A self-synthesised non-homogeneous MoS2/Fe–Co–N–BC composite catalyst as an activator for peroxomonosulfate activation for efficient degradation of perfluorooctanoic acid

In this study, in order to achieve efficient activation of persulfate, we added MoS2 as a co-catalyst to the iron, cobalt and nitrogen modified biochar (Fe–Co–N–BC) catalytic system. Analytical methods such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrated that the MoS2/Co–Fe–N–BC catalytic materials were successfully prepared. In the MoS2/Fe–Co–N–BC/PMS system, 97.5% of PFOA was removed within 180 min with Kobs of 0.074 min−1. Composites with different mass ratios of MoS2 and Co–Fe–N–BC/PMS in the non-homogeneous PMS system both exhibit excellent catalytic efficiency for TOC removal. In particular, MoS2/Fe–Co–N–BC obtained extraordinary catalytic efficiency through synergistic radical (SO4˙−, ˙OH) and non-radical (1O2, FeIV and FeV) processes, which was proved by the quenching experiments and the EPR testing. The analysis of the activation mechanism reveals that the three redox ion pairs Fe2+/Fe3+, Co2+/Co3+ and Mo4+/Mo6+ simultaneously participated in the activation of PMS, realizing multi-path electron transfer. And MoS2 played an excellent co-catalysis role in promoting the cycling of the valence states of the ions. Compared to Fe3+ and Co3+, the low valence states of Fe2+ and Co2+ can activate PMS more rapidly and produce more ˙OH and SO4˙−. However, the recycling efficiency of Fe2+ and Co3+ in the Fe–Co–N–BC system is low, and the presence of MoS2 improves the efficiency of Fe3+ and Co3+ reduction to Fe2+ and Co2+, respectively. The possible degradation pathways of PFOA were proposed. This study provides some references for the design of polymetallic-doped catalysts to degrade difficult-to-degrade organic pollutants.