Bentonites with grafted aminogroups: Synthesis, protolytic properties and assessing Cu(II), Cd(II) and Pb(II) adsorption capacity

Abstract Bentonites with grafted methylaminopropyl (NHCH3-Bent), aminopropyl (NH2-Bent), ethylenediaminopropyl (En-Bent) and diethylenetriaminopropyl (Dien-Bent) groups were synthesized by silylation procedure. The successful covalent grafting of silylating agents on the bentonite was confirmed by 29Si NMR, FTIR and thermal analysis. The effects of polar (ethanol) and non-polar (dioxane) solvents on grafting process were compared. The samples prepared in ethanol showed the increase of d001 value from initial 1.44 nm to 1.63–2.05 nm proportionally to the loading amount of grafted silane. However, an almost constant value of d001 (1.96–2.10 nm) was observed for all samples obtained in dioxane, which may be related to more efficient intercalation of the nonpolar solvent. High concentration of grafted aminogroups (0.7–1.6 mmol g−1) resulted in almost four times increase of adsorption capacity of Cu(II), Pb(II) and Cd (II) ions (1.35–0.91 mmol g−1) compared to the initial bentonite (0.23–0.25 mmol g−1). The modification with aminosilanes shifted the affinity sequence of the initial bentonite Pb(II) > Cd(II) > Cu(II) to Cu(II) > Pb(II) > Cd(II).