Complex-assisted one-step synthesis of ion-exchangeable titanate nanotubes decorated with CdS nanoparticles A ´ kos Kukovecz * , Ma ´ria Hodos, Zolta ´n Ko ´ nya, Imre Kiricsi Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Bela te ´r 1, H-6720 Szeged, Hungary Received 8 June 2005; in final form 15 June 2005 Available online 7 July 2005 Abstract Trititanate nanotubes were prepared from anatase TiO 2 in 10 M Na 2 S solution kept at 130 °C for 2 weeks. On the basis of this reaction, we devised a novel synthesis method which allows the preparation of titanate nanotubes decorated with CdS nanoparticles in one step. The key feature of the suggested method is controlling the rate of CdS formation by introducing Cd 2+ ions as a Cd–EDTA complex into the synthesis mixture. The nanotubes obtained are several hundred nm long, tend to aggregate into rod-like structures and are fully covered by CdS nanoparticles with an average diameter of 5.3 nm. Ó 2005 Elsevier B.V. All rights reserved. 1. Introduction Hydrothermally obtained ion-exchangeable titanate nanotubes have commanded considerable attention recently because of their ease of synthesis [1], high potential for Li-storage [2–4], peculiar spiral cross-sec- tion [5] and heavily disputed formation mechanism [6–9]. Since their electronic structure differs considerably from that of other TiO x nanocrystals [10], they are not as suitable for standalone photocatalytic applications as, e.g., anatase. On the other hand, their high surface area and tubular morphology have initiated heteroge- neous catalytic studies where the titania tubes served as support to, e.g., Au [11] and Pt [12,13] nanoparticles. Another catalytic research direction is photoactivation by isomorphous substitution (framework doping) which has been successfully accomplished for Fe [14] and N dopants [15]. Photocatalytic activity can also been bestowed on titanate systems by decorating them with suitable semiconductor quantum dots. CdS doping has been successfully carried out for multi-wall carbon nanotubes before [16,17], and CdS/TiO x nanocompos- ites obtained by layered assembly [18] or as core/sheath heterostructures [19] have also been reported. We have recently described the first successful synthe- sis of ion-exchangeable trititanate nanotubes decorated with CdS quantum dots in a two-step process which involves bubbling H 2 S through an aqueous suspension of Cd 2+ -exchanged titanate nanotubes at room temper- ature [20]. Here, we report on a novel complex-assisted one-step synthesis of CdS-decorated titanate nanotubes. Because of the ease of the synthesis, the suggested new method can be scaled up more easily than the original two-step process and it is also environmentally more benign. 2. Experimental Undoped trititanate nanotubes were synthesized by mixing 2 g anatase TiO 2 into 150 cm 3 aqueous solution of Na 2 S (concentrations were varied, see below) in a Teflon-lined autoclave which was held at 130 °C for several days without shaking or stirring. After cooling to room temperature, the autoclave was opened and 0009-2614/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2005.06.073 * Corresponding author. Fax: +36 62 544 619. E-mail address: kakos@chem.u-szeged.hu (A ´ . Kukovecz). www.elsevier.com/locate/cplett Chemical Physics Letters 411 (2005) 445–449