Adsorption on Na-Montmorillonite of 1,10-Phenanthroline and Quinoline in Single and Binary Aqueous Solution

Abstract

Abstract The adsorption of single aqueous solutions and binary mixtures of 1,10-phenanthroline (OP) and quinoline (Q) on Na-montmorillonite was studied. The isotherms were obtained at 28°C and pH = 11. 1,10-phenanthroline showed a higher values of adsorption on the clay (2.213mmol/g) than quinoline (1.577mmol/g). On the basis of these values a specific surface of 799.6m2/g was determined on the montmorillonite for OP adsorption and 555.6m2/g for Q. 1,10-phenanthroline shows a higher affinity for the clay surface than quinoline, both in pure solution and in binary mixture, especially at low equilibrium concentrations. In the mixtures with an initial concentration of 1:1, the isotherm of OP adsorption can be fitted to the Langmuir equation and reaches a maximum adsorption of 1.810mmol/g, whereas in the case of Q the adsorption isotherm fits the Freundlich equation. Based on the free area unoccupied by OP molecules, and assuming re-accommodation of the aromatic ring on the surface of the clay, the maximum adsorption of Q at this concentration was calculated to be 0.827mmol/g. The diminishing maximum adsorption of OP at other concentrations in the presence of a constant quantity of Q on the surface corresponds to a quadratic equation as a function of the quantity of quinoline adsorbed.The obtained data could not be fitted to the competitive Langmuir adsorption model or to the two- or multi-surface Langmuir models, since adsorption of Q in aqueous solutions with OP does not correspond to the classic Langmuir equation.