The effects of formation and functionalization of graphene-based membranes on their gas and water vapor permeation properties

The gas and water vapor permeabilities of graphene-based membranes can be affected by the presence of different functional groups directly bound to the graphene network. In this work, one type of carboxylated graphene oxide (GO-COOH) and two types of graphene oxide synthesized i) under strong oxidative conditions directly from graphite (GO-1) and ii) under mild oxidative conditions from exfoliated graphene (GO-2) were used as precursors of self-standing membranes prepared with thicknesses in the range of 12-55 mu m via slow-vacuum filtration preparation method. It was observed that the permeabilities for all tested gases decreased in order GO-2 > GO-1 > GO-COOH and depended on both the arrangement of graphene sheets and their func-tionalization. The GO-1 membrane with a high content of oxygen-containing groups showed the best performance for water vapor permeability. The GO-2 membrane with a thickness of 43 mu m exhibited a disordered GO sheet morphology and, therefore, unique gas-separation performance towards H-2/CO2 gas pair, showing high hydrogen permeability while keeping extremely high H-2/CO2 ideal selectivity that exceeds the Robeson 2008 upper bound of polymer membranes.