Anodic aluminium oxide

Oliveira GB, Eilho JLL, Chaves MEC, Azevedo WM, Carvalho LB (2008) Enzyme immobilization on anodic aluminium oxide/polyethyleneimine or polyaniline composites. React Fund Polym 68(l) 27-32... 

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]. 

Abbreviations AAO anodic aluminium oxides ANSA 5-aminonaphthalene-2-sulfonic acid APS—Ammonium persulphate ASA — Anthracene Sulfonic acids CB — conduction band CPs — conducting polymers CSA... 

SEM was used for morphological studies of anodic aluminium oxide films, formed at various formation current densities up to a formation voltage of 60 V. The total thickness of the films was determined by cross-section SEM micrographs as shown in Figure 23.1, but it should be emphasised that one can not clearly identify barrier and porous layers of the oxide film by using this technique. 

Figure 23.1 High-resolution cross-sectional SEM micrograph of an anodic aluminium oxide film of 66 nm formed at 0.3 mA/cm and a formation voltage of 60 V (Al thickness remaining 633 nm).

To interpret the impedance data, a model of the anodic aluminium oxide film must be established. The anodic aluminium oxide film is a sandwich film consisting of two layers, a barrier layer and a porous layer (Figure 23.4A [2]). 

Figure 23.3 Bode plots of natural and anodic aluminium oxide films. The aluminium oxide film was formed at 2.5 mA/cm and a formation voltage of 60 V, experimental (points) and fitting (lines).

Figure 23.4 Two-layer model of the anodic aluminium oxide film (A) and associated equivalent circuit (B)...

The average capacitance and specific resistivity of the barrier aluminium oxide films are determined to be 430. .. 470nF/cm and 1.3. .. 2.4 10 " Qcm, respectively. By using the anodisation factor of 1.2 nm/V for the films formed at low formation voltage, dielectric constants of 5.8. .. 6.4 are calculated from the measured capacitance values. The comparatively low dielectric constant is in agreement with the formation of an amorphous anodic aluminium oxide film as discussed above rather than a crystalline structure for which a higher dielec-... 

Fig. 14. Growth (in direction G) followed by dissolution (direction D) of anodic aluminium oxide film. The "loop is an ellipsometric signature of a spontaneous substrate roughening-self-smoothing cycle.

Anodic aluminium oxide Successfully depleted surface [31]... 

In a template synthesis, CP is polymerized within the pores or channels of a nanoporous template to obtain the controlled structure and morphology upon removal of the template. Templates can be either a masking of a confined area that CP can grow in or a structured surface that CP is deposited upon. Masking type templates, namely nanoporous anodic aluminium oxide (AAO also commonly known as AI2O3, alumina, or anodise ) [113-118], hydrogels [119,120] and latex particles [121-130], have been used to prepare nanoscale fibrils, particles, and tubules of CPs. 

Using porous anodic aluminium oxide films, Routkevitchand associates electrodeposited very thin CdS nanowires [49]. The alumina membranes were typically 1 - 3-pm thick with pore sizes ranging from 9 to 35 nm. The CdS was electrodeposited, using ac electrodeposition, from a DMSO solution containing CdCl2 and elemental S. The porous alumina, as anodized, was separated from the A1 by a dense oxide... 

Shi and co-workers prepared polythiophene films with different roughnesses by electrochemical polymerization of thiophene in boron trifluoride-diethyl etherate (BFEE) [42]. The highest WCA of 116° on polythiophene film was observed. To further increase the WCA, aligned polythiophene nano-tubes were synthesized using anodized aluminium oxide (AAO) as template. The WCA increased to 134° (Fig. 7). As a comparison, the WCA of polythiophene polymerized in acetonitrile solution was measured to be less than 75°. 

Carturan G, Dal Toso R, Boninsegna S, Dal Monte R (2004) Encapsulation of functional cells by sol-gel silica actual progress and perspectives for cell therapy. J Mater Chem 14(14) 2087-2098 Cho S, Lee S, Jeong SH, Kim Y, Kim SC, Hwang W, Park J (2013) Anodic aluminium oxide membranes for immunoisolation with sufficient oxygen supply for pancreatic islets. Integr Biol 5(5) 828-834... 

Most of the work that has been carried out using porous membranes as hard templates was done on porous alumina (anodic aluminium oxide, AAO) or track-etched polycarbonate membranes. The general principle of nanotube formation relies on a continuous polymer film being formed on the inside of the pores that remains as a tubular structure once the template is removed. There are several possibilities as to how this polymer film can be formed inside the pore. A film can be obtained by wetting the pore with a polymer melt or a polymer solution. Alternatively, the polymerization of monomers... 

European Patent 0178831, Porous Films of Anodic Aluminium Oxide, to R.C. Furneaux, Alcan Int. Ltd., 23 April, 1986. 

Cho, S.H., Walther, N.D., Nguyen, S.T. Hupp, J.T. (2005). Anodic aluminium oxide catalytic membranes for asymmetric epoxidation, Chem. Commun. pp.5331-3. 

Ghorbani M., Nasirpouri R, Irajizad A. and Saedi A. (2006), On the growth sequence of highly ordered nanoporous anodic aluminium oxide ,Mater Design, 27, 983-88. 

Abstract Membrane reactors with a catalyst bed are designed to be used in various reactions, such as hydrogenation, dehydrogenation, oxidation and reforming reactions. The catalyst can be introduced into the reactor as a bed in several ways in the form, for example, of pellets, extrudates or tablets or it can be incorporated in the reactor as a catalytic membrane wall. However, in many cases, the studies concentrate on the membrane itself, the development of catalysts is ignored, and commercial catalysts are used in the experiments. Most of the catalysts tested are aluminium oxide (alumina, AI2O3) based, as alumina is a mature support and already well proven in convectional reactors. However, some new catalyst materials such as carbon nanotubes (CNTs), carbon black, gels and anodic aluminium oxide (AAO) are developed as innovative catalyst supports and catalysts, since there is also a need for new catalysts for membrane reactors. 

Kordas K, T6th G, Levoska J, Huuhtanen M, Keiski R, Harkonen M, George T G, Vahakangas J (2006) Room temperature chemical deposition of palladium nanoparticles in anodic aluminium oxide templates. Nanotechnology, 17, 1459-1463. 

---