X-ray photoelectron spectroscopy (XPS) op adsorbed zinc on amorphous hydrous ferric oxide

The adsorption of Zn on amorphous hydrous ferric oxide (HFO) was monitored using both solution measurements of the non-absorbed Zn and X-ray photoelectron spectroscopy (XPS) measurements of the adsorbed Zn. Solution results suggest that, at low adsorption densities and/or low pH's, the mechanism of Zn adsorption may be similar to the adsorption of Cd, Cu and Pb. However, at higher adsorption densities and higher pH's, there is an apparent change in Zn speciation. Chemical shift and adsorbate thickness values derived from XPS provide information on the mechanism of the surface adsorption of Zn. The XPS studies show that submonolayer coverages of Zn are largely chemically adsorbed at solution pH's less than 6.5, while at higher pH's the Zn is partially hydrolyzed to form a surface layer containing physisorbed Zn(OH)2 which may exceed monolayer thicknesses.