Si-containing Akaganeite

Dissolve 40.4 g Fe(N03)3 9 H2O in 1 L twice distlled water and add sufficient Si solution (Titrisol, Merck SiCU with 1000 mg Si/L in 14% NaOH) to give a Si/Fe ratio of 0.07. Hold the solution in a 1 L polyethylene bottle in a 70 °C oven for 24 hr. Wash the yellow precipitate and dry at 50 °C. 

The method produces 2.25 g akaganeite with a surface area of 30-40 m /g. The crystals are approximately somatoidal and between 200-400 nm long. 

This material contains 2.3 mol% Si. Si is released congruently with Fe upon dissolution and is, therefore, considered to be homogenously distributed within the akaganeite crystals, probably in the tunnels (Cornell, 1992). 

There was no effect of silicate (0.3-1 mol%) on the crystal size, probably because the silicate molecule is uncharged at low pH. 

Increasing the phosphate concentration (up to 2 mol%) reduced the spindle length from 500 nm to 100-200 nm (Kandori et al. 1992). 

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