Hydrothermal preparation of carbon microspheres from mono-saccharides and phenolic compounds

Isolated carbon microspheres in a diameter range of 1–4 μm were prepared by hydrothermal treatment of mono-saccharides (xylose for pentose and fructose for hexose) with phenolic compounds–phenol, resorcinol, and phloroglucinol. It was found that addition of these compounds, particularly phloroglucinol, into a sugar solution led to a substantial increase (roughly 20-fold) of the carbon yield. Mono-saccharides are dehydrated into furan compounds during hydrothermal carbonization, and these compounds subsequently react with phloroglucinol, as revealed by examination of high-performance liquid chromatograms. Through elemental analysis and spectroscopic studies, it was found that several oxygen functionalities including hydroxyl, carbonyl, carboxyl, ether, quinone, and ester groups were located throughout the carbon spheres derived from sugars and phloroglucinol. On the basis of the carbon formation mechanism, the C–O–C bond formed by linkage of OH groups of phenolic compounds preferentially exists at the core of carbon spheres whereas the outer carbon surface contains reactive oxygen functionalities such as hydroxyl, carbonyl, carboxylic, and ester groups, corresponding with results obtained with sugar-derived carbon materials.