From hydrothermal carbonization to blue hydrochars and activated carbons : Adsorption of volatile organic compounds and heavy metals

Abstract: Hydrothermal carbonization of carbohydrate and biomass is a straightforward method for preparing hydrochars at low temperature. Hydrochars are more carbonized than their precursors. Hydrochars themselves are carbon precursors for preparing activated carbons. Activated carbons are porous materials that can be used for water and air purification. In my first study (Paper I), I have focused on hydrothermal carbonization of glucose in presence of iron (II)sulfate. By changing the concentration of iron (II) sulfate, with a catalytic amount, blue hydrochars were formed at the bottom of the autoclave. The blueness was related to thin film interference. The thin film hydrochars were more carbonized than spherical hydrochars and the yield of HTC has increased in presence of iron (II)sulfate. The second study (Paper II) is focused on the activation of hydrochars with H3PO4 and H3PO4+FeCl3. We showed that ultramicroporsity and impregnated iron phosphate species enhance the adsorption of VOCs at low pressure. The ACs were impregnated with Fe(PO3)2 and it is shown that Fe(PO3)2 acts as an activation agent which opens up for future studies. In the third study (Paper III), H3PO4 activated carbons were prepared and impregnated with FeS and FeSe. ACs were used for the removal of Cd2+ and Pb2+ in the third study. The uptake of heavy metals by FeS/AC and FeSe/ACs was significantly increased compared to other studies in the literature. In the last study (Paper IV), prickly pear seed biomass from agro sector in Tunisia was hydrothermal carbonized. The hydrochars were then activated into ACs by CO2 activation. The life cycle assessment of the HTC and activation process was investigated.