Hydrogel based on chitosan, itaconic acid and methacrylic acid as adsorbent of Cd2+ ions from aqueous solution

Abstract

A hydrogel has been synthesized by ionic crosslinking of chitosan (Ch) with itaconic acid (IA), followed by a free radical polymerization and crosslinking of Ch/IA network by adding methacrylic acid and the crosslinker. The resulting material (Ch/IA/MAA hydrogel) was characterized by spectral (Fourier transform infrared (FTIR)), thermal (thermogravimetric analysis (TGA)) and structural (SEM/EDX and atomic force microscopy (AFM)) analyses. The prepared hydrogel was investigated as potential adsorbent for removal of Cd2+ ions from aqueous solution. The effect of various physico-chemical parameters such as pH, adsorbent dosage, adsorbate concentration and contact time was studied in batch experiments. The results of spectral analyses of Cd-loaded hydrogel have shown that active functional groups are -NH2, -OH and -COOH. SEM/EDX analysis and AFM surface topography and phase images indicated that apart from the adsorption on the surface of the hydrogel, sorption takes place in the bulk, as well. The experimental kinetic and equilibrium data were better fitted by pseudo-second order kinetic model and Langmuir adsorption isotherm. The parameters obtained in thermodynamic studies showed that the adsorption of Cd2+ on Ch/IA/MAA hydrogel was spontaneous and exothermic in nature. Desorption studies were carried out using acid leaching (HNO3) and it has been shown that the regenerated hydrogel can be reused three times without any loss of adsorption capacity. The maximum adsorption of 285.7 mg/g has been obtained at pH 5.5 and the results of adsorption/desorption experiments implies that the Ch/IA/MAA hydrogel may be used as efficient sorbent for removal of Cd2+ ions from aqueous solution.