Influence of synthesis conditions on structural properties of MCM-48

The influence of synthesis variables such as time, cetyltrimethyl ammonium hydroxide (CTAOH) concentration, water content, pH, temperature and silica source on the structural properties of Si-MCM-48 is investigated. Time-dependent studies on the progressive development of MCM-48 have indicated that synthesis time is a crucial parameter, which influences the unit cell parameter. The formation of different mesophases was observed when the concentration of CTAOH and pH of the initial gel were varied. The Si-29 MASNMR results showed that the (Q(2) +W-3)/Q(4) ratio decreases with the increase in synthesis temperature. On account of increase in W units at high-temperature synthesis run, Si-MCM-48 with highly polymerized silica walls with lower surface area was obtained when compared with Si-MCM-48 prepared at lower temperature. Such effect was not significant when Si-MCM-48 was synthesized at the same temperature but using silica sol as a source in place of fumed silica. (c) 2008 Elsevier Ltd. All rights reserved.