The Synthesis of Hierarchical Porous Silica Materials

Recent interest is being devoted to the development of hierarchically ordered porous structures (ordered on multiple lengthscales with controlled multiscale porosity), because 

SBA-15 made at low temperatures contains micropores and mesopores. The micropore volume of SBA-15 could be systematically controlled by varying synthesis parameters (some were mentioned above) for example, the synthesis temperature and the TEOS/ 

An ordered mesoporous aluminosilicate with completely crystalline zeolite ZSM-5 wall structure has been synthesized with mesoporous carbon CMK-3 as template.11741 

Stucky11751 developed a procedure for the synthesis of sponge-like silica membranes with 3-D meso-macrostructures. The process utilizes multiphase media composed of a mesoscopically ordered block copolymer-silica phase that macroscopically separates from an electrolyte phase. The different characteristic lengthscales in hierarchically organized composite structures can be independently adjusted. 

Mixed solutions of cationic surfactants and nonionic poly(ethylene glycol) or block copolymers were employed for the synthesis of monolithic trimodal porous silica.[176] Lyotropic mixtures of block copolymers of different lengths with hydrophilic linear PEO chains were also applied to their nanocasting into bimodal micro-mesoporous silica to formulate the dependence of the mesopore sizes and the microporosity on the lengths or sizes of the hydrophobic and the hydrophilic blocks, but the mesostructures were worm-type in morphology and several hundred nanometers or more in size. 

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