Synthesis, characterization and absorbability of Crocus sativus petals hydrothermal carbonized hydrochar and activated hydrochar

An environmentally friendly adsorbent for the removal of lead (II) ions from aqueous solutions was prepared by hydrothermal carbonized of KOH activated Crocus sativus petals, generated as an agricultural residue. The influence of the operating parameters in the hydrothermal carbonization process on Pb 2+ adsorption capacity was evaluated by an artificial neural network method. The pore structure, morphology, functional groups and elemental composition of the activated hydrochar were characterized. The reaction temperature and residence time were found to be the main parameter affecting the physicochemical properties of the produced hydrochar. The optimal conditions of hydrothermal carbonization towards lead ions adsorption were as follows: temperature of 180 °C, residence time of 11.5 h, water/biomass ratio of 10 and ZnCl 2 /biomass ratio of 1.5, resulting in an adsorption capacity of 89.52 mg g −1 . The optimal hydrochar was selected for further investigation, including the kinetics and isotherms of adsorption.