Different greenhouse gases contribute to climate change. Apart from the well-known carbon dioxide, methane and nitrous oxide are examples of greenhouse gases. Perfluorocarbons (PFCs) are greenhouse gases with high chemical stabilities and high atmospheric lifetimes. They have been introduced as replacements, e.g., for freons, because they are not harmful to the ozone layer. However, they have high global warming potentials, and thus, a negative influence on global warming. The selective adsorption of PFCs by porous materials could help to alleviate this problem.

Michael Mastalerz, University of Heidelberg, Germany, and colleagues have developed a porous organic cage (POC) decorated with fluorinated side-chains (pictured above on the right) with unprecedentedly high selectivities for the adsorption of PFCs over other gases. The team synthesized POCs with alkyl-, partially fluorinated alkyl-, and fluoroalkyl groups (pictured from left to right; called H-cage, HF-cage, and F-cage, respectively) and compared their gas sorption properties. The cages were prepared from triamino triptycene and different terphenyl-based bis-salicylaldehydes, which were connected by imine bonds.

The team found that the materials were isomorphous, with very similar pore structures and crystal packing. This allowed them to investigate the influence of the degree of fluorination in the side-chains. They discovered that the fluorinated F-cage showed an affinity for fluorinated gases, while the non-fluorinated H-cage showed a preference for non-fluorinated alkanes. The F-cage showed high uptakes and excellent selectivities for PFCs over nitrogen. This insight could be useful for the design of porous materials for the removal of PFCs from the atmosphere.

• Highly Selective Adsorption of Perfluorinated Greenhouse Gases by Porous Organic Cages,
  Ke Tian, Sven M. Elbert, Xin‐Yue Hu, Tobias Kirschbaum, Wen‐Shan Zhang, Frank Rominger, Rasmus R. Schröder, Michael Mastalerz,
  Adv. Mater. 2022.
  https://doi.org/10.1002/adma.202202290