Selective O2/N2 Separation Using Grazyne Membranes: A Computational Approach Combining Density Functional Theory and Molecular Dynamics

The separation of oxygen (O₂) and nitrogen (N₂) from air is a process of utmost importance nowadays, as both species are vital for numerous fundamental processes essential for our development. Membranes designed for their selective molecule separation have become the materials of choice for researchers, primarily due to their ease of use. The present study proposes grazynes, 2D carbon-based materials consisting of <i>sp</i> and <i>sp</i>² C atoms, as suitable membranes for separating O₂ and N₂ from air. By combining static density functional theory (DFT) calculations with molecular dynamics (MD) simulations, we address this issue through a comprehensive examination of the thermodynamic, kinetic, and dynamic aspects of the molecular diffusions across the nano-engineered pores of grazynes. The studied grazyne structures have demonstrated the ability to physisorb both O₂ and N₂, preventing material saturation, with diffusion rates exceeding 1 s^-1 across a temperature range of 100-500 K. Moreover, they exhibit a selectivity of <i>ca.</i> 2 towards O₂ at 300 K. Indeed, MD simulations with equimolar mixtures of O₂:N₂ indicated a selectivity towards O₂ in both grazynes with <i>ca</i>. twice as many O₂ filtered molecules in the [1],[2]{2}-grazyne and with O₂ representing ca. 88% of the filtered gas in the [1],[2]{(0,0),2}-grazyne. [1],[2]{2}-grazyne shows higher permeability for both molecules compared to the other grazyne, with O₂ demonstrating particularly enhanced diffusion capacity across both membranes. Further MD simulations incorporating CO₂ and Ar confirm O₂ enrichment, particularly with [1],[2]{(0,0),2}-grazyne, which increased the presence of O₂ in the filtered mixture by 26% with no evidence of CO₂ molecules.