Alumina nanopore membrane

A further aspect to be considered is that supported ILs can also host chemicals, for example, complexing agents, which could further enhance the selectivity in the separation. This concept opens up the possible use of ILs supported on a membrane, particularly ceramictype nano-membranes (e.g., an alumina nanoporous membrane obtained by anodic oxidation) to develop novel systems that can combine catalysis and separation. The concept is shown in Figure 2.14. 

Figure 16.2.1 Pore density vs. pore diameter in alumina nanoporous membranes prepared in the three electrolytes indicated. Reproduced with permission from http //www.synkera.com/. (for colour version see colour section at the end of the book).

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.)... 

This advantage can be used for growing nanowires (wires with nanometric diameter). Nanoporous membranes that can be fabricated by the anodic oxidation of aluminum are appropriate templates. This process leads to the formation of an alumina layer with parallel nanopores, as shown in Fig. 15A, which can then be filled by electrodeposition. Fig. 15B shows a schematic view of a multilayer nanowire and Fig.l5C a transmission electron microscopy image of a Cu/ CuCoNi layered nanowire grown in the nanopores. 

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

Osteoblasts were cultured on alumina nanoporous templates. Figure 16.11 shows SEM images of an osteoblast on the cross-section of a nanoporous alumina membrane that had been cracked. To visualize the extension of the cell processes into the pores, a second high magnification image was taken of the attachment area between the cell and membrane. It can be noted that... 

The method is based on the simple but effective idea that the pores of a host material can be used as a template to direct the growth of new materials. Historically, template synthesis was introduced by Possin (1) and refined by WilUams and Giordano (2) who prepared different metallic nanowires with widths as small as 10 nm within the pores of etched nuclear damaged tracks in mica. It was further developed by Martin s group (3-5) and followed by others (6) with the number of examples and applications (7) continually increasing. The nanoporous membranes usually employed as templates are alumina or track-etched polymeric membranes which are widely used as ultrafiltration membranes. Recently, metal nanostmctures have also been obtained using the pores created by self-assembly in block copolymer structures under the influence of electric fields and high temperatures (8,9). 

Comparison between alumina and track-etched polymer nanoporous membranes... 

The first procedure reported for the production of metal nanorods is called template synthesis.This method entails the preparation or deposition of the desired material within the cylindrical and monodisperse pores of a nanopore membrane. Martin and coworkers used polycarbonate filters, prepared by the track-etch method, and nanopore aluminas prepared electrochemically from Al foil, as template materials. This method allows the preparation of cylindrical nanostructures with monodisperse diameters and lengths, and depending on the nature of the membrane and the synthetic method used, these may be solid nanowires or hollow nanotubes. 

Properties of alumina manbranes and polymer membranes, like chanical/thermal stabilities and pore density, are often quite different, and selection of the proper material for desired applications is important Chanical modification has proven useful to impart functionality to nanoporous membranes. For alumina manbranes in particular, growth of thin sol-gel films on the walls of the membrane provides an opportunity to functionalize membranes with organosilanes (e.g., triethoxy-or trichlorosilanes). Deposition of gold films also provides a method for chemical modification... 

A prevalent use for the nanoporous membranes detailed previously, particularly the highly ordered structure of alumina, is to fabricate reproducible nanoscale materials through a method called template synthesis. Briefly, the composition material of desired nanostructures is grown or deposited into a nanoporous membrane the new nanostructures are then separated from the original membrane via mechanical or chemical means. Dependent on the synthetic approach used, this process can produce nanoscale arrays " or individual nanostructures like wires, nanotubes or nanoparticles. Template synthesis also has been used to produce biological nanostructures through the deposition of biomolecules into nanoporous membranes. For a more detailed explanation on... 

The deposition of nanowires and nanotubes into tanplates was pioneered by Martin. In template deposition, the materials are deposited into nanoporous manbranes, such as anodized aluminum or track-etch polymers. The nanoporous membranes function as nanosized beakers that constrain the crystal growth. Figure 17.10 shows TEM micrographs of Au nanowires with a diameter of 70 nm and polypyrrole nanotubes with an outside diameter of 90 nm and an inside diameter of 20-30 nm that were eleclrodeposited into an alumina nanoporous tanplate. ... 

Another method of template-assisted synthesis, mainly used for the growth of metal nanowires, involves the deposition of metal into the cyUndrical pores or channels of an inert, non-conductive nanoporous electrode material. Track etch membranes, porous alumina, nanoporous conductive rubber polymers, metals, semiconductors, carbons and other solid materials have been used as templates to prepare nanometer-sized particles, fibrils, rods and tubules. The experimental set... 

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. 

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)... 

They consist of a thin layer (<10 fxm) of a nanoporous (3-1OA) carbon film supported on a meso-macroporous inorganic solid (alumina) or on a carbonized polymeric structure [15]. They are produced by pyrolysis of polymeric films. The following two types of membranes are produced ... 

---