Visible light-mediated persulfate activation by magnetite: Wavelength-specific radical generation and bisphenol AF transformation pathways

This study systematically investigated the degradation of bisphenol AF (BPAF) using a visible light-assisted magnetite/persulfate (Vis/magnetite/PS) system. Visible light irradiation significantly enhanced the activation efficiency of PS by magnetite, leading to improved BPAF removal. Under the optimal conditions, a removal efficiency of 91.7 % was achieved. Notably, while magnetite exhibited specificity toward PS activation, the system also demonstrated exceptional versatility by achieving 99 % degradation efficiency for methylene blue. Monochromatic light irradiation revealed wavelength-dependent degradation kinetics, with BPAF removal efficiencies following the order as: Vis > purple > red > blue > green > yellow light. Significant elevation in superoxide radical and singlet oxygen contribution rates occurred when transitioning from standard irradiation to monochromatic light or darkness. Four primary transformation pathways of BPAF were identified: hydroxylation, sulfate addition, bond cleavage, and coupling reactions. Photocoupling was found to selectively increase the abundance of hydroxylated and coupled products. The system reduced operational costs compared to zero-valent iron-based systems, owing to the utilization of natural sunlight and unprocessed magnetite ore. These findings provide fundamental insights into the wavelength-dependent synergism between light and magnetite in PS activation, offering a scalable and eco-friendly strategy for water and wastewater remediation.