An insight into the fate of Cu2+ and zero-valent iron during removal of Cu2+ by nanoscale zero-valent iron

Abstract

Aim: The transformation of zero-valent iron (Fe0) and Cu2+ during Cu2+ removal by nanoscale zero-valent iron (nZVI) has not been properly investigated using modern analytical techniques, despite its importance in environmental toxicology and surface chemistry associated with wastewater treatment/groundwater remediation. This study critically examines the phenomenon using a variety of modern instruments that characterize the physical and chemical properties of materials and provides extensive comprehension of the subject. Methods: As-prepared nZVI was used to remove Cu2+ in 5 mmol/L CuSO4. The morphological and structural characteristics of the Cu2+ and nZVI after removal were investigated with the aid of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS). Results: Complete removal of Cu2+ by the nZVI was achieved within 60 min and remained constant till 120 min. The Cu2+ got reduced into cuprite (Cu2O) and copper metal (Cu0) (the crystals of both transformation products were cubic), while the Fe0 nanoparticles transformed into lath-like lepidocrocite (γ-FeOOH) and twin-rod goethite (α-FeOOH). The mechanism of Fe0 transformation was that the Fe2+ produced by Fe0 corrosion and oxidation by Cu2+ was hydrolyzed and oxidized to form hydropyrite, which was later converted into lepidocrocite and goethite with the assistance of Fe2+. The transformation of Cu2+ was due to the strong reduction property of Fe0. The toxicity and bioavailability of the transformed products were lower than those of Cu2+ and Fe0 nanoparticles. Conclusion: The findings are critical in understanding the fate of Fe0 nanoparticles and Cu2+ during Cu2+ removal by nZVI and can provide guidance for the application of nZVI technology.