Preparation of double-skinned polyamide composite membranes for enhanced forward osmosis desalination

Mixed cellulose ester (MCE) porous substrates were first modified by using polyvinyl alcohol (PVA) solutions. Double-skinned polyamide forward osmosis (FO) membranes were fabricated by way of interfacial polymerization on PVA-modified MCE substrates. Field emission scanning electron microscopy was used to observe the morphology change of PVA-modified MCE substrates and the corresponding polyamide active layers. Fourier transform infrared was employed to detect the functional groups of the polyamide layer. Atomic force microscope (AFM) was used to probe membrane topography and surface roughness. The hydrophilicity and mechanical strength of synthesized double-skinned polyamide membranes were, respectively, evaluated by using contact angle and tensile testing experiments. When subjected to the test of FO desalination, the synthesized membrane exhibited satisfactory separation performances with enhanced mechanical strength and long-term stability. Using deionized water as the feed solution and 1 M NaCl aqueous solution as the draw solution, the water flux was 11.32 L m(-2) h(-1) and the reverse salt flux was as low as 0.58 g m(-2) h(-1). Compared with available FO membranes in the literature, the synthesized membrane with double-skinned structure should be promising for enhancement of FO performance and long-term operation capacity in practical desalination processes.