Fine-tuning channel structure and surface chemistry of stable bismuth-organic frameworks for efficient C₂H₄ purification through reversely trapping CO₂ and C₂H₂

One-step C₂H₄ purification from ternary C₂H₄/C₂H₂/CO₂ mixtures is of prime importance but challenging in chemical industries, owing to similar physicochemical properties of the three gases. Herein, we investigated the potential of ultramicroporous Bi-MOFs modified with –CHO, –COOH, –NO₂, -F, -Cl, -Br, and -I for C₂H₄ purification. These MOFs featured good thermodynamic and thermal stability and exhibited precise regulation of channel sizes and surface structures/electronegativity. Their separation performances for CO₂/C₂H₄, C₂H₂/C₂H₄, and CO₂/C₂H₂ were theoretically investigated by grand canonical Monte Carlo, density functional theory, and transient breakthrough simulations. Results showed that introducing –CHO/–COOH/–NO₂ enlarged the difference of adsorption uptakes between CO₂, C₂H₂, and C₂H₄ favoring efficient separation of corresponding mixtures, in which Bi-MOF-CHO showed the highest selectivity for CO₂/C₂H₄, C₂H₂/C₂H₄, and CO₂/C₂H₂, with values of 58.6 (64.5), 11.8 (11.5), and 7.7 (21.5) under 50/50 (1/99) at ambient conditions. The enhanced separation performance is attributed to the synergism of pore size limitation, fine-tuned surface structure, and high surface electronegativity, resulting in special CO₂ recognition, moderate enhancement for C₂H₂, but negligible influence on C₂H₄ adsorption. This work provides an effective strategy to design high-performance adsorbents for one-step C₂H₄ purification from ternary C₂H₄/C₂H₂/CO₂ mixtures.