Organosilicas with chemically immobilized 3-aminopropyl and Methyl Red-containing sur-face groups were prepared by sol-gel condensation of tetraethyl orthosilicate and(3-aminopropyl)triethoxysilane in the presence of dye as part of the mixed micelles or dye-containing silane as silica source.The hexagonally arranged mesoporous structure of syn-thesized materials was confirmed by low-temperature nitrogen adsorption-desorption,x-ray diffraction,and TEM studies.Chemical composition of MCM-41-type organosilicas was established by FT-IR spectroscopy and chemical analysis of surface layer.Sorption of Methyl Red by organosilicas was studied from diluted phosphate buffer solutions in dependence of medium pH,duration of contact,and equilibrium concentration of dye.It was found that effective removal of Methyl Red takes place at pH values within a range of 2.5-5.Kinetic curves of Methyl Red sorption on organosilicas were analyzed by the Lagergren,Ho-McKey,and Weber-Morris kinetic models.It was found that the pseudo-second-order model fits the kinetics of Methyl Red sorption on all synthesized materials and the intraparticle diffu-sion is not the only one mechanism controlling the rate of Methyl Red sorptive removal.The parameters of equilibrium sorption of Methyl Red on organosilicas of MCM-41 type were cal-culated using Langmuir,Freundlich,Redlich-Peterson,and Brunauer-Emmett-Teller models.Sorption of acid dyes with geometry similar or substantially different from Methyl Red on mesoporous silicas was studied from single and binary component mixtures in aqueous so-lutions with pH 4.8 and 5.5.It was found that selective sorption process is highly dependent on the structural characteristics and protolytic state of silica surface as well as acid dye.