One-pot preparation of reduced graphene oxide from liquid nitrogen tetroxide via redox potential control

Abstract

Reduced graphene oxide (RGO) was prepared by redox method with liquid nitrogen tetroxide (N2O4) as oxidant source and sodium borohydride (NaBH4) as reducing agent, which could provide an effective way for the treatment and reuse of liquid propellant oxidants. After N2O4 was pretreated with 60 wt% hydrogen peroxide (H2O2), fluorocarbon surfactants (FC-4330), a nonionic polymerized yellow viscous liquid that can significantly reduce the surface tension of the solvent at very low concentrations, was added to the mixture of N2O4 and natural graphite. In order to simplify the synthetic route of graphene, we introduced the redox potential (ORP), a comprehensive index to measure the degree of redox of the reaction system, by which we successfully fused the oxidation stage and reduction stage in the same reaction vessel, in other words, the one-pot method for preparation of RGO has been successfully realized. This method can also be used to accumulate graphene products and determine the yields directly without the necessity to purify and deal with numerous intermediate products. Furthermore, the redox potential of the reaction system was continuously optimized and precisely regulated by automatic sample injection to create the best redox atmosphere for the preparation of RGO, so as to achieve the purpose of improving the yield and quality of graphene. Finally, the optimal process conditions for the preparation of RGO by one-pot method were obtained, that is, the optimal initial ORP range was [1700, 1750] mV at the oxidation stage and [−1200, −1180] mV at the reduction stage. The graphene products can eventually be exfoliated easily between layers with uniform fold distribution, more concentrated particle size distribution and smaller microcrystal size, and simultaneously the stacking number of layers can be stabilized at 1 or 2 layers.