Efficient activation of PMS via sandwich-like N-encapsulated cobalt-doped MXene composites: Structural properties and degradation mechanisms

Iopamidol (IPM), a widely used iodinated contrast agent, has been increasingly detected as an environmental pollutant, raising concerns due to its persistence and potential ecological and health risks. To address this issue, various amounts of Co with nitrogen coating were in-situ decorated on the surface of Ti 3 C 2 T x MXene nanosheets (denoted as C x MN) to efficiently activate of peroxymonosulfate (PMS) for degradation of IPM. The C x MN composites were thoroughly characterized, revealing that the introduction of Co increased the interlayer spacing of C x MN and give it a sandwich-like appearance. The C 0.2 MN catalyst, with a balanced Co doping amount, demonstrated superior performance in activating PMS. Under a wide range of pH, 99.8 % of IPM was degraded in 10 min with k obs of 0.3439 min −1 in C 0.2 MN /PMS system. Quenching experiments, EPR analysis, and XPS characterization revealed hydroxyl radical ( • OH), sulfate radical (SO 4 •－ ), singlet oxygen ( 1 O 2 ) as the major reactive species responsible for the degradation of IPM in the C 0.2 MN/PMS system, formed through the co-action of (i) Co 3+ /Co 2+ redox cycle, (ii) O V , (iii) Co 4+ , and (iv) MXene support. The degradation pathways of IPM were proposed based on the identification of its intermediates in C 0.2 MN/PMS system and the DFT calculations. Additionally, the ecotoxicity of IPM and its intermediates was evaluated using ECOSAR model. Furthermore, C 0.2 MN demonstrated excellent stability and reusability after four cycling experiments, and the long-term applicability of C 0.2 MN/PMS system was comprehensively estimated in fixed-bed column experiments. This research has significant potential for water treatment and pollutant removal applications. • The MXene surface was successfully decorated in situ with different contents of N, Co. • C 0.2 MN catalysts enable rapid activation of PMS for IPM degradation over a wide pH range. • Synergistic mechanism via Co 3 ⁺/Co 2 ⁺ redox cycle, Ov, and MXene support. • The long-term stability and practical potential of the C 0.2 MN/PMS system in water treatment.