Carbon ink modified α-MnO2 as a peroxymonosulfate activator for enhanced degradation of organic pollutants via a direct electron transfer process

Abstract

Transition metal oxides and carbon can activate peroxymonosulfate (PMS) to decompose organic contaminants. The combination of two materials can facilitate the adsorption of oxidants and pollutants on the catalyst and improve electron transfer efficiency. In this study, carbon nanoparticles-MnO2 composites (IC-MnO2) were synthesized by coating carbon ink on α-MnO2 and applied in PMS activation for acid orange 7 (AO7) degradation. The results showed that carbon nanoparticles were uniformly loaded on the α-MnO2 surface. Complete degradation of AO7 (20 mg/L) can be achieved in 15 min in the IC-MnO2/PMS system with a first-order kinetic rate constant of 0.22 min−1. Electrochemical analysis, quenching experiments, electron paramagnetic resonance, PMS decomposition, and removal of various contaminants demonstrated that AO7 could be efficiently degraded via a direct electron transfer pathway. A galvanic oxidation system containing the salt bridge and two separate cells was further established to confirm the electron transfer mechanism of the catalytic system. The study expands MnO2 applications by compositing nanocarbon materials in advanced oxidation processes and sheds light on the direct electron transfer mechanism.