Interactionof divalent cations Zn,Cd and Hg on surface of silica gelwith aminoethanethiolas evaluated by calorimetric titration

Calorimetric titration was applied to study the interaction of zinc, cadmium and mercury on surface of silica gel modified with 2-aminoethanethiol, using 3-chloropropyltrimetoxysilane as precursor silylating agent. The anchored Sil–SNH₂ surface gave 0.70 mmol g^–1 of molecules covalently bonded per gram of silica. This surface displayed a chelating moiety containing sulfur and nitrogen basic centers, which are potentially capable of extracting cations from aqueous solutions, such as MCl₂ (M=Zn, Cd, Hg). This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. The data were adjusted to modified Langmuir equation. The sequence of the maximum retention capacity was Hg>Cd>Zn. The processes of cation interactions showed exothermic enthalpies. The calculated ΔG values are in agreement with the spontaneity of the proposed reactions and conformed to the values found by using Langmuir model applied to these systems. The endothermic entropic values, as expected, indicated that the reactions are favorable.