Order hexagonal

The XRD pattern of Ti-MCM-41 synthesized by the modified synthesis method is presented in Fig. 1, Here we observe more than three distinguishable peaks, which can be indexed to dififermt (hkl) reflections of hexagonal structure. These are the (100), (110), (200), and (210) peaks [5]. The highest intensity of (100) peak su ts that this material has a highly ordered hexagonal structure. 

Figure 5. TEM images of nearly perfectly ordered hexagonal close-packed monolayers of (a) 1.5nm TCgBIP-Au and (b) 1.6nm TCgBIP-Au nanoparticles. Insets show FFT spots of each monolayer, (c) HRTEM image of 1.5 nm TCgBIP-Au nanoparticles. (Reprinted from Ref. [12], 2006, American Chemical Society.)...

Structural and textural characterisation of pure SBA-15 and hybrid GFP/SBA-15 Pure SBA-15 and GFP/SBA-15 hybrid were characterised by X-ray powder diffraction, HRTEM and volumetric analysis. Calcined SBA-15 (Fig. 1, curve A) show the typical XRD pattern of an ordered hexagonal network of mesopores with (10), (11) and (20) reflections. The presence of well resolved (11) and (20) peaks indicate that the calcined material used for the preparation of the hybrid materials have a long-range order. The hexagonal XRD pattern was still clearly observed in the hybrid material (GFP/SBA-15), as all the three main reflections were found (Fig. 1, curve B), indicating that the sonication and the GFP physical adsorption does not affect the framework integrity of the material. 

The reason why the hybrid micelles evolve from sphere to cylinder is not yet completely understood, but it results from the fact that when silica species are adsorbed onto the surface of the micelles, the average curvature of the micelles is decreasing [9], Polymerisation of silica species by condensation leads to precipitation of the ordered hexagonal mesoporous material. 

Figure 1.14 In a novel synthetic route made possible by the versatility of the sol-gel process, using spray-drying of the precursor sol affords spheres of mesoporous ORMOSIL whose surface consists of highly ordered hexagonal domains. (Reproduced from ref. 30, with permission.)... 

Note 3 By contrast with a smectic B mesophase, a crystal B mesophase has correlations of positional order (hexagonal) in three dimensions, i.e., correlations of position occur within and between layers. 

Fig 1A shows the XRD pattern of the calcined MCM-41 sample synthesized from C,6TMAB-silica and aluminosilicate systems with the Si/Al = oo(sample I) and 37(sample II) by using the delayed neutralization process. In both materials, there exist at least 4 sharp XRD peaks, which indicate well-ordered hexagonal structure of MCM-41. It means that the incorporation of aluminum into silica framework could not have significant effect on the arrangement of MCM-41 mesostructure. When the nitrogen adsorption-desorption isotherms... 

In previous literature, the type B hysteresis was ascribed to a lamellar-like structure that commonly observed in the pillared materials.[13,14] Here its existence in our mesoporous materials is associated with some internal defects in the channels. To further understand such hysteresis behavior, we compared the microtomed ultra-thin sections TEM micrographs of these two samples. In Fig. 2A, B, we show the typical parallel channels of MCM-41 and the well-ordered hexagonal mesoporous in pure silica sample(I). However in Fig. 2 C, D, one can obviously find the aluminosilicate(II) possessing the normal well-aligned MCM-41 nanochannels with extensive voids interspersed. The white void parts were attributed to the structural defects. These structural defects are not the lamellar form but the irregularly shaped defects. The size of the defects is not uniform and distributes between 5.0-30.0 nm. nanometers. Therefore, these aluminosilicate mesoporous materials were composed of structural defects-within-well-ordered hexagonal nanochannels matrix. 

The lamellar—.hexagonal transformation of Zr02 is likely to be initiated first by the removal of some of the surfactant species, followed by the curling of the surfactant bilayer in order to minimize the surface/interface energy as shown in Fig. 4(a) and (b).13,15 The curled bilayers transform to cylindrical rods to further minimize the surface energy as shown in Fig. 4(c) and the cylindrical rods assemble to give the ordered hexagonal structure shown in Fig. 4(d). In order to examine... 

We consider first the textural properties of a typical wormhole Ti-HMS in comparison to well ordered hexagonal Ti-MCM-41 and Ti-SBA-3 analogs prepared by S+I and S+XT electrostatic assembly pathways. Table 1 provides the surface areas and pore volumes that characterize the framework mesoporosity (Vfr) and textural porosity (Vtx). The total mesoporosity (Vtotai) is the sum of these two values. Each mesostructure contains 2 mole % Ti and exhibits a HK pore size near 2.8 nm. The values in parenthesis in the table are for the corresponding pure silicas. Note the very high ratio of textural to framework mesoporosity for the HMS molecular sieves (Vtx/Vfr = 1.06) compared to the hexagonal molecular sieves (Vtx/Vfr = 0.03). As will be shown below, the textural porosity of HMS catalysts can improve catalytic activity by facilitating substrate transport to the active sites in the mesostructure framework. 

Schematic representation of the Dho columnar phase with an ordered hexagonal arrangement of the columns of disc-shaped molecules with a regular period of the discs within the columns. The director is parallel to the columns and normal to the plane of the discs.

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