Shiny Takaishi1
Tohoku University1
Hydron isotopes such as deuterium (D) and tritium (T) play important roles not only in the fundamental research but also in the industry. D has been used as NMR solvents, tracer, moderator in nuclear reactors, and silicon semiconductive devices. D and T are also used as the nuclear fusion reactors, which will be expected as a future energy supply. T is contaminated with water in the nuclear waste, and its removal will be beneficial from the viewpoint of environmental protection.<br/>Natural abondance of D is 0.015 % (mainly in the sea water) and distillation process at 20 K is used to concentrate D to produce D<sub>2</sub> gas, which is energy-intensive process. Recently, quantum sieving has been extensively studied as a new technique of the hydrogen isotope separation. Beenakker and co-workers proposed the concept of kinetic quantum sieving (KQS), which utilize the difference of the diffusion rate in the small pore due to the thermal de Broglie wavelength between H and D. More recently, chemical affinity quantum sieving (CAQS) has been studied, which utilizes the difference of zero-point energy (ZPE) and resultant adsorption enthalpy (Δ<i>H</i>) among the hydrogen isotopes. Although CAQS potentially enables the hydrogen isotope separation at higher temperatures, the operating temperature was still below 200 K due to the small Δ<i>H</i>.<br/>From the viewpoint of Δ<i>H</i>, metal-dihydrogen complex is one of the most appealing candidates for this target. The first metal-dihydrogen complex was reported by Kubas and coworkers in 1984, and hundreds of compounds were reported so far. In the metal-dihydrogen complexes, chemical bond is formed between metal and dihydrogen molecule, whereas H-H bond is kept albeit it is elongated and weakened. This can be regarded as an intermediate of physisorption and chemisorption, and therefore, moderate adsorption enthalpy and fast ad/desorption kinetics could be achieved. In spite of such advantages, there has rarely been studied on the hydrogen adsorption of the dihydrogen complexes in the solid state.<br/>We have recently studied the hydrogen adsorption of solid-state dihydrogen complexes and found that Δ<i>H</i> of D<sub>2</sub> is significantly larger than that of H<sub>2</sub> in the most of dihydrogen complexes. In the presentation, we discuss the possible mechanisms of this phenomenon. In addition, we also report the demonstration of the separation of H<sub>2</sub> and D<sub>2</sub> using column chromatography at ambient temperature.