Screening of Zirconium-Based Metal-Organic Frameworks for Efficient Simultaneous Removal of Antimonite (Sb(III)) and Antimonate (Sb(V)) from Aqueous Solution

Seven kinds of zirconium-based metal-organic frameworks (Zr-MOFs) with different aperture size and organic linkers functionalized with different functional groups (-NH2, -OH, and -SO3H) were screened for their ability to remove antimonite (Sb(III)) and antimonate (Sb(V)) anions from water. Zr-bound hydroxides in Zr-MOFs can simultaneously remove both Sb(III) and Sb(V) via a mechanism of anion exchange. For antimony removal by UiO-66-NH2, the anion exchange seemed to be strengthened due to the Lewis acid-base interactions between the -NH2 groups on the BDC ligand and the antimony oxyanions. Among seven kinds of Zr-MOFs selected here, NU-1000 exhibited fast adsorption kinetics and high removal capacity for both Sb(III) (136.97 mg/g) and Sb(V) (287.88 mg/g), which was much higher than many antimony adsorbents described to date. Uptake of antimony at low concentrations of 100 μg/L (with a remaining antimony concentration of only ∼2 μg/L in 10 min) disclosed that current U.S. Environmental Protection Agency standards for antimony can be reached by using NU-1000 as an adsorbent. Additionally, the effects of coexisting anions such as As(III), As(V), PO43-, SO42-, NO3-, and F- on the antimony adsorption onto NU-1000 were also studied. Finally, the Sb adsorption mechanism of NU-1000 was studied via X-ray photon spectroscopy and attenuated total reflection infrared spectroscopy techniques to explore the important characteristics that make NU-1000 a compelling candidate for wastewater management.