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Many materials with varied characteristics have been used for water purification and separation applications. Recently discovered graphene oxide (GO), a two-dimensional derivative of graphene has been considered as a promising membrane material for water purification due to its excellent hydrophilicity, high water permeability, and excellent ionic/molecular separation properties. This review is focussed on the possible versatile applicability of GO membranes. It is also known that selective reduction of GO results in membranes with a pore size of $0.35 nm, ideally suited for desalination applications. This article presents the applicability of graphene-based membranes for multiple separation applications. This is indeed the first review article outlining a comparison of GO and r-GO membranes and discussing the suitability for applications based on the porosity of the membranes.

Permeance indicates how fast the gas molecule transports through the membrane, usually expressed in gas permeation unit (GPU, 1 GPU = 10 −6 cm 3 (STP) cm −2 scmHg −1 ), while selectivity represents how efficiently the gas is separated from the mixture during the transportation. The nature of molecular transportation in membranes depends on the porosity and type of membrane materials, which can be understood by using mechanisms based on solution-diffusion, size-dependent molecular sieving, Knudsen diffusion, and Poiseuille flow. [3] Materials such as zeolites, [4][5][6] metalorganic frameworks (MOFs), [7][8][9] and carbon-based constituents [10][11][12][13][14] in the form of membranes have been intensively studied as gas barriers in the past. These materials are featured by tuneable nanosized pores, which provide sites for gas