Antifouling and stability enhancement of electrochemically modified reduced graphene oxide membranes for water desalination by forward osmosis
Mohamed Edokali, Mozhdeh Mehrabi, Oscar Céspedes, Chao Sun, Sean M. Collins, David Harbottle, Robert Menzel, Ali Hassanpour
Abstract
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.