An innovative method for separating isotopes

Researchers have succeeded in developing an innovative method for separating deuterium using a special family of organic materials whose pore sizes change due to gas adsorption

[by Dr. Nachmani Moshe]

Updated research carried out by an international team of researchers led to the development of an innovative separation method for deuterium, using a special family of organic materials whose pore dimensions change due to gas adsorption. The innovative method allows deuterium atoms to flutter out of the nozzles of the material at a faster rate than hydrogen atoms, following the adsorption of the hydrogen gas. The study, which has long been published in the scientific journal Journal of the American Chemical Society, demonstrated that the dynamic changes in the diameter of the nozzles can provide a great opportunity for the separation of mixtures containing molecules with similar structures or sizes that require precise tuning of the nozzle diameter.

Flexible 'Metal-Organic Frameworks' (MOFs) belong to a unique group of materials that show a dynamic change in the diameter of the nozzles inside them, following an external stimulus. In these materials, the adsorption or desorption, the changes in temperature and even the mechanical pressure applied to them, cause the diameter of the nozzles to expand or contract, a process similar to the breathing mechanism.

As part of this study, the researchers examined the dynamic mechanism of a MIL-53(Al) type system for efficient separation of hydrogen isotopes. The research itself has attracted a lot of attention in academia due to the fact that this is the first ever attempt to utilize the structural flexibility of organometallic frameworks to separate hydrogen isotopes. With the help of this internal mechanism, it will be possible to selectively adsorb and release the required gas components. Under cryogenic temperature conditions (minus 233 degrees Celsius), narrow 0.26 nm diameter nozzles within the material expanded to larger 0.85 nm diameter nozzles in response to the adsorption of hydrogen gas. The expansion itself starts at the entry point and progresses towards the core. In the core, the deuterium atoms vibrate much faster than the hydrogen atoms. The pulsing of the deuterium atoms occurs closer to the core where narrower holes are found. As a result, only the deuterium atoms remain within the spatial structure. The researchers systematically changed the structure of the nozzles by changing the temperatures, pressure and adsorption time, with the aim of finding the optimal conditions. Thanks to this method, a large amount of deuterium is obtained (12 mg) per 1 gram of adsorbent. For comparison, in previous studies, the amount of separated deuterium was only 5 mg per one gram of adsorbent.

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