Reconsideration of the role of hydrogen peroxide in peroxymonocarbonate-based oxidation system for pollutant control.

Advanced oxidation processes that utilize peroxymonocarbonate (HCO ₄ ^- ), generated in-situ through the reaction of HCO ₃ ^- and H ₂ O ₂ , are employed for the removal of pollutants in water. Nevertheless, the precise role of H ₂ O ₂ in these processes remains a subject of debate. This study established a HCO ₄ ^- -based oxidation system using NaHCO ₃ and H ₂ O ₂ for the degradation of acetaminophen and investigated the activation mechanisms of coexisting oxidants. Under thermal activation conditions, the OO bond in HCO ₄ ^- (HOOCOO ^- ) was more readily cleaved than the OO bond in the co-existing oxidant H ₂ O ₂ (HOOH), leading to the generation of reactive oxygen species (ROS). Based on kinetics and ROS evaluation, H ₂ O ₂ primarily served to form HCO ₄ ^- rather than converting to ·OH or O ₂ , with HCO ₄ ^- acting as the primary oxidant for degradation through the formation of CO ₃ ^·- and ·OH. In this oxidation system, H ₂ O ₂ utilization efficiency for ·OH production reached 27.34 %, ·OH yield reached 24.15 % and acetaminophen degradation efficiency realized 83 % at 60 °C with 20 mM HCO ₃ ^- and 20 mM H ₂ O ₂ . The apparent activation energy of acetaminophen degradation and HCO ₄ ^- activation were calculated as 90.83 kJ mol ^-1 and 18.81 kJ mol ^-1 , respectively. Moreover, a novel CO ₂ -derived HCO ₄ ^- -based system led to a comparable acetaminophen degradation efficiency of 82 % and a higher k _obs of 0.028 min ^-1 . The system optimization and ROS evaluation suggest that high concentration of H ₂ O ₂ inhibited the degradation and quenched CO ₃ ^·- and ·OH to yield ·O ₂ ^- and ¹ O ₂ . Furthermore, EPR analysis and quenching experiments indicate that CO ₃ ^·- was mainly responsible for acetaminophen degradation. This work provides fundamental understanding of the HCO ₄ ^- -based oxidation system.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2024 Elsevier Ltd. All rights reserved.)