Magnetite Nanocrystals

1 Maghemite and Magnetite Nanocrystals One of the first syntheses of magnetite nanocrystals employed aqueous solutions of FeCl2 and FeCfi, and was reported by Massart [95]. The chemical reaction leading to the Fe304 phase occurred at pH 8-14 under airless conditions the process can be expressed as  

The thermal decomposition of organometallic compounds in high-boiling solvents in the presence of stabilizers has been widely investigated, and is currently used for the synthesis of Fe304 and y-Fe203 nanocrystals. Iron carbonyls [68, 98], acetylacetonate [99] and iron fatty acid salts [100, 101] are the typical precursors, while oleic acid and other fatty acids, as well as oleylamine and other aliphatic amines, are the most frequently used surfactants. The important parameters for controlling 

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. 

A simple, inexpensive and reprodudble method for produdng monodisperse Fe304 nanocrystals by the pyrolysis of iron-oleates was independently proposed in 2004 by the groups of Peng [100], Hyeon [101], and Colvin [104]. In this case, the 

Chemical Society (c) 80 nm Fe304 cubes. Reproduced with permission from Ref [108] 2009, American Chemical Society (d) 7- 6203 tetrapods. Reproduced with permission from Ref [109] 2006, American Chemical Society. 

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Li, Z Sun, Q. and Gao, M.Y. (2005) Preparation of water-soluble magnetite nanocrystals from hydrated ferric salts in 2-pyrrolidone mechanism leading to Fe304. Angewandte Chemie International Edition, 44 (1), 123-126. 

Emulsifier-free miniemulsion polymerization with [2, 2-azobis (2-amidinopropane) dihydrochloride (V50)] as initiator was also used for the encapsulation of oleic acid/magnetite nanocrystals in styrene [156, 157] or chloromethyl-styrene for further functionalization [158]. 

The magnetite nanocrystals we discussed in Chapter 33 are used by nature in ways we do not fully understand, but they appear to allow certain species to detect the earth s magnetic field and use it to navigate. 

Ye, X.R. Daraio, C. Wang, C. Talbot, J.B. Jin, S. (2006), Room temperature solvent-free synthesis of monodisperse magnetite nanocrystals. J. Nanosci Nanotechnol., 6 852-... 

With use of Fe (II)-stearate as the precursor, the magnetite nanocrystals of about 3 nm in size can be prepared by using alkylamine as the activation reagents [337]. In a typical synthesis, 0.622 g of iron stearate and 0.269 g of octadecylamine were mixed with 5 mL of octadecene and heated to 300 °C under an argon atmosphere. The... 

Kim, J. et al (2008) Multifunctional uniform nanoparticles composed of a magnetite nanocrystal core and a mesoporous silica shell for magnetic resonance and fluorescence imaging and for drug delivery. Angew. Chem., Int Ed., 47 (44), 8438-8441. 

Xu, F. et al (2009) Superparamagnetic magnetite nanocrystal clusters a sensitive tool for MR cellular imaging. Nanotechnology, 20 (40), 405102. 

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