Construction of flexible dibenzimidazole-linked covalent organic frameworks for capturing iodine pollutants

Imidazole has a high iodine uptaking capacity thanks to its electron-rich nature, but there are no reports of flexible dibenzimidazole-linked COFs for iodine adsorption. Herein, we present a series of dibenzimidazole-linked COFs, which were formed via Schiff base polymerization of 3,3′- diaminobenzidine (DAB) and 1,2,4,5-benzenetetramine tetrahydrochloride (TAB) with the knots containing ether bonds, NOP–6–CHO and TPT–3–CHO, under different catalytic conditions for the first time (TPT − 3 − CHO + DAB→TDAB, TPT − 3 − CHO + TAB→TTAB, NOP − 6 − CHO + DAB →HDAB, and NOP − 6 − CHO+ TAB→HTAB). TDAB, TTAB, HDAB, and HTAB have large specific areas of 2087, 1912, 2164, and 2001 m 2 g −1 , certain crystallinity and stability. TDAB, TTAB, HDAB, and HTAB showed up to 4.95, 4.86, 5.88 and 6.00 g g −1 iodine adsorption capacities respectively under 77 °C/air conditions, and showed rapid adsorption rates at 25 °C in cyclohexane solution and aqueous solution. The iodine adsorption behaviors conformed to the fitting of the pseudo-first-order model. The plentiful N-heterocycic structure of dibenzimidazole is favorable for electron transfer, which boosts the generating (poly)iodide ions and increases the amounts of iodine adsorbed. For economic reasons, the current novel materials also showed a certain degree of reusability and conserved the iodine capture ability after several regeneration cycles.