Creating Copper Sites For Capturing Hydrogen

Separating isotopes has always been a bit of a challenge. Traditionally there are five methods for isolating isotopes these being: containing the gas with a semi-permeable membrane as lighter isotopes will diffuse through faster; electromagnetic deflection where heavier isotopes will experience less acceleration for a given force; centrifuges where lighter elements are thrown outwards more; electrolysis where the heavy ions, having less mobility, are evolved less often at the electrodes; and finally there is a method involving two plates, one hot and one cold, as thermal diffusion rates leave the heavy isotopes nearer the cold wall. (There is technically also a sixth way as some chemical reactions of exchange develop biased isotope concentrations such as the catalysed reaction between hydrogen and water vapour where the water is found to contain almost three times as much deuterium as the hydrogen gas does.)

The separation of hydrogen has always been the easiest of all elements as the isotopes are relatively much more more different to each other with deuterium being twice the mass of protium. Despite this the separating processes are still very costly and requires some extreme amounts of energy to get a high quality of separation between protium, deuterium and tritium. Ideally the one that is required is deuterium and the main problem is removing the radioactive tritium from heavy water deposits so that the deuterium can continue on to be used in experimental procedures. In order to achieve this separation scientists have constructed a metal organic framework to act as a membrane for the hydrogen separation called Cu(I)-MFU-4l pictured below:

Figure 1
Thank you to nature.com and the paper of topic for this image

This is a combination of metal and organic atoms witch has had specific copper sites activated in order to bind to hydrogen molecules. At just 100 K the Dover H2 separation factor was eleven meaning that for every protium molecule that got through eleven deuterium made it through first. Such an incredibly high separation factor is because there is constant interchange between the hydrogen of the gas and the that adsorbed and held on the structure. Through a series of experimental tests it was found that this ability to react and trap deuterium persists even when the temperature is raised above 100 K. This material could be used to purify the heavy hydrogen mixtures allowing both the deuterium and tritium to go to their intended applications.

Paper links: Capture of heavy hydrogen isotopes in a metal-organic framework with active Cu(I) sites

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