Porous thiourea-grafted-chitosan hydrogels: Synthesis and sorption of toxic metal ions from contaminated waters

Novel adsorbents based on chitosan and its derivatives are continuously developed to remove heavy metal ions and organic pollutants from contaminated waters. In this study, porous hydrogels based on chitosan functionalized with thiourea groups (CHITU) were prepared through cryogelation technique and were evaluated for the sorption of Cu2+, Cd2+, Co2+ and Ni2+ from simulated contaminated waters. The CHITU hydrogels were characterized by FTIR, NMR, SEM, EDX, TGA and rheology measurements, while their heavy metal ions sorption capacity was determined using ICP-OES. The maximum experimental adsorption capacities of CHITU hydrogels towards Cu2+, Cd2+, Co2+ and Ni2+ were 129.8 mg/g, 134 mg/g, 83.4 mg/g and 132.5 mg/g (experimental conditions: temperature = 25 °C, contact time =24 h and pH = 5), respectively. The fitting of equilibrium and kinetics sorption data with various empirical models gave evidence that the sorption process of all metal ions was best described by the Sips and pseudo-second order models, respectively. Reutilization of CHITU hydrogels in three consecutive sorption/desorption/regeneration cycles showed that they possess completely renewable sorption properties. In comparison with other literature available on CHI-based sorbents, the CHITU hydrogels designed herein have similar sorption properties for Cu2+, but superior sorption properties for Co2+, Cd2+ and Ni2+. Hence, they can be considered as promising matrices for the removal of various heavy metal ions from contaminated waters.