Rational Design of Luminescent Thiazolo[5,4- d ]thiazole Decorated Covalent Organic Polymer (COP) for Efficient Iodine Sorption and CO2 Capture

Abstract

Volatile and highly soluble isotopes such as 129I and 131I pose severe environmental and biological hazards, necessitating sorbent materials capable of stable and efficient capture under harsh conditions. Covalent organic polymers (COPs), with their robust covalent backbones, tunable porosity, and heteroatom-rich architectures, provide an attractive platform for iodine sequestration. In this work, we present two thiazolo[5,4-d]thiazole (TzTz)-based conjugated organic polymers─MD-COP-01 and MD-COP-02─synthesized via oxidative polymerization of carbazole- and imidazo[1,2-a]pyridine-derived monomers. Incorporation of electron-deficient TzTz acceptors with moderately electron-rich donor units, particularly imidazo[1,2-a]pyridine, generates rigid donor–acceptor frameworks that are both luminescent and highly interactive toward iodine. The polymers MD-COP-01 and MD-COP-02 exhibited moderate to high surface areas of 27 and 399 m2 g–1, respectively, with MD-COP-01 displaying exceptional iodine sorption affinity, achieving uptakes of 275 wt % in vapor and 331 mg g–1 in solution with >90% removal efficiency. The combined DFT, Raman, XPS, and EDX elemental mapping analyses provided compelling evidence that charge-transfer interactions are the primary driving force behind the remarkable iodine uptake exhibited by MD-COP-01, underscoring the critical role of S/N-rich binding sites. A prototype for continuous iodine separation has also been demonstrated here, offering an excellent dynamic adsorption performance and practical potential of MD-COP-01 for continuous iodine capture and water purification. Additionally, MD-COP-01 exhibited a CO2 uptake of 1.53 mmol g–1 at 273 K and 1.12 mmol g–1 at 298 K, while MD-COP-02 showed comparable adsorption capacities of 1.58 mmol g–1 and 1.00 mmol g–1 at the respective temperatures. Overall, these findings broaden the functional scope of TzTz-based porous frameworks and establish their potential as robust, tunable, and highly efficient adsorbents for nuclear-waste iodine capture and environmental remediation.