Sorption of Rare Earth Cations by SiO2–TiO2-Crown Ether Composites

Abstract

The immobilization of crown ethers (dibenzo-18-crown-6, dibenzo-21-crown-7, dibenzo-24-crown-8) during the sol–gel synthesis of mixed oxides SiO₂–TiO₂ is used to obtain composites that firmly hold an organic molecule in an inorganic matrix, as is confirmed via IR spectroscopy and elemental analysis. The properties of sorption with respect to rare earth element (REE) cations are studied under acidic and neutral conditions. The efficiency (S, %) and capacity (Q, mg/g) of sorption grow substantially upon moving from the initial oxides and crown ethers to their composites. The sorption of REE cations from dilute solutions (2 × 10⁻⁴ mol/dm³) is found to be 89.1–95.1% for composite dibenzo-18-crown-6–SiO₂–TiO₂, whose sorption capacity for concentrated solutions of rare earth elements (0.1 mol/dm³) is 6.1–34.5 mg/g. The sorption of lanthanum cations by composite dibenzo-18-crown-6–SiO₂–TiO₂ is studied using the isothermal Langmuir (R² = 0.9915), Freundlich (R² = 0.8745), Temkin (R² = 0.9506), and Dubinin–Radushkevich (R² = 0.9754) models.