Selective trace bromide ion removal from chloride ion-dominated solutions using defective Zr-based metal-organic frameworks

The removal of bromide ions (Br- ) from water is critical, as these ions can generate bromate and brominated disinfection by-products that are toxic, carcinogenic, and corrosive. Previous research has not focused on the removal of Br- from water with a heavy presence of chloride ions (Cl- ). To address this research gap, we proposed a defective Zr-based metal-organic framework (MOF) to selectively remove trace Br- in environments with high concentrations of Cl-. We demonstrated that the open acidic sites on the secondary building units in a defective Zr-based MOF-808 (MOF-808-Cl) selectively removed the trace Br- in the presence of high concentration of Cl- using varying degrees of electrostatic interactions induced by their own polarizability. The Brremoval was performed with the mixed mechanism of ion-exchange and -adsorption, with contributions of approximately 70% and 30%, respectively. The Br- was successfully removed when the concentration of Cl- was 100 times higher than that of Br- . Our findings demonstrate the potential of MOF-808-Cl for industrial applications requiring trace ion removal and can provide insights for future research on selective ion removal in a competitive environment.