Transmission electron micrographs of nanocavity-filled titanium oxide nanorods. Click to enlarge.

In the first paper, Wei-Qiang Han at Brookhaven’s Center for Functional Nanomaterials (CFN) and lead author on both papers and his collaborators describe a new synthesis method to make iron-doped titanate nanotubes—hollow tubes measuring approximately 10 nanometers in diameter and up to one micrometer long.

These experiments were also aimed at improving the material’s photoreactivity. The scientists demonstrated that the resulting nanotubes exhibited noticeable reactivity in the water-gas-shift reaction.

Although the activity of the iron-doped nanotubes was not as good as that of titanium oxide loaded with metals such as platinum and palladium, the activity we observed is still remarkable considering that iron is a much less expensive metal and its concentration in our samples was less than one percent.

—Wei-Qiang Han

The researchers also observed interesting magnetic properties in the iron-doped nanotubes, and will follow up with future studies aimed at understanding this phenomenon.

In the second study, the scientists enhanced the ability of titanium oxide to absorb light.

Titanium dioxide’s ability to absorb light is one the main reasons it is so useful in industrial and medical applications.

—Wei-Qiang Han

Many scientists have explored ways to improve the light-absorbing capability of titanium oxide by doping the material with added metals. Han and his coworkers took a new approach and enhanced the material’s light-absorption capability by introducing nanocavities, completely enclosed pockets measuring billionths of a meter within the 100-nanometer-diameter solid titanium oxide rods.

Transmission electron micrographs of nanocavity-filled titanium oxide nanorods (bottom) and iron-doped titanium oxide nanotubes (top). Both are being investigated as photocatalysts for reactions to produce hydrogen gas. The improved light-absorption of the nanocavity-filled nanorods also makes them ideal new materials for sunscreen. (Click image for hi-res version)

The resulting nanocavity-filled titanium oxide nanorods were 25% more efficient at absorbing certain wavelengths of ultraviolet A (UVA) and ultraviolet B (UVB) solar radiation than titanium oxide without nanocavities.

Our research demonstrates that titanium oxide nanorods with nanocavities can dramatically improve the absorption of UVA and UVB solar radiation, and thus are ideal new materials for sunscreen.

—Wei-Qiang Han

The cavity-filled nanorods could also improve the efficiency of photovoltaic solar cells and be used as catalysts for splitting water and also in the water-gas-shift reaction to produce pure hydrogen gas from carbon monoxide and water.

To manufacture the nanocavities, the team heated titanate nanorods in air. This process evaporated the water and transformed titanate to titanium oxide, leaving very densely spaced, regular, polyhedral nanoholes inside the titanium oxide.

Materials developed in these studies were analyzed using several of Brookhaven Lab’s tools and methods for the characterization of nanostructures, including transmission electron microscopy and various techniques using x-ray and infrared beams at the Lab’s National Synchrotron Light Source (NSLS).

This research was funded by the Office of Basic Energy Sciences within the US Department of Energy’s Office of Science.

Collaborators on the Advanced Materials paper include Lijun Wu, Robert F. Klie, and Yimei Zhu, all of Brookhaven’s Center for Functional Nanomaterials (CFN). For the Journal of Physical Chemistry paper, collaborators include Brookhaven chemists Wen Wen and Jonathan Hanson; Ding Yi, Mathew Maye, and Oleg Gang of the CFN; Zhenxian Liu of the Carnegie Institution of Washington; and Laura Lewis, formerly at the CFN and now at Northeastern University.