Anti-swelling polyethyleneimine-modified MXene nanofiltration membranes for efficient and selective molecular separation

Two-dimensional (2D) MXene-based nanofiltration membranes could sustainably and rapidly produce clean water. However, the challenges related to the severe swelling of the MXene membranes in water should be overcome before the practical application. In this work, the negatively charged MXene-based membrane is modified by positively charged polyethyleneimine (PEI) with various PEI:MXene ratios. The PEI-MXene is deposited on a polyacrylonitrile (PAN) substrate as a top membrane to prepare an anti-swelling composite PEI-MXene/PAN membranes with outstanding mechanical strength and stability. Interestingly, when the interlayer spacing of the top Mxene layers are tuned between ca. 14.15 and ca. 14.52 angstrom, the resultant PEI-MXene/PAN membranes exhibit the excellent ability of size sieving. For instance, PEI-MXene(1:1)/PAN membrane presents high flux performance to Acid Blue 90 (AB90), Congo Red (CR), and Direct Red 80 (DR80) (i.e., 563.9, 882.6, and 633.6 L m(-2) h(-1), respectively) at 0.2 MPa, and remarkable rejection rates, that is, 99.3%, 99.82%, and 99.9%, respectively. Besides, the PEI-MXene(0.5:1)/PAN possesses the highest flux of 1528.1 L m(-2) h(-1) and outstanding rejection rate of 99.9% to dye of AB8GX. Moreover, the proposed strategy can be extended to the modification of other 2D material nanofiltration membranes.

Automated summary

In this study, MXene-based nanofiltration membranes were successfully modified to overcome the severe swelling issue in water, resulting in composite PEI-MXene/PAN membranes with excellent mechanical strength and stability. The modified membranes exhibited outstanding size sieving ability after tuning the interlayer spacing of the MXene layers, with high flux and remarkable rejection rates.