Amorphous silicas have been functionalized by two different methods. In the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the silica surface to give the chlorinated silica Cl-Sil. In a second reaction, multifunctionalized N,S donor compounds were incorporated to obtain the functionalized silicas, which are denoted as L-Sil-Het (where L=mercaptothiazoline, mercaptopyridine or mercaptobenzothiazole). In the homogeneous route, the functionalization was achieved through a one-step reaction between the silica and an organic ligand containing the chelating functions; this gave the modified silicas denoted as L-Sil-Hom. The functionalized silicas were characterized by elemental analysis, IR spectroscopy and thermogravimetry. These materials were employed as adsorbents for mercury cations from aqueous and acetone solutions at room temperature. The results indicate that, in all cases, mercury adsorption was higher in the modified silicas prepared by the homogeneous method. Figure.