STUDY OF INTERACTIONS BETWEEN METAL IONS AND CROWN ETHERS IN LIQUID ORGANIC MEMBRANE SYSTEMS.

Considering the toxic properties of heavy metals and their effects on the environment, there is an increasing interest in studying their interactions with different ligands and searching for possibilities to remove those ions from the environment. Compared to other ligands, crown ethers possess the highest selectivity as ligands for metal cations, due to their "macrocyclic effect". In this paper, interactions between Pb(II), Cd(II) ions and various crown ethers (18 crown-6, benzo-18-crown-6, dibenzo-18-crown-6, dicyclohexane-18-crown-6 ether), were analyzed. The UV/VIS spectrometric method was used to record absorption diagrams of "model systems" of varying complexity. Cd(II) and Pb(II) ions were monitored using flame atomic absorption spectrometry. In different organic solvents used (chloroform, dichloromethane), UV/VIS and FAAS measurements showed that higher absorption intensity caused more stable complexes in the membrane, complicating the release of ions. With the benzo-18-crown-6 ether as ligand, Pb(II) ions released into the aqueous phase at a rate higher than 60%, compared with Cd(II) ions released at a rate of 49%. In a model system containing a nonionic surfactant (TX-100), metal ions interact more intensely with the membrane, and cation release is reduced in the aqueous phase, indicating that the reverse micellar aggregates incorporate metal ions that result in higher absorption intensities. According to the macrocycle selected, the presence of benzo- and cyclohexyl groups (B18C6, DB18C6, DCH18C6) probably reduces interactions between substituted macrocyclic ligands and metal cations, resulting in lower values of Pb(II) and Cd(II) ions measured in the aqueous phase compared with a model system with 18 crown-6 ether. [ABSTRACT FROM AUTHOR]