(571e) Reduced Graphene Oxide (rGO) Membranes for Water Treatment Applications

Graphene oxide (GO) membranes have recently been studied for separations of molecules in nanoscales. With an interlayer spacing of 1.3-1.5 nm, GO nanochannels can reject dyes (rejection> 95%, size: 1.3 nm) depending on the size of dye and can have moderate rejections for divalent ions. It provides a robust active layer for separations as compared to polymeric membranes. However, GO is readily dispersible in water due to the presence of the different oxygen-containing functionalities like carboxylic, hydroxyl, and epoxy on the basal plane and along the edge. GO layer can be peeled off the porous substrate easily under the shear force exerted by water, thus limiting its practical applications. This study focusses on the reduction of graphene oxide membranes and understands its impact on stability in aqueous environment. Catalytic properties of these membranes in advance oxidation are also explored.

GO membranes were synthesized using vacuum filtration for varying loading of GO on porous microfiltration membrane (Nanostone PVDF 200). GO membranes were further chemically reduced using either NaBH₄, or ascorbic acid. Reduced graphene oxide membranes (rGO) were more hydrophobic as compared to GO membranes. Characterization of rGO membranes was carried out to understand reduction of oxygen containing functionalities, and to quantify the mechanical strength of the film.

The rGO membrane was observed to be stable in a crossflow membrane setup. The membrane had a rejection of 95% for neutral red dye (1.3 nm diameter) and 35% rejection for CaSO₄. GO is known to possess antibacterial properties and thus makes it suitable for applications where biological fouling is severe. We investigated the fouling behavior of these membranes in the presence of Humic acid (HA), and bovine serum albumin (BSA), and compared it with commercial nanofiltration membranes (Nanostone Inc. NF8 and DOW NF270).

GO and rGO also have been reported to have catalytic properties in advanced oxidation processes. This makes these membranes interesting as no transition metal catalyst are involved. We observed that rGO membranes had better efficiency in the decomposition of sodium persulfate (to generate sulfate free radicals). This project is supported by, NSF KY EPSCoR program, and by NIH-NIEHS-SRC, and by Australian Research Council (through Monash University).