Theoretical Study of the Adsorption of 2-Propanol onto Silica Surfaces on the Basis of and Density Functional Calculations

Abstract

The adsorptive interactions of 2-propanol (2-PrOH) molecules with silica surfaces were investigated using ab initio and density functional calculations. Two cluster models of silica were chosen to represent the terminal ≡SiOH groups and the siloxane bridges ≡Si–(O) 2 –Si≡ on the silica surface. The Hartree–Fock (HF) and Density Functional Theory (DFT) approaches, employing a 6–31G(d) basis set, were used to calculate the geometries, electronic structures, vibrational frequencies and adsorption energies of the adsorption complexes formed. The calculated adsorption energies were corrected for zero-point vibrational energies (ZPVE) and basis set superposition errors (BSSE). The results favoured a most likely surface configuration for the physisorbed species in which 2-PrOH molecules are bound to exposed silanol groups via two hydrogen bonds, with the alcoholic –OH group acting simultaneously as a proton acceptor and donor. Moreover, bonding of 2-PrOH with strained surface siloxane bridges (≡Si–O–Si≡) was shown to lead to chemisorption of the alcohol molecule. These findings have been shown to help interpreting reported infrared spectroscopic results of in-situ experimental studies.