Hexagonal pores

XRD and TEM analysis on template-removed MSU-Ge-2 evidenced the presence of a well-defined, long-range periodicity of the hexagonal pore structure (Fig. 3). The low-angle powder XRD pattern of as-prepared and template-removed mesoporous MSU-Ge-2 indicates a pore periodicity of 4.8 and 4.0 nm, respectively. The pore-to-pore distance (4.0 nm) determined from XRD... 

FIGURE 7.21 (a) Possible preparative route for the formation of MCM-41 by liquid crystal templating (b) computer graphic of ethane and methane molecules inside one of the hexagonal pores of MCM-41. See colour insert following page 356. (Courtesy of Vladimir Gusev, Romania.)... 

FIGURE 7.21(b) Computer graphic of ethane and methane molecules inside one of the hexagonal pores of MCM-41. 

Polysilane-based nanostructured composites were synthesized by the inclusion of poly(di-w-hexylsilane) (Mw = 53,600) into mesoporous, Si-OH-rich silica with a pore size of 2.8 nm.81 Two PL bands are observed for the composite. A narrow band at 371 nm, assigned to a PDHS film on a quartz substrate is blue shifted by 20 nm, a shift attributed to the polymer being incorporated into the pores.82 The size of the monomeric unit of the PDHS is about 1.6 nm, so only one polymer chain can be incorporated into a mesopore with a diameter of 2.8 nm. The narrow PL band at 350 nm is due to the reduction of the intermolecular interactions between polymer chains. This narrow PL band at 350 nm is assigned to the excited state of the linear polymer chain.81 Also, a new broad band of visible fluorescence at 410 nm appeared, which is assigned to localized states induced by conformational changes of the polymer chains caused by its interaction with the silanol (Si-OH) covered pore surface. Visible luminescence in nanosize PDHS is observed only when the polymer was incorporated in hexagonal pores of 2.8 nm and is not seen for the polymer incorporated into cubic pores of 2.8 nm diameter or hexagonal pores of 5.8 nm diameter. 

Jessensky, O., Muller, F., and Gosele, U., Self-organized formation of hexagonal pore arrays in anodic alumina. Appl. Phys. Lett. 72,1173 (1998). 

HRTEM images (Figure 2) reveal that calcined 3D SBA-15 samples (without TMB) at 403 K have ordered hexagonal pore arrangements and the center-to-center distance of adjacent channels is 10.2 nm, in accordance with XRD results. Figure 2a clearly shows some mesotunnels with the size of 2 3 nm randomly distributed on the silica wall of 3D SBA-15. After addition of TMB, HRTEM images also show that the size of the tunnels... 

Figure 8 Configurations of Ar atoms adsorbed at 77 K in a hexagonal pore having a largest dimension of 10 nm at (a) P = 0.1 Po, (b) P = P = 0.22 Po, (c) P = 0.44 Po. Black spheres correspond to the hydrogen atoms which delimitate the pore surface, the white spheres are argon atoms.

The t wo-stage porous an odization w as ma de f rom th e f ront s ide of the samples. At the first stage, the 5 pm thick porous anodic alumina layer with ordered matrix of hexagonal pores was formed due to the self-organization process. The anodization time was about 5 min. 

Ag(PhTpCF3)(C2H4)j obtained from the lithium poly(pyrazolyl)-borate salt, AgOTf and ethylene, has a planar three-coordinate silver center whereas the ethylene-free [Ag(PhTpCF3)] adopts a helical structure with a hexagonal pore.199... 

HRSTEM High resolution scanning transmission electron microscopy HRTEM High resolution transmission electron microscopy MCM-41 Silica with hexagonal pore structure (Mobil recipe)... 

SBA-15 Silica with hexagonal pore structure (Santa Barbara recipe)... 

Figs 4a and 4b illustrate the Transmission electron microscopy images of the composite silicate-carbon materials. These figures display the hexagonal pore symmetry and a uniform pore diameter of about 3.5 nm. The corresponding Energy Dispersive Spectroscopy (EDS) of the silicate-carbon microanalysis indicates an overall composition of 61 wt. % C, 23 wt. % of O and 16 wt. % Si. 

The XRD patterns of the calcined samples are shown in Figure 1. In the small angle range (SAXRD) it can be observed that (i) sample A shows three broad dilfraction peaks, indicating the formation of a mesophase with a hexagonal pore arrangement (ii) sample D shows diffraction peaks, which can be deconvoluted into three peaks also attributable to the hexagonal pore array ... 

Mesoporous carbon was obtained by sucrose carbonization in the pores of MCM-4 silica spheres with subsequently dissolution of the silica. The carbon was impregnated with the ZSM-5 synthesis gel and the crystallization was carried out under hydrothermal conditions. After burning off the carbon, ZSM-5 with a bimodal mesopore system showing mean diameters around 2 and 30 nm was obtained. Nevertheless, the hexagonal pore array of the MCM-41 was not reproduced in the ZSM-5. 

In this paper we will describe the preparation and properties of ZSM-5 synthesized by sequential nano-casting using mesoporous silica spheres with a hexagonal pore arrangement analogous to MCM-41 as starting material. 

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