Insight into the characteristics of carbonized ZIF-8 for the separation of Kr and Xe

Abstract

The effective capture and separation of radioactive krypton (Kr) and xenon (Xe) generated during nuclear processes remain challenging due to their chemical inertness and trace concentrations. This study focuses on the development of carbonized ZIF-8 derivatives (CZIFs) for enhanced Kr and Xe adsorption. ZIF-8 was synthesized and carbonized at 650, 800, and 950 °C, with CZIF-950 exhibiting optimal structural properties, including a high surface area (820.8 m² g⁻¹) and microporous architecture. Characterization via BET, XRD, and SEM revealed that carbonization induced structural reorganization, forming amorphous carbon frameworks with enhanced porosity. Adsorption experiments demonstrated superior performance for CZIF-950, achieving Kr and Xe capacities of 27.81 mL g⁻¹ and 78.75 mL g⁻¹ at 298 K and 1 bar, respectively, alongside high selectivity (Kr/Xe: 12.79; Xe/N₂: 55.42). Cyclic stability tests confirmed negligible capacity loss after 10 adsorption–desorption cycles, while irradiation experiments (up to 50 kGy) revealed robust structural and adsorptive integrity. Breakthrough experiments under mixed-gas conditions highlighted practical separation efficacy, with Xe/Kr selectivity reaching 3.21 for low-concentration mixtures. Density functional theory (DFT) calculations identified ZnN₄ sites as critical contributors to enhanced adsorption via interfacial polarization effects. These findings underscore CZIF-950 as a promising candidate for Kr and Xe separation in nuclear waste management, offering insights into the design of high-performance adsorbents for radioactive gas capture.