Solid State Nuclear Magnetic Resonance 28 (2005) 135–141 129 Xe NMR study of Xe adsorption on multiwall carbon nanotubes K.V. Romanenko a,b,Ã , A. Fonseca c , S. Dumonteil c , J.B. Nagy c , J.-B. d’Espinose de Lacaillerie b , O.B. Lapina a , J. Fraissard b a Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk, Russia b Laboratoire de Physique Quantique, UMR CNRS 7142, Ecole Supe´rieure de Physique et de Chimie Industrielles (ESPCI), 75231 Paris Cedex 05, France c Laboratoire de Resonance Magnetique Nucleaire, FUNDP, 61 Rue de Bruxelles, B-5000 Namur, Belgium Received 30 May 2005; received in revised form 5 July 2005 Available online 18 August 2005 Abstract 129 Xe NMR spectroscopy has been used to study the adsorption of Xe on multi-wall carbon nanotubes (MWCNT). The results obtained have shown the 129 Xe NMR ability to probe the intercrystalline (aggregate) and the inner porosity of CNT. In particular, the effects on porosity of tubes openings by hydrogen exposure and of ball milling were examined. Dramatic changes observed in the 129 Xe NMR spectra after moderate ball milling of MWCNTs were attributed to the destruction of the initial intercrystalline pore structure and to the Xe access inside the nanotubes. To examine the exchange dynamics the mixture of as-made and milled MWCNTs was studied with one- and two-dimensional (1D and 2D) 129 Xe NMR. The exchange between the interior of milled nanotubes and the aggregate pores of as-made MWCNTs was fast on the NMR acquisition time scale. The Xenon exchange between the interior of the as-made MWCNTs and the large aggregate pores occurred on a longer time scale of 10 ms, as was established by 2D 129 Xe NMR exchange spectroscopy. Variable temperature 129 Xe NMR data were also discussed and analyzed in terms of the fast exchange approximation. r 2005 Elsevier Inc. All rights reserved. Keywords: 129 Xe NMR; Carbon nanotubes; Porosity 1. Introduction Carbon nanotubes (CNT) are attractive for funda- mental materials science investigations and industrial applications. Electrical and thermal conductivity, high durability, gas storage capacity, adsorption and mole- cular sieving are properties of CNT currently being investigated. A great number of publications have appeared since the discovery of CNT in 1991 [1]. However, the CNT family has not been extensively examined by 129 Xe NMR [2,3], a well-established technique for the characterization of porous silicates [4]. In fact, an extension of 129 Xe NMR to the field of carbon nanomaterials could have many useful applica- tions, as it has for numerous silica-based materials. The first problem to solve when studying adsorption on CNT is the precise identification of adsorption sites. Generally two principal surface sites are inherent in CNT: (1) intercrystalline or aggregate pores correspond- ing to the external surface; (2) 1-D nanoscale cavities in the central core of the nanotubes. The important role of intercrystalline (aggregate) pores in adsorption, capil- larity or other physico-chemical properties has been demonstrated in Ref. [5]. This type of pore appears to have a huge adsorption capacity responsible for 78.5% of the total adsorbed amount [5]. Therefore an under- standing of the intercrystalline pore structure in relation to the aggregation mechanisms is necessary for the development of efficient gas-storage materials. In a study of single-wall CNT bundles [6], volumetric ARTICLE IN PRESS www.elsevier.com/locate/ssnmr 0926-2040/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ssnmr.2005.07.004 Ã Corresponding author. fax: +7 383 2 34 30 56. E-mail address: kostaromavita@ngs.ru (K.V. Romanenko).