Enhanced permanganate activation by g-C₃N₄ under visible light irradiation: Unraveled mechanism involving Mn(V) and photo-induced electron

Permanganate [Mn(VII)] needs to be activated to improve its reactivity towards refractory organic contaminants in practice. Herein, visible light (VL) and graphitic carbon nitride (g-C₃N₄) were introduced to enhance the activation of Mn(VII) for the first time. Sulfamethoxazole (SMX) can be degraded effectively by VL/Mn(VII)/g-C₃N₄ system in neutral and alkaline environments. Different from conventional Mn(VII) activation and photocatalytic processes, the performance of VL/Mn(VII)/g-C₃N₄ system in various real water samples was superior than Milli-Q water. Mn(V) was found to be the dominant active species responsible for SMX degradation. Photo-induced electron (e_cb^–) of g-C₃N₄ under VL irradiation was proved to be the initiator of Mn(VII) activation. Density functional theory calculations revealed the strong affinity of g-C₃N₄ for Mn(VII), which can resist the interference of water substrates on the Mn(VII) activation process by photo-induced e_cb^–. This work deepens the understanding of reactive manganese intermediates in the Mn(VII) activation system.