nanotubular

Nanotubular denotes materials and structures characterized by hollow, tube-like morphologies at the nanometer scale. Nanotubes can be single-walled or multi-walled, and they commonly form from carbon or other elements and compounds. The term is used to describe carbon nanotubes as well as inorganic nanotubes such as boron nitride, silica, and transition metal oxide nanotubes. The distinctive geometry yields a high length-to-diameter ratio and pronounced curvature at the nanoscale.

In carbon systems, single-walled carbon nanotubes (SWNTs) consist of a single graphene sheet rolled into a cylinder, while multi-walled carbon nanotubes (MWNTs) contain several concentric graphene walls. The electronic properties of CNTs are highly sensitive to chirality and diameter, spanning metallic and semiconducting behavior. BN nanotubes are structurally similar but are typically insulating and thermally robust.

Synthesis methods for nanotubular materials include chemical vapor deposition, arc discharge, and laser ablation, with CVD enabling better control of diameter, orientation, and yield. Inorganic nanotubes can also form by template-assisted growth or electrochemical routes. Purity and defect control remain important challenges for scalable production.

Key properties include high mechanical strength, large aspect ratio, and, for CNTs, exceptional electrical and thermal conductivity in some specimens. In BNNTs, high thermal stability and oxidation resistance are notable. These properties enable applications in nanocomposites, nanoscale electronics, sensors, energy storage, and catalysis, as well as potential uses in hydrogen storage and environmental remediation.

Overall, nanotubular materials represent a versatile class of nanostructures whose behavior can be tailored through composition, structure, and synthesis, driving ongoing research across science and engineering.