Adsorption of heavy metal ions on crown ether adsorbents

Abstract

Granular entrapped adsorbents of crown ether-phosphotungstic acid (PW) and crown ether-phosphomolybdic acid (PMo) in polyacrylamide were prepared by the sol-gel method and used for the adsorption of various heavy metals ions such as Ag⁺, Pb²⁺, Hg²⁺, Cd²⁺, Fe³⁺ and Zn²⁺. Dibenzo-18-crown-6-PW (or-PMo)/polyacrylamide adsorbent gave high adsorption and a high selectivity for large metal ions such as Ag⁺, Pb²⁺ and Hg²⁺, but not for smaller ions. In contrast, small heavy metal ions such as Cu²⁺, Fe³⁺ and Zn²⁺, but not larger ions, were strongly adsorbed by 12-crown-4-PW (or-PMo)/polyacrylamide adsorbent. The effects of pH and solvents on the adsorption were investigated. A dibenzo-18-crown-6-PMo adsorbent film was also prepared and successfully applied to the selective adsorption of Ag⁺ ions from an aqueous solution containing various metal ions, and the Ag⁺ ions on the film could be determined quantitatively by X-ray fluorescence analysis.