As frontier materials, graphene oxide (GO) and graphene have penetrated almost all research areas and advanced numerous technologies in sensing, electronics, energy storage, catalysis, water treatment, advanced composites, biomedical, and more. However, the affordable large-scale synthesis of high-quality GO and graphene remains a significant challenge that negatively affects its commercialisation. In this article, firstly, a simple, scalable approach was demonstrated to synthesise high-quality, high yield GO by modifying the improved Hummers method. The advantages of the optimised process are reduced oxidation time, straightforward washing steps without using coagulation step, reduction in cost as eliminating the use of phosphoric acid, use of minimum chemical reagents, and increased production of GO per batch (~ 62 g). Subsequently, the produced GO was reduced to reduced graphene oxide (rGO) using three different approaches: green reduction using ascorbic acid, hydrothermal and thermal reduction techniques. The GO and rGO samples were characterised using various microscopy and spectroscopy techniques such as XRD, Raman, SEM, TEM, XPS and TGA. The rGO prepared using different methods were compared thoroughly, and it was noticed that rGO produced by ascorbic acid reduction has high quality and high yield. Furthermore, surface (surface wettability, zeta potential and surface area) and electrical properties of GO and different rGO were evaluated. The presented synthesis processes might be potentially scaled up for large-scale production of GO and rGO.

    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Synthesis of GO
        2.3 Synthesis of ascorbic acid reduced graphene oxide (AA-rGO)
        2.4 Synthesis of hydrothermally reduced graphene oxide (H-rGO)
        2.5 Synthesis of thermally reduced graphene oxide (T-rGO)
        2.6 Characterisation
    3 Result and discussion
        3.1 Structural and morphological characterisation
        3.2 Surface and electrical conductivity properties
    4 Conclusion
    Acknowledgements 
    References

• Neeraj Kumar(Centre for Nanostructures and Advanced Materials, Department of Chemical Sciences, University of Johannesburg)
• Katlego Setshedi(Centre for Nanostructures and Advanced Materials)
• Mike Masukume(Centre for Nanostructures and Advanced Materials)
• Suprakas Sinha Ray(Centre for Nanostructures and Advanced Materials, Department of Chemical Sciences, University of Johannesburg)