Support-free multi-walled carbon nanotubes-based membrane for forward osmosis applications

This study aims to fabricate a thin-film composite membrane with high water flux and low reverse solute flux for the application in a forward osmosis (FO) system. Instead of using traditional non-woven fabric or polymer materials, multi-walled carbon nanotubes (MWCNTs) layers prepared via the vacuum filtration method to reinforce the membrane are fabricated. In this work MWCNTs are modified by the mixture of polydopamine (PDA) and polyvinyl alcohol (PVA) to enhance the mechanical strength and hydrophilicity of the membrane, which is denoted as PVAm pCNTn. Finally, a polyamide (PA) active layer, used as molecular selection, is synthesized on the PVAmpCNTn film using the interfacial polymerization method, which is assigned as PVAmpCNTnPA. Experimental results show that PDA and PVA improve adherence among the MWCNTs, strengthening the tolerance and increasing hydrophilicity of the membrane. Membrane performance is also affected by the amount of PVA(m) and PVA(n), and thickness can be controlled by adopting various amounts of MWCNTs suspension during the vacuum filtration process; the thinner membrane results in higher water flux because of lower flow resistance. In addition, the PVA concentration influences the pore size distribution and configuration within the membrane, as a result, affects the FO performance. The best FO performance are achieved by PVA0.25pCNT3-PA, with a water flux of 30.16 L m- 2 h-1 and reverse solute flux of 9.34 g-2 h-1. The excellent FO performance and the simple process used in this study indicate the great potential of this work in the FO application.