Synthesis of stable S- functionalized metal-organic framework using MoS42- and its application for selective and efficient removal of toxic heavy metal ions in wastewater treatment

Abstract

In this work, a novel sulfur functionalized porous metal-organic framework based on Cu(II) and benzene-1,3,5- tricarboxylic acid (Cu-BTC) was synthesized. Tetrathiomolybdate (MoS42−), inorganic sulfur-containing transition metal compound, was immobilized for the first time on the MOF for selective removal of heavy metal ions of Hg2+, Pb2+, Ni2+, Cd2+, and Zn2+ from wastewaters. The MoS4-MOF sorbent shows high potential with excellent selectivity for the sorption of a variety of soft Lewis acid heavy metal ions by M–S bonding interactions. The crystal phase and morphology of the as-prepared MoS4-MOF were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron spectroscopy, thermal gravimetric and Brunauer-Emmett-Teller (BET) analysis. Sorption isotherm corresponds with the Langmuir model and shows good agreement with monolayer coverage of the heavy metal ions on the MoS4-MOF surface through a chemical sorption process. The sorption kinetic curves for metal ions fitted well with the pseudo-second-order model. The MoS4-MOF displays selectivity order of Hg2+ > Cd2+ ∼ Pb2+ > Zn2+ > Ni2+. The enormous sorption capacities of 714.3–1000.0 mg g-1 and very high distribution coefficients (Kd) of 6.0 × 103-5.5 × 104 mL g-1 (C0 = 100 mg L-1) place the porous MoS4-MOF as a promising sorbent for the removal of polluted water. The synthesized MoS4-MOF showed good chemical stability and recyclability.The first immobilization of (NH4)2MoS4 on Cu-BTC MOFs which enhances the stability of S-functionalized MOFs, simplifies its storage problems & enhanced maximum sorption capacities.