摘要
Quantitatively analyzed 6PPD degradation and 6PPD-Q formation in UV/NOM. • • OH dominated 6PPD photodegradation, followed by 3 NOM* and 1 O 2 . • 3 NOM* and 1 O 2 mainly contributed to 6PPD-Q formation, while • OH played less. • 6PPD-Q molar yields followed the trend: 1 O 2 > 3 NOM* > • OH > direct photolysis. Photochemical transformation of the tire-derived antioxidant N -(1,3-dimethylbutyl)- N' -phenyl- p -phenylenediamine (6PPD) in sunlit waters has been recognized as an important source of 6PPD-quinone (6PPD-Q), a product with reported acute toxicity to coho salmon. However, the relative contributions of transient reactive species to 6PPD photodegradation and 6PPD-Q formation remain poorly understood. Here, we quantitatively evaluated the photochemical transformation mediated by natural organic matter (NOM), which serves as an important photosensitizer and significantly accelerates both 6PPD degradation and 6PPD-Q generation. Through radical scavenging and kinetic solvent isotopic effect experiments, we identified the excited triplet state NOM ( 3 NOM*), singlet oxygen ( 1 O 2 ), and hydroxyl radical ( • OH) as the key reactive species driving these processes. At 3 mg C /L NOM, their contributions to 6PPD degradation follow descending order: • OH (30.9 %) > 3 NOM* (27.4 %) > 1 O 2 (18.5 %) > direct photolysis (17.6 %). Interestingly, kinetic modeling revealed a shift in dominance for 6PPD-Q formation, with 3 NOM* and 1 O 2 contributing 38.7 % and 30.2 %, respectively, followed by • OH (26.1 %) and direct photolysis (4.7 %). This shift is due to the higher molar yields of 6PPD-Q from 1 O 2 (10.8 %) and 3 NOM* (9.4 %), compared to • OH (5.6 %) and direct photolysis (1.8 %). This quantitative understanding is essential for predicting the environmental fate of 6PPD and informing strategies to mitigate its ecological risks. Download: Download high-res image (347KB) Download: Download full-size image
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