Anodise alumina membranes

Whatman Anodise alumina membranes with polypropylene support rings (25-mm... 

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]. 

Figl Structural features of the mesoporous alumina membranes Schematic cross section (before removal of A1 backing) and schematic top view, together with an atomic force microscope AFM (Voltage) image for a membrane produced by anodisation at 40 V. 

Thin alumina membranes (Anodise ) with two different nominal pore diameters (20 nm and 200 nm) were obtained commercially (Whatman International Ltd., Maidstone, Kent, UK). These two types of membranes, designated subsequently as A20 and A200 respectively, had a thickness of 50 pm and an overall diameter of either 25 of 47 mm. X-ray diffraction analysis showed that the alumina in the as received membranes was almost amorphous. Subsequent thermal treatment up to 950 °C produced a crystalline structure (y-alumina), without any significant collapse in the porous structure. Here we describe, in general, the characterisation of the untreated membranes. 

Figure 11. Anisotropic SANS results for an oriented alumina membrane (Anodise, A20). In (a) the orientation is perpendicular and in (b) parallel to the incident neutron beam respectively. I(Qh) and I(Qv) correspond to scattering along the horizontal and vertical axes of the 2D detector, respectively.

Other strategies for producing hydrophobic membranes for MD are the modification of hydrophilic polymers or ceramic materials. Qtaishat et al. [144] produced two different types of hydrophobic surface-modifying macromolecules (SMMs) and prepared hydrophobic/hydrophilic polyetherimide composite membranes. The SMMs blended PEI membranes achieved better DCMD fluxes than those of a commercial PTFE membrane tested under the same conditions. Similarly fluorinated SMMs were used to modify hydrophilic poly(sulfone) [145]. Krajewski et al. [146] used lH,lH,2H,2H-perfluorodecyltriethoxysilane to create a hydrophobic active layer on commercial tubular zirconia membranes supported on alumina. The produced membranes were tested in air-gap MD (AGMD). Hendren et al. [147] used 1H,1H,2H,2H-perfluorodecyltriethoxysilane, trichloromethylsilane, and trimethylchlorosilane to modify, by surface grafting, two types of alumina Anodise ceramic membranes. The authors demonstrated that this surface treatment was effective and tested the produced membranes in DCMD. 

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