Adsorption 6, 169–174, 2000 c  2000 Kluwer Academic Publishers. Manufactured in The Netherlands. Methane Adsorption on Planar WS 2 and on WS 2 -Fullerene and -Nanotube Containing Samples E.B. MACKIE Department of Physics, Southern Illinois University, Carbondale, IL 62901, USA D.H. GALVAN Centro de Ciencias de la Materia Condensada-UNAM, Apartado Postal 2681, C.P. 22800, Ensenada, B. Mexico A.D. MIGONE Department of Physics, Southern Illinois University, Carbondale, IL 62901, USA Received September 2, 1999; Revised February 3, 2000; Accepted August 2, 2000 Abstract. Adsorption-desorption cycles were measured for methane on non-irradiated WS 2 , and on irradiated WS 2 (which contained, in part, WS 2 fullerenes and nanotubes). Both types of samples were further subdivided into three sets: one set received no further treatment, another set was heated under vacuum, and the last set was acid-treated and heated. The specific surface area was determined for each set; so was the presence or absence of a hysteresis loop in the adsorption-desorption cycles. The results of these two groups of measurements were correlated with the space available for adsorption. The implications of the results for the experimental determination of the dimensionality of gas adsorbed at the interior of nanotubes are discussed. Keywords: adsorption, WS 2 , nanotubes and fullerenes Introduction Nanotubes have very large aspect ratios: their diame- ters are several orders of magnitude smaller than their lengths (Ajayan and Ebbesen, 1997; Ijima, 1991). The nanotubes’ centers are hollow. The ends of the tubes are capped by atoms having a different symmetry from those in the walls of the tubes (Ajayan and Ebbesen, 1997). The caps can be opened using specific treat- ments (Dillon et al., 1997; Tsang et al., 1993, 1994). Open-ended nanotubes offer a unique environment for adsorption. Physical adsorption on planar substrates has long been used to produce effectively two-dimensional systems. Nanotubes used as substrates can, poten- tially, provide physical realizations of one-dimensional systems. Gas/nanotube systems, thus, have consider- able fundamental appeal. Adsorption phenomena on nanotubes are of interest from a practical perspective, as well. Several possible applications have been suggested (e.g. using nanotubes for gas storage at room tempera- ture (Dillon et al., 1997), a possibility that could make economically feasible the use of hydrogen to power automotive vehicles). Aside from graphite and carbon, nanotubes have been produced from BN (Chopra et al., 1995), WS 2 (Tenne et al., 1992; Margulis et al., 1996; Galvan et al., 1998; Tenne, 1999), and MoS 2 (Margulis et al., 1993). All these materials have in common a bulk structure consisting of layers with strong interlayer couplings and weak intralayer bonds (Tenne, 1999). While pro- duction of carbon nanotubes generally requires extreme