High-Flux Nanofibrous Composite Reverse Osmosis Membrane Containing Interfacial Water Channels for Desalination

A nanofibrous composite reverse osmosis(RO) membranewith a polyamidebarrier layer containing interfacial water channels was fabricatedon an electrospun nanofibrous substrate via an interfacial polymerizationprocess. The RO membrane was employed for desalination of brackishwater and exhibited enhanced permeation flux as well as rejectionratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO) and sodium periodate systems and surface grafting with differentalkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl,and octadecanyl groups. The chemical structure of the modified nanocellulosewas verified subsequently by Fourier transform infrared (FTIR), thermalgravimetric analysis (TGA), and solid NMR measurements. Two monomers,trimesoyl chloride (TMC) and m-phenylenediamine (MPD),were employed to prepare a cross-linked polyamide matrix, i.e., thebarrier layer of the RO membrane, which integrated with the alkylgroups-grafted nanocellulose to build up interfacial water channelsvia interfacial polymerization. The top and cross-sectional morphologiesof the composite barrier layer were observed by means of scanningelectron microscopy (SEM), atomic force microscopy (AFM), and transmissionelectron microscopy (TEM) to verify the integration structure of thenanofibrous composite containing water channels. The aggregation anddistribution of water molecules in the nanofibrous composite RO membraneverified the existence of water channels, demonstrated by moleculardynamics (MD) simulations. The desalination performance of the nanofibrouscomposite RO membrane was conducted and compared with that of commerciallyavailable RO membranes in the processing of brackish water, where3 times higher permeation flux and 99.1% rejection ratio against NaClwere accomplished. This indicated that the engineering of interfacialwater channels in the barrier layer could substantially increase thepermeation flux of the nanofibrous composite membrane while retainingthe high rejection ratio as well, i.e., to break through the trade-offbetween permeation flux and rejection ratio. Antifouling properties,chlorine resistance, and long-term desalination performance were alsodemonstrated to evaluate the potential applications of the nanofibrouscomposite RO membrane; remarkable durability and robustness were achievedin addition to 3 times higher permeation flux and a higher rejectionratio against commercial RO membranes in brackish water desalination.

Automated summary

In this study, a nanofibrous composite reverse osmosis (RO) membrane with interfacial water channels was fabricated through interfacial polymerization on an electrospun nanofibrous substrate. The membrane showed enhanced permeation flux and rejection ratio for desalination of brackishwater. Nanocellulose was prepared and modified with different alkyl groups, and a cross-linked polyamide matrix was formed on the nanofibrous substrate through interfacial polymerization to build up the water channels. The performance of the nanofibrous composite RO membrane was compared with commercially available RO membranes, demonstrating significantly higher permeation flux and rejection ratio, as well as excellent antifouling properties and long-term stability.