Performance evaluation of reduced graphene oxide membrane doped with polystyrene sulfonic acid for forward osmosis process

Abstract

Forward osmosis (FO) has emerged as one of the most promising energy efficient technology for desalination, water and wastewater treatment and reclamation. The practical application of the FO process depends on high water permeability and low reverse salt flux of the membrane. This study reports the use of graphene oxide (GO) and polystyrene sulfonic acid (PSS) polymer to enhance the permeation properties and selectivity of the FO-membrane. Size fractionation of GO flakes resulted in different size ranges (3–5 µm, large-sized flake (LF); 1–2.5 µm, medium-sized flake (MF); 0.4–0.8 µm, small-sized flake (SF). The different size flakes were coated on the porous nylon membrane support using a vacuum filtration method followed by thermal reduction to yield reduced graphene oxide (rGO) membrane. The membrane coated with MF provides optimum water flux (Jv) of 26.3 L per square meter per hour (LMH) and specific reverse salt flux (SRSF) of 0.2 g per liter g/L for the FO application. The subsequent addition of the PSS onto rGO membranes improved the hydrophilicity of the rGO laminates rendering excellent water flux (34 LMH) and SRSF (0.18 g/L) in comparison to standalone rGO membrane. The PSS-rGO membrane coated with MF performed better than that of the rGO membrane and commercially available cellulose triacetate (FTS H2O™ CTA) FO membrane in terms of the water flux and SRSF. This study gives new insight into the use of varying size GO flakes and PSS for the fabrication of high-performance FO-membranes.