Kinetics, Isotherm and Thermodynamic Studies of the Adsorption of Reactive Red 239 Dye from Aqueous Solution by Chitosan 8B

The adsorption of reactive red 239 (RR239) dye onto chitosan 8B was studied in aqueous solution at various pHs, initial dye concentrations, ionic strengths and temperatures, respectively. The adsorption of dye onto chitosan 8B was confirmed by diffuse reflectance electronic absorption spectra. The adsorption of RR239 onto chitosan 8B was greatly influenced by solution pHs, initial dye concentrations, ionic strengths and temperatures. The kinetics and mechanism of dye adsorption process were analyzed by pseudo first-, second-order, Elovich and intraparticle diffusion kinetic models. The adsorption kinetics of RR239 dye followed a pseudo second-order model very well. The surface sorption and intraparticle diffusion mechanisms were involved in the actual sorption process. The equilibrium isotherm data were fitted well with the Langmuir model rather than the Freundlich, Temkin and Dubinin-Radushkevich models. The maximum dye adsorption onto chitosan 8B was estimated to be 163.93 μmol/g at 45°C. The activation energy (Ea) was obtained to be 23.30 kJ/mol. The computed thermodynamic parameters such as ΔG, ΔH, ΔS, ΔG, ΔH and ΔS confirmed that the adsorption of RR239 dye onto chitosan 8B was a spontaneous endothermic physisorption process. Desorption test was carried out in NaOH solution (pH 12.5) and the chitosan flakes could be reused.