Synthesis of Fullerene-, Carbon Nanotube-, and Graphene-TiO2 Nanocomposite Photocatalysts for Selective Oxidation: A Comparative Study

A series of TiO2-graphene (GR), -carbon nanotube (CNT), and -fullerene (C-60) nanocomposite photocatalysts with different weight addition ratios of carbon contents are synthesized via a combination of sol-gel and hydrothermal methods. Their structures and properties are determined by the X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), transmission electron microscopy (TEM), nitrogen adsorption-desorption, and photoelectrochemical measurements. Photocatalytic selective oxidation of benzyl alcohol to benzaldehyde is employed as a model reaction to evaluate the photocatalytic activity of the TiO2-carbon (GR, CNT, and C-60) nanocomposites under visible light irradiation. The results reveal that incorporating TiO2 with carbon materials can extend the adsorption edge of all the TiO2-carbon nanocomposites to the visible light region. For TiO2-GR, TiO2-CNT, and TiO2-C-60 nanocomposites, the photocatalytic activities of the composites with optimum ratios, TiO2-0.1% GR, TiO2-0.5% CNT, and TiO2-1.0% C-60, are very close to each other along with the irradiation time. Furthermore, the underlying reaction mechanism for the photocatalytic selective oxidation of benzyl alcohol to benzaldehyde over TiO2-carbon nanocomposites has been explored using different radical scavenger techniques, suggesting that TiO2-carbon photocatalysts follow the analogous oxidation mechanism toward selective oxidation of benzyl alcohol. The addition of different carbon materials has no significant influence on the crystal phase, particle size, and the morphology of TiO2. Therefore, it can be concluded, at least for nanocomposites of TiO2-carbon (GR, CNT, and C-60) obtained by the present approach, that there is no much difference in essence on affecting the photocatalytic performance of semiconductor TiO2 among these three different carbon allotropes, GR, CNT, and C-60. Our findings point to the importance of a comparative study of semiconductor-carbon photocatalysts on drawing a relatively objective conclusion rather than separately emphasizing the unique role of GR and joining the graphene gold rush.