Hydrogenation of Carbon Nanotubes and Graphite in Liquid Ammonia S. Pekker* Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 49, Hungary J.-P. Salvetat CNRS, Centre de Recherches sur la Matie ` re DiVise ´ e, 1b Rue de la Fe ´ rollerie, F-45071 Orle ´ ans Cedex 2, France E. Jakab Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 17, Hungary J.-M. Bonard Institut de Physique Expe ´ rimentale, Ecole Polytechnique Fe ´ de ´ rale de Lausanne, CH-1015 Lausanne, Switzerland L. Forro ´ Institut de Ge ´ nie Atomique, Ecole Polytechnique Fe ´ de ´ rale de Lausanne, CH-1015 Lausanne, Switzerland ReceiVed: February 18, 2001; In Final Form: June 14, 2001 We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, via a dissolved metal reduction method in liquid ammonia. The hydrogenated derivatives are thermally stable up to 400 °C. Above 400 °C, a characteristic decomposition takes place accompanied with the simultaneous formations of hydrogen and a small amount of methane. Transmission electron micrographs show corrugation and disorder of the nanotube walls and the graphite layers due to hydrogenation. The average hydrogen contents determined from the yield of evolved hydrogen correspond to the compositions of C 11 H for both types of nanotubes and C 5 H for graphite. Hydrogenation occurred even on the inner tubes of multiwall nanotubes as shown by the chemical composition and the overall corrugation. The thermal stability and structural results suggest the formation of C-H bonds in nanotubes and graphite. 1. Introduction In the past few years, the interesting physical properties of carbon nanotubes have attracted great attention among physicists and material scientists. The first experiments after the discovery 1 focused on preparation 2 and purification 3,4 techniques as well as on understanding the structure and physical properties 5 of the pristine nanotubes. Chemical modifications were restricted to a few reactions such as opening the tubes by selective oxidation 6-8 to fill the central hollow with various materials 9,10 and doping the tubes with alkali metals. 11,12 A more systematic study of the chemical reactivity is desirable for further practical application of the nanotubes. Recently, chemical functionaliza- tion came into focus 13-16 since it is an obvious way to modify the chemical and physical properties of the surface of the tubes. Functionalized nanotubes can undergo further chemical reactions producing composites with a variety of materials, like for example polymers. The chemical properties of carbon nanotubes lie between those of graphite and fullerenes. Graphite is chemically inert and, besides the ionic intercalated compounds, only fluorinated and oxidized derivatives can be produced without destroying the layer structure. 17 On the other hand, the functionalization of fullerenes is rather easy as illustrated by the thousands of covalent derivatives prepared so far. 18 Although most of the properties of nanotubes resemble those of graphite, the curvature of their graphene sheets may result in an increased chemical reactivity toward the formation of covalent bonds in the outer surface. Since hydrogenation can be considered as a prototype of chemical functionalization, in this paper we describe the preparation, structure and thermal stability of hydrogenated carbon nanotubes. To determine the reactivity of various carbonaceous materials with respect to hydrogenation we performed the same reaction on single-wall nanotubes (SWNT-s), multiwall nanotubes (MWNT-s), extracted fullerene soot and two types of graphite. 2. Experimental Section Powder of MWNT-s was produced by arc discharge 1 and purified by a nondestructive sedimentation method. 3 Aqueous SWNT suspension (Tubes@Rice) was filtered and dried, and the resulting “bucky paper” was annealed in a vacuum at 950 °C. Graphite powder was prepared by grinding of soft graphite rods (Johnson Mattey, ultra carbon). Besides graphite powder, turbostratic graphite flakes were also studied. The light-gray powder of this sample consisted of disk-shape particles with typical diameter of 100 nm and thickness of 20 nm. Fullerene * Corresponding author. E-mail: pekker@szfki.hu. 7938 J. Phys. Chem. B 2001, 105, 7938-7943 10.1021/jp010642o CCC: $20.00 © 2001 American Chemical Society Published on Web 07/26/2001