Microemulsion-mediated room-temperature synthesis of high-surface-area rutile and its photocatalytic performance

Nanosized titania having the rutile crystalline structure was synthesized at room temperature using a microemulsion-mediated system. The formed rutile particles had a diameter of 3 nm, which corresponds well with the droplet size of the water-in-oil microemulsion used for their preparation. The crystallinity was monitored by both X-ray diffraction (XRD) and electron diffraction, together with dark-field electron microscopy (TEM) and high-resolution TEM. The rutile had a high specific surface area (similar to 300 m(2)/g) according to N-2 adsorption and the BET equation. To our knowledge, this is the highest specific surface area ever reported for rutile. The rutile crystals aligned in a specific crystallographic direction forming elongated aggregates 200-1000 nm in size, as observed by TEM and high-resolution TEM. The titania formation was followed in situ using dynamic light scattering and UV-vis spectroscopy, and together with TEM and XRD performed on samples collected throughout the duration of the titania synthesis, the results gave support for a formation scheme involving the initial formation of amorphous titania followed by crystallization of rutile. The photocatalytic performance of the formed material was evaluated by in situ Fourier transform infrared spectroscopy and compared to that of a rutile sample having a lower specific surface area (similar to 40 m(2)/g). The TEM and formate adsorption experiments revealed that the high-surface-area rutile had a much higher fraction of (101) facets than the low-surface-area sample, which predominantly exposed (110) facets. In particular, a new bidentate formate (mu-formate) species bridge-bonded to the (101) facet could be identified with characteristic bands at 1547 and 1387 cm(-1). The photodegradation rate of this species was found to be similar to the mu-formate species on the (110) facet. However, the overall formate degradation rate was larger on the high-surface-area rutile sample because of a high concentration of the more readily photodegradable monodentate formate (eta(1)-formate) on that sample.