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

Abstract

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 Ti₃C₂T_x MXene nanosheets (denoted as C_xMN) to efficiently activate of peroxymonosulfate (PMS) for degradation of IPM. The C_xMN composites were thoroughly characterized, revealing that the introduction of Co increased the interlayer spacing of C_xMN and give it a sandwich-like appearance. The C_0.2MN 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_0.2MN /PMS system. Quenching experiments, EPR analysis, and XPS characterization revealed hydroxyl radical (^•OH), sulfate radical (SO₄^•－), singlet oxygen (¹O₂) as the major reactive species responsible for the degradation of IPM in the C_0.2MN/PMS system, formed through the co-action of (i) Co³⁺/Co²⁺ redox cycle, (ii) O_V, (iii) Co⁴⁺, and (iv) MXene support. The degradation pathways of IPM were proposed based on the identification of its intermediates in C_0.2MN/PMS system and the DFT calculations. Additionally, the ecotoxicity of IPM and its intermediates was evaluated using ECOSAR model. Furthermore, C_0.2MN demonstrated excellent stability and reusability after four cycling experiments, and the long-term applicability of C_0.2MN/PMS system was comprehensively estimated in fixed-bed column experiments. This research has significant potential for water treatment and pollutant removal applications.