PVDF membranes containing reduced graphene oxide: Effect of degree of reduction on membrane distillation performance

Hydrophobic polyvinylidene fluoride (PVDF) membranes have been successfully used in membrane distillation (MD) for desalination applications; however, there is still room for performance enhancements both regarding water flux and salt rejection. In this work, reduced graphene oxide (rGO) nanoplatelets with different degrees of reduction (36%, 58%, 65 and 69% removal of oxygen, as characterized by XPS) were incorporated as fillers in PVDF matrices in order to evaluate the effect of the oxygen content of the fillers in the MD performance. UV–Vis and Raman spectroscopies were also used to characterize the fabricated rGO. Changes in morphology of the prepared mixed matrix membranes (MMMs) were assessed via scanning electron microscopy (SEM) and were related to the increased hydrophilicity and viscosity of the casting solutions when fillers were added. MMMs containing 0.5 wt% rGO with an optimum degree of reduction of 58% exhibited an improved MD performance, with fluxes of ~7.0 L m⁻² h⁻¹ (LMH), representing an enhancement of ~169% in comparison with the plain PVDF membrane, without compromising salt rejection (>99.99%). Continuous testing for up to 96 h showed a stable performance of the developed MMMs, without compromising the quality of the permeate.