Fabrication and properties of silica monoliths with ultra large mesopores

Silica monoliths with ultra large mesopores of diameters over 25 nm and pore volumes in excess of 1.5 cm³ g^-1 were obtained by the hydrothermal treatment in aqueous ammonia solution of monolithic mesophases prepared by a direct templating of lyotropic liquid phase under high surfactant concentration. The process consists in the rearrangement of silica matrix structure from a template directed mesophase to that of a typical colloidal gel and is facilitated by template and silica extraction to the solution and basic conditions of the process. Silica of the monoliths hydrothermally treated in ammonia solution is somewhat less condensed than of untreated samples. The monoliths prepared using ethyl-silicate 40 as silica precursor posses slightly higher textural parameters than those synthesized using tetraethoxysilane. The size of pores depends on the concentration of ammonia in water solution and the time of treatment.