Synthesis silica nanotubes

Scheme 2. The synthesis route used in preparation of silica nanotube...

Figure 1.24 Silica nanotubes are formed by template synthesis using anisotropic materials (V307 H2Q, in this case.)...

Figure 1.26 Template synthesis using organic gels expands the versatility of the methodology, affording largely different silica nanotubes. (Reproduced from ref. 51, with permission.)...

Nakamura and Matsui [71] prepared silica nanotubes as a spin-off product of sol-gel synthesis wherein tetraethylorthosilicate (TEOS) was hydrolyzed in the presence of ammonia and D, L-tartaric acid. Ono et al. [72] showed that certain cholesterol derivatives can gelate tetraethyl orthosilicate (TEOS) to obtain tubular silica structures. Using cholesterol based gelators nanotubes of transition metal (Ti, V and Ta) oxides can also be prepared. The organogelators used in these processes are chiral diamino... 

The advantage of template synthesis is that organo or hydrogelator templates can direct the shape-controlled synthesis of oxide nanotubes. Recent reports describe the use of carbon nanofibers as a template for the shape-controlled synthesis of zirconia, alumina and silica nanotubes [78]. The shape of vapor grown carbon nanofiber... 

Synthesis of single silica nanotubes in the presence of citric acid J Mater Chem 11 465-468... 

Curved structures are not only limited to carbon and the dichalcogenides of Mo and W. Perhaps the most well-known example of a tube-like structure with diameters in the nm range is formed by the asbestos mineral (chrysotil) whose fibrous characteristics are determined by the tubular structure of the fused tetrahedral and octahedral layers. The synthesis of meso-porous silica with well-defined pores in the 2-20 nm range was reported by Beck and Kresge.6 The synthetic strategy involved the self-assembly of liquid crystalline templates. The pore size in zeolitic and other inorganic porous solids is varied by a suitable choice of the template. However, in contrast to the synthesis of porous compounds, the synthesis of nanotubes is somewhat more difficult. 

In case of silica nanotubes formed from TEOS and with [Pt(NH3)4](HC03)2 as templating salt, the synthesis products consist almost exclusively of nanotubes. As deduced from TEM-micrographs (Fig. 1), the portion of non-structured silica formed can be neglected. The lengths of the tubes vary between 50 nm and several pm and the iimer diameters range from 10 nm up to 300 nm with a maximum of frequency aroimd 50 nm. The silica walls are X-ray amorphous with a thickness of about 30-50 nm. 

FIGURE 24.2 Scanning electron micrographs. (A) The surface and cross section of a typical nanopore alumina template membrane prepared in the authors lab. Pores with monodisperse diameters that run like tunnels through the thickness of the membrane are obtained. (B) Silica nanotubes prepared by solgel template synthesis within the pores of a template like that shown in (A). After solgel synthesis of the nanotubes, the template was dissolved and the nanotubes were collected by filtration. (From Lee, S.B., Mitchell, D.T., Trofin, L., Li, N., Nevanen, T.K., Sbderlund, H., and Martin, C.R., Science, 296, 2198, 2002. With permission.)... 

Nanotubes of oxides of several transition metals, as well as of other metals, have been synthesized by employing different methodologies [24, 216-220]. Silica nanotubes were first produced as a spin-off product during the synthesis of spherical silica particles by the hydrolysis of tetraethylorthosilicate (TEOS) in a mixture of water, ammonia, ethanol and D,L-tartaric acid [216]. Since self-assembly reactions are not straightforward with respect to the desired product, particularly its morphology, templated reactions have been employed using carbon nanotubes to... 

Titania powders not only with particulate morphology in different nano-sizes but also with fibrous morphology were synthesized. Even synthesis of nanotubes was reported under hydrothermal conditions from NaOH solution [26-30] and also nanofibers from KOH solution [31,32]. Both nanotubes and nanofibers thus prepared were later clarified to be protonated titania (titanate) [33-36]. A comprehensive review was published on protonated titanate nanotubes [37]. Effects of remnant sodium content and annealing temperature were studied on the structure and photoactivity of the nanotubes [38]. Titanate nanowires and nanoribbons were also reportedly formed [39,40]. Nano-sized Ti02 powders were obtained by annealing of titanate nanotubes and nanofibers [41]. Mesoporous anatase-type Ti02 powder was prepared by selective dissolution of silica component in Ti-Si binary oxides [42]. 

H. S. Qian, M. Antonietti, and S. H. Yu, Hybrid Golden Fleece Unique approaches for synthesis of uniform carbon nanofibres and silica nanotubes embedded/confined with high population of noble metal nanoparticles and their catalytic performance. Adv. Eunct. Mater, 17, 637-643, 2007. 

Hierarchical silica nanotubes with radially oriented mesoporous channels perpendicular to central axis of tube Asymmetric No Costructure-directing agent used along with silica precursor. Chiral surfactant necessary. Modifying synthesis gel composition changes average inner diameter diameter of wall remains constant at 4nm. [13]... 

Figure 2.5 A typical method for the synthesis of nanosilica, without using catalysts or catalysts in the traditional sense. In this case, TEOS is condensed to form nanotubes on the surface of cylindrical micelles. After removal of the micelles and treatment of the TEOS nanotubes, silica nanotubes are formed. (Adopted from Ref [JO].)...

R. (2003) Novel silica nanotubes with a high aspect ratio-Synthesis and structural characterization. Advanced Materials, 15(18), 1538. 

Synthesis and characterization of silica nanotubes with radially oriented mesopores. Advanced Functional Materials, 18(4), 541-50. 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

There are several reports on the preparation of SiC nanowires in the literature but fewer on the preparation of SisKi nanowires.38-39 The methods employed for the synthesis of SiC nanowires have been varied. Since both SiC and Si3N, are products of the carbothermal reduction of SI02, it should be possible to establish conditions wherein one set of specific conditions favor one over the other. We have been able to prepare SijN nanowires,40 by reacting multiwalled carbon nanotubes produced by ferrocene pyrolysis with ammonia and silica gel at 1360... 

This paper describes a new synthesis route for the formation of silica and titania nanotubes filled with high amounts of Pt metal clusters up to 24.5 wt.%. To some extent, the mechanism of the synthesis has been explored. 

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