Mechanistic understanding of electron structure regulation by Co Ion-Doping on MnO2 nanocatalyst during optimizing peroxymonosulfate activation

Abstract

Controlling the electronic structure of the active centre through ion doping modulation has been widely recognized as an effective means to enhance catalytic activity, particularly for MnO2-based catalysts. However, existing models fail to fully elucidate the underlying mechanism behind this phenomenon. Here, we utilizes the quenching route to synthesize a variety of MnO2-based catalysts (named as Co-MnO2-Q) with different Co content, aiming to investigate the catalytic mechanism of MnO2 in activating peroxymonosulfate (PMS) and establish a correlation between its electronic structure and catalytic activity. Notably, the optimal catalyst (Co-MnO2-Q3) exhibited a rate constant (kobs) for Levofloxacin (LEVO) removal up to 0.105 min−1, which is eight times higher than that of pure MnO2 (0.013 min−1). Experimental and density functional theory (DFT) investigations have demonstrated that the adsorption of PMS on the constructed catalyst models is an exothermic process, which occurs spontaneously and effectively elongates the O–O bond. Meanwhile, DFT calculations reveal a positive correlation between Co-doped catalyst activity and upward shift of Mn 3d and O 2p band centres. Essentially, Co doping enhances the covalency of Mn–O bonds and increases electron density levels near the Fermi energy, thereby facilitating electron transfer from Mn sites to adsorbed PMS molecules and accelerating both PMS activation and catalytic degradation reactions. This study successfully establishes a descriptor that effectively characterizes the intrinsic activity enhancement of MnO2-based catalysts, providing valuable guidance for designing more advanced catalytic systems based on MnO2.