Akaganeite preparation

Chen, M., Jiang, J., Zhou, X. and Diao, G. (2008) Preparation of akaganeite nanorods and their transformation tosphere shape hematite. Journal for Nanoscience and Nanotechnology, 8, 3942-3948. 

There is a number of synthetic substitutes for natural ferritin and the properties of these have been compared with those of ferritin. The synthetic polysaccharide iron complex (PIC), has a magnetic blocking temperature of 48K (Mohie-Eldin et al. 1994). Iron-dextran complexes are used as a substitute for ferritin in the treatment of anaemia. The iron cores of these complexes consist not of ferrihydrite, but of very poorly crystalline akaganeite with magnetic blocking temperatures of between 150 and 290 K (Muller, 1967 Knight et al. 1999) which were lowered from 55K to 35 and 25K, if prepared in the presence of 0.250 and 0.284 Al/(A1 -i- Fe), respectively (Cheng et al.2001). 

Cornell, R.M. (1991) Simultaneous incorporation of Mn, Ni and Co in the goethite (a-FeOOH) structure. Clay Min. 26 427-430 Cornell, R.M. (1992) Preparation and properties of Si substituted akaganeite (P-FeOOH). Z. Pflanzenemahr. Bodenk. 155 449-453 Cornell, R.M. Giovanoli, R. Schindler, P.W. (1987) Effect of silicate species on the transformation of ferrihydrite into goethite and hematite in alkaline media. Clays Clay Min. 35 12-28... 

Akaganeite cannot be prepared at pHs above 5 because the OH ion is far more competitive than the chloride ion for structural sites. Akaganeite displays two morphologies somatoids or cigar shaped crystals and much smaller rod-like crystals. Samples of somatoids frequently contain a proportion of twinned crystals, whereas the rod-like crystals are never twinned. 

Forced hydrolysis of Fe solutions involves hydrolysing Fe(N03)3, Fe(C104)3 or FeCls solutions at a temperature close to 100 °C under strongly acidic conditions (pH 1-2). It is believed that, if hematite is prepared from Fe(N03)3 or Fe(C104)3, it forms from Fe hydroxy species (Johnston and Lewis, 1983, 1986), whereas, if hematite is prepared from FeCls, akaganeite may be an intermediate product which then transforms to hematite via solution (Hamada and Matijevic, 1981). 

To conclude, it is clear there is a strong dependence of the performance of synthetic hematite on the deposition technique. While methods such as spray pyrolysis and CVD consistently produce electrodes photoactive for water oxidation, solution-based methods such as sol-gel approaches have failed to produce especially photoactive hematite. This is certainly related to the quality of the prepared material in terms of crystallinity and impurity concentrations. Aqueous methods of preparing hematite typically pass through a phase containing iron hydroxide (e.g., akaganeite, lepidocrocite, or goethite) but primarily hematite is detected after at annealing at 500°C. However, it has been shown that at temperatures up to 800°C, a nonstoichiometric composition remains in hematite when prepared in this way... 

Figure 8.7. MonoUthic aerogels prepared via the epoxide addition method A. alumina, B. chromia, C. p-FeOOH (akaganeite), D. Ni(ll)-based aerogel, E. tungsten oxide, and F. tin oxide.

Membranes can act as both active and passive templates for the formation of well-defined nanostructures in a number of ways. In the biological realm, they have a limited role in the formation of nanowires, where virus capsids are much more effective, as described elsewhere in this volume (see Viruses as Self-Assembled Templates, Self-Processes). An interesting exception that takes place close to the membranes of living cells is the formation of iron oxyhydroxide (akaganeite, /1-FeOOH) in a natural ecosystem, in which polysaccharides are shown to be important as they are contained in the filaments of the inorganic material. It is believed that the sugar is extruded from the cell and then acts as a template to promote the formation of the mineral. On the other hand, entirely synthetic lipids can be used for the preparation of pipes of organically functionalized layered materials—clays —in... 

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