Oxidation of graphene was studied as a function of reaction kinetics (temperature, oxidation time), and mass transfer (ozone velocity). To understand the effect of reaction conditions on graphene porosity, the gas transport resistance model (Supplementary Note S1, Table , S4, and S5) was used to extract permeance from the graphene layer. For PG membranes, the increase in porosity due to oxidation was indicated by an obvious increase in gas permeance compared to the membranes based on as-synthesized graphene (colored data points in Figure ).