Pore incorporation in PG is indicated by a monotonic increase in ID/IG to 1.38±0.08 when the oxidation temperature was increased from 40 to 90 ℃ (Figure ). The intensity of the 2D peak decreased as a function of oxidation consistent with the formation of high-density O-clusters, which makes graphene nanocrystalline. As oxidation progressed, an obvious D' peak appeared on the shoulder of the G peak with a D'/G peak ratio higher than 0.8, which confirmed the formation of carbon vacancies in graphene. This was also confirmed by gas permeation studies (see next section).