FACILITATED TRANSPORT OF IONS THROUGH FIXED-SITE CARRIER MEMBRANES DERIVED FROM HYBRID ORGANIC-INORGANIC MATERIALS

Heteropolysiloxanes (HPS) or ormosils belong to the class of hybrid organic-inorganic materials prepared by sol-gel technology and satisfy two requirements necessary to prepare facilitated transport membranes: they are synthesized at low temperature and their organic functions allow the chemical grafting of carriers such as crown-ethers. The preparation of grafted benzo-15-crown-5 membranes and the results concerning transport experiments are reported here. It has been demonstrated that covalently bound carriers allow facilitated transport of K+ ions versus Li+ ions to take place with high diffusion rates, high facilitation factor and good selectivity. The special role of counter-ion is also put forward and discussed. A transport mechanism which fits the experimental results is proposed.