Janus membrane with unparalleled forward osmosis performance

We report the use of highly porous Janus membranes with unparalleled forward osmosis (FO) performance in terms of water flux and reverse salt flux. A porous Janus FO membrane, composed of a hydrophilic cellulose acetate layer and a hydrophobic polyvinylidene fluoride (PVDF) nanofiber layer, was fabricated by electrospinning. The resultant membrane exhibited outstanding FO performance, with a high water flux of 274.2 L m^-2 h^-1 and a low reverse salt flux of 1.65 g m^-2 h^-1 using 1 M NaCl draw solution. Different from the state-of-the-art thin film composite (TFC) membranes, the prepared Janus membrane demonstrates unparalleled FO performance via a nanofluidic diode model, whose high selectivity is determined by the air gap within the hydrophobic nanofiber layer that can effectively prevent the reverse salt diffusion. Wetting of the hydrophobic layer is the crucial issue in Janus FO membranes, which deserves further attention to extend the osmosis longevity.