Synthesis of shape-controlled and organic-hybridized hafnium oxide nanoparticles under sub- and supercritical hydrothermal conditions

► Supercritical hydrothermal method as a green process is used to synthesize HfO2 NPs. ► The effect of sub- and supercritical water on the NP morphology is investigated. ► The surface properties of NPs are controlled using organic surface modifiers. ► NP size and morphology were affected by modifiers with different functional groups.