Time-resolved photoluminescence of anatase/rutile TiO_2 phase junction revealing charge separation dynamics

Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an anatase/rutile TiO2 phase junction using time-resolved photoluminescence spectroscopy. Visible （-S00 nm） and near-infrared （NIR, -830 nm） emissions were monitored to give insight into the photoinduced charges of anatase and rutile in the junction, respectively, New fast photoluminescence decay components appeared in the visible emission of futile-phase dominated TiO2 and in the NIR emission of many mixed phase TiO2samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO2 increased, revealing that charge transfer from rutile to anatase was the main pathway. The charge separation slowed the microsecond time scale photolumines- cence decay rate for charge carriers in both anatase and rutile. However, the millisecond decay of the charge carriers in anatase TiO2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO2. Thus, charge separation at the anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at ana- tase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

Photodegradation of benzene by TiO_2 nanoparticles prepared by flame CVD process

Photodegradation of benzene at ppb levels by mixed-phase TiO2 nanoparticles, synthesized by the oxidation of TiCl4 in propane/air turbulent flame chemical vapor deposition （CVD） process, is investigated experimentally by using a tubular photoreactor with thin TiO2 films coated on the reactor wall by sedimentation. Effects of inlet benzene concentration from 10 to 300μg/m3, rutile mass fraction from about 20 to 50% and photoluminescence （PL） intensity of TiO2 nanoparticles on degradation degree are examined under the conditions of 70% relative humidity, 38 μg/cm2 catalyst loading, 24mW/cm2 UV irradiation of 254 nm and 5.7 s residence time in the reactor. Based on experimental results, separation of photoinduced electron （e-） and hole （h＋） pairs by rutile phase is discussed as photo-induced electron （e-） in anatase phase will migrate to rutile surface due to that the potential of conductive band of rutile is lower than that of anatase, leading to more holes ready on anatase surface for oxidation reactions.