Efficient photo-assisted activation of peroxydisulfate by a novel Z-scheme sulfur-doped C₃N₅/DyFeO₃ heterojunction for norfloxacin degradation: Activation mechanism and DFT studies on reaction pathways

Peroxydisulfate (PDS) activation is a crucial process for wastewater treatment in complicated water matrices. However, it is frequently limited because of poor selectivity, sluggish kinetics, and short lifetime of radicals. Therefore, in this study, an efficient sulfur-doped C₃N₅/DyFeO₃ (SCN/DyF) Z-scheme heterostructure catalyst was rationally developed using a simple wet-chemical strategy to photoactivate PDS, which can effectively degrade norfloxacin (NOR; 96.1%) in a water environment. The coupling of SCN/DyF catalyst with PDS shows favorable synergistic effect, with NOR degradation rate in the following order: SCN/DyF-1 (k = 0.0177/min) < SCN/DyF-2 (k = 0.0253/min) < SCN/DyF-3 (k = 0.0343/min) < SCN/DyF-4 (k = 0.0441/min) after 60 min of irradiation. The optimal SCN/DyF-4 achieved a higher NOR degradation under the reaction conditions of 0.6 g/L catalyst dosage, 10 mg/L NOR concentration, natural pH (6.7), and 2.0 mM PDS. The SCN/DyF heterojunction exhibited impressive PDS photoactivation performance because of its Z-scheme charge-transfer platform, accelerated redox cycle, and enhanced light absorption. Furthermore, the structural changes and chemical interactions between the main elements of the catalysts were systematically investigated. Two reaction routes for NOR degradation were identified by combining radical-trapping tests and electron spin resonance spectroscopy. Moreover, the ecotoxicity of the degraded NOR intermediates were confirmed through density functional theory calculations. This work provides an ideal platform for activating PDS systems using Z-scheme photocatalysts for real water remediation.