Synthesis of dithiocarbamate-functionalized mesoporous silica-based materials: interest of one-step grafting

Abstract

The classical approach to prepare dithiocarbamate-functionalized silica involves a two-step procedure based on the reaction of carbon disulfide with a pre-formed amine modified silica sample. A novel approach is proposed here, involving the direct grafting of silica surfaces with the aid of a siloxydithiocarbamate precursor. Functionalization has been applied to three silica samples (a non-ordered silica gel and two ordered mesoporous solids with distinct pore size) to evidence possible effects of mesostructural order and/or pore size of the materials. The performance of the one-step method has been compared to the two-step one and qualitatively discussed in terms of derivatization efficiency regarding the integrity of dithiocarbamate organo-functional groups. Thanks to complementary physico-chemical techniques (N₂adsorption/desorption, solid-state NMR, XPS, XRD), the interest of direct grafting has been clearly demonstrated as it allows to access in one step dithiocarbamate-functionalized silicas free of residual amine groups. Moreover, the use of a base in the two-step procedure is likely to induce some degradation of the silica materials. The advantageous features of the direct grafting process were also discussed with respect to Hg(II) adsorption to these materials.