Comparative Study of XPS and DFT with Reference to the Distributions of Al in Tetrahedral and Octahedral Sheets of Phyllosilicates

Abstract

Five phyllosilicate samples of dioctahedral smectite, mica, magnesium chlorite, saponite, and hectorite were studied using X-ray photoelectron spectroscopy (XPS) to determine the distribution of Al in the tetrahedral and octahedral sheets. The binding energies of the Al(2p) peaks in all the samples were obtained at 74.5 and 73.7 eV for octahedral and tetrahedral Al, respectively. The ratio of the peak areas follows the same trend as that of octahedral Al present in the phyllosilicate lattice. To confirm the experimental result, localized cluster models were generated from the pyrophyllite structure to calculate their density of states by the density functional theory (DFT). The DFT results match very well with XPS results with respect to the difference of binding energies of Al in the tetrahedral and octahedral sheet of phyllosilicates; so this method is a useful tool to measure the qualitative distribution of Al in the phyllosilicates.

Effect of exchangeable cation on the swelling property of 2:1 dioctahedral smectite—A periodic first principle study

“…From electrostatic calculations 20 it has been observed that the orientations of these hydroxyl groups are sensitive to the octahedral cation plane at the center of the clay layer. In our earlier study [21][22][23][24][25] we rationalized the structure property relationship in montmorillonite clays and observed that the hydroxyl groups expected to play a crucial role in the catalytic activity of dioctahedral clays. A recent study of Marry et al, 26 on monohydrated montmorillonite, suggested that Cs ϩ diffuse faster than Na ϩ , and the arrangement of clay surfaces play a significant part in the choice of sites occupied by cations as well in their mobility.…”

Correlation between hydroxyl fraction and O/Al atomic ratio as determined from XPS spectra of aluminium oxide layers

“…Also, the full widths at half-maxima (FWHMs), which were in the 1.70-1.90 eV range, do not suggest the presence of several components. 33,34 Only for the pseudoboehmite oxide a larger peak width was observed, probably due to charging effects. For the anhydrous amorphous oxide an additional component was present, which is due to a minor amount of an aluminiumenriched surface oxide.…”

Surface Crystal Chemistry of Phyllosilicates Using X-Ray Photoelectron Spectroscopy: A Review

“…Anderson and Swartz (1974) reported identical A1 2p binding energies for tetrahedral and octahedral aluminum in aluminosilicates. Ebina et al (1997) and Barr et al (1997) observed that the Al 2p binding energy increased with an increase in the ratio of octahedral to tetrahedral Al. Barr et al (1997) noted that a more positive octahedral sheet character coupled with the relatively net negative tetrahedral sheet results in ionic AlÀO bonds that are stronger in kaolinite and allophane than in Al 2 O 3 .…”