Poly(vinyl alcohol)/carbon nanotube (CNT) membranes for pervaporation dehydration: The effect of functionalization agents for CNT on pervaporation performance

Polymeric membrane-based pervaporation separation for desalination of salty water and dehydration from water/organic solvent mixtures is studied. In this work surface-functionalized carbon nanotubes (CNTs) are used to build up water-conduction pathways in poly(vinyl alcohol) (PVA) membranes. For probing the effect of functionalization agents for CNT on pervaporation separation performance, 4 agents, including PVA, polyethylenimine, lignin, and cellulose nanocrystal, have been included in the studies. The hydrophilicity of the functionalization agents, providing strong interaction between the functionalized CNT surfaces and water molecules, plays a critical role on construction of water-conduction pathways in the PVA/functionalized CNT membranes. Small amount of functionalized-CNTs (about 0.03 wt%) have exhibited significant effects on enhancing the permeation fluxes of the membranes. Among the functionalized CNTs, PVA-CNT shows the highest performance on enhancing the permeation fluxes of the corresponding membranes for desalination on a feeding solution of 3.5 wt% NaCl(aq). On the other hand, for dehydration on water/alcohol mixtures, ozonized lignin-functionalized CNTs are most effective for membrane modification. For a 70 wt% ethanol aqueous solution at 25 °C, the PVA/lignin-CNT membrane possessing 0.03 wt% of lignin-CNT exhibits a flux of 880 g m−2 h−1, compared to the value of 565 g m−2 h−1 found with the neat PVA membrane. The water concentrations of the permeated liquids for both membranes are above 99.95 wt%, corresponding to water separation factors above 4464. The increased fluxes could be attributed to the enhanced molecule mobility associating to the CNT-based water conduction pathways.