Influence of integrating graphene oxide quantum dots on the fine structure characterization and alcohol dehydration performance of pervaporation composite membrane

Graphene oxide quantum dots (GOQDs), a carbon-based nanomaterial resembling the structure of graphene oxide but with a smaller size of < 100 nm, was incorporated in a poly(vinyl alcohol) (PVA) dense selective layer supported on a polysulfone substrate to prepare a composite hybrid pervaporation (PV) membrane for alcohol dehydration. The addition of GOQDs into the PVA polymer matrix provided a tortuous path for the permeating molecules but augments the separation efficiency of the membrane. The presence of hydroxyl and carboxyl groups on the confined nanosize of GOQDs sheets attract the polar groups of the permeants within the polymer matrix. The physicochemical properties of the membrane were characterized. An interesting observation was found when the membranes with GOQD (PVAx-GOQD300) were tested for aqueous propanol isomers mixture, isopropanol (i-PrOH) and n-propanol (n-PrOH). The PVAx-GOQD300 membrane showed lower separation performance for linear alcohol compared with the sterically hindered alcohol. Positron annihilation lifetime spectroscopy (PALS) results revealed that membranes integrated with GOQD behaved differently in both propanol isomers. The PVAx-GOQD300 membrane showed larger free volume size in n-PrOH/water than i-PrOH/water mixtures while there was not much difference in the absence of GOQDs. PALS results justified the low separation of the membrane with linear alcohol/water mixtures. Furthermore, the long operating time, high operating temperature, and high water content in feed shows the potential stability of the membrane for practical application.