Colloidal suspensions of mercapto-functionalized nanosized mesoporous silica

Different synthesis routes yielding colloidal suspensions of mercapto-functionalized mesoporous silica particles of nanosize dimensions between 50 and 200 nm are presented. Mercaptopropylsilane was introduced into the silica networks through co-condensation. The mercapto group induces significant changes in the morphology, transforming highly ordered hexagonal particles either into filaments or small agglomerates with nanoscale domains. The addition of triethanolamine base instead of NaOH leads to the formation of colloidal suspensions of spherical particles having a diameter of ca. 100 nm. The grafting of the thiol group into the colloidal mesoporous silica was characterized with sorption measurements, thermal analysis, 29Si-MAS-NMR, and Raman spectroscopy. Oxidative treatment of the thiol groups anchored to the internal surface of the nanoscale mesoporous particles results in the formation of grafted sulfonic acid residues. The latter reaction proceeds to complete conversion as demonstrated with FT Raman spectroscopy.