Understanding structure-property relationships in graphene oxide-coated polymer membranes: The impact of flake size on dye and salt rejection

Graphene oxide (GO) membranes were fabricated using vacuum filtration and their performance in the removal of dye and salts from effluent was investigated. GO flake size is thought to influence the performance of composite membrane systems. Using smaller flake GO (SFGO) and larger flake GO (LFGO) systems, filtration studies demonstrated that both cationic Methylene Blue (MB) and anionic Methyl Orange (MO) could be effectively removed from water effectively using both systems. The highest removal rates of both dyes were achieved by the 0.10 mg/mL SFGO coating, rejecting 86.4% MB and 87.8% MO, at 2 bar with 5 mg/L dyes. For both GOs, the removal of MO was higher overall, which was attributed to electrostatic repulsion between the like-charged GO and dye. MB was found to adsorb strongly onto the GO coating. Desalination of NaCl, Na2SO4, MgSO4 and (NH4)6Mo7O24 was found moderately successful, with performance degrading significantly with permeated volume. This behaviour was attributed to the Donnan Effect and expansion of GO interlayer spacing, due to the intercalation of water molecules. The presence of Na2SO4 and MgSO4 in MB was demonstrated to degrade both flux and dye rejection capability of both GOs, due to the neutralisation of the electronegativity driven by the salt cations.