Chemically Stable and Heteroatom Containing Porous Organic Polymers for Efficient Iodine Vapor Capture and its Storage

Abstract

The uses of nuclear reactions are gaining importance in energy and medical therapy applications. Production and safe management of radioactive waste is a major operational challenge. Proper treatment and storage of nuclear waste are important while considering nuclear energy for various applications. While reprocessing used nuclear fuel (UNF), handling of volatile radioactive wastes (e.g., radioisotopes of iodine: 129I/131I) requires special attention. Iodine is present in off-gas streams as either molecular iodine (I2) or organic iodides. 129I is less radioactive than 131I, but has an extremely long half-life. Both are highly toxic, and their nearly quantitative retention from off-gas streams requires packing of iodine filters with efficient adsorbents. Thus, there is a need to develop materials with efficient iodine vapor capture/storage capabilities. Herein, a set of four porous organic polymers are presented that are rich in heteroatoms and possess abundant π-arene motifs with which p-orbitals on iodine can interact effectively via charge-transfer complexations. To mimic the conditions of a UNF reprocessing facility, gas-phase iodine capture experiments were performed under various conditions (dry/humid conditions and at 75 °C/25 °C). The maximum iodine uptake capacity of one of the materials (HPOP-4: 6.25 g/g at 75 °C and 4.35 g/g at 25 °C) is higher than several other iodine vapor adsorbents reported to date. The retention of trapped iodine by HPOPs at 25 °C is also quite remarkable with only 2–3% weight loss from iodine-loaded HPOPs, which makes HPOPs potential material for the storage/transportation of captured radioiodine. The results confirm desirable properties in HPOPs such as facile synthesis, high physiochemical stabilities, good moisture tolerance, rapid adsorption kinetics, and efficient reusability with low compromise in capture performance upon regeneration. These benefits render HPOPs as strong contenders for packing filters used for retaining radioiodine during cleaning either off-gas streams or annulus exhaust air (during “loss of coolant accident”).