Activated Carbons from Hydrothermal Carbonization and Chemical Activation of Olive Stones: Application in Sulfamethoxazole Adsorption

This work focuses on the production of activated carbons by hydrothermal carbonization of olive stones at 220 °C, followed by chemical activation with KOH, FeCl3 and H3PO4 of the hydrochar obtained. In addition, N-doped hydrochars were also obtained by performing the hydrothermal carbonization process with the addition of (NH4)2SO4. All hydrochars, N-doped and non-doped, showed low BET surface areas (4–18 m2 g−1). Activated hydrochars prepared using H3PO4 or KOH as activating agents presented BET surface areas of 1115 and 2122 m2 g−1, respectively, and those prepared from N-doped hydrochar showed BET surface area values between 1116 and 2048 m2 g−1 with an important contribution of mesoporosity (0.55–1.24 cm3 g−1). The preparation procedure also derived inactivated hydrochars with predominantly acidic or basic groups on their surface. The resulting materials were tested in the adsorption of sulfamethoxazole in water. The adsorption capacity depended on both the porous texture and the electrostatic interactions between the adsorbent and the adsorbate. The adsorption equilibrium data (20 °C) fitted fairly well to the Langmuir equation, and even better to the Freundlich equation, resulting in the non-doped hydrochar activated with the KOH as the best adsorbent.