Efficient Organic Iodide and Iodine vapour phase capture by Viologen-based organic framework

Abstract

Sequestration of radioactive organic iodide (ROIs) during fuel reprocessing in nuclear power plants is significant to ensure nuclear safety, protect the environment, and safeguard public health. Radioactive molecular Iodine (I2) and organic iodides, mainly Methyl Iodide (CH3I), coexist at low concentrations in the off-gas stream of nuclear power plants. Despite several materials being reported for the adsorption of ROIs, developing an effective adsorbent with high adsorption and retention efficiency, recyclability, and recovery is still a significant challenge. In this study, we aimed to understand the role of framework-integrated functionalities in organic iodide sequestration. We achieved this by varying the number of N-heteroatomic sites in a series of chemically stable porous covalent organic polymers (COPs). The study discovered that the I2 adsorption capacity in COPs is positively linked to the presence of N-heteroatomic or heterocyclic functionalities such as bipyridyl, pyridine, and triazine sites. The highest capacity of 5.53 g.g-1 was recorded at 348 K for triazine-based COP. On the other hand, the CH3I adsorption capacity showed a unique trend, with pyridine-based COPs exhibiting the highest adsorption efficiency of 4.92 g.g-1 and 3.47 g.g-1 at 423 K and 348 K, respectively, surpassing most of the adsorbents reported for methyl iodide capture. This work contributes to a deeper insight into I2/CH3I adsorption mechanisms.