Synthesis of coordination polymer by 2,2′-dithiodipropionic acid and selective removal of Hg(ii)/Pb(ii) in wastewater

Abstract

At present, the functionalized Zr-based coordination polymer for heavy metal ions removal are primarily implemented via post-synthesis, and it is still a challenge to reduce the concentration of heavy metal ions to wastewater discharge standard. In this work, the 2,2′-dithiodipropionic acid modified Zr-based coordination polymer (named as Zr-DTDPA) was prepared by direct synthesis. It presented extraordinary adsorption ability in the process of removing Hg(II)/Pb(II). The optimum pH for Hg(II) and Pb(II) absorption was 4.0 and 6.0, respectively, and the saturated adsorption capacity reached 960 mg/g and 478 mg/g. The adsorption process can be exceedingly fitted by Langmuir isotherm model and pseudo-second-order (PSO) kinetic model, which indicated that chemisorption played a dominant role. Additionally, the maximum selectivity coefficient reached 21.36 × 105 and 5605 for Hg(II) and Pb(II). Impressively, the residual contents of Hg(II) and Pb(II) were only 1.04 μg/L and 0.34 mg/L, which respectively reached the concentration standard of Hg(II) and Pb(II) in wastewater. Zr-DTDPA was easy to be regenerated, and the removal rate of Hg(II) had only decreased by 17.15% after ten consecutive cycles. The results of Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) suggested that the adsorption performance of Zr-DTDPA toward Hg(II)/Pb(II) was primarily determined by thiol/thio groups, and the adsorption mechanism was the interaction between sulfur atoms and Hg(II)/Pb(II) ions.