MONOLITHIC PERIODIC MESOPOROUS SILICA-GELS

We have synthesized monolithic, surfactant-templated particulate gels that have pore volumes and surface areas comparable to silica xerogels and aerogels. The gels have a complex microstructure with micro-, mes o- and macroscopic features that emerge over five orders of magnitude in length (1) amorphous silica walls (characterized by a broad distrib ution of Si-Si spacings of approximate to 0.4 nm), (2) periodic hexago nal arrays of 1-d channels within each particle (approximate to 3 nm c hannel diameter), (3) a feature in the gas adsorption measurements tha t indicates a second class of approximate to 10-50 nm diameter mesopor es, (4) particles that are approximate to 150 to approximate to 500 nm in diameter, (5) interparticle pores that are on the order of the par ticle size, and (6) fractal domains larger than the particle size (>10 000 nm). The microstructure can be controlled by the varying the init ial silica content, the template size, the drying conditions, or the c alcination conditions. The wet gel monoliths exhibit calculated densit ies as low as approximate to 0.02 g/cm(3); the dried and calcined gels have bulk densities that range from 0.3 to 0.5 g/cm(3). The materials possess large interparticle (1.1-2.2 cm(3)/g) and intraparticle (0.3- 0.6 cm(3)/g) porosities. (C) 1997 Elsevier Science B.V.