High-Temperature Oxidation of Single Carbon Nanoparticles: Dependence on the Surface Structure and Probing Real-Time Structural Evolution via Kinetics

O2-oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single nanoparticle mass spectrometry at temperatures (TNP) in 1100–2900 K range. It was found that oxidation, studied in the 1200 to 1600 K range, is highly sensitive to NP surface structure, with etching efficiencies (EEO2) varying by up to four orders of magnitude, whereas sublimation rates, significant only for TNP ≥ ~1700 K, varied by only a factor of ~3. Its sensitivity to NP surface structure makes O2 etching a good real-time structure probe, which was used to follow evolution of the NP surface structures over time as they were either etched or annealed at high TNP. All types of carbon NPs were found to have initial EEO2 values in the range near 10-3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10-6 Da/O2 collision), however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monotonically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions, and etched with complex time dependence, with multiple waves of fast-but-non-monotonic etching, separated by periods of near-inertness. Lastly, possible mechanisms to account for the complex etching behavior are proposed.