Adsorption of organic molecules on the highly ordered MCM-41 sorbent modified by different amounts of melamine

Abstract

Thermodynamic characteristics of adsorption of organic molecules on the ordered organosilylated composite MCM-41 with grafted trimethylsilyl groups (MMet) and modified by melamine deposited on the surface were studied by inverse gas chromatography. Mole changes in the internal energy and entropy of adsorption, the dispersion and specific components of the value proportional to the Helmholtz absorption energy, and the contribution of the methyl group to the heat of adsorption were calculated from the specific retention volumes. The change in the retention volumes was established to be determined by the dispersion component of the Helmholtz energy of adsorption, whereas the energy of specific interactions remains almost unchanged. After the adsorbent surface was coated by the second and third melamine layers, the changes in −ΔU and −ΔS for adsorption of the members of the homologous series of n-alkanes are so small that lie within admissible measurement inaccuracies. This phenomenon can be explained by the regularities of alkane adsorption in slit-like pores of the supramolecular structure of melamine.