Metal Meso-Tetraphenylporphyrine/TiO₂ Nanocompound Synthesized, Characterized By In-Situ Method And Photocatalysis Under Visible-Light Irradiation

Titanium dioxide is widely used as a semiconductor photocatalyst and its research has focused on considerable attention during the last decades on the area of chemistry, material and environment because of its long-term stability, no toxicity, good photocatalytic activity, and good photocatalytic activity. However, there is still a problem that photocatalytic efficiency is not high since TiO₂ has active only under ultraviolet (UV) light because of its wide band gap ³.2 eV and recombination of photogenerated electron-hole pairs results low photo quantum efficiency. The effective separateness of electron-hole pairs, therefore, is one of the important subjects for the increased utility of TiO₂ as a photocatalyst. In recent years, impurity doping has been widely performed by chemical synthesis and other methods in order to improve photoactivity. Porphyrins possess intensive absorption in the far red/near-IR region (Soret-band: 400-450nm, Q-band: 500-700nm), which are known for their excellent chemical light and thermal stability, and have appropriate redox properties for the sensitization of TiO₂, rendering them attractive for dye-sensitized nanostructured photocatalyst. Recently, metalloporphyrin sensitized TiO₂ has become the subject of studies. In most of the studies, metalloporphyrin- sensitized titania nanocompounds were prepared by the methods of dipping or forming Langmuir-Blodgett films. However, there are many problems: (1) metalloporphyrin (MTPP) isn't able to disperse uniformly in the substance of TiO₂ due to have a poor solubility in commonly organic solvents and a strong tendency to aggregate on the surface of TiO₂. (2) On the other hand, these preparing processes of organic/inorganic nanocompounds were complicated. (3) The interface between MTPP and TiO₂ is easily contaminated owing to the H2O or O2 is absorbed at the surface of TiO₂ particles before dipping or forming L-B films.As a result, the sensitized efficiency is not high.In our investigation, metalloporphyrin- sensitized TiO₂ nanocompounds are synthesized by an in- situ process. The original materials synthesized for metalloporphyrin and TiO₂, respectively, are used and the metalloporphyrins are prepared in the course of forming anatase phase of TiO₂ after calcination. It provides a simple and easy mean of synthesizing nano-size particles, which is essential for nanocatalysts. We prepare the different molar proportion between...