Facile synthesis of reduced-graphene oxide (rGO) has been conducted in this study using the extract of Caesalpinia sappan L. as a green reducing agent. Graphite sheets were first exfoliated using an improved Hummer process to produce graphene oxide (GO). Then, the reduced-graphene oxide (rGO) was obtained by reducing GO with Caesalpinia sappan L. extract at various concentrations in an autoclave hydrothermal process. Analytical methods such as XRD, Raman spectroscopy, FTIR, SEM-EDX, TEM, UV–visible absorption, TG-DTA, and zeta potential value were used to characterize the graphite, GO, and rGO materials. A cyclic voltammetric study was also conducted to measure the performance of the synthesized materials. All rGO show good electrochemical properties, and the highest oxidation and reduction currents are observed for rGO-10. The characterization results show that Caesalpinia sappan L. extract can effectively reduce GO to rGO, and the best rGO can be obtained by adjusting the level of the extract.

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.

Exfoliated graphene has been successfully synthesized using electrochemical exfoliation method followed by sonication of the graphite rod. Ammonium sulfate, sodium sulfate, ammonium oxalate, hydrogen peroxide, and ammonium persulfate were used as electrolytes. The effect of sonication time was studied for several products. The exfoliated graphene (EG) was characterized using XRD, Raman, FTIR, SEM-EDS, TEM and electrical con-ductivity measurement. The exfoliation using ammonium sulfate-ammonium persulfate as the electrolyte gives the highest mass-product, with a yield of almost 70%. Adding peroxide to the electrolyte reduces the mass of the exfoliated product. In addition, different sonication times results in different phenomena of particle size changes. The XRD data show that the EG has 2 theta = 26.4 degrees which is lower than its origin graphite. Raman data confirm that the EG has been obtained with the FWHM (G) value of 45-70 cm-1, and the resulting EG is a multilayer (2D peak). The O-H and C-C aromatic group has been assigned from FTIR spectrum. From SEM and TEM images, it was understood that the morphology of material is wrinkled, crumpled, and has a transparent zone, while from EDS data, it is found that the O/C value is in the range of 0.15-0.35. The electrical conductivity of EG reaches 52 S/cm.