Efficient As(V) and Hg(Ⅱ) removal from acidic wastewater by a sulphydryl functionalized UIO-66-NH2

Metal-organic frameworks (MOFs) have a high potential for removing heavy metal ions from wastewater. However, they could not remove opposite-charged metal species simultaneously by adsorption. In this study, a novel bifunctional MOF UIO-66-NH2(-SH) containing -NH2 and -SH functional groups (UIO-66-NH2(-SH), named Zr-DMBM) was fabricated by the ligand exchange method to serve as an adsorbent of electrostatically opposite As(V) and Hg(II). The structure-dependent adsorption of Zr-DMBM was optimised as Zr4+: BDC-NH2:-SH = 1:2:1 for As(V) and Hg(II). The removal rates of As(V) and Hg(II) were greater than 80 % over a wide pH range (pH = 1–9), with maximum adsorption capacities of 72.2 and 812.5 mg·g-1, respectively. For practical applications, microextraction column packing of Zr-DMBM was applied to efficiently and simultaneously remove As(V) and Hg(II) from wastewater. After As(V) and Hg(II) adsorption, the prepared column was easily regenerated using thiourea (0.1 M) and hydrochloric acid (0.1 M), and could be recycled five times without an evident reduction in adsorption capacity. The excellent performance of Zr-DMBM was attributed to the incorporation of -SH and –NH2 groups and its unique physicochemical properties. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that Zr-DMBM exhibited the same topological structure as UIO-66-NH2, and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of -SH groups in its structure. The adsorption kinetics further demonstrated the strong electrostatic attraction between Zr-DMBM and As(V) and Hg(II). Therefore, the combination of MOFs with microextraction column technology is a promising candidate for the simultaneous removal of As(V) and Hg(II) ions from wastewater. Moreover, the sulfhydryl-functionalised UIO-66-NH2 is suitable for industrial wastewater treatment owing to its excellent performance in a broad range of pH environments.