Block Copolymer-Templated Mesoporous Silica

Alternative triblock copolymers such as EO132PO50EO132 (Plmonic F-108), EO17PO59EO17 (P103), and EO27PO61EO27 (P104) were employed in time-resolved SAXS/X-ray diffraction studies of the formation of SBA-15 and SBA-16 in bulk sol-gel solutions [71-73]. The experimental data of the early stages of 

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R. Ryoo, C.H. Ko, M. Kruk, V. Antochshuk, and M. Jaroniec, Block-copolymer-templated Ordered Mesoporous Silica Array of Uniform Mesopores or Mesopore-Micropore Network J. Phys. Chem. B, 2000, 104, 11465-11471. 

C.Z. Yu, Y.H. Yu, L. Miao, and D.Y. Zhao, Highly Ordered Mesoporous Silica Structures Templated by Poly(butylene oxide) Segment Di- and Tri-block Copolymers. Microporous Mesoporous Mater., 2001, 44, 65-72. 

Sen T, Tiddy GJT, Casci JL, Anderson MW (2004) Synthesis and characterization of hierarchically ordered porous silica materials. Chem Mater 16 2044 Deng Y, Liu C, Yu T, Liu F, Zhang F, Wan Y, Zhang L, Wang C, Tu B, Webley PA, Wang H, Zhao D (2007) Facile synthesis of hierarchically porous carbons from dual colloidal crystal/block copolymer template approach. Chem Mater 19 3271 Luo Q, Li L, Yang B, Zhao D (2000) Three-dimensional ordered macroporous structures with mesoporous silica walls. Chem Lett 29 378... 

Block-Copolymer-Templated Synthesis of Ordered Silicas with Closed Mesopores... 

On the basis of the unit-cell size and pore diameter, one can estimate that the distance between adjacent spherical mesopores of the LP-FDU-12 sample calcined at 450°C was 6 nm. This distance is likely to correspond to the pore entrance length. Given that the pore entrance diameter (in the narrowest point) was 2 nm, the pore entrance length-to-diameter ratio was 3 1, and thus one can readily envision that the reduction of the pore entrance diameter through the thermal treatment would eventually lead to the closure of the entrance. The obtained ordered closed-pore silicas were white powders. It is clear that the block copolymer template was removed without the formation of the carbon residue, which was observed in an ordered closed-pore silica templated by PEO-PS copolymer. Pluronic (PEO-PPO-PEO) copolymers usually decompose at relatively low temperatures, so they may be inherently more convenient than PEO-PS copolymers, whose PS block has an appreciable tendency to carbonize. 

Ryoo R, Ko CH, Kruk M, Antochshuk V, Jaroniec M. Block-copolymer-templated ordered mesoporous silica array of uniform mesopores or mesopore-micropore network J Phys Chem B 2000 104 11465-71. 

Since this initial work there has been a plethora of literature on mesoporous molecular sieves. In addition to the silica and aluminosilicate frameworks similar mesoporous structures of metal oxides now include the oxides of Fe, Ti, V, Sb, Zr, Mn, W and others. Templates have been expanded to include nonionic, neutral surfactants and block copolymers. Pore sizes have broadened to the macroscopic size, in excess of 40 nm in diameter. A recent detailed review of the mesoporous molecular sieves is given in ref [73]. Vartuli and Degnan have reported a Mobil M41S mesoporous-based catalyst in commercial use, but to date the application has not been publicly identified.[74]. 

All major synthetic routes to mesoporous silica involve use of a template to achieve mesoporosity. The templates that are most commonly used are surfactants or block copolymers. Below we describe the synthetic strategies for mesoporous silica MCM-41 and SBA-15" , which are representative of this class of materials. 

The most successful example is the control of window size of caged mesoporous silica materials synthesized with block copolymer as templates. The pore-entrance diameter of SBA-16 increases as a function of synthesis or hydrothermal-treatment temperature. This is likely to be related to the known phenomenon of the decrease in hydrophilicity of PEO blocks as the temperature increases. In the mesostructure of the F127-silica composite, the cores of the (spherical) micelles are constituted by PPO blocks, whereas the micelle corona, which consists of PEO blocks, interacts with the silica framework. At lower temperature, PEO blocks are expected to favorably interact with hydrophilic silica species and thus to have a tendency to be intimately mixed with the silica framework. When the F127-silica composite is subjected to the treatment at higher temperatures,... 

Block copolymers are valuable supramolecular templates for the synthesis of ordered large-pore mesoporous silica and other metal oxides because of their simple templating ability, low-cost commercial availability, and biodegradability. 

Typical surfactant templates for mesoporous silica (e.g., ionic surfactants, nonionic block copolymers) can be used for the synthesis of PMOs. PMOs can have different framework compositions depended on the precursor used. 

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