Role of molybdenum disulfide (MoS2) nanosheets doping position on the thin-film nanocomposite (TFN) membrane during brackish water treatment

Brackish water desalination based on nanofiltration (NF) has been regarded as a feasible solution to address the scarcity of freshwater. However, the trade-off effect and membrane fouling are challenges for the thin-film composite NF membranes, restricting their further application in desalination. Herein, modified thin-film nanocomposite (TFN) membranes were constructed with molybdenum disulfide (MoS2) nanosheets incorporated either into the polyamide layer (P-TFN) or as an interlayer (I-TFN). The surface morphology, chemical element, electronegativity, pore size, hydrophilicity, separation performance and antifouling property of the membranes were systematically evaluated and compared. The P-TFN membrane exhibited superior salt rejection of Na2SO4 up to 98.4% and preeminent flux recovery ratios (FRRs) of 95.4% and 92.2% for humic acid (HA) and bovine serum albumin (BSA) filtration, respectively, which possessed high electronegativity and small effective pore size. While, without compromising its salt retention and foulant resistance, the I-TFN membrane exhibited 51% better permeability than the control TFC membrane, due to its unique crumpled structure of the PA layer and the “dragging effect” of the interlayer on water molecules. Furthermore, we elaborated on the mechanism underlying the differences in surface properties, and verified the effectiveness of the modified membranes in authentic brackish water desalination. Significantly, the comparison provides novel insight for the customization and regulation of the PA layer.