Direct determinations of energetic parameters at chitosan/Cr(VI) interfaces by means of immersion heat-conduction microcalorimetry

Abstract

Interaction parameters at epichlorohydrin-crosslinked chitosan beads/Cr(VI) interfaces from aqueous solutions was obtained by using immersion heat-conduction microcalorimetry. This technique permits simultaneous determinations of adsorbed amounts and interaction energies. The experimental variables evaluated were pH of the Cr(VI) solutions of 4.0 and 6.0, initial Cr(VI) concentration in solution of 0.50 and 5.00 × 10(-3) mol L(-1) and temperature of 25 and 45 °C. The calorimetric results were evaluated using a 2(3) full factorial design. The responses were the adsorption amounts (n(int)), the adsorption energies (Q(int)) and the adsorption enthalpies (Δ(int)H). The results indicated that all thermodynamic responses (adsorption energies and adsorption enthalpies) are all exothermic in nature. The initial Cr(VI) concentration in solution was the most important parameter in all responses evaluated in this study. Polynomial fits have pointed out that almost all interactive effects are statistically important on the values of n(int), Q(int) and Δ(int)H. It is concluded that the thermodynamical aspects of the Cr(VI) adsorption parameters are greatly influenced by the interactive factors and not by temperature changes alone.