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 Improvement in rejection and permeability of commercial silicon carbide membranes is achieved using polyelectrolyte multilayer membranes with a spacer of multiwalled carbon nanotubes in between. Up to 92% rejection for MgSO4 and a 60% rejection difference between MgCl2 and NaCl make these membranes appealing for nanofiltration and monovalent and divalent ion separations.