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-, meso- and macroscopic features that emerge over five orders of magnitude in length (1) amorphous silica walls (characterized by a broad distribution of Si-Si spacings of ≈0.4 nm), (2) periodic hexagonal arrays of 1-d channels within each particle (≈3 nm channel diameter), (3) a feature in the gas adsorption measurements that indicates a second class of ≈10–50 nm diameter mesopores, (4) particles that are ≈ 150 to ≈500 nm in diameter, (5) interparticle pores that are on the order of the particle size, and (6) fractal domains larger than the particle size (>10 000nm). The microstructure can be controlled by the varying the initial silica content, the template size, the drying conditions, or the calcination conditions. The wet gel monoliths exhibit calculated densities as low as ≈0.02 g/cm³; the dried and calcined gels have bulk densities that range from 0.3 to 0.5 g/cm³. The materials possess large interparticle (1.1–2.2 cm³/g) and intraparticle (0.3–0.6 cm³/g) porosities.