Synergistic effects between graphite nanosheets and OMS-2 to enhance the direct electron transfer process-based peroxymonosulfate activation for pollutants degradation

The abundant and low-cost manganese oxides have attracted increasing interest in peroxymonosulfate (PMS) activation. Nevertheless, the low zeta potentials and surface area of the catalysts lead to weak adsorptions of PMS and pollutants under neutral and basic conditions, and thus the low degradation efficiency. Herein, a promising hybrid from graphite nanosheets (GNs) and cryptomelane-type manganese octahedral molecular sieves (OMS-2) was developed by a simple redox method at room temperature. The catalysts possessed a high surface area and a great number of surface defects, which enhanced the adsorption of PMS; while the introduction of GNs increased the capacity of pollutants adsorption and the rate of electron transfer. Compared with pure OMS-2 and other catalysts, the hybrid catalyst showed a much higher performance for acid orange 7 degradation at pH 8.2 with a first-order rate constant of 0.414 min(-1), due to the above synergistic effects between OMS-2 and GNs. Based on quenching experiments, PMS decomposition and degradation of pollutants with different oxidation potentials, a direct electron transfer process through Mn-O-PMS complexes was identified to contribute the degradation. Moreover, a galvanic oxidation system was set up to further confirm the occurrence of the mechanism. Overall, this work provides an important step in developing Mn-based hybrids for organic pollutants degradation.