Thionine-interlinked multi-walled carbon nanotube/gold nanoparticle composites Zhijuan Wang a,b , Meiye Li c , Yuanjian Zhang a , Junhua Yuan a , Yanfei Shen a , Li Niu a, * , Ari Ivaska b a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate University of the Chinese Academy of Sciences, Chinese Academy of Sciences, Changchun 130022, PR China b Laboratory of Analytical Chemistry, Process Chemistry Centre, A ˚ bo Akademi University, Biskopsgatan 8, FI-20500 A ˚ bo-Turku, Finland c National Analytical Research Center of Electrochemistry and Spectroscopy, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China Received 13 February 2007; accepted 17 May 2007 Available online 2 June 2007 Abstract Multi-walled carbon nanotube (MWCNT)/thionine/gold nanoparticle composites were prepared by binding gold nanoparticles to the surfaces of thionine-coated carbon nanotubes. TEM images show gold nanoparticles distributed uniformly on nanotube walls and ends. UV–Vis, Raman, FT-IR, and zeta potential measurements were used to examine the properties of the resulting products. The composites demonstrate significant electrocatalytic activity for oxygen reduction. Although only gold nanoparticles were investigated here, the method could be easily extended to attach other metallic nanoparticles to the sidewalls of carbon nanotubes. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) can be considered ideal tem- plates for formation of one-dimensional nanoparticle assemblies due to their unique structural, mechanical, elec- tronic and thermal properties. However, pristine CNTs often exhibit poor solubility and tend to aggregate in aque- ous environments [1], lack fluorescence in the visible range [2], or may be toxic [3]. A promising approach to overcom- ing these limitations is surface functionalization with groups that confer desirable properties [4,5]. CNT/nanoparticle hybrid materials, in which nanoparticles are attached to CNT surfaces, have been reported to exhibit catalytic activ- ity, enhanced electrical conductivity, and hydrogen-sensing capability [6], suggesting broad potential application in optoelectronics [7], molecular sensors [8] and heterogeneous catalysis. In particular, nanometal-CNT composites, e.g., single-walled-carbon-nanotube (SWCNT)-supported plati- num [9] and multi-walled-carbon-nanotube (MWCNT)- supported Pd, Rh, and Rh/Pd [10], have been prepared by a variety of methods, including physical vapor deposition [11], thermal decomposition [12], electroless deposition [13], and polymer-assisted hybridization [14]. Certain properties of gold nanoparticles (e.g., quantized charging/discharging [15,16], conductivity [17], and cata- lytic [18] and photocatalytic [19] activity) suggest that gold-nanoparticle-functionalized MWCNTs may prove applicable in future fabrication of nanodevices, enabling further miniaturization of integrated circuits [20]. In this work, Au nanoparticles were non-covalently attached to MWCNTs in the presence of thionine (see Fig. 1). In solu- tion, thionine in protonated form (Thi + ) is shown to adsorb to MWCNT walls via p–p stacking interaction. Upon sub- sequent addition of negatively charged gold nanoparticles, electrostatic interaction with thionine serves to ‘‘glue’’ the 0008-6223/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2007.05.018 * Corresponding author. Fax: +86 431 8526 2800. E-mail address: lniu@ciac.jl.cn (L. Niu). www.elsevier.com/locate/carbon Carbon 45 (2007) 2111–2115