Calix[4]resorcinarenes as Stable, Metal-Free Unexplored and Unfathomed Material for Iodine Capture: Experimental and Theoretical Insights

Abstract

While nuclear power offers a viable solution to the ever-growing energy demands, the piling up of nuclear waste remains a looming threat, endangering life on Earth. Safe disposal of radionuclides, especially highly volatile ones such as iodine, is a grave concern to be addressed for operational safety. Even though porous adsorbents for iodine capture have been widely investigated, less focus has been directed toward nonporous materials. Herein, we describe the synthesis of nonporous, macrocyclic Calix[4]resorcinarenes (C4Rs) via a near solventless green protocol mediated by Keggin-type phosphovanadotungstic acid and avoiding the use of mineral acids. The applicability of the synthesized C4Rs for iodine absorption at elevated temperatures has been explored. Facile synthesis strategy and metal-free nature coupled with moisture and temperature stability endorse our interest in C4Rs as highly attractive substrates for iodine sorption, with the substituent functionalities playing an important role in adsorption efficiency. We hereby report a novel C4R, DEAS, with an exceptional iodine sorption capability. The retention of iodine in the macrocyclic framework, mainly in the form of polyiodides, could be ascertained through a detailed characterization. The adsorption was found to follow pseudo-second-order kinetics. The adsorption of iodine from an aqueous solution was also subjected to investigation. Furthermore, theoretical investigation into the guest–host interactions between C4Rs and I₂ has been attempted for better insights.