Voltage-enhanced ion sieving and rejection of Pb2+ through a thermally cross-linked two-dimensional MXene membrane

Highly stable and anti-swelling two-dimensional (2D) MXene (Ti2C3Tx) membranes can be applied for ion sieving and water purification under external voltage. This paper shows the effective ion sieving of mixed K+/ Pb2+ pairs and the high rejection of the heavy metal ions (Pb2+) through a thermal cross-linked 2D MXene membrane by exerting external voltage. Due to the dehydration and cross-linking of hydroxyls during the drying process, the interlayer spacing of MXene membrane is tuned to be 6.7 similar to 6.92 angstrom, which lies in the selective ion sieving size of the mixed K+ and Pb2+. The rejection of hydrated Pb2+ is up to 99%, while the hydrated K+ can smoothly transport the channels of MXene membrane under external voltage. For 365-nm-thick MXene membrane, the separator factor of mixed K+ and Pb2+ reaches up to 78 under an applied voltage of 16.5 V. Furthermore, the application of external voltage doesn't result in swelling of MXene membrane, showing stable separation of K+/Pb2+ pairs with effective rejection of Pb2+. The high rejection of Pb2+ and good anti-swelling demonstrate the stability of the resultant MXene membranes. Our work indicates that the thermal cross-linked MXene membrane is a promising alternative for ion sieving and the rejection of heavy metal ions.