XPS AND DFT STUDY ON THE MIGRATION OF LITHIUM IN MONTMORILLONITE

抄録

The distribution of lithium in montmorillonite was studied by using X-ray photoelectron spectroscopy (XPS) and compared with calculations based on the density functional theory (DFT). Interlayer Li ion in montmorillonite migrated to octahedral sites by heat treatments at a temperature range from 250 to 350 °C for up to 72 hours. Li (1s) binding energy of hectorite used for reference and Li exchanged montmorillonite were 55.0 and 57.0 eV, which were attributed to the octahedral and the exchangeable lithium, respectively. After the heat treatment at 250°C for 18 hours, a new component peak was appeared at 55.4 eV which was attributed to the octahedral lithium ion; and the ratio of the peak area to the total Li (1s) peak area was increased with prolonging the heat treatment. However, even after the heat treatment at 350°C for 72 hours, the lithium ions were distributed to the both sites.
Two distinct Li locations in smectites were studied using DFT calculations. One was in the ditrigonal cavity, and the other was in the octahedral sheet of smectite. The optimized structure of the cluster models suggested that the Li ion favorably interacts with a hydroxyl oxygen atom and/or basal oxygen atoms at the bottom of the ditrigonal cavity in the both cases. Calculated 1 s binding energy of the Li ion in the octahedral site was smaller than that of the Li ion in the ditrigonal cavity site, which shows good coincidence with the XPS chemical shift of the Li (1s) peak.