Hierarchically Imprinted Sorbents for the Separation of Metal Ions

Abstract

Molecular imprinting involves arranging monomers of polymerization synthesis around a template molecule so that complexes between the monomer and template molecules are formed. Subsequent polymerization of the monomer molecules results in trapping template molecules in a highly cross-linked amorphous polymer matrix. Extraction of the imprint molecules leaves a predetermined arrangement of ligands and a tailored binding pocket. Such imprinted polymers have been used to mimic antibody functions to resolve racemates, and to separate mixtures of metal cations. Thus far, the organization of precursor monomers has been achieved mainly in inhomogeneous organic polymer matrices, with little control over structural parameters, such as pore sizes and surface areas. The authors report the first synthesis of imprinted hybrid sorbent materials with precise control of not only adsorption sites but also pore structures. The concepts behind multilevel imprinting are as follows. Surfactant micelles and metal ions both act as templates in these hierarchically imprinted sorbents. The metal ion and the surfactant are removed from the silica matrix via acid leaching and ethanol extraction, respectively. This results in the formation of different-sized imprints within the silica matrix, each with a specific function.