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 ~ 6.92 Å, 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.