Enhanced simultaneous adsorption and detection of mercury (II) using functionalized metal − organic framework with defect structures

Abstract

Designing adsorption materials with high selectivity and sensitive detection is crucial for heavy metal removal. In this study, we introduced thiol, oxime, and thiourea functional groups, containing S, N, or both N and S elements, into the metal − organic framework (MOF-808, Zr6O4(OH)4(H3BTC)2(HCOO)6) to enhance its adsorption and detection capabilities for Hg2+. Moreover, by carefully controlling the molar ratio of the metal source, tricarboxyl and monocarboxyl ligands, we tailored the defects of MOF-808. The thiourea-modified materials demonstrated a record-breaking adsorption capacity (957.94 mg·g−1, 1.99 times that of unmodified materials) and distribution coefficient (743333 mL·g−1) for Hg2+, substantially exceeding that of other ions (separation factor of 105,086 for Hg2+/Zn2+). The material also showed excellent recoverability during ten consecutive cycles in Hg2+ adsorption. Furthermore, the modified MOF-808 displayed selective detection for Hg2+ with a high photochemical quenching coefficient (Ksv = 156.0 M−1). Theoretical calculations indicate that the thiourea group of MOF-808 favors the energetically advantageous Hg2+ capture and detection. These findings underscore the significance of MOF modification and defects engineering as vital strategies for optimizing the simultaneous removal and detection of heavy metal ions.