Controlled design of ordered and disordered pore architectures, geometries, and dimensions of HOM-type mesostructured monoliths and their hydrothermal stabilities

Nanometer-sized silica monoliths with ordered and disordered mesostructures (HOM type) were fabricated by using a simple and fast yet reproducible strategy of an instant direct-templating method of a number of nonionic n-alkyloligo(ethylene oxide), namely, Brij-type (C_xEO_y), and Triton- and Tween-type surfactants that have different molecular sizes and characteristics. A key feature of this design strategy is that the real control of the type of surfactant phases enabled the development of various types of surfactant/silica mesophases in ordered and disordered structures and in shape- and size-controlled cage and cylindrical pore geometries. Control over the flexibility of the formed silica/surfactant mesophases was strongly influenced by the phase composition domains, the extent of hydrocarbon solubilization, and the surfactant molecular nature (corona/core features). These key findings were the main factors for the generation of the cylindrical and cagelike pore systems with these nonionic surfactants. The fabricated 1D, 2D, and 3D structures show evidence that our design strategy could fulfill the growing demand for targeted applications and avoid the difficulties in preparing cage and cylindrical pore structures. Particularly important here was the hydrothermal stability of HOM mesostructures under boiling water (on the order of days). The hydrothermal stability of 2D and 3D HOM mesostructures was not only due to the thicker pore walls and the degree of framework cross-linkage but also due to the large morphological particle sizes of HOM monoliths. However, the formation of the large grain sizes in local HOM silica matrixes led to higher control over the dissolution of their framework during hydrothermal treatment.