Abstract
Electrospun nanofiber with interconnected porous structure has been studied as a promising support layer of polyamide (PA) thin-film composite (TFC) forward osmosis (FO) membrane. However, its rough surface with irregular pores is prone to the formation of a defective PA active layer after interfacial polymerization, which shows high reverse salt leakage in FO desalination. Heat-curing is beneficial for crosslinking and stabilization of the PA layer. In this work, a nanofiber-supported PA TFC membrane was conceived to be cured on a hot water surface with preserved phase interface for potential “defect repair”, which could be realized by supplementary interfacial polymerization of residual monomers during heat-curing. The resultant hot-water-curing FO membrane with a more uniform superhydrophilic and highly crosslinked PA layer exhibited much lower reverse salt flux (FO: 0.3 gMH, PRO: 0.8 gMH) than that of oven-curing FO membrane (FO: 2.3 gMH, PRO: 2.2 gMH) and achieved ∼4 times higher separation efficiency. It showed superior stability owing to mitigated reverse salt leakage and osmotic pressure loss, with its water flux decline lower than a quarter that of the oven-curing membrane. This study could provide new insight into the fine-tuning of nanofiber-supported TFC FO membrane for high-quality desalination via a proper selection of heat-curing methods.
Highlights
Water reuse is a feasible and effective way to alleviate water scarcity caused by high population pressure and rapid economic growth
The distinctive internal concentration polarization (ICP) during forward osmosis (FO) operation happens when the draw solution is diluted in the support layer by permeate water under FO mode or when the solutes from the feed solution are intercepted at the interface between the support layer and the inner surface of the active layer (PRO mode)
The formed rough PA film features a large number of balloon-like nodules due to the gas nanobubbles trapped between the PA layer and support layer escaped [30]
Summary
Water reuse is a feasible and effective way to alleviate water scarcity caused by high population pressure and rapid economic growth. The forward osmosis (FO) process, inspired by the natural osmosis phenomenon, can spontaneously occur when driven by the osmotic pressure difference (i.e., concentration difference) across the selective semipermeable membrane. It emerges with its distinctive advantages of lower pollution tendency, higher resilience after cleaning and lower energy consumption than conventional pressure-driven membrane technologies. Electrospun nanofiber membrane with a lower S value, owing to its high porosity, open and porous structure, which can favor the mass transfer and the alleviation of ICP inside the membrane, has been emerged as an effective alternative to the traditional phase-inversion support [12,13,14,15]
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