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TiO2 nanoparticles when subjected to UV irradiation exhibit blue coloration as electrons are stored within the particles. Upon contact with gold nanoparticles, a partial disappearance of the blue color is seen as the stored electrons are transferred from TiO2 to Au nanoparticles. The charge distribution between the semiconductor and metal nanoparticles causes the Fermi level to shift to more negative potentials. By employing C60/C60•- as a probe−redox couple, we were able to estimate the apparent Fermi levels of TiO2 and TiO2/Au nanoparticles. A Fermi level shift of −22 mV observed for the Au−TiO2 nanocomposite is indicative of improved charge separation in semiconductor−metal systems and demonstrates its usefulness for improving the efficiency of photocatalytic reactions.
Jakob et al. (Sat,) studied this question.