Sorbent concentration effect on adsorption of methyl orange on chitosan beads in aqueous solutions

Abstract

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(cs) on the adsorption equilibration of MO on CS beads. An obvious cs-effect was observed in the adsorption equilibration, i.e., the adsorption amount(Γ) was declined with cs increase. The classical Langmuir model adequately described the adsorption isotherm for each given cs. However, it could not be used to predict the cs-effect observed. The applicability of the Langmuir-SCA isotherm, a surface component activity(SCA) model equation, to fit the cs-effect data was examined. In the SCA model, the activity coefficient of sorbent surface sites, \(f_{H_2 O}^s \), was assumed to be a function of cs 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 cs-effect observed under the studied conditions. Furthermore, the effects of temperature(t), pH, and electrolyte(NaNO3) concentration(\(c_{NaNO_3 } \)) on \(f_{H_2 O}^s \) were examined. The results show that \(f_{H_2 O}^s \) clearly decreased with increasing t(20–35 °C) and pH(5–8), but no obvious change in \(f_{H_2 O}^s \) was observed as \(c_{NaNO_3 } \) varied in a range 0.001–0.010 mol/L. These results give a better understanding of the cs-effect.