Mechanism of Graphene Formation via Detonation Synthesis: A DFTB Nanoreactor Approach

• Published in: Journal of chemical theory and computation 2019-06, Vol.15 (6), p.3654-3665
• Main Authors: Lei, Tingyu, Guo, Wenping, Liu, Qingya, Jiao, Haijun, Cao, Dong-Bo, Teng, Botao, Li, Yong-Wang, Liu, Xingchen, Wen, Xiao-Dong
• Format: Article
• Language: English
• Subjects: Acetylene; Carbon; Chain branching; Chemical reactions; Chemical synthesis; Computational chemistry; Computer simulation; Detonation; Graphene; Molecular dynamics; Organic chemistry; Oxygen; Oxygen content; Quantum chemistry; Quantum mechanics; Vinylidene
• ISSN: 1549-9618; 1549-9626
• DOI: 10.1021/acs.jctc.9b00158

With the development of theoretical and computational chemistry, as well as high-performance computing, molecular simulation can now be used not only as a tool to explain the experimental results but also as a means for discovery or prediction. Quantum chemical nanoreactor is such a method which can automatically explore the chemical process based only on the basic mechanics without prior knowledge of the reactions. Here, we present a new method which combines the semiempirical quantum mechanical density functional tight-binding (DFTB) method with the nanoreactor molecular dynamic (NMD) method, and we simulated the reaction process of graphene synthesis via detonation at different oxygen/acetylene mole ratios. The formation of graphene is initiated by the breaking of acetylene (C2H2) molecules by collision into pieces such as H atoms, ethynyl (HCC•), and vinylidene (H2CC:) radicals. It is followed by the formation of long straight carbon chains coupled with a few branched carbon chains, which then turned into  a 2-D framework made of carbon rings. Trace oxygen could modulate the size of the rings during graphene formation and promote the formation of regular graphene with fused six-membered rings as we see, but the addition of high oxygen content makes more C-containing species oxidized to small oxide molecules instead of polymerization. The calculation speed of the DFTB nanoreactor is greatly improved compared to the ab initio nanoreactor, which makes it a valuable option to simulate chemical processes of large sizes and long time scales and to help us uncover the “unknown unknowns”.