MXene Nanosheet Tailored Bioinspired Modification of a Nanofiltration Membrane for Dye/Salt Separation

The use of 2D nanomaterials for membrane designation has proved promising to improve the membrane separation performance and endow a membrane with appealing functionalities. Inspired by the strong adhesion ability of dopamine (DA), the negatively charged MXene nanosheets and positively charged polyethylenimine (PEI) were anchored on the selective layer of the ultrafiltration membrane through a fast deposition reaction of polydopamine (PDA). The impact of MXene nanosheets on membrane surface morphology, chemical properties, and dye/salt separation performance of the MXene-based thin film composite (TFC) nanofiltration (NF) membrane was investigated. The best-performing M-4 membranes exhibited an excellent water permeance (up to 38.2 L m-2 h-1 bar-1), outstanding dye rejections (i.e., congo red: 99.7%, reactive blue: 99.6%, methyl blue: 98.5%, and coomassie brilliant blue G250: 99.5%) and low salt rejections (e.g., NaCl: 12.6% and Na2SO4: 29.9%). Besides, the operational stability of the M-4 membrane under acidic/alkaline conditions provides the possibility to apply the MXene-based membrane in extreme situations. This facile fabrication method identifies the potential of using MXene as an intercalant for regular molecular separation processes.