Investigation of High-Pressure and Temperature Behavior of Surfactant-Containing Periodic Mesostructured Silicas Manik Mandal, † Vincenzo Stagno, ‡ Yingwei Fei, ‡ and Kai Landskron* ,† † Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015, United States ‡ Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015, United States * S Supporting Information ABSTRACT: Surfactant-containing periodic mesostructured silica materials, namely SBA-16 and FDU-12, were studied under pressures between 1 and 4 GPa and temperatures between 100 and 400 °C. At 4 GPa crystallization of coesite can be achieved already at 200 °C. The mild transition of amorphous to crystalline silica is believed to be accomplished by the inbuilt hydroxyl groups present in the starting material. At 2 GPa the crystallization of quartz is accomplished at a temperature of 400 °C. Both quartz and coesite are obtained in nanocrystalline form. S ince the discovery of surfactant-templated periodic mesostructured silica-based materials, 1 many efforts have been made to explore various applications of these materials such as use as adsorbent, as catalyst support, and for the immobilization of guest molecules. 2 The initial motivation for their synthesis came from the fact that such materials would be able to fill the gap between ordered microporous (<2 nm of pore size) and macroporous (>50 nm) materials and that they could be superior compared to zeolites for the cracking of petroleum because of their better mass transport properties. 1 However, soon it was realized that due to the amorphous nature of the pore walls of such silica materials, they do not suffice in terms of the hydrothermal stability that is required for such applications. Only very recently, the first siliceous periodic mesoporous materials having crystalline pore walls were synthesized. 3 Tsapatis, Ryoo, and Corma reported the first zeolitic alumosilicates with periodic mesopores. 4-6 Our own group reported recently the first periodic mesoporous SiO 2 materials with crystalline coesite and quartz pore walls. 3,7 The periodic mesoporous quartz and coesite materials were synthesized by a high-pressure nanocasting route. Hereby, the mesoporous silica is filled with a carbon support before the high-pressure synthesis to produce a periodic mesostructured silica/carbon composite. The carbon has the role to stabilize the mesostructure at high pressure. After the high-pressure synthesis, the carbon is removed by oxidation in air. Previously, the high pressure behavior of surfactant containing periodic mesostructured silica (PMS) materials was studied by Tolbert et al. 8-10 In their studies, it was shown that under high pressure PMS materials do not lose mesostructural order and the silica walls remain amorphous. However, no studies are available for surfactant-containing PMS materials under high pressure and higher temperature. Temperature plays a significant role when combined with pressure in the transformation of amorphous to crystalline phase. It was of interest to us to understand the P-T behavior of such PMS materials. In this regard, here, we want to communicate the high-pressure and temperature behavior of as- synthesized (surfactant-containing) PMS materials. Our main hypothesis was that the silanol groups of as-synthesized periodic mesostructured silica materials can facilitate crystal- lization (and as such phase transition) by the formation of mineralizing water during condensation. Because the silanol groups are homogeneously dispersed in the material, one would expect the same for the water. This could allow for the crystallization of the silica at milder pressure and temperature conditions compared to our previously studied periodic mesostructured silica/carbon composites. A periodic meso- structured silica/carbon composite does not have silanol groups because of the high temperature needed for carbonization of the carbon precursor infiltrated into the silicas. In addition, it was of interest how the surfactant can substitute carbon as a support to stabilize the mesostructure at high pressure. To test our hypothesis, we prepared SBA-16 silica in its as- synthesized form, i.e. with Pluronic F127 inside the pores. This material has a body-centered cubic structure (Im3m symmetry), in which the pores are connected with each other to form a 3-D network with a unit cell parameter of ∼16 nm. 11,12 This material was subjected to high pressure and temperature in piston-cylinder apparatuses (details can be found in the Received: October 1, 2012 Published: December 17, 2012 Communication pubs.acs.org/crystal © 2012 American Chemical Society 15 dx.doi.org/10.1021/cg3017535 | Cryst. Growth Des. 2013, 13, 15-18