Crown Ether–SiO2–TiO2 Composites in the Sorption of Metal Ions from Acidic Aqueous Solutions

Abstract

Crown ether–SiO₂–TiO₂ composites were obtained by adding crown ethers (dibenzo-18-crown-6 or dibenzo-21-crown-7) during the sol–gel synthesis of SiO₂–TiO₂. The behavior of the composites in the sorption of several alkali, alkaline-earth, and rare-earth metal cations from acidic solutions was investigated. The crown ether–SiO₂–TiO₂ composites of the crown ethers showed higher efficiency and selectivity in the sorption of barium cations, as well as ytterbium cations in the presence of Sr(II), Ce(III), La(III), and Nd(III) compared to the parent crown ethers. It was established by FTIR spectroscopy that the crown ether molecule immobilized on the oxide surface has a distorted structure, which can explain the change in the selectivity of complex formation in going from crown ethers to their composites.