Size-dependent chemical reactivity of porous graphene for purification of exhaust gases

From the structural characteristics of pores evolving from the vacancy, the structure-dependent nature of localized states, and the role of electronic states in the reaction, we elucidate size effects on the chemical reactivity of porous graphene using density functional theory. The coupling of conjugated π electrons of graphene with localized defect states allows for the reduction reaction or adsorption of exhaust gases on the edge atoms. The charge redistribution, ascertained from the coupling response, activates the weak C-C bond states at the corners, facilitating the dissociation of exhaust gas (e.g., NO). The size matching effect makes that the dissociation barrier of NO on the vacancy is smaller than 8.30 kcal/mol; whereas, larger pores only capture NO. Following the coupling-response mechanism, we propose the structural requirements for chemical applications of porous graphene: the shape and size of the pores are comparable in scale with those of purified molecules.