Selective Metal-Ion Adsorptivities of Silica Gel Particles Impregnated with p-Sulfonatocalix[n]arenes (n=6 and 8) Having Fixed Steric Structure

Selective Metal-Ion Adsorptivities of Silica Gel Particles Impregnated with p-Sulfonatocalix[n]arenes (n=6 and 8) Having Fixed Steric Structure

¹ Department of Applied Chemistry, Faculty of Engineering, Sojo University, 4-22-1, Ikeda, Kumamoto-shi, Kumamoto 860-0082

(Received 1 June 2005, Accepted 24 November 2005)

Silica gel particles impregnated with the ion associates of water-soluble p- sulfonatocalix[n]arene (n=6, H₆L₆^6-; n=8, H₈L₈^8-) ions and methyltrioctylammonium ion (MTA⁺), MTA-L₆ and MTA-L₈, were prepared, and their adsorption properties for some metal ions were examined. The adsorbents that were impregnated in the first place with the ion associates of metal complexes, such as UO₂²⁺ or Ti⁴⁺, then eluted these metal ions by dilute sulfuric acid, i.e., complex-type adsorbents, indicated large and selective adsorptivities for UO₂²⁺ and Ba²⁺. The supporting condition of the ion associates was also stable. No adsorptivity was observed for the adsorbents prepared by impregnating directly with the ion associates of these calixarenes with MTA⁺, i.e., the free ligand-type adsorbents. Also, the supporting condition of the ion associates was less stable than those of the complex types in the presence of metal ions. In the former, it was estimated that these calix[n]arenes are fixed in a “cone” structure in which their hydroxyl groups are ordered conveniently for taking specific metal ions. On the other hand, the latter were estimated to consist of “alternate” type calix[n]arenes in which some of the hydroxyl groups are located on opposing sides to make the reaction with metal ion impossible.

Keywords : p-sulfonatocalix[n]arene; methyltrioctylammonium ion; ion associate; metal adsorbent.