Contribution of graphene oxide (GO)-containing polydimethylsiloxane (PDMS) binder to the surface modification of electrospun PVDF membrane towards development of photothermal vacuum membrane distillation (PVMD)

Abstract

Given the scarcity of water and energy resources and their potential to escalate into future crises, water and energy have emerged as the paramount challenges of the present century. To address these challenges, simultaneously, a novel membrane distillation (MD) technique named photothermal MD (PMD) has come to the forefront in recent years. The PMD is rapidly advancing, particularly in the field of desalination, towards increasing the use of sustainable solar energy. In this work, the surface of poly(vinylidene fluoride) (PVDF) electrospun membrane was turned into a photothermal surface by binding graphene oxide (GO) nanosheets using a binder solution made of polydimethylsiloxane (PDMS) with different concentrations (0.1, 0.5, 1, 2, 3 wt%). Subsequently, the environmentally-friendly low-pressure plasma polymerization method was employed to polymerize perfluorodecyl acrylate (PFDA) monomers on the surface of coated electrospun membrane to achieve an omniphobic surface. In this regard, the contact angles of water, oil, and ethanol/water (70/30 v/v) solution on the surface of the coated membranes were measured to be 144°, 124.4°, and 120.8°, respectively. Compared to the uncoated electrospun membrane, the one coated with GO-containing binder solution with optimum PDMS concentration of 0.1 wt%, showed a significant increase in flux by 41 % at 1 sun irradiation during photothermal vacuum MD (PVMD). In the PVMD process, the conventional method of feed heating was substituted with membrane surface heating utilizing solar energy. Additionally, vacuum was employed to facilitate the passage of water vapor through the membrane pores. This increment was further highlighted by salt rejection remained constant at 99.9 %. It was also found that PDMS concentration in the GO-containing binder solution adversely affects the membrane efficiency, exhibiting a decreasing trend from 54.1 % to 17.5 % when PDMS concentration increases from 0.1 to 3 wt%. Additionally, the long-term performance assessment of the prepared membrane coated with the binder solution with optimum PDMS concentration of 0.1 wt% demonstrated its acceptable resistance against wetting by the NaCl aqueous solution (35 g/L) containing 0.3 mM sodium dodecyl sulfate (SDS).