Abstract: Ionic liquids are promising green replacements for the traditional volatile organic solvents.The mechanism study of nanomaterials preparation in ionic liquids via ultrasonic irradiation has been rarely exploited.In this work,a simple,fast and green approach for the preparation of zinc oxide nanorods has been firstly achieved in room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with ultrasound.The as-prepared samples are characterized by X-ray diffraction,transmission electron microscopy.For comparison,zinc oxide nanomaterials have been prepared under the same experimental condition in triethylene glycol,a conventional organic solvent with low vapor pressure.It is found that nanorods with diameters of about 20 nm and lengths from 30 nm to 50 nm are obtained in ionic liquid via ultrasonic irradiation,while nanoparticles are obtained in the conventional organic solution.Photoacoustic spectroscopy (PAS) has been used to study the optical properties and quantum size effect of the samples.A possible mechanism is proposed to explain the formation of ZnO nanorods in the ionic liquid via ultrasonic irradiation,and a reaction model is also established.The result shows that ZnO nanorods can be obtained by combining the advantages of both room temperature ionic liquid and ultrasound.