Preparation of ion-imprinted silica gels functionalized with glycine, diglycine, and triglycine and their adsorption properties for copper ions

We report a new procedure for modifying the surface of silica gels with glycine, diglycine, and triglycine in the presence of copper ions to create a new type of copper-imprinted sorbent, which exhibits a high adsorption capacity and selectivity for copper ions. Our results show that copper adsorbed onto the copper-imprinted silica gel is 50% higher than that on nonimprinted silica gel at pH 4.5. The high adsorption capacity observed for the copper-imprinted silica gel is attributed to the stable copper complexes formed with two adjacent glycine, diglycine, or triglycine molecules with proper intermolecular distances obtained from the ion-imprinting procedure. Another possible reason for the high adsorption capacity is that the ion-imprinting procedure prevents the surface from being overcrowded; therefore, copper ions can form very stable 1:1 complexes with immobilized diglycine or triglycine. Interestingly, the imprinting effect is even more pronounced when the adsorption experiments are conducted in the presence of competing metal ions such as magnesium and calcium. The copper-imprinted silica gel exhibits a higher adsorption capacity than does the nonimprinted silica gel for all pH values, even when the concentrations of magnesium and calcium are 50 and 76 times higher than the concentration of copper.