In-situ deep eutectic solvent enhance hydrothermal carbonization of garden waste for methylene blue removal

Abstract

Modification of hydrochar requires either toxic chemicals or high temperature during the hydrothermal carbonization process, which are the main shortcomings for industrial upgrading and cleaner production of hydrochar. Herein, a novel green catalyst formed by in-situ deep eutectic solvent (DES, i.e. ChCl-H2O) and inorganic salt (FeCl3) was developed to prepare hydrochars derived from garden waste under low temperature for removing methylene blue (MB). The effects of key operational parameters including different temperatures (160 °C–260 °C), reacting time (3–9 h) on hydrochars performance were firstly evaluated. It was found that the adsorption capacity of hydrochar on MB reached its highest value of 169.19 mg/g at the optimal temperature of 180 °C for 5 h. Subsequent adsorption kinetics study showed that the obtained data fitted better to the pseudo-second-order kinetics. The results indicated that DES and inorganic salts could be used to effectively prepare hydrochar in hydrothermal carbonization process.