Release Time:2019-03-12  Hits:

Indexed by: Journal Article

Date of Publication: 2016-11-01

Journal: CHEMOSPHERE

Included Journals: Scopus、PubMed、SCIE、EI

Volume: 163

Page Number: 227-233

ISSN: 0045-6535

Key Words: Self-sensitized photodegradation mechanism; Singlet state oxygen; p-aminobenzoic acid; Density functional theory

Abstract: Self-sensitized photodegradation has been observed for diverse aquatic organic pollutants. However, photodegradation pathways have not been clarified in, previous experimental studies. Here, we attempted to probe self-sensitized photodegradation pathways of organic pollutants employing both photolytic experiments and density functional theory calculations. By performing photolytic experiments, we found that singlet state oxygen (O-1(2)) play an essential role in photodegradation of a sunscreen p-aminobenzoic acid (PABA). PABA can photogenerate O-1(2) and react fast with O-1(2). We hypothesized that PABA underwent O-1(2) induced self-sensitized photodegradation. By calculating transition states, intermediates and reaction barriers, we found that O-1(2) can oxidize PABA through electrophilic attacks on the benzene ring to abstract one H atom of the amino group following a 1,3-addition mechanism or to induce decarboxylation. Either pathway produces a hydroperoxide. O-O bond cleavage of the hydro peroxides occurring at ground states or the lowest triplet excited states can produce phenoxyl radical precursors of 4-amino-3-hydroxybenzoic acid and 4-aminophenol, which are photodegradation products detected in experiments. Thus, a viable O-1(2) self-sensitized photodegradation mechanism was unveiled for PABA. (C) 2016 Elsevier Ltd. All rights reserved.