Nanocrystal Synthesis Iron Oxides

Yu, W.W., Falkner, J.C., Yavuz, C.T. and Colvin, V.L. (2004) Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts. Chemical Communications, (20), 2306-2307. 

Gonzales M, Krishnan MK (2005) Synthesis of magnetoliposomes with monodisperse iron oxide nanocrystal cores for hyperthermia. J Magn Magn Mater 293 265-270... 

Heat-up is a simple but effective method of synthesizing highly uniform nanocrystals, which yields a degree of size uniformity comparable to that of the best result from the hot injection method. This method is adopted mainly for the synthesis of metal oxide nanocrystals. In this section, we describe the synthetic procedure of iron oxide nanocrystals via the heat-up method as a representative example (23-25). 

The precursors used for the iron oxide nanocrystal synthesis via the heat-up method are various iron carboxylatc complexes, including the most widely used iron-oleate complex. Generally, when heated, metal carboxylatc complexes thermally decompose at temperatures near 300°C or higher to produce metal oxide nanocrystals along with some byproducts, such as CO, CO2, H2, water, ketones, esters, and various hydrocarbons. It is thought that the decomposition reaction proceeds via the formation of thermal See radicals liom metal carboxylatc (26, 27) ... 

In the synthesis of the nanocrystals, a homogeneous iron-oleate solution prepared at room temperature is heated to 320°C, which is the thermal decomposition temperature of iron-oleate complex, and held at that temperature (24). As shown in Figure 6.13, the curve for the reaction extent of the thermal decomposition of iron-oleate complex in the solution shows a sigmoidal shape, which is typical of autocatalytic reactions. Interestingly, there is a time lag between the onset of the reaction extent curve and the initiation of the nanocrystal formation. As shown in the right of the figure, when the solution temperature just reaches 320°C, there is a trace amount of nanocrystals in the solution while about half of the iron-oleate complex has already been decomposed. This implies that iron oxide crystal is not a direct product of the thermal decomposition of iron-oleate complex. Rather, when iron-oleate complex is thermally... 

Interest in iron carbonyl as a precursor for nanomaterials has been revived during the past decade such that, in 2001, Hyeon et al. reported the synthesis of monodisperse 4—16 nm Y-Fe203 nanocrystals from iron pentacarbonyl in octyl ether in the presence of either oleic or lauric adds as surface ligands [68]. In this approach, highly reactive Fe(CO)5 first formed iron-oleate complexes, the subsequent decomposition of which at 300 ° C led to the formation of transient metallic iron spedes or strongly reduced iron oxocomplexes, followed by their oxidation to the y-FezOs phase by introducing (CH3)3NO into the reaction mixture. 

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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