This project studies the relationship between the carbonization temperature and ionic liquid (IL) ([Bmim] Cl and [Bmim]OAC) solution and its impact on the structure, properties and gasification reactivity of the hydrochar obtained from eucalyptus via hydrothermal carbonization (HTC). The structure of hydrochar was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy while its gasification reactivity with air was measured by thermogravimetric analysis at 340 degrees C. Results showed that the reactivity of hydrochar prepared in the presence of IL was much higher than that prepared using water. SEM analysis revealed some vesicles on the hydrochar surface during HTC at 220 degrees C, while Raman and XRD results showed more disordered crystal structure of the hydrochar in the presence of ILs. XPS and Raman results revealed that C-O contents on the hydrochar surface increased after adding IL which implied that IL can promote opening the loop of aromatic nucleus of biomass. This study provides important information for the preparation of highly active biochar based on IL assisted HTC of eucalyptus for practical applications. (C) 2020 Elsevier Inc. All rights reserved.