Rational design of stable carbon nitride monolayer membranes for highly controllable CO₂ capture and separation from CH₄ and C₂H₂

CO₂ capture and separation from natural and fuel gas are important industrial issues that refer to the control of CO₂ emissions and the purification of target gases. Here, a novel non-planar g-C₁₂N₈ monolayer that could be synthesized via the supramolecular self-assembly strategy was identified using DFT calculations. The cohesive energy, phonon spectrum, BOMD, and mechanical stability criteria confirm the stability of the g-C₁₂N₈ monolayer. Our DFT calculations and MD simulations designate the g-C₁₂N₈ monolayer to perform as a superior CO₂ separation membrane from CH₄ and C₂H₂ gas owing to the high CO₂ permeability and selectivity. Specifically, the CO₂ permeability ranges from 1.21 × 10⁷ to 1.53 × 10⁷ GPU, while the selectivity of CO₂/CH₄ and CO₂/C₂H₂ is 3.03 × 10³ and 3.10 × 10² at 300 K, respectively, much higher than the Robeson upper bound and most of the reported 2D membranes, and even at high temperatures, the g-C₁₂N₈ monolayer-based CO₂ separation membranes could operate with high performance. Further, at room temperature, the permeated CO₂ gas can adsorb on the g-C₁₂N₈ surface with moderate adsorption energy and high capacity. These results indicate that the g-C₁₂N₈ membrane exhibits high performance for controlling CO₂ capture and separation, which inevitably injects a new alternative of novel 2D membranes for CO₂ separation and capture from CH₄ and C₂H₂ in light of further experimental and theoretical research.