Composite reverse osmosis membrane with a selective separation layer of double-layer structure for enhanced desalination, anti-fouling and durability properties

High performance membrane is crucial for energy-efficient desalination of salty water and reclamation of wastewater. Commercially available reverse osmosis membranes manufactured by interfacial polymerization or phase inversion techniques usually face the obstacle of “trade-off” effect between water permeation ability and salt rejection capability. In this work, a novel approach of constructing selective separation layer of double-layer structure was proposed to break through the difficulty of fabrication of reverse osmosis membrane with both high water permeation and salt rejection capabilities. Selective separation layer comprising loose polyamide (PA) sub bulk and dense hydroxypropyl methylcellulose (HPMC)-modified polyvinyl alcohol (PVA) top skin was constructed by the technique of interfacial polymerization followed with surface coating and cross-linking. The double-layer selective separation layer was found to possess an enhanced balance in water and salt permeations and endow the composite membrane with both high water flux and salt rejection. The desired membrane with an optimized selective layer of PA2/PVA + HPMC0.2 achieved 99.4% salt rejection and 37.9 kg/m2 h MPa water permeance to brackish water, which were higher than those of commercial membrane BW30. Furthermore, the desired membrane also exhibited better separation and antifouling performances in reclamation of secondary industry effluent when compared with the state-of-the-art antifouling membrane BW30FR.