(383g) Controlling the Water Transport through Nanochannels of Ion-Intercalated Ti3C2Tx Mxene Membranes

Water transport along nanochannels has become an area of significant interest due to its potential applications in water purification, desalination, and energy generation. Over the past decades, capability of various nanomaterials has been explored for fast water transport. Among them, two-dimensional (2D) nanomaterials have shown exceptional promise, given their high surface area and unique lamellar structures. MXenes are 2D transition metal carbides, nitrides, and carbonitrides, with high hydrophilicity, excellent electrical conductivity, and rich surface chemistry. Since their discovery, they have demonstrated promising properties in various applications such as energy storage, water purification, electromagnetic interference shielding, and sensing. Their hydrophilic nature, combined with high metallic conductivity, sets them apart from most other 2D nanomaterials. From a potential application point of view, so far experimental studies have mainly focused on how ionic transport occurs in MXene nanochannels. However, a comprehensive study on water transport in these nanochannels, particularly concerning the interaction of water molecules with cations of varied hydration diameters, remains elusive. Therefore, increasing the affinity of water molecules towards the nanochannel walls through the intercalation of cations with different hydration diameters could provide an effective approach to achieve fast water transport through MXene-based nanochannels.

In this work, we combine experiments and theory to elucidate how intercalation of K⁺, Na⁺, Li⁺, Ca²⁺, and Mg²⁺, ions spanning a range of hydration diameters and binding affinities, controls interlayer spacing, hydrogen‑bond networks, and water flux in Ti₃C₂T_x membranes. By introducing K⁺, Na⁺, Li⁺, Ca²⁺, and Mg²⁺, we systematically expanded interlayer spacing and optimized hydrogen‑bonding networks, findings supported by DFT, so that larger hydrated cations widen nanochannels and enhance flux from ≈31.5 to 61.9 L·m^-2·h^-1. We explain this by showing that the slip length of the cation intercalated MXene membrane enhances exponentially with the hydrated diameter of the respective cation. Furthermore, our findings provide important insights into the water transport mechanism in MXene-based nanochannels in general and support the application of the Hagen-Poiseuille equation to describe water transport in these nanochannels.