A green manufacturing method of graphene oxide

Hummers' method is widely used for the synthesis of graphene oxide (GO) and is recognised as the standard; however, it involves the use of a solid oxidant (KMnO 4 ), which is difficult to handle, in concentrated sulfuric acid, and the oxidation reaction is quenched using H 2 O 2 , which produces oxygen gas and a large amount of liquid waste. An eco-friendly and safe protocol for GO synthesis without KMnO 4 powder and H 2 O 2 is urgently required. The Shinshu University-Sanwayuka (SUSY) method overcomes these issues by replacing KMnO 4 powder with a 40 % NaMnO 4 solution and H 2 O 2 with FeSO 4 . The SUSY method produced multilayered GO with a GO powder yield of 110 % relative to the amount of the graphite source, and the impurity content was 3.0 %. The π conjugated structure of SUSY-GO is similar to that of Hummers-GO. The oxidation efficiency of the NaMnO 4 solution was slightly higher than that of the KMnO 4 powder, providing a higher content of oxygen functional groups. The C/O ratio of SUSY-GO was 3.0, whereas that of Hummers-GO was 3.1. A small pilot plant of the SUSY method can produce 200 L/day of 0.3 wt% GO dispersion. The estimated production cost of 1 kg of GO and the amount of liquid waste by the SUSY method are approximately 76,400 yen and 592 L, respectively, whereas those by the improved Hummers' method are 91,100 yen and 930 L. Moreover, monitoring and detoxification systems of explosive Mn 2 O 7 gas are installed in the SUSY method, enabling the safe, eco-friendly, and scalable manufacturing of GO. • Reducing the explosion risk by oxidation with NaMnO 4 solution instead of KMnO 4 • Less liquid waste and explosive gas • 200 L/day of 0.3 wt% graphene oxide (GO) dispersion • Production of high-quality intrinsic GO dispersion • Mn 2 O 7 gas monitoring and detoxifying system is installed.