(531b) Highly Selective Holey Graphene Oxide Membranes for Gas Separation

Graphene oxide (GO) nanosheets stacked in parallel with sub-nanochannels have been demonstrated with an excellent size-sieving ability for membrane-based gas separation. However, pristine GO sheets are almost impermeable to all gases, so gas molecules can only diffuse through these tortuous nanochannels, leading to low gas permeability. Drilling nanopores on GO sheets will reduce the tortuosity of the gas transport path and thus increase gas permeability while retaining the sharp size-sieving ability. Herein, nanopores were created on GO sheets by etching with hydrogen peroxide to prepare holey GO (HGO) sheets. The pore size of HGO can be tuned from several nanometers to ~100 nm by increasing the etching time. The as-prepared HGO sheets are highly dispersible in water and can be made into membranes by vacuum filtration. Increasing the etching time increases gas permeability. For example, the HGO membrane with an etching time of 4 h (HGO-4h) shows He permeability of 5.8 Barrers at 35 ^oC, which is much higher than the pristine GO membranes (0.97 Barrer), while both membranes show similar He/N₂ selectivity of ~200. Moreover, the microstructure of HGO membranes can be controlled by tuning the pH of HGO solution. For example, when the pH value decreases to 2, the obtained HGO-4h membrane shows the He permeability of 57 Barrers, which is ten times that of membranes obtained at pH value of ~6. The HGO-4h membranes (pH = 2) exhibit He/N₂ selectivity of 1300 and He/CH₄ selectivity of 1800 at 35 ^oC, which surpasses the 2008 Robeson’s upper bound for He/N₂ and He/CH₄ separation.