Peroxymonosulfate promoted dioxygen activation with Mn(II)-nitrilotriacetic acid complexes for sulfadiazine degradation

Abstract

In the field of peroxymonosulfate (PMS) activation technology, there is a pressing need to reduce PMS consumption and enhance its utilization rate. The present study demonstrates that the introduction of dissolved oxygen (DO) into the Mn(II)-nitrilotriacetic acid (NTA)-activated PMS system significantly enhances the degradation efficiency of sulfadiazine and increases the PMS utilization rate from approximately 15.0 to 41.3 %. Mechanistic analysis reveals that the Mn(II)-NTA/PMS system generates sulfate radicals as well as intermediate valent manganese species in the absence of DO; while in the presence of DO, Mn(II) is oxidized to Mn(III) by dioxygen to form superoxide anions and Mn(III), which can be further oxidized by PMS to higher valence states such as Mn(V) and Mn(VII). Consequently, the production of free radicals decreases while intermediate valent manganese species become more abundant. Additionally, O2•− can also reduce both Mn(VII) and Mn(IV) back to their lower oxidation state (Mn(II)). The cooperative interactions between these active species enhance the efficiency of catalytic cycles of manganese species. Moreover, the influence of multiple factors, the degradation products, and their associated toxicity assessment were investigated. Overall, this research provides valuable insights into the design of highly efficient PMS and DO activation systems.