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LETTERSAll-solid-state Z-scheme in CdSAuTiO2 three-component nanojunction systemHIROAKI TADA1*, TOMOHIRO MITSUI1, TOMOKAZU KIYONAGA1, TOMOKI AKITA2 AND KOJI TANAKA21Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan2National Institute of Advanced Industrial Science and Technology, Midorigaoka 1-8-31, Ikeda, Osaka 563-8577, Japan *e-mail: [email protected] online: 10 September 2006; doi:10.1038/nmat1734Natural photosynthesis, which achieves ecient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in ananospace, highlights the importance of a technique for site-selective coupling of dierent materials to realize articial high-eciency devices1. In view of increasingly serious energy and environmental problems, semiconductor-based articial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed2,3. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction eciency. Here, we report a simple technique for forming an anisotropic CdSAuTiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially xed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.Semiconductors are a key material in modern optoelectronic and photoelectrochemical devices, and unique electronic states resulting from the quantum size eect and high dispersion with downsizing make them even more interesting from the perspective of both fundamentals and potential applications. Recently, the coupling of semiconductors with molecules and other solids on the nanoscale has been reported to improve the performance of various devices, including solar cells4,5, photoluminescence6 and electrochromic devices7 and biosensors8. On the other hand, in articial photosynthetic systems consisting of isolated semiconductor particles and redox mediators (Ox/Red), water splitting to hydrogen and oxygen has recently been shown to proceed via a Z-scheme2,3. However, the Ox and Red mobile in solutions can compete with the reduction in PS1 and the oxidation in PS2, respectively, to reduce the reaction eciency. Using a simple photochemical technique, we have been able to construct a site-selective CdSAuTiO2 nanojunction achieving an all-solid-state Z-scheme.Au particles with a mean size of 3.4 nm were rmly deposited on the anatase TiO2{101} surface with an orientation relationship of Au{111} TiO2{101} by the depositionprecipitation method (see Supplementary Information, Fig. S1)9. A...