Low-Cost Activated Grape Seed-Derived Hydrochar through Hydrothermal Carbonization and Chemical Activation for Sulfamethoxazole Adsorption

Featured Application: Hydrothermal carbonization is presented as an alternative management way to valorize biomass wastes, and transform them in high-value solid products. Activated carbons were prepared by chemical activation with KOH, FeCl3 and H3PO4 of the chars obtained via hydrothermal carbonization of grape seeds. The hydrochars prepared at temperatures higher than 200 degrees C yielded quite similar proximate and ultimate analyses. However, heating value (24.5-31.4 MJ.kg(-1)) and energy density (1.04-1.33) significantly increased with carbonization temperatures between 180 and 300 C. All the hydrochars showed negligible BET surface areas, while values between 100 and 845 m(2).g(-1) were measured by CO2 adsorption at 273 K. Activation of the hydrochars with KOH (activating agent to hydrochar ratio of 3:1 and 750 degrees C) led to highly porous carbons with around 2200 m(2).g(-1) BET surface area. Significantly lower values were obtained with FeCl3 (321-417 m(2).g(-1)) and H3PO4 (590-654 m(2).g(-1)), showing these last activated carbons important contributors to mesopores. The resulting materials were tested in the adsorption of sulfamethoxazole from aqueous solution. The adsorption capacity was determined by the porous texture rather than by the surface composition, and analyzed by FTIR and TPD. The adsorption equilibrium data (20 degrees C) fitted the Langmuir equation well. The KOH-activated carbons yielded fairly high saturation capacity reaching up to 650 mg.g(-1).