Effect of phase composition on the photocatalytic activity of titanium dioxide obtained from supercritical antisolvent.

Photocatalytic activity of TiO nanoparticles is highly dependent on their phase composition. The coexistence of anatase and rutile phases in a single nanoparticle eases the electron transfer process between the phases, and favors the separation of photogenerated pairs. In this work, highly photoactive mixed-phase TiO nanostructures were prepared by supercritical antisolvent precipitation (SAS), an environmentally friendly technology. It is shown here that this methodology has the remarkable ability to produce highly porous (515 m/g) and crystalline TiO nanoparticles. The phase composition of as-prepared TiO samples can be tailored through annealing process. Several mixed-phase TiO samples were tested to assess the correlation between photocatalytic activity and phase composition. The photocatalytic performance is strongly affected by the anatase-rutile ratio, since the synergism between phases enhances the charge separation, reducing the recombination effect of the photogenerated pairs (e/h). It was found that the nanocatalyst composed by 7.0 wt% of rutile phase and 93.0 wt% of anatase phase, named as TiO_650, presented the highest photodegradation for both methyl orange (MO) and methylene blue (MB) dyes. Interestingly, TiO samples prepared by SAS have superior photoactivity than the benchmark photocatalyst names as P25, which is a widely used TiO material composed of anatase and rutile phases.