Investigation of the effects of different zwitterions in fabricating smart PVDF/graphene pervaporation membranes

Abstract

Although membrane separation processes including pervaporation have demonstrated their as an efficiency in chemical waste treatment and resource recovery, the increasingly complex wastes generated by different industrial sectors make it almost impossible for a single membrane that has a fixed set of properties to handler these kinds of contaminants. For this reason, stimuli responsive membranes that have tunable and switchable properties are necessary to be developed. In this research, we explore the impacts of zwitterion compounds as additives to previously formulated PVDF-graphene membrane where graphene was used to facilitate β-phase induction of PVDF, enhancing its piezoelectric properties. The incorporation of zwitterions intended to even promote the β -crystal phase of PVDF, which is also facilitated by an optimized quantity of graphene. The quantified β phase of pristine PVDF- (68.7 %) was observed to increase to 79.4 %-86.32 %, when different zwitterions are added. Moreover, output voltages from piezoelectric testing of membranes under various weights generated a voltage signal up to 1.69 V for the membrane with the 3-(1-Pyridinio-1-propanesulfonate) zwitterion, named as PGzc membrane. Upon employing these membranes to dehydrate isopropanol by pervaporation, it was found out that PG shows a permeation flux (Pf) of 95.49 ± 9.18 g/m2h and 77 % water concentration in permeate (Wcp) while the PGzc.membrane displayed a Pf and Wcp of 988.84 ± 51 g/m2h and 30 %, respectively. But upon application of an external voltage, it was found out that PGzc's Wcp rises from 30 % to 83 % with increasing voltage and while the Pf gradually falls from 988.84 ± 51 g/m2h to 432.51 ± 19 g/m2h. These findings indicate that the addition of an appropriate zwitterion could significantly influence the piezoelectric properties of PVDF-graphene membranes, enhancing their tuning capability under electrical stimulation. This development is important for separation processes and technologies aimed at creating a sustainable society.