Selective Capture of Bromine over Iodine by a Nanometer-Sized Covalent Organic Framework Containing Imines and Hydrazones

The safe storage and transportation of elemental bromine are challenging due to its volatile, toxic, and corrosive nature. Efficient bromine removal is, therefore, a topical research domain. Previously reported Br2 capture materials suffer from limitations such as aqueous instability and poor halogen retention. Herein, we report a facile and scalable synthesis of a nanoscalar covalent organic framework (COF-2H1) that can efficiently remove various forms of bromine from different media. This is possible due to the favorable interactions between electrophilic bromine with the pi-electron-rich substituents (imine and hydrazone linkage) present on the covalent framework of COF-2H1. The uptake capacities of 11.29 and 15.34 g/g, respectively, from water and cyclohexane solutions are higher than those for previously reported bromine adsorbents. Purification of bromine industrially from a mixture of bromine, iodine, and interhalogen compounds (IBr) poses a technological challenge. COF-2H1 can selectively capture bromine over iodine in halogen mixtures. Thus, COF-2H1 provides a viable solution to the difficulties associated with processes to obtain pristine bromine.