Improving graphenic quality by oxidative liberation of crosslinks in non-graphitizable carbons

Abstract

This work assesses the potential for improving the crystallinity of non-graphitizable carbon materials by oxidative liberation of crosslinks. A model non-graphitizable carbon – sucrose char and two commercial carbon blacks of varied nanostructure have been used to study crystallinity improvements at two oxidative burnout levels. The virgin materials have been compared to their partially oxidized counterparts at a series of heat treatment temperatures using X-ray diffraction for bulk crystallinity analysis and high-resolution transmission electron microscopy for nanostructural characterization. Remarkable improvements were observed in the case of sucrose char where non-graphitizable sponge-like particles transformed into highly ordered graphenic flakes by the mechanism of oxidative liberation of crosslinks. The in-plane crystallite size and stacking height tripled after the liberation of the restrictive crosslinks. Molecular level changes after partial oxidation have been assessed using Raman spectroscopy while X-ray photoelectron spectroscopy is used to assess changes in elemental composition. Notable improvements were also observed in carbon blacks with the development of longer and lower tortuosity lamellae accompanied by expanded particle sizes. Fringe analysis algorithms have been applied to obtain lamellae statistics and highlight nuances in the nanostructure changes after partial oxidation and heat treatment.