Deciphering competitive water–toluene adsorption mechanisms on oxide surfaces

Abstract

Understanding how polar and nonpolar molecules compete for oxide surfaces is essential for controlling interfacial reactivity and hydrophobicity. Herein, we report the coupling of in situ FTIR spectroscopy with an extended IAST–Freundlich model to quantitatively probe water–toluene co-adsorption on SiO₂, Al₂O₃, and TiO₂. This integrated approach links vibrational fingerprints to thermodynamic parameters, revealing both site selectivity and surface restructuring under mixed-vapor conditions. Quantitative analysis shows that SiO₂ exhibits the highest water uptake owing to its large surface area, while TiO₂ features stronger but more localized hydroxyl interactions; Al₂O₃ displays intermediate, reversible adsorption governed by Lewis acidity. Spectral evolutions distinguish three competitive regimes: water displacement by toluene on SiO₂, co-adsorption on Al₂O₃, and complete water-driven substitution on TiO₂. The combined FTIR–IAST framework establishes a consistent hierarchy of adsorption affinities and offers a transferable strategy for quantitative spectroscopic evaluation of competitive adsorption on heterogeneous catalysts.