Aqueous photofate of crystal violet under simulated and natural solar irradiation: Kinetics, products, and pathways.
In this work photodegradation rates and pathways of an illegal veterinary drug, crystal violet, were studied under simulated and solar irradiation with the goal of assessing the potential of photolysis as a removal mechanism in the aquatic environment. Factors influencing the photodegradation process under simulated sunlight were investigated, including pH, humic acid, Fe(2+), Ca(2+), [Formula: see text] , and [Formula: see text] , of which favorable conditions were optimized by the orthogonal array design. The degradation processes of crystal violet conformed to pseudo first-order kinetics, with different rate constants under different conditions. Reactive oxygen species such as hydroxyl radical, singlet oxygen, and superoxide anion participated in the indirect photolysis process, leading to much higher decolorization efficiencies than those of direct photolysis and hydrolysis. Contrasting to simulated irradiation, solar irradiation led to complete decolorization. Sixty-four products were identified by high resolution liquid chromatography-time-of-flight mass spectrometry and gas chromatography-mass spectrometry, elucidating relatively complete mineralization through photolysis. Based on the analyses of the degradation products and calculations of the frontier electron density, transformation pathways were proposed as singlet oxygen addition, N-demethylation, hydroxyl addition, decomposition of conjugated structure, the removal of benzene ring and the ring-opening reaction. As a result, small products generated as carboxylic acids, alcohols and amines, which were not likely to cause severe hazards to the environment. This study provided both a reference for photodegradation of crystal violet and future safety applications and predictions of decontamination of related triphenylmethane veterinary drug under environmental conditions.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
Yong
Y
Li
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
Shaogui
S
Yang
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China. Electronic address: envidean@nju.edu.cn.
Cheng
C
Sun
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
Lianhong
L
Wang
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
Qingeng
Q
Wang
D001639:Bicarbonates / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D005840:Gentian Violet / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D009566:Nitrates / Q000737:chemistry; D010782:Photolysis / Q000528:radiation effects*; D017382:Reactive Oxygen Species; D013472:Sunlight; D019155:Veterinary Drugs / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D001639:Bicarbonates; D009566:Nitrates; D017382:Reactive Oxygen Species; D019155:Veterinary Drugs; D014874:Water Pollutants, Chemical; D007501:Iron; D005840:Gentian Violet; D002118:Calcium
Crystal violet; Density functional theory computation; Mechanism; Photodegradation; Simulated/natural condition; Veterinary drug