Ionic Functionalization of Multivariate Covalent Organic Frameworks to Achieve Exceptionally High Iodine Capture Capacity.

Abstract

Adsorption-based iodine (I 2 ) capture is of great potential for the treatment of radioactive nuclear waste. Here we employ a "multivariate" synthetic strategy to construct ionic covalent organic frameworks (iCOFs) with large surface area, high pore volume, and abundant binding sites for I 2 capture. The optimized material iCOF-AB-50 exhibits static I 2 uptake capacity of 10.21 g·g -1 at 75 °C, and dynamic uptake capacity of 2.79 g·g -1 at ~400 ppm of I 2 and 25 °C, far exceeding the performances of previously reported adsorbents under similar conditions. It also shows fast adsorption kinetics, good moisture tolerance, and full reusability. The promoting effect of ionic groups on I 2 adsorption has been elucidated by experimentally identifying the iodine species adsorbed at different sites and calculating their binding energies. This work demonstrates the essential role of balancing the textural properties and binding sites of the adsorbent in achieving high I 2 capture performance.