X-ray photoelectron spectroscopic study of hydrated aluminas and aluminas

Abstract

X-ray photoelectron spectra of hydrated aluminas (boehmite, diaspore, bayerite, and gibbsite), transition aluminas (y, δ, η, θ, X, and k –Al₂O₃) and corundum (α-Al₂O₃) have been studied for spectral characterization of each compound. The O1s spectra are shifted 0.2–1.2 eV to higher binding energy (E_b) in the order of α-Al₂O₃ < boehmite, diaspore < bayerite, gibbsite, and this agrees with the order of bulk OH/Al molar ratio in samples. The E_b and FWHM values of O1s spectra of transition aluminas depend on the ratio OH/O, i.e., the amount of OH⁻ ions chemisorbed on them, and tend to decrease toward those of α-Al₂O₃ with increasing calcination temperature. Therefore, it is considered that an attracting effect of the proton on valence electrons in the hydroxyl oxygen causes the increased binding energy between core electrons and oxygen atomic nuclei. The broad O1s spectra of boehmite and diaspore can be deconvoluted into equal contribution from the two oxygen species in O₂₋ and OH₋ ions in their structures.