Tubular inorganic nanostructures I. Kiricsi * ,A ´ . Fudala, D. Me ´hn, A ´ . Kukovecz, Z. Ko ´nya, M. Hodos, E. Horva ´th, M. Urba ´n, T. Kanyo ´, E ´ . Molna ´r, R. Smajda Applied and Environmental Chemistry Department, University of Szeged, 6720 Szeged, Rerrich Be ´la te ´r 1, Hungary Received 28 January 2005; received in revised form 21 April 2005 Available online 22 August 2005 Abstract Tubular inorganic nanostructures are high aspect ratio nanomaterials possessing few nanometer wide inner channels. We report on our studies about engineering the chemical composition, morphology and pore size of carbon, silica and titania nanotubes as well as of mesoporous silicate MCM-41. The former three systems represent three different classes of inorganic nanotubes, since they feature circular, angular and spiral cross-sections, respectively. Besides being interesting on their own right, some of these systems exhibit superior catalyst support properties as well. Ó 2005 Elsevier B.V. All rights reserved. PACS: 61.46.+w; 81.05.Rm; 81.07.De Keywords: Nanotube; Carbon; Silica; Titania; Property engineering 1. Introduction Tubular inorganic nanostructures are often research objects of different chemical, physics and material sci- ence laboratories. The continuously growing interest for these materials can be explained by their peculiar properties originating from their compositions and tubular structures. The chemical composition of these structures includes silicates [1], titanates [2], various metal oxides [3], sulfides [4], carbon [5], and also their composites [6]. Oxides and carbon are used very fre- quently as adsorbents [7], catalyst supports [8] or cata- lysts [9] in chemistry, or—due to their semi-conductive and photoelectronic properties—in physical and elec- tronic applications as well. Tubular structures are formed as individual tubes such as the multiwall carbon nanotubes [5], in bundles like the singlewall carbon nanotubes [10], in ordered, well defined structures like e.g. MCM-41 silicates [11], or in less ordered structures such as the SBA-15 meso- porous silicates [12]. As far as the morphology of the tubes is concerned, there are tubes of circular [5], rectan- gular [13] and spiral [14] cross-sections, usually in the 1 to 20 nm range. Some methods for pore size engineering have been described as well. The length of the tubes varies from several ten nanometers to several micro- meters. In this paper we report our results obtained in the course of investigating the synthesis and characteriza- tion of tubular nanostructures. For engineering of the morphology of the nanostructures we show ordered structures of silicate nanotubes in hexagonal, angular and spherical morphology. We discuss the formation mechanism of spiral nanotubes synthesized from titania. On the material science side we show results on nanotubes from carbon, silicate and carbon–silicate nanotubes, and report the introduction of metal nano- particles into the elementary tubes of mesoporous silicates. 1567-1739/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2005.07.042 * Corresponding author. Tel.: +36 62 544 478; fax: +36 62 544 619. E-mail address: kiricsi@chem.u-szeged.hu (I. Kiricsi). www.elsevier.com/locate/cap www.kps.or.kr Current Applied Physics 6 (2006) 212–215