Theory of genus reduction in alkali-induced graphitization of nanoporous carbon

Abstract

Exposure to elemental Cs generates graphitic domains within nanoporous carbon at only 50°C, well below the typical graphitization temperatures of Ͼ1000°C. We present a model of nanoporous carbon, the wormhole, which can express the fundamental topological elements of graphitization: a negative-curvature analog to C 60 fullerene. The pathway to wormhole annihilation comprises an initial Stone-Wales transformation and a subsequent unzipping of the defect. This complex ϳ100-atom collective defect disintegrates with the formation of only two dangling bonds. Our ab initio calculations show that while the activation barrier against reduction in topological genus is indeed lowered by interaction with alkali, an additional chemical constituent must be involved to account for this remarkable local graphitization of nanoporous carbons at near-room temperature.

Stability of two-dimensional BN-Si structures

“…The key challenge of identifying lowest-energy periodic configurations, as demonstrated in previous studies 36 , is that they can occur at arbitrarily large n. Our search for n = 3 reveals an even more stable structure, Fig theorem, the matching number of 5-and 7-member rings ensures the same genus of the framework, as discussed in Ref. 38. The network rearrangement lowers the energy further by 11 meV/atom with respect to that of (iii).…”

Designing rigid carbon foams

“…Much less emphasis has been placed on structures with negative Gaussian curvature 4,5,6,7,8,9,10,11,12,13,14,15,16,17,18 , related to foams, which may be equally rigid and exhibit unusual electronic and magnetic properties. These systems, also called schwarzites, are space-filling contiguous structures formed of sp 2 bonded carbon.…”

Molecular‐Level Understanding of the Carbonisation of Polysaccharides

“…12, 18 Regarding the formation of wormhole‐like connections, this is likely only after 300 °C, in which micropores can be seen. These could be a result of decomposition and evolution of entrapped decomposition products/gases helping to form interconnecting pores within the start of the predominantly sp 2 ‐carbon structure 19. Before this temperature, there is little micropore content, and hence, networks of interconnecting structures, rather than individual units with large mesopore domains from the known starch structure.…”

“…To summarise, changes in both texture and chemical functionalities are directly linked to the thermal treatment temperature employed to produce the Starbon material. This is explained by a temperature induced molecular (carbon) linearization towards graphitic‐like structures; a product of carbon sp 2 hybridisation and transformation from non‐equilibrium forms of sp 2 carbon towards optimal homogenously structured/bonded carbon domains that expel curvature through topological events 19. This results in an increase in the long‐range structural order reflective of the polysaccharide self‐assembly derived from the precursor gel state.…”