Synthesis and characterization of cubic thiol-functionalized periodic mesoporous organosilicas as effective mercury ion adsorbents

Well-ordered thiol-functionalized periodic mesoporous organosilicas (SH-PMO) with ethane bridging groups and cubic Pm3n symmetry for aqueous mercury removal have been synthesized via co-condensation of tetramethoxysilane (TMOS) with 1,2-bis(trimethoxysilyl)ethane (BTME) and 3-mercaptopropyltrimethoxysilane (MPTMS) in a highly acidic medium by using cetyltriethylammonium bromide (CTEABr) as the template. The SH-PMO materials thus obtained have been characterized by X-ray diffraction, nitrogen physical sorption, thermogravimetric analysis, and solid-state 29Si and 13C NMR spectroscopy. We have found that it is necessary to employ a controlled amount of BTME in order to preserve the cubic mesoporous structure in the resulting material when a high quantity of mercaptopropyl groups is incorporated. Direct evidence of the presence of chemically attached thiol and ethane moieties is provided by 29Si and 13C magic angle spinning (MAS) NMR spectroscopy. The maximum content of the attached thiol group (–SH) in the mesoporous framework is 2.40 mmol/g. The total access of the Hg2+ ions to every complexation site, i.e., an Hg/S ratio close to 1, in the SH-PMO materials is also demonstrated, and a maximum mercury loading capacity of 464 mg/g is achieved. This makes its effectiveness for mercury ion trapping comparable to that of the highest capacity materials previously reported. 13C cross-polarization magic angle spinning (CPMAS) NMR demonstrates that the 13C chemical shift of the carbon atom adjacent to the –SH group is highly sensitive to the Hg2+ ion binding.