Simulation of adsorption equilibria on hybrid materials: Binding of metal chlorides with 3- n-propylpyridinium silsesquioxane chloride ion exchanger

The quantitative description of cooperativity effects at binding of low-molecular reagents with active reactive centers of hybrid materials requires the elaboration of convenient and reliable meaningful models and calculation procedures. The model of fixed polydentate centers was analyzed as a prospective tool for simulation of adsorption equilibria. The model was shown to be flexible and adaptive. At the theoretic foundations, it is equivalent or more general as compared with another approaches. The procedure for constructing the models fitting the experimental data within their errors and the corresponding calculation tools were discussed. The special attention was paid to the problem of simultaneous determination of sorption capacities and equilibrium constants. To overcome this difficulty the strategy involving the fuzzy sets theory was proposed. The elaborated methods were used to characterize a new material, 3- n-propylpyridinium silsesquioxane chloride ion exchanger. Adsorption of Fe(III), Cu(II), Zn(II), Cd(II), and Hg(II) chlorides by the material from ethanol solutions was studied at 298 K. The material was found to possess a high affinity to metal chlorides. The sorption capacities of the material and the constants of adsorption equilibria were determined. The material demonstrates the following order of affinity: FeCl 3 > CuCl 2, HgCl 2 > CdCl 2 > ZnCl 2. On the base of simulation, the negative cooperativity in the case of the CuCl 2 adsorption was concluded, while adsorption of other chlorides is accompanied by the positive cooperativity. Experimental (points) and simulated (lines) isotherms for CdCl 2 adsorption. Fixed tetradentate centers (solid line) and fixed bidentate centers (dotted line).