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 °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 (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) 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.