Topology of Disordered 3D Graphene Networks

Abstract

Disordered carbons comprise graphene fragments assembled into three-dimensional networks. It has long been debated whether these networks contain positive curvature, as seen in fullerenes, negative curvature, as proposed for the schwarzite structures, or zero curvature, as in ribbons. We present a meshbased approach to analyze the topology of a set of nanoporous and glassy carbon models that accurately reproduce experimental properties. Although all three topological elements are present, negatively curved structures dominate. At the atomic level, analysis of local environments shows that sp-and sp 3 -bonded atoms are associated with line defects and screw dislocations that resolve topological complexities such as termination of free edges and stacking of low curvature regions into ribbons. These results provide insight into the synthesis of porous carbon materials, glassy carbon and the graphitizability of carbon materials.

Catalysis-free transformation of non-graphitising carbons into highly crystalline graphite

“…This combustion route to graphite unifies past literature models of graphitisation, which have been the subject of ongoing debate. While pentagons 35 and heptagons 36 have both been proposed as sources of positive and negative curvature, respectively, a key aspect of our mechanism is their arrangement in lines as proposed more recently [29][30][31][32][33][34] . The pentagon/heptagon chains can be understood as the (unspecified) cross-links proposed by Franklin, which locked nanocrystallites together 3 , while collapse of the structure is reminiscent of the "falling cards" model of Dahn et al 37 .…”

“…This idea is consistent with studies of carbon nanohorns and nanotubes where oxidation occurs preferentially at pentagonal rings [23][24][25] and is exploited to access internal cavities by etching the tips [26][27][28] . Experimental and theoretical works [29][30][31][32][33][34] have shown that defects such as pentagons, heptagons and octagons are arranged in lines, forming extended defects. An example of a model of a porous carbon showing these extended defects is depicted in Fig.…”

“…An example of a model of a porous carbon showing these extended defects is depicted in Fig. 6a 32 . The extended lines of non-hexagonal carbon are the basis for a thought experiment to explain the unexpected graphitisation seen here.…”

“…The atomistic model is from refs. 32,43 . d Oxygen content determined from XPS of samples of PVDC after different number of pulses.…”

Stone–Wales defects preserve hyperuniformity in amorphous two-dimensional networks

“…Moreover, a recent study of amorphous 2D silica reveals that the distribution of silicon atoms possesses the remarkable property of DHU (45). In a wider context, amorphous carbon-based systems have been extensively studied, including graphene sheets (54)(55)(56), cross-linked graphene network (57), and amorphous glassy carbon and carbon fibers (58,59), to name a few.…”