CO2-favored metal-organic frameworks SU-101(M) (M = Bi, In, Ga, and Al) with inverse and high selectivity of CO2 from C2H2 and C2H4

Inversely removing trace CO2 from C2H2 and C2H4 by adsorbents has been considered as a promising energy efficient alternative to traditional cryogenic distillation or chemisorption for the purification of C2H2 and C2H4. However, few adsorbents could realize one-step separation for CO2/C2H2 and CO2/C2H4 because of lack of specific recognition of CO2 and high separation selectivity as well as the similar molecular sizes and physical properties between CO2 and C2H2/C2H4. Herein, we selected the water-stable and easily scalable Bi-MOF (SU101) as the adsorbent platform, which features ultramicropores and rich basic carbonyl oxygen sites and thus is expected to favor the CO2 adsorption. Al, In, and Ga ions were used to replace the Bi metal centers to tune the pore size and pore surface charge. The inversely selective capture characteristics of CO2 from C2H2 and C2H4 in SU-101(M) (M = Bi, In, Ga, and Al), both hydrated and activated, were theoretically investigated by grand canonical Monte Carlo simulations and density functional theory, highlighting the effects of coordinated water and metal centers. The results show that it is the synergistic effect of pore size limitation and carbonyl O charge regulation by coordinated water that leads to the special recognition of CO2 and the inverse CO2/C2H2 and CO2/C2H4 separation in hydrated SU-101 materials, compared to the activated counterparts. SU-101(Al) shows the highest selectivity for CO2/C2H2 (15.5) and CO2/C2H4 (8.3) under ambient conditions. Our work provides a general guidance for rational design of MOF adsorbents for the applications of separating CO2/C2H2 and CO2/C2H4 inversely.

Automated summary

This study investigates the inverse separation of CO2 from C2H2 and C2H4 using water-stable and easily scalable Bi-MOF (SU101) adsorbents. By tuning the pore size and pore surface charge through the replacement of Bi metal centers with Al, In, and Ga ions, the special recognition of CO2 and the inverse separation of CO2/C2H2 and CO2/C2H4 are achieved through the synergistic effect of pore size limitation and carbonyl O charge regulation by coordinated water. The results provide guidance for the rational design of MOF adsorbents for the inverse separation of CO2/C2H2 and CO2/C2H4.