Surface Modification of Colloidal Silica by Sulfonation Route for Super-Hydrophilicity

Colloidal silica was chemically modified by a two-step method including an olefin sulfonation route as a preliminary study for super-hydrophilic applications. The hydrophobic vinyl groups were initially bonded chemically to the hydroxylated silica surface using the trichlorosilane coupling agents. The vinyl-terminated silica was then sulfonated by addition reaction with chlorosulfonic acid. The modified silica was investigated using DRIFT, TGA, element analysis, solid-state 29Si- and 13C CP-MAS NMR. The vinyl-terminated specimen showed a characteristic IR absorption band at 1600 cm−1 and a weight loss of approximately 3% starting at 350°C while the 29Si NMR peaks at 70.9 and 79.8 ppm and 13C NMR at 136 ppm and 129.8 ppm were assigned to a vinyl group bonded to silica. Elemental analysis of the sulfonated silica indicated the presence of sulfur, carbon and hydrogen. Thermal decomposition in range 150–600°C was due to the presence of sulfonated organics and unreacted vinyl groups while the new signals on 13C NMR, which were in the range 70–15 ppm, were assigned to sulfonated carbons.