Z-scheme S, B co-doped g-C₃N₄ nanotube@MnO₂ heterojunction with visible-light-responsive for enhanced photodegradation of diclofenac by peroxymonosulfate activation

In this study, the manganese dioxide (MnO₂) nanosheets were successfully embedded onto boron and sulfur co-doped g-C₃N₄ (CNBS) nanotubes to construct the flower-like core–shell CNBS@MnO₂ heterojunction with Z-scheme structure for the enhanced photodegradation of diclofenac (DCF) in the presence of peroxymonosulfate (PMS) and 460-nm visible light. The CNBS@MnO₂ provides large specific surface area and reduced interfacial resistance for rapid electron transport. Moreover, the redox cycling of Mn species effectively activates PMS to produce sulfate radicals for DCF photodegradation. The PMS-based photodegradation of DCF over CNBS@MnO₂ displays the excellent photodegradation performance after 15 min of irradiation, and the efficiency is highly dependent on initial pH, ion species, and concentrations of PMS and DCF. The CNBS@MnO₂ also shows its excellent stability and reusability over ten cycles. Besides, h⁺, O₂^●− and SO₄^●− are the dominantly reactive species for the enhanced degradation of DCF over Z-scheme CNBS@MnO₂ heterojunction. The possible reaction mechanism as well as the degradation pathway of DCF over CNBS@MnO₂ in the presence of PMS is also proposed. Results clearly highlight the superior photoactivity of Z-scheme CNBS@MnO₂ toward micropollutant degradation by PMS activation, which can open an avenue to fabricate the g-C₃N₄ nanotube@metal oxide structure as an effective activator for water and wastewater purification.