High-surface-area functionalized nanolaminated membranes for energy-efficient nanofiltration and desalination in forward osmosis

Stacking two-dimensional nanosheets into laminar membranes to create nanochannels has attracted widespread attention at both fundamental and practical levels in separation technology. Constructing space-tunable and long-term stable sub-nanometre channels provides original systems for nanofluidic investigations and accurate molecular sieving. Here we report a scalable strategy for the preparation of non-swelling, covalently functionalized MoS2 membranes with tunable cohesion energy and interlayer space ranging from 3.5 to 7.7 Å, depending on the nature of the functional groups attached to the MoS2 nanosheets. We evaluated the relationship between the capillary width, surface chemistry, stacking disorder and sieving behaviour of the membranes in forwards osmosis (FO). By combining experimental investigations and numerical simulations, we determined that functionalization with aryl groups induces the formation of a capillary width of 7.1 Å and an interlayer stiffness as low as 5.6 eV Å−2, leading to controlled stacking defects. We also report the fabrication of membranes with an area of up to 45 cm2 that demonstrate a salt rejection as high as 94.2% for a continuous operating time of 7 days. Furthermore, the desalination strategy in FO has a specific energy consumption of 4 × 10−3 kWh m−3, which compares favourably with commercial FO membranes. One of the problems of water-treatment membranes based on two-dimensional materials is that they tend to swell once in operation in water. A new strategy is presented for the preparation of non-swelling, covalently functionalized molybdenum disulfide membranes with tunable interlayer space and cohesion energy of the laminates.