New insight into the co-removal of arsenic and cadmium from wastewater by using thiol-functionalized UiO-66: A mechanistic study and real water test

Industrial wastewater is normally a complex matrix, and few reported MOFs have considered the co-removal of anion and cation contaminants from wastewater. In this study, we synthesized a highly stable thiolfunctionalized MOF (UiO-66-SH) to achieve the coadsorption of As(V) and Cd(II) in an aqueous solution. The morphology, functional groups and thermal properties of UiO-66-SH were examined. The prepared UiO-66-SH possessed an octahedral structure (size: 0.8-2 mu m) with a large surface area (224 m2/g). TEM-EDX mapping showed a uniform distribution of S and Zr throughout UiO-66-SH. The FT-IR spectra showed peaks for -SH at 2566 cm-1, indicating that -SH was successfully incorporated into UiO-66. Adsorption batch experiments showed that both As(V) and Cd(II) were rapidly taken up by UiO-66-SH in the first 6 h, and the removal rates were over 70% and 88%, respectively, after 24 h. The maximum As(V) and Cd(II) adsorption capacities were 52.31 and 77.42 mg/g. The optimum pH values for As(V) and Cd(II) adsorption were 3 and 5, respectively. Except for Pb(II) and phosphate, anions, cations, and humic acid had almost no effect on As(V) and Cd(II) co-removal by UiO-66SH. Spectral analysis indicated that surface hydroxyl groups (Zr-OH) and -SH groups played vital roles in As(V) and Cd(II) adsorption by participating in inner-sphere coordination interactions. A real water test showed that a very small amount of UiO-66-SH could decrease the concentration to below the emission standard within 6 h. Our study demonstrated that UiO-66-SH is a promising adsorbent for treating As- and Cd-cocontaminated mining wastewater, ensuring the environmental safety of wastewater emission.