Photonic Properties of Nanostructured Photocatalysts

CURTI M.; PEPE A.; GRELA M.A.; MENDIVE C.

Kyoto

Conferencia; 2nd International Conference on Photocatalysis and Solar Energy Conversion: Development of Materials and Nanomaterials (PASEC-2); 2013

Kyoto University

The use of wide band-gap semiconductors for water and air treatment by means of Advanced Oxidation Processes is a research topic which gathers every year new and creative projects exploring the huge variety of interesting open questions. In the particular case of TiO2, one of the most exciting challenges is to extend its absorption to the visible region in order to efficiently take advantage of the solar light. One of the multiple and existing strategies is to structure the semiconductor at a nanometric scale, i.e., in the order of the wavelength of the interacting radiation. These particular nanostructured systems are called photonic crystals, and the wavelengths of choice are those corresponding to their slow photons. Such photons, which propagate within the crystal with a much reduced group velocity, may therefore meet the chance of being absorbed by the semiconductor with higher probability. Consequently, they are selected to fall in the visible spectral range where the semiconductor poorly absorbs. And upon their absorption, it follows the creation of additional redox species (electron-hole pairs) able to enhance the pristine photocatalytic activity of the semiconductor. Of special interest are those photonic crystals made of compact packed air spheres in a semiconductor matrix, i.e., TiO2. Such systems are usually called inverse opal structures. In this work TiO2 inverse opals are prepared using polymeric opals as templates. The templates are produced by self-assembly of polystyrene nanospheres employing a methodology based on the capillary phenomenon. The resulting inverse opals are thoroughly characterized by UV-vis spectroscopy and field emission scanning electron microscopy. The systems thus obtained are compared to the same semiconductor material without being nanostructured as a photonic crystal, in order to identify the action of the slow photons. The photocatalytic activity of the systems is monitored using the spin trapping technique by means of Electron Paramagnetic Resonance.