Synthesis of dithioglycol-functionalized periodic mesoporous organosilicas for the simultaneous removal of mercury ions and organic dyes from water

Abstract

A novel ethylene-bridged silsesquioxane was synthesized by a heat-induced thiol–ene addition reaction of 2-acetylthioethanethiol to 1,2-bis(triethoxysilyl)ethene. Upon deacetylation, the formed organosiloxane precursor bearing the dithiol moiety (–SCH₂CH₂SH) self-assembled into a sulfur-rich PMO material in the presence of the structure-directing agent under acidic conditions. The loading of sulfur-bound ligands in the PMO framework can be adjusted by co-condensing the precursor with tetraethyl orthosilicate. The structure of the resulting PMOs was characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, and nitrogen adsorption and desorption studies. The PMO prepared by using the thio-bis-silane precursor alone can be used for efficient and fast capture of mercury ions from water with a saturation Hg(II) uptake capacity of 1253 mg g⁻¹ and recycled several times with negligible loss in the adsorption efficiency. This material also showed a high adsorption selectivity for Hg(II) over other competitive metal ions like Zn²⁺, Pb²⁺, Fe³⁺, Cu²⁺ and Mn²⁺. Remarkably, the new adsorbent proved to be effective for simultaneously removing Hg(II) and rhodamine B (RhB) from simulated sewage with removal rates of over 97% and 91% for both at 100 ppm, respectively, indicating its potential for the practical application in environmental remediation.