Adsorption of 2,2'-dipyridyl onto silica modified by Cu2+ ions

The dependences of dipyridyl adsorption from solutions onto highly dispersed silica modified by Cu2+ ions on pH and dipyridyl concentration were studied. The data obtained were used for the determination of the compositions and stabilities of the ternary surface complexes which are formed in this system. Two methods were used for the calculations: one is based on material balance equations and the other is analogous to Bjerrum's method. The equilibrium constant of the reaction of the first dipyridyl molecule binding with Cu2+ ions on the surface (K-1) is greater than that of the second dipyridyl molecule (K-2), as is usually observed for complex formation in solutions. The difference between K-1 and K-2 depends on the concentration of Cu2+ ions on the surface.