Adsorption of 1,10-phenanthroline on montmorillonites|poly(vinyl alcohol) complexes as a function of pH

Adsorption of 1,10-phenanthroline (OP) was studied on calcium (Ca−Mt) and sodium (Na−Mt) montmorillonites and on samples of these containing different quantities of adsorbed poly(vinyl alcohol) (PVA): Ca−Mt/PVA1, 230, Ca−Mt/PVA2, 300 and Na−Mt/PVA, 590 mg/g, as a function of the OP concentration and the pH of the dispersions. The Langmuir and Freundlich equations were used to analyze the adsorption isotherms. Since OP adsorption on these materials is very dependent on the pH, the maximum adsorption values were determined at pH 4, 6 and 8. OP adsorption on Ca−Mt at pH 8 is of the same magnitude as at pH 6, whereas on Ca−Mt/PVA1 and Ca−Mt/PVA2 adsorption decreases in direct proportion to the quantity of PVA on the surface. PVA adsorption on Ca−Mt does not give rise to the formation of a material of exfoliated structure. Such structure is formed on Na−Mt/PVA, which has an OP adsorption isotherm fitting the Langmuir equation with a maximum OP adsorption of 3.57 mmol/g, and also the Freundlich equation, showing it to be a more complex system than in the presence of a divalent cation like Ca2+. The isotherm can also be fitted to the Freundlich equation of adsorption, just like Na−Mt/PVA, whose distribution coefficient decreases at the pH increases.