Using a smaller amount of treated P25 takes longer but works just as well, he said. "Either way, it's green and it's cheap."
The team started modifying titanium dioxide two years ago. Li, an assistant professor in civil and environmental engineering whose specialties include water and wastewater treatment, approached Barron to help search for new photocatalytic nanomaterials to disinfect drinking water.
The revelation came when students in Barron's lab heated titanium dioxide, but it wasn't quite the classic "aha!" moment. Graduate student and co-author Michael Liga saw the data showing greatly enhanced performance and asked fellow graduate student Huma Jafry what she had done. Jafry, the paper's first author, said, "I didn't do anything," Barron recalled.
When Barron questioned Jafry, who has since earned her doctorate, he discovered she used silicone grease to seal the vessel of P25 before heating it. Subsequent testing with nonsilicone grease revealed no change in P25's properties, whether the sample was heated or not. Remarkably, Barron said, further work with varying combinations of titanium dioxide and silicone dioxide found the balance between the two at the time of the discovery was nearly spot-on for maximum impact.
Barron said binding just the right amount of silica to P25 creates an effect at the molecular level called band bending. "Because the silicone-oxygen bond is very strong, you can think of it as a dielectric," he said. "If you put a dielectric next to a semiconductor, you bend the conduction and valence bands. And therefore, you shift the absorption of the ultraviolet (used to activate the catalyst)."
Bending the bands creates a path for e
|Contact: David Ruth|