Graphitization by Metal Particles

Graphitization of carbon offers a promising route to
upcycle waste
biomass and plastics into functional carbon nanomaterials for a range
of applications including energy storage devices. One challenge to
the more widespread utilization of this technology is controlling
the carbon nanostructures formed. In this work, we undertake a meta-analysis
of graphitization catalyzed by transition metals, examining the available
electron microscopy data of carbon nanostructures and finding a correlation
between different nanostructures and metal particle size. By considering
a thermodynamic description of the graphitization process on transition-metal
nanoparticles, we show an energy barrier exists that distinguishes
between different growth mechanisms. Particles smaller than ∼25
nm in radius remain trapped within closed carbon structures, while
nanoparticles larger than this become mobile and produce nanotubes
and ribbons. These predictions agree closely with experimentally observed
trends and should provide a framework to better understand and tailor
graphitization of waste materials into functional carbon nanostructures.