Short synthesis of ordered silicas with very large mesopores

Abstract

SBA-15 silicas with cylindrical mesopores of diameter from 10 to ∼30 nm were synthesized within hours (2.5–7.5 hours) instead of one or more days required in hitherto reported syntheses of large-pore SBA-15 with (100) interplanar spacing above 13 nm. The synthesis was carried out using Pluronic P123 surfactant, 1,3,5-triisopropylbenzene swelling agent and silica hydrolysis/condensation catalyst, NH₄F, under low-temperature initial synthesis conditions (12–17 °C) similar to those used in our earlier report on the synthesis of SBA-15 with a wide range of pore diameters (10–26 nm). Herein, it is shown that the low temperature step at which the ordered material forms can be shortened to one hour and the mesoporous material can be recovered at this stage. However, the attainment of a larger pore size and/or better structural ordering requires a hydrothermal treatment, which can be as short as 1–6 hours, if appropriately high temperature (150–170 °C) is selected. Additionally, improved synthesis conditions are reported for ultra-large-pore SBA-15 with (100) interplanar spacing of 25–30 nm. Standard SBA-15 synthesis without a swelling agent was also streamlined. Moreover, the synthesis of large-pore FDU-12 silica with face-centered cubic structure of spherical mesopores using Pluronic F127 surfactant and 1,3,5-trimethylbenzene swelling agent can be shortened to ∼9 hours. The streamlined synthesis procedures can be followed by surfactant removal via calcination with high ramping rate and short dwell time. The synthesis approach based on a short self-assembly step and short high-temperature hydrothermal treatment provides a convenient way to produce large-pore ordered mesoporous silicas suitable for numerous applications.