Portraits of Soot Molecules Reveal Pathways to Large Aromatics, Five-/Seven-Membered Rings, and Inception through π-Radical Localization.

Incipient soot early in the flame was studied by high-resolution atomic force microscopy and scanning tunneling microscopy to resolve the atomic structure and orbital densities of single soot molecules prepared on bilayer NaCl on Cu(111). We resolved extended catacondensed and pentagonal-ring linked (pentalinked) species indicating how small aromatics cross-link and cyclodehydrogenate to form moderately sized aromatics. In addition, we resolved embedded pentagonal and heptagonal rings in flame aromatics. These nonhexagonal rings suggest simultaneous growth through aromatic cross-linking/cyclodehydrogenation and hydrogen abstraction acetylene addition. Moreover, we observed three classes of open-shell π-radical species. First, radicals with an unpaired π-electron delocalized along the molecule's perimeter. Second, molecules with partially localized π-electrons at zigzag edges of a π-radical. Third, molecules with strong localization of a π-electron at pentagonal- and methylene-type sites. The third class consists of π-radicals localized enough to enable thermally stable bonds, as well as multiradical species such as diradicals in the open-shell triplet state. These π-diradicals can rapidly cluster through barrierless chain reactions enhanced by van der Waals interactions. These results improve our understanding of soot formation and the products formed by combustion and could provide insights for cleaner combustion and the production of hydrogen without CO2 emissions.

Laser-induced transformation of graphitic materials to two-dimensional graphene-like structures at ambient conditions.

Laser processing of carbon compounds towards the formation of graphene-based structures gains ground in view of the practicality that lasers offer against other conventional graphene preparation methods. The current work explores the viability of low-cost lasers, operating at ambient conditions, for the transformation of various graphitic materials to structures with graphene-like atomic arrangements. Starting materials are at two opposing sides. On one side stands the typical graphite crystal with Bernal stacking and strong sp 2 character, while nanocrystalline graphitic powders are also investigated. It is demonstrated that graphene-like structures can be prepared either by starting from a well-organized Bernal-stacked network or by irradiating nanocrystalline carbon. The current findings document that laser processing at minimal chamber conditions shows high potential for preparing high-quality graphene-based structures starting from low-cost materials. Apart from being scalable, the proposed method is adaptable to current technological platforms emerging as a viable and eco-friendly graphene production technology.