Adsorption of Iodine on Adamantane-Based Covalent Organic Frameworks

Radioactive iodine is severely hazardous to human health and the environment because of its high specific activity and environmental mobility. In this article, three covalent organic frameworks (COFs) (named as DbTd-COF, DpTd-COF, and DaTd-COF) were prepared for the removal of iodine in both gas and solution states. The COFs were obtained by the solvothermal reaction of 1,3,5,7-tetrakis (4-formylphenyl) adamantane (TFPA) with benzidine, 2,5-diaminopyridine, and p-phenylenediamine, respectively. The obtained samples were characterized by SEM, FT-IR, TGA, and nitrogen adsorption-desorption analysis. The rigid linker of phenzyl chains helps to improve the stability of the polymer. DbTd-COF and DaTd-COF show excellent thermomechanical stability with a decomposition temperature of over 400 degrees C. DbTd-COF and DaTd-COF show good uptake capacities of 4.93 and 4.48 g g(-1) for iodine vapor capture, respectively. DpTd-COF shows a slightly smaller iodine uptake of 3.43 g g(-1). XPS results indicated that iodine was captured in the form of its polyiodide anions. A better recyclability can be obtained after four cycle runs. In addition, DaTd-COF shows good removal of iodine (concentration: 500 mg L-1) from cyclohexane solution with an adsorption capacity of 666.79 mg g(-1).