Modeling of hydrated cations transport through 2D MXene (Ti3C2Tx) membranes for water purification

Abstract

Two-dimensional (2D) MXene membranes with high thermal and mechanical stability have shown great promise for water purification and desalination given their low energy consumption and high efficiency. In this work, we used a one-dimensional (1D) steady-state ion sieving and rejection model to describe the transport of hydrated cations through 2D lamellar MXene (Ti3C2Tx) membranes under transmembrane pressure field and external electric field. The model was validated using experimental data on the permeation fluxes of the 365 nm-thick MXene membrane with an interlayer spacing of 7.8 Å under transmembrane pressure of 0.2 atm at 298 K and under an external electric field between 0.1 and 8.25 V. The regressed model diffusion coefficients of penetrant (Di,pc) through the MXene membrane under transmembrane pressure field were 1.98 × 10−7 m2 h−1 for K+ and 1.77 × 10−7 m2 h−1 for Na+. Under the external electric field at 298 K and fixed starting solution concentration of 50 mg L−1 for K+ or Na+ cation, the diffusion coefficient of penetrant (Di,ec) from the regression were 2.55 × 10−9 m2 h−1 for K+ and 1.21 × 10−9 m2 h−1 for Na+. By applying the regressed parameters from both operation modes into the one-dimensional ion sieving and rejection models, the effects of interlayer spacing, potential voltage, temperature, and thickness on the permeation and rejection of hydrated K+ and Na+ cations through the MXene membrane can be effectively simulated. The use and modification of a theoretical model for ionic transport through 2D MXene (Ti2C3Tx) membranes we reported here can provide essential insights to guide future membrane design and determine its applicability of water desalination.