Developing novel amine-linked covalent organic frameworks towards reversible iodine capture

Radio iodine is one of the essential gaseous pollutions needed to be removed by the growth in nuclear energy consumption. The current paper deals with preparing an amine-linked covalent organic framework (COF) with certain advantages compared to the mainstream rigid imine-linked COFs. The flexibility and abundance of the NH groups in the structure provide an excellent medium for adopting iodine from liquid and gas phases. A hydrazone-linked COF (Hz-COF) was synthesized in a room temperature solvent-mediated method, and its linkages were reduced using NaBH4 (NH-COF). The synthesized Hz-COF and NH-COF were utilized in the iodine adsorption experiment from solution and gas phases. The NH-COF exhibited an excellent iodine uptake from gas phase at 80 °C as high as 2.60 g g−1 that is higher than Hz-COF at the same conditions (2.05 g g−1). More interestingly, NH-COF represents a qe of 173 mg g−1 for iodine uptake from iodine solution (300 mg L−1). The iodine adsorption isotherm is best fitted to the Langmuir model, and the adsorption kinetic obeys the pseudo-second-order model. The flexibility of NH-COF and the presence of –NH– groups in the NH-COF structure endows it with accommodative adaptability to guest molecules, increasing the adsorption capacities compared to Hz-COF. Full reusability, high thermal and chemical stabilities, and a high level of polar functional groups made NH-COF an excellent adsorbent for I2 capture performance.