Efficient Removal of Pb2+ from Aqueous Solution by an Ionic Covalent–Organic Framework: Molecular Simulation Study

An ionic covalent–organic framework (ICOF-1 containing sp3 hybridized boron anionic centers formed by spiroborate linkage and dimethylammonium ions) is explored as an ion exchanger for the removal of lead (Pb2+) ions from aqueous solution. From molecular simulations, the Pb2+ ions are observed to exchange with the nonframework DMA+ ions in the ICOF-1. At a concentration of 600 ppm, the Pb2+ ions are completely exchanged and reside in the ICOF-1, while the DMA+ ions are in a dynamic equilibrium with the solution. It is revealed that the exchange between Pb2+ and DMA+ is governed by the stronger attraction of Pb2+ with the negatively charged ICOF-1 framework. The radial distribution functions and mean-squared displacements further show that the exchanged Pb2+ ions are in a closer proximity to the ICOF-1 framework with a smaller mobility than DMA+ ions. The simulation study provides microscopic insight into the ion-exchange process between Pb2+ and DMA+, and it suggests that the ICOF-1 might be an intriguing candidate for water purification.