Selective molecular separation with conductive MXene/CNT nanofiltration membranes under electrochemical assistance

MXene-based membranes have drawn tremendous attention due to their high permeability and selectivity. To prevent MXene from restacking and enrich nanochannels for water transport, carbon nanotubes (CNT) are intercalated between MXene nanosheets to fabricate MXene/CNT nanofiltration membranes in the present study. The membrane shows a high permeance of 30.4 L m−2 h−1 bar−1 and a high rejection ratio (>90%) toward organic molecules with the size larger than 2 nm. More importantly, the rejection ability for the negatively charged chemicals can be further improved by a voltage applied during filtration process. The rejections of orange G and methyl orange increase from 64.8 ± 1.9% and 27.2 ± 3.8% to 96.3 ± 3.2% and 87.8 ± 3.1%, respectively when a voltage of 3.0 V is applied with the membranes as the cathode. The improvement is ascribed to the enhanced electrostatic repulsion between the negatively charged dyes and the membrane cathode. With the benefit of the mechanism, binary and ternary dye mixtures with different charges can be selectively separated by the MXene/CNT membrane for wastewater treatment and selective recycling of reusable resources from wastewater.