Sorption of acid dyes onto GLA and H2SO4 cross-linked chitosan beads

The feasibility of chitosan and cross-linked chitosan beads as efficient adsorbents for the removal of Acid Blue 25 (AB 25) and Acid Red 37 (AR 37) from aqueous solution was studied by using batch adsorption techniques. Glutaraldehyde (GLA) and sulphuric acid were employed as cross-linking reagents. The effect of process parameters like pH, agitation period, agitation rate and concentrations of dyes on the extent of AR 37 and AB 25 adsorption by chitosan and cross-linked chitosan beads was investigated. The best interpretation for the equilibrium data was given by the Langmuir isotherm, while the pseudo-second-order kinetic model could best describe the adsorption of these acid dyes. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were estimated and adsorption process was spontaneous and exothermic. The desorbed chitosan, chitosan–GLA and chitosan–H2SO4 beads can be reused to adsorb the acid dyes. Results also showed that chitosan, chitosan–GLA and chitosan–H2SO4 beads were favourable adsorbers.