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

[Display omitted] •We synthesized the defective MOF-808 (MOF-808-Cl) having Cl− counter ions inside.•The presence of Cl− in MOF-808-Cl was confirmed by structural analysis using single crystal structure analysis.•The removal was contributed by both adsorption and substitutional mechanism.•The contribution ratio was 30% for vacant-site adsorption and 70% for substitution.•Effective Br− removal occurred even when Cl− was 100 times greater than Br−. 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.