Sorbent Concentration Effect on Adsorption of Methyl Orange on Chitosan Beads in Aqueous Solutions

The adsorption of methyl orange(MO) on chitosan(CS) beads in aqueous solutions was investigated by a batch equilibration technique. Special emphasis was focused on the effect of sorbent concentration(c_s) on the adsorption equilibration of MO on CS beads. An obvious c_s-effect was observed in the adsorption equilibration, i.e., the adsorption amount(Γ) was declined with c_s increase. The classical Langmuir model adequately described the adsorption isotherm for each given c_s. However, it could not be used to predict the c_s-effect observed. The applicability of the Langmuir-SCA isotherm, a surface component activity(SCA) model equation, to fit the c_s-effect data was examined. In the SCA model, the activity coefficient of sorbent surface sites,ƒ_H2O^s,was assumed to be a function of c_s due to the deviation of a real adsorption system from an ideal one, arisen from sorbent particle-particle interactions in real systems. The results show that the Langmuir-SCA isotherm could accurately describe the c_s-effect observed under the studied conditions. Furthermore, the effects of temperature(t), pH, and electrolyte(NaNO₃) concentration(c_NaNO3) on ƒ_H2O^s were examined. The results show that ƒ_H2O^s clearly decreased with increasing t(20-35℃) and pH(5-8), but no obvious change in ƒ_H2O^s was observed as c_NaNO3 varied in a range 0.001-0.010 mol/L. These results give a better understanding of the c_s-effect.