Low-Temperature Graphene Growth and Shrinkage Dynamics from Petroleum Asphaltene on CuO Nanoparticle

Abstract

This study investigates graphene synthesis catalyzed by metal oxide nanoparticles under low-temperature conditions. Instead of using high-purity precursors, petroleum asphaltene was selected as a carbon source. Asphaltene-coated nanoparticles (CuO, Fe2O3, and Al2O3) were prepared through a mixing, heating, and separation procedure then placed inside a vacuum furnace for graphene synthesis. CuO was identified as an effective catalyst in generating several micron-sized graphene sheets, while the other two nanoparticles failed to catalyze the reaction. The graphene was characterized by Raman and Fourier transform infrared spectroscopies as well as scanning and transmission electron microscopies. A subsequent in situ microscope experiment was performed to directly observe the graphene growth and shrinkage dynamics on CuO. Real-time monitoring of the graphene growth dynamics revealed that both the reaction temperature and the time needed for graphene growth were much lower than those in conventional chemical vapor deposition methods. CuO nanoparticles served as a substrate for graphene synthesis at low temperature (450 °C) and also acted as an oxidant at a higher temperature (800 °C) that consumed the newly synthesized sheet. Comprehensive analyses of graphene nucleation, asphaltene pyrolysis, and the movement and transportation of the carbon backbone were performed to interpret the data.