Hydrothermal synthesis, characterization, and KOH activation of carbon spheres from glucose

Carbon spheres (CSs) with controllable sizes and rich in oxygen-containing groups were fabricated using a simple hydrothermal treatment of glucose. The effects of the hydrothermal parameters, including the concentration of glucose, reaction temperature, duration, and the second hydrothermal treatment were investigated. The obtained CSs were then activated using KOH for the eventual preparation of porous carbon spheres. A scanning electron microscope was used to characterize the morphology and size of the CSs. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to analyze the functional surface groups. N(2) adsorption–desorption isotherms were used to analyze the porous structure of the CS. The results revealed that the morphologies and size distribution of the CSs can be controlled by adjusting the experimental parameters. A hydrothermal temperature between 180 and 190°C over 4-5h was suitable for CS formation. Under these conditions, the size of the CS increased with the concentration of glucose. Mono-dispersed CSs with good morphologies and large numbers of oxygen-containing functional groups (primarily -OH and C=O) can be obtained using a 0.3mol/L glucose solution that is hydrothermally treated at 190°C for 4h. The resulting CSs sizes were about 350nm in diameter. After a second hydrothermal treatment, the sizes of CSs grew nearly 250nm without damage to its morphology or broadening of their size distribution. Porous CSs with perfectly spherical shapes and fully developed structures (S(BET)=1282.8m(2)/g, V(micro)=0.44cm(3)/g) could then be obtained via KOH activation.