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

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 Si-29 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 door 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 dm (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).