Developing thiosemicarbazide-modified/ion-imprinted chitosan for selective cadmium ion biosorption

To ensure environmental and industrial sustainability, cadmium ions (Cd(II)) must be extracted from effluents. However, high-efficiency Cd(II) extraction remains elusive due to issues with slow rates and low selectivity. An ion-imprinting method was used in this study to imprint Cd(II) onto a thiosemicarbazide-chitosan derivative (TCCS) synthesized via an unconventional synthetic route. Following the amide bond formation between cyanoacetyl units and chitosan, thiosemicarbazide was used to modify the –CN residues to obtain the desired TCCS derivative. After that, the Cd(II) ions were coordinated with the TCCS before being cross-linked with epichlorohydrin (ECH) and eluted by a H+/EDTA solution, leaving rigid coordination cavities. The developed Cd-TCCS was able to preferentially identify Cd(II) when compared to non-imprinted sorbent, resulting in significantly higher adsorption capabilities (qm = 305 ± 1 mg/g) and enhanced adsorption selectivity. Also, the pseudo-second-order kinetics model was a good fit for the data, indicating that adsorption is mainly mediated by chemisorption or coordination mechanisms, which were confirmed by the FTIR and XPS investigations. This study expands our understanding of the factors that influences the biosorption of Cd(II) from aqueous media and gives a direction for the development of novel biosorbents with high capacity and excellent selectivity.