Photoluminescent Nanostructures from Graphite Oxidation

The graphite intercalation compound (GIC) of 3:1 sulfuric to nitric acid mixture was used to produce photoluminescent (PL) nanostructures by oxidizing micrographite, nanographite, nanographite platelets, onion-like-carbon, and highly oriented pyrolytic graphite. The GIC used in this work is a Stage I intercalation compound that expands the graphitic planes to a maximum degree; this expansion was visible as a blue color for these graphitic materials in suspension with the GIC solution. The GIC intercalates into the graphitic layers to facilitate oxidation, resulting in graphite oxide, which may be fully exfoliated to graphene oxide. This treatment produced carbon nanostructures that were colloidally stable and photoluminesced across the visible wavelength range. It was possible to control the PL color of the reaction suspension by tuning the reaction temperature or reaction time; higher temperatures or longer reaction times caused a blue shift in the PL wavelength. Various graphitic oxide nanostructures were observed in the reaction suspension with increasing reaction time, including nanoribbons, graphene-like nanoplatelets, and round single-digit nanoparticles. Using separation methods for a PL orange reaction supernatant solution, it was possible to isolate individual PL colors spanning the visible wavelength region. These PL colors exhibit a blue shift in emission wavelength with filters that decreased in molecular weight or as the migration distanced increased in a denaturing polyacrylamide gel. Chemical functionalization of the PL blue carbon product from the oxidation of nanographite platelet allowed for the fluorescent coating of silica beads