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

The uses of nuclear reactions are gaining importancein energyand medical therapy applications. Production and safe management ofradioactive waste is a major operational challenge. Proper treatmentand storage of nuclear waste are important while considering nuclearenergy for various applications. While reprocessing used nuclear fuel(UNF), handling of volatile radioactive wastes (e.g., radioisotopesof iodine: I-129/I-131) requires special attention.Iodine is present in off-gas streams as either molecular iodine (I-2) or organic iodides. I-129 is less radioactivethan I-131, but has an extremely long half-life. Both arehighly toxic, and their nearly quantitative retention from off-gasstreams requires packing of iodine filters with efficient adsorbents.Thus, there is a need to develop materials with efficient iodine vaporcapture/storage capabilities. Herein, a set of four porous organicpolymers are presented that are rich in heteroatoms and possess abundant pi-arene motifs with which p-orbitals on iodine can interacteffectively via charge-transfer complexations. To mimic the conditionsof a UNF reprocessing facility, gas-phase iodine capture experimentswere performed under various conditions (dry/humid conditions andat 75 degrees C/25 degrees C). The maximum iodine uptake capacity of oneof the materials (HPOP-4: 6.25 g/g at 75 degrees C and 4.35 g/g at 25 degrees C) is higher than several other iodine vapor adsorbents reportedto date. The retention of trapped iodine by HPOPs at 25 degrees C isalso quite remarkable with only 2-3% weight loss from iodine-loadedHPOPs, which makes HPOPs potential material for the storage/transportationof captured radioiodine. The results confirm desirable propertiesin HPOPs such as facile synthesis, high physiochemical stabilities,good moisture tolerance, rapid adsorption kinetics, and efficientreusability with low compromise in capture performance upon regeneration.These benefits render HPOPs as strong contenders for packing filtersused for retaining radioiodine during cleaning either off-gas streamsor annulus exhaust air (during "loss of coolant accident").