Co(II) and Zn(II) Coordination Polymers with π-Conjugated Ligands for Enhanced Iodine Uptake in Vapor and Aqueous Media.

The efficient removal of radioiodine from an aqueous solution is crucial for the sustainable advancement of nuclear energy and environmental conservation. In this work, two π-conjugated nonporous coordination polymers, namely, {[Co(bqdc)(dpe)(HO)]·HO} (Co-CP) and [Zn(bqdc)(dpe)] (Zn-CP) (bqdc = 2,2'-biquinoline-4,4'-dicarboxylate and dpe = 1,2-di(4-pyridyl)ethylene) were successfully synthesized and characterized. Single crystal X-ray analysis demonstrated that Co-CP and Zn-CP have different crystal structures. Co-CP displays the 1D chain via bidentate and monodentate coordination modes of bqdc and dpe, respectively, whereas Zn-CP presents a threefold interpenetrated 3D framework through bridging bidentated ligands. Both CPs exhibit a nonporous nature with high π-electron richness in the structural framework. Both compounds can adsorb iodine in vapor and solution phases with high adsorption capacity. The iodine adsorption capacities in the vapor phase at 70 °C are 3.54 and 1.57 g/g for Co-CP and Zn-CP, respectively. In addition, Co-CP and Zn-CP exhibit effective iodine adsorption in aqueous solutions with capacities of 2315.86 and 2032.97 mg/g, respectively. The adsorption kinetics, adsorption isotherms, competing anion adsorption, and iodine adsorption in real water samples were studied. The iodine adsorption mechanism is due to electron transfer from the effective sorption sites of CPs to iodine, forming the charge transfer complex, which was confirmed by FTIR, PXRD, EDX, and XPS techniques. They can also be reused to capture iodine in an aqueous solution with the ability to retain a high level of effectiveness.