Development of maghemite nanoparticles supported on cross-linked chitosan (γ-Fe2O3@CS) as a recoverable mesoporous magnetic composite for effective heavy metals removal

A mesoporous magnetic composite, gamma-Fe2O3-functionalized cross-linked chitosan (gamma-Fe2O3@CS), was developed as an efficient adsorbent to remove cadmium (Cd2+) ions from contaminated water media. The as-prepared composite was characterized by FESEM, TEM, EDS, VSM, BET and XRD techniques. Several parameters affecting the removal efficiency including surface area, solution pH, contact time, adsorbent dose, initial Cd2+ concentration and temperature were evaluated and discussed. The average crystallite size of gamma-Fe2O3 was found to be 26.5 nm. The highest magnetization saturation of adsorbent was 25.1 emu/g. The adsorption rate belonged gamma-Fe2O3@CS composite was much higher than that gamma-Fe2O3 and CS, which reflects a synergistic effect between the maghemite and CS particles on the removal of Cd2+. Based on the adsorption capacity normalized by surface area, the value of Cd2+ adsorbed on adsorbents follows the order of gamma-Fe2O3@CS > CS > gamma-Fe2O3. The equilibrium time was 60 min and the monolayer maximum adsorption capacity was found to be 15.2 mg/g. Under optimized experimental conditions, complete removal of 5 mg/L of Cd2+ was achieved. Cycling tests revealed that gamma-Fe2O3@ CS was recyclable to remove Cd2+ ions during five consecutive cycles and the removal efficiency still remains at 783%. Kinetic and isotherm of adsorption were in good agreement with pseudo-second-order and Langmuir models, respectively. The adsorption process was endothermic and spontaneous in nature. Cd2+ adsorption mechanism on gamma-Fe2O3@CS follows ion-exchange and monolayer chemical adsorption. (C) 2017 Elsevier B.V. All rights reserved.