Design and Performance Evaluation of Hybrid Nanofiltration Membranes Based on Multiwalled Carbon Nanotubes and Polyelectrolyte Multilayers for Larger Ion Rejection and Separation

A polyelectrolyte multilayer (PEM) membrane of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) is deposited on top of a thick-layer micrometer range of multiwalled carbon nanotubes (MWCNTs) assembled on a porous silicon carbide (SiC) tubular membrane support. MWCNTs are assembled "layer-by-layer" alternating oxidized CNTs and poly(allylamine hydrochloride)-modified CNTs. The MWCNTs layer is crosslinked by annealing after the assembly. The MWCNT layer acts as a spacer between the PDADMAC/PSS PEM and the SiC support. The MWCNT support increases water permeability in 42% compared with the PEMs deposited without MWCNTs. Hybrid MWCNT-PEM membranes show high rejection for divalent ions, which increases directly with flux. A rejection up to 92% is measured for MgSO4 and there is up to a 60% rejection difference between MgCl2 and NaCl, making the hybrid MWCNT-PEMs highly appealing for nanofiltration and monovalent and divalent ion separations