Challenges of using natural extracts as green reducing agents in the synthesis of rGO: A brief review

Reduced graphene oxide (rGO) has attracted much attention because of its high thermal conductivity, electrical properties, Young's modulus, mechanical strength, optical transmittance as well as theoretical areas. This material is widely used for various applications and normally produced by the reduction of graphene oxide (GO). Currently, the reducing agents used in the rGO synthesis such as hydrazine are harmful to the environment. Therefore, multiple searches for eco-friendly reducing agents have been conducted to replace the toxic ones. This brief review discusses the challenge of using natural extracts as reducing agents and several techniques commonly utilized in the synthesis of rGO from GO. Furthermore, the chemical components and mechanism involved in the reduction process are reviewed and compared. Some mechanisms involved in the GO reduction are discussed from the view point of the chemical contents in the plant extracts. Several fundamental characterization techniques, such as UV-Vis, FTIR, XRD, and Raman spectroscopies are also described. These main characterizations are utilized to justify the success of the reduction process with the hope that it can be used as an initial screening before a complete characterization of the synthesized rGO is conducted. Moreover, the developing use of natural reducing agents faces some challenges, including the complexity of the compounds in the natural extracts and the reproducibility of the synthesis method. This review summarizes the strategy for applying natural agents to reduce GO to rGO so that it can help researchers finding the novel green extracts and use it effectively in the rGO synthesis process.