Ultraefficient Li+/Mg2+ separation with MXene/CNT membranes under electric field assistance
Similar physicochemical properties render the separation of Li + /Mg 2+ from salt lake brine difficult for two-dimensional (2D) membranes. Herein, ultraefficient Li + /Mg 2+ separation was achieved under the influence of an electric field using MXene/carbon nanotube (CNT) membranes developed on tubular ceramic substrates via thermal crosslinking. Crosslinking reactions between CNTs and MXene yielded well–intercalated CNTs between MXene nanosheets, forming antiswelling MXene/CNT membranes (MCMs) (interlayer spacing: 8.04 Å) suitable for Li + /Mg 2+ separation. At 2.8 V applied voltage, the MCMs exhibited Li + flux of 0.0491 mol m −2 h −1 and high Li + /Mg 2+ selectivity of 54.5, which outperform existing state–of–the–art 2D membranes. Specifically, under a positive electric field, Li + with a small hydration diameter and low hydration energy permeated through the membrane nanochannels more easily than Mg 2+ , increasing and decreasing Li + and Mg 2+ flux, respectively. Additionally, Mg 2+ retention was enhanced via the complexation of enriched Mg 2+ with –OH and –COOH on the membrane surface. The MXene membrane surface was thus reconfigured to be positively charged, inducing effective Mg 2+ rejection. This study offers a novel and practical approach for efficiently separating Li + /Mg 2+ as well as monovalent/multivalent ions.
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