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

Abstract

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 Br⁻ removal 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.