© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2010, 22, 3317–3321 3317 www.advmat.de www.MaterialsViews.com COMMUNICATION By Li Zhao, Xiufang Chen, Xinchen Wang,* Yuanjian Zhang, Wei Wei, Yuhan Sun, Markus Antonietti, and Maria-Magdalena Titirici* One-Step Solvothermal Synthesis of a Carbon@TiO 2 Dyade Structure Effectively Promoting Visible-Light Photocatalysis [∗] L. Zhao, X. F. Chen, Dr. X. C. Wang, Dr. Y. J. Zhang, Prof. M. Antonietti, Dr. M. M. Titirici Colloid Chemistry Departament Max-Planck Institute for Colloids and Interfaces Am Muehlenberg 1, 14424, Potsdam (Germany) E-mail: xcwang@fzu.edu.cn; magdalena.titirici@mpikg.mpg.de L. Zhao, Prof. W. Wei, Prof. Y. H. Sun Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan 030001(China) X. F. Chen, Dr. X. C. Wang Research Institute of Photocatalysis Fuzhou University Fujian 350002 (China) DOI: 10.1002/adma.201000660 The development of sunlight harvesting chemical systems to catalyze relevant reactions, i.e., water splitting, CO 2 fixa- tion, and organic mineralization, is the key target in artificial photosynthesis but remains a difficult challenge. Titanium dioxide (TiO 2 ) has been widely used as a photocatalyst for solar energy conversion and environmental applications because of its low toxicity, abundance, high photostability, and high efficiency. [1–4] However, the application of pure TiO 2 is limited, because it requires ultraviolet (UV) light, which makes up only a small fraction ( <4%) of the total solar spectrum reaching the surface of the earth. Therefore, over the past few years, considerable efforts have been directed towards the improvement of the photocatalytic efficiency of TiO 2 in the visible (vis)-light region. [5–7] This has been mainly achieved by introducing various dopants into the TiO 2 structure which can narrow the bandgap. The initial approach to dope TiO 2 materials was achieved using transition metals ions such as V, Cr, or Fe. [6,8–10] However, such metal doped materials lack the necessary thermal stability, exhibit atom diffusion and a remarkably increased electron/hole recombination of defect sites, which results in a low photocata- lytic efficiency. [11] Non-metal doping has since proved to be far more successful and has been extensively investigated. Thus, numerous reports on TiO 2 doped with B, F, N, C, S, or I have demonstrated a significant improvement of the visible-light photocatalytic efficiency. [4,12–16] Among these, carbon doping received particular attention. For example, carbon-doped TiO 2 for water splitting has been reported by Khan et al., [4] as easy accomplished via the controlled combustion of metallic Ti in a natural gas flame at 850 °C. Hashimoto et al. synthesized C-doped anatase TiO 2 powders by a two-step oxidative annealing of commercial TiC at 300 °C and 600 °C. [17] Sakthivel and Kisch synthesized carbon-modified TiO 2 by hydrolysis of titanium tetrachloride with tetrabutylammo- nium hydroxide, followed by further heat treatment at 500 °C. [18] Morawski et al. reported a new preparation method of carbon- TiO 2 by the carbonization of n-hexane deposited on TiO 2 at high temperatures. [19] Here, the visible response strongly depends on the form of C in the TiO 2 lattice. [20,21] An active debate regarding the fundamental nature of the non-metal species causing the visible-light absorption in such modified-TiO 2 materials has continued in the community, and two theses have coexisted for several years: i) the non-metal substitutes a lattice atom (i.e., doping), and ii) the non-metal forms chromophoric complexes at the surface (i.e., sensiti- zation). For nitrogen-modified TiO 2 catalysts, substitution doping of lattice O by N, and O vacancies and F-type color centers induced by nitrogen sources during synthesis were proposed by Asahi, [1] Serpone [22] and others, whereas species such as NO x and various other nitrogen oxide complexes were also proposed to sensitize TiO 2 when subjected to visible light irradiation. [23–25] Very recently, Kisch and co-workers have sug- gested that the activity of urea-derived TiO 2 -N in visible light was ascribed to the sensitization of TiO 2 by melon. [26] Indeed, this is circumstantially supported by our recent studies on poly- meric melon as a water-splitting photocatalyst, being a solid- state “dye” semiconductor with a HOMO–LUMO gap of 2.7 eV and a suitable LUMO level to allow charge transfer from the polymer to TiO 2 . [27] Sensitization of TiO 2 and AgCl by the plasmon state of the noble metal (in particular nanostructured Ag and Au) for visible-light photocatalysis has also been documented. In these systems, the collective dipole oscillations of the surface plasmon is believed to create electron–hole pairs by inter-band transition. [28] Here, we show for the first time that the surface of nanometer- sized carbon materials can also show collective polarization modes and therefore, these optical absorption transitions are feasible to sensitize TiO 2 which then acts as a novel “dyade”- type structure, [29–31] with an improved TiO 2 hole reactivity, while the electron is taken up by the carbon component. This results in an improved photocatalytic activity over the complete spec- tral range. In order to avoid carbon from doping directly into bulk TiO 2 lattice our hybrid TiO 2 /C is synthesized at low temperature under solvothermal conditions by a one-step carbonization of furfural [32] in the presence of Ti-isopropoxide, allowing for the formation and co-assembly of carbon and TiO 2 into an inter- penetrating C/TiO 2 nanoarchitecture containing 12.6% carbon.