Activation of peroxymonosulfate by g-C3N4/ε-MnO2 microspheres for nonradical pathway degradation of organic pollutants in water: Catalytic mechanism and degradation path

ε-MnO2 has the potential to activate persulfate for the elimination of organic contaminants. However, the sluggish electron transfer caused by the excessive structural defects and the easy agglomeration during preparation and reaction severely suppresses the catalytic activity of ε-MnO2. Herein, g-C3N4 modified ε-MnO2 composites (g-C3N4/ε-MnO2) are synthesized by precipitation method coupling with calcination, and their catalytic activities are investigated vis peroxymonosulfate (PMS) activation for removal of acid orange 7 (AO7) in aqueous solution. Characterization results show that the g-C3N4 nanosheets modified ε-MnO2 nanoparticles are assembled to form the hierarchical microspheres, which not only can provide abundant active sites but also can effectively promote electron mobility for the degradation of AO7. Consequently, the g-C3N4/ε-MnO2 composites deliver high catalytic performance in activating PMS, resulting in 98.5 % of AO7 is degraded in 80 s, which is much better than the bare ε-MnO2. Nonradical pathways dominate the degradation process of AO7 and 1O2 is the main ROS. Density functional theory calculations demonstrate that PMS activation is more easily achieved on the surface of the g-C3N4/ε-MnO2 than the bare g-C3N4 and ε-MnO2. The possible degradation mechanisms for g-C3N4/ε-MnO2/PMS system include the interaction between PMS and ε-MnO2 and electron transfer to PMS in the redox cycle of Mn(II), Mn(III), and Mn(IV). This work provides insight into the promotion of efficient MnO2 catalysts in PMS activation for the degradation of organic pollutants.