Regulation of Adenine-Based Metal–Organic Frameworks with Rich Lewis Basic Sites for the Selective Separation of C ₂ H ₂ from C ₂ H ₂ /C ₂ H ₄ and C ₂ H ₂ /CO ₂ Mixtures

The development of efficient adsorbents for the selective separation of C2H2 from gas mixtures containing impurities of C2H4 and CO2 during C2H2 production is critically important and challenging. In this study, two adenine-based MOFs, Zn-AD-BDC and Cu-AD-BDC, were fabricated as adsorbents. The obtained materials feature rich Lewis basic sites (LBS) within their pore environments, which serve as the primary adsorption sites for C2H2 binding. Notably, Cu-AD-BDC, with abundant micropores and a higher density of LBS within the pore channels compared to Zn-AD-BDC, demonstrated superior C2H2 separation performance. Adsorption isotherms and breakthrough curve experiments revealed that Cu-AD-BDC demonstrated remarkably higher C2H2 adsorption capacity and greater adsorption selectivity for C2H2 over C2H4 and CO2 than Zn-AD-BDC. Computational simulations further elucidated that the enhanced C2H2 separation of Cu-AD-BDC results from the synergy between its specific microporous structure and the interactions of LBS with gas molecules through the strong C–H···N/O hydrogen bonds and C–H···π interactions, which facilitate the selective adsorption of C2H2 from the gas mixtures.