Mesoporous anodic alumina

The paper summarizes recently investigated properties of a structure microporous xerogel/mesoporous anodic alumina , doped with erbium, terbium and europium. An enhancement of green, red and infiared photoluminescence (PL) from the structure associated with intra-transitions of bivalent lanthanides in xerogels is discussed. 

Itoh N, Tomura N, Tsuji T, Hongo M. Deposition of palladium inside straight mesopores of anodic alumina tube and its hydrogen permeabihty. Microporous Mesoporous Mater. 2000 39(1-2) 103. 

On the other hand, a multicolour luminescent image, on the basis of a single phosphor embedded in mesopores or macrocavities of anodic alumina films, can be fabricated using blue PL that is specific for some films. Examples of such blue PL recorded for three types of electrolyte, are presented in Fig. 3. The origin of the blue PL from PAA is considered to be related to generation F-centres during anodizing of aluminium or excitation of residual chemical components absorbed from the electrolytes [8,9]. 

Methods of electrochemical deposition have been used in combination with syntheses on template and in mesoporous media. Thus, the nanowires are easily formed in the mesoporous matrices. The nanowire electrodeposition has been developed for Co [357-361,379], Ni [358-362,370,374], FePt [376], FeCo [364], FeNi [356], CoPt [363]. The traditional patterns are polycarbonates [380], anodized alumina [356, 362] and mica [363]. More information about the electrodeposition of nanostructures can be found in Table 5.12. 

Martin CR (1994) Nanomaterials a membrane-based synthetic approach. Science 266 1961-1966 Martin CR (1996) Membrane-based synthesis of nanomaterials. Chem Mater 8(8) 1739-1746 Masuda H, Fukuda K (1995) Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina. Science 268 1466-1468 Mishra JK, Bhunia S, Baneqee S, Baneqi P (2008) Photoluminescence studies on porous silicon/ polymer heterostructure. J Lumin 128 1169-1174 Moller K, Bein T (1998) Inclusion chemistry in periodic mesoporous hosts. Chem Mater 10(10) 2950-2963... 

O Callaghan, J.M., Petkov, N., Copley, M.P., Arnold, D.C., Morris, M.A., Amenitsch, H., and Holmes, J.D. (2010) Time-resolved SAXS studies of periodic mesoporous organosilicas in anodic alumina membranes. Microporous Mesoporous Mater., 130, 203-207. 

Mesoporous alumina membranes ( anodic aluminium oxide , or AAO) are prepared by anodic oxidation of aluminium metal [1,2]. The cylindrical pores, perpendicular to the membrane surface, form hexagonal arrays of straight non-intersecting channels with pore densities up to lO Vcm. Their diameters are controllable within the range 5 - 100 nm as a linear function of anodisation voltage. These membranes are used as molecular sieves, and have also found application as templates for metallic nanowires [3,4,5,6], metal elusters and colloids [7,8], and carbon nanotubes [9,10]. 

The most simple pore morphologies (Figs. 2.1A and B) are those of more or less straight cylindrical or conical-shaped pores. This type of pore is formed in so-called track etch and in "anopore" membranes. The latter is obtained by anodic oxidation of A1 metal foils and results in porous (amorphous) alumina (mesoporous) membranes. A detailed discussion is given by Burggraaf and Keizer in Ref. [1]. These types of membrane are useful for fundamental trans-... 

In proton exchange membrane fuel cells, perhaps the most divulgate type of fuel cells, a proton-conducting polymer membrane acts as the electrolyte separating the anode and cathode sides. Porous anaodic alumina (Bocchetta et al., 2007) and mesoporous anastase ceramic membranes have been recently introduced in this field (Mioc et al., 1997 Colomer and Anderson, 2001 Colomer, 2006). 

As stated above, a variety of deposition techniques have been developed in recent years to produce amorphous alumina coatings (112—115), among them the anodization of aluminum. Amorphous aluminas, denoted as a-Al203 or sometimes as P-AI2O3, can also be prepared by conventional liquid-phase reactions (134), by the decomposition of some hydroxides, or by sol-gel procedures aimed at the preparation of mesoporous materials. In several instances, IR (110) and Raman (135) spectra have demonstrated that amorphous aluminas may contain impurities originating from the... 

Fig. 1 Examples of morphologies of semiconductor nanostructures, (a) metal assisted Si etching and formation of Si-NWs. Electrochemical formation of (b) microporous silicon, (c) ZnO nanorods, (d) porous CdSe using porous alumina template, (e) CdTe nanowires using alumina template, (1) CdS nanowires using alumina template, (g) mesoporous Xi02 film using doctor blade method, (h) self-ordered anodic Xi02 nanotubes and (i) cross section image of the same Xi02 nanotubes (reproduced with permission from Ref. 8,27,28,45 8).

Other methods to prepare porous membranes include pyrolysis for carbon membranes, heat treatment and leaching for mesoporous glass membranes, and anodization for alumina membranes. The microporous carbon membranes are prepared by coating a polymeric precursor such as polyfurfuril alcohol and polycarbosilane on porous substrates, followed by controlled pyrolysis under N2 atmosphere [15]. The carbon membrane structure is determined by the fabrication variables, including the polymeric solution concentration, solvent extraction, heating rate, and pyrolysis temperature [16]. 

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