O2-Oxidation of Individual Graphite and Graphene Nanoparticles in the 1200 to 2200 K Range: Particle-to-Particle Variations and the Evolution of the Reaction Rates and Optical Properties

TL;DR

This study investigates how individual graphite and graphene nanoparticles oxidize at high temperatures, revealing particle-to-particle variations, changes in reactivity over time, and evolving optical properties during oxidation.

Contribution

It provides detailed insights into the particle-specific oxidation kinetics and surface structure evolution of graphite and graphene nanoparticles at high temperatures.

Findings

Oxidation efficiency peaks between 1200-1500 K and drops above 2000 K.

Significant nanoparticle-to-nanoparticle variations in oxidation rates.

Reactivity decreases non-monotonically as particles react, due to surface structural changes.

Abstract

The kinetics for O2 oxidation of individual graphite and graphene platelet nanoparticles (NPs) were studied as a function of temperature (1200 to 2200 K) at varying oxygen partial pressures, using a single nanoparticle mass spectrometry method. NP temperature (TNP) was measured by measuring the NP thermal emission spectra during the kinetics studies. The initial oxidation efficiency is found to peak in the 1200 to 1500 K range, dropping by an order of magnitude as TNP was increased above 2000 K. There were large NP-to-NP variations in the oxidation rates, attributed to variations in the NP surface structure. In addition, the oxidation efficiencies decreased, non-monotonically, as the NPs reacted, by factors of between 10 and 300. This evolution of reactivity is attributed to changes in the NP surface structure due to the combination of oxidation and annealing. The optical properties, including wavelength dependence of the emissivity, and the absorption cross section for the 532 nm heating laser, also tend to evolve as the NPs oxidize, but differently for each individual NP, presumably reflecting differences in the initial structures, and how they evolve under different reaction conditions.