Synergic morphology engineering and pore functionality within a metal–organic framework for trace CO2 capture

Abstract

CO₂ capture, especially under ultralow-pressure regions (400–10 000 ppm), is extremely essential and challenging to keep the prolonged manual operation in confined spaces and reduce CO₂ corrosion in natural gas. Although many MOFs have been covered for CO₂ capture, they usually suffered from unheeded morphology engineering associated with diffusion kinetics and unbridgeable CO₂ adsorption under ultralow pressure. Herein, we have successfully targeted pyrazine-functionalized Co-MOF (1a′) nanocrystals having dapper hexahedral morphology through skillfully integrating morphology engineering and pore functionality. The yielded 1a′ paradigm with snug pore microenvironment afforded record-high adsorption performance for trace CO₂ capture (1.36 mmol g⁻¹ at 400 ppm and 5.7 mmol g⁻¹ at 10 000 ppm), yet eclipsed adsorption behavior for CH₄ and N₂ at 298 K. The decent pore geometry awarded 1a′ with superior property for CO₂/CH₄ and CO₂/N₂ separation, giving higher IAST selectivity (1454 for 15/85 CO₂/N₂ and 494 for 50/50 CO₂/CH₄). Besides, 1a′ showed an improved hydrophobic nature, with a desired CO₂/H₂O uptake ratio of 0.45 and improved diffusion selectivity (D_M,CO2/D_M,H2O) of 17.7. Breakthrough tests visualized that 1a′ could realize high-purity CO₂ (>96%), yielding maximum CO₂ productivity (162 and 164.9 litres per kilogram for 18/85 CO₂/N₂ and 50/50 CO₂/CH₄). Modeling simulations have cooperatively revealed the structure–property relationship between guest molecules and the framework. This work presents an advanced benchmark adsorbent for low-concentration CO₂ capture from flue gas and natural gas.