Graphene oxides as nanofillers in polysulfone ultrafiltration membranes: Shape matters

While a number of graphene oxide (GO) materials have been evaluated as nanofillers in ultrafiltration membranes, there remain outstanding questions regarding GO material properties relating to membrane structure(s) and eventual performance (i.e. structure-performance relationships). In this work, we synthesize, apply, and evaluate GO analog materials of different shape, flat GO and crumpled GO (CGO), as nanoscale fillers in polysulfone (PSF) ultrafiltration membranes. GO/CGO-PSF composite membranes were synthesized via phase inversion, characterized using both microscopic and spectroscopic techniques, and compared with respect to permeability, rejection, and anti-fouling properties. Experimental results show that graphene shape alone results in varied performance. Observed differences are attributed to the (more) effective dispersion/stability of CGO nanoparticles in solvent (NMP) as a result of shape effects, which lowers the tipping mass percentage after which the effect of viscosity increase outweighs that of hydrophilicity increase. Our results also suggest that the change(s) in membrane porosity is likely to be a more important factor compared to surface hydrophilicity in determining ultrafiltration membrane performance when graphene oxides are applied with these mass percentages. In addition to the effect of GO shape, this study also highlights the importance of nanoparticle dispersibility/stability in organic solvents when constructing the process-structure-performance relationships for nano-enabled ultrafiltration membranes synthesized via phase inversion.