THERMODYNAMICS OF ADSORPTION OF ORGANIC-COMPOUNDS AT THE SILICA-GEL NONPOLAR SOLVENT INTERFACES

The standard free energy changes (DELTAG0) of the adsorption processes have been calculated by the Langmuir parameters of the adsorption of n-fatty alcohols, cyclohexanone, toluene, and oxyaromatic compounds at the silica gel/carbon tetrachloride and silica gel/cyclohexane interfaces. The results suggested that: (1) for the n-fatty alcohol homologues, the values of DELTAG0 followed an empirical formula -DELTAG0 = 23.5 - 3.80 ln n (kJ . mol-1), where n is the number of carbon atoms in the alcohol chain, and the hydroxyl groups on the silica gel showed properties similar to those in water or alcohol molecules in forming a hydrogen bond with the fatty alcohol molecules; (2) for the aromatic compounds, the values of DELTAG0 decreased in the order of toluene, anisole, benzaldehyde, benzoic alcohol, and benzoic acid due to the different strengths of hydrogen bonds between their molecules and the surface silanol groups; (3) the value of DELTAG0 for the pretreated silica gel to adsorb cyclohexanone has some relation to the concentration of the surface silanol group. (C) 1994 Academic Press, Inc.Chemistry, PhysicalSCI(E)EI11ARTICLE123-2816