A Novel Nanoporous Graphite Based on Graphynes: First Principles Structure and Carbon Dioxide Preferential Physisorption

Abstract: Ubiquitous graphene is a stricly 2D material representing an ideal adsorbing platform due to its large specific surface area as well as its mechanical strength and resistance to both thermal and chemical stresses. However, graphene as a bulk material has the tendency to form irreversible agglomerates leading to 3D graphitic structures with a significant decrease of the area available for adsorption and no room for gas intercalation. In this paper a novel nanoporous graphite formed by graphtriyne sheets is introduced: its 3D structure is theoretically assessed by means of electronic structure and molecular dynamics computations within the DFT level of theory. It is found that the novel layered carbon allotrope is almost as compact as pristine graphite but the inherent porosity of the 2D graphyne sheets and its relative stacking leads to nanochannels that cross the material and whose sub-nanometer size could allow the diffusion and storage of gas species. A molecular prototype of the nanochannel is used to accurately determine first principles adsorption energies and enthalpies for CO2, N2, H2O and H2 within the pores. The proposed porous graphite presents no significant barrier for gas diffusion and it shows a high propensity for CO2 physisorption with respect to the other relevant components in both pre- and post-combustion gas streams.