Multiwalled carbon nanotubes (MWCNTs) are finding increasing use in a variety of applications such as scanning probe microscope tips, hydrogen storage devices, catalyst support, and energy storage devices. Carbon nanotubes (CNTs) are often modified to prepare templates for advanced sensing technologies. A number of studies have reported attempts to functionalize the surface of CNTs for improved templating. A recent study by researchers from Virginia Tech has yielded CNTs functionalized with a uniform layer of metal oxide on the nanotube surface that afford high yield with low costs.

Previous studies have mostly resulted in CNTs functionalized with metal nanoparticles. There has been limited success with coating CNTs with oxides. In the November 2010 issue of the Journal of the American Ceramic Society (DOI: 10.1111/j.1551-2916.2010.04154.x; p. 3618), V. Bedekar, S. Priya, and their colleagues from Virginia Tech introduce a technique to prepare MWCNTs uniformly coated with BaTiO₃.

Scanning electron micrograph of multiwalled carbon nanotubes coated with BaTiO₃.

In this two-step process, CNTs were first immersed in nitric acid to incorporate surface –OH functional groups that act as sites for BaTiO₃ attachment. The acid-functionalized CNTs were immersed in a solution of barium titanium ethylhexanoisopropoxide and isopropanol. Transmission electron micrographs revealed that the MWCNTs were uniformly coated by BaTiO₃ with thickness in the range of 5–20 nm. Changes in chemical composition resulting from surface functionalization were characterized using a combination of infrared and x-ray energy-dispersive spectroscopy.

The research team said that these surface-functionalized CNTs will find use in diodes, sensors, and smart textiles.