Peptization-Hydrothermal Method as a Surfactant-Free Process toward Nanorod-Like Anatase TiO2 Nanocrystals

The transparent TiO2 sol contained of anatase crystallites was prepared by peptization of anatase TiO2 precipitates. With the hydrothermal treatment of TiO2 sol at 150 degrees C, the dispersible and nanorod-like TiO2 nanocrystals were formed by an oriented attachment mechanism. After further hydrothermal treatment of the mixture of nanorod-like TiO2 nanocrystals and the original sol, branched and nanoring-like nanostructures in the anatase phase were obtained. The as-prepared TiO2 nanocrystals were characterized by X-ray diffraction, FT-Raman spectrometry, UV/Vis absorption spectrometry, and transmission electron microscopy (TEM). TEM results indicated that TiO2 nanocrystals were nanorod-like, and more complex microstructures such as the ring-like and branched TiO2 nanostructures with diameters less than 10 nm were formed especially in the two-step hydrothermal treatment. The adsorption of ruthenium dye (N719) over the nanocrystals with different microstructures was investigated. The adsorption results showed the nanorod-like anatase TiO2 nanocrystals had a high capacity for the ruthenium dye adsorption. The powders were used as electrodes of dye-sensitized solar cells and showed a conversion efficiency of 5.75 % under 1 sun illumination unit of simulated sunlight. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)