Modified magnetic-metal organic framework as a green and efficient adsorbent for removal of heavy metals

Abstract

A novel adsorbent was prepared for fast and selective removal of heavy metal ions Hg(II), Cd(II) and Pb(II). The adsorbent was simply prepared by immobilizing tripeptide glutathione on the surface of a magnetic metal-organic framework (Fe3O4-ZrMOF). The microcrystalline structure of ZrMOF provided a high surface area in an ordered structure for deposition of large amounts of glutathione. All measurements were performed by electrothermal atomic absorption spectroscopy (EAAS). Adsorbent structure was studied by using X-ray diffraction (XRD), energy dispersive X-ray (EDX), and Fourier-transform infrared (FT-IR) spectroscopic methods, transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), Zeta potential measurement, and BET analysis. Computational modeling was used to obtain optimized structures for the adsorbent before and after binding to the heavy metals, which showed the most stable adduct for Hg attached to Fe3O4-ZrMOF@GSH (ΔGº = −1068.45 kJmol−1L−1). In removal procedure, the effective factors were discussed and optimized, such as the dosage of adsorbent, initial pH of solution, contact time, and initial concentration of metal ions. The maximum adsorption capacity (Qm) for Hg, Cd, and Pb was calculated to be 431, 393, and 397 (mg g−1), respectively. The proposed adsorbent was able to remove 95–99% of these ions from the solution, under optimum conditions in 20 min. Adsorption isotherm and kinetics for Hg(II), Cd(II), and Pb(II) on Fe3O4-ZrMOF@GSH were well described by Langmuir model and pseudo-second-order kinetics, respectively.