APPLICATIONS OF TECHNOLOGY:
- Solar energy
- Air and water purification / decontamination
- Absorb energy over the entire solar spectrum
- Narrow band gap - 1.54 eV
- Stable after extensive use and storage
- Production method may expand optical absorption of other semiconductor nanostructures
Sam Mao and a team of scientists at Berkeley Lab have developed a titanium dioxide nanoparticle that absorbs energy over the entire solar spectrum. These photocatalysts can be used to efficiently convert solar radiation to fuel (hydrogen) and purify air and water containing contaminants.
The Berkeley Lab invention uses hydrogenation, doping, or a combination of both to engineer disorder into a certain region of the titanium dioxide nanoparticles. The resultant nanostructures have substantial and stable photocatalytic activity and absorb photons over the whole solar spectrum, including the visible and near infrared wavelengths. The concept of disorder engineering opens a new route for manipulating the optical absorption of semiconductor nanostructures, potentially expanding the types of materials used for clean energy and environmental technologies.
In tests, the disorder-engineered titanium dioxide nanocrystals had a significantly narrower band gap (1.54 eV) than that of the unmodified nanocrystalline material (3.30 eV). When irradiated with a solar simulator, these particles catalyzed the splitting of water to produce hydrogen gas at a rate that was two orders of magnitude higher than that of known semiconductor photocatalysts. Moreover, they maintained this catalytic efficiency over weeks of use and after storage in the dark.
Their photocatalytic activity in purifying contaminated water was also tested. The particles were placed in a solution of methylene blue, a common contaminant of water and a model for other nitrogenous pollutants. When exposed to solar radiation, the nanoparticles rapidly and completely catalyzed the degradation of methylene blue.
Most of the existing titanium dioxide semiconductors used for solar-driven photocatalysis have an electronic band gap in the ultraviolet (UV) range and therefore cannot absorb radiation at other wavelengths. As a result, the approximately 90% of solar radiation that falls in the visible and infrared range is wasted in titanium dioxide solar cells. Doping—adding metal or non-metal impurities to titanium dioxide crystals—has been used with limited success to narrow the band gap and extend absorption to the visible and IR ranges. The Berkeley Lab technology, however, achieves the long-sought goal of absorbing energy over the entire solar spectrum.
DEVELOPMENT STAGE: Functional prototype.
Published Patent Cooperation Treaty patent application WO 2010/104717 available at www.wipo.int. Available for licensing or collaborative research.
FOR MORE INFORMATION:
Krotz, D. “A Dash of Disorder Yields a Very Efficient Photocatalyst,” Berkeley Lab News Center, January 28, 2011.
SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:
REFERENCE NUMBER: IB-2686