INFLUENCE OF THE NATURE OF ACTIVE SURFACE SITES OF HIGHLY DISPERSE OXIDES ON ADSORPTION OF HEAVY METAL IONS

摘要

Different surface sites of silica, alumina, titania, and related mixed oxides, and pre-adsorbed poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG), affect the interaction with Ni(II), Cd(II), and Pb(II) studied using adsorption and potentiometric titration methods. Bridging hydroxyls (Bronsted acid sites) capable of taking part in ion-exchange reactions, and pre-adsorbed polymers, enhance the adsorption of metal ions at pH < 7. At pH > 7 PVA adsorbed on silica slightly enhances the adsorption of metal ions but pre-adsorbed PEG gives the opposite result. PEG has only electron-donor functionalities (C-O-C) which reduce the number of possible adsorption sites. PVA has COH groups with both electron-donor and proton-donor properties, which can effectively interact with metal ions and their hydroxy species.