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

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 23 full factorial design. The responses were the adsorption amounts (nint), the adsorption energies (Qint) and the adsorption enthalpies (ΔintH). 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 nint, Qint and ΔintH. 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.

Immersion microcalorimetry was employed to obtain energetic parameters at chitosan/Cr(VI) interfaces from aqueous solutions. The interaction thermodynamics is affected by the interactive factors and not by temperature changes alone.Figure optionsDownload high-quality image (97 K)Download as PowerPoint slideResearch highlights
► The crosslinked chitosan beads have nearly spherical shape with few pores and smooth surface (average size of 0.90 ± 0.12 mm).
► The asymmetric shapes of the calorimetric plots suggest heterogeneity of the adsorption sites of chitosan.
► The initial Cr(VI) concentration in solution was the most important parameter in all responses evaluated by factorial design.
► All thermodynamic responses (adsorption energies and adsorption enthalpies) are all exothermic in nature.
► Binary and ternary effects were very important in the factorial analysis of the adsorption thermodynamic parameter.