Nano zero-valent iron (nZVI) has attracted much more attention for its potential applications in the fields of environmental contaminant remediation and detoxification.
In this study, we investigated the anoxic Cr(VI) removal with core-shell Fe@Fe2O3 nanowires. It was found the surface area normalized Cr(VI) removal rate constants of Fe@Fe2O3 nanowires first increased with increasing the iron oxide shell thickness and then decreased, suggesting that Fe@Fe2O3 nanowires possessed an interesting core-shell structure dependent Cr(VI) removal property. Meanwhile, the Cr(VI) removal efficiency was positively correlated to the amount of surface bound Fe(II). This result revealed that the core-shell structure dependent Cr(VI) removal property of Fe@Fe2O3 nanowires was mainly attributed to the reduction of Cr(VI) by the surface bound Fe(II) besides the reduction of Cr(VI) adsorbed on the iron oxide shell via the electrons transferred from the iron core. The indispensable role of surface bound Fe(II) was confirmed by Tafel polarization and high-resolution X-ray photoelectron spectroscopic depth profiles analyses. X-ray diffraction patterns and scanning electron microscope images of the fresh and used Fe@Fe2O3 nanowires revealed the formation of Fe(III)/Cr(III)/Cr(VI) composite oxides during the anoxic Cr(VI) removal process. This study sheds a deep insight into the anoxic Cr(VI) removal mechanism of core-shell Fe@Fe2O3 nanowires and also provides an efficient Cr(VI) removal method.
Phosphate ions widely exist in the environment. Previous studies revealed that the adsorption of phosphate ions on nanoscale zerovalent iron would generate a passivating oxide shell to block reactive sites and thus decrease the direct pollutant reduction reactivity of zerovalent iron. Given that molecular oxygen activation process is different from direct pollutant reduction with nanoscale zerovalent iron, it is still unclear how phosphate ions will affect molecular oxygen activation and reactive oxygen species generation with nanoscale zerovalent iron. In this study, we systematically studied the effect of phosphate ions on molecular oxygen activation with Fe@FeO nanowires, a special nanoscale zerovalent iron, taking advantages of rotating ring disk electrochemical analysis. It was interesting to find that the oxygen reduction pathway on Fe@FeO nanowires was gradually shifted from a four-electron reduction pathway to a sequential one-electron reduction one, along with increasing the phosphate ions concentration from 0 to 10 mmol·L. This oxygen reduction pathway change greatly enhanced the molecular oxygen activation and reactive oxygen species generation performances of Fe@FeO nanowires, and thus increased their aerobic 4-chlorophenol degradation rate by 10 times. These findings shed insight into the possible roles of widely existed phosphate ions in molecular oxygen activation and organic pollutants degradation with nanoscale zerovalent iron.
In this study, amorphous FeB alloy modified magnetitenanocomposites (Fe 3 O 4-FeB) were facilely synthesized by interfacialreduction of commercialFe 3 O 4 nanoparticles with NaBH 4. TEM, CS-STEM integrated with EDS, Mössbauer spectroscopyanalysis confirmed the formation of Fe 3 O 4-FeB, where a shell of amorphous FeB nanoparticles with 2-4 nm in size was surrounded on the inner magnetite Fe 3 O 4 part.Fe 3 O 4-FeB displayed a promotedCr(VI)removal efficiency compared withthe bare Fe 3 O 4 counterpart, the interfacial reduced Fe 3 O 4 nanoparticles with hydrogen and/or with hydrazine hydride. XPS analysis evidenced that reduction of Cr(VI) on surface of the Fe 3 O 4-FeB was the major contribution to the Cr(VI) removal. Tafel polarization analysis of the Fe 3 O 4-FeB and aqueous boron speciesmeasurement indicated thathigh Cr(VI) removal efficiencywith Fe 3 O 4-FeB was highly depended on amorphous FeB alloy shell, in which boron element containing free electrons could accelerate the electron transfer from Fe to the adsorbed Cr(VI), as well reduce Fe(III) to Fe(II) and thus promote the Fe(III)/Fe(II) cycles.The efficient Cr(VI) removal under a wide range of pH values and its easy magnetic separationmake the Fe 3 O 4-FeB be a potential for Cr(VI) contaminated water
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