Natural polyphenols can be oxidized into reactive quinones, which might play a key role in the removal of specific contaminants in natural polyphenol-related advanced oxidation processes (AOPs). In this study, peracetic acid (PAA) was employed in combination with natural protocatechuic acid (PCA) to remove sulfonamide antibiotics (SAs) from water. More than 95% removal of sulfamethoxazole (SMX) and other SAs was observed in the PCA/PAA system, and neutral pH conditions (5.0–8.0) were more conducive to the removal of SMX. The PCA/PAA system exhibited a great anti-interference ability against complex water matrices. ortho-Quinone, generated from the oxidation of PCA by PAA, played a dominant role in the SMX removal. Electrons tended to transfer from SMX to the generated ortho-quinones and form covalent bonds, resulting in the production of less toxic oligomers via the overlooked polymerization pathway. A reduction in the toxicity of the SMX solution was found following treatment with the PCA/PAA system. More interestingly, several polyphenols structurally related to PCA could also facilitate SMX removal using PAA as the oxidant. Overall, this study proposes a novel strategy for developing reactive quinones dominated AOPs with robust anti-interference performance, as well as enhances the understanding of contaminant removal via an overlooked polymerization pathway in natural polyphenol-related AOPs.
Hydrolysis reactions comprise a widely studied class of abiotic transformation processes that impact the environmental fate of many organic contaminants. While hydrolysis rates are typically measured in buffered solutions in order to predict transformation rates in the environment, rate constants measured in laboratory buffers are often higher than values in corresponding natural water samples. In this Perspective, we summarize these discrepancies and prior explanations provided for their occurrence. Through modeling using two linear free energy relationships (i.e., the Swain–Scott and the Bro̷nsted relationships), we propose a simple but overlooked alternative explanation─namely, that hydrolysis reactions are often much more sensitive to constituents in laboratory buffers than often assumed. We suggest that buffers employed in standard practices (e.g., at 50 mM or higher concentrations recommended by regulatory guidelines) are expected to significantly catalyze many hydrolysis reactions by acting as nucleophiles or bases. Finally, we recommend strategies to successfully measure hydrolysis rates for more accurate predictions of contaminant transformation in environmental systems.
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