Gas Adsorption Evidence of Single-Wall and Multi-Wall Carbon Nanotube Opening
- PDF / 329,129 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 103 Downloads / 201 Views
A9.5.1
Gas Adsorption Evidence of Single-Wall and Multi-Wall Carbon Nanotube Opening Moulay-Rachid Babaa1, Edward McRae1, Nicole Dupont-Pavlovsky1, Sandrine Delpeux2, Francois Beguin2, Fabrice Valsaque1, Jaafar Ghanbaja1. 1 Laboratoire de Chimie du Solide Minéral, UMR CNRS 7555, Université Henri Poincaré – Nancy 1, B.P. 239, 54506 Vandoeuvre cedex, France 2 Centre de Recherche sur la Matière Divisée, CNRS-Université, 1B rue de la Férollerie, 45071 Orléans cedex 02, France ABSTRACT Carbon nanotubes offer a surface very similar to that of graphite, a reference substrate in physisorption experiments aimed at studying substrate-adsorbate interactions. The curvature, however, introduces new questions. What are the effects of this on condensation pressures or heats of adsorption? Can one experimentally distinguish between different adsorption sites? In this study, we compare adsorption isotherms of several simple gases (Kr, Xe, CCl4) on singlewall (SWNTs) and multi-wall carbon nanotubes (MWNTs), before and after opening. For mechanically opened SWNTs, the accessibility of the adsorption sites and the molecular arrangements of the adsorbed gases are discussed. With the much bigger, well-defined MWNTs, the “cutting method” called upon a nitric acid treatment followed by a CO2 oxidation. TEM investigations and physisorption studies clearly revealed tube opening and that the inner channels became accessible to Kr molecules. INTRODUCTION Since the early research works on carbon nanotubes (CNTs), effort has been made to open nanotubes so as to encapsulate elements and molecules [1]. This has allowed creating 1D wires and showing the existence of various compounds with structural parameters different than those of bulk 3D materials [2, 3] because of the confinement. Over the past years, several theoretical studies have further suggested that adsorption might take place inside the tubes if they could be opened. The present study shows that opening tubes can indeed be done and that evidence is provided by adsorption isotherms. A physisorption isotherm of simple molecules on a uniform surface such as graphite displays vertical steps representative of 2D phase transitions corresponding to the deposition of successive monomolecular layers. Concerning CNTs, which consist of coaxially rolled, seamless graphene sheets, two steps can be distinguished in simple gas adsorption isotherms which result from the condensation of the adsorbed phase on the uniform patches of the outer surface. In the case of closed SWNTs, which are organized in bundles, the first step has been attributed to adsorption in the grooves and the largest interstitial channels, and the second has been assigned to adsorption on the external convex surface of the individual outermost tubes making up the bundle [4,5,6]. In the case of closed MWNTs, both steps are thought to represent successive condensations on the external surface of the nanotubes [7,8]. In this paper, we show that it is possible, using adsorption measurements coupled with TEM observations, to give evide
Data Loading...
