Cobalt oxide nanocrystals

Liang, Y., et al., Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes. Journal of the American Chemical Society, 2012.134(38) p. 15849-15857. 

A very recent novel hquid-phase route to hollow nanocrystals of cobalt oxide and cobalt sulfide takes advantage of the Kirkendall effect (Section 6.4.1). Injection of sulfur or oxygen into a colloidal cobalt nanocrystal dispersion created hollow nanocrystals of... 

Apart from solvothermal methods, thermolysis of precursors in higli boiling solvents, the sol-gel method, hydrolysis and use of micelles have been employed to synthesize the metal oxide nanocrystals. Thus, Park et al. have used metal-oleates as precursors for the preparation of monodisperse Fe,0, MnO and CoO nanocrystals. 1-Octadecene, octyl ether and trioctylamine have been used as solvents. Hexagonal and cubic CoO nanocrystals can be prepared by the decomposition of cobalt acetylaceto-... 

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... 

Zhu et al. [109] proposed an environmentally innocuous method of preparation by using a single-step solvothermal route in ethanol solutions. The procedure leads to simultaneous rGO reduction and iron or cobalt oxide precipitation due to the fact that the GO/rGO layers act as heterogeneous nucleation seeds during the precipitation of the metal oxide nanocrystals. In a related approach, Han et al. [110] were able to obtain Li4Ti50i2 particles anchored to rGO by solvothermal treatment of H2O/ EtOH-based suspensions of graphite oxide and the oxide powder. The process involves reduction of GO and attachment of the mixed oxide nanoparticles within a single step. 

Using a similar procedure, based on the thermal decomposition of a metal-surfactant complex followed by mild oxidation, we synthesized highly crystalline and monodisperse nanocrystals of cobalt ferrite (CoFc204), manganese ferrite (MnFe204) MnO, and Ni [5]. 

Solution phase chemical synthesis is a convenient way for making surfactant coated magnetic nanoparticles, as described in various reviews [12-18]. Monodisperse Co nanoparticles with standard deviation less than 10% are synthesized by decomposition of Co2(CO)8 [19-22] or Co(rj3-C8Hi3X n4-C8Hi2) [23] and reduction of cobalt salt [24,25] in the presence of oleic acid and trialkylphosphine, or trialkylphosphine oxide, or alkylamine. Monodisperse iron nanoparticles are normally prepared from decomposition of Fe(CO)5 [26-28]. However, metallic iron-based particles from this decomposition procedure are difficult to characterize due to the chemical instability. A recent synthesis using decomposition of Fe[NSiMe3)2]2 offers a promising approach to monodisperse Fe nanocrystals [29]. 

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