London Dispersive and Lewis Acid-Base Surface Energy of 2D Single-Crystalline and Polycrystalline Covalent Organic Frameworks

Abstract

This paper is devoted to an accurate determination of the London dispersive, polar free energy of adsorption, Lewis acid γs+ and Lewis base γs− components of the polar surface energy γsAB of 2D single-crystalline and polycrystalline covalent organic frameworks such as TAPPy-TPA-COFs. The obtained results showed the highest values of polar and total surface energy of the polycrystalline COF relative to those of the single-crystalline COF. Inverse gas chromatography (IGC) at infinite dilution was used to quantify the various surface parameters of the different materials. The net retention times of the adsorption of n-alkanes and several polar solvents on single-crystalline and polycrystalline covalent organic frameworks were obtained from IGC measurements. The free surface Gibbs energy of adsorption was obtained for the various organic molecules at different temperatures from their net retention volume values. The separation between the London dispersive energy and the polar energy of adsorbed molecules was carried out by using a new thermodynamic parameter PSX chosen as new indicator variable and taking into account the deformation polarizability and the harmonic mean of the ionization energies of solvents and solid materials, derived from the London dispersion equation. The obtained results gave higher acidity (KA=0.22) for the 2D polycrystalline COF than that of the single-crystalline COF (KA=0.15) and an equivalent basicity of the two COFs. The obtained results are very promising for the accurate determination of the surface thermodynamic parameters of adsorption of organic solvents on solid surfaces.