This work reports the synthesis, characterization, and potential environmental applications of periodic mesoporous organosilicas (PMOs) having high surface area and large pore size as well as featuring framework and channel multifunctional groups. PMOs under study were obtained by direct co-condensation of tetraethyl orthosilicate (TEOS) and other mixed organosilanes, namely, tris[3-(trimethoxysilyl)-propyl]isocyanurate (ICS), bis[3-(triethoxysilyl)propyl]tetrasulfide (4S), N-(3-triethoxysilylpropyl)4,5-dihydroimidazole (IM), and ureidopropyltrimethoxysilane (UR). Presence of the aforementioned ligands generated metal-chelating sites within the PMO framework and on their pore walls as well as contributed to the structural changes observed upon introduction of mixed ligands of particular properties and chemical composition. The synthesis conditions used permitted a fine-tuning of chemical and structural properties of PMOs as potential adsorbents for mercury(II) ions.