Thiol-functionalization of metal-organic framework by a facile coordination-based postsynthetic strategy and enhanced removal of Hg²⁺ from water

The presence of coordinatively unsaturated metal centers in metal-organic frameworks (MOFs) provides an accessible way to selectively functionalize MOFs through coordination bonds. In this work, we describe thiol-functionalization of MOFs by choosing a well known three-dimensional (3D) Cu-based MOF, i.e. [Cu₃(BTC)₂(H₂O)₃]ₙ (HKUST-1, BTC=benzene-1,3,5-tricarboxylate), by a facile coordination-based postsynthetic strategy, and demonstrate their application for removal of heavy metal ion from water. A series of [Cu₃(BTC)₂]ₙ samples stoichiometrically decorated with thiol groups has been prepared through coordination bonding of coordinatively unsaturated metal centers in HKUST-1 with –SH group in dithioglycol. The obtained thiol-functionalized samples were characterized by powder X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy, infrared spectroscopy, and N₂ sorption–desorption isothermal. Significantly, the thiol-functionalized [Cu₃(BTC)₂]ₙ exhibited remarkably high adsorption affinity (Kd=4.73×10⁵mLg⁻¹) and high adsorption capacity (714.29mgg⁻¹) for Hg²⁺ adsorption from water, while the unfunctionalized HKUST-1 showed no adsorption of Hg²⁺ under the same condition.