Mechanism of interaction between gaseous atoms and graphite determined from the back edge of atomic absorption signal with graphite furnace atomic absorption spectrometry.

Abstract

The energetics of interactions between gaseous atoms and pyorolytic graphite (PG) were investigated by the Gibbs free energy change (ΔG) determined from the back edge of atomic absorption (AA) signa. The Gibbs free energy was estimated by assuming an equilibrium state among the interactions between an analyte atom (M) and a PG surface. Because of its poor reactivity, lead was used as a standard to define a ΔG value of Zero to calculate the loss rate of a hypothetical M_(g) without interactions. The kinetic parameters for M were calculated using a diffusion loss model. The ratio of the experimental loss rate to the hypothetical loss rate was used to determine the equilibrium constant (K) for the interaction between M and the PG surface, from which ΔG was calculated. The slope of a linear relationship of ΔG vs. the activation energy (E_a) of atomization for individual atoms on the PG surface was consistent with that of ΔG vs. the binding energy of adatoms with graphene. It was proposed that the interaction between M_(g) and the PG surface was caused by the binding to sites of top-C for Au, C-C bridge for Ag and Pb, a hexagonal hole of sixfold sites within C-ring for Co, Fe and Ni, a pair of terminal-C on zigzag edge for Cr, top-subedge for Mn, and active sites in adjacent graphite layers controlling intercalation for Cu.