SiO 2 nanospheres and tubes obtained by sol–gel method C. Anastasescu a , M. Anastasescu a , V.S. Teodorescu b , M. Gartner a , M. Zaharescu a, ⁎ a Institute of Physical Chemistry “I. Murgulescu”, Spl. Independentei 202, Sect.6, 060021, Bucharest, Romania b National Institute of Material Physics, 105 bis Atomistilor Street, 077125, Bucharest-Măgurele, Romania abstract article info Available online 16 June 2010 Keywords: Sol–gel processing; Precipitation; Structure of nanoscale materials; Transmission electron microscopy; Atomic force microscopy (AFM) Multifunctional nanomaterials with one-dimensional structure have become very attractive because of their potential applications in biochemistry (bioseparation and biointeraction), drug delivery, catalysis, nanotechnology (optical sensors). In this work we report on the synthesis of SiO 2 nanospheres and tubes, in a solution of tartaric acid (TTA), pure water and absolute ethanol, starting with tetraethyl orthosilicate (TEOS) via the addition of ammonium hydroxide. In order to characterize the obtained material, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), thermogravimetric and thermodifferential analysis (DTA/TGA), FT-IR spectroscopy and spectroellipsometry (SE) were used. The tubes have an outer diameter of 0.1–0.2 μm and length of some microns containing also spherical nanoparticles. The dimensions of the obtained nanotubes are tunable, their diameter and length depending on the synthesis conditions. In the presence of meso-tartaric acid no hollow tubes but nanospheres are obtained. The SiO 2 tubes and nanospheres have similar structure but very different morphologies. The large surface area and the distinctive inner and outer surfaces represent a great advantage of the nanotubes over conventional nanoparticles, making these materials suitable for doping and differential functionalization. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The discovery of the C nanotubes in 1991 has opened the interest for synthesis of analogous inorganic compound nanotubes. The first inorganic nanotubes obtained were layered d-metal dichalcogenides MX 2 (M= Mo, W; Ta; X =S, Se) as well as boron nitride (BN), carbide (BC x ) and carbonitride (B x C y N z ). Other type of chalcogen- ides (InS, ZnS, Bi 2 S 3 , TiS 2 , TiSe 2 , CdS, CdSe, Ag 2 S) were also synthesized. Semiconducting materials, such as: SiGe, InGe/GaAs, InGaAs/GaAs, SiGe/ Si and InGeAs/GaAs and nanotubes of metals: Co, Sb, Se, Bi are also known. In the recent years p-, d- and f-metal (Si, Al, Ge, Ti, Nb, Ta, Zr, V, Mo, Dy, and Tb) oxides were also obtained as nanotubes [1]. The interest for SiO 2 based nanotubes is connected to their potential application in several fields as catalysis, separation science, nanotechnology [2] or drug delivery [3]. As a matter of fact, SiO 2 hollow tubes were first prepared by Nemetscheck and Hofman much earlier than the carbon nanotubes discovery, namely in early fiftieth of the last century. Two high temperature methods were used: the SiO disproportionation reac- tion [4] and the reaction of silica and silicon metal in high vacuum at 1200 °C [5]. Among the more recent methods of preparation at low temper- ature of this type of materials, the most frequently used is the sol–gel procedure. The first preparation of the SiO 2 hollow tubes by sol–gel method was realized by Nakamura and Matsui, using TEOS as reagent and DL-tartaric acid as templating agent in alcoholic medium and by addition of ammonia [6]. The method proposed by Nakamura and Matsui was applied in numerous other SiO 2 syntheses [7,8] but also other templating agents as peptidic lipids [9] or metal salts [10] were used. By doping with Ag, the SiO 2 tubular samples have shown antibacterial properties [11]. Silica nanotubes with a layer of magnetite (Fe 3 O 4 ) nanoparticles on the inner surface of the nanotube using porous alumina film as template, were also obtained [3], following the previously reported “surface sol–gel” methods [12–14]. The nanotubes have magnetic properties and are used for drug delivery. Luminescent silica nanotubes loaded with coumarion laser dye and with anthracene laser dye were also prepared by sol–gel co- condensation of functional dyes and TEOS in a cholesterol-based organogel system [15]. In the present work the influence of the experimental conditions of the sol–gel process were investigated in order to obtain either pure hollow SiO 2 tubes or SiO 2 nanoparticles in an attempt to obtain new information on their structure and morphology. 2. Experimental 2.1. Samples preparation The synthesis of the SiO 2 nanomaterials was based on the method established by Nakamura and Matsui [6]. In our study the influence of Journal of Non-Crystalline Solids 356 (2010) 2634–2640 ⁎ Corresponding author. E-mail address: mzaharescu@icf.ro (M. Zaharescu). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.03.038 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol