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A simple method has been developed for direct synthesis of magnetic multi-walled carbon nanotubes (MWCNTs) homogeneously decorated with size -controllable Fe nanoparticles (Fe-NPs) encapsulated by graphitic layers on the MWCNT surface by pyrolysis of ferrocene. These composites have similar C/Fe atomic ratio of similar to 10 and exhibit sufficiently high saturation magnetization for magnetic separation in a liquid phase. Moreover, with 0, similar to 1, similar to 2 wt% sulfur as growth promoter, the size of Fe-NPs can be controlled with an average diameter of similar to 5, similar to 22 and similar to 42 nm, respectively. When compared to time-consuming wet-chemical methods, the simplicity of this method should allow easy large-scale production of these magnetically functionalized MWCNTs, which can be used as catalyst supports with high stability for effective magnetic separation in liquid-phase reactions, especially under acid/basic conditions. (C) 2008 Elsevier Ltd. All rights reserved.