The biomineralization capacity of the photosynthetic marine diatom Nitzschia frustulum was harnessed to fabricate Si–Ge oxide nanocomposite materials. Germanium was incorporated into the diatom cell by a two-stage cultivation process. In stage 1, the N. frustulum cell suspension was grown up to cell density of 3 × 106 cells/mL in 0.35 mM silicic acid within a bubble-column photo- bioreactor. In stage 2, when all of the soluble silicon was consumed,0.10 mM Ge(OH)4 or a mixture of 0.020 mM Ge(OH)4 and 0.25 mM Si(OH)4 were added to Si-starved cells. The cells assimi- lated soluble germanium by a surge uptake mechanism. The cell mass was thermally annealed in air at 800°C for 6 h to oxidize carbonaceous materials. The thermally annealed cell biomass was characterized by TEM-EDS, FT-IR, and XRD. These measurements confirmed the formation nanostructured Ge–Si oxides composed of CaSiO3 and Ca3 GeO5.
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