More efficient isotope separation in sight

The lightest of all elements, hydrogen, is in great demand due to its promising role as a sustainable resource in the energy transition. A team from Leipzig University and TU Dresden, as part of the Hydrogen Isotopes 1,2,3H Research Training Group, has made an important breakthrough in the efficient and cost-effective provision of isotopes.

These are the three forms in which hydrogen occurs in nature—as protium, deuterium or tritium. The international team of researchers has taken a big step towards realizing its dream of separating hydrogen isotopes at room temperature at low cost. The team’s findings have been published in Chemical Science.

Protium, or hydrogen-1, is the most common form of hydrogen. Deuterium, known as heavy hydrogen, is playing an increasingly important role, for example, in the development of more stable and effective pharmaceuticals. A mixture of deuterium and tritium, “super-heavy” hydrogen, serves as the fuel for nuclear fusion, a sustainable energy source of the future.

One of the unsolved problems in hydrogen research is how to provide these isotopes in a highly pure form in an efficient and cost-effective way, as they have very similar physical properties. Current isotope separation processes are not very efficient and consume vast amounts of energy.

“It has been known for almost 15 years that porous metal-organic frameworks can, in principle, be used to purify and separate hydrogen isotopes. However, this has only been possible at very low temperatures, around minus 200 degrees Celsius—conditions that are very costly to implement on an industrial scale,” says Professor Knut Asmis from the Wilhelm Ostwald Institute for Physical and Theoretical Chemistry at Leipzig University and spokesperson for the Research Training Group.

He adds that the separation mechanism is based on the strongly favored adsorption of one of the isotopes present on one of the free metal centers in the porous solid. Adsorption is a process by which atoms, ions or molecules from a gas or liquid adhere to a solid, often porous, surface.

The doctoral researchers of the 1,2,3H Research Training Group, Elvira Dongmo, Shabnam Haque and Florian Kreuter, who are all members of one of the research groups led by Professor Thomas Heine (TU Dresden), Professor Knut Asmis and Professor Ralf Tonner-Zech (both Leipzig University), have now gained a deeper insight into the influence of the framework environment on binding selectivity.

This means the question of why one of the isotopes is more likely to stick than the other. This was deciphered in detail in the present study through a synergistic interplay between state-of-the-art spectroscopy, quantum chemical calculations and chemical binding analysis on a model system.

“For the first time, we have been able to show the influence of the individual atoms of the framework compounds on adsorption. We can now optimize them in a targeted manner in order to obtain materials with high selectivity at room temperature,” says Heine.