magnetite nanoparticles (SMNP) are promising for in situ remediation of arsenic-contaminated soils.
However, a molecular level understanding has been lacking. Here, we carried out XAFS studies to bridge
this knowledge gap. Fe K-edge XAFS spectra indicated that the FeeO and FeeFe coordination numbers of
SMNP were lower than those for bare magnetite particles, and these coordination numbers decreased
with increasing starch concentration. The decrease in the average coordination number at elevated
stabilizer concentration was attributed to the increase in the surface-to-volume ratio. Arsenic K-edge
XAFS spectra indicated that adsorbed arsenate on SMNP consisted primarily of binuclear bidentate (BB)
complexes and monodentate mononuclear (MM) complexes. More BB complexes (energetically more
favorable) were observed at higher starch concentrations, indicating that SMNP not only offered greater
adsorption surface area, but also stronger adsorption affinity toward arsenate.