Recyclable Fe₇₈Si₉B₁₃ amorphous alloy for Fenton-like degradation of norfloxacin: Catalytic durability, pH-dependent transformation behavior, and ecological risks

Fe₇₈Si₉B₁₃ maintained stable NOR degradation during ten reuse cycles. • Surface chemical evolution of Fe₇₈Si₉B₁₃ was revealed after catalytic cycling. • Thirty transformation products enabled the proposal of five pH-dependent NOR pathways. • QSAR predicted pathway-dependent ecological risks of NOR transformation products. Fe₇₈Si₉B₁₃ amorphous alloy was employed as a heterogeneous Fenton-like catalyst for norfloxacin (NOR) degradation, with emphasis on pH-dependent transformation behavior and ecological implications of generated intermediates beyond parent-compound removal. The Fe₇₈Si₉B₁₃/H₂O₂ system achieved rapid NOR degradation, with complete removal within minutes under acidic conditions, and maintained catalytic activity during ten consecutive cycles. Structural and surface analyses demonstrated that the amorphous framework remained stable during repeated reactions, accompanied by surface oxidation and chemical-state changes. The transformation of B species from B B to B O during cycling suggested a possible contribution of B evolution to maintaining catalytic performance. High-resolution mass spectrometry identified 30 transformation products and revealed five NOR transformation pathways under acidic and weakly acidic conditions. Density functional theory (DFT) calculations further demonstrated that pH-dependent protonation states altered the electronic distribution and radical-reactive regions of NOR, providing molecular-level insights into pathway variations. Under acidic conditions, transformation products were mainly associated with pathways I–III, whereas weakly acidic conditions were mainly associated with pathways IV and V, leading to distinct transformation profiles and QSAR-predicted ecotoxicity characteristics. These findings highlight that the environmental performance of Fenton-like oxidation processes should be evaluated by integrating degradation efficiency, transformation behavior, and ecological risks of generated intermediates. Download: Download high-res image (211KB) Download: Download full-size image