Convenient arc-electrodeposition technique to synthesize CdS nanotubes at room temperature

Abstract

Over the past few years, shape control of nanomaterials has raised significant concerns in the fabrication of onedimensional (1D) nanomaterials such as nanowires, nanotubes and interesting nanobelts [1]. These 1D nanostructures are ideal systems for investigation of the relationship between the properties (e.g. electrical transport, optical and magnetic behaviors) and dimensionality [2]. For example, considerable progress has been made in the synthesis of 1D semiconductor nanostructured materials due to their unique properties [3]. Especially, much more efforts have been focused on the fabrication of nanotubes. A particularly significant breakthrough in the preparation of MX2 (M: Mo or W; X: S or Se) nanotubes was made by Tenne and co-workers [4]. Later, various approaches to other nanotubes such as BN [5], vanadium oxide [6], InS [7] and metal Bi [8] have also been reported. Recently we explored a novel convenient arcelectrodeposition technique to prepare shapecontrolled metal nanorods [9], nanorods or nanotubes of metal oxides and hydroxides [10]. The so-called arcelectrodeposition technique is based on the momentary contact of two metallic electrodes on an electrolyte aqueous solution, forming instantaneous circulation between two electrodes and the arc discharge sparks at the point ends of the electrodes. The arc discharge of the electrodes releases great exothermic heat, leading to dissolution of the metallic electrodes in a form of metallic clusters into the aqueous solution. The produced metallic clusters either aggregate into metal nanowires or are oxidized into the corresponding oxides and further grow into nanorods or nanotubes. Herein we extend the arc-electrodepostion technique to prepare CdS nanotubes at room temperature. The basic experimental setup and procedure for the preparation of the CdS nanotube by the arcelectrodepostion technique at room temperature are similar to those in our previous reports [9, 10]. In the present work, the mixture of Na2S and KCl aqueous solution was used as electrolyte solution. Two highpurity metallic Cd filaments of 1 mm in diameter were employed as electrodes with the applied alternating current (AC) voltage of 100 V. In the arc-electrodeposition process, the colorless transparent electrolyte aqueous solution turned into yellow gradually, indicating the formation of CdS nanoparticles. The produced solution was allowed to stand for 24 h. The final product was collected by centrifugation, followed by washing using distilled water and ethanol several times. The phase identification of as-prepared product was conducted at room temperature using an X-ray diffractometer (Cu Kα, Philips X’pert system). A transmission electron microscope (Jeol 2010) was employed to observe particle morphology. Fig. 1 shows the XRD trace of as-prepared CdS nanoparticles using this technique, in which two Cd metallic wires of 1 mm in diameter were employed as electrodes and an aqueous solution containing 0.1 M Na2S and 0.1 M KCl as electrolyte medium. In this XRD pattern, all the detectable peaks are indexed as those from CdS according to the standard card (JCPDSICDD 10-0454). The morphology of the as-prepared CdS was examined by TEM observation. The typical image is shown in Fig. 2a. It can be seen that the CdS nanoparticle obtained using this arc-electrodeposition technique under the conditions mentioned above exhibits a tubular structure in nanoscale. The length of the nanotubes ranges from 50 nm to 80 nm, and the outer diameter is around 10–15 nm with the inner that of 3–8 nm. A magnified TEM image, as shown in Fig. 2b, further reveals this structure. The formation mechanism of the CdS nanotubes produced by the present arc-electrodeposition technique was proposed as follows: