A unique nanocomposite C-TiO2 was prepared by the growth of TiO2 on carbon nanoparticles using a simple hydrothermal procedure. Transmission electron microscopic (TEM) measurements showed that the nanocomposites exhibited an average core diameter of approximately 5 nm with a rather well-defined lattice space (0.4 nm) that was somewhat larger than that (0.38 nm) of the (100) crystalline planes of anatase TiO2. This lattice expansion was accounted for by the formation of surface defect dipoles of the nanosized TiO2 particles. X-ray photoelectron spectroscopic (XPS) measurements suggested that partial charge transfer occurred from carbon nanoparticles to TiO2 by the interfacial Ti-O-C linkages, which led to effective diminishment of the C-TiO2 photoluminescence as compared to that of pure TiO2 or carbon nanoparticles, suggesting intimate electronic interactions between the carbon and TiO2 components in the nanocomposites. Such unique characteristics were then exploited for the effective photocatalytic degradation of organic pollutants, as exemplified by methylene blue, by C-TiO2 under UV photoirradiation. Experimental measurements showed that the photocatalytic activity of C-TiO2 nanocomposites was about twice that of TiO2 alone, whereas little activity was observed with carbon nanoparticles. This was attributed to the electron-accepting sites on the carbon nanoparticles that facilitated interfacial charge separation.

Au-TiO2 nanocomposites were prepared by chemical deposition of gold nanoparticles onto TiO2 nanocolloids that were synthesized by a hydrothermal method. Transmission electron microscopic measurements showed that the TiO2 colloids exhibited an average diameter of about 5 nm and clearly defined lattice fringes that were consistent with those of anatase TiO2 and formed rather large agglomerates that spanned a few hundred nanometers in length. Additionally, gold nanoparticles were found to be embedded within the TiO2 matrices, and the size increased with increasing gold loading but all ranged from 10 to 50 nm in diameter. Consistent results were obtained in X-ray diffraction measurements. Electrochemical studies demonstrated that the resulting Au-TiO2 nanocomposites exhibited apparent electrocatalytic activity in oxygen reduction that was markedly improved as compared to that of TiO2 particles alone, as reflected in the onset potential, number of electron transfers involved, and kinetic current density. Among the series, the best catalyst for oxygen reduction was identified with the Au/Ti atomic ratio of 5.2%. The enhanced oxygen reduction kinetics was ascribed to the dissociation of water and formation of surface-adsorbed hydroxyl moieties that was facilitated by the loading of gold nanoparticles onto the TiO2 colloids.

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