Systematic XPS study of gallium-substituted boehmite

Abstract

Abstract: Ga-substituted boehmites were synthesized using a soft-chemistry route in the presence of poly(ethylene oxide) surfactant under hydrothermal conditions. The effect of Ga-substitution was studied by X-ray diffraction and X-ray photoelectron spectroscopy. Initial precipitates were amorphous (minor bayerite). After hydrothermal treatment, XRD showed broad reflections at low Ga-substation indicating low crystallinity and formation of pseudoboehmite. This was confirmed by high-resolution XPS of Al 2p, Ga 2p, and O 1s. The Al 2p binding energy of 74.03 eV was closer to boehmite than pseudoboehmite, probably caused by the Ga-substitution in the structure. The O 1s showed the presence of O, OH, and H2O. The ratio of (total O)/(Al + Ga) showed an excess of O as expected for pseudoboehmite. The ratio of (O + OH)/Al + Ga) was also slightly larger than the theoretical value of 2 for boehmite. High concentrations of added Ga (10, 20 %) resulted in amorphous material after hydrothermal treatment. Graphical Abstract: [Figure not available: see fulltext.]