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

Abstract

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/H₂ (S_CO2/H2 = 50) and CH₄/H₂ (S_CH4/H2 = 11) at 298 K. In addition, molecular dynamic simulations reveal that the self-diffusivities of CO₂, CH₄ and H₂ 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.