Turning waste into wealth: Efficient and reversible iodine capture by decoration of coordinative allylic moiety to a flexible covalent organic framework and its application for catalysis

Abstract

Two types of flexible N-acylhydrazone-linked 2D COFs based on the triazine-containing monomer and the allyl or propyl group modified terephthalic dihydrazide monomer were synthesized. The effect of the synthesis temperature on the surface morphology and crystallinity was studied and the results demonstrated that the synthesis temperature could lead to significant changes in the surface morphology of COFs. What’s more, the coordinative allylic moiety decorated COF (TFDH-Allyl-IV) achieved an excellent iodine adsorption capacity of 6.32 g/g and 1228.04 mg/g in vapor and in n-hexane solvent, respectively. The controlled experiments including XPS, Raman spectra, solid-state 13C NMR studies and the DFT calculations demonstrated that the high adsorption capacity was endowed by the incorporation of the distal C = C bonds with iodine, generating a relatively stable I2:olefin complex. What’s more, the iodine-loaded adsorbent (I2@TFDH-Allyl-IV) could be employed as efficient reusable molecular iodine supported catalyst for organic reactions, such as the Friedel-Crafts-type reactions and oxidative cyclization reactions, which extended the potential application scope of these COFs.