Membrane potential and fixed-charge density across TiPO4–VPO4 composite membranes for uni-univalent electrolyte solution

The TVP composite membranes were prepared by sol–gel process, and the membrane potential has been measured for characterizing the ion-transport phenomena across a charged membrane using electrolytes (KCl, NaCl and LiCl). The membrane potential offered by the electrolytes is in the order of LiCl > NaCl > KCl, and the membrane is found to be cation-selective. The results have been used to estimate fixed-charge density, distribution coefficient, charge effectiveness and transport properties of electrolytes of this membrane. The fixed-charge density is the most important parameter, governing transport phenomena in membranes. It is estimated by the TMS method; it is dependent on the feed composition due to the prefential adsorption of some ions. The results indicate that the applied pressure is also an important variable to modify the charge density and, in turn, the performance of membrane. The order of charge effectiveness of the electrolytes in membrane depends on the ionic radii of the counter-ions. The experimental results for membrane potential are quite consistent with the theoretical prediction. The morphology of the membrane surface is studied by scanning electron micrographs (SEM).