Gao
authors.initials: G
authors.lastname: Zhanqi
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Ji
authors.initials: J
authors.lastname: Yuefei
authors.affiliation: School of Life Science, Huzhou University, Huzhou 313000, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Xiaobin
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China. Electronic address: envidean@nju.edu.cn.
authors.forename: Sun
authors.initials: S
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Shaogui
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Wang
authors.initials: W
authors.lastname: Lianhong
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Wang
authors.initials: W
authors.lastname: Qingeng
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Die
mesh_terms: D001639:Bicarbonates / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D004396:Coloring Agents / Q000737:chemistry / Q000528:radiation effects*; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D009566:Nitrates / Q000737:chemistry; D010782:Photolysis; D017382:Reactive Oxygen Species / Q000737:chemistry; D012394:Rosaniline Dyes / Q000737:chemistry / Q000528:radiation effects*; D013472:Sunlight; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D001639:Bicarbonates; D004396:Coloring Agents; D006812:Humic Substances; D009566:Nitrates; D017382:Reactive Oxygen Species; D012394:Rosaniline Dyes; D014874:Water Pollutants, Chemical; C005095:malachite green; D007501:Iron; D002118:Calcium
keywords: Malachite green; Pathways; Photodegradation; Products; Simulated/natural conditions