Adsorption of acid dyes from aqueous solutions by the ethylenediamine-modified magnetic chitosan nanoparticles

The adsorption characteristics of Acid Orange 7(AO7) and Acid Orange 10 (AO10) from aqueous solutions onto the ethylenediamine-modified magnetic chitosan nanoparticles (EMCN) have been investigated. The EMCN were essentially monodispersed and had a main particle size distribution of 15-40 nm and saturated magnetization of 25.6 emu/g. The adsorption experiments indicated that the maximum adsorption capacity occurred at pH 4.0 for AO7 and pH 3.0 for AO10, respectively. Due to the small diameter and the high surface reactivity, the adsorption equilibrium of AO7 and AO10 onto the EMCN reached very quickly. Equilibrium experiments fitted well with the Langmuir isotherm model, and the maximum adsorption capacity of the EMCN at 298 K was determined to be 3.47 mmol/g for AO7 and 2.25 mmol/g for AO10, respectively. Thermodynamic parameters such as enthalpy change (ΔHo), free energy change (ΔGo) and entropy change (ΔSo) were estimated and the results indicated that the adsorption process was spontaneous and exothermic. Furthermore, the EMCN could be regenerated through the desorption of the dyes in NH4OH/NH4Cl solution (pH 10.0) and could be reused to adsorb the dyes again.