In recent past carbon allotropes like carbon nanotubes, graphene and graphene quantum dots have attracted the interest of both industry and the scientific fraternity for their incredible electrical, thermal, optical and mechanical properties. Graphene is monolayer of carbon atoms bound in honeycomb lattice structure. The current work states a comparatively easier and inexpensive chemical route for synthesis of graphene oxide (GO) from graphite and preparation of reduced graphene oxide (rGO) by thermal treatment. GO has been prepared by introducing some modifications over improved Hummers method or more widely known as Tour’s method. The method reports only 7.5% less yield than Tour’s method whereas, requirement of acid and oxidizer have been cut off by 40% and 33%, respectively.
Thermal reduction of GO has been observed by exfoliation and weight loss of the end product. GO has high amount of oxygen containing functional groups in its lattice, which are responsible for its difference in physical properties as compared to graphene. Elimination of the functional groups due to sudden thermal shock and evolution of gasses viz. water, CO and CO2 create a huge pressure in GO lattice which leads to exfoliation. Exfoliation of graphene sheets has been analyzed both qualitatively and quantitatively by FESEM analysis and from measurement of specific surface area respectively. Enhancement of specific area has measured to be almost 9 times from GO to rGO. The current work reports in detail, the onset temperature of thermal exfoliation which is found to be 325 oC. Present work also determines the impact of reduction temperature on carbon-oxygen ratio of the end product. At higher temperature, carbonyl and epoxy groups are eliminated as CO, CO2 by taking out carbon atoms from the graphene oxide plane, which causes defect in the lattice and this affects its carrier transport properties. At reduction temperature of 350 oC highest carbon-oxygen ratio has been obtained. From FTIR analysis removal of oxygen containing functional groups at different reduction temperatures has been studied. Thermal degradation kinetics of GO and rGO have also been performed from TGA data. Thermal degradation rate of GO is found to be concentration independent and is a sole function of temperature.
Presence of graphene quantum dots has been detected by TEM analysis of rGO specimens. Graphene quantum dots have potential applications in the field of bio-imaging, bio-sensing, photovoltaic devices and in light emitting devices. Fluorescence property of the quantum dots have also been investigated in present study.