A new insight into surface oxidation of Fe-based metallic glass for azo dye degradation

Removing azo dyes from effluents poses an environmental and socio-economic challenge due to their carcinogenic and mutagenic risks. The Fenton-like reaction using Fe-based metallic glass (MG) is feasible for wastewater remediation; however, the oxidation-induced passive film will impede the further reaction of Fe-based catalysts, especially for Fe-based MG recycled from end-of-life soft magnetic products. Here, the oxidation behavior of Fe_73.5Si_13.5B₉Cu₁Nb₃ MG ribbons and the consequential effect on the degradation performance of acid orange 7 have been systematically investigated. When the Fe-based MG is oxidized at low temperatures (<520 °C), a continuous and dense oxide layer forms, shielding the zero-valence iron (ZVI) from interacting with dye molecules. As the oxidation temperature rises to 580–680 °C, numerous α-Fe(Si) nanocrystals and CuO nuclei will appear and degrade the protective oxide film during the rapid high-temperature oxidation (RHTO), enhancing the azo dye decolorization rate. Further oxidation at higher temperatures (>700 °C) will increase the oxide layer thickness and consume ZVI, thereby blocking the Fenton-like reactions. Notably, the RHTO could reactivate the inactivated Fe-based MG and endow the inactivated MG with a high dye degradation constant k of 1.5 min⁻¹, indicating a promising method for reusing the end-of-life Fe-based MG electronic products for textile dye wastewater treatment.