Model for Self-Rolling of an Aluminosilicate Sheet into a Single-Walled Imogolite Nanotube

Imogolite is an attractive inorganic nanotube, formed from weathered volcanic ashes, that also can be synthesized in nearly monodisperse diameters. It has found a variety of uses, among them as an effective arsenic retention agent, as a catalyst support and as a constituent of nanowires. However, long after its successful synthesis, the details of the way it is achieved are not fully understood. Here we develop a model of the synthesis, which starts with a planar aluminosilicate sheet that is allowed to evolve freely, by means of classical molecular dynamics, until it achieves its minimum energy configuration. The minimal structures that the system thus adopts are tubular, scrolled, and more complex conformations as well, depending mainly on temperature. The minimal nanotubular configurations that we obtain are monodispersed in diameter and quite similar in diameter both to those of weathered natural volcanic ashes and to the ones that are synthesized in the laboratory. A tendency toward nanotube agglomeration is also observed, in agreement with experiment.