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

Abstract

A mesoporous magnetic composite, γ-Fe2O3-functionalized cross-linked chitosan (γ-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 γ-Fe2O3 was found to be 26.5nm. The highest magnetization saturation of adsorbent was 25.1emu/g. The adsorption rate belonged γ-Fe2O3@CS composite was much higher than that γ-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 γ-Fe2O3@CS>CS>γ-Fe2O3. The equilibrium time was 60min and the monolayer maximum adsorption capacity was found to be 15.2mg/g. Under optimized experimental conditions, complete removal of 5mg/L of Cd2+ was achieved. Cycling tests revealed that γ-Fe2O3@CS was recyclable to remove Cd2+ ions during five consecutive cycles and the removal efficiency still remains at 78.3%. 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 γ-Fe2O3@CS follows ion-exchange and monolayer chemical adsorption.