Potentials of ion-exchanged synthetic zeolite–polymer membranes

Abstract

Membranes were prepared from synthetic zeolites, NaA, NaCaA, NaX and ion-exchanged NaCaA and NaX with Cu^II and Fe^III ions, using the technique of embedding the microcrystals in a low-viscosity epoxide resin system. These membranes were found to be selective to cations with slopes close to the Nernstian value. In all cases it was found that the degree of adhesion of the polymer phase to the zeolitic phase decided the extent of deviation of the membrane e.m.f. vs. pM slopes from ideal behaviour. Membranes made from NaCuX and NaCaA were found to give excellent adhesion between the two phases. On the contrary, membranes constructed from Fe^III ion-exchanged zeolites showed low adhesion ability. Furthermore, the membrane FeX obtained from broken-down zeolitic structure showed very poor performance owing to its bad adhesion properties combined with the low concentration of counter ion in the membrane structure. In general, membranes with good adhesion properties like NaCuX showed slopes close to the Nernstian value.