Facile Synthesis of Highly Crystalline Schiff-Base Covalent Organic Frameworks for Efficient Iodine Adsorption

Crystalline covalent organic framework (COF) materials have demonstrated remarkable potentials in the field of adsorption, in particular adsorption of radioactive substances with extremely environmental hazards, owing to their high specific surface area, few structural defects, and excellent stability. So far, most highly crystalline COFs including Schiff-base COFs are mainly synthesized via traditional solvothermal methods, which, however, inevitably generate waste liquid and require high reaction temperatures and prolonged reaction times with the large-scale production thus limited. The rapid and efficient synthesis of highly crystalline COFs is still a key challenge. Herein, following the 4-dimethylamino pyridine (DMAP)-mediated melt polymerization process, Schiff-base COFs were efficiently synthesized with a short reaction time, low temperature required and no pollution waste generated, resulting in different Schiff-base COF materials that exhibit high crystallinity and porosity, and large specific surface areas, as well as excellent stabilities toward both acidic and alkaline conditions. Encouragingly, the obtained Schiff-base COF materials demonstrated excellent iodine adsorption capacities with COF-Sptza achieving saturated iodine adsorption capacities of 10.77 g/g (1077.3% by mass), at 75 °C under ambient pressure, owing to their electron-rich heteroatom active sites, which makes it one of the most efficient iodine adsorption COF materials for application in nuclear waste treatment.