Towards visible light applications of TiO2 nanostructures

Abstract

In recent years titanium dioxide nanostructures have been studied intensively in many fields of applications, including environmental issues such as self-cleaning, bacteria killing, or energy related areas like solar cells, water splitting, etc. Owing to its availability titanium dioxide is one of the major candidates for applications in greener energies. However, the drawback of using titanium dioxide for energy application is the large band gap: about 3.2 eV. This gap corresponds to absorption of photons with a wavelength around 390 nm, which is in the ultraviolet region that occupies only less than 5% of the solar radiation. This wide band gap makes it inappropriate for immediate use in solar cells, in spite of the fact that it has been identified as the most effective photocatalyst. Nonetheless, there are still many researchers trying to effectively reduce its band gap by doping different elements such as nitrogen, carbon, and many others. Among all the possible ways nitrogen and carbon have been shown to effectively extend the absorption spectra of into the visible light region, greatly increased the possibilities of applications in energy problems. Particularly, research groups in our university had shown that combination of anatase and rutile nanostructures, plus the help of carbon, can absorb light wave all the way from ultra violet to infrared, making it more promising in converting solar energy to produce electricity or split hydrogen and oxygen from water. Even though the absorption spectrum has been pushed towards visible light and even infrared, the absorption is still poor compared to the ultra violet region. It is then important to study in detail the effects and properties of carbon containing mixed phase titanium dioxide, in order to find ways to increase the absorption efficiency in the visible region, hence to provide low cost and sustainable solutions to energy and environmental problems.