Functionalized metal-organic frameworks for heavy metal ion removal from water.

Water purification is becoming increasingly important due to the scarcity and industrial contamination of water. Although traditional adsorbents such as activated carbon and zeolites can remove heavy metal ions from water, they have slow kinetics and low uptake. To address these problems, metal-organic framework (MOF) adsorbents have been developed, which are characterized by facile synthesis, high porosity, designability, and stability. Water-stable MOFs, such as MIL-101, UiO-66, NU-1000, and MOF-808, have attracted considerable research interest. Thus, in this review, we summarize the developments of these MOFs and highlight their adsorption performance characteristics. Moreover, we discuss functionalization methods that are typically used to improve these MOFs' adsorption performance. This minireview is timely and will help readers understand the design principles and working phenomena of next-generation MOF-based adsorbents.

Towards the fastest kinetics and highest uptake of post-functionalized UiO-66 for Hg2+ removal from water.

Recent advances in adsorbents have improved the removal of mercury ions from wastewater. Metal-organic frameworks (MOFs) have been increasingly used as adsorbents due to their high adsorption capacity and ability to adsorb various heavy metal ions. UiO-66 (Zr) MOFs are mainly used because they are highly stable in aqueous solutions. However, most functionalized UiO-66 materials are unable to achieve a high adsorption capacity because of the undesired reactions that occur during post-functionalization. Herein, we report a facile post-functionalization method to synthesize a MOF adsorbent with fully active amide- and thiol-functionalized chelating groups, termed UiO-66-A.T. UiO-66-A.T. was synthesized via a two-step reaction by crosslinking with a monomer containing a disulfide moiety, followed by disulfide cleavage to activate the thiol groups. UiO-66-A.T. removed Hg2+ from water with a maximum adsorption capacity of 691 mg g-1 and a rate constant of 0.28 g mg-1 min-1 at pH 1. In a mixed solution containing 10 different heavy metal ions, UiO-66-A.T. has a Hg2+ selectivity of 99.4%, which is the highest reported to date. These results demonstrate the effectiveness of our design strategy for synthesizing purely defined MOFs to achieve the best Hg2+ removal performance to date among post-functionalized UiO-66-type MOF adsorbents.