First-principles study on the CH4 adsorption performance of Mn-modified N-doped graphdiyne

NGDY has high-N atom doping rate, many active sites, large pore size, outstanding thermal stability, and excellent lithium-ion storage properties. The mixed adsorption of the Mn-modified NGDY (Mn-NGDY) system has been studied with the first principles approach, which shows the effects and the mechanism of action about the modified Mn atom and H-2 molecules on the adsorption of CH4. From the results, more electrons are transferred from the Mn atom to the neighboring six-membered ring, making the Mn atom positively charged and forming a strong Coulomb interaction with the substrate. There is Coulomb interaction between the first two methane molecules and Mn atoms, and CH4 molecules have strong polarization phenomenon under this interaction, which causes the surrounding CH4 molecules of the first layer (The CH4 molecules around the first two CH4 molecules) inducing polarization along the XY plane (parallel substrate), and the surrounding CH4 molecules of the second layer inducing polarization along the Z-axis direction, which improve the adsorption properties of other CH4 molecules. In the first layer, the interaction forces of the adsorbed CH4 molecules region mainly come from the interaction forces between CH4 and the substrate, and the interaction forces between CH4 molecules dominate in the adsorption of second layer. Polarization of H-2 molecules along the Z-axis direction causes the formation of a weak negative center above it, which promotes the adsorption of CH4 molecules above it. For the 2Mn-NGDY system, a maximum of 72 CH4 molecules and 4 H-2 molecules can be adsorbed simultaneously on both sides, when the average adsorption energy and adsorption amount reach -0.169 eV and 73.41 wt%.