Charge- and Size-Selective Ion Sieving Through Ti3C2Tx MXene Membranes.

Nanometer-thin sheets of 2D Ti3C2Tx (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m(2)) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 Å) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides.