Enhanced ionic recognition by a functionalized mesoporous sol-gel: Synthesis and metal ion selectivity of diaminoethane derivative

A newly developed double-imprinting methodology was extended to synthesize mesoporous sol-gels that contain a diaminoethane functional group. Formation of a bis[(3- trimethoxysilyl)propyl] ethylenediamine metal complex, followed by hydrolysis and condensation with tetraethylorthosilicate in the presence of dodecylamine surfactant resulted in the formation of the solid xerogel. Acid washing protonated the amino groups that release the metal ions. This resulted in the formation of binding sites that are uniquely designed with the coordination environment the metal ion prefers. Mesopores were formed by the extraction of the surfactant micelles to give this material relatively large surface areas and good mass-transfer characteristics. A copper (II) imprinted gelshowed significantly more enhancement of copper (II) uptake capacities at various concentrations than did a nonimprinted gel made without the metal ion template. The imprinted material also exhibited improved selectivity for removal of copper (II) from Cu²⁺-Zn²⁺ aqueous solutions. A sample of the copper imprinted sorbent, which absorbed a total of 99.3% of the copper from a 10^-4 mol/L aqueous solution, removed 95% within 15 minutes. This material has copper distribution coefficients (K_d) as high as 12 000 at 10^-4 mol/L. A separation factor, K > 85, with respect to copper (II) was achieved with an aqueous Cu²⁺-Zn²⁺ system at pH 5.0.