Catalytic activation of PS/PMS over Fe-Co bimetallic oxides for phenol oxidation under alkaline conditions

Highlights: • Co and Fe showed a synergistic mechanism on the catalyst surface. • PS showed a higher oxidant utilization rate than PMS in the treatment of phenol. • PS showed a lower residual TOC in solution than PMS after reactions. • Non-radical mechanisms in PS-FeCo₂O₄ system showed better application potential. In this study, we compared the differences between bimetallic oxides FeCo₂O₄ catalyzing the oxidation of phenol by peroxydisulfate (PS) and peroxymonosulfate (PMS) under near neutral and alkaline conditions. Phenol could be completely oxidized and removed in both PMS and PS systems. X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations showed that there was a synergistic mechanism between Co and Fe on the catalyst surface. Although the PMS-FeCo₂O₄ system reached the fastest reaction rate of 1.5 × 10⁻¹ min⁻¹, it showed a higher oxidants consumption and more residual total organic carbon (TOC) (36%) in solutions after reactions. Quenching experiments and electron paramagnetic resonance (EPR) analysis showed that sulfate radical (SO₄⁻), hydroxyl radical (OH) and singlet oxygen (¹O₂) played important roles in the oxidation of phenol in PMS system. While in the PS-FeCo₂O₄ system, in addition to free radical reactions, the non-radical mechanisms between PS and the catalyst surface played a major role in phenol oxidation, and the soluble organic matter in the PS system could be completely removed. Thus, PS has a better application prospect in the treatment of phenol. This discovery has certain guiding significance for catalyst modification and doping to improve catalyst activity and the choice of oxidant.