Fabrication of thin film composite poly(amide)-carbon-nanotube supported membranes for enhanced performance in osmotically driven desalination systems

The search for lower energy consumption desalination systems has been driving research in the past decade towards the investigation of osmotically driven membrane processes, such as forward osmosis (FO) or osmotic distillation (OD). Despite similarities with reverse osmosis (RO) membranes, thin film composite (TFC) for FO membranes require careful design to reduce salt concentration polarization formation within the large pores composing the supporting layer. An investigation of a novel, highly stable, robust support made solely of carbon nanotubes (CNTs), which could find applications in both RO and FO was undertaken. TFC membranes were fabricated by interfacially polymerizing for the first time a dense poly(amide) (PA) layer on self-supporting bucky-papers (BPs) made of hydroxyl-functionalized entangled CNTs. These hydrophilic supports exhibited low contact angle with water (<20°), high water uptake capacity (17. wt%), large porosity (>90%), making it a promising material when compared with poly(sulfone) (PSf), the traditional polymer used to fabricate TFC membrane supports in RO. In addition, the impact of the support hydrophilicity on the stability of the interfacially polymerized film and on water adsorption was investigated by oxygen-plasma treating various potential support materials, exhibiting similar geometrical properties. The morphology and salt diffusion of both CNT BP and PSf supports were investigated, and the novel BP-PA composite membranes were found to be superior to commercially available TFC membranes.