Croconic acid-based zwitterionic conjugated porous polymer featuring nitrogen-rich triazine cores for enhanced iodine capture

Abstract

Increased nuclear energy consumption leads to the enormous release of hazardous gases such as iodine into the environment. To address this concern, two zwitterionic Conjugated Porous Polymers (CPPs) CTTz and STTz have been synthesized by incorporating nitrogen-rich TTz with zwitterionic CA/SA under catalyst-free solvothermal conditions to achieve efficient multi-state iodine adsorption. The multiple active binding sites serve their dominance in trapping iodine species effectively. The polymers demonstrated exceptional iodine adsorption capabilities in both vapour phase and solution phases, with ?6.4 g/g and ?1.1 g/g iodine adsorption for CTTz and ?4.6 g/g and ?1.6 g/g for STTz, respectively. The zwitterionic backbones (CA/SA) in the polymer framework facilitated the formation of charge transfer complexes with iodine species, and the presence of triazine moieties enhances adsorption. The exceptional iodine capturing by CTTz and STTz lasted over a period of five cycles (?80 %). The iodine-loaded and recovered CPPs were analyzed using FTIR, FESEM, BET, XRD, and Raman spectroscopic studies, revealing the capture and release of different iodine species (I<inf>2</inf>, I<inf>3</inf>-, and I<inf>5</inf>-) by adsorbents. These findings offer valuable insights for designing and developing advanced zwitterionic adsorbent materials for effective dual-phase iodine capture and removal. Environmental implication: Uncontrolled release of radioactive iodine from nuclear energy sources poses a significant environmental and public health risk due to its volatility, mobility, and potential for bioaccumulation. Thus, it is essential to develop highly efficient, regenerable, and chemically stable adsorbents for removing iodine contamination in both vapour and solution phases. This study presents CTTz and STTz synthesised using Tris(4-aminophenyl)triazine and croconic/squaric acid building blocks, demonstrating exceptional iodine capture in both phases. Their robust structures, rich in nitrogen, oxygen and ionic binding sites, enable efficient charge-transfer complex formation with iodine species under ambient conditions. These results promote next-generation adsorbent development for nuclear waste management and provide a viable solution for preventing iodine radionuclide environmental contamination. © 2025 Elsevier B.V.