Development of mesoporous structures of composite silica particles with various organic functional groups in the presence and absence of ammonia catalyst

Development of mesoporous structures of composite silica particles with various organic functional groups was investigated by using a two-step process, consisting of one-pot sol-gel process in the presence and absence of ammonium hydroxide and a selective dissolution process with an ethanol-water mixture. Five different organosilanes, including methyltrimethoxysilane (MTMS), 3-mercaptopropyltrimethoxysilane (MPTMS), phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), and 3-aminopropyltrimethoxysilane (APTMS) were employed. The mesoporous (organically modified silica) ORMOSIL particles were obtained even in the absence of ammonium hydroxide when the reaction mixture contained APTMS. The morphology of the particles, however, were different from those prepared with ammonia catalyst and the same organosilane mixtures, probably because the overall hydrolysis/condensation rates became slower. Co-existence of APTMS and VTMS was essential to prepare mesoporous particles from ternary organosilane mixtures. The work presented here demonstrates that organosilica particles with desired functionality and desired mesoporous structures can be obtained by selecting proper types of organosilane monomers and performing a facile and mild process either with or without ammonium hydroxide.