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

Abstract

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.