Biosynthesis and Electron Microscopy Characterization of Diatom Nanocomposites
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Biosynthesis and Electron Microscopy Characterization of Diatom Nanocomposites Timothy Gutu and Jun Jiao Department of Physics, Portland State University Clayton Jeffryes, Tian Qin, Chih-hung Chang, and Gregory L. Rorrer Department of Chemical Engineering, Oregon State University ABSTRACT The fabrication of Si-Ge oxide composites in a two-stage photobioreactor cultivation process was systematically optimized by increasing the amount of germanium assimilated into the diatom cells. In this optimization process of the synthesis of Si-Ge oxides that maintain the original morphology of the diatoms, high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) both equipped with an energy dispersive X-ray spectrometer were extensively used to characterize the evaluation of the chemical composition and structural properties of the processed diatoms. INTRODUCTION Scientists have long realized the important role that diatoms will play in biotechnological development [3]. Diatoms are microscopic unicellular algae that live in marine and freshwater bodies. They are capable of taking up soluble silicon from their surrounding liquid environment, which they convert into silica (SiO2) nanoparticles during biosynthesis of their silica-based cell wall. The ability of diatoms to make complex, nanoscaled, three-dimensional silica shells called “frustules” offers attractive possibilities for their applications to nanobiotechnology [1] and synthesis of new materials. For example, silicon in the shell can be replaced with other elements by chemical processes while preserving the intricate patterns of the frustule [2]. However, research that has been done so far in manipulating diatom metabolism to biologically fabricate frustules that are composed of nanocomposite metal oxide semiconductor materials has not explored ways of optimizing the fabrication process. Ability to control the fabrication process, in our case, to control the germanium doping concentration is critical. In this study, effort was focused on obtaining a specifically desired value of an optoelectronic property by controlling the amount of germanium absorbed by diatom cells. For example, the amount of germanium required to give best photoluminescence properties can be experimentally determined, results of which will be published elsewhere. Biological processes have been developed to incorporate atoms other than silicon into the silica diatom frustule while maintaining the frustule’s detailed morphology. This process has allowed us to fabricate silicon-germanium (Si-Ge) oxide nanocomposites that possess optoelectronic properties [4]. Diatoms carry out this process under ambient conditions of temperature and pressure and produce no environmental pollutants. In this study, several electron microscopy and microanalysis techniques were used to characterize the morphologies and elemental composition of the processed diatoms and
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more importantly to assess and direct the optimization of the fabric
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