Nanoporous alumina

Xi D, Pei Q (2007) In situ preparation of free-standing nanoporous alumina template for polybithiophene nanotube arrays with a concourse base. Nanotechnology 18 095602... 

An alumina matrix may be prepared with high pore density (more than 60 %) and pore diameters ranging from 5 to 250 nm. Ruiz-Hitzky et al. [214] immobilized GOD in nanoporous alumina membranes with regular hexagonal arrays of highly ordered cylindrical pores aligned perpendicularly to the membrane surface. GOD was anchored in the membrane by the highly hydrophilic chitosan biopolymer. Full activity was maintained for at least 50 hours. 

Metal oxide nanotubes have been synthesized by a diverse variety of fabrication routes. For example titania nanotubes, and nanotube arrays, have been produced by deposition into a nanoporous alumina template [48-51], sol-gel transcription using organo-gelators as templates [52,53], seeded growth [54], hydrothermal processes [55-57] and anodic oxidation [58-65]. 

It should be mentioned that alternative possibilities to prepare similar membranes include the use of a porous alumina membrane as matrix, with the titania nanotubes grown in the channels. Nanoporous alumina membranes are commercial products, also synthesized by anodic oxidation. The commercial Whatman Corporation anodic membrane has holes of about 20-nm diameter at the top of the membrane and about 200-nm diameter at the bottom of membrane. Within these pores Ti02 nanotubes fabricated by template synthesis and water vapour hydrolysis could be grown, but non-uniform membrane characteristics are obtained due to the non-uniform pores of the commercial alumina... 

Nanoporous materials are of great interest for example for their photoluminescent properties (silicon) or possible use as templates (alumina). The types of synthesis of these materials are numerous and the etching/ anodization influences the results [27 - 29]. A detailed studied of Cherenkov radiation in nanoporous alumina membranes has been done which explains the existence of low energy peaks around 7-8 eV [30] (Figure 9 left). Whereas for a cylindrical hole in alumina the simulation does not show a peak, a cylindrical shell of alumina does. The Cherenkov radiation is confined in the shell, as in a wave guide, and a peak appears. If an effective... 

Figure 9. Left experimental spectrum obtained in the center of a hole in porous alumina. Right three LELS relativistic simulations. (Reprinted from Surface Science 532-535 Zabala N, Rivacoba, Garcia de Abajo F.J. and Pattantyus A., Cherenkov radiation effects in EELS for nanoporous alumina membranes, 461-467 Copyright (2003) with permission from Elsevier)...

Yang and coworkers also used a surface imprinting approach to prepare nanotube membranes that exhibit selectivity for the molecule estrone.77 In this study, the silica nanotubes with pore diameters of 100 nm were synthesized within the cylindrical pores of nanopore alumina membranes. A covalent assembly approach was used to prepare the imprint.77 Zhang and coworkers have also recently shown how silica nanotubes can be used as an imprinting scaffold.78 In this example, trinitrotoluene (TNT)... 

A typical embodiment for the porous layer technology is described in several patents and patent applications, e.g., a US patent application in 2006. This patent application describes a method for the preparation of silicon dioxide dispersions wherein the surface of the silicon dioxide is modified by treatment with the reaction products of a compound of trivalent aluminum with amino-organo-silane. The invention relates to recording sheets for inkjet printing having such a dispersion incorporated in the porous inkreceiving layer. Another US patent describes the preparation of nanoporous alumina oxide or hydroxide which contains at least one element of the rare earth metal series with atomic numbers 57 to 71. 

Figure 4. AFM image of Ar -milled (9 min) hexagonally ordered nanoporous alumina. Reprinted with permission from ref 40. Copyright 2002 American Chemical Society.

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.)... 

NANOPOROUS ALUMINA PANELS FOR BACKLIGHT ENHANCEMENT IN LIQUID CRYSTAL DISPLAYS... 

UNS S31600) module housing 1 m in length containing nanoporous alumina membrane tubes sealed to headers at both ends of the module. When heated from 25 to 425 °C, the steel module housing will expand approximately to 6.4 mm (CTE is 16 x 10 S/°C),22 whereas the alumina membranes will expand only to 3.2mm (CTE is 8.0 x 10 6/°C).23 In this example, it is likely that the alumina membrane tubes will either crack or separate from the seals at each end of the tubes. 

Likewise, a thin nanoporous alumina membrane deposited onto a porous stainless steel support will likely fail unless efforts are taken to match the CTE of these diverse layers. This may be done by building up layers on the support such that a gradient in CTE is achieved. Also, thin metal membranes deposited on porous ceramic membranes have historically exhibited poor durability with respect to cracking and general membrane failure due, at least in part, to mismatched CTE. 

Grimm S et al (2008) Nondestructive replication of self-ordered nanoporous alumina membranes via cross-linked polyacrylate nanoflber arrays. Nano Lett 8(7) 1954-1959... 

To avoid high-pressure drop and clogging problems in randomly packed micro-structured reactors, multichannel reactors with catalytically active walls were proposed. The main problem is how to deposit a uniform catalyst layer in the microchannels. The thickness and porosity of the catalyst layer should also be enough to guarantee an adequate surface area. It is also possible to use methods of in situ growth of an oxide layer (e.g., by anodic oxidation of a metal substrate [169]) to form a washcoat of sufficient thickness to deposit an active component (metal particles). Suzuki et al. [170] have used this method to prepare Pt supported on nanoporous alumina obtained by anodic oxidation and integrate it into a microcatalytic combustor. Zeolite-coated microchannel reactors could be also prepared and they demonstrate higher productivity per mass of catalyst than conventional packed beds [171]. Also, a MSR where the microchannels are coated by a carbon layer, could be prepared [172]. 

Li Y, Yin X-F, Chen F-R, Yang H-H, Zhuang Z-X, Wang Z-R (2006) Synthesis of magnetic molecularly imprinted polymer nanowires using a nanoporous alumina template. Macromolecules 39 4497 499... 

Xu T, Zangari G, Metzger RM (2002) Periodic holes with 10 nm diameter produced by grazing Ar+ milling of the barrier layer in hexagonally ordered nanoporous alumina. Nano Lett 2 37 1... 

Figure 7. Schematic diagram of a nanoporous alumina membrane.

Figure 8. Atomic force microscopic (AFM) image of the surface of a nanoporous alumina membrane.

P-18 - Template synthesis and characterization of nanoporous alumina with narrow pore size distribution from inorganic salts... 

Dickey E. C., Varghese O. K., Ong K. G., Gong D. W., Paulose M., and Grimes C. A., Room temperature ammonia and humidity sensing using highly ordered nanoporous alumina films. Sensors, 2, 91-110, 2002. 

Another way to template thin films of nano-sized cylinders perpendicular to the surface is to start with a preformed membrane of track-etched polycarbonate or nanoporous alumina. A fiuid dispersion of a filler material can be drawn into the pores. Anodized aluminum oxide was the template for construction of lithium ion nanobatteries having many parallel cells filled with the solid state electrolyte PEO-LiOTf (poly(ethylene oxide)-lithium trifluoromethanesulfonate) and the electrodes coated on the top and bottom surfaces of the film (41). 

Besides nanoporous alumina template, nanoporous polycarbonate (PC) is another popular choice for the growth of CPNWs. PPV and PEDOT nanowires of a few hundred nanometers have been prepared by CVD and electrochemical methods, respectively, using PC templates [55,58],... 

FIGURE 20.2 (a) The surface and cross section of a typical nanopore alumina template membrane prepared in the authors lab. The mono-... 

Template-synthesized polymers [143,144] are expected to have applications in miCToelectronics, dmg delivery, bioencapsulation, ultratrace chemical analysis and second-order tanplates for the growth of other nanoarrays. Carbon nanotube electronics are expected to provide a viable alternative to silicon. The development of an array of transistors using carbon nanotubes and the development of computer circuits using single-walled carbon nanotube was recently reported by IBM [ 145]. Carbon nanotubes also find use as cold cathode flat panel display [146]. Carbon nanotubes can also be used to encapsulate [147] other materials like Fe and Co. Well-ordered carbon nanotubes have been synthesized [148-150] in nanoporous alumina m brane template. 

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