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.