Monodisperse-porous Mn5O8 microspheres as an efficient catalyst for fast degradation of organic pollutants via peroxymonosulfate activation

Monodisperse-porous Mn5O8 microspheres with multiple oxidation states were used as an efficient heterogeneous catalyst for the fast degradation of organic pollutants via peroxymonosulfate (PMS) activation. The presence of Mn(ii), Mn(iii), and Mn(iv) phases on the surface of the microspheres was shown by X-ray photoelectron spectroscopy. For the degradation studies, methylene blue (MB) and tetracycline (TC) were selected as the model organic pollutants. The removal process included both adsorption and chemical degradation stages for both pollutants. By using the Mn5O8-PMS system, complete removal of MB was achieved and 70% of TC was removed in a degradation period of 5 min. The high surface area originating from the porous nature and the crystalline phase found in the microspheres should provide very short removal periods with the selected pollutants. No significant change was observed in the removal behavior in the pH range of 3.3-9.0. The highest first order-rate constants were obtained as 0.961 min(-1) and 0.570 min(-1) for MB and TC, respectively. These values were approximately up to 24-fold higher with respect to similar degradation systems. The degradation runs performed using radical scavengers with the Mn5O8-PMS system demonstrated the presence of superoxide anion (O-2*(-)) and singlet oxygen (O-1(2)) radicals. The degradation efficiency decreased to 99.3% with MB and 89.3% with TC over five consecutive degradation runs. Final Mn concentrations lower than 0.14 ppm obtained at the end of the degradation runs demonstrated that monodisperse-porous Mn5O8 microspheres were a highly stable oxidation catalyst for the fast degradation of organic pollutants in an aqueous medium.