A spectroscopic investigation of phosphate adsorption onto iron oxides

Abstract

Phosphate adsorption on a thin Fe2O3 film prepared in ultrahigh vacuum (UHV) was carried out in a liquid flow cell and subsequently returned to UHV for spectroscopic examination. Variations in exposure time to phosphatic solutions of differing pH were used to determine the adsorption/desorption kinetics, speciation of the adsorbed phosphate, and the absolute phosphate coverage. Rapid uptake of phosphate occurred in the first 10 min of exposure resulting in coverages of 3×1014 molecules per cm2, followed by a 20 min induction period, and then continued phosphate adsorption. Auger electron spectroscopy (AES) indicated that he maximum phosphate coverage realized in this study was ∼1×1015 molecules cm−2. X-ray photoelectron spectroscopy (XPS) showed that phosphorus shifted to more oxidized states during longer exposures to phospatic solutions.