Ball milling treatment of Mn3O4 regulates electron transfer pathway for peroxymonosulfate activation

Abstract

Heterogeneous metal catalysts have attracted considerable interest in advanced oxidation processes (AOPs) for wastewater treatment by activating peroxymonosulfate (PMS). However, it remains challenging to the rational design of efficient reaction pathway for high-performance contaminants removal by regulating the inherent structure of metal oxides. Herein, a high-energy ball milling method was employed to modulate the electronic structure of hausmannite (denoted as BM Mn3O4), which achieved the switching of singlet oxygen into electron transfer process (ETP)-dominated activation of PMS for efficient removal of bisphenol A - an emerging organic pollutant. The reaction pathway was evidenced through galvanic oxidation process, electrochemical techniques, and in-situ Raman spectroscopy, confirming the electrons transferred from pollutants to metastable PMS* complex with BM Mn3O4 serving as electron shuttle. The ETP mechanism was verified to be closely correlated with decreased eg occupancy of Mn in BM Mn3O4, offering high spatial overlapping with O 2p orbital in PMS for generating PMS* complex. Benefitting from the fine-tuned ETP, BM Mn3O4/PMS system showed enhanced intrinsic activity, higher PMS utilization efficiency, and practical applicability for selective oxidation of electron-rich pollutants. This study provided new insights into rational design of reaction-oriented catalysts for environmental engineering.