Improved adsorption performance of activated carbon covalently functionalised with sulphur‑containing ligands in the removal of cadmium from aqueous solutions

Cadmium is a heavy metal that has high toxic potential. Biological absorption of cadmium can cause severe disease. Cadmium ions are frequently removed from the aqueous environment via adsorption. In this paper, commercially available granular activated carbon (AC) was covalently functionalised with three sulphur-containing ligands—thiodiglycol, thiourea and cysteine. The ligands were introduced in order to improve adsorption capacity for the removal of cadmium ions from aqueous solutions. The AC functionalised with cysteine and thiourea had twice the adsorption capacity of Cd(II) than the pristine AC. The introduction of sulphur-containing ligands also improved the adsorption kinetics, i.e. the adsorption kinetic rates were ca. 2–10 times higher than the pristine AC. This enhancement of the adsorption performance was systematically studied in terms of morphology, texture, structural features, the content of sulphur-containing ligands and surface chemistry.