Graphene oxide-based nanomaterials : synthesis, optical characterisation and supercapacitor
Date of Issue2012
School of Physical and Mathematical Sciences
This thesis concerns the study of effect of functional groups on graphene oxide (GO). Functional groups strongly affect the optical properties of GO and they can be used to facilitate the preparation of GO derivatives. This thesis systematically investigates the synthesis, optical characterization and applications of GO-based materials, with an emphasis on the influence of the oxygen-containing groups on their chemical and optical properties. The research can be divided into three sections as shown below.First, the identification of the thickness of GO by white light contrast spectroscopy, which is discussed in Chapter 4. This topic has rarely been studied because of the weak optical absorbance that originates from both the large optical gap caused by sp3 hybridization of the functional groups and the adsorbed water on GO sheets. In our work, we have successfully identified the number of layers of GO (≤10 layers) and deduced the complex refractive index of GO sheets (≤10 layers) as nGO = 1.2-0.24i. For GO sheets of a few layers (≤10 layers), both the optical contrast (at ~580 nm) and the G band intensity increase linearly with the thickness. In comparison with Raman spectroscopy, in which laser-induced reduction of GO cannot be absolutely avoided, contrast spectroscopy is a non-destructive and more efficient approach. Simulation results based on Fresnel’s equations agree well with the evolution of the optical contrast and the trend of G band intensity in accordance with the number of layers. The refractive index of GO can be precisely calculated by this method, which can subsequently be used as a basis for further examination of the optical properties of GO. Overall, we proposed a simple and rapid approach to determine the number of layer of GO on the Si/SiO2 substrate by measuring the optical contrast values, which can also be applied to other graphene-based and two-dimensional materials.