Physical adsorption of xenon in open single walled carbon nanotubes: Observation of a quasi-one-dimensional confined Xe phase

Abstract

The adsorption of Xe into carbon single walled nanotubes with both closed and open ends has been investigated using temperature programmed desorption and other surface analytical tools. It has been found that opening the ends of the nanotube by chemical cutting increases both the kinetic rate and the saturation capacity of the nanotubes for Xe at 95 K. Further enhancement in Xe adsorption kinetics and capacity are achieved by treating the nanotubes in vacuum at 1073 K where CO, CO 2 , CH 4 , and H 2 are evolved. On this basis it is postulated that surface functionalities such as ϪCOOH block entry ports for adsorption at the nanotube ends and at the defect sites on the walls. The thermal destruction of these functionalities leads to enhanced adsorption. The denser phase of Xe inside the saturated nanotubes desorbs by zero-order kinetics (E d ϭ26.8Ϯ0.6 kJ/mol͒. It is postulated that a quasi-one-dimensional Xe confined phase in equilibrium, with a two-dimensional Xe gas phase on the exterior, provides a phase transition governing the zero-order kinetics desorption process.

Adsorption on Carbon Nanotubes Studied Using Polarization-Modulated Infrared Reflection−Absorption Spectroscopy

“…It is thus possible to observe weakly interacting surface species under finite steady-state reagent pressures. Although the present work has focused entirely on IR-spectroscopic aspects, the use of a metallic substrate 15 will also facilitate the application of surfacesensitive electron spectroscopies such as AES and XPS.…”

Nanoparticle-assisted microwave absorption by single-wall carbon nanotubes

“…Since the nanotubes were not intentionally exposed to H 2 , the H 2 observed is attributed to the decomposition of hydrogen containing compounds on the nanotubes at high temperatures, as previously reported. 6,7 The large amount of H 2 in our experiment is likely due to the high temperature of 1850°C reached by the nanotubes.…”

NMR Study of Preferential Endohedral Adsorption of Methanol in Multiwalled Carbon Nanotubes

“…Because of their large adsorptive capacity and high electron and thermal conductivity, CNTs have many potential applications as, for example, heterogeneous catalysts, 1−3 storage media, 4,5 and gas sensors, 6 for which understanding of the gas−nanotube interactions is rather important. Adsorption isotherm, 7,8 infrared (IR) spectroscopy, 9,10 temperature programmed desorption (TPD), 11,12 and Raman spectroscopy 13,14 have been widely employed to study the adsorption of the gas molecules in CNTs. As compared to these methods, nuclear magnetic resonance (NMR) is a nondestructive technique and can provide bulk information on the adsorption sites, mechanisms, and strengths of adsorbates on nanotubes.…”