A comparative study of DFT and XPS with reference to the adsorption of caesium ions in smectites

Chemical states of Cs ion adsorbed on dioctahedral smectites were studied u sing X-ray photoelectron spectroscopy (XPS) and molecular orbital calculati ons based on the density functional theory (DFT). Smectites investigated we re montmorillonite, montmorillonite-beidellite, Fe-montmorillonite, and non tronite. It was found that montmorillonite samples kept approximately 50% o f adsorbed Cs ions after a treatment by BaCl2 aqueous solution, which were the highest values among the smectite samples. Cs(4d) binding energy was sl ightly shifted towards a lower energy by 0.2-0.8 eV after a BaCl2 treatment , which suggests that plural adsorption sites exist on the smectite surface . Stable Cs adsorption sites and the adsorption energies were determined by DFT calculations. As a result, Cs ion is adsorbed strongly on a basal oxyg en hexagonal hole. The chemical shift of the calculated Cs(4d) peak gave th e same tendency as shown in the XPS measurements. (C) 1999 Elsevier Science B.V. All rights reserved.