Core–Shell Structure Dependent Reactivity of Fe@Fe2O3 Nanowires on Aerobic Degradation of 4-Chlorophenol

In this study, core–shell Fe@Fe2O3 nanowires with different iron oxide shell thickness were synthesized through tuning water-aging time after the reduction of ferric ions with sodium borohydride without any stirring. We found that these Fe@Fe2O3 nanowires exhibited interesting core–shell structure dependent reactivity on the aerobic degradation of 4-chlorophenol. Characterization results revealed that the core–shell structure dependent aerobic oxidative reactivity of Fe@Fe2O3 nanowires was arisen from the combined effects of incrassated iron oxide shell and more surface bound ferrous ions on amorphous iron oxide shell formed during the water-aging process. The incrassated iron oxide shell would gradually block the outward electron transfer from iron core for the subsequent two-electron molecular oxygen activation, but more surface bound ferrous ions on iron oxide shell with prolonging aging time could favor the single-electron molecular oxygen activation, which was confirmed by electron spin resonance spectroscopy with spin trap technique. The mineralization of 4-chlorophenol was monitored by total organic carbon measurement and the oxidative degradation intermediates were analyzed by gas chromatography–mass spectrometry. This study provides new physical insight on the molecular oxygen activation mechanism of nanoscale zerovalent iron and its application on aerobic pollutant removal.