Confining manganese-based peroxymonosulfate activation in carbon nanotube membrane for phenol degradation: Combined effect of oxygen vacancy defects and nanoconfinement

Abstract

In this study, an open ends carbon nanotube (OCNT) membrane, which confined fine-tuned oxygen vacancy defects (Odef) modified MnOx inside OCNT (MnOx-in-OCNT), was developed for enhancing peroxymonosulfate (PMS) activation towards phenol (PE) removal. The MnOx-in-OCNT membrane filtration coupled with PMS activation process (MFPA process) achieved outstanding removal (100%) of PE at a high permeate flux of 585.0 L m2 h−1 bar−1 (residence time of only 8.8 s). The unit degradation rate (2 min running time) and mass transfer rate of MnOx-in-OCNT were 2.0 and 8.4 times higher than that of CCNT (closed caps CNT) membrane with surface-loaded MnOx (MnOx-out-CCNT) MFPA process, and its catalytic performance was much superior to MnOx-in-OCNT powder reactions and MnOx-in-OCNT membrane batch reactions. The PMS activation mechanism experienced an obvious enhancement yield of reactive oxygen species (ROS) from MnOx-out-CCNT to MnOx-in-OCNT MFPA process. The enhanced PMS activation and boosted ROS yield of MnOx-in-OCNT was mainly attributed to the co-effect of the fine-tuned Odef and nanoconfinement. The contact frequency between PMS, pollutant and Odef was greatly enhanced via nanoconfinement effect, leading to the enhanced yield of SO4•− and •OH. Meanwhile, the O2 was enriched and reacts with enhanced Odef under nanoconfined-space to produce O2•− and 1O2. Then, the co-enhanced ROS (SO4•−, •OH, 1O2 and O2•−) displayed wide applicability for phenolic pollutants removal owing to their presence of –OH. Finally, the possible degradation pathway of PE was deduced by DFT calculations and HPLC analysis.