Post-synthetic modification of zeolitic imidazolate framework-90 via Schiff base reaction for ultrahigh iodine capture

Abstract

The post-synthetic modification of zeolitic imidazolate frameworks (ZIFs) is an effective strategy for preparing new materials that exhibit superior performance compared to their parental ZIFs. Herein, we quantitatively transformed the aldehyde group of ZIF-90 into mono- and bis-Schiff bases, and the resulting compounds ZIF-90-I–ZIF-90-III still retained the crystallinity and their parental structures. Importantly, ZIF-90-III with the highest amount of mono-Schiff base showed the maximum iodine uptake capacities of 6600 mg g⁻¹ and 1826 mg g⁻¹ for iodine vapor and iodine/cyclohexane solution, respectively, which are 1.5- and 3.4-fold as much as that of ZIF-90, being among the highest reported to date for metal–organic frameworks (MOFs). Noteworthily, activation energies for iodine adsorption of ZIF-90 and its post-synthetic derivatives were speculated experimentally, which was firstly investigated for MOFs. Meanwhile, adsorption kinetics, iodine species during iodine adsorption process and the related theoretical calculations were also studied in detail.