Ministrante: Prof. Dr. Hemerson Pablo Silva Castro
Local: Miniauditório
Resumo: Since the first report on the photoelectrochemical water splitting using TiO2 and UV light to produce hydrogen,[1] many efforts have been devoted to developing suitable photocatalytic materials in order to improve hydrogen conversion efficiency. Among various photo active materials, (Ti, Ta) oxides present some of the greatest photocatalytic activity for water splitting under UV irradiation. Parallel to the material choice, researchers have also intensively investigated control over the nanoscale architecture and shape of photocatalysts. When a nanocatalyst absorbs photons with energies above the electronic band gap between valence and conduction bands, electrons are excited and promoted to the conduction band;[2] these generated electron-hole pairs migrate to the catalyst surface where reduction and oxidation of water occurs if the valence and conduction band have adequate energies. The efficiency of photocatalysis essentially depends on the amount of photogenerated charges and their recombination time. Recently, studies have suggested that the geometric shape of the semiconductor — such as nanorods, nanowires, nanospheres and nanotubes — includes different parameters in length, diameter, and effective surface area; these variations can affect the photocatalytic properties[3,4] and significantly impact the photocatalytic activity in water splitting[3–8]. Generally speaking, the shape used for photocatalytic solar applications are either bulk or nanospheres of TiO2 (P-25).[9,10] However, in the last 20 years, significant efforts have lead to the synthesis of 1D nanostructured semiconductor photocatalysts, such as nanotubes (NT's) and nanorods (NR’s). Such structures improve light absorption and the lifespan of electron-hole excitation, therefore augmenting photocatalysis performance as well. In fact, the photocatalysis process starts with the light-matter interaction. In this sense, if the scattering and absorption of the light are controlled, the optical parcel of the water splitting process can be optimized. Therefore, the first step in improving photocatalysis is accurately understanding the light scattering and absorption in these systems. In the case of colloidal suspensions, the optical properties of such disordered structures inherit the multiple light scattering characters, which can be used to develop new applications.[11] The scattering and absorption of light depend not only on the mass or volume, but also on their dimensions and geometric shape. In this context, controlling the nanostructure geometry may optimize the light scattering and absorption for enhanced photocatalytic hydrogen production, as observed experimentally.[3] In order to check the hypothesis that the H2 photocatalytic production have a greater dependence of the light scattering, we have generated H2 using Ta2O5 nanocatalysts with three different shapes and investigated the role played for the light in these systems. [1] A. FUJISHIMA, K. HONDA, Nature 1972, 238, 37.
[2] A. Kudo, Y. Miseki, Chem. Soc. Rev. 2009, 38, 253.
[3] H. Xu, X. Chen, S. Ouyang, T. Kako, J. Ye, The Journal of Physical Chemistry C 2012, 116, 3833.
[4] J. Giblin, M. Kuno, The Journal of Physical Chemistry Letters 2010, 1, 3340.
[5] S. C. Warren, E. Thimsen, Energy Environ. Sci. 2012, 5, 5133.
[6] B. Liu, K. Nakata, S. Liu, M. Sakai, T. Ochiai, T. Murakami, K. Takagi, A. Fujishima, The Journal of Physical Chemistry C 2012, 116, 7471.
[7] L. Han, L. Wang, K.-K. Chia, R. E. Cohen, M. F. Rubner, M. C. Boyce, C. Ortiz, Advanced Materials 2011, 23, 4667.
[8] I. S. Cho, Z. Chen, A. J. Forman, D. R. Kim, P. M. Rao, T. F. Jaramillo, X. Zheng, Nano Letters 2011, 11, 4978.
[9] M. A. Henderson, Surface Science Reports 2011, 66, 185.
[10] K. Maeda, Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2011, 12, 237.
[11] D. S. Wiersma, Nature Photonics 2013, 7, 188.
[12] R. V Gonçalves, P. Migowski, H. Wender, D. Eberhardt, D. E. Weibel, F. C. Sonaglio, M. J. M. Zapata, J. Dupont, A. F. Feil, S. R. Teixeira, The Journal of Physical Chemistry C 2012, 116, 14022.