Of a range of materials that have been investigated in pursuit of greater utilization of solar energy, currently one of the most studied semiconductor photocatalysts is titanium dioxide, TiO2, which has an electronic band gap in the ultraviolet (UV) wavelength regime. The effectiveness of a given semiconductor in solar-driven photocatalytic processes is determined by the semiconductor’s ability to absorb visible and infrared light that dominates the solar spectrum, and its ability to suppress rapid recombination of photo-generated electrons and holes. Nanocrystalline TiO2 with a large surface area that can facilitate a fast rate of surface reactions has emerged as a semiconductor photocatalyst, which potentially can play an important role in solar-driven energy and environmental technologies. However, despite decades of extensive research, the true potential of TiO2 has not been fully realized. To increase the limited optical absorption of TiO2 in the visible and infrared, there have been efforts to vary the chemical composition of TiO2 by adding controlled dopants that generate donor or acceptor states in the band gap; but its absorption in the visible and infrared remains weak.
We have developed a different approach to increasing the visible and infrared optical absorption of TiO2 by introducing a disordered surface layer on TiO2 nanocrystals. An ensemble of such nanocrystals retains the benefits of crystalline TiO2 quantum structures for photocatalytic processes, while structural disorders together with hydrogen at the surface enhance the visible and infrared absorption. Disorder-engineered TiO2 nanocrystals exhibit good efficiency and stability in photocatalytic decomposition of organics and production of hydrogen. Applications of solar-driven photocatalysis would be economical compared to the processes that primarily rely on UV radiation. Furthermore, the concept of disorder engineering introduced here opens a direction for altering optical and electronic properties in semiconductor nanostructures.
Professor Samuel S. Mao received his Ph.D. degree from the University of California at Berkeley in 2000. Since then he has been leading a multidisciplinary research team at Lawrence Berkeley National Laboratory and the University of California at Berkeley, developing clean energy technologies and exploring materials science. He has published over 150 peer-reviewed journal articles, which have received more than 27,000 citations. He is a frequent speaker at many leading universities and has delivered invited keynote and plenary speeches at more than 100 international conferences. He has served as a technical committee member, program review panelist, grant proposal reviewer, and national laboratory observer for the U.S. Department of Energy. He is a co-founder of the First International Conference on Energy Nanotechnology, the First International Symposium on Transparent Conducting Materials, and the First International Workshop on Renewable Energy. He was also a general chair for the 2011 Spring Materials Research Society (MRS) Meeting, and a co-chair of the 2012International Conference on Clean Energy. He is the recipient of the 2011 “R&D 100” Award for his technological innovation and 2008 Berkeley MEGSCO Faculty Teaching Award for his dedication to higher education. He is also an inventor of 50 patents in the U.S. and abroad, and a founder of eight high-tech companies. In 2013, he established the Institute of New Energy, an international non-profit organization that develops and commercializes clean energy and environment technologies to benefit society irrespective of boarders.