Performance comparison of differently dried graphene oxide-based membranes for desalination by forward osmosis

This study aims to explore the influence of freeze-drying (FD), vacuum-drying (VD), and oven-drying (OD) on the physicochemical properties, structural integrity, and desalination efficiency of graphene oxide (GO) membranes in Forward Osmosis (FO). Mixed cellulose ester (MCE) membranes were modifed with thin GO active layers, optimised by the design of experiments (DoE) protocol, without the use of additional chemical coupling or crosslinking additives. Membranes were fabricated using commercial GO dispersions, followed by drying under the three methods, and then characterised to determine their physicochemical and morphological properties. The results demonstrated that the drying method had a significant impact on the properties of GO membranes: FD effectively preserved the structural framework and functional groups; VD led to moderate deoxygenation; and OD resulted in pronounced structural compaction and extensive loss of oxygen-containing functionalities. Consequently, FD-GO exhibited high hydrophilicity, VD-GO showed moderate hydrophilicity, and OD- GO displayed reduced wettability. The findings also revealed that FD-GO membranes exhibited high water flux, achieving up to 11.28 L/m2.h at a low GO concentration (0.033 mg/mL), due to their preserved porous structure and high hydrophilicity. In contrast, OD-GO membranes showed the highest salt rejection rates, up to 99.67 % at 1 mg/mL concentration, attributed to their compact structure and smaller interlayer spacing due to the loss of oxygen groups. VD-GO membranes provided a balance between water flux and salt rejection, demonstrating intermediate performance. These results suggest that optimal drying techniques can significantly impact the design and scalability of next-generation GO-based FO membranes, enabling efficient, environmentally friendly, chemical-free desalination solutions suitable for industrial applications.