Synthesis of 4-acylpyrazolone Schiff base ligand grafted silica and selectivity in adsorption of lanthanides from aqueous solutions

The Schiff base form of the 4-acylpyrazolone ligand was immobilized on the silica surface by reaction of 3-aminopropyl silica with 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one in 97% yield, producing grafted silica with 0.77 mmol/g ligand loading. This surface modified silica was shown to be selective in the adsorption of Yb³⁺ ions from dilute aqueous solutions, for which 98% adsorption was observed from a 1.0×10⁻⁵ mol/L aq. solution at pH 6.7, after 24 h at room temperature. Six other lanthanides studied Eu³⁺, Gd³⁺, Nd³⁺, Tb³⁺, Sm³⁺ and La³⁺ showed moderate to weaker adsorptions of 39%, 28%, 16%, 12%, 11% and 5% respectively under similar conditions.