Adsorption of reactive dye onto cross-linked chitosan/oil palm ash composite beads

Adsorption of reactive dye from aqueous solution onto cross-linked chitosan/oil palm ash composite beads (CC/OPA) was investigated in a batch system. Kinetic and isotherm studies were carried out by considering the effects of various parameters, such as initial concentration (50-500 mg/L), contact time, pH (2-13), and temperature (30,40, 50 degrees C). It was found that the dye uptakes were much higher in acidic solutions than those in neutral and alkaline conditions. Langmuir, Freundlich, Redlich-Peterson, and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The Redlich-Peterson isotherm fits the experimental data significantly better than the other isotherms. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed a pseudo-second-order model. The pseudo-first-order and pseudo-second-order rate constants for different initial concentrations were evaluated and discussed. Thermodynamic parameters such as standard Gibbs free energy (Delta G degrees), standard enthalpy (Delta H degrees), and standard entropy (Delta S degrees) were evaluated by applying the Van't Hoff equation. The thermodynamics of reactive dye adsorption onto cross-linked chitosan/oil palm ash composite beads indicates its spontaneous and endothermic nature. (c) 2007 Elsevier B.V All rights reserved.