September 30, 2022

In the background: light microscopy images of the single crystal structures of the rigid organic cage compound. Front: ball and stick model of the single crystal structure, gray: carbon, white: hydrogen, red: oxygen, blue: nitrogen, green: fluorine. Credit: Prof. dr. dr. Michael Mastalerz

Greenhouse gas emissions contribute significantly to global warming. Not just carbon dioxide (CO2) but also fluorinated gases, including so-called per- or polyfluorocarbons or PFCs, play an important role in this development. Researchers from the Institute of Organic Chemistry at the University of Heidelberg led by Prof. dr. Michael Mastalerz have recently developed new crystalline materials that can selectively adsorb the molecules of such carbon-fluorine bonds. The Heidelberg researchers hope that these porous crystals could be useful for targeted binding and recovery of PFCs.

Polyfluorinated carbons are organic compounds of various lengths in which the hydrogen atoms of alkanes are partially or completely replaced by fluorine atoms. These atoms are chemically very stable. They are not ubiquitous in nature and are mainly used for etching processes in the semiconductor industry, in eye surgery and in medical diagnostics as contrast enhancers for certain ultrasound examinations.

“Unlike CO2integrated into natural material cycles, PFCs accumulate in the atmosphere and remain there for thousands of years before breaking down,” says Prof. Mastalerz. So compared to carbon dioxide, PFCs have a much greater global warming potential – the impact of one PFC molecule is virtually equivalent to 5,000 to 10,000 CO2 molecules. That makes polyfluorocarbons a permanent problem that is not only contributing to global warming now, but accelerating it, according to the researcher.

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With his research group at the Institute of Organic Chemistry of the University of Heidelberg, Prof. Mastalerz has developed a new type of crystalline material that can very selectively adsorb polyfluorocarbons and bind them to the inner surface. The porous crystals are based on rigid organic cage compounds bearing fluorine-containing side chains on the interconnected supports. These side chains react according to the like attracts like principle via fluorine-fluorine interactions with the PFC molecules, depositing them on the inner surface of the material.

In their experiments, the Heidelberg researchers proved that the crystals they developed bind certain fluorine-containing gases such as octafluoropropane or octafluorocyclobutane about 1,500 to 4,000 times stronger than dinitrogen, the main component of air. According to Prof. Mastalerz these numbers represent extremely high selectivities to bind such PFCs.

Currently, Prof. Mastalerz and his team are working on further increasing the selectivity of the crystals and transferring the process to other fluorinated gases, such as those used in medical anesthesia. “I see huge development potential in this area,” says the researcher. He hopes that the adsorbent can be used for the recovery of polyfluorocarbons at the point of use.

The research results have been published in Advanced materials.

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More information:
Ke Tian et al, Highly selective adsorption of perfluorinated greenhouse gases by porous organic cages, Advanced materials (2022). DOI: 10.1002/adma.202202290

Provided by the University of Heidelberg