Template-free, low temperature synthesis of binary and ternary metal oxide nanostructures
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Template-free, low temperature synthesis of binary and ternary metal oxide nanostructures Sanjaya Brahma, Pallavi Arod, and S.A. Shivashankar Materials Research Centre, Indian Institute of Science, Bangalore-560012, India ABSTRACT We report synthesis of some binary and ternary metal oxide nanostructures using microwave irradiation-assisted chemical synthesis, either in the presence or absence of a surfactant/structure directing agent. The method is simple, inexpensive, and yields nanoparticles of desired metal oxides in minutes, and requires no conventional templating. Nanoparticles of some functionally advanced binary/ternary metal oxides (MnO2, ZnO, CuO, ZnMn2O4 etc) have been synthesized using metal acetylacetonates as the starting precursor material and microwave as the source of energy, in a process developed in detail in our laboratory. The nanoparticle size varies from 7-50 nm. Emphasis has been placed on the synthesis of ZnO nanostructures, particularly ZnO nanoshells, which do not require any surfactant/structure-directing agent for synthesis. There is a systematic variation in the morphology of the ZnO nanostructures with variation of process parameters, such as microwave power, microwave irradiation time, type of solvents, surfactants/structure-directing agents and its type and concentration. The as-prepared powder sample may either need a very brief exposure to heat to remove the surfactant or no postsynthesis processing, and is found to be well-crystallised. Determination of their crystallinity, actual shape, and orientation was made using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). INTRODUCTION Metal oxide nanoparticles/nanostructures have been the subject of intense research recently because of significant variation of properties (physical, chemical, electronic and optical) in nanometer regime. Oxides in particular are of interest because of their compositional characteristics: cations with mixed valence states, resulting from anion non-stoichiometry. Such variation leads to the possibility of tuning electrical, magnetic, chemical and optical properties. Synthesis of metal oxide nanoparticles such as Cr2O3 [1], Fe2O3 [2], SnO2 [3], and CeO2 [4] using a surfactant in the growth medium has been reported. However, the methods used to prepare such nanoparticles are often energy- and time-consuming. Surfactant-mediated growth of metal oxide nanostructures has been studied recently in great detail but, in many cases, the synthesis is tedious and time consuming and in some cases it needs lengthy post-synthesis processing to get the desired purified powder material. It is therefore desirable to modify the synthesis procedure where the need for any kind of post-synthesis processing is removed, thereby increasing homogeneity and purity of the powder material, thus making the synthesis procedure simple, inexpensive, less cumbersome, and time-saving. We have thus investigated the potential of using microwave-assisted chemical reactions to obtain nanostructures
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