Natural zeolite modified with 4-(3-triethoxysilylpropyl) thiosemicarbazide as an effective adsorbent for Cu(II), Co(II) and Ni(II)

Background Natural zeolite heulandite (ZH) has been functionalized with 4-(3-triethoxysilylpropyl)- thiosemicarbazide (TSC) to increase the adsorption capacity of Cu(II), Co(II), and Ni(II) ions. Methods The functionalization is confirmed by nitrogen adsorption/desorption (BET), XRD, 1H, 13C NMR, FT-IR, and SEM-EDX techniques. The thermal stability of the modified zeolite is investigated by the TGA-DSC method. The adsorption of Cu(II), Co(II), and Ni(II) ions with the modified zeolite (ZH-TSC) is studied in one- and multi-ionic aqueous solutions with pH = 5.0. Significant findings The functionalization is accompanied by the significant structural changes in the surface of the zeolite. Grafting of TSC onto the zeolite decreases specific surface area and specific volume of pores and micropores of the material, the zeolite surface becoming more uniform and less porous. The adsorption capacity of ZH-TSC is found to be 0.46 mmol/g (29.5 mg/g), 0.42 mmol/g (24.9 mg/g) and 0.28 mmol/g (16.6 mg/g) for Cu(II), Co(II) and Ni(II), respectively. The adsorption of heavy metal ions on the surface of the modified zeolite ZH-TSC is mainly contributed by the formation of chelate complexes due to the donor-acceptor interaction of metal ions with nitrogen and sulfur atoms of the thiosemicarbazide fragment. Localization of Ni, Co, Cu coincides with the position of the coordination centers. Modified zeolite ZH-TSC can be used in environmental science, engineering, or medicine as an effective adsorbent/entero(hemo) adsorbent of heavy or toxic metals.