Mesostructured carbon

S.S. Kim and T.J. Pinnavaia, A Low Cost Route to Hexagonal Mesostructured Carbon Molecular Sieves. Chem. Commun., 2001, 2418-2419. 

First preliminary variants of DDM were applied in the full-profile X-ray diffraction structure analysis of a series of new silica mesoporous materials and ordered nanopipe mesostructured carbons. DDM allowed stable back-ground-independent full-profile refinement of the structure parameters of these advanced nanomaterials, a result that was unattainable by any other method. To date, DDM has been applied to many various mesoporous and mesostructured substances. The structural parameters of a series of face-centred cubic (Fm3m), body-centred cubic Im3m), and two-dimensional hexagonal (pGmm) mesoporous silicates were determined by DDM from synchrotron XRD. A comprehensive structural analysis of mesoporous silicates SBA-16 (cage-type cubic Irriim), their carbon replicas, and silica/carbon composites was performed by applying DDM. The structure of MCM-48 mesoporous silicate materials was analysed in detail by DDM from different laboratory and synchrotron XRD data. The pore wall thickness of both as-made and... 

The morphology of ordered mesostructured carbons is another important factor with respect to their practical applications. Various macroscopic morphologies are required, for example, films (in sensor, separation and optical applications), uniformly sized spheres (in chromatography) or transparent monoliths. Using suitable synthesis strategies, it is possible to control the external shape of the templated mesoporous carbon materials to generate powders, films and membranes, spheres, hollow spheres, rods, fibres, nanowires, nanotubes and monoliths. 

Kim CH, Lee DK, Pinnavaia TJ. Graphitic mesostructured carbon prepared from aromatic precursors. Langmuir 2004 20 5157-9. 

For many oxides, including mixed metal oxides, of catalytic interest, preparing a high-surface-area solid with thermally stable porous structure was extremely difficult until recentiy. The hard templating procedure provides a systematic solution to this problem. Nanocasting that makes use of a mesostructured solid template is a special case. Both mesostructured silica and mesostructured carbon have been demonstrated so fer as hard templates. Rather precise replicas of these nanomolds have been obtained for a variety of oxide-type perovskites. Unprecedented specific surface areas in the 150-200 m /g were reached. 

Fig. 16.6 Schematic illustration of the different steps applied to prepare mesostructured carbon...

Scheme 1. The various steps in the synthesis of gold-containing mesostructured carbons [adapted from ref 5],...

The catalyst layer is composed of multiple components, primarily Nafion ion-omer and carbon-supported catalyst particles. The composition governs the macro- and mesostructures of the CL, which in turn have a significant influence on the effective properties of the CL and consequently the overall fuel cell performance. There is a trade-off between ionomer and catalyst loadings for optimum performance. For example, increased Nafion ionomer confenf can improve proton conduction, but the porous channels for reactanf gas fransfer and water removal are reduced. On the other hand, increased Pt loading can enhance the electrochemical reaction rate, and also increase the catalyst layer thickness. 

Figure 2. Plot of interlayer distance versus carbon number (exclusive of head groups) of surfactant chain for mesostructured MoS-L materials.

Three novel mesostructured tungsten sulfides, designated as MTS-W, MTS-M and MTS-C, were prepared by the condensation reaction of (NH4)2WS4 in the presence of octadecyltrimethylammonium bromide (OTAB) under refluxing conditions in water, methanol and carbon tetrachloride at 373 K, 338 K and 350 K, respectively. The three as-synthesized metal sulfides all have a layered structure with the d-spacing of 31 A, 30 A or 37 A. Partial removal of the organic surfactants from the layer galleries can be achieved by solvent extraction. 

In addition to mesostructured metal oxide molecular sieves prepared through supramolecular assembly pathways, clays, carbon molecular sieves, porous polymers, sol-gel and imprinted materials, as well as self-assembled organic and other zeolite-like materials, have captured the attention of materials researchers around the globe. Clays, zeolites and sol-gel materials are still very popular because of their extensive and expanding applications in catalysis and separation science. Novel carbons and polymers of ordered porous structures have been synthesized. There are almost unlimited opportunities in the synthesis of new organic materials of desired structural and surface properties via self-assembly or imprinting procedures. 

In order to elucidate the importance of the role of in situ formed carbon in the formation of well-organized, highly crystalline mesoporous transition metal oxides, as-synthesized Ti02 was directly calcined under air to 700°C while keeping all other conditions the same as for the CASH method. As expected, the BET surface area of the resulting material was only 0.2 m2 g-1 and no porous structure could be detected by TEM imaging. This implies that the mesostructure completely collapsed. The crystallite size of this sample, heat treated to 700°C in air is 31.5 nm (calculated... 

CMK-n1 carbon mesostructured by Korea Advanced Institute of Science and Technology (family of mesoporous carbon materials)... 

Vidano and Fischbach, 1978). Moreover, the relative intensities of the Raman bands at 1590 and 1350 cm-1 indicate that the graphite-like domains were roughly 60 A in diameter (Tuinstra and Koenig, 1970). This size of the carbon aggregates confirmed the hypothesis of occluded surfactant molecules in the mesostructured phosphate. 

MSU-G mesostructures are obtained through the S°I° assembly of silica in the presence of a RNH(CH2)2NH2 gemini amine surfactant in which the R group contains between 8 and 22 carbon... 

In a detailed study, mesostructured zirconia has been prepared by using various amphiphilic surfactants with different headgroups (anionic and nonionic) and different tail lengths (1-18 carbons) as templates. Removal of snrfactants leads to the loss of structural order and a decrease ofthe siuface area. However, the presence of phosphates and snlfates in the walls may improve the stability. 

Carbon (C)-aerogels have been investigated for one decade as a promising material for electrochemical applications in supercapacitors, fuel cells and waste water treatment [1,2], C-aerogels are nanoporous, electrically conducting and monolithic materials that provide the unique possibility to tailor the carbon properties on a molecular scale. The surface area and the degree of microporosity can be adjusted almost independently of the overall porosity for which mainly meso- and macropores are responsible. Whereas the mesostructure is determined by the stoichiometry of the reactants in the precursor solution, the pyrolysis conditions control the micropore structure of the material [3,4]. High pyrolysis temperatures will increase the electrical conduchvity [5], an important property for many electrochemical applications. 

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