Colloids and Surfaces A: Physicochem. Eng. Aspects 292 (2007) 83–85 Short communication A simple route for the attachment of colloidal nanocrystals to noncovalently modified multiwalled carbon nanotubes Maciej Olek, Michael Hilgendorff, Michael Giersig ∗ Center of Advanced European Studies and Research (CAESAR), Ludwig-Erhard Allee 2, 53175 Bonn, Germany Received 9 March 2006; received in revised form 2 May 2006; accepted 11 May 2006 Available online 17 May 2006 Abstract A simple strategy for the fabrication of multiwalled carbon nanotubes (MWNTs)–nanocrystal (NC) heterostructures is shown. Different nanopar- ticles can be covalently coupled to functionalized carbon nanotubes (CNTs) in a uniform and controllable manner. MWNTs have been functionalized by a polymer wrapping—technique that is non-invasive, and does not introduce defects to the structure of CNTs; the polymer is noncovalently adsorbed on the MWNT’s surface. Moreover, this method ensures good dispersion and high stability in any commonly used organic or inorganic solvent. In this manner, our strategy allows the attachment of various colloidal nanoparticles to CNTs, independent of their surface properties, i.e. hydrophilic or hydrophobic. © 2006 Published by Elsevier B.V. Keywords: Carbon nanotubes; Composites; Nanoparticles; Functionalization 1. Introduction The unique mechanical, optical, and electrical properties [1–3] of carbon nanotubes (CNTs) make them very attractive building blocks for the fabrication of advanced materials with improved performance or even with new properties. However, the functionalization of CNTs requires chemical modifications of their surface, in order to overcome the poor solubility in solvents, and polymers to ensure good processability of car- bon nanotubes. Several functionalization strategies have been reported recently. They are based on the covalent (“grafting-to” and “grafting-from”) [4–6] and non-covalent (polymer wrapping [7–9], – stacking interaction [10], adsorption of surfactants [11]) coupling of surfactants to CNTs. The covalent function- alization strategy in many cases exploits oxidized nanotubes in amidation or esterification reactions [6], which significantly alters the optical, mechanical and electrical properties of CNTs due to the modifications introduced to the graphene structure by oxidation [3,12]. Obviously, oxidation leads to numerous side defects along the entire length of CNTs, and consequently dis- ∗ Corresponding author. Tel.: +49 228 6956210; fax: +49 228 6956187. E-mail address: giersig@hmi.de (M. Giersig). rupts the  bonding symmetry of the sp2 hybridization, thus it affects properties of the CNTs. Collins et al. [13,14] has shown that it is possible to manipulate the electrical properties of MWNTs by the sequential destruction of individual nanotube shells. The utilization of oxidized CNTs also leads to random coverage of carbon nanotubes with nanocrystals (NCs) in par- ticular, nanoparticles (NPs) tend to be attached at the ends of carbon nanotubes and defect sides, where the concentration of carboxylic groups is the highest. In this context the non- covalent modification of carbon nanotubes is of great advantage because no disruption of the sp2 graphene structure occurs and nearly all of the CNTs’ properties are preserved. Recently, it was shown, that the physical properties of CNTs can be significantly affected, beside chemical surface modifications, by the attach- ment of inorganic-, organic-, and biological objects [15]. This leads to new methods for the invention of novel one-dimensional (1D) hybrid materials. Numerous strategies have been presented where CNTs were successfully coupled to various nanoparti- cles, such as metals, ceramics [16–18], and, semiconductors [12,19–25]. Enhanced or even new properties of those CNT- NP heterostructures were reported; which again opens up new potentials for a broad range of applications including elec- tronic and optic devices, sensors, solar cells, and catalytic materials. 0927-7757/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.colsurfa.2006.05.014