Adsorption of metal ions on novel 3-n-Propyl(Methylpyridinium) silsesquioxane chloride polymers surface. Study of heterogeneous equilibrium at the solid-solution interface

Abstract

Polymers Si3Py+Cl- (A) and Si4Py+Cl- (B), 3-n-propyl(3-methylpyridinium)silsesquioxane and 3-n-propyl(4-methylpyridinium)silsesquioxane chlorides, respectively, were prepared by the sol-gel processing method. The ion exchange capacities (mmol g-1) were 0.90 and 0.81 for (A) and (B) respectively. Considering the reaction nSiPy+Cl-(s) + M2+(sln) + 2Cl-(sln) (SiPy+)nMCl2+nn-(s), the values of the stepwise equilibrium constants obtained were: (A) CuII: logK(2)1= 4.14(0.03), logK(2)2= 2.91(0.04); ZnII, logK(2)1= 3.3(0.3), logK(2)2= 4.9(0.3); (B) CuII: logK(2)1= 3.82(0.03), logK(2)2= 3.00(0.04); ZnII, logK(2)1= 3.93(0.03), logK(2)2= 3.55(0.08), being K(2)1 and K(2)2 the equilibrium constants for adsorption of the species MCl42- and MCl3-, respectively. For adsorption of ZnII on Si3Py+Cl-, K(2)2 > K(2)1, indicating positive cooperativity, i.e., the adsorption of MCl42- enhances the adsorption of MCl3- species on the adsorbent surface. For the other cations, K(2)1 > K(2)2, indicating that adsorption of MCl42- depresses the adsorption of MCl3- species, indicating negative cooperativity. © 2009 Sociedade Brasileira de Química.