Hydroxyl-functionalized Ni7-cluster-based MOF for cost-effective acetylene separation

Abstract

Designing adsorbents for the efficient separation of challenging gas pairs, such as C₂H₂/C₂H₄ and C₂H₂/CO₂, is a crucial yet demanding goal in separation science. Here, we implemented a pore-engineering strategy to tailor the pore environment of a metal-organic framework (MOF) via functional groups, thereby enhancing its C₂H₂/C₂H₄ and C₂H₂/CO₂ selectivity performance. The introduction of hydroxyl (–OH) groups into Ni7-MOF not only reduces pore dimensions but also promotes a multitude of guest-host interactions within the confined pore environment. The hydroxyl-functionalized Ni7–OH demonstrates high selectivity for C₂H₂ over C₂H₄ and CO₂ between 273 and 308 K. Dynamic breakthrough experiments further confirm its dual-functional capability. Compared to Ni7-MOF, Ni7–OH delivers superior ethylene-purification efficiency, while additionally enabling highly effective C₂H₂/CO₂ separation, allowing high-purity C₂H₂ (> 99.9%) to be recovered through mild temperature-swing desorption. The introduction of hydroxyl groups fine-tunes the binding environment, differentially strengthening the key C–H⋯Ni interaction that favours C₂H₂ over C₂H₄ and CO₂, as supported by density functional theory (DFT) calculations. With its excellent stability, regeneration ability, and balanced performance, Ni7–OH represents a promising adsorbent for energy-efficient C₂H₂ removal from C₂H₄ streams and C₂H₂ recovery from C₂H₂/CO₂ mixtures.