ABSTRACT
Great progress has been achieved in ultrasound-assisted synthesis of a variety of nanomaterials. This chapter reviews the recent advances in nanostructured metal oxides. Two different ultrasound-assisted synthetic methods, namely sonochemistry and ultrasonic spray pyrolysis, are discussed. The principle and mechanisms are briefly introduced and detailed synthesis, characterization, and applications are described. Perspectives for both methods are also presented. 4.1 IntroductionNanostructured metal oxides with unique optical, electrical, and magnetic properties are promising candidates for diverse applica-tions in electronics, catalysis, sensors, environmental remediation,
magnetic storage, and biotechnology (Sue et al., 2006). These prop-erties are dependent not only on the composition but also on the particle size, morphology, surface area, and crystallinity (Zhou et al., 2006). Various approaches have been developed for the control-led synthesis of metal oxide nanoparticles. These include sol-gel, mechanochemical, chemical vapor deposition, electrochemical, hy-drothermal/solvothermal, solid-state, coprecipitation, microwave-assisted, microemulsion, and combustion methods (Sue et al., 2006). However, most of these methods are laborious, highly energy-con-suming, and not environmental-friendly due to the involvement of high temperature calcination, long reaction time, and the require-ment of toxic-stabilizing agents. Thus, facile, time-saving, green, and effective approaches are desirable. The utilization of high-intensity ultrasound in the synthesis of nanomaterials including metal, metal oxide, metal chalcogenides, and carbides has been widely studied for many years. It has been considered as an alternative to satisfy the above-mentioned requirements (Bang and Suslick, 2010; Gedanken, 2004). Also, the ultrasound-assisted method could generate novel materials with unique properties. The primary physical phenomena associated with ultrasound that are responsible for materials synthesis are cavitation and nebulization, corresponding to the sonochemical and ultrasonic spray pyrolysis (USP)-assisted methods. This chapter focuses on the ultrasound-assisted synthesis of metal oxide nanoparticles with different functions.
