Gas-Phase Reduction And Doping Mechanism Of Graphene Oxide

Physicists Andre Geim and Konstantin Novoselov from Manchester University firstly manufactured graphene from graphite in the lab in 2004. Due to the special structure and unique electrical properties, graphene has been a rapidly rising star on horizon of materials science and shown promising applications in biomedicine, energy, electronics etc. Although graphene has more peculiar excellent properties, but cost-effective and mass production of graphene with high quality is still very difficult.To prepare graphene sheets with high quality, various method have been developed, including mechanical exfoliation, chemical vapor deposition(CVD), reduction of graphene oxide, epitaxy, thermal decomposition of silicon carbide etc. Among them-, chemical reduction of graphene oxide represents an important route towards large-scale production of graphene sheets for many applications. Graphene oxide contains carbon, hydrogen and oxygen in various ratios, obtained by treating graphite with strong oxidizers., The layer structure of graphite is retained after oxidation, but the layers are buckled and the interlayer spacing is larger than graphite due to the formation of carbonyl(C=O), hydroxyl(-OH), phenol and other functional groups. After reduction of dispersed graphene oxide, graphene films are yielded.Methods for reduction of graphene oxide include thermal reduction, chemical reagent reduction, photocatalyst reduction, electrochemical reduction, solvothermal reduction etc. In addition to the various reduction methods, gas-phase annealing has been demonstrated to most efficiently reduce GO, yet it had been challenging to completely reduce the oxygen groups, partly because the molecular understanding of the reaction processes is largely lacking.In this thesis, we compare the reduction of graphene oxide in different environments using molecular dynamics simulations. We find that NH3 affords more efficient reduction of hydroxyl and epoxy groups than H2 and vacuum annealing partly due to lower energy barriers. Furthermore, we show that with the combination of vacancies and oxygen groups, pyridinic- or pyrrolic-like nitrogen can readily be incorporated into graphene. All of these nitrogen configurations lead to n-doping of the graphene. At last, a suggestion to produce high quality graphene material in experiment is proposed.