Adsorption of anionic dyes in acid solutions using chemically cross-linked chitosan beads

Abstract

One kind of adsorbents with high adsorption capacity of anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption of four reactive dyes (RB2, RR2, RY2, RY86), three acid dyes (AO12, AR14, AO7) and one direct dye (DR81) from aqueous solutions by the cross-linked chitosan beads. The adsorption capacities had very large values of 1911–2498 (g/kg) at pH 3–4, 30 °C, which were 3.4–15.0 and 2.7–27.4 times those of the commercial activated carbon and chitin, respectively. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir model agreed very well with experimental data ( R 2 > 0.9893). The kinetics of adsorption, the ADMI color value and decolorization efficiency for different initial dye concentrations were evaluated by the pseudo first-order and second-order models. The data agreed very well with the pseudo second-order kinetic model. The adsorption capacity increased largely with decreasing solution pH and adsorbent dosage. The free energy changes Δ G 0 for adsorption of anionic dyes in acidic solutions at 30 °C were evaluated. The negative values of Δ G 0 indicate overall adsorption processes are spontaneous.