Yang Dankun, Rochat Sebastien, Krzystyniak Matthew, Kulak Alexander, Olivier Jacques, Ting Valeska P, Tian Mi
Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR, U.K.
School of Engineering Mathematics and Technology, University of Bristol, Bristol BS8 1TW, U.K.
ACS Appl Mater Interfaces. 2024 Mar 13;16(10):12467-12478. doi: 10.1021/acsami.3c17965. Epub 2024 Feb 29.
Porous organic cages (POCs) are nanoporous materials composed of discrete molecular units that have uniformly distributed functional pores. The intrinsic porosity of these structures can be tuned accurately at the nanoscale by altering the size of the porous molecules, particularly to an optimal size of 3.6 Å, to harness the kinetic quantum sieving effect. Previous research on POCs for isotope separation has predominantly centered on differences in the quantities of adsorbed isotopes. However, nuclear quantum effects also contribute significantly to the dynamics of the sorption process, offering additional opportunities for separating H and D at practical operational temperatures. In this study, our investigations into H and D sorption on POC samples revealed a higher uptake of D compared to that of H under identical conditions. We employed quasi-elastic neutron scattering to study the diffusion processes of D and H in the POCs across various temperature and pressure ranges. Additionally, neutron Compton scattering was utilized to measure the values of the nuclear zero-point energy of individual isotopic species in D and H The results indicate that the diffusion coefficient of D is approximately one-sixth that of H in the POC due to the nuclear quantum effect. Furthermore, the results reveal that at 77 K, D has longer residence times compared to H when moving from pore to pore. Consequently, using the kinetic difference of H and D in a porous POC system enables hydrogen isotope separation using a temperature or pressure swing system at around liquid nitrogen temperatures.
多孔有机笼（POC）是由离散分子单元组成的纳米多孔材料，具有均匀分布的功能性孔隙。通过改变多孔分子的大小，特别是将其调整到3.6 Å的最佳尺寸，这些结构的固有孔隙率可以在纳米尺度上精确调节，以利用动力学量子筛分效应。先前关于用于同位素分离的POC的研究主要集中在吸附同位素数量的差异上。然而，核量子效应也对吸附过程的动力学有显著贡献，在实际操作温度下为分离H和D提供了额外的机会。在本研究中，我们对POC样品上H和D吸附的研究表明，在相同条件下，D的吸附量高于H。我们采用准弹性中子散射来研究D和H在POC中在不同温度和压力范围内的扩散过程。此外，利用中子康普顿散射来测量D和H中单个同位素物种的核零点能量值。结果表明，由于核量子效应，POC中D的扩散系数约为H的六分之一。此外，结果还表明，在77 K时，D在孔与孔之间移动时的停留时间比H长。因此，利用多孔POC系统中H和D的动力学差异，可以在液氮温度左右使用变温或变压系统进行氢同位素分离。
