Nanoparticles of microporous materials

The hydrolysis and condensation of tetraethoxy silane in the presence of st ructure directing agents, such as the tetraalkylammonium cations, results i n the formation of microporous siliceous particles with average sizes in th e range 2 to 5 nm, the size being a function of the hydrolysis conditions a nd the composition of the mixture. Increased dilution favors larger particl es while increased pH results in smaller particles. The option of isomorpho us substitution of silicon for either alumina or titania is also shown to r esult in nano-sized particles were the substituted metals exist in the tetr ahedral coordination.