This paper rationalizes the green and scalable synthesis of graphenic materials of different aspect ratios using anthracite coal as a single source material under different supercritical environments. Single layer, monodisperse graphene oxide quantum dots (GQDs) are obtained at high yield (55 wt %) from anthracite coal in supercritical water. The obtained GQDs are ∼3 nm in lateral size and display a high fluorescence quantum yield of 28%. They show high cell viability and are readily used for imaging cancer cells. In an analogous experiment, high aspect ratio graphenic materials with ribbon-like morphology (GRs) are synthesized from the same source material in supercritical ethanol at a yield of 6.4 wt %. A thin film of GRs with 68% transparency shows a surface resistance of 9.3 kΩ/sq. This is apparently the demonstration of anthracite coal as a source for electrically conductive graphenic materials.
We report the exfoliation of graphite and simultaneous N doping of graphene by two methods: supercritical ammonia treatment and liquid-phase exfoliation with NHOH. While the supercritical ammonia allowed N doping at a level of 6.4 atom % in 2 h, the liquid-phase exfoliation with NHOH allowed N doping at a level of 2.7 atom % in 6 h. The N doped graphene obtained via the supercritical ammonia route had few layers (<5) and showed large lateral flake size (∼8 μm) and low defect density (I/I < 0.6) in spite of their high level of N doping. This work is the first demonstration of supercritical ammonia as an exfoliation agent and N doping precursor for graphene. Notably, the N doped graphene showed electrocatalytic activity toward oxygen reduction reaction with high durability and good methanol tolerance compared to those of commercial Pt/C catalyst.
International audienceGaN quantum dots (QDs) are prepared in a one-step continuous process using anhydrous solvents at supercritical conditions (and temperatures below 450 °C) in short residence times, typically less than 25 s. The as-prepared QDs exhibit a strong luminescence in the ultraviolet (λmax ~ 350 nm) in agreement with the synthesis of quantum-confined GaN nanoparticles
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.