Metal oxide-based nanostructures nanoparticles

With the advent of synthetic methods to produce more advanced model systems (cluster- or nanoparticle-based systems either in the gas phase or on planar surfaces), we come to the modern age of surface chemistry and heterogeneous catalysis. Castleman and coworkers demonstrate the large influence that charge, size, and composition of metal oxide clusters generated in the gas phase can have on the mechanism of a catalytic reaction. Rupprechter (Chap. 15) reports on the stmctural and catalytic properties of planar noble metal nanocrystals on thin oxide support films in vacuum and under high-pressure conditions. The theme of model systems of nanoparticles supported on planar metal oxide substrates is continued with a chapter on the formation of planar catalyst based on size-selected cluster deposition methods. In a second contribution from Rupprecther (Chap. 17), the complexities of surface chemistry and heterogeneous catalysis on metal oxide films and nanostructures, where the extension of the bulk structure to the surface often does not occur and the surface chemistry is often dominated by surface defects, are discussed. 

Other uses of nanostructured chromophores may include fluorescent nanoparticles or nanoparticle-based porous materials that change their light absorption or emission when a toxin is encountered. Some metal oxides and POMs already exhibit such properties. Likewise, electrochemical properties, including induced photocurrents, could be sensitive to encountering a toxin. Clearly, both decontamination and detection are relevant aspects here. Basic research is needed on the design and synthesis of engineered nanostructures whose electronic structures, thermal catalytic, photophysical (emission), and photocatalytic properties are strongly perturbed by the presence or absence of toxic compounds. 

Hollow Magnetic Nanocrystals Hollow nanoscale stmctures were first obtained by Y. Yin during the sulfurization of cobalt nanocrystals at elevated temperatures [145]. This process was found to lead to the formation of hollow cobalt sulfide nanocrystals such that, depending on the size of the cobalt nanocrystals and the cobalt sulfur molar ratio, different stoichiometries of hollow cobalt sulfide could be obtained. Hollow nanostmctures are usually formed through the nanoscale Kirkendall effect, which is based on the difference in diffusion rates of two species, and results in an accumulation and condensation of vacancies [146]. This phenomenon was first observed by Kirkendall at the interface of copper and zinc in brass in 1947 [147]. As a typical example of the nano-Kirkendall effect, the controllable oxidation of iron nanoparticles by air can lead to the formation of hollow iron oxide nanostructures, as shown in Figure 3.137. During the course of metal nanoparticle oxidation, the outward diffusion of metal occurs much faster in... 

Much work has been focused on the synthesis of metal, alloy, and metal oxide nanostructures in order to enhance their activities. Nanoparticle-based catalysts... 

Besides the conducting polymer-based nanostructured materials, organic hybrid nanocomposites, especially chitosan and Nafion, metal/metal oxide nanoparticles are being explored for effective and efficient biosensor fabrication. Such hybrid nanocomposites show properties different from their parent constituent precursors and are dependent on concentration of precursors, their morphology, and novel interfacial characteristics. 

Incorporation of an inorganic secondary component into the matrix of conducting polymers is a useful approach to improve the functionality of conducting polymer-based nanocomposites. Nanoparticles of metal or metal oxide and other nanostructures such as graphene, carbon nanotubes (CNT) are used as dispersoid within conducting polymer matrix depending on the requirements. The shape, size, aspect ratio and the interfacial adhesion between the matrix and dispersoid affect the properties of the hybrid nanocomposites [28]. The synthesis, properties, and applications of different conducting polymer-based hybrid nanocomposites are discussed below. 

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