Synthesis of highly porous inorganic adsorbents derived from metal-organic frameworks and their application in efficient elimination of mercury(II)

Innovative solid-phase adsorbent is needed urgently for highly efficient extraction of mercury (Hg(II)) from aqueous solution. Herein, highly porous inorganic materials, including ZrOx, ZrOxyPhos and ZrSulf, were obtained from topotactic transformations of metal–organic frameworks (MOFs) via a facile ligand extraction process, which preserved the original MOF morphology and introduced useful functionalities. ZrOx and ZrOxyPhos exhibited high adsorption efficiency for Hg(II). And ZrSulf showed fastest adsorption kinetics (1.1 × 10⁻² g/(mg min)) and highest adsorption capacity (824 mg/g) among the obtained three inorganic materials due to the presence of accessible sulfur-based functionality, which surpassed most of other benchmark porous adsorbents. Moreover, ZrSulf showed good regeneration ability and excellent selectivity for Hg(II) in the presence of other coexisting metal ions, such as Cd(II), Ni(II), Co(II), Mn(II) and Zn(II), and other inorganic cations, such as K⁺ and Na⁺. The excellent adsorption performance of ZrSulf towards Hg(II) can be traceable to the covalent bond formation with sulfur-based functionality combined with ion exchange with Na. Given its low-cost and easy preparation nature, ZrSulf could be potentially valuable candidates for the elimination of Hg(II) from aqueous media. Changing the MOF templates and using different digest solutions will introduce different metal and structural possibilities, which demonstrates the potential of such ligand extraction method for synthesizing porous inorganic adsorbents for heavy metal ion decontamination.