Silver(I)-Functionalized COF-LZU1 for High-Performance CO₂/CH₄ Separation

Using porous materials for CO₂/CH₄ separation is an ecofriendly and energy-efficient method. Covalent organic frameworks are crystalline porous frameworks linked by covalent bonds with precisely adjustable pore size and pore chemistry and are considered potential porous adsorbent materials. At present, various methods/materials for the purification and separation of industrial mixtures have been widely studied. In this study, silver ions (Ag⁺) were successfully anchored to a classical COF: COF-LZU1. This modification utilized the π-complexation interaction between Ag⁺ and CO₂ to enhance the adsorption and separation efficiency for CO₂. The resulting composite, designated as Ag@COF-LZU1 (1.5 equiv, containing 1.5 equiv of Ag⁺), exhibited the highest CO₂ uptake of 34.1 cm³/g and demonstrated a remarkable CO₂/CH₄ selectivity factor of 32.1 at 298 K and 1 atm. Breakthrough experiments indicated that the modified COF-LZU1 displayed a prolonged retention time. Furthermore, the stability of COF-LZU1 after Ag⁺ anchoring was confirmed through three consecutive breakthrough experiments, which revealed no significant variation in the penetration time. The selective adsorption mechanisms of COF-LZU1, both prior to and following the anchoring of Ag⁺, were elucidated by using density functional theory calculations. This study presents a novel approach for developing adsorbents targeting the capture of CO₂ in practical industrial applications.