The Enhanced Li⁺/Ca²⁺ Selectivity of Ion Exchange Membranes (IEM) by Polypyrrole (PPy) Coating with P-Toluene sulfonate (TS^-) Dopant

Ion separation is important for modern industry, in fields such as desalination, battery and biological processes. Ion exchange membranes (IEM) are promising in separating ions of opposite charges. However, it is challenging to separate like-charged ions by commercial ion exchange membranes. Our previous research found that polypyrrole coating enhances nitrate selectivity by PPy Coating. Using computational methods of simulation, we have found that cation selectivity is more challenging. One of our bigger challenges was with the Lithium Ion due to its small size and similar structure of cations.

The scope of the current work is the effect of doped polypyrrole (PPy), a conductive polymer, on the enhanced ion selectivity of Li⁺ transport with respect to other ions, in this case Ca²⁺ with the goal to improve Li⁺ transport of modified Cation Exchange Membranes. In this talk, we focus on the role of two types of dopants in PPy in enhancing Ion Selectivity: p-Toluene sulfonate (TS^-) and chloride (Cl^-). We studied the mean square displacement for diffusivity, and hydration shell, ion pairing and energy landscape for molecular mechanisms. Our approach has enabled us to study the long term and short-term trends of ionic movement in our simulated time scales. Our preliminary results show that TS^- has slightly better selectivity between Li⁺ and Ca²⁺. Our goal is to thoroughly examine the relative ion transport of Li⁺ and Ca²⁺ in PPyTS and extend our research to other molecules and their diffusive membranes under the same conditions with other conductive polymers and dopants.