First-principles study on the design of metal-decorated N-doped γ-graphyne as a high capacity CH4 adsorbent

Abstract

Nitrogen doping γ-graphyne (γ-NGY) is a recently synthesized carbon nitride two-dimensional material with a large specific surface area and unique structure. Based on the first-principles method, the CH4 adsorption properties of γ-NGY are calculated, and a substrate structure Ti-decorated γ-NGY is designed. The results show that the center of the rhombus hole of γ-NGY is the best CH4 adsorption position, and the adsorption energy is −0.145 eV. The most stable binding position of the Ti atom on γ-NGY is also the rhombus hole. The binding energy of a Ti atom is −5.737 eV, and the average binding energy of two Ti atoms is −4.88 eV. Ti-γ-NGY successfully adsorbs 24 CH4 molecules on both sides with an average adsorption energy of −0.184 eV and the storage capacity of 69.12 wt. %. After doping N atoms, the hole size increases, and the negative charges are concentrated on N atoms. The adsorption of CH4 by γ-NGY is mainly the intermolecular force, and the adsorption energy is slightly increased. After the Ti atom transfers the negative charge to the substrate, a strong electric field is formed between the positively charged Ti atom and the negatively charged substrate. The adsorption energy of CH4 molecules near the Ti atom is greatly increased, and the Coulomb attraction between CH4 and Ti atom is dominant. The adsorption energy of the CH4 molecule far away from the Ti atom is also improved, and the intermolecular force between negatively charged substrates and polarized CH4 molecules plays a dominant role in the adsorption.