Methane adsorption properties of N-doped graphdiyne: a first-principles study

N-doped graphdiyne (N-graphdiyne) is a new kind of alkynyl carbon material whose structure resembles graphdiyne. This study describes the Mn-modified N-graphdiyne (Mn-N-graphdiyne) system on methane (CH4) adsorption properties based on first principles. We found that the modifications of the Mn atom could significantly improve the adsorption of CH4 by N-graphdiyne. Two Mn atoms can adsorb 36 CH4 molecules upon double-sided modification, with average adsorption capacity and storage capacities of approximately - 0.158 eV and 0.585 g g(-1), respectively. The adsorption of the first CH4 molecule by the Mn-N-graphdiyne system, which is mainly affected by the Mn atoms, involves a strong Coulomb interaction with Mn accompanied by the highest adsorption energy. Subsequently, an increase in the distance between CH4 molecules and Mn atoms increases leads to a weakened Coulomb interaction. The adsorption of CH4 molecules is then mainly affected by the van der Waals force between the substrate N-graphdiyne, and the adsorption energy decreases. The N-graphdiyne system has a larger acetylene chain macroporous position than GDY owing to the doping of N atoms, which provides sufficient adsorption space and adsorption sites for CH4.