Spray assisted layer-by-layer assembled one-bilayer polyelectrolyte reverse osmosis membranes

A single-bilayer polyelectrolyte reverse osmosis membrane was fabricated by a spray assisted layer-by-layer assembly approach using a polysulfone ultrafiltration membrane as a substrate, polyethyleneimine (PEI) as an adhesion promoter, poly(allylamine hydrochloride) (PAH) and poly(sodium-4-styrene sulfonate) (PSS) as polycation and polyanion, glutaraldehyde as a crosslinker and Pluronic F127 amphiphilic triblock copolymer as a surface modifier. The resulting active layer is ultrathin (ca. 70 nm) and has a flat, dense and uncharged surface in neutral solution. The salt rejection and permeate flux of the membrane gradually increases from 92% to 94%, and 11 L/m2 h to 30 L/m2 h respectively for a 2 g/L NaCl feed solution as the operating pressure increased from 1.6 MPa to 4.0 MPa. Additionally, the membrane shows good separation performance stability and protein fouling resistance using bovine serum albumin as a foulant model. The glutaradehyde plays a key role in enhancing salt rejection by forming imine bonds within the PEI layer and the PEI/PAH interlayer. The Pluronic F127 surface modifier improves the permeate flux due to its hydrophilicity and the resulting induced swelling providing channels for water flow. Further, the "brush-like" structure of the hydrophilic polyethylene oxide moieties on the membrane surface improves fouling resistance.