Mesoporous-macroporous architectures

Another family of synthesis strategies uses small solid particles as additional templates to micellar templating to create hierarchical pore structures. These small solid particles as additional templates consist of colloidal crystals, biomaterials, macroporous polymers, salts, and ice crystals. This combination of surfactant and small solid particles offers an efficient way for the generation of ordered and interconnected mesoporous-macroporous architectures, small solid particles creating macropores and surfactant micelles creating mesopores. 

Li F, Wang ZY, Stein A (2007) Shaping mesoporous silica nanoparticles by disassembly of hierarchically porous structures. Angew Chem Int Ed 46 1885 Lebeau B, Fowler CE, Mann S, Farcet C, Charleux B, Sanchez C (2000) Synthesis of hierarchically ordered dye-functionalised mesoporous silica with macroporous architecture by dual templating. J Mater Chem 10 2105... 

Xue C, Tu B, Zhao D (2008) Evaporation-induced coating and self-assembly of ordered mesoporous carbon-sihca composite monoliths with macroporous architecture on polyurethane foams. Adv Funct Mater 18 3914-3921... 

One of new trends today in sol-gel chemistry is the use of supercritical carbon dioxide as a solvent during sol-gel polymerization or for extraction of the resulting product. The initial aUcoxysilane is mixed with anhydrous 99% HCO2H and sol-gel polymerization of the mixture is then carried out in supercritical CO2 in an autoclave (40°C, 41.4-55.2 MPa). Gel formation proceeds over 12h and then CO2 is slowly removed (8 h). This procedure favors for the formation of highly porous monolithic composites with the mesopore and macropore architectures. Components that sharply enhance the ability of Si02 to adsorb water may also be introduced at the stage of formation. For example, selective water adsorbents, such as CaCl2 and LiBr, bind up to 53 wt% of H20. " " ... 

Designing a specific material architecture. 3D hierarchical carbon [79,80], 3D aperiodic [79,81,82] or highly-ordered hierarchical carbons are representative samples with multimodal pore structure to optimize the performance of the capacitors. The micropore, mesopore and macropore structure of such three-dimensional hierarchical carbons are generally perfectly interconnected. 

The field of mesoporous materials has developed rapidly since the first reports on these materials in 1992, as these last examples show. The trend is to utilize inexpensive, multifunctional micelle- or aggregate-forming surfactants or templates which may adopt many different liquid crystal-like configurations in aqueous solution. Formation of a silicate structure with well-defined pore dimensions and connectivity may then be accomplished by the appropriate choice of the synthetic conditions. Additional microporous and macroporosity may be incorporated by using macroporous host materials, as in the case of Stucky of the work by and coworkers, who created mesophases with unprecedented architecture.[47]... 

Orchard, 1995). Such a modification of aggregate architecture results in a complex and discontinuous pattern in pore spaces of various sizes and shapes (Haider and Guggenberger, 2005) and would thus greatly influence the physical, chemical, and biological properties of soils. The dimension of pore sizes ranges from <2 nm (micropores) to 2 to 50 nm (mesopores) to >50 nm (macropores). The pore neck... 

Zeolites are widely used as acid catalysts, especially in the petrochemical industry. Zeolites have several attractive properties such as high surface area, adjustable pore size, hydrophilicity, acidity, and high thermal and chemical stability. In order to fully benefit from the unique sorption and shape-selectivity effects in zeolite micropores in absence of diffusion limitation, the diffusion path length inside the zeolite particle should be very short, such as, e.g., in zeolite nanocrystals. An advantageous pore architecture for catalytic conversion consists of short micropores connected by meso- or macropore network [1]. Reported mesoporous materials obtained from zeolite precursor units as building blocks present a better thermal and hydrothermal stability but also a higher acidity when compared with amorphous mesoporous analogues [2-6]. Alternative approaches to introduce microporosity in walls of mesoporous materials are zeolitization of the walls under hydrothermal conditions and zeolite synthesis in the presence of carbon nanoparticles as templates to create mesopores inside the zeolite bodies [7,8]. 

One goal of nanoscience in general and in the field of nanoporous materials " in particular is to achieve control over the architecture of matter on the nanoscale (1-100 nm). Because porous materials are divided into the subgroups microporous (voids smaller than 2 nm). mesoporous (voids between 2-50 nm). and macroporous (voids larger than 50 nm), it becomes obvious that these materials are raw models for nanostructured matter. Three... 

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