Trade.Information

Topic Name: Exchange transition phenomenon involving ambient gas and water molecules

Category: Nanocharacterization

Research persons: Associate Professor Yutaka Maniwa's , Hiromichi Kataura, chief of the Self-Assembled Nano-Electronics Group

Location: AIST Tokyo,-3-1, Kasumigaseki,Chiyoda-ku, Tokyo 100-8921,Tel:+81-3-5501-0900, Japan

Details

Associate Professor Yutaka Maniwa's group with the Graduate School of Science and Engineering of Tokyo Metropolitan University (President: Junichi Nishizawa) and Hiromichi Kataura, chief of the Self-Assembled Nano-Electronics Group at the Nanotechnology Research Institute of the National Institute of Advanced Industrial Science and Technology (President: Hiroyuki Yoshikawa) (hereinafter referred to as AIST) jointly demonstrated the adsorption of water molecules into a Single-Walled Carbon Nanotube (SWCNT) under different gas ambiences and discovered the "exchange transition" phenomenon involving ambient gas and water molecules.

The "exchange transition"-characterized as an exchange between molecules of water inside the SWCNT and ambient gas molecules -was verified for seven types of ambient gas: argon, krypton, oxygen, nitrogen, methane, ethane, and carbon dioxide. The conditions for occurrence of exchange transition depend on the type of gas. For example, with methane at one atmosphere and -30°C or below, water molecules are expelled from the SWCNT and replaced by methane molecules which penetrate into the SWCNT. In contrast, when helium, hydrogen, or neon was used, water molecules remained stable inside the SWCNT at temperatures of -170°C or below (Figure 1). Using this phenomenon, the water-filled SWCNT can be used as a molecule-selective nanovalve.

In addition, the sudden change in electrical resistance of the SWCNT film due to the exchange transition can be used to create a new gas sensor that permits the selection of gases without any special chemical treatment, coating, or the like. Tokyo Metropolitan University and AIST plan to put the gas sensor and the molecule-selective nanovalve to practical use and invite the participation of companies possessing related technologies.

The results of the present research were published in the on-line version of the scientific journal Nature Materials under the title "Water-filled single-wall carbon nanotubes as molecular nanovalves" on January 21, 2007 (GMT). Part of it has received support from the Japan Science and Technology Agency/Core Research for Evolutional Science and Technology (CREST).

Background and History of Research

The behavior of water and gas molecules in nanospace is an important issue in such areas as nanotechnology and energy storage but has not been fully explained. It was previously known that water can be easily adsorbed in a normal environment into a single-walled carbon nanotube (SWCNT) containing a cylindrical cavity about 1 nm in diameter (Figure 2) in spite of the hydrophobic nature of the SWCNT wall, but the behavior with a coexisting gas was totally unknown.

The phenomenon of water adsorption into hydrophobic SWCNT was suggested in 1999 by Dr. Maniwa with the Graduate School of Science of Tokyo Metropolitan University (currently the School of Science and Engineering of Tokyo Metropolitan University) and Dr. Kataura (currently with AIST), and later experimentally confirmed in 2002. Moreover, it was demonstrated that the ring-shaped ice formation (ice nanotube or ice-NT) theoretically predicted by Drs. Koga and Tanaka (currently with the School of Science of Okayama University) was actually observed inside the SWCNT. The dependency of the formation of ice-NT and its structure on the SWCNT diameter was further investigated and it became clear that the melting point increases with smaller diameters, and that thin nanotubes allow for the formation of ice-NT at room temperature. Unlike previous experiments which were carried out in vapor ambiences, this time we examined in detail the adsorption of water into the SWCNT when coexisting with several types of gases.

Details of Research

Electrical resistance measurements, NMR tests, X-ray diffractometer (XRD) tests and computer simulation were carried out using a high-purity SWCNT material in whose preparation the diameter was set to 1.35nm by means of control based on the laser ablation method. XRD tests were carried out at Photon Factory BL1B of the High Energy Accelerator Research Organization, an inter-university research institute corporation.

Ten types of gases (hydrogen, helium, neon, argon, krypton, oxygen, nitrogen, methane, ethane, and carbon dioxide) were investigated under one atmosphere at a temperature range from room temperature down to -180°C. As a result, we discovered that at low temperature or high pressure, water molecules inside the SWCNT exchanged with molecules from the gas ambience ("exchange transition").

The temperature at which exchange transition occurs depends heavily on the type of gas and pressure. For instance, using methane under one atmosphere, water molecules inside the SWCNT were expelled and replaced by methane which penetrates into the SWCNT at temperatures below approximately -30°C. On the other hand, using helium, hydrogen, or neon, water molecules remained stable inside the SWCNT at temperatures as low as -170°C (Figure 1). The clear dependency on the type of gas as illustrated in Figure 1 can be explained as a phenomenon peculiar to nanospaces. In addition, computer simulations showed that this phenomenon makes it possible to use water-filled SWCNT as a molecule-selective nanovalve (Figure 3)

Moreover, measurements of the dependency of electrical resistance on temperature indicated sudden changes in electrical resistance of the SWCNT film due to exchange transition (Figure 4). These changes can be applied in new types of gas sensors that can select gases without any special chemical treatment or coating.

Details of announcement dissertation

Magazine name: Nature Materials
Title: Water-filled single-wall carbon nanotubes as molecular nanovalves
Also author name: Yutaka MANIWA, Kazuyuki MATSUDA, Haruka KYAKUNO, Syunsuke OGASAWARA, Toshihide HIBI, Hiroaki KADOWAKI, Shinzo SUZUKI and Yohji ACHIBA and Hiromichi KATAURA


Details of announcement dissertation

* Monolayer carbon nano- tube (SWCNT: Single-Wall Carbon Nanotube)
The carbon nano- tube to consist of only the carbon atom, diameter 0.4~50nm and length the approximately 1~ several 10? It is m one dimensional characteristic nano- material. The chemical structure is displayed making round graphite layer, being something which it connects, the number of layers calls those just 1 the monolayer carbon nano- tube, method of winding the graphite layer depends (degree of spiral) and electronic structure becomes metal and/or becomes semiconductor. The structure of SWCNT (diameter and helical structure) it can appoint group of two integers (m, n) due to. This is called the exponent of SWCNT.

* Nano- meter
As for 1 nano- meters 1/1000000000 meter. Small atoms the several were arranged are size.

* Ice nano- tube (ice-NT: ice NanoTube)
The figure 2 (the right) it shows, the ring where the water molecule is connected with hydrogen bond 1 crystal of the water where the structure which accumulates dimensionally is new. From average diameter 1.17 in the SWCNT sample of 1.44nm, ice-NT of 4 types of 8 member rings is verified from 5 member rings.