Ternary 3D/2D/3D direct dual Z-scheme MOF-on-MOF-derived α-Fe2O3/g-C3N4/Fe-MOF photocatalyst for boosted sunlight-driven removal of metronidazole: effect of coexisting ions, mechanistic insights, and water matrices

A direct solid ternary dual Z-scheme photocatalyst, 3D/2D/3D α-Fe₂O₃/g-C₃N₄/Fe-MOF (FCM), was fabricated for efficient removal of metronidazole (MTZ) under sunlight irradiation. About 98.5% of 25 mg L⁻¹ MTZ was effectively degraded with a catalyst dosage of 20 mg per 50 mL under 90 min of sunlight irradiation. Moreover, a total organic carbon (TOC) removal of 78.5% was achieved within the same duration under optimal conditions. The simultaneous transfer of photogenerated electron–hole pairs in the two Z-scheme pathways described here can significantly accelerate the charge separation and enhance ROS production. The effect of catalyst dose, initial MTZ concentration, inorganic cations (Na⁺, Mg²⁺, Ca²⁺, and Al³⁺), inorganic anions (Cl⁻, CO₃²⁻, NO₃⁻, and SO₄²⁻), organic compounds (SDS, urea, HA, and acetone), and different water matrices on the degradation of MTZ by FCM was analyzed systematically. Furthermore, comprehending the spatial separation and transfer of photogenerated charge carriers as well as the formation of ROS at the heterojunction interface is critical for understanding the photocatalytic degradation mechanisms. Consequently, a plausible MTZ breakdown route and charge transfer pathway were established based on the radical scavenging experiments, ESR and LCMS analysis. A high degradation efficiency of the dual Z-scheme MOF-on-MOF-derived 3D/2D/3D α-Fe₂O₃/g-C₃N₄/Fe-MOF photocatalyst under all simulated experiments and different water matrices highlights its excellent photoactivity and establishes its potential use in visible-light-driven photocatalytic application in wastewater remediation.