Acid-free synthesis of mesoporous silica using trihlock copolymer as template with the aid of salt and alcohol

Under acid-free conditions using tetraethyl orthosilicate (TEOS) as the silica source and triblock copolymer P123 as the template, mesoporous silica materials of either ultra-large mesoporous cellular foam (MCF) or two-dimensional (2D)-hexagonal p6mm pore arrangement were synthesized with the aid of salt and alcohol. The pore structure was varied with the concentrations of P123 and NaCl and the presence of alcohol in the synthesis solution. The porous network of the resulting MCF structure obtained in the aqueous solutions containing TEOS, P123, and NaCl was changed from closed window cell to open window cell when the concentrations of P123 and NaCl were increased. On the other hand, when a proper amount of ethanol was added as cosolvent, mesoporous silica with 2D-hexagonal pore arrangement similar to that of SBA-15 and MSU-H was obtained. The resultant materials possessed high surface area (626-896 m(2)/g), mesopores (6.3-6.6 nm in diameter) of reasonable pore size distribution (2.5-3.0 nm), and large porosity (0.91-1.13 cm(3)/g). On the basis of the Si-29 magic angle spinning NMR spectra, the mesoporous materials synthesized under acid-free conditions have better cross-linked silica framework than those prepared in an acidic environment such as SBA-15. The pore ordering was retained even after boiling the material in water for 72 h. Moreover, the pore size distribution was narrowed down to 1.0-1.7 nm, attributed to the re-organization of the silica framework during the hydrothermal treatment.