The structural change of diatom by heating

Abstract

It is known that the diatom has siliceous cell wall. The cell wall consist of upper and lower tow valves which called frustules. The frustules are a porous quality and characteristic various forms therefore the morphological feature has been emphasized before. The micro scale structure is investigated in detail by the development of the electron microscope. But the structure of nano-scale is hardly researched. In this work, we unveil details about the structure in molecular-atomic level and its change by heating using X-ray diffraction and micro-FTIR measurement. Analyzing nanoscale structure of diatom frustules may offer information about interaction between organic-inorganic. Diatom used for structure analysies of the silica-based compound in frustles were collected from acidic hot spring at Kamuiwakka Falls, Shiretoko Peninsula, Hokkaido, Japan. The hot spring water was strong acid the pH of lies between 1.0 ti 2.0. The diatom sample is heated in electric furnace. Then the sample was analyzed by using scanning electron microscopic and energy-dispersion X-ray spectroscopy (SEM-EDX), fourier transform infared absorbance spectroscopy (FT-IR) and powder X-ray diffraction spectrometer (XRD). X-ray diffraction pattern in unheated diatom sample show characteristic broad in amorphous materials. The X-ray diffraction profile and EDX analysis decide that diatom frustule is amorphous silica similar to silica gel. Additionally, weak peak due to crystalline phase present indicate that crystoballite, quartz and other silicate minerals are obtained diatom silica. FTIR spectrum appears band derives from SiO₄ tetrahedra and indicate that organic matter, Si-OH and molecule water exist in the structure. By heating treatment, they disappeared. Si-O peak sifted to high wavenumber and became sharp. First diffraction sharp peak in XRD shape change high temperature. The fact may suggest that middle range structure of frustule change somehow. It possible that crystallization advanced slightly increasing intensity of peak due to crystalline phase.