Journal of Alloys and Compounds 480 (2009) 534–536 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Surface functionalization of multi-walled carbon nanotubes via electron reduction of benzophenone by potassium metal T.P. Chua, M. Mariatti ∗ , A. Azizan, A.A. Rashid School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia article info Article history: Received 15 December 2008 Received in revised form 17 January 2009 Accepted 22 January 2009 Available online 6 February 2009 Keywords: Nanostructured materials Surface and interface Microstructure Thermal analysis Transmission electron microscopy abstract The covalent sidewall functionalization of multi-walled carbon nanotubes (MWCNTs) via the electron reduction of benzophenone by potassium metal is reported. Fourier transform infrared spectroscopy (FTIR) results show that diphenylcarbinol (DPC) groups were successfully grafted to the MWCNTs side- walls after 10 days of reaction time. Raman and UV–vis spectroscopies reveal the presence of covalent sidewall functionalization. The percentage of residues for DPC-MWCNTs was found to be lower than that for pristine MWCNTs, which indicates the existence of functional groups on the sidewalls of DPC- MWCNTs. It is shown that the sidewall of the DPC-MWCNTs was covered by non-uniform layer of DPC, as observed by transmission electron microscopy (TEM). Results from Raman spectroscopy, FTIR, TGA, UV–vis spectroscopy and TEM confirm that the functionalization of the covalent sidewalls of MWCNTs was successfully performed by this method. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanotubes (CNTs), discovered in 1991 [1] by Iijima, are of keen interest to material scientists due to their remarkable physical, mechanical, chemical and electronic properties, which exceed those of many other materials [2–5]. Such properties make carbon nanotubes ideally suitable as the “ultimate material” for next-generation composites [6]. These properties are attractive for applications in many scientific and technological fields, such as polymer composites [7], electronic structures [8] and biological systems [9]. Although several studies have focused on produc- ing nanocomposites [2–4], many practical challenges concerning their properties remain, compromising the full realization of their enormous potential. For example, many experiments indicate that carbon nanotubes in composites are weaker or only slightly stronger than the neat matrix [10]. This has been found to be pri- marily due to a combination for several factors, namely poor CNT dispersion, inadequate alignment, and weak interfacial bonding [11]. It was reported that covalent sidewall functionalizations can be used to overcome some of these difficulties [11,12]. In order to improve the properties of CNTs, several methods for sidewall functionalization have been developed, such as the addition of carbine [13], fluorine [14] and potassium. Covalent side- wall functionalization of single wall carbon nanotubes (SWCNTs) by one-electron reduction of benzophenone by potassium has been ∗ Corresponding author. Tel.: +60 4 599 52 62; fax: +60 4 594 10 11. E-mail address: mariatti@eng.usm.my (M. Mariatti). carried out by Wei and Zhang [15]. This functionalization process is reported to have successfully introduced diphenylcarbinol groups onto the sidewalls of the nanotubes. In this study, a similar method was repeated on multi-walled carbon nanotubes (MWCNTs), and due to the slight differences between SWCNTs and MWCNTs, the optimal reaction time has also been investigated. 2. Experimental 2.1. General Multi-walled carbon nanotubes (MWCNTs) with a purity of >95%, outer diame- ters of <10 nm and lengths of 1–2 m were supplied by ShenZhen Nanotech Port Co., Ltd., China. The chemicals used in this study were toluene (supplied by J.T. Baker), benzophenone (supplied by Fluka) and potassium, ethanol and dried ethanol (sup- plied by Merck). Structural characterization of MWCNTs was done using a Renishaw invia Raman Spectroscope. Ar + lasers with a wavelength of 514nm were used to characterize the functionalized MWCNTs and pristine MWCNTs. FTIR spectra in KBr pellets were recorded on a PerkinElmer Spectrum One FTIR spectrometer. Ther- mal study was carried out using thermogravimetric analysis (TGA) (PerkinElmer Pyris 6 instrument) at a heating rate of 10 ◦ C/min in a nitrogen environment. Ultraviolet–visible (UV–vis) spectra were measured using a PerkinElmer Lambda 35 UV–vis spectrometer. The morphology of the samples was analyzed by transmis- sion electron microscopy (TEM), with a Philips CM12 equipped with an analysis Docu Version 3.2 image analysis system. 2.2. Preparation of diphenyl-carbinol-functionalized MWCNTs (DPC-MWCNTs) A solution consisting of 30 mg of MWCNTs and 40 mg of potassium (40 mg) in 150ml toluene was ultrasonicated for 10min, and then 0.179g of benzophenone were added to the solution. The mixture was stirred at 80 ◦ C in a nitrogen envi- ronment for 12 h. Afterwards, an additional 255 mg of benzophenone and 56 mg of potassium were added to the mixture. The mixture was further stirred for 5 days and 10 days at 80 ◦ C and cooled at room temperature. Dried ethanol was then added to 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.01.093