Polymer - Carbon Nanotube Composite Membranes for Water Desalination

A.R. Ramadan, A.M.K. Esawi, N. El Badawi, A.O. Rashed
The American University in Cairo,

Keywords: carbon nanotubes, membranes, desalination


Carbon nanotubes (CNTs) gained attention as possible additives to desalination membranes following molecular dynamics simulations which established superfast water flow inside the nanotubes. Experimental investigations of water mass transport inside CNTs reported significant increases of water flow rates. This led to interest in the use of CNTs in desalination membranes, where CNTs were added to a variety of polymers, primarily for reverse osmosis (RO) applications. A more limited number of studies reported the use of CNTs as fillers in membranes used in forward osmosis (FO) applications. Findings reported here pertain to investigations conducted of the use of CNTs as nanofillers in RO cellulose acetate membranes, as well as in FO polysulfone/polyamide thin film membranes. Used CNTs were functionalized in order to improve their dispersion in the polymer matrices. RO cellulose acetate membranes with dispersed CNTs were prepare by phase inversion, with CNT contents of 0.0005%, 0.005% and 0.01% by weight. On the other hand, FO thin film membranes were prepared by interfacial polymerization of the polyamide rejection layer on top the polysulfone support layer. Different amounts of CNTs, namely: 0.01%, 0.05%, 0.1% and 0.2% by weight, were incorporated in the polyamide rejection layer. Blank membranes were also prepared for each set. Membrane morphologies were characterized by field emission scanning electron microscopy (FESEM) and nitrogen adsorption. Membrane performance was determined through measuring water permeation and salt rejection. Findings show that the incorporation of CNTs in the polymer matrices improved water permeation for both RO and FO membranes. Corresponding salt rejection values show a limited decrease for RO membranes and more noticeable decrease in FO membranes with improved water permeation. Improvements in water permeation are believed to be due to changes in membrane morphology and porosity. The findings reveal the promising use of CNTs as additives in polymeric membranes for the improvement of membrane performance, specifically water permeation, in water desalination applications in both RO and FO modes.