Non-covalently-functionalized CNTs incorporating poly(vinyl alcohol) mixed matrix membranes for pervaporation separation of water-isopropanol mixtures

Abstract

Poly(vinyl alcohol) (PVA) / modified carbon nanotubes (CNTs) mixed matrix membranes (MMMs) were prepared to study the pervaporation (PV) dehydration of aqueous azeotrope isopropanol mixture. CNTs were modified by wrapping different amount (5–14 wt%) of poly(styrenesulfonate) (PSSA) and poly(vinylpyrrolidone) (PVP) on CNT respectively. ATR, XRD, FESEM, TGA and tensile tests were used to characterize the modified carbon nanotubes and the membranes. For carbon nanotubes wrapped lower amount of poly(styrenesulfonate), the pervaporation results showed that the separation factor remarkably increased and the flux slightly decreased by increasing the content of the modified nanotubes from 0 to 3 wt%, while a reverse trend was observed with further incorporation of the nanotubes up to 5 wt%. Interestingly, increasing poly(styrenesulfonate) density around nanotubes’ sidewalls led to non-ideal effects such as interchain coiling of poly(styrenesulfonate) and formation of rigidified coiled-coil aggregations, so the best PV results were achieved at lower wrapping of poly(styrenesulfonate). However, wrapping nanotubes by poly(vinylpyrrolidone) resulted in fabrication of nanocomposites without evidence of defects or agglomerations and enhanced thermal and mechanical properties. Among all prepared membranes, the best PSI (303) was obtained by embedding 4 wt% of poly(vinylpyrrolidone)-wrapped-nanotubes into poly (vinyl alcohol) that could be attributed to good compatibility and interactions between the fillers and the matrix. Hydrogen bonding between carbonyl groups of poly(vinylpyrrolidone) and hydroxyl groups of poly(vinyl alcohol), formation of hydrophilic channels and helical wrapping of poly(vinylpyrrolidone) chains instead of interchain coiling were responsible for the observed improvement in separation performance of the membranes containing PVP-wrapped-CNTs.