Enhanced Removal Of Methylparaben Mediated By Cobalt/Carbon Nanotubes (Co/Cnts) Activated Peroxymonosulfate In Chloride-Containing Water: Reaction Kinetics, Mechanisms And Pathways

Chloride ion (Cl-) widely presents in natural water and wastewater, which can significantly affect the performance of sulfate radical-based advanced oxidation processes (SR-AOPs). However, few studies are available now on the generation of chlorinated by-products in the peroxymonosulfate (PMS) based systems. Here a novel catalyst (cobalt/carbon nanotubes, Co/CNTs) was synthesized and used as a PMS activator to remove methylparaben (MeP) with and without Cl-. The morphology and chemical composition of the fresh and used Co/CNTs were characterized by TEM, SEM, XRD, BET, and XPS. Results revealed that Co/CNTs exhibited significant catalytic activity toward MeP removal, and the removal efficiency increased with the augment of reaction temperature and concentrations of Co/CNTs and PMS. In the absence of CI 83.2% of 10 mu M MeP was degraded within 60 mM by using 2 mg/L Co/CNTs and 100 mu M PMS at 25 degrees C with pH 7.0. However, complete removal of MeP was achieved within 20 mM in the presence of 100 mM Cl-, which enhanced the apparent rate constant by a factor of 4.3. Consequently, TOC removal was enhanced from 8.1% to 19.2% within 60 mM. Through the quenching experiments, both SO4 center dot- and center dot OH were found responsible for MeP degradation without Cl-, while Cl-2(-center dot) was the main reactive oxygen species (ROS) with 100 mM Cl-. Based on the intermediates identified via TOF-LCMS, four potential reaction pathways were proposed, including hydrogen abstraction coupling reaction, hydroxylation, center dot OH attack, and Cl-2(-center dot) attack. The intermediates also exhibited decreased toxicity compared to the parent compound based on the ecotoxicity evaluation. In addition, Co/CNTs + PMS system achieved over 60% MeP removal from real wastewater with elevated PMS concentration, indicating the process applicability. These findings provide valuable information of SR-AOPs to facilitate organic contaminants removal in Cl--containing water.