Benzothiazole-Derived Covalent Organic Framework for Multimedia Iodine Uptake

Abstract

Nuclear energy holds the chief portion of the global primary energy mix that comes with the major issue of releasing volatile nuclear wastes viz. radioiodine (¹²⁹I and ¹³¹I) into air and water bodies during nuclear fuel reprocessing. The efficient capture of volatile radioiodine has attracted a major attention worldwide due to the severe health and environment effects. Among various porous materials, covalent organic frameworks (COFs) are the intriguing class of porous organic materials with crystallinity, synthetically pre-designable functionalities to achieve tunable properties. Herein, a new benzothiazole based COF (COF-3) obtained by the condensation of 2,6-dimainobenzothiazole and 2,4,6-triformylpholoroglucinol is reported with tetragonal pore topology (pore volume = 0.305 cc g⁻¹; BET surface area = 57.9 m² g⁻¹). The electron rich heteroatoms in the frameworks play a crucial role in adsorbing electron deficient iodine molecules and therefore, the benzothiazole-derived COF is envisioned to be potent material for efficient iodine adsorption. The synthesized COF showed the iodine adsorption capacity of 1.07 g g⁻¹ in vapor phase and 109.0 mg g⁻¹ from n-hexane solution. A reference COF (COF-4) with no thiazole group derived from 1,4-phenylenediamine and 2,4,6-triformylpholoroglucinol with hexagonal pore topology (pore volume = 0.937 cc g⁻¹) and BET surface area 133.9 m² g⁻¹ showed adsorption of iodine from n-hexane solution with capacity 149.5 mg g⁻¹. The study revealed that although the presence of heteroatoms in the framework facilitates the iodine adsorption by converting the molecular iodine into the polyiodides; the factors such as BET surface area, pore topology and pore volume also play a major role in the adsorption of iodine molecules.

Graphical Abstract