Peracetic acid (PAA) is a widely used disinfectant, and combined UV light with PAA (i.e. UV/PAA) can be a novel advanced oxidation process for elimination of water contaminants. This study is among the first to evaluate the photolysis of PAA under UV irradiation (254 nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high quantum yields (Φ254nm = 1.20 and 2.09 mol·Einstein−1 for the neutral (PAA0) and anionic (PAA-) species, respectively) and also showed scavenging effects on hydroxyl radicals (k•OH/PAA0 = (9.33±0.3)×108 M−1·s−1 and k•OH/PAA- = (9.97±2.3)×109 M−1·s−1). The pharmaceuticals were persistent with PAA alone but degraded rapidly by UV/PAA. The contributions of direct photolysis, hydroxyl radicals, and other radicals to pharmaceutical degradation under UV/PAA were systematically evaluated. Results revealed that •OH was the primary radical responsible for the degradation of carbamazepine and ibuprofen by UV/PAA, whereas CH3C(=O)O• and/or CH3C(=O)O2• contributed significantly to the degradation of naproxen and 2-naphthoxyacetic acid by UV/PAA in addition to •OH. The carbon-centered radicals generated from UV/PAA showed strong reactivity to oxidize certain naphthyl compounds. The new knowledge obtained in this study will facilitate further research and development of UV/PAA as a new degradation strategy for water contaminants.
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Structural Features Promoting Photocatalytic Degradation of Contaminants of Emerging Concern: Insights into Degradation Mechanism Employing QSA/PR Modeling
Although heterogeneous photocatalysis has shown promising results in degradation of contaminants of emerging concern (CECs), the mechanistic implications related to structural diversity of chemicals, affecting oxidative (by HO•) or reductive (by O2•−) degradation pathways are still scarce. In this study, the degradation extents and rates of selected organics in the absence and presence of common scavengers for reactive oxygen species (ROS) generated during photocatalytic treatment were determined. The obtained values were then brought into correlation as K coefficients (MHO•/MO2•−), denoting the ratio of organics degraded by two occurring mechanisms: oxidation and reduction via HO• and O2•−. The compounds possessing K >> 1 favor oxidative degradation over HO•, and vice versa for reductive degradation (i.e., if K << 1 compounds undergo reductive reactions driven by O2•−). Such empirical values were brought into correlation with structural features of CECs, represented by molecular descriptors, employing a quantitative structure activity/property relationship (QSA/PR) modeling. The functional stability and predictive power of the resulting QSA/PR model was confirmed by internal and external cross-validation. The most influential descriptors were found to be the size of the molecule and presence/absence of particular molecular fragments such as C − O and C − Cl bonds; the latter favors HO•-driven reaction, while the former the reductive pathway. The developed QSA/PR models can be considered robust predictive tools for evaluating distribution between degradation mechanisms occurring in photocatalytic treatment.
more » « less- Award ID(s):
- 2019077
- PAR ID:
- 10488276
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 28
- Issue:
- 6
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 2443
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules28062443
