Effect of inorganic salt addition during synthesis on pore structure and hydrothermal stability of mesoporous silica

Mesoporous materials were synthesized without and with the addition of salt s such as NaCl and NH4Cl and were characterized using different analytical techniques. The hydrothermal stability was investigated by water treating t hese mesoporous materials at 373 K for various times in closed bottles. Add ition of salts resulted in transformation of mesophase, which depends stron gly on the kinds and concentration of salts added. When added with NaCl, th e mesoporous materials experienced phase transformations in the sequence MC M-41 --> KIT-1 --> MCM-41 --> KIT-1 --> amorphous phase as the NaCl/surfact ant molar ratio increased. However, addition of NH4Cl led to the formation of disordered mesoporous materials. Mesoporous materials with high hydrothe rmal stability could be prepared by addition of a suitable amount of salts and the materials maintained their initial mesoporous structure after hydro thermal treatment at 373 K for at least 120 h in closed bottles. For mesopo rous materials without salt addition or with addition of salts with unsuita ble molar ratios, mesopores would collapse and the pore size distribution b ecame very large after hydrothermal treatment. (C) 2001 Elsevier Science B. V. All rights reserved.