Sulfur-containing iron nanocomposites confined in S/N co-doped carbon for catalytic peroxymonosulfate oxidation of organic pollutants: Low iron leaching, degradation mechanism and intermediates

The poor performance and severe metal leaching of iron-based Fenton-like catalysts during reaction are the main bottlenecks that suppress their practical applications. Herein, a well-defined structure was achieved by confining catalytically active but unstable sulfur-containing iron species within S/N co-doped porous carbon ([email protected]) through a simple pyrolysis route. The hierarchically porous and highly conductive carbon host not only provided abundant exposed active sites and fast mass/electron-transfer, but also prohibited the aggregation of iron composites during catalysis. The synergistic effects of confined iron nano-composites and heteroatoms (S/N) significantly elevated the activation of peroxymonosulfate (PMS). As a result, the [email protected]/PMS system exhibited excellent catalytic degradation performance for various contaminants including dyes, phenolic compounds, and antibiotics. Importantly, a low iron leaching was detected during usage due to the nano-confinement effect of carbon layers, and therefore solves the long-term issue of secondary pollution caused by metal leaching. Furthermore, the underlying degradation mechanism of [email protected]/PMS system was systematically investigated by radical quenching tests, EPR analysis, and chronoamperometry experiments. It was found that the superoxide anion radical (O2−) was the predominant free radicals that contributed to the radical oxidation of organic pollutants, while the electron transfer mediation on [email protected] resulted in the non-radical oxidation. Additionally, the LC-MS results coupled with time-dependent HPLC spectra validated that the degradation efficiency and intermediate products were significantly dependent on solution pH and background species. This work provides new insight into the design and activation mechanism of iron-based PMS activators.