A Study On The Environmentally Friendly Methods For Preparation Of Graphene And Its Composites

Graphene is a two-dimensional carbon material, which is composed of mono-layer carbon atoms tightly packed in hexagnol symmetries. Graphene has outstanding electrical, mechanical, optical and thermal properties, and holds great potential for applications in electronic devices, chemical/biological sensors, energy storage devices and composites. So far, several fabrication routes for the production of graphene have been established, such as micromechanical exfoliation, chemical vapour deposition, epitaxial growth, the reduction of graphene oxide (GO) solution, and organic synthesis. Up till now, the reduction of GO solution has become the most popular approach due to its easy processing, large-scale yield and low cost.However, in typical reduction routes, highly toxic reductants such as hydrazine and dimethylhydrazine are always involved. The utilization of these reductants which are detrimental to the environment and human health may lead to hazardous preparation process and money-consuming treatment of the waste. Hence, we developed two environmentally friendly routes for preparation of graphene.Route 1: We developed a chemical route to prepare reduced graphene oxide (RGO) by the reduction of the exfoliated GO by tannic acid, which is a natural product with very low cost. The characterization results of tannic acid reduced GO demonstrates that the oxygen-containing functional groups in GO have been effectively removed by tannic acid. In addition, the obtained reduced GO can form homogeneous and stable dispersions in several different solvents due to the interaction between aromatic rings of the tannic acid and reduced GO. Furthermore, we also establish a one-pot method to fabricate RGO/Ag hybrids by making use of both the reducing ability and the chelating ability of tannic acid. The results show that tannic acid can simultaneously reduce the GO and the Ag+ ion while subsequently anchor the Ag nanoparticles on the surface of reduced GO.Route 2: We produced defect-free graphene based on liquid-phase exfoliation of graphite. We demonstrate that gelatin, a natural protein compound, is able to exfoliate graphene sheets from graphite in aqueous phase under sonication. The obtained graphene is free of defects and the gelatin-stabilized dispersion can reach a relatively high concentration via a short-time sonication. Furthermore, we developed a simple and effective way for the fabrication of gelatin-graphene nanocomposites based-on the pristine gelatin-stabilized graphene dispersions. The defect-free graphene showed good dispersion in polymer matrix and remarkable capability to improve the mechanical properties of gelatin. Thus this method shows great potential as an alternative of the traditional methods for fabrication of polymer/graphene composites which usually contain complex procedures for synthesis of reduced graphene oxide.