O3-based oxidation of graphene was conducted in a tubular furnace (Nabertherm, 90 cm heating zone) hosting a 1.5 m long, 12 cm in diameter quartz tube (Figure ). O3 (2 l min -1 ) was produced from a commercial O3 generator (Absolute Ozone, Atlas 60) and stabilized for at least 30 min to reach 8 wt% (O3/O2) as analyzed by a O3 monitor (2B Technologies, Model 106-H).