Interfacial reactions and speciation identification during arsenic treated with nanoscale zerovalent iron (nZVI) in...

This perspective briefly summarized the progress of inorganic arsenic (As) treated with nanoscale zerovalent iron (nZVI) in water over the past two decades. The intrinsic interfacial reaction between As and nZVI encompassed multiple effects, such as complexation, oxidation, reduction, and co-precipitation, ascribed to core-shell structure of nZVI and environmental behavior of As in water. Surface complexation occurred via ligand exchange of arsenate anions with Fe-OH groups on the iron oxide shell. However, interfacial oxidation of As(III) to As(V) was attributed to form a Fe(III) oxide-Fe(II)-As(III) ternary surface complex under anoxic conditions, as well as generate reactive oxygen species (e.g., H₂O₂, •OH) from iron reacted with O₂ under oxic conditions. Reduction of As(III) to As(0) was followed by subsurface accumulation near the Fe(0) core. Advanced characterization techniques, including high-resolution X-ray photoelectron spectroscopy, in situ X-ray absorption spectroscopy, spherical aberration-corrected scanning transmission electron microscope, and density functional theory combined with quick-scanning extended X-ray absorption fine structure, have unraveled the multi-tiered distributions of As on nZVI at atomic scale. This review highlights critical gaps in understanding As-Fe redox dynamics and advocates for future research to engineer nZVI with tailored surface properties for enhanced As sequestration.