We report here on the synthesis of highly functionalized carbonaceous materials by means of the hydrothermal carbonization of different saccharides (glucose, sucrose, starch and cellulose) at temperatures in the 170-250°C range. Under hydrothermal conditions, the chemical structure of the saccharides is heavily transformed, via dehydration, condensation or polymerization and aromatization processes. As a result, a carbon-rich solid product is obtained, which we have denoted hydrochar. It is made up of spherical micrometer-sized particles, with tuneable sizes through the modification of the synthesis conditions (i. e. the concentration of aqueous saccharide solution, the temperature of hydrothermal treatment, the reaction time and type of saccharide). From a chemical point of view, the microspheres possess a core-shell structure consisting of a highly aromatic nucleus formed by small clusters of condensed benzene rings and a shell containing a high concentration of hydrophilic oxygen functional groups (i.e. hydroxyl/phenolic, carbonyl or carboxylic). These material acts as a carbon sink, making hydrothermal carbonization of saccharides an efficient way to sequestrate atmospheric CO_2. Moreover, they constitute an excellent precursor for the synthesis of graphitic carbon nanocoils with a high crystallinity and an accessible surface area.
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