Control of the morphology and chemical properties of carbon spheres prepared from glucose by a hydrothermal method

Carbon spheres (CSs) with regular shapes (phi 300-1200 nm) and numerous oxygen groups (-OH, C6H5-C=O, and C=O) were prepared by a simple glucose hydrothermal process. CSs were studied by x-ray powder diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, x-ray photoelectron spectra, and elemental analysis. Their size was directly proportional to temperature and glucose concentration. Their shape could be controlled by temperature and reaction time. To prepare CSs (phi 300-800 nm) with regular shapes and smooth surfaces, temperature and reaction time in the range of 180-230 degrees C and 3-4 h, respectively, were optimal. The chemical properties of the CSs were affected by temperature. A phase transformation from amorphous to turbostratic structure took place at T > 230 degrees C. The number of oxygen groups decreased as the temperature increased, and T <= 230 degrees C were optimal to prepare oxygen-rich CSs. Comparison of oxygen contents and O/C ratios indicated a further carbonization, and the degree was directly related to temperature. A possible formation mechanism for the CSs is proposed.