Calorimetric investigation of metal ion adsorption on 3-glycidoxypropyltrimethylsiloxane + propane-1,3-diamine immobilized on silica gel

The silylant precursor agent 3-glycidoxypropyltrimethoxysilane was covalently anchored onto a silica gel surface followed by propane-1,3-diamine molecule incorporation using a heterogeneous route (SiHT). On another series, the precursor agent was previously reacted with diamine to give the silylant agent in homogeneous condition, before immobilization (SiHM). The degrees of immobilization were 0.80 and 1.53 mmol g−1 for SiHT and SiHM, respectively. Both grafting surfaces were employed to extract the divalent cations nickel, copper, cobalt and zinc from aqueous solutions. This cation/nitrogen interactive process was calorimetrically followed to give exothermic enthalpy, negative free Gibbs energy and positive entropy values. These favorable thermodynamic data are more pronounced for copper on both surfaces, with a higher tendency for SiHM, due to the larger amount of available nitrogen atoms in the pendant chain covalently attached to the inorganic silica backbone.