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The combination of small-angle X-ray scattering and qualitative porosimetry is applied to the puzzling phenomenon of overly large specific surface areas in some mesoporous silicas. Geometrical calculations, considering the relationship between structure, lattice parameter, and specific surface area, reveal the latter to be at least 1 order of magnitude smaller than experimental values obtained from sorption experiments, indicating the presence of micropores. Selective investigation of the mesopore system reveals that up to 63% of the specific surface area is due to microporosity. A relationship between the undirected creation of porosity and supramolecular templating is discussed.

Lyotropic phase morphologies of amphiphilic poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymers are studied using transmission electron microscopy, small-angle X-ray scattering, smallangle neutron scattering, and polarized optical microscopy. The PB-PEO block copolymers form type-1 lyotropic phases comprising disordered micellar solutions (L1), spheres arranged on a bcc lattice (I1), hexagonally packed cylinders (H1), and lamellae (LR). Increasing molecular weight destabilizes the I1 and H1 phases and lowers the degree of order. For high molecular weight block copolymers the increase in chain conformational entropy leads to the formation of the sponge phase (L3). The transmission electron micrographs allow a detailed analysis of packing defects and epitaxial relations of the block copolymer lyotropic phases.

This study reports the lyotropic phase behavior of two poly(ethylene oxide)-b-poly(butadiene) diblock copolymers and their cross-linking in the mesophase under retention of the mesoscopic order. The lyotropic phase behavior in water was characterized by polarized light microscopy and small-angle X-ray scattering (SAXS) in the concentration range from 0 to 100 wt % and in a temperature range between 20 and 100 °C. Depending on polymer composition and concentration micellar, hexagonal, lamellar, and cubic phases are found. Their ranges as well as pronounced coexisting phase regions were determined. Several of these mesophases were cross-linked via γ-irradiation to form mesostructured hydrogels. It is shown that the cross-linked polymer gel essentially maintains the parental lyotropic order, as proven by SAXS, polarized light microscopy, and transmission electron microscopy (TEM). TEM enables imaging of the polymer gel structure and thereby the visualization of the liquid-crystalline mesophase morphologies in themselves. The lyotropic mesophases as well as the lyotropic gels were used as templates for the synthesis of mesoporous silica, which is expected to give a negative solid copy of the ordered soft matter structure. The influence of the different templates on the silica structure formation is discussed.

A new way for preparation of microporous silica containing metal nanoparticles inside pores is described. Special amphiphilic block copolymers, polybutadiene-b-poly(ethylene oxides), are used in a first step as nanoreactors for the preparation of metal nanoparticles inside their micelle cores and then as templates where the micelles act as porogens. The final product after calcination of the polymer is silica where catalytically interesting nanoparticles with controlled size, shape, and distribution are located on the pore walls. Control for nanoparticle growth and location is provided by the reduction conditions.

The synthesis of mesoporous ceramic oxides with pore sizes between 2 and 50 nm is a recent trend in materials science. Most mesoporous silicas are prepared using ionic low molecular weight surfactants as structure-directing agents and sometimes inert oils as swelling additives.[1] This process, involving the precipitation of a surfactant-rich gel phase, is restricted to the synthesis of materials with pore sizes smaller than 8 nm, as the silica walls are too thin to support a larger-pore network. The use of bulk lyotropic liquid crystal phases of low molecular weight non-ionic surfactants [2±4] as templates partially solves the problem of mechanical stability. The wall thickness depends on the amount of inorganic precursor present in the preparation mixture, because the nanostructure is a result of directly casting the lyotropic bulk phase. However, surfactants are only available with restricted lengths of the hydrophobic chain, so that again the pore diameter is limited to approximately 4.5 nm.Casting the lyotropic phases of amphiphilic block copolymers (ABCs) is the method of choice for the synthesis of mechanically stable large-pore systems.[5] Here, the solidification of a siliceous precursor takes place in the aqueous domains of the microphase-separated medium, hence producing a monolithic cast of the original supramolecular aggregate. In addition, the ABC liquid crystal approach affords coherent porous coatings and macroscopic objects with continuous pore systems. [6] This approach was subsequently adopted by Chmelka et al., [7] who employed commercially available Pluronic-type triblock copolymers and obtained materials with pore diameters between 4.7 and 30 nm, and wall thicknesses between 3 and 5 nm. Their observations confirm the superiority of polymeric templates as porogens. [6] In this contribution, we present new non-ionic polymer templates with improved water-solubilities and a broader range of accessible molecular weights, which allows pore diameters of ceramic nanostructures to be extended beyond the known limits of this casting procedure. Templating the lyotropic aggregate structure of poly(butadiene-bethylene oxide) (PB-PEO) was studied over a wide range of block lengths, block length ratios and polymer concentration. The resulting silicas were characterized by transmission electron microscopy (TEM), porosimetry, and small-angle X-ray scattering (SAXS). The results demonstrate the great potential inherent in ABC templating as the method of choice for pore design in ceramic oxides. The polymers used in the experiments and their analytical data are summarized in Table 1. Table 1. Physical data of the amphiphilic block copolymers.[a] GPC measurement using CHCl 3 for the precursor PB (PB standard), the PEO block length is calculated from 1 H-NMR spectra (M n = number average molecular weight´10 3 kg/mol).[b] Repeat units.[c] Polydispersity, GPC in CHCl 3 , RI.The lyotropic phase behavior of the amphiphilic block copolymers in water was studied by polarized-light optical microscopy, as SAXS experime...

Mesoporous inorganic oxides with pore sizes between 2 nm and 50 nm are a welcome supplement to crystalline zeolites (pore size up to 1.2 nm). Mesoporous catalysts are required when one reactant is too big or too hydrophobic to penetrate the zeolite pores. Classical techniques for the synthesis of mesoporous silicas employ low molecular weight ionic amphiphiles as structure-directing additives and, if necessary, inert oils as swelling agents. [1±3] These processes, however, have some disadvantages. On one hand, structure control turns out to be difficult because the surfactant assembly undergoes phase transitions. [4] Furthermore, the inorganic nanostructure at pore sizes exceeding 5 nm is mechanically unstable and collapses, as the wall thicknesses are not sufficient to support the 3D inorganic network. On the other hand, the majority of the pores are either undefined with respect to size or not accessible from the outside, [5] which complicates functionalization of the material by incorporation of other elements or organic substituents.Another motive behind the search for new routes to mesoporous materials is that some practical applications require pores that are even larger than those available by precipitation techniques, i.e., pores of up to 100 nm are frequently demanded.A considerable improvement in the sol-gel synthesis of mesoporous silica was accomplished via a templating procedure involving liquid-crystalline (LC) phases of low molecular weight amphiphiles, where the problems described above could be solved. [6,7] Here, polyreaction of the watersoluble monomeric, inorganic precursor (e.g., silicic acid) is restricted to the hydrophilic domains of the LC mesophase, and condensation of the inorganic material results in a monolithic cast or blueprint of the LC structure. This procedure was further improved with respect to pore size and mechanical performance of the materials by use of amphiphilic block copolymers as templates. [8] In contrast to the systems described first, the products of the LC approach are not necessarily powders, but can be obtained as macroscopic monoliths or porous coatings. A more comprehensive discussion of the different pathways towards mesoporous materials and the abilities and advantages, including relevant references, is to be found elsewhere. [9] Here, we present a novel variation of the template route, which extends the existing methods to larger pore sizes. In this approach, polymer latex particles in the size range 20 nm < d < 400 nm, a narrow particle distribution, with different surface functionalities are employed as templates. These templates are readily available, inexpensive, and can be removed after inorganic network formation by simple calcination, i.e., burning off the organic matter at 350 C.A crucial point in this special templating process is the compatibility of the template with the generated silicic network. For classical non-ionic surfactant templates, this coupling is achieved via hydrogen bonds between the silanol groups of the silica and the oxyge...

The synthesis of inorganic oxides with controlled mesoporosity has developed since the beginning of the decade into one of the fastest moving research topics in modern materials chemistry. Whilst classical mesoporous silica synthesis employs low molecular weight organic amphiphiles as structure-directing agents in a sol±gel reaction mixture [1±4] to generate three-dimensional structures, the recent utilization of pre-assembled liquid crystalline surfactant [5] and polymer [6±8] templates has extended the synthetic possibilities. The use of high molecular weight block copolymers as templating agents has enabled the tailoring of pore size and framework architecture, extended the inorganic mesophase length scale and allowed the production of bulk inorganic monoliths as opposed to powders.[9±12] The larger pore sizes of these structures (2 to 50 nm) compared to microporous zeolitic materials (less than 1.2 nm) makes them particularly interesting for catalytic processes involving bulky substrates. The production of modified porous silicas containing well-dispersed noble metal nanoparticles and clusters distributed homogeneously throughout the pore channels has been a further challenge in the area of catalysis.[13±19] Conventional incorporation of metals involves the treatment of pre-formed solid supports, although in situ metal introduction techniques during support synthesis have also been reported. Heterogeneous metal distributions within the support, particle coalescence and decomposition, and catalyst leeching are some of the problems encountered during testing of materials prepared by these methods.Here we report on a specific method for direct inclusion of noble metal nanoparticles into a host framework which circumvents the need for post-synthesis functionalization of the support. A simple and convenient two-step reaction is presented in which prefabricated inorganic/organic hybrids are incorporated directly in a silica templating procedure to generate mesoporous silicas with high pore-connectivity and hosting a homogeneous distribution of noble metal particles. The approach combines the use of spherical functionalized polymer microgels [20] as nanosized exotemplates for the controlled growth of metal colloids [21] and as endotemplates during the casting of mesoporous sol±gel silicas.[22]A typical preparative procedure involves the initial synthesis of noble metal±polymer microgel hybrids. For this, poly(styrene sulfonate) microgels (70±90 nm in diameter) are loaded with noble metal ions and complexes. Reduction of the metal salts through the addition of sodium borohydride results in the formation and retention of metal particles within the microgel interior. These precursor hybrids are then added to a well-documented sol±gel recipe for the casting of mesoporous silica from ordered polystyreneblock-poly(ethylene oxide) mesophases utilizing tetramethoxysilane (TMOS) as the silica precursor.[8] The polymeric carrier mediates compatibility with the silicic network and ensures the positioning of the metal particl...