Preparation of polyamide thin film composite forward osmosis membranes using electrospun polyvinylidene fluoride (PVDF) nanofibers as substrates

Abstracts In this study, we explored the feasibility of using electrospun polyvinylidene fluoride (PVDF) nanofibers as substrates to make high-performance forward osmosis (FO) membrane. Polyamide thin films were successfully formed via interfacial polymerization directly on two electrospun PVDF nanofiber substrates, ES-1# and ES-2#, having different surface properties in terms of pore size and surface roughness. The surface structure, water permeability and salt rejection of resultant thin film composite (TFC) FO membranes were characterized by a series of measurements including SEM image observation, XPS characterization and inherent separation property tests. Experimental results revealed that a denser low permeable polyamide layer was formed on the S1# substrate with relatively smaller pore sizes (mean pore size: 0.28 ± 0.08 μm; maximum pore size: 0.49 ± 0.16 μm), while a looser polyamide layer with higher water permeability was attained on the S2# substrate with larger pore size (mean pore size: 0.41 ± 0.01 μm; maximum pore size: 0.63 ± 0.04 μm). The difference in polyamide layer structure was believed to be associated with the substrate structure, leading to different cross-linking degrees during the interfacial polymerization. The basic forward osmosis performance of resulting TFC membranes were investigated and a water flux of 30.4 L/m 2  h was achieved when the active layer was oriented towards the 1.0 M NaCl draw solution while the ratio of reverse salt flux to water flux was able to be kept as low as 0.21 g/L, suggesting the good potential of electro-spun nanofiber membranes used as substrates for making FO membranes.