Faster photodegradation rate and higher dioxin yield of triclosan induced by cationic surfactant CTAB

• Published in: Journal of hazardous materials 2014-06, Vol.275, p.210-214
• Main Authors: Qiao, Xianliang, Zheng, Xiaodong, Xie, Qing, Yang, Xianhai, Xiao, Jie, Xue, Weifeng, Chen, Jingwen
• Format: Article
• Language: English
• Subjects: Anionic speciation, Dioxin yield; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - radiation effects; Applied sciences; Cationic; Cetrimonium Compounds - chemistry; Chemical engineering; CTAB; Dioxins - chemistry; Exact sciences and technology; Hydrogen-Ion Concentration; Photodegradation; Photolysis; pKa; Pollution; Reactors; Sodium; Sunlight; Surface-Active Agents - chemistry; Surfactants; Triclosan; Triclosan - chemistry; Triclosan - radiation effects; Ultraviolet Rays; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - radiation effects
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2014.05.012

•Anionic and neutral surfactants inhibit the photolysis of triclosan.•Cationic CTAB accelerates the photodegradation of triclosan during pH 5∼9.•CTAB changes the apparent pKa value of triclosan and increases anionic triclosan from 4% to 89% at pH=7.•CTAB increases the yield of 2,8-DCDD about 7 times in the photolysis of triclosan. Triclosan has received extensive attention as it has been frequently detected in the aquatic environment. Photolysis was found to be a major pathway governing the fate of triclosan in the aquatic environment. However, the effects of surfactants that usually coexist with triclosan, on the photodegradation of triclosan, are largely unknown. In this study, the effects of selected surfactants on the photodegradation of triclosan were investigated experimentally. The results show that anionic sodium dodecyl benzene sulfonate, sodium dodecyl sulfate and neutral polyoxyethylene (20) sorbitan monooleate inhibit the photolysis of triclosan, whereas cationic cetyltrimethylammonium bromide (CTAB) significantly accelerates the photodegradation rate of triclosan. The interactions between the hydrophilic group of CTAB and anionic triclosan lead to the apparent decrease of pKa of triclosan from 8.4 to 6.1, which increase the fraction of anionic triclosan from 4% to 89% in neutral solution. A red shift in the UV–VIS absorption spectrum is exhibited, thus leading to the increased photodegradation rate of triclosan. The accelerations caused by CTAB were observed under xenon lamp and Hg lamp irradiances, as well as under natural sunlight. Effect of CTAB demonstrated pH dependence with significantly enhancement under pH 5∼9 and inhibition at pH=3. The presence of CTAB also increased the yield of 2,8-dichlorodibenzo-p-dioxin from the photolysis of triclosan about 7 times at pH=7.