Boosting Iodine Capture via Ammonization of a Multicomponent-Based Covalent Organic Framework

Abstract

Adsorption-based iodine capture offers an effective strategy for managing radioactive nuclear waste. In this study, a carboxylic acid–functionalized covalent organic framework (COF─COOH) was synthesized via a multicomponent Doebner reaction and postsynthetically modified with aqueous ammonia to produce an ionic framework, [COF─COO⁻][NH₄]⁺. A nonfunctionalized analog, COF─TpTta, was also synthesized for comparison. Iodine vapor uptake at 75°C followed the order [COF─COO⁻][NH₄]⁺ (2.4 ± 0.092 g/g) > COF─COOH (1.8 ± 0.07 g/g) > COF─TpTta (1.5 ± 0.082 g/g). Spectroscopic analyses revealed that COF─TpTta and COF─COOH primarily captured iodine via charge–transfer interactions, whereas [COF─COO⁻][NH₄]⁺ utilized an additional electrostatic and hydrogen bonding mechanism between iodine species and ammonium carboxylate groups. This dual-binding mechanism enhanced iodine uptake by 60% over COF─TpTta despite reduced surface area, pore size, and pore volume. [COF─COO⁻][NH₄]⁺ retained over 80% of its gaseous phase iodine adsorption capacity after four cycles, maintained iodine loading over 30 h, and exhibited high iodine uptake (225 ± 16.76 mg/g) from n-hexane following Langmuir-type adsorption. These results demonstrate that tailored binding-site chemistry, rather than solely textural optimization, can drives superior iodine capture. This ionic COF design strategy offers a versatile and robust platform for synthesizing next-generation radioiodine adsorbents.