Mechanisms of Selective Ion Transport in Layered MoS₂ and Graphene Oxide Membranes

Two dimensional materials such as MoS₂ and graphene are excellent scaffolds for nanometer and even angstrom scale fluidic channels. Unique chemical and physical phenomena arise in channels for which the size of the confined species has the same order as the confining dimensions. Here, we exploit the interlayer gallery of functionalized MoS₂ and graphene oxide to study the selective transport of ions through &lt; 1 nm quasi two dimensional channels. In graphene oxide, we find that the permeance of Cu²⁺ is high relative to that of other divalent ions (Mg²⁺/Ca²⁺/Co²⁺). From the X-ray absorption spectra and pair distribution functions of saturated graphene oxide membranes, we determine that the enhanced flux of Cu²⁺ is a result of its strong coordination with carboxylic acid functional groups¹. In MoS₂, we find, surprisingly, that the relative adsorption of Pb²⁺ and Cu²⁺ reverses when MoS₂ is functionalized with carboxylic acid groups (the membrane uptake of Pb²⁺ is higher when functionalized)². Infrared spectroscopy reveals that this reversal is a result of the unique bidentate binding of Pb²⁺ in the functionalized MoS₂ channels. Here, we also discuss our recent investigation of the ion transport through pores in few-layer MoS₂. <br/><br/>[1] Wang, Mingzhan, et al. "Tuning transport in graphene oxide membrane with single-site copper (II) cations." Iscience 25.4 (2022): 104044.<br/><br/>[2] Wang, Mingzhan, et al. “Anomalous Ion Transport Across Angstrom-scale Channels Enabled by Surface Chemistry.” Manuscript in preparation (2022).