Degradation of phenanthrene by peroxymonosulfate activated with bimetallic metal-organic frameworks: Kinetics, mechanisms, and degradation products

Abstract

In this study, bimetallic metal-organic frameworks (FeCo-BDC) containing the (BDC = 1,4-benzenedicarboxylic acid) metalloligand unit, linked by Fe(II) and Co(II) cations, were synthesized successfully with different stoichiometric ratio of precursors. FeCo-BDC were investigated by XRD, FT-IR, SEM, XPS, ICP-MS, BET, and TEM techniques. Effects of stoichiometric ratio of precursors, peroxymonosulfate (PMS) concentrations, catalyst dosages, and initial pH on the phenanthrene degradation were evaluated. The results indicated that 99.0% of phenanthrene removal efficiency was achieved at pH 3.15, 50 mg/L FeCo-BDC-2, 0.6 mM PMS, 1.0 mg/L phenanthrene and 30 min reaction time. Based on the scavenger experiments and electron paramagnetic resonance (EPR) analyses, SO4−, OH, and O2− were identified as the dominant Reactive Oxygen Species (ROS) and responsible for the phenanthrene degradation. It was interesting to find that the signals of DMPO-OH/SO4− transformed to DMPOX with the addition of tert butyl alcohol (TBA). The intermediate products of phenanthrene were identified by GC–MS and the possible degradation pathway was proposed, whereas two intermediates containing sulfur atom were detected for the first time in the Sulfate Radicals-based Advanced Oxidation Processes (SR-AOPs). These interesting findings will guide the development of metal-organic frameworks as catalysts of PMS and enrich our understanding of the SR-AOPs for wastewater treatment.