Highly efficient α-Mn2O3@α-MnO2-500 nanocomposite for peroxymonosulfate activation: comprehensive investigation of manganese oxides

In this paper a nanorod alpha-Mn2O3@ alpha-MnO2-500 nanocomposite demonstrated the highest efficiency and remarkable stability in persulfate activation compared with other manganese oxide based catalysts including alpha-MnO2, beta-MnO2, gamma-MnO2, delta-MnO2, alpha-Mn2O3, Mn3O4, etc. This catalyst was easily fabricated using one spot calcination treatment at 500 degrees C, and a minimal amount of leached Mn ions was detected during the degradation of organic contaminants. The significant performance in persulfate activation was elucidated from the unique structure and physical-chemical properties of alpha-Mn2O3@ alpha-MnO2-500. Evidenced by XRD and HRTEM, alpha-Mn2O3@ alpha-MnO2-500 consisted of a well mixed phase structure of tetragonal alpha-MnO2 and cubic alpha-Mn2O3 with high crystalline quality. XPS and the inhibition effect by phosphate confirmed the existence of surface hydroxyl groups (0.926 mmol g(-1)) on alpha-Mn2O3@ alpha-MnO(2)500, while FTIR, Raman and ionic strength experiments further demonstrated that the formation inner-sphere interaction was the key step in PMS activation. Supported by XPS and CV, the mixed valence states in the alpha-Mn2O3@ alpha-MnO2-500 nanocomposite exhibited a more effective redox property, which favored electron transfer between Mn species (MnIV 4 MnIII), and generated SO4 center dot-, (OH)-O-center dot and even O-1(2) for the degradation of various hydrocarbon contaminants. Also, the activation energy of alpha-Mn2O3@ alpha MnO2-500/PMS for phenol degradation was only 24.7 kJ mol(-1), much lower than that of alpha-MnO2 (38.7 kJ mol(-1)) and alpha-Mn2O3 (44.9 kJ mol(-1)). This Mn catalyst with much lower toxicity can be considered as a green approach in environmental remediation.