Thermal decomposition of graphene armchair oxyradicals

Abstract

Energetics and kinetics of the thermal decomposition of oxyradicals with oxygen bonded to a graphene armchair edge were investigated. Phenanthrene, benzoperylene, and an 11-ring polycyclic aromatic hydrocarbon (PAH) were selected as substrates to model the armchair edge, with a total of five different oxyradicals studied. The elementary steps of the reaction pathways were analyzed using density functional theory. Rate coefficients over the ranges of 1500–2500K and 0.01–10atm were obtained by solving the master equations. The computed rate coefficients were found to be temperature, pressure, and substrate-size dependent. The results revealed that the decomposition rate of an oxyradical with oxygen positioned on the outside of a corner armchair edge is faster than the rate with oxygen positioned to the inside of the edge. The trends in the computed oxyradical decomposition rates could be rationalized by the structural characteristics of the substrates. The decomposition rates computed for the armchair edge oxyradicals are shown to be similar to those previously obtained for corner zigzag edge oxyradicals. This implies that given an arbitrary shaped PAH, oxidation should preferentially occur at armchair and corner-zigzag sites, leaving resistant to oxidation inner zigzag sites essentially intact. Considering that growth of both armchair and zigzag edges proceeds at effectively the same rate, we expect to find proliferation of zigzag-edge surfaces on soot particles formed in flame environments.