Analytical Sciences

The Effect of UV Irradiation on the Reduction of Au(III) Ions Adsorbed on Manganese Dioxide

Hironori OHASHI,*¹ Hiroyuki EZOE,*² Yoshihiro OKAUE,*¹ Yasuhiro KOBAYASHI,*³ Shuji MATSUO,*⁴ Tsutomu KURISAKI,*² Akane MIYAZAKI,*⁵ Hisanobu WAKITA,*^2,*⁴ and Takushi YOKOYAMA*¹

*1 Department of Chemistry, Faculty of Science, Kyushu University, Chuo-ku, Fukuoka 810-8560, Japan
*2 Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180, Japan
*3 Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan
*4 Advanced Materials Institute, Fukuoka University, Jonan-ku, Fukuoka 814-0180, Japan
*5 Department of Environmental Science and Engineering, Interdisciplinary Graduate School of Science and Technology, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan

The effect of UV (ultraviolet) irradiation on the adsorption of Au(III) ions on manganese dioxide and their reduction to Au(0) (gold with 0 valence state) was investigated using XPS (X-ray photoelectron spectroscopy) and ¹⁹⁷Au Mössbauer spectroscopy. The UV irradiation accelerated the adsorption and the reduction. From the fact that the proportion of Au(0) estimated from Au 4f XPS spectra for surface analysis was significantly smaller than that from ¹⁹⁷Au Mössbauer spectra for bulk analysis, we deduced that Au(0) was interpenetrated to the inside of manganese dioxide (into deeper places than about 30 Å) where XPS is impossible to detect. The content of surface hydroxyl groups on manganese dioxide also increased due to the UV irradiation. The relationship between the charge in the content of hydroxyl groups and the interpenetration of Au(0) is discussed.

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