Middle support layer formation and structure in relation to performance of three-tier thin film composite forward osmosis membrane

Abstract

In recent years, nanofibers have been directly used as the support layer for developing high-flux forward osmosis (FO) membrane due to their high porosity and low tortuosity. However, the rougher surface and larger pore size weaken the adhesion to the polyamide (PA) active layer. Conventional FO membrane made of phase inversion support layer exhibits favorable mechanical stability, however the water flux is poor due to severe internal concentration polarization (ICP). In order to simultaneously reduce the ICP and enhance the mechanical stability of FO membrane, a thin film composite (TFC) FO membrane composed of three layers was prepared, namely bottom electrospun hydrophobic/hydrophilic interpenetrating network composite nanofibers (HH-IPN-CNF) support layer, a phase separation formed microporous polyvinylidene fluoride (PVDF) middle support layer, and the top PA active layer formed by interfacial polymerization. The factors including polymer concentration, coagulation bath composition and the gate height of the casting blade that affect the mid-layer structure formation were investigated, respectively. With the mid-layer of FO membrane cast under different conditions, water flux ranged from 10.39 to 30.62LMH, by using 0.5M NaCl draw solution and deionized water feed solution. The TFC FO membrane with high structure integrity may be promising candidate for engineered osmosis.