Synthesis and properties of polysiloxane xerogels containing tetrasulfide groups

Abstract

Polysiloxane xerogels with a functional group content of 1.1–1.9 mmol/g have been obtained by the hydrolytic condensation of the alkoxysilanes Si(OC2H5)4 and [(C2H5O)3Si(CH2)3S2]2 in the 2 : 1, 4 : 1, and 8 : 1 ratios. It has been demonstrated by 13C and 29Si CPMAS NMR spectroscopy that the xerogels have a polysiloxane framework with dipropyl tetrasulfide bridges, silanol groups, unhydrolyzed ethoxyl groups, and hydrogen-bonded water molecules on the surface. The xerogels have a porous structure. As the molar ratio of the reacting alkoxysilanes is increased in the above-specified range, the specific surface area of the xerogel increases (from 89 to 312 m2/kg) and the same is valid for other structure-adsorption characteristics. The synthesized polysiloxane xerogels readily sorb Hg2+ from acidified solutions. Their static sorption capacity can be as high as 1.5 g Hg per gram of sorbent. However, in the course of time, the 1 : 1 complexes forming on the xerogel surface undergo transformations accompanied by the release of mercury sulfide and/or Hg2+ reduction to mercury metal.