Kinetics and thermodynamics of β-carotene and chlorophyll adsorption onto acid-activated bentonite from Xinjiang in xylene solution

Abstract

The kinetics and thermodynamics of β-carotene and chlorophyll adsorption from xylene solution onto acid-activated bentonite (AAB) within the temperature range 65–95 °C were investigated. Adsorption of β-carotene was described well with the Langmuir isotherm, whereas chlorophyll adsorption was determined well with the Freundlich isotherm, and the experimental data on chlorophyll adsorption were also fitted by the Langmuir isotherm to a certain extent, as reflected by correlation coefficients ( R 2) over 0.9865. In addition, the adsorption of β-carotene and chlorophyll onto AAB are favorable. The pseudo-second-order model was found to explain the kinetics of adsorption of both pigments more effectively. Increase of temperature enhanced the adsorption rate and equilibrium adsorption capacity of β-carotene and chlorophyll on AAB. The activation energy for the sorption of β-carotene and chlorophyll on AAB was 19.808 kJ/mol and 16.475 kJ/mol, respectively. The thermodynamic parameters Δ H θ, Δ S θ and Δ G θ, computed from K F of the adsorption isotherm constant, were 21.766 kJ/mol, 92.244 J/K mol and −9.554 kJ/mol respectively for the adsorption of β-carotene on AAB at 65 °C, and for adsorption of chlorophyll on AAB at 65 °C were 31.051 kJ/mol, 93.549 J/K mol and −0.729 kJ/mol, respectively. The adsorption of β-carotene and chlorophyll in xylene solution on AAB was a spontaneous and endothermic process with increasing in the randomness at the solid–solution interface.