Synthesis of porous Mn/Co composite oxides as an efficient peroxymonosulfate activator for removal of methylene blue

Co3O4 has been regarded as a promising heterogeneous catalyst for peroxymonosulfate (PMS) activation to remove organic pollutants. However, its catalytic ability needs to be further improved from a practical point of view. In this work, we prepared porous Mn/Co bimetallic composite oxides as PMS activator via a facile oxalate route. A series of composites with different Mn/Co molar ratios were prepared, and their catalytic performances were comparatively assessed using methylene blue (MB) as the degradation model. The results showed that the catalyst with a Mn/Co molar ratio of 1:2 (Mn1Co2) exhibited optimal MB removal efficiency. More than 90% of MB could be removed within 25 min under the reaction conditions: catalyst dosage of 0.04 g·L−1, PMS concentration of 0.6 mmol·L−1, pH range of 5–9, and reaction temperature of 25 °C. Moreover, •OH, •SO4-, •O2- and 1O2 were identified as reactive oxygen species in the reaction system according to the electron paramagnetic resonance (EPR) results. Besides, it was found that a MB degradation rate over 83% could be maintained after five consecutive recycling runs, indicating the excellent catalytic stability of Mn1Co2. The superb catalytic performance of Mn1Co2 is ascribed to both higher cobalt content and the synergistic effect between Mn and Co. Therefore, it is expected that porous bimetallic Mn1Co2 composite oxides have good application prospects in treating organic dye wastewater.