Metal and Water sorption characteristics of Nafion Membranes: Role of pretreatment and Complexing Agents

Nafion ionomer with excellent properties have been topic of research for very long time. The unique properties give scope for further research and gaining an insight to the sorption process. Permselectivity of membrane allows the separation of cations of interest. However, in practice, selectivity is achieved by modification of experimental parameters including solution pH and composition. Many studies involve the use of complexing agents to reduce the interference of the various ions in mixture. Therefore, it became crucial to understand the effect of complexing agents on the uptake property of Nafion membrane. Prior studies have established the effect of pretreatment on membrane sorption property. In this study, the effect of both pretreatment as well as presence of complexing agent on sorption of Cu an Zn ions have been studied. The studies were carried out using orthophenanthroline as a model complexing agent both in solution as well as membrane phase. It is seen that pretreatment has a major role in affecting the uptake capacity. Interestingly it was seen that the presence of orthophenanthroline within the membrane resulted in selectivity reversal. In order to obtain an understanding of the experimental results as well as the mechanism, density functional theory (DFT) based calculations have been carried out.