Two Confined Phases of Argon Adsorbed Inside Open Single Walled Carbon Nanotubes

• Published in: Langmuir Vol. 20; no. 14; pp. 5940 - 5945
• Main Authors: Jakubek, Zygmunt J, Simard, Benoit
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.07.2004
• Subjects: Adsorption; Argon - chemistry; Combinatorial Chemistry Techniques - methods; Nanotubes, Carbon - chemistry; Surface Properties; Temperature; Thermodynamics
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la0358872

Isothermal adsorption of Ar on single walled carbon nanotubes (SWNTs) has been studied at 77 and 87 K. The SWNTs have been grown by laser vaporization of a graphite pellet containing 0.6% (atomic) Ni/Co catalyst. The nanotubes have been prepared for argon adsorption measurements by prolonged outgassing of as-grown material in a vacuum at room temperature (295 K), at elevated temperatures of up to 475 K, and by oxidization for 2 h in dry air at 470 K. Formation of two condensed phases of Ar in the interior of SWNTs has been observed at 77 K. The low-density phase is formed at 155(5) μTorr, while the high-density phase, at 120(5) μTorr. At 87 K, only a single phase has been observed at 185(5) μTorr. Condensation at both 77 and 87 K appears to be the first-order phase transition. Onset of the quasi-one-dimensional linear (one-channel) phase and the quasi-two-dimensional monolayer (six-channel) phase formation on the external surface of bundles has been observed at 77 K near 0.0017 and 0.8 Torr, respectively, and at 87 K near 0.018 and 5 Torr, respectively. Isosteric heats of adsorption for the one-channel phase, the first external layer, and the second external layer have been determined to be equal to 137, 107, and 70 meV, respectively.