Investigation of Efficient Iodine Adsorption Properties of Covalent Organic Framework Gels with Free Amino Groups Adsorption Sites

Radioactive iodine is a critical pollutant that poses substantial threats to our daily lives, making the capture of radioactive iodine an essential issue. Covalent organic frameworks (COFs) have emerged as ideal candidates for iodine trapping owing to their large surface area, high porosity, and tunable structures. Herein, we designed and prepared two COF gels by an amino protection strategy, TAPB-NH₂-DHTP and TAPB-DHTP. TAPB-NH₂-DHTP is a COF gel containing free amino groups. Its maximum iodine adsorption capacity reaches 4.62 g·g^–1 under static conditions at 75 °C, significantly surpassing than of TAPB-DHTP at 3.82 g·g^–1 (without free amino groups). In liquid iodine tests, the adsorption efficiency of TAPB-NH₂-DHTP exceeded 90%, with a maximum adsorption capacity of 665.1 mg·g^–1. The COF gel also showed high selectivity for iodine even in the presence of various interfering ions. In both gaseous and liquid iodine adsorption experiments, TAPB-NH₂-DHTP consistently outperformed TAPB-DHTP, demonstrating superior adsorption effects. The mechanism of iodine adsorption by these COF gels was investigated. Results indicate that introducing free amino groups into the monomer significantly increases active sites for iodine binding. Simultaneously, the free electron-donor amino groups enhance charge transfer within the COF framework, which improves the binding capacity for iodine of the adsorbent materials. This research provides further insights and strategies for the development and performance enhancement of materials aimed at efficient iodine trapping.