Unravelling the synergism of catalytic oxidation and filtration in Co-Mn-oxide impregnated ceramic membrane for intensified degradation of recalcitrant micropollutant with peroxymonosulfate

Abstract

In this study, catalytic ceramic membrane (CCM) impregnated with uniform and high purity Co-Mn-oxide was fabricated via citrate sol–gel method. It was applied to activate peroxymonosulfate (PMS) for degradation of sulfamethoxazole (SMX). Due to the synergistic effect between the two cations, the Co-Mn bimetallic oxides exhibited significantly higher catalytic activity in activating PMS and degrading organic pollutants in comparison to their single oxides. Minimum calcination temperature of 700 °C was required to form the highly activating Co-Mn-oxide while higher calcination temperature reduced its catalytic activity. The effect of catalyst loading and the SMX:PMS ratio was investigated, and excessive catalyst loading, and oxidant dosage were found to be detrimental to the SMX removal efficiency. The investigation revealed the importance of process parameters in achieving achieve optimal performance of CCM/PMS process, achieving low specific oxidant consumption of 1.2 M PMS M−1 TOC. The ratio between catalyst loading in CCM, oxidant concentration and pollutant concentration influenced the availability of active sites on the catalyst to activate oxidants in the process and the possibility of self-scavenging of the generated reactive oxidizing species (ROS). The role of various ROS generated and mechanism of activation of PMS by the catalyst was investigated through radical scavenging experiments and electron paramagnetic resonance (EPR) spectroscopy test. Co2+ can be regenerated from the Mn2+/Mn3+/Mn4+ redox conjugate triplet and concurrently activate PMS to generate ROS, significantly enhancing its catalytic performance. Additionally, based on LC-QTOF analysis, the intermediates, and the possible degradation pathway of SMX degradation in this hybrid process were determined. Overall, the investigation of CCM fabrication and hybrid process operation parameters could provide an insight in the hybrid process to intensify the oxidant utilization and pollutant removal.