Azadeh Askarinejad - Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box ۱۴۱۵۵-۴۸۳۸,
S Khanjani
N Soltazadeh
Z Rashidi Ranjbar

The development of metal oxide nanocrystals has been intensively pursued because of their useful applications in catalysis, energy storage, magnetic data storage, sensors and ferrofluids [1-4]. A spinel structure is formed by a nearly closepacked fcc array of anions with holes partly filled by the cations can be represented by the formula AB2O4 [5], where A represents metallic ions located in A interstitial (tetrahedral) sites and B metallic ions located in B (octahedral) sites. Spinel cobalt oxide (Co3O4) is considered to be an important functional material, and has been widely used in electrochemistry, magnetism, catalysis and energy storage [6-14]. Many methods have been attempted to prepare nanoscale cobalt oxide, including solid state reaction [15], hydrothermal reaction [16], sodium nitrate-mediated synthesis [17,18], and microwave irradiation [19] and so on. Manganese oxide (Mn3O4, trimanganese tetroxide, Hausmannite) is currently used in many industrial application domains as catalysis, magnetism, electrochemistry or air decontamination. In order to offer better performances due to its size and/or its morphology toward these applications, Mn3O4 is prepared by various methods. The properties of the metal oxides are influenced by the structure and morphologies including crystallite sizes, orientations, stacking manners and aspect ratios, which are sensitive to the preparation methodology used in their synthesis [20].Recently, sonochemical synthesis, an alternative means to the general synthetic methods, has been used in the preparation of many materials. Ultrasound induces chemical changes due to cavitation phenomena involving the formation, growth, and instantaneously implosive collapse of bubbles in liquid, which can generate local hot spots having a temperature of roughly 5000 °C, pressures of about 500 atm, and a lifetime of a few microseconds [21]. These extreme conditions can drive chemical reactions such as oxidation, reduction, dissolution, and decomposition, which have been developed to fabricate a variety of metal, oxide, sulfide, and carbide nanoparticles [22-26].In this study, nano-crystalline transition metal oxide (Co3O4, Mn3O4) powders are prepared via a one-step sonochemical method. Metal oxide particles with different crystallite sizes, morphologies and degree of crystallinity are obtained at various conditions. The powders were characterized by XRD, TGA/DTA, SEM, TEM and FTIR spectroscopy