Chemical modification of reduced graphene oxide membranes: enhanced desalination performance and structural properties for forward osmosis

Graphene oxide nanosheets offer an insight breakthrough into the development of novel and efficient laminated graphene oxide (GO)-based forward osmosis membranes, with high hydrophilicity and outstanding desalination performance. However, fabrication of desirable and promising GO-based nanocomposite membrane which can overcome the on-going trade-off between forward osmosis (FO) performance and dimensional stability, remains to be unachievable prior to its practical application. In this study, to overcome performance and stability challenges, polyethyleneimine (PEI) was used to reduce GO (rGO), crosslink and surface modification for performance enhancement. The cross-linked rGO was then deposited on a hydrophilic nylon support layer (modified by polydopamine, pDA, for structural stability) using vacuum filtration method. The resulting PEI:rGO/pDA membrane showed excellent water flux (25.5 LMH), high sodium chloride (NaCl) salt rejection (98.9%), and low reverse solute flux (0.91 gMH) in lab-scale tests. The combination of crosslinking GO with PEI and modifying the support layer with polydopamine (pDA) enhanced the membranes hydrophilicity and structural stability. The incorporation of PEI into GO resulted in compacted nanochannels, improving molecular/ions separation. Moreover, the pDA coating enhanced desalination performance and reduced internal concentration polarisation effects, further improving the membrane durability and integrity through the formation of numerous binding sites for firmly anchoring with the PEI:rGO nanocomposite structure.