Transformation of nanoscale zero-valent iron with antimony: Effects of the Sb spatial configuration

Abstract Increasing research has unmasked multifaceted functions of nanoscale zero-valent iron (nZVI) for metal(loid) separation. In this work, the solution and surface chemistry of nZVI reacting with Sb(III) and Sb(V) are investigated. Results show the spatial configurations of antimony complexes have significant impact on removal rate. The reaction rate constant of Sb(III) keeps about one order of magnitude higher than that of Sb(V) over a wide range of antimony concentration (5–50 mg/L) and solution pH (3.0–11.0). Density functional theory calculations suggest that the Fe-O bond cleavage is the rate-limiting step. The asymmetric quadrihedron structure of Sb(OH)3 favors Fe-O bond cleavage on nZVI surface with lower energy barrier (ΔG = 0.878 eV) than that of the octahedral symmetric structured Sb(OH)6− (ΔG = 1.618 eV). Microscopic and electrochemical evidence confirm that the faster coordination allows Sb(III) uniformly deposit on nanoparticles and generates a thin antimony film, impeding the further dissolution of inner Fe. While the slower coordination of Sb(V) gathers only diminutive exposure and allows continuous and extensive nZVI oxidation. Abundant corrosion products promote Sb(V) removal capacity to 103.1 mg/g, which is larger than that of Sb(III) (91.74 mg/g). This new perspective might be equally applicable to nZVI reactions with other oxyanions such as arsenic and selenium.