Structural and Capacitive Properties of Graphene Obtained by a Green Method of Graphene Oxide Reduction

M. Raić, D. Sačer and M. . Kraljic Rokovic

Abstract
In this study, a green method was applied in order to reduce graphene oxide (GO). Reduction was carried out at 80 °C in the presence of phenolic compounds from olive leaf extract (OLE), and olive mill wastewater (OMW) as a reducing agent. Owning to the natural origin of the reducing agent, this method is environmentally friendly. Reduction was carried out at pH=7 and pH=10 in the presence of OLE, and at pH=10 in the presence of OMW. The reduction process was monitored using UV/Vis spectroscopy. The structural properties of the reduced graphene oxide (rGO) samples were characterized by Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Structural studies demonstrated that a part of the oxygen functionalities in the graphene oxide structure had been removed, which resulted in increased electrical conductivity as proved by the four-point probe method. Better reduction efficiency, as well as better capacitive properties, were obtained at increased pH value. Capacitive properties of rGO were determined using the cyclic voltammetry technique. The influence of the different reducing agents, OLE and OMW, on rGO capacitive properties is also shown in this work.

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Keywords
graphene, graphene oxide, capacitive properties, olive leaf extract, olive mill wastewater