Green synthesis of water-soluble graphene nanosheets under solvent-free condition and in-situ anchored with MnO2 as supercapacitor

Abstract

Since the direct dispersion of hydrophobic graphene nanosheets (GNS) in water without the assistance of dispersing agents such as polymeric or surfactant stabilizers are generally considered as an insurmountable challenge, current research aims to develop GNS using a green and solvent-free method. This method is an environmental eco-friendly approach and lets GNS get produced directly from graphite in simple conditions without using any toxic acids and reagents. This method is implemented at the shortest possible time without high temperatures and long synthesis times by using green and non-toxic citric acid as a cheap and eco-friendly intercalation agent at 100 °C without any need for any additional purification. This procedure is a promising route for the generation of stable GNS in water. In the second step, we utilized in-situ synthesis through a green method to develop graphene-MnO2 nanocomposite by anchoring MnO2 nanoflowers on graphene sheets. In this approach, there is no need for any additional purification or adding any materials or catalysis. The specific capacitance of 213 F g−1 was obtained for the graphene-MnO2 nanocomposite at a scan rate of 10 mV s−1.which makes it a great candidate for supercapacilator applications. In addition, the synthesized nanocomposite retained 90.25% of the initial capacitance after 500 cycles of charge–discharge at a current density of 40 A g−1. The work provides a new approach for synthesized GNS with the functional group without needing reduction agent and in situ anchored GNS with MnO2 nanoflowers nanocomposite at a green and eco-friendly condition, suggesting GNS and its nanocomposite have potential uses in many different areas of research.