Porous Z-scheme MnO2/Mn-modified alkalinized g-C3N4 heterojunction with excellent Fenton-like photocatalytic activity for efficient degradation of pharmaceutical pollutants

A porous Z-scheme MnO2/Mn-modified alkalinized g-C3N4 catalyst (MnO2/CNK-OH-Mn) was fabricated by calcination-impregnation method. MnO2/CNK-OH-Mn exhibited higher Fenton-like photocatalytic activity in degrading tetracycline than pure g-C3N4 and alkalinized g-C3N4. The optimal MnO2/CNK-OH-Mn-15(%) showed the highest catalytic activity with 96.7% tetracycline removal and 74.9% total organic carbon (TOC) removal efficiency due to the enhanced reactive oxygen species generation. The tetracycline degradation process followed two pathways, and the formation of NO3- further revealed deep mineralization of tetracycline to inorganic substance during the photocatalytic degradation. The highest center dot OH yield of MnO2/CNK-OH-Mn-15(%) was attributable to synergism of surface grafted hydroxyl groups, Z-scheme charge transfer and H2O2 activation via redox cycles of Mn(IV)/Mn(III)/Mn(II). The Fenton-like photocatalytic mechanism of Z-scheme MnO2/CNK-OH-Mn was presented. Moreover, MnO2/CNK-OH-Mn-15% can effectively dispose of pharmaceutical wastewater with 77.1% chemical oxygen demand (COD) removal.