Synergistic activation of persulfate by heat and cobalt-doped-bimetallic-MOFs for effective methylene blue degradation: Synthesis, kinetics, DFT calculation, and mechanisms

Metal-organic frameworks (MOFs) effectively remove hazardous contaminants and are widely used for wastewater treatment. In this work, Co-doped bimetallic MIL-88B(Fe/Co) was synthesized via the hydrothermal method to activate potassium persulfate (KPS) for methylene blue (MB) degradation. XRD, IR, XPS, and SEM were conducted to investigate the crystalline structure, chemical valence state, and morphology of MIL-88B(Fe/Co). The synthesis time and Fe3+ /Co2+ molar ratio were optimized. Results showed that 10% Co-doped MIL-88B(Fe/Co) could efficiently activate KPS to achieve 100% MB removal in 15 min, thereby indicating that Co2+ could accelerate metal-to-metal charge transfer during activation. A quadratic model was established by fitting the experimental data to optimize the degradation parameters. The reaction system with a temperature of 70 °C, KPS concentration of 30 mM, MOFs concentration of 0.8 g/L, and initial pH of 10 could effectively remove 99.85% MB in 5 min. Quenching experiments and EPR analysis revealed that·OH, 1O2, and·O2− were the dominant reactive oxygen species (ROS) during MB degradation. The active sites (N15, N7, S10, and N18) most vulnerable to ROS attack in MB were identified by DFT calculation. MB degradation intermediates were identified through MALDI.