Abstract
Carrier-assisted transport through liquid membranes is one of the important applications of supramolecular chemistry. This work investigates the use of synthetic carrier (ionophore) for the separation of metal ions. We have tested the effect of structure of ionophore on the separation of metal ions. For this purpose, we have used a new series of non-cyclic ionophores having different end groups and chain length (R 1–R 5). 1,5 bis (2-naphthyloxy)-3-oxapentane (R 1), 1,8 bis (2-naphthyloxy)-3,6-di-oxaoctane (R 2), 1,11 bis (2-naphthyloxy)-3,6,9-tri-oxaundecane (R 3) 1,11-(dianthraquinonyloxy) 3,6,9-trioxaundecane (R 4), 1,8 (dianthraquinonyloxy) 3, 6-dioxaoctane (R 5) have been used in extraction, bulk liquid membrane (BLM) and supported liquid membrane (SLM) transport of alkali (Li +, Na +, K +) and alkaline earth metal cations (Ca 2+, Mg 2+). The supported liquid membrane consisted of a porous cellulose nitrate and and an onion membrane support impregnated with ionophore using chloroform as a solvent. The results reveal that ionophores R 1, R 2 and R 3 are better extractants for K + while R 4 and R 5 are better extractants for Ca 2+. Among these ionophores R 3 and R 4 are best extractants for K + and Ca 2+ ions. The results of BLM reveal that ionophores R 1, R 2 and R 3 transport Na + at a greater extent, while R 4 and R 5 transport Ca 2+ and K + at a greater extent. In SLM experiments using a cellulose nitrate membrane support, it was observed that naphthyl end group bearing ionophores (R 1–R 3) transports Na + > K +, and anthraquinone bearing ionophores (R 4 and R 5) transport K + > Na + > Ca 2+ respectively. In the onion membrane support R 4 transports Ca 2+ and Na + equally and R 5 transports K + selectively. On comparing the membrane support, the cellulose nitrate membrane is found better support for the transport of metal ions. The results suggest that due to the presence of different end groups and chain lengths the selectivity of non-cyclic ionophores towards metal ions is enhanced. Thus selectivity of ionophores may have fruitful application in ion selective electrodes and separation of metal ions.
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