Adsorption and Reactivity of CO₂ on Defective Graphene Sheets

Density-functional calculations have been performed to investigate the adsorption of CO(2) on defected graphite (0001) represented by a single graphene sheet. The interaction with a vacancy defect gives a computed molecular binding energy of approximately 136 meV in a strong physisorbed state. Subsequently, chemisorption by lactone group formation will occur after overcoming a barrier of approximately 1 eV relative to the gas phase, with an exothermicity of about 1.4 eV. Further reaction paths from this chemisorbed state lead to dissociation of the CO(2) through the formation of epoxy groups followed by oxygen recombination and desorption of O(2), after overcoming successive energy barriers of approximately 0.9 and approximately 1.0 eV. The global minimum ("O(2) desorbed + graphene sheet") entails an energy release of about 3.4 eV with respect to the initial state.