Synthesis of Carbon Microspheres from Starch by Hydrothermal Process

This study showed a facile catalyst-free method to synthesize carbon microspheres (CMSs) viahydrothermal and carbonization process using various types of starch as starting materials. Inhydrothermal process, starch was hydrolyzed, dehydrated, and polymerized to form carbonmicrospheres in water as a medium without involving any hazardous solvents. After hydrothermalprocess, the dried products were treated by heat in carbonization process under nitrogen atmosphere todevelop their pore system of carbon microspheres. The two main types of starch, modified starch andnative starch, were employed to address differences in particle size and morphology of resultingcarbon microspheres. The SEM images clearly illustrated that the carbon microspheres have theirperfect spherical morphology and smooth surface. The particle size distributions of the products with asize range of 0.4-4.0 μm were determined by laser diffraction technique (Mastersizer). The particlesize and particle size distribution of carbon microspheres strongly depended on types of starch. Inother words, carbon microspheres from modified starch tended to smaller in particle size than carbonmicrospheres from native starch because of water-solubility of modified starch higher than nativestarch. After carbonization process, structural CMSs characterization performed by X-ray diffractiontechnique (XRD) indicated semi-hexagonal graphite structures which would be suitable for secondarylithium ion application. Elemental compositions of the carbonaceous products determined by energydispersive X-ray spectroscopy (EDX), indicated that a main component was carbon being inert tomany chemical reactions. Furthermore, these carbon materials have specific BET areas in the range of400-500 m2/g which were formed during carbonization process. All N2 adsorption-desorptionisotherms of these carbon materials have type I isotherm regarding to IUPAC classification thatindicated micropore system.