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A red metallic oxide photocatalyst

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Abstract

Light absorption across the bandgap in semiconductors is exploited in many important applications such as photovoltaics, light emitting diodes and photocatalytic conversion. Metals differ from semiconductors in that there is no energy gap separating occupied and unoccupied levels; however, it is still possible to excite electrons between bands. This is evidenced by materials with metallic properties that are also strongly coloured. An important question is whether such coloured metals could be used in light harvesting or similar applications. The high conductivity of a metal would preclude sufficient electric field being available to separate photocarriers; however, the high carrier mobility in a metal might also facilitate kinetic charge separation. Here we clearly demonstrate for the first time the use of a red metallic oxide, Sr1−xNbO3 as an effective photocatalyst. The material has been used under visible light to photocatalyse the oxidation of methylene blue and both the oxidation and reduction of water assisted by appropriate sacrificial elements.

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Figure 1: Ultraviolet–visible absorbance spectra (converted from diffuse reflectance spectra) for Sr1−xNbO3 (x=0.1, 0.15 and 0.2).
Figure 2: Schematic of band structure for a metallic conductor.
Figure 3: Photocatalytic performance of as-prepared strontium niobates under visible light irradiation.
Figure 4: Schematic of possible photocatalytic-type processes to drive solar redox processes.

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Acknowledgements

We thank the Engineering and Physical Sciences Research Council (EPSRC) and National Science Foundation (NSF) for financial support and G. Liu (Institute of Metal Research, Chinese Academy of Science) for assistance with reflectance measurements and X-ray photoelectron spectroscopy measurements, S. Ni (University of Science & Technology of China) for theoretical calculations, H. Früchtl and M. Buehl (St Andrews), M. Hoffman (Caltech) and P. Robertson (Robert Gordon University) for helpful discussions. P.E. thanks Sasol UK and Energy Technology Partnership (ETP) for studentship support.

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X.X. performed the synthesis and collected data with C.R. and P.E., and J.T.S.I. analysed the results and wrote the paper.

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Correspondence to Chamnan Randorn or John T. S. Irvine.

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The authors declare no competing financial interests.

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Xu, X., Randorn, C., Efstathiou, P. et al. A red metallic oxide photocatalyst. Nature Mater 11, 595–598 (2012). https://doi.org/10.1038/nmat3312

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