Calorimetric study of amino modified talc matrices and copper salts. An evidence of the chelate effect

The surface of natural talc was modified with organosilanes (H3CO)(3)SiR, for R= -(CH2)(3)NH2, -(CH2)(3)NH(CH2)(2)NH2 and -(CH2)(3)NH(CH2)(2)NH(CH2)(2)NH2, resulting in the inorganic-organic hybrids TC1, TC2 and TC3. These aminated talcs contain 4.38, 2.56 and 2.03 mmol g(-1) of immobilized organic chains for TCx (x=1 to 3), respectively. The chemisorption isotherm data obtained by a batchwise process were adjusted to a modified Langmuir equation, to give the maximum adsorption capacity TC1 > TC2 > TC3. The chelate effect was illustrated through calorimetric titration, giving the highest enthalpic values for TC2 and TC3 hybrids and favoured for sulfate counter anion. The enthalpic and entropic values indicated favourable reaction between copper-basic nitrogen center atoms on pendant chain covalently bonded to the inorganic backbone.