Synthesis and characterization of magnetic carboxymethyl chitosan-poly(acrylic acid-itaconic acid) hydrogel for the efficient adsorption of malachite green

A new type of magnetic hydrogel (Fe3O4/CMC-co-p[AA-IA]) adsorbent was synthesized using magnetic carboxymethyl chitosan (CMC) matrix with acrylic acid and itaconic acid monomers by radical graft copolymerization and it was applied to the adsorption of malachite green (MG) aqueous solution. The chemical structural characteristics of hydrogel adsorbent were characterized by Fourier transform infrared spectra (FT-IR), scanning electrons microscope (SEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and X-ray diffraction (XRD). These characteristics revealed that acrylic acid and itaconic acid monomers were successfully grafted onto the CMC backbone. Hydrogel adsorbent in deionized water has an excellent swelling ratio. To optimize the effect of various factors including pH, adsorbent dosage, ionic strengthen, initial concentration, contact time, and temperature on the adsorption capacity of MG dye were investigated in a batch. The adsorption equilibrium in the adsorption process follows the Langmuir isotherm adsorption and belongs to the monolayer adsorption. For describing the adsorption kinetics of MG dye, the pseudo-second-order kinetic model is more suitable appropriately than the pseudo-first kinetic model. The thermodynamics model shows that the adsorption process is endothermic and spontaneous. After five cycles of adsorption and desorption, the hydrogel adsorbent also has better adsorption efficiency. These results show that the adsorbent has a better swelling capacity and a better adsorption performance.