Electroconductive MXene-based composite membrane with stable interlayer spacing for electro-enhanced separation performance

Abstract

Electroconductive membranes are of interest because their selectivity-permeability and fouling resistance are improved with electrical assistance. MXene lamellar membranes are competitive candidates. However, the swelling problem of MXene membranes has not been adequately addressed, especially at dynamic voltages, resulting in weakened separation performance. In this study, carboxylated cellulose nanofibers intercalated MXene membranes with stable interlayer spacing were developed by constructing column-to-beam structure and mortise-tenon connection. The results showed that the interlayer spacing and membrane pore size of the MX/CN composite membrane were almost invariable before and after electro-assisted filtration. Benefiting from the anti-swelling properties and good electrical conductivity, the MXene composite membranes showed a significant increase in the retention of typical monovalent and divalent inorganic salts at external voltages (from 46.2 % and 80.4 % at 0 V to 60.6 % and 88.7 % at 2.0 V for NaCl and Na₂SO₄, respectively), as well as a slight increase in the flux. This enhancement mechanism was attributed to the increase of the Stern layer in the adjacent nanosheets of lamellar membranes under electrical assistance. In addition, external voltage was also effective in improving the fouling resistance and enrichment performance of MXene composite membranes for actual textile wastewater, which might be due to the enhanced electrostatic repulsion and electrokinetic behavior under electrical assistance. This work aims to offer new insights into the advancement of electroconductive membranes with a stable structure for desalination and wastewater treatment.