Comparative study of XPS and DFT with reference to the distributions of Al in tetrahedral and octahedral sheets of phyllosilicates

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.