Site Dependent Hydrogenation in Graphynes: A Fully Atomistic Molecular Dynamics Investigation
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Site Dependent Hydrogenation in Graphynes: A Fully Atomistic Molecular Dynamics Investigation Pedro A. S. Autreto and Douglas S. Galvao Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas, 13083-970, Campinas, São Paulo, Brazil. ABSTRACT Graphyne is a generic name for a carbon allotrope family of 2D structures, where acetylenic groups connect benzenoid rings, with the coexistence of sp and sp2 hybridized carbon atoms. In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics and structural changes of the hydrogenation of α, β, and γ graphyne forms. Our results showed that the existence of different sites for hydrogen bonding, related to single and triple bonds, makes the process of incorporating hydrogen atoms into graphyne membranes much more complex than the graphene ones. Our results also show that hydrogenation reactions are strongly site dependent and that the sp-hybridized carbon atoms are the preferential sites to chemical attacks. In our cases, the effectiveness of the hydrogenation (estimated from the number of hydrogen atoms covalently bonded to carbon atoms) follows the α, β, γ-graphyne structure ordering. INTRODUCTION The chemistry of carbon is very rich and this richness is due, mainly, to the fact that there are three possible different hybridizations (sp, sp2 and sp3) [1]. This characteristic allows a plethora of distinct allotropes, some of them discovered in the last few decades, such as fullerenes, nanotubes, and more recently, graphene [1,2]. Graphene is a two-dimensional array of hexagonal units sp2 bonded C atoms, which has been studied theoretically since late 1940s as a model to describe some properties of graphite [3]. Although graphene exhibits several remarkable and unique mechanical and electronic properties, there are some difficulties to be overcome before a real graphene-based nanoelectronics becomes a reality. These difficulties are mainly related to its zero bandgap value, which precludes its use in some digital electronics applications, like transistors and diodes. Diverse approaches have been tried to solve this issue, such as; application of strain, quantum confinement in nanoribbons, and chemical functionalization. Chemical functionalization is quite appealing since it can be used to open the electronic gap of structure as well as directly change the interaction of graphene with its environment. Other reasons that make functionalization attractive are that it can be also exploited to drug delivery, hydrogen storage, defect manipulation, magnetic devices, etc. [4,5]. However, controlled graphene functionalization has been only partially successful, with many issues still unsolved [6,7]. In part due to this, there is a renewed interest in other two-dimensional graphene structures, such as graphynes [8]. Graphyne (see Figure 1) is a generic name for a carbon allotrope family of 2D structures, where acetylenic groups connect benzenoid rings, with the coexistence of sp and sp2 hybridized carbon atoms. Similarly t
