Large-scalepreparationofcarbon-encapsulatedcobalt nanoparticlesbythecatalyticmethod B.H.Liu a ,J.Ding a, * ,Z.Y.Zhong b ,Z.L.Dong c ,T.White c ,J.Y.Lin b a Department of Materials Science, Faculty of Science, National University of Singapore, Lower Kent Ridge Road, Singapore 119260, Singapore b Physics Department, National University of Singapore, Singapore 119260, Singapore c Environmental Technological Institute of Singapore, Singapore 637723, Singapore Received6December2001;infinalform5April2002 Abstract Withstrategicalselectionofthewater-solublesodiumchloride(NaCl)asthesupportingmaterial,werealizedlarge- scaleproductionofcarbon-encapsulatedcobaltnanoparticleswithaproductivityofalmost100%.Theproductscanbe fullyseparatedfromthesupportingmaterialsbysimplewashingprocess.WhenNaCl,NaFandAl 2 O 3 wereusedas supporting materials, the morphologies of the carbon products changed from carbon-encapsulated magnetic nano- particles (CEMNs) to an intermediate state (quasi-nanocages) between CEMNs and carbon nanotubes (CNTs), and thentoCNTs,respectively.NaClshowsstronginhibitingeffectsonthegrowthofCNTs,favoringtheformationof CEMNs. Ó 2002PublishedbyElsevierScienceB.V. 1. Introduction Magnetic metal nanoparticles (such as Fe and Co)havewiderangeofapplicationssuchashigh- densitymagneticdatastorage,magnetictonersin xerography, magnetic inks and ferrofluids [1,2]. However,thepooroxidationresistanceofthebare metalnanoparticlessetsagreatbarricadeforfur- ther exploring their applications. In the past few years, carbon-encapsulated magnetic nanoparti- cles (CEMNs) have aroused great research inter- ests around the world due to the fact that the protective carbon layers prevent the rapid envi- ronmental degradation of bare metal nanoparti- cles. Moreover, the carbon coatings can endow thesemagneticparticleswiththebiocompatibility andstabilityinmanyorganicandinorganicmedia. These combined attributes make CEMNs the in- terestingcandidatesformanybio-engineeringap- plications including drug delivery, biosensors, magnetic hyperthermia and magnetic contrast agentsformagneticresonanceimaging[3,4]. Various techniques have been developed for synthesizingCEMNs,suchasstandardcarbonarc techniques [5], tungsten arc technique [6], magne- tron and ion-beam co-sputtering, [7] RF plasma torch technique [8], and modified arc deposition technique [9]. However, these techniques are ap- parently not suitable for producing CEMNs in 24June2002 ChemicalPhysicsLetters358(2002)96–102 www.elsevier.com/locate/cplett * Correspondingauthor.Fax:+65-776-3604. E-mail address: masdingj@nus.edu.sg (J.Ding). 0009-2614/02/$-seefrontmatter Ó 2002PublishedbyElsevierScienceB.V. PII:S0009-2614(02)00592-4