Enhanced oxidative and adsorptive removal of arsenite by the heterogeneous interfacial reaction of sulfidated nanoscale zerovalent iron

Abstract

Sulfidated nanoscale zero valent iron (S-nZVI) synthesized using a one-step approach is used to remove As(III) in anoxic water. The reaction between S-nZVI and As(III) follows pseudo-second-order kinetics, and the rate constant is 0.28015 g mg⁻¹ min⁻¹, which is 14 times higher than that of pristine nZVI 0.02005 g mg⁻¹ min⁻¹. The rapid reactive rate is attributed to the sulfur dopant in the metallic iron crystal lattice forming polysulfide iron (FeS_x). Electrochemical impedance spectroscopy of S-nZVI reacted with As(III) in water and demonstrated a smaller ohm resistance and super electron transfer efficiency. Interfacial goethite (α-FeOOH) in S-nZVI can oxidize As(III) to As(V). Synergistic effects of FeS_x and α-FeOOH enhance the oxidization of As(III) to As(V) from ∼10% to ∼45% compared with nZVI, as evaluated by X-ray photoelectron spectroscopy (XPS). Arsenic atoms diffuse the inner area of S-nZVI based on atomic scale transmission electron microscopy – energy dispersive spectroscopy mapping and XPS with ion etching technique and can be tightly immobilized as hardly soluble As₂S₃ and As₂S₅ precipitates by sulfur owing to its high affinity of arsenic. This study provides a facile strategy to sequestrate toxic metals from aquatic environments and highlights the vital properties determined by the structure.