Efficient membrane fouling mitigation in self-cleaning piezoelectric PVDF-graphene loose nanofiltration membranes for sustainable textile wastewater treatment

Despite the effectiveness and eco-friendly nature of membrane separation in wastewater treatment, the notable and unavoidable fouling problem in conventional membranes has become a substantial challenge within the field of membrane technology. Due to this factor, there is significant potential in alleviating this issue through the creation of responsive membranes capable of self-cleaning. This study introduces the fabrication of loose nanofiltration (LNF) membranes using electro-responsive poly(vinylidene fluoride) (PVDF)/graphene (PVDFGr), which exhibit self-cleaning capabilities when subjected to an external voltage. In this membrane system, varying amounts of graphene triggers the self-assembly of PVDF chains to have a dominant β-phase that is responsible for its distinctive piezoelectric characteristic. Upon subjecting the PVDF1Gr1 membrane with the best piezoelectric property to an AC voltage of 36 V during the foulant filtration test, there was no apparent change in its original permeance value for over 120 min unlike the control membrane that showed a continuously declining value. This proves that the membrane could effectively mitigate fouling through the inverse piezoelectric effect. By responding to an applied voltage, the membrane undergoes a deformation that causes its self-vibration, thereby expelling foulants from the membrane. Moreover, during NF testing, it was found out that this membrane has a Congo red (CR) rejection of up to 96.4 %, and sodium chloride (NaCl) rejection of 1.6 %. This high dye rejection and high salt transmission indicate that this piezoelectric membrane could be applied for efficient textile wastewater treatment where dyes and salts can be separated from each other, and hence sustainably recover these valuable resources.