6PPD-quinone degradation by unactivated peroxymonosulfate via direct oxidation and enhanced generation of 1O2

Abstract

N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine-quinone (6PPDQ) is extremely toxic to aquatic organisms, which has attracted extensive attention. Hence, the degradation of 6PPDQ from aquatic environments is currently one of the urgent environmental issues to be addressed. In this work, peroxymonosulfate (PMS) was used to degrade 6PPDQ without activators avoiding some constraints such as high energy consumption and introduction of secondary pollution. ¹O₂ was an important active species in the degradation of 6PPDQ by PMS without activation. 6PPDQ could increase production yield of ¹O₂, which further degraded 6PPDQ. Contributions of ¹O₂ and direct PMS oxidation to 6PPDQ degradation varied with pH values (79 % and 21 % at pH = 9.0, respectively). The increase of temperature, PMS initial concentration and pH values was conducive to improve the degradation efficiency of 6PPDQ. HCO₃^– and Fe³⁺ significantly accelerated the degradation of 6PPDQ with complete degradation within 60 min. In addition, two degradation pathways containing 8 intermediates were proposed, which mainly involved C-N bond cleavage and hydroxyl addition. Additionally, theoretical calculations demonstrated the high reactivity of N atoms on 6PPDQ, supporting that degradation intermediates were primarily formed through reactions involving N atoms. Meanwhile, the toxicity evaluation of reaction products indicated that transformation products were all less toxic than 6PPDQ, suggesting a process of decreasing toxicity. These results demonstrate the potential application of removing 6PPDQ by unactivated PMS from environmental waters.