Size-controlled graphene oxide for highly permeable and fouling-resistant outer-selective hollow fiber thin-film composite membranes for forward osmosis

Abstract

Size-controlled graphene oxide (SGO) nanosheets, which are uniform and smaller in size than 2 μm, were successfully incorporated into a polyamide (PA) layer for preparing an outer-selective hollow fiber (OSHF) thin-film nanocomposite (TFN) membrane for forward osmosis (FO) applications by vacuum-assisted interfacial polymerization (VAIP). Here, we specifically demonstrate that the SGO nanosheets in amine aqueous solution were horizontally aligned and stacked on the surface of a membrane substrate by vacuum suction from outside to inside in the VAIP; the SGO nanosheets were then well-incorporated into the thin PA layer with less physical damage. In addition, the SGO nanosheets' effective loading inside the PA layer under the VAIP was much higher than that under the typical interfacial polymerization (IP), since there is no issue about the particle loss from air or nitrogen blowing to remove excess amine solution. The benefit would be highly cost-effective in terms of the nanomaterial's use in a TFN membrane production. As a result, the optimum OSHF TFN membrane incorporated with SGO at 0.0005 wt% (SGO5) exhibited outstanding FO performance, including higher water flux at 39.0 L m-2 h-1 and lower specific reverse solute flux at 0.16 g L-1, using a 1 M NaCl draw solution. Furthermore, this study demonstrates the effect of graphene oxide (GO)'s lateral size toward the short water pathway, and GO's stable incorporation and hydrophilicity of the PA thin film. In the fouling test using artificial wastewater, SGO-incorporated membranes exhibited enhanced fouling resistance and cleaning efficiency against the foulant-rich solution. This novel TFN membrane is therefore a good candidate to address FO's challenges for wastewater treatment or desalination.