Quantitative adsorption studies using X-ray photoelectron spectroscopy

Inorganic anion adsorption on hydrous ferric oxide (HFO) and calcite was investigated through X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and secondary ion mass spectrometry (SIMS). Methods which have been proposed for the quantitation of adsorbate coverages on rough surfaces by XPS are reviewed and tested. The effect of inelastic mean free path values and binding energy differences between surface and bulk species is examined. F{dollar}sp{lcub}-{rcub}{dollar} adsorption on HFO was used as a model system. F{dollar}sp{lcub}-{rcub}{dollar} surface coverages calculated from solution F{dollar}sp{lcub}-{rcub}{dollar} ion selective electrode (ISE) measurements are used to evaluate the quantitative XPS results. All of the methods evaluated give reasonable results if surface and bulk species have similar binding energies. The Dreiling three-layer model agrees with surface coverages from ISE data if large differences in binding energy exist.; Adsorption of SO{dollar}sb4sp{lcub}-2{rcub}{dollar}, PO{dollar}sb4sp{lcub}-3{rcub}{dollar}, and S{dollar}sb2{dollar}O{dollar}sb3sp{lcub}-2{rcub}{dollar} decrease with in increasing pH over the range 4-8. The Dreiling three-layer model was used to determine surface coverages from XPS results. Speciation of the adsorbed anions as a function of pH was determined through correlation of changes observed in XPS and DRIFTS spectra. SO{dollar}sb4sp{lcub}-2{rcub}{dollar} adsorbs as a bidentate species; no significant changes in adsorption with pH are noted. XPS and DRIFTS spectra for PO{dollar}sb4sp{lcub}-3{rcub}{dollar} change with pH. Adsorption of HPO{dollar}sb4sp{lcub}-2{rcub}{dollar} is suggested at pH 4. As pH increases, increasing spectral contributions from adsorbed tridentate PO{dollar}sb4sp{lcub}-3{rcub}{dollar} are observed. The orientation of S{dollar}sb2{dollar}O{dollar}sb3sp{lcub}-2{rcub}{dollar} on the HFO surface appears to change with pH. At pH 5, spectra indicate adsorption through both the S{dollar}sp{lcub}-2{rcub}{dollar} and one or more sulfato-oxygens. At pH 7, only adsorption through the sulfato-oxygens occurs.; Distinguishing between adsorption and coprecipitation is difficult using conventional bulk analysis techniques. Lead coprecipitated with and adsorbed on calcium carbonate was analyzed using XPS and SIMS. Only the adsorbed samples had Pb levels which were detectable by XPS. SIMS depth profiles indicate an approximately uniform Pb distribution with depth while samples containing adsorbed Pb show significant surface enrichment.