Kinetics and thermodynamics of indanthrene textile dye adsorption onto chitosan

Abstract

The kinetics and equilibrium of Indanthrene Olive Green (IOG) adsorption on chitosan, from aqueous solutions, have been investigated. The chitosan was characterized by XRD, average degree of deacetylation (DD), TGA/DTG, IR, SEM and specific BET surface area. Batch adsorptions experiments were carried out in different pH and dye concentration. An acidic pH condition (4.0 to 6.0) was favorable to the adsorption process. The adsorption followed second-order rate kinetics and the experimental equilibrium data followed Langmuir isotherm, suggesting that chemisorption might be the major adsorption mode. The adsorptions also occurred on chitosan fibers, being significantly lower than that of crushed chitosan. Thermodynamic parameters (δG°, δH°, and δS°) were calculated. The positive values of δH° (161.7 kJ mol-1) and 7delta;S° (559.9 J mol-1 k-1) suggest that the adsorption is endothermic and that during this adsorption process the randomness of the system increases. A simplified adsorption model is also proposed.