CoNi Alloy Nanoparticles Embedded in Metal-Organic Framework-Derived Carbon for the Highly Efficient Separation of Xenon and Krypton via a Charge-Transfer Effect

Separation of xenon from krypton is of industrial interests due to their wide applications in medical imaging, spacecraft propellants, insulation, commercial lighting and lasers. There is an urgent demand to develop an alternative separation technology to replace capital and energy intensive cryogenic distillation, which is the most popular in separation of Xe/Kr. Adsorption separation based on task-specific adsorbents is significant and promising. Herein, we propose a new strategy for Xe/Kr separation using MOF derived Ni/C and Ni_0.5Co_0.5/C adsorbents via orbital hybridization. Gallate-based MOFs were used as precursors to prepare a series of carbon adsorbents by activating agent-free pyrolysis. Adsorption tests and breakthrough experiments were used to evaluate the performances of these carbon adsorbents. The optimal carbon adsorbent, Ni_0.5Co_0.5/C-700, exhibits relatively high Xe uptake (1.42 mmol/g) at ambient conditions. Moreover, the IAST selectivity of Xe/Kr at ambient conditions and Henry’s selectivity of Xe/Kr for Ni_0.5Co_0.5/C-700 are high (24.1 and 20.5, respectively), surpassing all carbon adsorbents and most top-performing MOFs reported to date. The density functional theory calculations reveal that the great affinity with Xe benefits from the presence of Ni and Co nanoparticles in carbon adsorbents. 5pz orbital of Xe has closer energy level to metal orbitals than that of Kr, providing greater mixing and stronger interaction. Facile preparation process, high adsorption capacity, record-high separation selectivity and high stability ensure this adsorbent a promising candidate in industrial use. And the proposed new strategy provides new ideas for the adsorption separation of inert gases in the future.