Two-dimensional graphitic C3N5 materials: promising metal-free catalysts and CO2 adsorbents

Graphitic carbon nitrides (CNs) have attracted wide attention because of their unique physical and chemical properties. However, the extended applications of amorphous CNs are limited due to their non-porous nature. In this work, a two-dimensional graphite-like CN material, g-C3N5, with a crystalline porous structure as well as high nitrogen content, is proposed. The optical, electronic and catalytic properties of g-C3N5 have been investigated systematically by using the density functional theory. Results indicate that the visible-light absorption region of g-C3N5 is broadened significantly, and its catalytic activity in the oxygen reduction reaction (ORR) is enhanced greatly, compared to other graphitic CN materials. Furthermore, grand canonical Monte Carlo calculations indicate that g-C3N5 exhibits preferable affinity for CO2 due to the intrinsic basicity of the CN material, and therefore shows notable adsorption selectivity of CO2/H-2 (S-CO2/H2 = 50) and CH4/H-2 (S-CH4/H2 = 11) at 298 K. In addition, molecular dynamic simulations reveal that the self-diffusivities of CO2, CH4 and H-2 in g-C3N5 are comparable with those in most 3D porous COFs and MOFs. In short, the 2D g-C3N5 material not only possesses the advantages of CN materials, but also exhibits promising applications in metal-free ORR catalysis, gas adsorption and separation.