Track-etched membrane as a thin substrate with straight pores to fabricate polyamide forward osmosis membrane

Controlling the internal concentration polarization in forward osmosis (FO) membranes by minimizing the substrate thickness is critical to enhancing the water flux. This study aimed to achieve the fabrication of an ultra-thin FO membrane by forming the polyamide (PA) active layer on a thin and straight-bore film, a so-called track-etched (TE) membrane. The polycarbonate TE membrane had a uniform pore size of 0.22 µm and a thickness of 25 µm. The PA active layer was successfully formed only by creating a thin m-phenylenediamine solution layer on the smooth TE membrane surface before interfacial polymerization. The TE- FO membrane with low porosity (14 %) provided a water flux of 21 L/m²h and a reverse salt flux of 8.0 g/m²h when evaluated with a 1.0 M NaCl draw solution. Further evaluations showed the potential of increasing water flux by increasing the TE substrate porosity (14 %) and reducing the apparent PA active layer thickness (504 nm). These results suggest the potential of achieving a high-water flux FO membrane using a thin TE substrate and ultimately improving the validity of FO membrane-based water treatment.