Surface studies of phosphate adsorption on thin film Fe{sub 2}O{sub 3}

Phosphate adsorption on thin Fe{sub 2}O{sub 3} 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 phosphate solutions of differing pH were used to determine the adsorption/desorption kinetics, speciation of the adsorbed phosphate, and the absolute phosphate coverage. Two distinct states of adsorbed phosphate were found, with activation energies of desorption in vacuum corresponding to 284 and 405 kJ mol{sup -1}. Auger electron spectroscopy (AES) indicated that the maximum phosphate coverage realized in this study was approximately one monolayer. X-ray photoelectron spectroscopy (XPS) showed shifts in the iron and phosphorus binding energies as the reactant solution pH was varied from 5 to 11. XPS also showed that the total amount of adsorbed phosphorus decreased with increasing pH.