Synergistic activation of peroxymonosulfate between Co and MnO for bisphenol A degradation with enhanced activity and stability.

In this work, a novel material of Co Nanoparticles anchored on MnO nanorods wrapped in carbon layers (Co/MnO-X@C) is successfully synthesized and applied to activate peroxymonosulfate (PMS) for Bisphenol A (BPA) degradation. More than 98% of BPA is removed by Co/MnO-0.32@C within 1 min. The reaction rate constant of Co/MnO-0.32@C (3.516 min) is much larger than Co@C (1.076 min) and MnO@C (0.006 min). The leached Co ions from Co/MnO-0.32@C (0.97 mg/L) is only 1/5 of Co@C (4.96 mg/L) after the catalytic reaction. The high activity and low leaching rate of Co indicate the synergistic effect between Co and MnO during PMS activation. Density functional theory (DFT) calculations reveal MnO modified with Co is favorable for the adsorption and activation of PMS and the release of reactive oxidation species (ROSs). The XPS results indicate the presence of Co(III)/Mn(II) redox cycle, while the generated Co(II) and Mn(III) is used for PMS activation, thus proving the synergistic effect further. The open circuit potential (OCP) test proves the direct electron-transfer (DET) exists on the surface of Co/MnO-X@C. Therefore, both radical and nonradical processes are present in the (Co/MnO-0.32@C)/PMS system. This work provides effective materials and synergistic theory between Co and MnO for environmental remediation.