Low-cost synthesis of large graphene oxide flakes by the total oxidation of large natural graphite flakes

• In-situ monitoring reveals that large graphite flakes can be fully oxidized while remaining largely intact given sufficient time, contrary to previous assumptions. • Increasing oxidizer concentration by minimizing solvent (H2SO4) enables full oxidation of gram-scale large graphite flakes in a semi-solid state, reducing reagent consumption. • Adjusting reaction temperature balances graphite oxidation and Mn(VII) self-decomposition, leading to successful oxidation of 200-, 100-, and 50-mesh natural graphite. • The method yields large graphene oxide flakes with average sizes of 27.3, 58.7, and 116.2 μm from respective mesh sizes, offering a scalable and cost-effective production strategy.