Reversible anion-dependent iodine uptake in nonporous pseudopolymorphic coordination polymers

Abstract

Three new nonporous mercury(II) coordination polymers (CPs) containing the ditopic 1,1′-(1,4-phenylene)bis(3-(pyridin-4-yl)urea) ligand (4,4-pbubp), namely, {[Hg(4,4-pbubp)Cl₂](DMSO)₃}_n (CP1), {[Hg(4,4-pbubp)Br₂](DMSO)₃}_n (CP2) and {[Hg(4,4-pbubp)I₂](DMSO)₄}_n (CP3) were synthesized and characterized structurally through infrared analysis, elemental analysis (CHNS), TGA, PXRD and single-crystal X-ray diffraction analysis. All of these compounds formed 1D polymeric zigzag chains self-assembled in the crystal into higher-dimensional structures through various hydrogen-bonding interactions involving the urea functional group and several DMSO solvent molecules. These CPs were examined as potential adsorbents for the reversible uptake of iodine from the solution. Theoretical analysis of the adsorption kinetics and isotherms was applied to examine the iodine adsorption data. The results correlated effectively with the pseudo-second-order kinetic model and the Freundlich isotherm model. Our results showed that in this family, the iodine uptake capacity was dependent on the anion (CP1 > CP2 > CP3), and the compound which contained chloride anions (CP1) showed the highest capacity to remove iodine. The maximum uptake capacity of 262.01 mg g⁻¹ iodine over CP1 at room temperature based on the Freundlich model was achieved. After iodine adsorption, compounds@I₂ were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDAX) as well as Raman spectroscopy.