Metal–organic frameworks (MOFs) are composed of metal centers and organic linkers. Generally, MOFs are crystalline, porous materials. They are useful, e.g., in catalysis or gas separation. Acetylene (C₂H₂), for example, is a commonly used chemical feedstock. CO₂ often is a byproduct of acetylene production, thus, efficient separation processes for C₂H₂/CO₂ mixtures would be useful.

Yong Cui, Shanghai Jiao Tong University, China, Banglin Chen, University of Texas at San Antonio, USA, and colleagues have prepared two isostructural, chiral, nickel-based MOFs designed for efficient acetylene uptake and C₂H₂/CO₂ separation, i.e., Ni₂(L-asp)₂(bpy), or “MOF-NH₂“_, and Ni₂(L-mal)₂(bpy), or “MOF-OH”. These MOFs were synthesized from either L-aspartic acid and nickel carbonate or L-malic acid and nickel acetate, respectively, which were combined with 4,4′-bipyridyl (bpy) in solvothermal reactions. The researchers point out that the MOFs are prepared from inexpensive compounds and the reaction is scalable up to kilograms.

The synthesized frameworks both form one-dimensional channels. The team investigated the adsorption behavior of MOF-NH₂ and MOF-OH and found that acetylene is preferentially adsorbed in the MOFs’ channels over carbon dioxide in both cases. MOF-OH, in particular, showed the highest acetylene storage density to date (0.81 g mL^–1 at ambient conditions) and is stable in air and in water. Thus, the material could be useful for selective C₂H₂ adsorption and purification.

• Efficient C₂H₂/CO₂ Separation in Ultramicroporous Metal–Organic Frameworks with Record C₂H₂ Storage Density,
  Wei Gong, Hui Cui, Yi Xie, Yingguo Li, Xianhui Tang, Yan Liu, Yong Cui, Banglin Chen,
  J. Am. Chem. Soc. 2021.
  https://doi.org/10.1021/jacs.1c07191