Graphene, a two-dimensional honeycomb sp2 carbon lattice has received enormous attention because of the potential for various applications such as the electrodes of photovoltaic devices and batteries, next generation flexible electronics and even antibacterial coatings [1][2]. Interest in the application of graphene is mainly due to its high electrical conductivity, flexibility and huge tuneability of the properties of graphene-based materials [3][4]. For example, the semi-metal character of pristine graphene can be changed to semiconducting [5], insulating [6] or superconducting [7] by control of size or chemical functionalization. To utilize graphene's unique properties and potential adaptability, several graphene synthesis methods have been developed. Mechanical exfoliation is the earliest technique to isolate monolayer graphene, but the yields are limited. Chemical Vapour Deposition (CVD) epitaxial growth exploits catalytic metal substrates such as Ni or Cu and can produce large area and high-quality graphene directly on the substrate, but the requirements of high temperature and the multi-step transferral process are major difficulties for cheap, industrial-scale production [4] [8]. Chemical exfoliation of graphene using Hummers' method is attractive for producing solution-processed graphene oxide (GO), but subsequent chemical or thermal treatments can only partially remove its oxygen content so that electrical properties cannot be fully restored [9][8]. Numerous other synthesis techniques have been developed to overcome these limitations, including solvent-assisted Liquid-Phase Exfoliation (LPE) [10][8] or the formation of graphite intercalation compounds [11], but extensive sonication processes are required that limit the size and yield of thin graphene flakes [4]. Furthermore, due to its low solubility, the exfoliated graphene is usually dispersed in high-boiling-point solvents, which creates difficulties for subsequent film preparation. Therefore a low-cost, solution-processable method that can lead to high-quality graphene film is desirable [4].
展开▼
