Non-Graphitizing Carbon: Its Structure and Formation from Organic Precursors

Abstract

Non-graphitizing carbon, or char, has been intensively studied for decades, but there is still no agreement about its detailed atomic structure. The first models for graphitizing and non-graphitizing carbons were proposed by Rosalind Franklin in the early 1950s, and while these are correct in a broad sense, they are incomplete. Subsequent models also fail to explain fully the structure of non-graphitizing carbons. The discovery of the fullerenes and related structures stimulated the present author and others to put forward models which incorporate non-hexagonal rings into hexagonally-bonded sp2 carbon networks, creating a microporous structure made up of highly curved fragments. However, this model has not been universally accepted. This paper reviews the models that have been put forward for non-graphitizing carbon and outlines the evidence for a fullerene-like structure. This evidence comes from transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. Finally, the influence of precursor chemistry on the structure of graphitizing and non-graphitizing carbons is discussed. It is well established that carbonization of oxygen–containing precursors tends to produce non-graphitizing carbons. This may be explained by the fact that the removal of oxygen from a hexagonal carbon network can result in the formation of pentagonal carbon rings.