Hydrothermal synthesis of multiwall carbon nanotubes

Multiwall open-end and closed carbon nanotubes with the wall thickness from several to more than 100 carbon layers were produced by a principally new method-hydrothermal synthesis-using polyethylene/water mixtures in the pres ence of nickel at 700-800 degreesC under 60-100 MPa pressure. An important feature of hydrothermal nanotubes is a small wall thickness, which is about 10% of the large inner diameter of 20-800 nm, Closed nanotubes were leak-t ight by virtue of holding encapsulated water at high vacuum and can be used as test tubes for in situ experiments in transmission electron microscope (TEM). Raman microspectroscopy analysis of single nanotubes shows a well-or dered graphitic structure, in agreement with high-resolution TEM. The hydro thermal synthesis has the potential for producing multiwall nanotubes for a variety of applications. The fabrication of nanotubes under hydrothermal c onditions may explain their presence in coals and carbonaceous rocks and su ggests that they should be present in natural graphite deposits formed unde r hydrothermal conditions.