Scalable Syntheses of Graphene Oxide and Reduced Graphene Oxide using Cascade Design Oxidation and Highly Basic Reduction Reactions

Abstract

This present work describes the scalable synthetic methods of oxidation and reduction reactions for producing graphene oxide and reduced graphene oxide nanomaterials. Cascade design of Mn(VII)-based oxidation reaction is applied to convert graphite into multilayer graphite oxide powder, the precursor of single-layer graphene oxide nanosheets. Since exothermic heats, relevant chemical ratios, and combinative strategy are utilized, the cascade design process saves considerable amounts of heating energy, chemical reagents, and synthetic time. In the next stage, the hydrated multilayer structure of graphite oxide is exfoliated in water with the support of sonication. Graphene oxide nanosheets are electrostatically stabilized and chemically reduced using highly basic ammonia solution at pH >11 and a temperature of 90 °C. Alkaline ammonium hydroxide solution is considered an environmentally friendly and inexpensive chemical agent for synthesizing reduced graphene oxide nanosheets assembled in a hydrogel structure. Hydrated reduced graphene oxide nanosheets in the supramolecular hydrogel can be ultrasonically exfoliated to produce homogeneous aqueous dispersions. The general protocol of oxidation-reduction reactions sequentially synthesizes graphite oxide powder, graphene oxide nanosheet, reduced graphene oxide hydrogel, and reduced graphene oxide nanosheet for various scientific research and multidisciplinary applications. Prospective development of the synthetic approach from laboratory scale to industrial production is envisioned to elaborate on the potential.