Epoxide silylant agent ethylenediamine reaction product anchored on silica gel – thermodynamics of cation–nitrogen interaction at solid/liquid interface

The silylant agent 3-glycidoxypropyltrimethoxysilane has the epoxide ring opened by incorporating an ethylenediamine molecule under homogeneous conditions, to yield a new silylant agent, which is then anchored on silica gel. Based on nitrogen elemental analysis a large degree of immobilization gives 1.59 mmol g−1, and consequently, a drastic decrease in surface area of the original silica from 420.8 ± 3.4 to 70.6 ± 0.5 m2 g−1 is observed for the immobilized surface. The basic centers attached on pendant groups have the capacity to extract cations from aqueous solution, whose adsorption process is adjusted to the Langmuir model. Similar profiles of adsorption were obtained on the isotherms with values 3.06, 2.91, 1.57 and 1.24 mmol g−1 in the maximum of the curves for copper, cobalt, zinc and nickel, respectively. Thermodynamic data were obtained from calorimetric titration, indicating a spontaneity of these interactive reactions, caused by the favorable exothermic enthalpy due to the cation/basic center interaction in the solid/liquid interface and endothermic entropy originating from the increase in free water molecule content in the medium, which were displaced from the anchored surface, and the cation desolvation process, as the bond is formed.