Advancements in chemical oxidation-reduction reactions and supramolecular hydrogels of graphene-based materials

Graphene is one of the most important carbon materials in the global trend of nanotechnology application and sustainable development. Beside liquid-phase exfoliation, solid-phase exfoliation, chemical vapour deposition and electrochemical methods, the most popular technology for large-scale production of graphene-based nanosheets is the chemical route of oxidation-reduction reactions. Chemical conversion of natural/artificial graphite into graphite oxide (GrO) requires a strong oxidation reaction, typically using manganese (VII) oxidant in improved Hummers methods, to generate numerous oxygen-containing functional groups on graphene planes in multilayer graphite structure. Ultrasonic exfoliation of hydrated multilayer GrO in water produces an aqueous dispersion of graphene oxide nanosheets (GO) for next reduction reaction, restoring conductiveπ-conjugated graphene domains in reduced GO (RGO). While green reducing agents like vitamin C and sugars are eco-friendly choices, highly alkaline solutions emerge as an efficient approach to synthesizing non-stacked RGO. Among strategies for preventing graphene restacking through hydrophobic force andπ-πinteraction, bioinspired supramolecular graphene-based materials are excellent to preserve and produce solution-processable nanostructures for a variety of applications. In this review, advancements in chemical oxidation and reduction reactions for synthesizing GO and RGO are highlighted, particularly mechanism of cascade design oxidation process using manganese (VII) oxidant, mechanism of GO reduction reaction using highly alkaline solutions, and the reversible self-assembly of graphene-based materials. Moreover, the review summarizes the conceptualization, density functional theory calculation and experimental syntheses of supramolecular hydration structures of graphene-based hydrogels, including multifunctional applications in aqueous dispersions, water purification, photocatalysis, biosensing, antibacterial hydrogels, polymer nanocomposites, nanostructured coatings and energy devices.