Photocatalytic surface sites on SO42−/TiO2 were investigated by pyridine adsorption and in situ Fourier transform infrared (FT-IR) spectroscopy. Results revealed that the sulfate-modification not only increased the number of strong Lewis acidic sites, but also induced a large amount of strong Brønsted acidic sites on the surface of TiO2. Pyridine molecules were chemically captured on Brønsted and Lewis acidic sites on the SO4 2−/TiO2 surface. These pyridine molecules were progressively decomposed to final products of CO2 and H2O under actual photocatalytic conditions. The high photocatalytic performance of SO42−/TiO2 can be explained by the improved surface acidities that favor the adsorption of both oxygen and pyridine molecules. Moreover, the Lewis acidic sites could react with H2O and was then converted to Brønsted acidic sites, leading to the activation of the water. This conversion promoted the formation of hydroxyl groups on the catalyst surface, which could also contribute to the high photocatalytic reactivity of SO42−/TiO2.

Hollow metal oxide fibers [TiO2 and Fe2O3] have been prepared by using activated carbon fibers [ACFs] as the templates, through a simple impregnation and heat treatment. The resulting products, as compared to ACFs, possessed not only a similar morphological feature upward to the micrometer scale but also different surface nanostructures with unique morphology. The TiO2 fibers displayed overlapped “wormlike” surface and a hierarchical structure with two distinguishable layers, the inner layer and the outer layer, which were composed of the particles of 7 and 15 nm, respectively. It was also found that the reaction temperature had a significant effect on the TiO2 surface morphology. The Fe2O3 fibers exhibited a rough and crinkle-like surface and were also composed of hierarchical particles. Both TiO2 and Fe2O3 fibers possessed the hierarchical pore structure with mesopores in the walls of the large hollow channel. Such porous architecture favored the resultant TiO2 with better apparent photoactivity than P25 titania for degradation of gaseous acetone and would also make the materials useful for further application in other fields.

Sol-gel prepared mixtures of silica or zirconia with titania are shown to have significantly higher activities than pure titania for the complete photocatalytic oxidation of ethylene. These higher activities are only apparentwhen the respective catalysts are stabilized by sintering. The differences become even more pronounced when the catalysts are used in a tubular reactor. Optimum mixture concentrations are found to be 12 wt % zirconia and 16 wt % silica in titania. Both catalyst types exhibit activity maxima with respect to sintering temperature. It is hypothesized that the maxima arise from opposing effects of densification and phase transformation versus beneficial sintering. A comparison of our catalyst compositions with literature in this area suggests that the increase in activity due to the addition of silica or zirconia may be a result of higher surface acidity. However, isoelectric point measurements employing the unsintered and sintered catalysts show no conclusive increase in surface acidity. The effects of sintering temperature on the surface area, porosity, and crystal structure of the catalysts are also presented.

A porous β-Ga2O3 photocatalyst has been successfully prepared. The photocatalyst was characterized by XRD, N2 adsorption-desorption, TEM, UV/vis, and FTIR techniques. The photocatalytic activity of the sample was evaluated by the decomposition of benzene in air under UV light illumination and was compared with that of the commercial titania [Degussa P25] and Pt/P25. Results revealed that the synthesized Ga2O3 was porous β-Ga2O3 and was highly photoactive for mineralizing benzene and its derivatives [e.g., toluene and ethylbenzene] to CO2 under ambient conditions. The photocatalytic conversion of benzene over β-Ga2O3 was about 1 order of magnitude higher than that over P25, and no obvious deactivation of β-Ga2O3 was observed during the prolonged operation of 80 h. The high activity and long-term stability of the Ga2O3 have been ascribed to its stronger oxidative capability and higher specific surface area in comparison with P25.

TiO2 fibers were fabricated through heat treatment of titanium alkoxide dissolved in a solvent (ethanol and toluene) under autogenous pressure, using activated carbon fibers as templates. For comparison, a supercritical CO2 process was also employed. The difference in the solvent’s affinity for water led to a large difference in the morphology of TiO2 fibers produced. Moreover, the fibers synthesized using toluene in our relatively mild conditions exhibited a similar pore size distribution and surface area to those made using supercritical CO2.