Antifouling and stability enhancement of electrochemically modified reduced graphene oxide membranes for water desalination by forward osmosis

In this study, an innovative electro-oxidative technique was employed to create graphene-based forward osmosis (FO) membranes. This involved constructing Polyethyleneimine crosslinked reduced graphene oxide (PEI:rGO) layers on scalable flat-sheet substrates functionalized with polyethylene glycol-Poly(3,4-ethylene-dioxythiophene)-poly (styrenesulfonate) (P:P:P) via electrophoretic deposition. Under the optimized electric potential of 10 V, we successfully combined PEI:rGO laminates with P:P:P support layers, resulting in a highly porous structure. The double-sided coated PEI:rGO membrane (DS-PEI:rGO) exhibited superior performance compared to the single-sided PEI:rGO membrane (SS-PEI:rGO). DS-PEI:rGO showed higher ion salt rejection (95 %) than that of SS-PEI:rGO (90.1 %) but slightly lower than the commercially-available Cellulose Triacetate (CTA-FO) membrane (99.3 %) in lab-scale FO desalination process. Interestingly, the resultant DS-PEI:rGO membrane exhibited reduced specific salt flux (0.014 g/L) compared to SS-PEI:rGO and CTA-FO membrane (0.017 g/L and 2.549 g/L, respectively). The antifouling properties of PEI:rGO membranes were assessed using synthetic seawater with sodium alginate. Under a 3.0 V DC potential, both PEI:rGO membranes experienced a 30 % increase in recovered flux compared to membranes without an electric field. This improvement was attributed to electro-oxidation mechanisms between PEI:rGO and oppositely charged ions, along with the unique nanocomposite structure formed by PEI:rGO and P:P:P chains, contributing to enhanced membrane integrity.