Thermodynamic study of adsorption of linear aliphatic monohypric alcohols and monocarboxylic acids from n-Heptane and n-Decane solutions onto α-iron (III) oxide immobilized in photosynthetic membranes

Abstract

Differential heats of adsorption at 298.2 K of a series of linear aliphatic monohydric alcohols C nH 2n +1OH (n = 2–14) and linear aliphatic monocarboxylic acids C nH 2n +1COOH (n = 1–13), from n -heptane and n -decane solutions (0.00005-0.03 molar fractions), onto α-Fe 2O 3 immobilized by photosynthetic membranes, prepared by photochemically grafting an epoxy-diacrylate copolymer onto cellulose, were measured. Langmuir-type treatment of data allowed us to calculate thermodynamic constants and adsorption heats for monolayer saturation, from which thermodynamic functions (free energy, enthalpy, and entropy) (saturated system as standard) were then computed. Mean areas occupied by adsorbed molecules in the monolayer coincided with those obtained for the unsupported sorbent, by allowing only about 20% of decrease of surface area, as a consequence of immobilization. Behaviour of immobilized sorbent is compared with that of ‘free’ α-Fe 2O 3. The sensitivity of adsorption measurements both to study configuration of adsorbed molecules, solvent-solute and solute-solute interactions