Harnessing Dicarboxylic Acid Groups in Heteroatom-Enriched Covalent Organic Polymers (COPs) for Enhanced Iodine Sorption Efficiency

As the global demand for clean and sustainable energy grows, nuclear power is emerging as a key component of the future energy landscape due to its incredibly low carbon emissions and unmatched energy density. However, ensuring the safety and environmental sustainability of nuclear energy is paramount, particularly in managing radioactive fission products such as iodine, which poses significant health risks, including thyroid cancer. Effective iodine capture is thus crucial for mitigating environmental contamination and safeguarding public health. The present study addresses this challenge by designing covalent organic polymers (COPs) with appended dicarboxylic acid (−COOH) groups on a triazine-based heteroatom-enriched architecture for high-capacity iodine capture from solutions and vapors. The synthesized polymers, 1,3-Diacid and 1,4-Diacid COPs, demonstrated exceptional iodine adsorption capabilities, harnessing the benefits of the carboxylic acid (−COOH) moiety. In the vapor phase, these polymers achieved reversible molecular iodine uptake capacities of up to 330 wt % (3.3 g/g) and 240 wt % (2.4 g/g) at 85 °C and 1 bar, respectively. In the solution phase, 1,3-Diacid and 1,4-Diacid COPs removed up to 92% and 86% iodine from a 300 mg/L iodine cyclohexane solution within 60 min, with adsorption capacities of 769 and 555 mg/g, respectively. The sorption kinetics followed a pseudo-second-order model, and both systems adhered to the Langmuir adsorption model, indicating monolayer adsorption on homogeneous sites. Notably, the carboxylic acid group significantly influenced iodine sorption by offering additional binding sites within the COP. 1,3-Diacid COP exhibited a significantly higher adsorption capacity over 1,4-Diacid COP, possibly due to the close proximity of the two binding sites for reinforced interactions. Furthermore, the polymers demonstrated reusability without significant efficiency loss, making them promising candidates for rapid and enhanced iodine capture in environmental remediation applications.