Nanoscale zero-valent iron (nZVI) possesses unique chemistry and capability for the separation and transformation of a growing number of environmental contaminants.A nZVI particle consists of two nanoscale components,an iron (oxyhydr)oxides shell and a metallic iron core.This classical core-shell structure offers nZVI with unique and multifaceted reactivity of sorption,complexation,reduction and precipitation due to its strong small particle size for engineering deployment,large surface area,abundant reactive sites and electron-donating capacity for enhanced chemical activity.For over two decades,research has been steadily expanding our understanding on the reaction mechanisms and engineering performance of nZVI for soil and groundwater remediation,and more recently for wastewater treatment.