Understanding selective transport of same-charge ions in polymeric membranes*

Selective transport of ions is desirable in many applications, such as water cleaning, rare-earth extraction, and battery technology. Polymeric membranes have been used to separate ions from water, and between ions of different charges, without introducing harmful chemicals to the environment. However, it remains challenging for membranes to separate ions of the same charge, such as chloride and nitrate. A physical understanding of the mechanisms of the selectivity of same-charge ions by polymeric membranes is needed for developing or inventing membranes with improved ion selectivity. Here we use molecular dynamics to investigate the transport of same-charge ions in polymeric membranes, and we elucidate the effects of ion hydration, membrane polarity and ion concentration on the partition and diffusion of same-charge ions in the membrane. The research provides insights for the dynamic research efforts to achieve precise same-charge-ion selectivity in polymeric membranes.