Real roles of perylene diimides for improving photocatalytic activity.

Three novel visible-light-driven composite photocatalysts: five-membered O-heterocyclic annulated perylene diimide doped TiO (PDI-1/TiO), 1-phenol-,'-dicyclohexyl perylene-3,4,9,10-tetracarboxylic diimide doped TiO (PDI-2/TiO), and ,'-dicyclohexyl perylene diimide doped TiO (PDI-3/TiO), were synthesized using a hydrothermal synthesis method. The effects of introducing PDIs with different structures into TiO were evaluated by assaying the photodegradation rate of Methylene Blue (MB). The photoactivities of the PDI-1/TiO and PDI-2/TiO catalysts were better than that of PDI-3/TiO. This is because the large surface area of PDI-1 nanorods and PDI-2 nanobelts extended the 1D charge carrier channel, which facilitated electron transfer to the TiO surface and improved the photocatalytic activity of the composites. The PDI-1/TiO composite showed the highest photoactivity, and the activity remained at 86.4% after four reuse cycles. The extended π-π stacking of self-assembled PDI-1 and the strong interactions between self-assembled PDI-1 and TiO played significant roles in accelerating charge transfer and decreasing recombination of photogenerated electron-hole pairs. The steric hindrance of the phenoxy substituent at the bay position of PDI-2 prevented the PDI-2 nucleus from contacting TiO and weakened the interaction between PDI-2 and TiO, which further resulted in the low photoactivity of PDI-2/TiO. This work provides a practical way to improve the performances of traditional organic and inorganic composite photocatalysts.