Stepwise customizing pore environments of C₂H₂-selective frameworks for one-step C₂H₄ acquisition from ternary mixtures

One-step purification of C₂H₄ from ternary C₂H₂/C₂H₄/C₂H₆ mixture is crucial but challenging since the primary physical properties of C₂H₄ all fall between C₂H₂ and C₂H₆. Hence, we report an effective approach for purifying C₂H₄ through stepwise customizing pore environments on C₂H2-selective materials. Utilizing SIFSIX-1-Cu as a prototype material, we incorporated one or two methoxyl groups onto 4,4 `-bipyridine to obtain isomorphic framework SIFSIX-1-Cu-OMe and SIFSIX-1-Cu-(OMe)₂ respectively. As expected, pore sizes gradually decrease, while C₂H₆ binding sites increase. Ultimately, the C₂H₆/C₂H₄ (10/90) selectivity gradually increases from 1.18 (SIFSIX-1-Cu) to 1.27 (SIFSIX-1-Cu-OMe) and finally to a remarkably high value of 1.79 (SIFSIX-1-Cu-(OMe)₂). As anticipated, SIFSIX-1-Cu-(OMe)₂ can achieve one-step acquisition of polymer-grade C₂H₄ (>= 99.95 from C₂H₂/C₂H₄/C₂H₆ (1/90/9) mixture with high productivity of 6.82 L/kg. Furthermore, theoretical calculations indicate that the pore surface of SIFSIX-1-Cu-(OMe)₂ is beneficial to preferentially capture C₂H₂ and C₂H₆, and thus realizes one-step purification of C₂H₄.