Azo-Bridged Calix[4]resorcinarene-Based Porous Organic Frameworks with Highly Efficient Enrichment of Volatile Iodine

The effective capture and storage of volatile radionuclide iodine from the nuclear waste stream is of paramount importance for environment remediation. In this work, we report the first examples of azo-bridged calix[4]resorcinarene-based porous organic frameworks (CalPOFs), synthesized by diazocoupling reaction of 4,4'-biphenyldiamine and C-alkylcalix[4]resorcinarenes (RsC(n)s; n stands for the associated alkyl chain length) under mild conditions. The resulting CalPOFs are permanently porous, and their porous properties could be adjusted by varying the alkyl chain lengths of RsC(n)s. With the alkyl chain length increasing from methyl, ethyl to propyl, the Brunauer-Emmett-Teller surface areas are decreasing from 303, 154 to 91 m(2) g(1) for CalPOF-1, CalPOF-2 and CalPOF-3, respectively. The presence of a great many of effective sorption sites including azo (-N=N-) groups, macrocyclic pi-rich cavities and phenolic units in the skeleton as well as permanent porous structures provides these materials with ultrahigh iodine vapor uptake up to 477 wt %. Further, thorough studies revealed that the capacities for removing iodine vapor are in the order of CalPOF-1 (477 wt %) > CalPOF-2 (406 wt %) > CalPOF-3 (353 wt %), which are dependent on their surface areas, and also the densities of the azo and RsC(n) units. In addition, detailed analyses of iodine-loaded CalPOF-1 suggested that chemisorption is the major process in this adsorbent, illustrating the big chance to explore versatile CalPOFs to capture volatile toxic vapors.