The effect of water content on the preparation of mesoporous monoliths and films

Mesoporous films and monoliths with different thicknesses have been synthesized through evaporation-induced self-assembly in the presence of nonionic block copolymer templates. At the same reactant molar ratio, mesoporous thin films (similar to 300-500 nm in thickness) dip-coated on glass substrates have two-dimensional(2D) hexagonal mesostructures (p6m), while monoliths (similar to 1 mm in thickness) formed in containers have centered rectangular structures (cmm). The different evaporation time in the two cases leads to different condensation extent of the silica species and finally induces different mesostructures. Water also plays an important role in the evaporation process and the range of water ratio in starting components where monoliths with centered rectangular structures are favored has been studied. As-synthesized monoliths with cmm structure show a certain degree of thermal stability during calcination, but are not stable during hydrothermal treatment and undergo a structure evolution to p6m; however, the calcined monoliths with cmm structure are hydrothermally stable, possibly due to its thick silica walls. (c) 2004 Elsevier Inc. All rights reserved