Formation of hydroxylated derivatives and coupling products from the photochemical transformation of polyfluorinated dibenzo-p-dioxins (PFDDs) on silica surfaces. (September 2019)

• Record Type: Journal Article
• Authors: Qu, Ruijuan; Pan, Xiaoxue; Li, Chenguang; Liu, Jiaoqin; Wang, Xinghao; Zeng, Xiaolan; Wang, Zunyao
• Is Part Of: Chemosphere. Volume 231(2019)
• Page Start: 72
• Page End: 81
• Publication Date: 2019-09
• Subjects: Polyfluorinated dibenzo-p-dioxins -- Surface photolysis -- Silica -- Kinetics -- Reaction products; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.05.074
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Polyfluorinated dibenzo- p -dioxins (PFDDs) are dioxin compounds that have been detected in industrial fluoroaromatic chemicals and can cause adverse effects to organisms. In this work, the photochemical behaviors of PFDDs congeners on silica was systematically investigated. The pseudo-first-order rate constants ( k, h −1 ) of surface photolysis changed with the substitution number and position of fluorine atoms, and the tetra-fluorinated PFDDs tended to degrade more efficiently. Octafluorinated dibenzo- p -dioxin (OFDD) was selected as a representative to explore the reaction mechanisms. Product analysis showed that OFDD was decomposed into hydroxylated PFDDs (OH-PFDDs) and hydroxylated polyfluorinated diphenyl ethers (OH-PFDEs) via hydroxyl substitution and (OH radical mediated or direct) C–O bond cleavage. Coupling elimination reaction was also observed, resulting in the formation of three-membered and four-membered ring compounds. According to the extracted peak areas in mass spectra and the energy barrier in potential energy surface, direct homolysis of C–O bond occurs as the dominant reaction pathway. This work could provide some new insights into the environmental fate of dioxin compounds. Graphical abstract: Image 1 Highlights: Photochemical behaviors of PFDDs congeners on silica surface were examined. Photoreactivity of PFDDs depends on fluorine atoms and their positions. OH-PFDDs and OH-PFDEs were formed via hydroxyl substitution and C–O bond cleavage. Coupling elimination reaction produced 3-membered and 4-membered ring compounds.